Effect of Pre-strain on Microstructure and Stamping Performance of High-strength Low-alloy Steel

In this study, pre-strain ranging from 0 to 0.12 was applied through uniaxial tension on high-strength low-alloy (HSLA) specimens with four kinds of grain size. Effect of pre-strain and grain size on mechanical property was investigated through tensile tests. Microstructures of the pre-strained and tensile tested samples were analyzed, respectively. The 30.8° v-bending and following flattening, as well as Erichson cupping tests, were performed on the pre-strained samples. Results show the elongation ratio of grain and dislocation density increases with pre-strain. Yielding platform is removed when pre-strain is larger than 0.06 while yielding plateau period decreases with pre-strain less than 0.06 due to reduction of pinning effect. The 30.8° v-bending and the following flattening tests are successfully accomplished on all the pre-strained samples with different grain size. Decrease in grain size, along with increase in pre-strain, causes increase in strength and decrease in elongation rate as well as cupping value. Pre-strain causes very slight effect on bending ability, much less than that on mechanical property and cupping test value. Reciprocal impact of the pre-strain and grain size on HSLA steel deformability is inconspicuous.