Effect of hydrogen, residual stress and strain-induced martensite on delayed cracking of duplex stainless steel

Abstract

The effects of the hydrogen content, residual stress, and presence of strain-induced martensite on the delayed cracking behavior of duplex stainless steels after deep-drawing were investigated. These effects were compared with those of metastable austenitic stainless steels. Deep-drawing and slow strain rate tests (SSRT) were conducted over hydrogen pre-charged metastable austenitic and duplex stainless steel sheets. Delayed cracking was found to be accelerated by cathodic hydrogen charging. However, the effect of the hydrogen content on the delayed cracking was negligible under a specific residual stress level. The residual stress was found to greatly increase upon the formation of the strain-induced martensite phase. Thus, the main factor affecting the delayed cracking was the formation of the strain-induced martensite phase during the deep-drawing step. As revealed by the SSRT, the duplex stainless steels showed the highest hydrogen sensitivity after charging in terms of reduction of the tensile elongation and the fracture strength. On the other hand, the duplex stainless steel exhibited much higher resistance to delayed cracking compared with the metastable austenitic stainless steels since the strain-induced martensite phase was formed to a lower extent in the former material during deep drawing.