Cr-Mo합금강의 용접후열처리에 따른 균열감수성 평가에 관한 연구 = A study on Evaluation of PWHT Cracking susceptibility of the Cr-Mo steel alloys

다국어 초록 (Multilingual Abstract)

This study was undertake to provide fundamental and basic metallurgical information on the behavior of the heat affected zone(HAZ) in Cr-Mo steel welds as well as practical information on their relative weldability.
The test methods were varied to investigate the effect of post weld heat treatment (PWHT), metallurgical structure and restraint (externally applied) on the weld cracking susceptibility.
This study is used to C-ring test method. The C-ring test, normally employed for evaluating susceptibility to stress-corrosion cracking, was determine to be a suitable and small scale test to evaluate PWHT cracking susceptibility. This test incorporates all aspects of the ideal test outlined by Baker.
It is possible to incorporate an actual weld, to introduce a notch into the coarse grained HAZ, to load the coarse grained HAZ to any level of stress and, most importantly, since the c-ring is an approximately constant strain type test, the stress decreases with time at temperature in a manner similar to that of an actual weldment.
Four test conditions were employed for C-ring testing, utilizing two PWHT temperatures, 620℃ and 680℃, and three stress levels, 690MPa, 550MPa, and 410MPa. The 690MPa stress was used at both PWHT temperatures in order to determine the effect of temperature on cracking.
The samples generated during testing provided test data as well as metallographic specimens for examination by optical and electron optic techniques (SEM). Evaluation of the metallographic specimens defined the effect of microstructure on the weld cracking susceptibility.

목차 (Table of Contents)

• Nomenclatures ⅲ
• List of Tables ⅲ
• List of Figures ⅳ
• List of Photographs ⅳ
• 제 1장 서론 1
• 1.1 연구 배경 1
• 1.2 연구 동향 4
• 1.3 연구 목적 7
• 제 2장 이론적 고찰 8
• 2.1 용접후열처리 8
• 2.1.1 용접후열처리 효과 8
• 2.1.2 용접후열처리 문제점 9
• 2.1.3 용접후열처리 조건 11
• 2.1.4 용접후열처리 실시상의 주의점 16
• 2.2 용접저온균열 16
• 2.2.1 용접균열의 분류 16
• 2.2.2 저온균열(Cold Cracking) 19
• 2.2.2.1 저온균열 발생 원인 19
• 2.2.2.2 지연균열(Delayed Cracking) 20
• 2.2.2.3 ？？칭균열(Quenching Crack) 22
• 2.2.2.4 라멜라 티어링(Lamellar Tearing) 22
• 2.2.3 재열균열 (SR Cracking) 23
• 2.2.3.1 분류 23
• 2.2.3.2 특징 23
• 2.2.3.3 균열방지 방안 24
• 제 3장 실험재료 및 방법 25
• 3.1 시험편 제작과 평가방법 25
• 3.2 C-ring 시험의 평가방법 28
• 제 4장 실험결과 및 고찰 30
• 4.1 3Cr-1Mo과 2¼Cr-1Mo강의 C-ring 시험 결과 30
• 4.2 2¼Cr-1Mo강과 3Cr-1Mo강의 C-ring 시험에 대한 광학
• 현미경 관찰 및 파면시험 평가 32
• 제 5장 결론 38
• 참고문헌 39
• Abstract 42