Performance Evaluation at Cryogenic Temperature with Cryogenic Materials Applications in Ships: A Review
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Abstract
Abstract
The increasing demand for liquefied hydrogen (LHS) as a clean energy carrier necessitates the development of structural materials capable of withstanding extreme cryogenic conditions. This paper reviews three primary candidate materials austenitic stainless steels, high nickel steels, and high-manganese steels focusing on their mechanical properties, fracture toughness, and susceptibility to hydrogen embrittlement. Austenitic stainless steels provide excellent toughness and hydrogen resistance but are limited by low strength and high cost. Conventional 9%Ni steels have demonstrated reliable performance in LNG service, while newly developed 13-15%Ni steels exhibit stable fracture toughness down to lower temperature, extending their applicability to LH2 environments. High-manganese steels offer an attractive balance of high toughness, strength, and cost effectiveness; however, further validation of hydrogen embrittlement resistance and international standardization are required before large-scale implementation. The comparative evaluation highlights that each alloy system presents distinct advantages and limitations, and that future efforts should focus on comprehensive cryogenic testing and the establishment of consistent qualification standards to ensure safe and efficient deployment of LH2 storage and transportation systems.
1. Introduction
In response to the accelerating climate crisis, the International Maritime Organization (IMO) has adopted the initial Green House Gas (GHG) reduction strategy under resolution Marine Environment Protection Committee (MEPC) 304(72), which sets ambitious targets for reducing carbon dioxide emissions in the shipping sector 40% by 2030 and 70% by 2050 compared to 2008 levels1). Additionally, research efforts are being made in various fields to respond to various climate changes2-8). The shift toward carbon-neutral fuels is central to achieving these targets. Among alternative fuels, hydrogen, especially in liquefied form (LH2), is gaining attention for its high gravimetric energy density (120 MJ/kg) and its potential to produce zero carbon emissions at the point of use9,10). To meet global carbon neutrality targets, the adoption of zero-emission fuels is no longer optional but essential. Among emerging alternatives, eco-friendly fuels such as liquefied hydrogen (LH2) and ammonia have attracted considerable attention, and research and development efforts toward their practical application are accelerating. For ammonia, mitigating its inherent toxicity remains a critical challenge, whereas for liquefied hydrogen, ensuring material and system stability under cryogenic temperature conditions (approximately -253 °C) presents a significant technical hurdle11-18).
The structural integrity of cryogenic hydrogen storage systems is governed not only by thermal and mechanical loads but also by the interaction between hydrogen and material microstructure. At cryogenic temperatures, many metals exhibit a ductile-to-brittle transition, making them susceptible to sudden fracture. Moreover, hydrogen atoms can diffuse into the metal lattice, particularly at stress concentrators, leading to hydrogen embrittlement and delayed cracking phenomena19). Materials commonly considered for LH2 containment include austenitic steels, nickel-based alloys, and aluminum alloys. These materials are selected based on their cryogenic toughness, hydrogen compatibility, and weldability. However, even these materials must be evaluated under actual service conditions, including repeated thermal cycling, pressure fluctuations, and exposure to high-purity hydrogen20). Recent research has also demonstrated the importance of fracture mechanics-based evaluation, including crack tip opening displacement (CTOD), fatigue crack growth rates under hydrogen charging, and impact energy tests at sub-zero temperatures21). These assessments are essential to validate the long-term durability and safety of storage tanks and pipelines used in hydrogen-fueled ships.
In the pursuit of global carbon neutrality, the utilization of liquefied hydrogen (LH2) as an energy carrier has become a strategic priority. Its application, however, presents significant technical challenges, particularly in terms of materials selection for storage and transport systems operating under ultra-low temperatures (~20 K). Hydrogen is primarily stored through high-pressure compression, cryogenic liquefaction at extremely low temperatures, or absorption into metal hydrides22,23). Among these methods, cryogenic liquid hydrogen (LH2) storage is particularly advantageous due to its exceptionally high gravimetric energy density and superior volumetric storage efficiency24-26). The successful implementation of LH2 infrastructure depends critically on the identification and qualification of structural materials capable of withstanding severe cryogenic environments while maintaining mechanical integrity and resistance to hydrogen-induced degradation. Traditionally, materials used in high-temperature or ambient environments have served as the baseline for engineering applications. However, their performance must be re-evaluated under cryogenic conditions to assess their suitability for LH2 service. This necessitates a thorough investigation of fundamental mechanical properties including yield strength, toughness, and fracture resistance at low temperatures. Despite growing interest, existing literature contains only limited experimental data on material performance in such extreme environments27-32).
This study aims to address this gap by consolidating existing evaluation frameworks and test standards relevant to the cryogenic application of structural metals. The scope includes: (1) a comparative review of the advantages and limitations of candidate materials proposed for low temperature use, and (2) an examination of the minimum evaluation items required to verify mechanical performance and ensure structural reliability under cryogenic temperature conditions. The findings are expected to inform material selection and design strategies for next-generation hydrogen infrastructure.
2. Characteristics of cryogenic materials
Liquefied hydrogen (LH2), with a boiling point of -253 °C, demands materials capable of maintaining structural integrity at cryogenic temperatures. Such cryogenic materials must exhibit not only sufficient strength and ductility but also excellent fracture toughness, resistance to thermal contraction, and weldability[33,34). Commonly utilized materials for cryogenic applications include austenitic stainless steel 316L, aluminum alloys, high manganese austenitic (H-Mn), and high nickel (H-Ni) steels.
Table 1 provides a summary of the characteristics of structural materials proposed for cryogenic environments with mechanical properties. Candidate materials for liquefied hydrogen (LH2) applications include body-centered cubic (BCC) H-Ni steels, FCC austenitic stainless steels, and H-Mn steels. These materials have demonstrated reliable fracture resistance at cryogenic temperatures, as evidenced by their successful deployment in liquefied natural gas (LNG) storage tanks. Owing to their favorable combination of strength, toughness, and hydrogen compatibility, they are currently regarded as the most promising material systems for structural applications in LH2 storage and transpor- tation. Austenitic stainless steels offer excellent hydrogen resistance and corrosion performance but is limited by low strength and high cost. H-Ni steels steel provides a balanced trade-off between cost and performance, though hydrogen embrittlement in welded zones remains a concern. H-Mn steel has emerged as an attractive alternative, combining low cost with high toughness and strength. However, further validation and standardization are required for broader adoption in liquefied hydrogen storage systems. Austenitic stainless steels, such as 304L and 316L, typically exhibit yield strengths of 200-300 MPa and tensile strengths of 500-700 MPa, combined with excellent elongation (40-60%) and Charpy impact toughness exceeding 200 J at -196 °C. Although these steels offer outstanding cryogenic toughness and hydrogen resistance, their relatively low strength and high cost remain limitations. In contrast, H-Ni BCC steels, represented by 9%Ni and 13-15%Ni grades, provide higher yield (500-700 MPa) and tensile strengths (700-900 MPa), but with reduced ductility (20-30%) and moderate toughness of 150-250 J. They have been successfully applied to LNG storage tanks; however, hydrogen embrittlement in weld zones is a concern. H-Mn steels, typically containing 22-25% Mn, combine relatively high yield strength (400-600 MPa) with tensile strengths up to 1000 MPa and elongation of 40-60%, while maintaining Charpy impact toughness above 200 J at -196 °C.
The comparative advantages and disadvantages of STS316L austenitic stainless steel, 9%Ni steel, and H-Mn steel were examined. With respect to each material’s cryogenic performance, hydrogen embrittlement resistance, mechanical properties, weldability, and standardization status, it was summarized the essential information required to support safe and efficient liquefied hydrogen (LH2) storage in line with the expansion of hydrogen infrastructure. As the global shift toward carbon neutrality accelerates, hydrogen is emerging as a key energy carrier, and the safe storage of liquefied hydrogen is essential for large-scale transportation and utilization. The selection of structural materials for LH2 tanks is critical, as they must simultaneously endure ultra-low temperatures (~20 K), resist hydrogen-induced degradation, and satisfy stringent mechanical and regulatory requirements34). Among the materials capable of meeting these demands, STS316L, H-Ni steel, and H-Mn steel have garnered increasing attention due to their superior mechanical properties and industrial feasibility under cryogenic conditions35-37).
2.1 Characteristics of Stainless Steel for cryogenic use
Stainless Steel, a low-carbon modification of 18Cr- 12Ni-2Mo stainless steel, has long been favored for cryogenic applications owing to its stable austenitic structure38,39). The selection of structural materials for LH2 storage tanks involves trade-offs between mechanical performance, hydrogen compatibility, cost, and regulatory compliance35). STS316L remains the gold standard for hydrogen resistance due to its stable austenitic structure and excellent corrosion behavior, but it suffers from relatively (compare with other cryogenic steels such as 9%Ni steel and H-Mn steel) low yield strength40,41). Liquid hydrogen and LNG are both cryogenic fluids; however, notable differences arise when comparing the design of liquid hydrogen fuel tanks with that of existing LNG fuel tanks. The boiling point of liquid hydrogen is -253 °C, whereas that of LNG is -163 °C, resulting in a liquefaction temperature difference of approximately 90 °C. Furthermore, the latent heat of vaporization of liquid hydrogen is 31 kJ/L, which is considerably lower than that of LNG at 226 kJ/L42). From a manufacturing perspective, STS316L exhibits excellent weldability with commonly used processes such as GTAW and GMAW. When proper welding parameters are applied, the formation of delta-ferrite is minimized, thereby preserving low-temperature toughness. However, its relatively low yield strength (~290 MPa) requires the use of thicker sections, which increases both weight and cost43,44). Additionally, the high content of nickel (Ni) and molybdenum (Mo) contributes to the material’s overall high cost. The ASTM A240A240M specification outlines the requirements for chromium and chromium-nickel stainless steel plate, sheet, and strip used in the construction of pressure vessels and general structural applications. It covers a variety of grades, including commonly used austenitic stainless steels such as Type 304, 304L, 316, and 316L, and defines criteria for chemical composition, mechanical properties (e.g., tensile strength, yield strength, elongation), heat treatment, and permissible tolerances. The standard also specifies requirements for product marking, certification, and testing methods to ensure quality and consistency in critical applications such as cryogenic service, chemical processing, and marine environments45).
2.2 Characteristics of high Ni steel for cryogenic use
9%Ni steel demonstrates excellent low-temperature mechanical performance due to quenching and tempering treatments and has been widely adopted for use in LNG tanks33). The combination of tempered martensite and retained austenite imparts a high yield strength of approximately 600 MPa and exceptional impact toughness down to -196 °C. Recent studies have reported Crack Tip Opening Displacement (CTOD) values exceeding 0.25 mm and Charpy impact energies greater than 100 J at cryogenic temperatures46,47). Cryogenic Ni steels, typically containing 3-12 wt% Ni and less than 0.1 wt% C, possess high strength, good weldability, and excellent toughness at cryogenic temperatures, and are therefore widely used in various engineering applica- tions. For instance, 9Ni steel (containing 9 wt% Ni) has been extensively employed in the fabrication of liquefied natural gas (LNG) storage tanks due to its exceptional Charpy impact energy of approximately 280 J at 77 K48,49). Therefore, it is in great need for industrial applications to develop new Ni-saving and/or Ni-free cryogenic steels to reduce the manufacturing cost of LNG tanks. Numerous studies have reported that retained austenite, located along martensite lath boundaries or at prior-austenite grain boundaries, plays a pivotal role in achieving high cryogenic toughness and a low ductile-brittle transition temperature (DBTT) in cryogenic Ni steels, such as 12Ni steel50), 9Ni steel51,52), 7Ni steel52-54), 5Ni steel55), and 4.5Ni steel56).
Mu et al.57) investigates the cryogenic fracture toughness of weld metals in 9%Ni steels using Flux-Cored Arc Welding (FCAW) with a Ni-Cr-Mo-Nb filler. CTOD tests were conducted at room temperature (23 °C) and cryogenic conditions (-193 °C) to assess performance under extreme environments. Welds with lower precipitate content exhibited higher CTOD values, indicating improved fracture toughness. Crack propagation at -193 °C showed a transition to intergranular fracture modes, influenced by precipitate content and grain boundary structure. However, at ultra-low temperatures approaching -253 °C such as those found in LH2 storage standard 9%Ni steels may not offer sufficient fracture resistance58). For a 230,000 m³ aboveground liquefied hydrogen tank (0.2 MPa, atmospheric insulation), the required wall thickness was calculated as 47 mm for SUS304L and 28 mm for H-Ni steel. At 20 K, 15% Ni steel showed higher cryogenic toughness than 12% Ni steel, and both satisfied the KIC requirement of 132, likely due to the lower yield strength of the 15% Ni alloy59). Kim et al.58) that while several materials like STS316L, 9%Ni steel, and H-Mn steel show promising performance in cryogenic and hydrogen environments, standardization gaps still exist for LH2-specific applications. It emphasizes the urgent need to establish consistent testing standards, including fracture toughness and hydrogen compatibility evaluations, to ensure safety and reliability. In Japanese research efforts have proposed increasing the Ni content to 13-15% to improve ductility and fracture toughness under these more extreme conditions, however, there is no document published as an official report yet. Economically, 9%Ni steel remains a compelling option, offering strong performance at a lower cost than STS316L due to its reduced alloying content and the absence of Mo60).
Nonetheless, 9%Ni steel is relatively susceptible to hydrogen embrittlement, particularly in welded joints and the heat-affected zone (HAZ). Wang et al.61) was demonstrated that the addition of approximately 1 wt% Ni promotes the formation of retained austenite and facilitates dislocation emission, thereby enhancing both impact toughness and elongation of pipeline steel; however, when the Ni content exceeds 3 wt%, increased martensite and carbide formation leads to reduced ductility. Under hydrogen-charging conditions, the 1 wt% Ni steel exhibited the highest resistance to hydrogen embrittlement, whereas steels containing more than 2 wt% Ni showed increased susceptibility. These results indicate the existence of a threshold Ni concentration, above which both mechanical performance and hydrogen embrittlement resistance deteriorate. Fig. 1 confirms that a greater elongation loss occurs when a higher hydrogen charging current is applied. The influence of Ni on the toughness and strength of steel remains consistent under both hydrogen charging currents. The steel exhibits the highest elongation and tensile strength at a Ni concentration of Ni = 1 %, while further increases in Ni content lead to a gradual decline in both properties. When the Ni concentration exceeds 3 %, the elongation, yield strength, and tensile strength fall below those of the Ni-free specimens. Therefore, Ni additions can enhance the hydrogen embrittlement resistance of pipeline steel when the concentration is below 2 %, whereas concentrations above 2 % increase its susceptibility to hydrogen embrittlement. Elongation can thus be employed as an indicator for evaluating hydrogen embrittlement susceptibility61). Yu et al.62) investigated GTAW, SAW, and SMAW for nickel-based weld metals in liquid hydrogen tanks. The results showed that GTAW and SMAW produced relatively fine and uniform microstructures, while SAW generated much coarser grains with a strong {100} texture. Hardness values of weld metals were similar to the base 13% Ni steel (~250 HV), but the HAZ consistently reached 300-450 HV due to martensite formation. GTAW exhibited the most stable hardness distribution, whereas SAW displayed local softening at the weld center. FEM simulations confirmed that GTAW weaving technique promoted dendrite fragmentation and grain refinement, whereas SAW created larger molten pools that favored coarse columnar grain growth. From a hydrogen embrittlement perspective, the fine grains of GTAW and SMAW are advantageous in reducing susceptibility, while the coarse {100} oriented grains of SAW may increase cracking risk under hydrogen exposure. Overall, GTAW with weaving provided the most favorable balance of microstructure and hardness for cryogenic applications, highlighting the importance of welding method optimization for LH2 tank safety62). In this regard, Ni steel is recognized to exhibit a weakness in resistance to hydrogen em- brittlement. This concern may be mitigated through alloy optimization, including increased Ni content to stabilize the retained austenite phase and reduce diffusible hydrogen pathways. 9%Ni steel is a well-rounded alternative with solid cryogenic toughness and lower material cost, yet it requires mitigation strategies against hydrogen embrittlement in welded and heat-affected zones (HAZ)63).
The strain stress curves under hydrogen charing of (a) 200A/m2 (b) 500 A/m2, edited from reference 61
Although commercially available H-Ni alloys specifically designed for liquefied hydrogen applications have yet to be fully developed, conventional 9%Ni steels have already demonstrated excellent cryogenic stability in LNG and related applications. H-Ni steels containing 13% to 15% nickel are currently under development in countries such as Japan and Korea, and are anticipated to serve as promising candidate materials for future liquefied hydrogen storage and transport systems.
2.3 Characteristics of H-Mn steel for cryogenic use
H-Mn steel typically contains 18-30 wt% manganese and is highly suitable for cryogenic environments. Its FCC structure and twinning-induced plasticity (TWIP) mechanism result in excellent energy absorption under low temperatures. H-Mn steels are generally rolled within the recrystallization region to achieve excellent cryogenic toughness64,65,69-72). However, their yield strength typically remains below 400 MPa64-72). Although lowering the rolling temperature can effectively increase the yield strength, this approach significantly impairs cryogenic toughness. Recently, several strategies have been proposed to strengthen H-Mn steels. For instance, Park et al.73) enhanced the yield strength of H-Mn austenitic steel through a cold rolling-annealing process, but the cryogenic Charpy impact energy obtained was relatively low. Similarly, Li et al.74) developed a bimodal-grained TWIP steel using a cold rolling-aging annealing method, achieving a yield strength of 744 MPa and a Charpy impact energy of 100 J cm-2 at -196 °C35). H-Mn steel of weldability was also favorable, with minimal cold cracking and no need for post-weld heat treatment. The material is progressing toward IMO IGC/IGF code listing and commercialization for cryogenic fuel tanks75). The alloy also displays high work- hardening capability, which enhances strain uniformity and ductility during cryogenic deformation. The material exhibits excellent thermo plasticity with no traditional ductility trough and a maximum reduction of area of 89.4% at 1275 °C. Dynamic recrystallization and high stacking fault energy (>120 mJ/m²) promote superior ductility and dislocation slip. Inclusions such as Al2O3, AlN, MnO, and MnS(Se) were identified as critical factors affecting ductility and fracture behavior at elevated temperatures76,77).
Furthermore, H-Mn steels exhibit favorable weldability, with minimal risk of hot cracking or embrittlement, and typically do not require post-weld heat treatment (PWHT)78). However, the hydrogen behavior of TWIP steels under service conditions is still being investigated. Some studies suggest that stacking faults and twin boundaries may serve as hydrogen trapping sites, though no critical embrittlement phenomena have been reported to date79). In addition, H-Mn steel is currently undergoing inclusion in ASME and ISO standards for LNG80), and it is expected to be officially listed under the IMO IGC and IGF Codes by 2026.
H-Mn steel has already been applied to cryogenic LNG systems, demonstrating its safety and reliability in both marine and land-based storage tank applications. Ongoing studies are evaluating its mechanical properties and overall performance for potential use in cryogenic liquefied hydrogen environments. In addition, several national research initiatives are actively pursuing the development and qualification of H-Mn steel for liquefied hydrogen service. Full-scale commercialization and material standardization for LH2 applications are anticipated upon completion of these developmental efforts in the near future.
3. Mechanical Properties at Cryogenic Temperature
3.1 Tensile properties at cryogenic temperature
The tensile behavior of structural materials under cryogenic and hydrogen environments is critical for their application in liquefied hydrogen storage systems. The mechanical performance, particularly yield strength (YS) and ultimate tensile strength (UTS), generally improves as temperature decreases, while ductility, often represented by elongation at fracture, declines82-84). Austenitic stainless steels such as STS316L and STS304L are widely known for their excellent mechanical stability at cryogenic temperatures due to their fully austenitic FCC structure, which provides high ductility and work-hardening capability even under severe thermal contraction77,85,86).
STS304L, which shares similar compositional characteristics but lacks molybdenum, also demonstrates robust cryogenic performance. In tensile testing at 20 K, STS304L achieved yield strengths exceeding 1050 MPa and UTS values above 2400 MPa, albeit with evidence of discontinuous yielding and serrated flow due to dynamic strain aging effects. The elongation to fracture remained above 25%, and fracture surface analysis revealed a transition from ductile dimples to mixed- mode cleavage and tearing ridges with decreasing temperature87). These properties make STS316L and STS304L attractive candidates for structural components in cryogenic systems, including liquefied hydrogen (LH2) tanks. Notably, in 2021, Kawasaki Heavy Industries successfully deployed STS304L for the world’s first LH2 liquefaction and transport system, validating its structural integrity and hydrogen compatibility under full-scale operational conditions38). Both materials maintain structural integrity and ductility under extreme cold, positioning them as reliable solutions for cryogenic and hydrogen infrastructure.
For H-Mn steel, their austenitic FCC structure, combined with the twinning-induced plasticity (TWIP) effect, contributes to superior low-temperature tensile behavior. Chen et al.88) has shown that H-Mn TWIP steel exhibits UTS values exceeding 1000 MPa at cryogenic temperatures (77 K), with elongation retained above 40%, indicating excellent ductility and uniform deformation behavior under strain hardening. This makes H-Mn steels especially attractive for cryogenic applications where both strength and toughness are required86,87).
Additionally, TWIP steels exhibit strain-induced twinning, which delays necking and enhances uniform elongation. This deformation mechanism is particularly advantageous at cryogenic temperatures, where conventional materials often exhibit brittle fracture behavior. According to Chen et al.88) demonstrated that TWIP steels maintain uniform elongation above 40% at cryogenic conditions due to the activation of mechanical twinning, which effectively distributes strain and suppresses early necking. While these characteristics make TWIP steels promising candidates for cryogenic structural applications, further research is needed to understand the combined effects of hydrogen and low temperatures on their mechanical stability. In particular, Kim et al.63) reported that although the TWIP structure mitigates macroscopic hydrogen-induced brittle failure, features such as stacking faults and twin boundaries may act as reversible hydrogen traps, potentially influencing fracture behavior under hydrogen exposure. Similarly, Park et al.89) emphasized the importance of evaluating the performance of H-Mn steels under dynamic and hydrogen-rich cryogenic environments, as the synergistic effect of these conditions remains insufficiently characterized. Sohn et al.90) examined the influence of Mn (19 and 22 wt.%) and Al (0 and 2 wt.%) contents on the tensile and Charpy impact properties of austenitic H-Mn steels at -196 °C. The results revealed that Al addition increased the yield strength and improved toughness by suppressing stress-induced martensitic transformation. In contrast, the 19Mn and 22Mn steels exhibited extensive formation of ε- and α′-martensite, which caused severe ductility loss and a pronounced reduction in impact energy (10-17 J). Meanwhile, the 19Mn2Al and 22Mn2Al steels showed deformation dominated by twinning with minimal martensite formation, thereby retaining relatively high cryogenic impact energy (~40 J). With increasing Mn and Al contents, the tensile strength decreased while elongation increased, whereas the yield strength remained nearly unchanged. In Fig. 2 An increase in Mn and Al contents resulted in a decrease in tensile strength accompanied by an increase in elongation, while the yield strength showed little variation. The addition of Al completely eliminated the occurrence of serrated flow. At cryogenic temperature (-196 °C), both the yield and tensile strengths exceeded their room- temperature counterparts; however, elongation was considerably reduced (Fig. 2(a), (b)). This reduction was particularly severe in the 19Mn and 19Mn-2Al steels, whereas the 22Mn steel showed a relatively smaller loss in elongation (Fig. 3(b)). In contrast, the 22Mn-2Al steel exhibited negligible sensitivity of elongation to temperature. Although the tensile strength was largely unaffected by Mn content, it was consistently lower in the Al-containing steels than in the Al-free steels, while the yield strength was enhanced by Al addition. At -196 °C, serrated flow disappeared in all of the steels investigated (Fig. 2(c))90).
Yield strength, tensile strength, elongation and engineering tensile stress-strain curves of the four high-Mn steels at room and cryogenic temperatures, edited from reference 90
Strain rate dependence of yield strength and ultimate tensile strength, edited from reference 91
H-Ni steels, such as 9-15%Ni alloys, also show enhanced tensile properties at cryogenic temperatures. Shin et al.91) investigated the tensile properties of quenched and tempered 9% Ni steel under static and dynamic loading at room temperature (293 K) and cryogenic temperature (77 K), with strain rates from 10-3 to 5 × 10² s-1. At 77 K, yield and tensile strengths increased significantly to 904 MPa and 1093 MPa compared with 642 MPa and 713 MPa at 293 K, confirming strong low-temperature hardening. Strain-rate hardening was also observed: at 293 K, strengths rose by ~30% at 250 s-1, while at 77 K yield strength increased by ~20% though ultimate strength remained nearly constant. A notable result was that elongation was largely unaffected by temperature or strain rate, even at 77 K and high strain rates, indicating preserved ductility. Fractography consistently showed ductile dimpled fracture surfaces without evidence of brittle failure. Overall, the study demonstrated that 9% Ni steel combines increased strength and stable ductility at cryogenic conditions, making it highly resistant to brittle fracture and well suited for LNG storage tank applications. Fig. 3 illustrates the relationship between strain rate and both yield and ultimate strength. At 293 K, yield strength increased only slightly up to a strain rate of about 1 s-1, but beyond this point a marked hardening effect appeared, resulting in yield and ultimate strengths that were roughly 30% higher than under static conditions. At 77 K, yield strength also rose with increasing strain rate, showing gains of about 14% at 3.3 × 10-1 s-1 and 20% at 250 s-1 compared with the static case. Unlike yield strength, however, ultimate strength at 77 K remained nearly constant regardless of strain rate. These findings suggest that the influence of strain rate on yield strength is less pronounced at 77 K than at 293 K, because the strengthening caused by low-temperature hardening is already significant91).
9%Ni steel, widely used in LNG storage tanks, demonstrates excellent tensile performance at cryogenic temperatures, particularly at -196 °C. This performance is attributed to its dual-phase microstructure of tempered martensite and retained austenite, which offers a balance of strength and toughness. At -196 °C, the yield strength increases to approximately 600-700 MPa, while the ultimate tensile strength (UTS) reaches up to 1000 MPa, depending on heat treatment and alloy condition63,92). Although elongation decreases at cryogenic temperatures, it remains sufficient to prevent brittle fracture, thereby enabling safe use in LNG environ- ments. However, under ultra-low temperature conditions such as -253 °C-the boiling point of liquefied hydrogen-the mechanical performance of conventional 9%Ni steel begins to degrade. Fracture toughness values, such as CTOD and impact energy, decrease significantly, and the material may approach the ductile-to-brittle transition temperature63). Conventional 9%Ni steel performs reliably at -196 °C, its limitations at -253 °C have prompted the development of H-Ni steels in Korea and Japan. These new alloys offer enhanced mechanical stability and fracture resistance, positioning them as strong candidates for next-generation liquefied hydrogen containment systems. In response to these challenges, Japan has recently initiated the development of H-Ni steels with nickel contents increased to 13-15 wt% to stabilize the austenite phase and enhance low-temperature toughness for LH2 service59). These advanced steels are designed to maintain high strength and CTOD performance even at -253 °C, addressing the limitations of conventional 9%Ni grades. The applicability of high-strength 15% Ni steel for large liquefied hydrogen tanks, demonstrating an allowable stress of 230 MPa-1.68 times higher than SUS304L-and a required fracture toughness of 171 MPa√m at 20 K, which was satisfied by both the base metal and welded joints. These results indicate that 15% Ni steel offers the advantage of reducing the structural weight of large liquefied hydrogen tanks compared with the use of thicker SUS304L plates59).
3.2 Fracture Toughness Characteristics
Structural steels used for cryogenic applications must retain high fracture toughness at cryogenic temperatures such as -165 °C (for LNG) and -253 °C (for LH2). Among commonly evaluated metrics, CTOD provides a direct measure of crack-tip plasticity and resistance to fracture. Fracture toughness degradation becomes particularly significant at cryogenic temperatures, necessitating stringent mechanical integrity evaluations for structures such as ships and offshore platforms. In accordance with classification society requirements such as those outlined by the International Association of Classification Societies (IACS) minimum fracture toughness levels are mandated based on service temperature and structural location. For applications involving liquefied hydrogen (LH2), where service temperatures reach approximately -253 °C, it is essential to ensure sufficient fracture resistance to prevent brittle failure. Among the established assessment methods, the CTOD parameter is widely used to evaluate fracture toughness, especially for materials susceptible to brittle or cleavage fracture initiated by ductile crack growth. However, some high-toughness materials used in cryogenic environments exhibit ductile fracture behavior even at -253 °C93). Therefore, incorporating both CTOD and J-integral measurements may provide a more comprehensive understanding of crack driving forces and contribute to ensuring fracture safety under cryogenic conditions.
STS316L austenitic stainless steel, owing to its fully FCC structure, shows exceptional fracture behavior. According to Li et al.,94) at cryogenic temperatures, 316L stainless steel exhibited significantly increased yield and tensile strengths, with maximum elongation (42%) observed at 173 K. Deformation was governed by the transformation of γ-austenite to ε- and α′-martensite, while deformation twinning at 173 K enabled a superior combination of strength and ductility. The marked reduction in stacking fault energy with decreasing temperature was identified as the key factor controlling these mechanisms. Also, STS 304 stainless steel exhibited significantly increased tensile strength with decreasing temperature, while yield strength remained nearly unchanged and elongation dropped sharply at 193 K. The initiation fracture toughness (Jc) decreased markedly down to 193 K and then remained almost constant to 111 K, whereas the tearing modulus decreased linearly with temperature. Fractographic analysis revealed that the reduction in fracture toughness at cryogenic temperatures was closely associated with a decrease in the critical stretch zone width and dimple size. Fig. 4 shows that Jc decreases significantly as the temperature is lowered to 193 K, however remains nearly constant between 193 K and 111 K95).
The effect of temperature on initiation fracture toughness (Jc), edited from reference 95
Nickel steels have long been employed for cryogenic applications at temperatures down to -165 °C, with the applicable service temperature determined by the nickel content. For LNG storage vessels operating at -165 °C, 9% Ni steel is predominantly used, while grades containing 3-7% Ni have also been developed. More recently, efforts have been directed toward developing nickel steels capable of withstanding even lower temperatures, down to -253 °C, for potential application in liquefied hydrogen storage. Mu et al.46) showed that the CTOD toughness of H-Ni steel welds at cryogenic temperature is strongly influenced by precipitates. Welds with fewer precipitates exhibited higher CTOD values at both room and cryogenic temperatures, while increased precipitate size and quantity promoted intergranular crack propagation and reduced fracture resistance. 9%Ni steel has long been used in LNG storage tanks due to its tempered martensite and retained austenite microstructure, which allows it to achieve CTOD values in the range of 0.25-0.30 mm at -165 °C.
Park et al.,96) study investigated the fatigue crack growth rate (FCGR) and fracture toughness of nickel alloy steels with Ni contents ranging from 3.5% to 9% at room and cryogenic temperatures. Results showed that increasing Ni content enhanced fracture toughness by stabilizing retained austenite, while FCGR decreased with higher Ni content, particularly at low temperatures. Microstructural analysis confirmed that larger prior austenite grain size in higher Ni steels improved cryogenic toughness. The fatigue ductile-to- brittle transition (FDBT) temperature decreased with higher Ni levels, and no brittle failure was predicted within operating cryogenic conditions. Fig. 5 shows that the critical CTOD values of nickel alloy steels increase with higher nickel content. It is well established that nickel stabilizes austenite, and the critical CTOD value increases with the amount of retained austenite97-100). Therefore, the critical CTOD value is strongly influenced by the nickel content. It is anticipated that 9% Ni steel will exhibit reduced fracture toughness when exposed to an environment of -253 °C, with fracture surfaces transitioning toward quasi-cleavage or brittle morphology, particularly in the coarse-grained heat-affected zone (CGHAZ). To overcome this limitation, high-nickel alloys (13-15 wt% Ni) have been developed in Korea and Japan, demonstrating improved austenite stability and CTOD values up to 0.24 mm at -253 °C46).
Comparision of the critical CTOD values for nickel alloy steels with different nickel contents(Black color: 3.5Ni, Red color: 5Ni, Purple color: 7Ni and Blue color: 9Ni), edited from reference 96
H-Mn steels are another promising class of cryogenic materials. Their mechanical twinning promotes strain hardening and suppresses necking, resulting in high toughness. An et al.101) evaluated the fracture safety of H-Mn steel for LNG storage and fuel tanks under cryogenic conditions. CTOD value at -165 °C was around 1.05mm in base metal and 0.51mm in HAZ. As shown in Fig. 6, the minimum CTOD value of the H-Mn steel weld metal is 0.48 mm or more at -165 °C. Thus, it can be said that there was no risk of brittle fracture. Furthermore, the allowable crack lengths for preventing unstable ductile fracture were 600 mm and 480 mm, respectively, in the WM and HAZ under the largest allowable stress conditions. In Fig. 7 show the relationship between the fracture resistance and crack length for each allowable stress. The fracture safety evaluation showed that H-Mn steel weld joints do not exhibit unstable ductile fracture under the allowable stresses defined for B-type and C-type LNG tanks. Even with large or initial cracks, the critical stress for unstable fracture was much higher than the design stresses, confirming a sufficient safety margin.
CTOD test results at -165°C with base metal and weld joints, edited from reference 101
Ductile fracture instability analysis for crack in SAW at -165°C, edited from reference 101
These results confirm that while conventional 9%Ni steel is reliable at -165 °C, its applicability at -253 °C requires enhancements such as increased Ni content or alternative materials. Austenitic stainless steels and H-Mn steels offer superior cryogenic fracture toughness, with the latter providing a favorable balance of strength, ductility, and cost for future LH2 infrastructure.
3.3 Hydrogen Embrittlement Behavior of Cryogenic Structural Materials
The behavior of structural materials in hydrogen-rich environments has garnered increasing attention due to the expanding role of hydrogen in clean energy systems, particularly for liquefied hydrogen (LH2) storage and transportation applications. Materials employed in such environments must withstand synergistic effects of cryogenic temperatures (e.g., -253 °C) and hydrogen exposure, which can significantly alter their mechanical performance through hydrogen embrittlement (HE). Most studies on hydrogen embrittlement have concentrated on BCC-structured materials, primarily evaluating their tensile behavior under uniaxial loading (SSRT: slow strain rate tensile tests). Moreover, research on the effects of hydrogen embrittlement in FCC structured materials remains scarce.
Experimental techniques such as SSRT, disk rupture tests, and CTOD under hydrogen-charged environments are essential to quantify HE susceptibility. For instance, Dietzel102) proposed a modified CTOD test under gaseous hydrogen to assess crack arrest and propagation characteristics at cryogenic temperatures. This study applied crack-tip opening displacement (CTOD) and crack-tip opening angle (CTOA) methods to evaluate hydrogen embrittlement in high-strength steels and welded joints. Constant extension rate tests under hydrogen charging revealed that hydrogen significantly reduced crack-growth resistance, changing fracture behavior from ductile tearing to quasi-cleavage with secondary cracking at low displacement rates. CTOD/CTOA were shown to be effective parameters for characterizing hydrogen-assisted cracking, offering advantages over conventional linear elastic fracture mechanics (LEFM) or J-integral approaches, particularly for thin-sheet and welded structures. Moreover, diffusion analyses and thermal desorption spectroscopy (TDS) are increasingly employed to understand hydrogen transport and trapping behavior in candidate materials103). In contrast, only a limited number of quantitative investigations have addressed hydrogen embrittlement under bending loads through CTOD based fracture toughness assessments using used full thickness steel plate. Standardization efforts, including ASTM F1459, ISO 11114, and ISO/TR 15916, are ongoing to define suitable test protocols and safe design limits for hydrogen service.
Hydrogen embrittlement is a phenomenon where the ingress and presence of hydrogen within metallic materials cause a loss of ductility and toughness, often culminating in premature fracture. The primary mechanisms proposed include hydrogen-enhanced decohesion (HEDE), hydrogen-enhanced localized plasticity (HELP), and hydride formation, each dominating depending on the material system and environmental conditions104,105). Gabetta et al.,105) report that hydrogen embrittlement (HE) in pipeline steels requires the simultaneous presence of hydrogen, tensile stress, and material susceptibility, with the latter being the most critical factor. Current standards such as NACE and EFC provide only simplified guidelines, which do not fully capture the complexity of crack initiation and propagation in real service environments. The study emphasizes that quantitative evaluation based on crack growth rate, corrosion rate, and actual operating conditions is essential, rather than a simple “susceptible/non- susceptible” classification. At cryogenic temperatures, the mobility of hydrogen is reduced, but trapping at microstructural sites such as dislocations, grain boundaries, and twin boundaries can still result in significant embrittlement106).
Austenitic steels like 304L and 316L exhibit relatively good resistance to HE due to their FCC lattice structure, which supports high hydrogen solubility and low diffusivity107). For example, 316L retains ductile fracture characteristics even under hydrogen-charged conditions at room and cryogenic temperatures108). Fig. 8 shows the dimples in the shear stressfracture region of the non-, Ar-, and H-exposed specimens. The shear stress-fracture region also contained large and small dimples. The large dimples were typically elongated; the small ones were similar in size and appearance in both the normal and shear stress-fracture regions.108) Ando et al.109) observed that the CTOD values of 316L stainless steel under hydrogen exposure at -196 °C remained above 0.2 mm, indicating good fracture resistance. However, under extreme hydrogen concentrations or strain rates, even austenitic steels can experience localized plasticity and micro void coalescence leading to fracture. This study examined the effects of uniformly distributed hydrogen on the tensile properties and fracture morphologies of Type 316L stainless steel. Hydrogen charging reduced ductility by promoting localized shear deformation and void sheet formation, which refined the dimple structure on fracture surfaces. These findings indicate that hydrogen can induce ductile damage in 316L stainless steel through microstructural changes associated with void nucleation and growth109).
Morphologies of shear stress-fracture regions in non-, Ar- and H-exposed specimens, edited from reference 108
Koyama et al.80) investigated the hydrogen embrittlement behavior of H-Mn TWIP steels. Hydrogen charging significantly reduced elongation and impact toughness by promoting localized deformation through twinning and dislocation activity, which facilitated crack initiation. Although high Mn content and stable microstructures mitigated the degradation to some extent, susceptibility to hydrogen embrittlement remains a critical concern for their cryogenic applications. The influence of hydrogen on these steels is complex. While no catastrophic brittle fracture has been observed, twin boundaries and stacking faults have been identified as potential hydrogen trap sites, which could initiate damage under cyclic or high-strain conditions110,111). Further research is needed to clarify the interaction of twinning and HE under cryogenic-hydrogen synergistic conditions.
H-Ni steels, such as 9%Ni and newly developed 13-15%Ni variants, have been widely used in LNG tank construction and are being adapted for LH2 applications. Wang et al.,61) investigated the influence of nickel concentration (0-5 wt.%) on the toughness and hydrogen embrittlement resistance of X80 pipeline steel through tensile tests, Charpy impact tests, and molecular dynamics simulations. The results showed that steel with 1% Ni exhibited the highest toughness and best resistance to hydrogen embrittlement due to the promotion of retained austenite and reduced stacking fault energy. However, when Ni content exceeded 3%, carbide and martensite formation led to decreased toughness and increased hydrogen embrittlement sensitivity, indicating a critical threshold for Ni addition. Seong et al.,112) evaluated the fracture toughness of 9% Ni steel under cryogenic conditions with and without hydrogen charging using CTOD tests at -80, -100, -130, and -160 °C. Without hydrogen, fracture toughness decreased with lower temperature, while hydrogen- charged specimens showed reduced toughness at higher cryogenic temperatures (-80 °C, -100 °C) due to hydrogen embrittlement. However, at -160 °C, the fracture toughness of hydrogen-charged and uncharged specimens converged, indicating that the temperature effect dominates over hydrogen embrittlement at extremely low temperatures. Fig. 9 show the fracture toughness of non charged hydrogen specimens decreased consistently with decreasing temperature, while hydrogen-charged specimens exhibited an increase. At -80 °C, hydrogen-charged specimens showed a marked reduction in toughness due to the combined effects of hydrogen and low temperature. At -160 °C, however, fracture toughness values with and without hydrogen were nearly identical, indicating that at extremely low temperatures the influence of hydrogen embrittlement diminishes and temperature becomes the dominant factor.
4. Conclusions
This study reviewed three candidate materials for liquefied hydrogen (LH2) storage and transport: austenitic stainless steels, H-Ni steels, and H-Mn steels. For austenitic stainless steels, the review confirmed their excellent hydrogen resistance and toughness, however also highlighted their limitations of relatively low strength and high cost. For H-Ni steels, it was shown that conventional 9%Ni grades provide a proven balance of strength and toughness for LNG service, while newly developed 13-15%Ni steels are capable of maintaining fracture toughness and CTOD resistance down to -253 °C, thus extending applicability to LH2 envi- ronments. For H-Mn steels, the analysis demonstrated their attractive combination of high strength, excellent toughness, and cost competitiveness; however, their application to LH2 tanks requires further validation of hydrogen embrittlement resistance and the establishment of international standards.
Taken together, the comparative evaluation clarifies that each alloy system offers distinct advantages and limitations, and material selection for LH2 storage must therefore consider cryogenic toughness, hydrogen compatibility, weldability, and cost simultaneously. Future work should emphasize systematic qualification testing and standardization to ensure the safe deployment of these steels in large-scale LH2 storage and transportation systems. In addition, a comprehensive review of the mechanical properties and fracture toughness at -253 °C should be undertaken to ensure reliable performance in liquefied hydrogen environments. Since no international standards currently exist for material qualification at such ultra-low temperatures, it is imperative to accumulate systematic experimental data and fracture toughness databases. Establishing these benchmarks will not only support the development of unified standards but also provide a foundation for the safe design and certification of large-scale LH2 storage and transportation systems.
Acknowledgments
This study was funded by Chosun University grant number 2025.