Fracture toughness evaluation of a high-strength cold-drawn Type 304 stainless steel wire

摘要

This study shows that stress relieving to reduce axial residual stress can affect fracture behavior. Fracture toughness, Kc values, for two conditions of a 1.1 mm type 304 stainless steel wire were reported. For a given crack size, a/D, the stress-relieved wire showed higher fracture strength values than the as-drawn wire. This was shown to be related to the reduction of axial residual stress at the center of the wire. The average Kc value for stress-relieved wire was 53 MPa√m and that for as-drawn wire was 49 MPa√m. These values compared well with previously reported values for a 0.965 mm AISI 1095 wire (50.5 MPa√m) and a 0.965 mm AISI 1075 wire (56.4 MPa√m). SEM fractographs documenting fracture surface topography of various fracture modes were presented. Fracture behavior of pre-cracked type 304 stainless steel wires appears to be different than that of high carbon wires shown in previous reports. A patented process was introduced in which a wire rope manufactured from high toughness stress relieved wires exhibited the highest strength, and efficiency. In this process, wires were first stress relieved to substantially reduce the magnitude of axial residual stress at their center. In a subsequent stranding process, the strand was compacted in such a way that a compressive residual stress of as high as 545 MPa was induced on the outer wire surfaces. The application of this fracture toughness test methodology can prove to be very useful in future studies concerning the influence of microstructure and process variables in the tensile and fatigue fracture behavior of high-strength cold-drawn wires.