High Strength Steel solutions for powertrain applications

Abstract

ArcelorMittal focuses on both mechanical performances and machinability while designing new steel grades. ArcelorMittal has developed specific programs for machinability testing in turning, low and high speed drilling and gear machining. Machinability is evaluated through cutting forces, chip shape, surface quality and tool life. Gear machining is one of the main machining operations involved in powertrain manufacturing operations. The literature proposes many papers dealing with this process however there are too few studies interested in steel machinability evaluation while gear machining. This paper focuses on a particular gear manufacturing process, i.e. gear hobbing, and more precisely on steel machinability for gear hobbing applications. Tools as well as kinematics of gear hobbing are quite complex. This paper proposes a comprehensive experimental protocol for machinability testing. This protocol is based on a European standard. Tests are performed on a machine tool using a commercially available cutting tool. Tests provide the range of cutting conditions for five different steel grades. Both steels have a ferrite-pearlite structure with yield stress from 530 to 800 MPa and ultimate tensile stress from 680 to 900 MPa. Four grades are devoted to bar machining. The last one is devoted to forming and then machining operations. Many metallurgical solutions are investigated to enhance machinability such as lead addition or increase in sulfur content or calcium treatment. This paper analyses the influence of steel composition and structure on machinability. It shows the relevance of metallurgical solutions for machinability enhancement even for powertrain applications. Cutting conditions clearly depend on the metallurgical solution even if specific cutting force is finally close. The main difference is found on tool wear with tool life ratio from 1 to 1.5.