1999 Volume 85 Issue 3 Pages 229-235
Cracking parallel to the wire axis (longitudinal cracking) occurs during or after the drawing of metastable austenitic stainless steel wires. In this paper, the mechanism of cracking was investigated in relation to the behavior of deformation induced martensitic transformation, hydrogen content and residual stress in the steel wires drawn under different several conditions. Results obtained are as follows:
(1) Martensite formed through deformation induced transformation is of lath-structure, but the lath-structure is broken and changed to dislocation cell structure during heavy drawing, which is characterized with the poor ductility.
(2) Microcracks are formed around inclusions and carbide particles which are just in the heavily deformed martensite with dislocation cell structure. This leads to the cracking parallel to the wire axis.
(3) Such a cracking occurs not only during drawing but also during aging at room temperature after drawing with the asist of residual stress and diffusive hydrogen.
(4) Main reason for the cracking is thought to be stress concentration at inclusions and carbide particles which results in the formation of microcracks, and the structural change of martensite, existence of hydrogen and residual stress are secondary factors which promote the crack initiation.