Korean Journal of Metals and Materials (대한금속재료학회지)

The Korean Institute of Metals and Materials (대한금속재료학회)
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Evaluation of Microstructure and Mechanical Properties on Post-Weld Heat Treatment in the Heat Affected Zone of SA508 Gr.4N Ni-Mo-Cr Low Alloy Steel for Reactor Pressure Vessel

원자로압력용기용 SA508 Gr.4N Ni-Mo-Cr계 저합금강 용접열영향부의 용접후열처리에 따른 미세조직과 기계적 특성 평가

  • 이윤선 (한국원자력연구원 원자력재료연구부) ;
  • 김민철 (한국원자력연구원 원자력재료연구부) ;
  • 이봉상 (한국원자력연구원 원자력재료연구부) ;
  • 이창희 (한양대학교 신소재공학과)
  • Received : 2008.08.25
  • Published : 2009.03.25
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Abstract

The heat-affected zone (HAZ) of SA508 Gr.4N Ni-Mo-Cr low alloy steel, which has higher Ni and Cr contents than SA508 Gr.3 Mn-Mo-Ni low alloy steel, was investigated on the microstructure and mechanical properties. The HAZ was categorized into seven characteristic zones (CGCG, FGCG, ICCG, SCCG, FGFG, ICIC and SCSC-HAZ) according to the peak temperature from the thermal cycle experienced during multi-pass welding. Post Weld Heat Treatment (PWHT) was conducted in the temperature range of $550{\sim}610^{\circ}C$ for 30 hours to evaluate the effect of PWHT conditions on the microstructure and mechanical properties. Before PWHT, CGHAZ and FGFGHAZ showed high yield strength (YS) ranging from 1000 to 1250 MPa, while YS of SCSCHAZ decreased from 607 MPa (observed for base metal) to 501 MPa. The Charpy impact energies of sub-HAZs fell below 100J at $-29^{\circ}C$, except in the SCSCHAZ. By applying PWHT to sub-HAZ specimens, YS decreased as the PWHT temperature increased. In the case of CGHAZs and FGFGHAZ heat-treated at $610^{\circ}C$, YS dropped drastically to the range of 654~686 MPa. From the Charpy impact test, the upper-shelf energy (USE) increased to approximately 250J and Index temperature ($T_{68J}$) decreased below $-50^{\circ}C$. Specifically, in FGFG, ICIC and SCSC-HAZ, $T_{68J}$ was below -110, which was lower than the case of base metal.

Keywords

Acknowledgement

Supported by : 지식경제부

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