Effect of multipass cold plastic deformation and heat treatment on the mechanical properties of C250 marageing steel for aerospace applications

Abstract

The present investigation is aimed to reduce the cost of production of various components fabricated by using cold rolled C250 marageing steel in the aerospace applications like landing gears of aeroplane and spacecraft. As cast C250 marageing steel was forged and solution annealed as per the specification of the customer. Forged C250 steel was cold rolled from 15 to 300%. Microstructure analysis revealed that grains got refined and elongated in the direction of cold working. Cold drawing increases the hardness, tensile strength and yield strength. However, loss in ductility and impact strength was observed. Scanning electron microscope fractographs of tensile and impact samples showed elongation of the dimples in cold working direction. The increase in cold working reduces the size of dimples indicating the transformation of fracture nature from the ductile-to-brittle regime. At higher cold working, >170% led to intergranular tearing and resulted in a loss of impact and mechanical properties of the steel. Further, cryogenic treatment of cold rolled C250 steel delayed ageing causing increase in tensile and yield strength with a marginal loss in ductility. The cost estimation of C250 steel revealed a significant cost saving (Indian Rupees [INR] 7500/1000 kg) for components made from different diameters of cold rolled steel over the solution annealed steel.