Formation of optimal structure and properties of automotive pearlite steel during cold processing

Abstract

Abstract Special requirements for structural and mechanical properties are applied to core fasteners manufactured on cold-forming machines made of automotive pearlitic steel. Mill products come as an original unit to manufacture various fasteners of hot-rolled steel, which can not be used for forming hardware due to the poor quality of the structure and surface layer. Therefore, the calibration rod undergoes intermediate heat treatment before drawing. In addition, products of strength grade 8.8 and higher, obtained from alloy steels on cold-forming machines, are quenched during tempering, which often leads to decarburization, cracking and bending of finished products, which increases the labor intensity, energy intensity and, consequently, the final cost. The article suggests a method for producing rolled products from automotive pearlitic steel 35Cr and 38CrA, including an isothermal process that excludes full annealing, quenching when tempering rod-shaped products and preventing decarburization, risks and curvature. The design, caused by passing through the drawing die, strengthening the surface by reducing and rolling the thread, provides mechanical properties of bolts and studs M8 strength grade 8.8 and 9.8.