Cr-Mo 합금강의 후열 처리 균열 감수성 평가

김상진,김기수,이영호 대한공업교육학회 2006 대한공업교육학회지 Vol.31 No.1

This C-ring test, normally employed for evaluating susceptibility to stress-corrosion cracking, was determined to be a suitable small scale test to evaluate PWHT(Post-Weld Heat Treatment) cracking susceptibility. This test is possible to incorporate an actual weld, to introduce a notch into the coarse grained HAZ(Heat Affected Zone), to load the coarse grained HAZ any level of stress ad, 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 steel weldment. The procedure employed in making the C-ring was presented in the experimental procedure section, however, several points deserve further discussion. The walls of the weld groove are made along radial lines form the center of th var in order to obtain an HAZ which is oriented perpendicular to the walls of the machined C-ring. Therefore, the plane of maximum stress will be aligned through the HAZ and, therefore, crack propagation will not be forced to deviate form the plane of maximum stress in order to remain in the coarse grained HAZ as is the case with the Y groove test. 초기 응력부식균열에 대한 감수성 평가 시험법인 C링 시험법(C-ring Test)은 용접부의 후열처리 균열감수성을 평가하는 시험법으로 적합하다고 알려져 있다. C링 시험법은 실제 용접부 열영향부에 노치를 제작하여 잔류응력이 열영향부에 미치는 영향을 평가할 수 있다는 장점을 가지고 있다. 따라서 본 연구에는 C링 시험법을 이용하여 원자력 발전소 압력용기에 사용되는 Co-Mo강의 용접부 결함 발생 현상을 검토 하고자 Co-Mo강에 대하여 후열처리를 실시하였으며, C링 시험법을 통하여 용접 열영향부의 후열처리 균열을 평가하고자한다. 결론은 다음과 같다.바나듐 모디파이 합금(AMAX 3Cr­1Mo­0.1V, JSW 3Cr­1Mo­V­Ti­B 및 JSW 2¼Cr­1Mo­V­Ti­B강)은 Berkeley 3Cr­1½Mo­ ½Ti 및 2¼Cr­1Mo합금강보다 후열처리 균열에 대한 감수성 보다 높게 나타났다.C-ring 시험에 있어서 바나듐 모디파이 합금은 2종의 후열처리조건과 3종의 응력조건에서 모두 균열을 나타냈으나 Berkeley 3Cr­1½Mo­½Ni강과 Luken 2¼Cr­1Mo­0.1C재료는 690㎫와 더 이상의 응력조건에서 2종의 후열처리를 실시하는 조건에서도 균열이 발생하지 않았다.C-ring 시험결과, 균열깊이는 바나듐 모디파이 재료인 경우, 낮은 후열처리온도와 비교해서 높은 후열처리온도인 경우가 감소하고 있다.C-ring 시험에 대한 SEM분석결과 균열은 오스테나이트 결정 입계를 따라 파괴되는 파괴양상을 나타내고 있으며 연성파면은 나타나지 않았다.

음향방출법에 의한 고 장력강 용접부의 부식손상 특성 평가

나의균,김훈 한국비파괴검사학회 2003 한국비파괴검사학회지 Vol.23 No.3

본 연구의 목적은 음향방출법을 이용하여 고 장력강 용접부의 응력부식균열특성을 평가하는데 있다. 이를 위해 용접재와 후열처리재를 대상으로 인공해수에서 저 변형률로 하중을 가하면서 응력부식균열을 일으키고, 동시에 음향방출법에 의해 손상과정을 감시하였다. 부식환경은 전위계에 의해 제어되었으며, 시험편에는 각각 -0.8 V와 -1.1 V의 전위값을 가하였다. -0.8 V인 부식환경 하에서 일층 용접부는 후열처리재에 비해 단위 시간당 AE counts 수가 훨씬 많이 발생하였으며, 응력부식균열과정에서 균열의 발생 및 합체가 가장 활발하게 이뤄지고 있음을 누적 AE counts의 결과로부터 확인할 수 있었다. 가해진 전위 값이 -1.1 V인 경우, 일층 용접재의 파단시간은 이층 용접재에 비해 줄었고, AE counts수는 이층 용접재에 비해 현저히 많이 발생하였다. AE진폭 범위는 -0.8 V일층 용접재에서 가장 높았고, -1.1 V 일층 용접재에서 가장 작은 값을 보였는데, fractography분석결과 AE 진폭범위는 균열의 크기 및 폭과 밀접한 관계가 있음을 알 수 있었다. This study is to evaluate the characteristics of SCC at the welded region of high strength steel using acoustic emission(AE) method. Specimens were load by a slow strain rate method in synthetic seawater and the damage process was monitored simultaneously by AE method. Corrosive environment was controlled using the potentiostat, in which -0.8 Vand -1.1 V were applied to the specimens. In the case of one-pass weldment subjected to -0.8 V, much more AE counts were detected compared with the PWHT specimen. It was verified through the cumulative counts that coalescence of micro cracks and cracks for the one pass weldment with -0.8 V were mostly detected. In case of the one pass weldment subjected to -1.1 V, time to failure became shorter and AE counts were produced considerably as compared with that of the two pass weldment. It was shown that AE counts and range of AE amplitude have close relations with the number and size as well as width of the cracks which were formed during the SCC.

Alloy617 용접부의 부식 및 부식피로균열성장 특성 평가

황정호(Hwang Jeong Ho),박영수(Park Young Soo),이주화(Lee Ju Hwa),배동호(Bae Dong Ho) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11

In this study, electrochemical corrosion and corrosion fatigue crack growth characteristics of a multi-pass welded Ni-base super Alloy617 were assessed. In 3.5 wt.% NaCl, glacial acetic acid and distilled water environment, corrosion rate of Alloy 617 weld linearly increased with temperature increase and was much sensitive to corrosion than base material. And by electrochemical corrosion reaction, Cr and Mo which were related with corrosion-resistance and strength were precipitated. In 70 , 3.5 wt.% NaCl solution, corrosion fatigue crack growth rate of Alloy 617 weld was assessed as 1.6 times in before PWHT condition and 1.82 times in after PWHT condition than that in air condition. These results were expected due to precipitation of Cr, Mo and degradation of the weld by corrosion. And they accelerate the inter-granular corrosion and fatigue crack growth rate.

이종금속 용접에 사용되는 ER309L 용접금속의 기계적 성질에 미치는 후열처리의 영향

최한글 한국산업기술융합학회 2023 산업기술연구논문지 (JITR) Vol.28 No.3

STS309(L) is widely used as a welding material for dissimilar welding of carbon steel and stainless steel. In general, austenitic stainless steel does not perform post-weld heat treatment (PWHT) to relieve thermal stress even after welding due to a sensitization. However, in the case of dissimilar joints between carbon steel and stainless steel, PWHT is often performed to relieve the thermal stress resulting from welding in carbon steel. Nevertheless, the stainless steel side may be subjected to heat treatment during PWH, leading to a deterioration in the mechanical properties of the stainless steel. Therefore, in this study, we investigated the effects of PWHT duration on the ferrite volume fraction, ferrite number, and mechanical properties. Through this, we aimed to determine the maximum post-heat treatment duration. The chemical composition did not change with an increase in the post-heat treatment time; however, the elongation and ferrite number decreased, and the tensile strength increased.

철도차량 대차프레임의 용접 및 보수용접의 잔류응력 특성평가

서정원,권석진,구병춘,이찬우,이동형 한국도시철도학회 2020 한국도시철도학회논문집 Vol.8 No.4

The bogie frame of a railway vehicle requires a service life of 25 years or more, and because of repeated fatigue loads during operation, cracks occur in the welding part. There are several ways to repair cracks, but in the case of a bogie frame, repair welding is performed by GMAW after removing the cracks. Residual stress inevitably occurs in the weld, which has a great influence on the fatigue strength and varies depending on the material and welding method. In this paper, the residual stress characteristics of SM490A, the material used in the bogie frame, were evaluated for welding and repair welding. For this, finite element analysis procedures for welding and repair welding were presented, and specimens were prepared and tests were performed. In addition, the change of residual stress according to the post weld heat treatment(PWHT) was investigated through F.E. analysis. 철도차량의 대차프레임은 25년 이상의 수명을 요구되고, 주행 중에 반복적인 피로하중이 작용하므로 용접부위에서 균열이 발생한다. 균열을 보수하는 방법은 여러 가지가 있지만, 대차프레임의 경우에는 균열을 제거한 후 가스메탈아크용접으로 보수용접을 실시한다. 용접부에서는 잔류응력이 필연적으로 발생하고 이는 피로강도에 커다란 영향을 미치며 재료 및 용접방법에 따라서 달라진다. 본 논문에서는 대차프레임에서 사용하고 있는 재료인 SM490A에 대한 용접 및 보수용접에 대한 잔류응력 특성을 평가하였다. 이를 위하여 용접 및 보수용접에 대한 유한요소해석 절차를 제시하였고, 시험편을 제작하여 이에 대하여 검증하였다. 또한, 후열처리 조건에 따른 잔류응력변화를 유한요해석을 통하여 조사하였다.

보일러 배관용 P92 파이프강의 기계적 특성 및 미세조직에 관한 연구

김범수(Beom Soo Kim),손태하(Tae Ha Son),민택기(Taek Ki Min) 대한설비공학회 2012 설비공학 논문집 Vol.24 No.11

The hardness and strength test was performed to make the manufacturing process of SA213 P92 boiler pipe steel. And the microstructure change was studied to find out the cause of room temperature property of P92 steel, ie, low hardness and strength property. The room temperature property of P92 steel depends on the improper normalizing and cooling rate. Especially, Ferrite was formed and the steel had low hardness when the temperature was decreased slowly under the cooling rate 1℃/min after normalizing at the temperature around Ac1 to Ac3. The critical heat treatment temperature and cooling rate was over 900℃ and over 10℃/min to satisfy the minimum yield and tensile stress which was laid down by ASME Code.

SS400 용접부의 피로강도에 미치는 쇼트 피닝의 영향

김진헌(Jin-Hern Kim),구병춘(Byeong-Choon Goo),김현규(Hyun-Gyu Kim),정성균(Seong-Kyun Cheong) 한국철도학회 2009 한국철도학회논문집 Vol.12 No.6