Effect of Welding Heat Input and PWHT Cooling Rate on Mechanical Properties of Welded Region at SAW of  1.25Cr-0.5Mo Steel for Pressure Vessel

Lee, Dong-Hwan; Park, Jong-Jin

Journal of KWJS 2004;22(5):26-31.
Published online November 12, 2004.

[기술논문] 압력용기용 1.25Cr-0.5Mo 강의 Submerged Arc Welding시 입열 및 PWHT 냉각속도가 용접부 기계적 성질에 미치는 영향

Effect of Welding Heat Input and PWHT Cooling Rate on Mechanical Properties of Welded Region at SAW of 1.25Cr-0.5Mo Steel for Pressure Vessel

Dong-Hwan Lee, Jong-Jin Park

Abstract

In order to propose the optimum welding condition for field application, the effects of welding heat input and cooling rate at PWHT on the mechanical properties were investigated. Submerged arc welding of l.25Cr-0.5Mo steel for pressure vessel was conducted at welding heat inputs of 15.2KJ/cm, 30.9KJ/cm, and 44.8KJ/cm, and cooling rates of l84℃/hr, 55℃/hr, and 20℃/hr at PWHT. From the test results, as the welding heat input increase up to 30.9KJ/cm, the changes of microstructure and impact toughness were small. At the heat input of 44.8KJ/cm, however, toughness decreased obviously due to the coarsening of coarse-grained HAZ and formation of ferrite at bainite grainboundary of weld metal. On the other hand, cooling rates at PWHT did not effect on the changes in microstructure and mechanical properties. Even though tensile strength and impact toughness at all welding conditions of this study were above the minimum specification requirement, it was confirmed that heat input of 30.9KJ/cm was the optimum welding condition to improve welding performance by higher heat input.