Effect of Residual Stress and Strain-Induced [alpha]'-Martensite on Delayed Cracking of Metastable Austenitic Stainless Steels

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 45; no. 3; p. 1238
• Main Authors: Papula, Suvi, Talonen, Juho, Hänninen, Hannu
• Format: Journal Article
• Language: English
• Published: New York Springer Nature B.V 01.03.2014
• Subjects: Austenitic stainless steel; Martensitic stainless steel; Metallurgy; Residual stress
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-013-2090-3

The role of residual stresses and strain-induced [alpha]'-martensite in delayed cracking of metastable austenitic stainless steels was studied by means of Swift cup tests, measurement of residual stresses by X-ray diffraction and ring slitting, and [alpha]'-martensite content determination. Low-Ni, high-Mn austenitic stainless steels, e.g., AISI 201, were compared with Fe-Cr-Ni austenitic stainless steels. The presence of [alpha]'-martensite seemed to be a necessary prerequisite for delayed cracking to occur in austenitic stainless steels with typical internal hydrogen concentrations (<5 ppm). Stable low-Ni austenitic stainless steel was not prone to delayed cracking. The low-Ni metastable grades showed more severe cracking at lower degree of deformation and lower volume fraction of [alpha]'-martensite than that of the metastable 300-series grades. The limiting [alpha]'-martensite content, below which delayed cracking did not occur, decreased along with the nickel content of the material. The strain-induced martensitic transformation substantially increased the magnitude of residual stresses in deep-drawn cups. One explanation for high sensitivity of the low-Ni grades to delayed cracking after deep drawing is their higher residual stresses compared to that of the Fe-Cr-Ni grades. Alloying elements of the stainless steels, nickel, and carbon in particular, influence the sensitivity to delayed cracking through their effect on the properties of the [alpha]'-martensite.[PUBLICATION ABSTRACT]