Effect of Heat Treatment on the Microstructure and Tensile Properties of CU-Bearing Steel Rods

The U.S. automotive tire industry consumes more than 3.6 million tons of materials to manufacture 300 million tires annually. To ensure materials-related sustainability, it is important to enable the use of a greater recycling rate of steel scrap in the manufacturing of new tires. However, impurities like copper compromise the performance of steel wires that are cold-drawn from ~5.5 mm diameter rods. This article investigates copper precipitation in sensitized steel wire rods and their mechanical properties subjected to varying heat treatment procedures. The amount of copper precipitated in sensitized zones as a function of Cu concentration in the steel samples is quantified using scanning electron microscopy. Preliminary findings indicate that an increase in cooling rate during the heat treatment procedure increases the amount of Cu precipitated in the sensitized zones and increases the geometric footprint of the sensitized zones. Tensile tests on heat-treated 5 mm-diameter wire rods showed a higher strain and slightly lower peak stress as the cooling rate decreased. This research thus contributes to a better understanding of the influence of Cu concentration on the microstructure and performance of steel wires used in tire manufacturing, thereby allowing for the enhanced use of scrap steel.