Stress Relief Cracking of Ferritic Steels: Part Two

요약:

Known also by a range of synonyms, Stress-Relief Cracking (SRC) is intergranular cracking in the heat affected zone (HAZ) or weld metal that occurs during exposure to in-service temperatures or post-weld heat treatments.
The different impurities and tramp elements have a direct impact, mostly detrimental, on the SRC process and we explore further each element and how they affect the materials overall susceptibility to stress relief cracking.

During the application of such a heat treatment to the weld HAZ of Cr - Mo - V steels, carbides are precipitated from the supersaturated solid solution in a manner similar to that which would occur in a normal tempering operation. The type and morphology of the carbide precipitates depend in detail upon the composition of the parent plate and of the weld metal, and on the temperature of the stress relieving heat treatment. Many workers, have observed that a stress relief heat treatment of welded low, alloy steel results in increased precipitation of fine alloy carbides within the matrix of the weld HAZ. The occurrence of precipitate free zones adjacent to the grain boundaries has also been reported in some investigations, but not in a consistent manner.

Stress relief cracking is a common cause of weld failures in many creep resistant precipitation strengthened alloys. The general definition of SRC is intergranular cracking in a welded assembly that occurs during exposure to elevated temperatures produced by post-weld heat treatments (PWHT) or high temperature service. The coarse-grained heat-affected zone (CGHAZ) is the most susceptible region of a weldment. SRC occurs mainly in ferritic alloy steels.

Alloying and tramp elements can have a large influence on the stress-relief cracking susceptibility of a material. Mo, V, and Cr are commonly added to steels to improve mechanical properties, but it is also these elements that form carbides that precipitate in the grain interiors during post-weld heat treatment and increase the susceptibility to stress-relief cracking. In general, those elements that promote the formation of detrimental M2C and M4C3 carbides or act as grain boundary embrittling elements increase the susceptibility to SRC. Elements generally considered to be detrimental to SRC are Mo, V, C, Nb, Cu, AI, and tramp elements such as S, P, Sb, As, and Sn.

Alloying elements or impurity elements can generally be placed into one of five categories:
1) promoters of segregation that act as co-segregators with impurities such as Mn;
2) promoters of segregation that do not segregate such as Cr;
3) scavengers that prohibit segregation such as Ti and Mo;
4) grain boundary embrittlers such as Si, P, S, As, Sn, Sb;
5) improve grain boundary cohesion such as carbon;

Table 1 seen below is a brief summary of the effects of each element with respect to stress-relief cracking susceptibility:



Table 1: The effects of each element with respect to stress-relief cracking susceptibility


References

1. R. A. Tait: Stress relief cracking in creep resisting low alloy ferritic steels, PhD Dissertation, July 1976, University of Cambridge, Stress Relief racking - Bob_Tait.pdf, Accessed August 2020;

2. Y. Jin, H. Lu, C. Yu, Y. Liu: Stress-relief cracking susceptibility and Microstructural Characteristics of Modified T23 Steel, Transactions of JWRI, Special Issue on WSE2011, 2011, p.45-46;

3. J. G. Nawrocki: A study on the stress-relief cracking susceptibility of a new ferritic steel, These and Dissertation, Lehigh University, 1998, Paper 513, Accessed May 2020;

기술 자료 검색

검색할 어구를 입력하십시오:

검색 범위

본문
키워드

머릿글
요약

Total Materia Extended Range는 수천개 금속 합금의 열처리 조건 및 하중 조건에 대한 파괴 공학 변수 데이터베이스를 포함하고 있습니다. K1C, KC, 균열 성장 및 Paris 법칙 변수와 이에 대응되는 균열 성장 그래프가 제공됩니다.

단조 특성도 참조를 위해 추가되어 있으며 단조 특성을 통해 예상되는 빠진 변수의 추정치도 필요한 곳에는 포함되어 있습니다.

신속 검색에 검색할 재질명을 입력합니다. 원하신다면 국가/규격을 지정하신 후 검색 버튼을 클릭합니다.


결과 리스트에서 재질을 선택하시면, 일련의 규격 사양 소그룹이 나타납니다.


Total Materia 파괴 공학 데이터는 규격 사양서와 무관하므로, 어떠한 소그룹 내의 링크를 클릭하셔도 파괴 공학 데이터를 검토하실 수 있습니다.

데이터는 표로 출력되며, 가능한 곳에는 Paris 곡선(Region II)와 함께 출력되어 있습니다. 데이터 출처에 관한 정확한 참조가 각 데이터에 주어져 있습니다.


Total Materia 데이터베이스를 사용해 보실 수 있는 기회가 있습니다. 저희는 Total Materia 무료 체험을 통해 150,000명 이상의 사용자가 이용하고 있는 커뮤니티로 귀하를 초대합니다.