Microstructure And Mechanical Properties Of Temperformed Spring Steel

The microstructure and mechanical properties of 60Si2Mn spring steel subjected to quenching and temperforming were investigated in this work.The steel was quenched in oil and then temperformd by rolling at different temperatures at a liner speed of 0.8 m/s and a reduction of 50%. Microstructure morphology before and after temperforming were observed by optical microscopy (OM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). In addition, the comparison in microstructure and properties between temperforming and traditional tempering samples was made.Results show that the microstructure in temperformed samples was composed of incompletely recrystallized ultrafine-grained ferrite and nanoparticles of cementite distributed dispersively. The average ferritic grain size of 118 nm and the average cementite particle size of 32 nm were obtained in the sample rolled after heating at 580 ?C for 8 min.By comparing the mechanical properties of samples with different temperforming process, the optimum process can be determined to be temperforming at 580 ?C after holding 8 min. Using the mini tensile sample described in ASTM E8?04 standard, the mechanical properties of the sample treated by the optimum process were measured as follows: the tensile strength 1505 MPa, the yield strength 1400 MPa, the total elongation 6.9%, the yield ratio 0.93. Using the mini impact sample with Charpy?U notch described in ASTM E23?02, the impact energy was measured to be 16 J. The hardness of the sample was determined to be about HRC44.6. Comparing with the traditionally treated sample, the tensile strength, yield strength, yield ratio and hardness increased by 11.6%, 15.5%, 5.7% and 9.3%, respectively, and the elongation decreased slightly and the area reduction did not drop.Delaminated morphologies of tensile and impact fractures were formed in tempformed samples, and the micro-morphologies of these fractures exhibited as micro-dimples. Three-point bending fatigue is a typical "fish eye" fracture. Fatigue cracking within the sample is mainly caused by non-metallic inclusions that composed of Al, O, Mg and Ti.