Effects of solution treatment and cold rolling on microstructure and mechanical properties of stainless steel for surgical implants

To obtain basic data for developing manufacturing processes for stainless steels for implant application, we determined how solution treatment and cold rolling affect the microstructure and mechanical properties of stainless steels. The grain size of the austenitic (gamma) phase in solution-treated ISO 5832 stainless steel tended to increase with solution-treatment temperature. The effects of solution-treatment temperature on the 0.2% proof strength (60.2%PS) and ultimate tensile strength (sigma(UTS)) of this stainless steel were almost negligible, while total elongation (T. E.) tended to increase slightly with solution-treatment temperature. The mechanical properties of ISO 5832 stainless steel solution-treated at 1075 degrees C for 30 min were as follows: sigma(0.2%PS), 303 +/- 3 MPa; sigma(UTS), 670 +/- 2 MPa; T. E., 65 +/- 2%; and reduction of area (R. A.), 71 +/- 2%. In the TEM image of 20% cold-rolled ISO 5832 stainless steel, many dense dislocations, which were produced by cold rolling, were observed. The sigma(0.2%Ps) and sigma(UTS) of the cold-rolled stainless steel increased as the draft increased, whereas the T. E. decreased linearly with an increase in the draft. The sigma(0.2%PS), sigma(UTS), T. E., and R. A. of 20% cold-rolled ISO 5832 stainless steel were 758 6 MPa, 890 2 MPa, 22 2%, and 68 +/- 4%, respectively. In the microstructural observation of solution-treated high-N stainless steel, CrNbN and Mn2SiO4 were observed. The mechanical properties of this stainless steel were as follows: sigma(0.2%PS), 436 4 MPa; CUTS, 830 4 MPa; T. E., 37 2%; and R. A., 48 +/- 7%.