Effect of Cooling Rate after Hot Rolling and of Multistage Strain Aging on the Drawability of Low-Carbon-Steel Wire Rod

摘要

Tensile testing was used to simulate the multistage strain aging occurring in low-C steel during the relatively short intervals between dies in a multiple-die wire-drawing machine. The effects were examined of three simulated post-hot-rolling cooling rates and three thermal treatments on the strain-aging susceptibility of a high- and a low-N steel. This was measured by applying a 6 pet tensile strain, followed by aging at either 65 deg or 100 deg C for 20 seconds, and then pulling the specimen to failure at room temperature. Increases in flow stress and decreases in the elongation to fracture both indicated high susceptibility to strain aging. It was found that the nitrogen content, the cooling rate from the hot-rolling temperature to about 300 deg C, as well as the cooling rate below 300 deg C, all have dramatic effects on the strain-aging behavior. Moreover, multistage strain aging is more severe than single-stage strain aging. The implications of these observations on increasing the drawability of low-carbon-steel wire are discussed.