Diode laser surface treatment of bearing steel for improved sliding wear performance

The high carbon Cr-bearing SAE 52100 steel grade in hardened and tempered condition is widely used for production of bearings in the automotive, machinery, wind turbine and construction industries. It is extensively used for these applications due to various technological advantages like high hardness, strength and good formability coupled with low cost. However, many-a-times, excessive wear along with noise/vibration causes premature failure and/or necessitate early replacement of bearings. Furthermore, contact fatigue and bulk toughness are observed to be inadequate in heavy duty/load applications. Engineering the surface of prior-hardened bearing steel by laser surface hardening to further enhance surface hardness without affecting the bulk can be gainfully utilized for tailoring tribological properties to improve life. In the present work, the effect of pulsed-wave (PW) mode of hardening on surface hardening of 52100 bearing steel with prior through-hardened condition is investigated with analysis of case depth, hardness, microstructure and tribological properties are discussed in detail. Results indicated enhanced microstructural refinement with partially dissolved carbide globules in PW mode as compared to that processed under Continuous-wave (CW) mode. 25-30% higher peak hardness could be achieved in PW mode with retention in core strength as compared to that of CW counterpart. Sliding wear testing results showed five-fold and three-fold improvements in un-lubricated and lubricated conditions in laser processed surface as compared to that of untreated counterpart. On the whole, the PW mode of processing showed vast improvement in hardness and sliding wear resistance.