Wear resistance enhancement of QT700-2 ductile iron crankshaft processed by laser hardening

[Display omitted] •The mixed microstructures of laser hardened QT700-2 ductile iron, including martensite, austenite and graphite nodules, are obtained simultaneously by tailoring the laser process parameters.•The hardness of laser hardened QT700-2 ductile iron (greater than 800 HV) is 3 times greater than that of base material (250–300 HV).•The wear depth of laser hardened QT700-2 ductile iron reduces from 17.57 μm to 11.45 μm, and the coefficient of friction reduces from 0.8 to 0.6.•The combined influence of hardening effect and self-lubricating mechanism contributes to the improvement in hardness and wear performance of laser hardened QT700-2 ductile iron. As an important component of automotive engines, the crankshaft usually requires surface treatment to improve its service reliability and lifetime. This work provided a detailed laser parameter study to enhance the wear performance of the QT700-2 ductile cast iron crankshaft sample (thickness of 10 mm), using a fiber laser (maximum power of 2000 W) hardening system. FEA temperature field simulation was performed to initially estimate an appropriate parameter range, and then verified by single factor experiments to evaluate the individual laser parameter effect. The microstructural observation unveiled an evolution from pearlite in the base material to fine needle-shaped martensite with graphite nodules and retained austenite in the laser hardened layer, where phase transformation was found to be more dependent on laser scanning speed. With the optimized laser parameter set, the hardened layer hardness increased from 250 HV to more than 800 HV, reducing the corresponding wear depth from 17.57 μm to 11.45 μm and coefficient of friction from 0.8 to 0.6. The significantly enhanced wear performance was mainly resulted from wear mechanisms transition from sever ploughing wear in the base material to mild adhesive wear in the laser hardened region.