Influence of pre-straining on mechanical properties of HSLA steel by using ball indentation technique

Ball indentation technique has been employed to explore the possibilities for revealing the effect of pre-strain on mechanical properties of two groups of high-strength low-alloy steels. These steels were pre-strained up to 5%. Results are presented here for 1, 3, 4, and 5% of pre-strain effect on these steels. The dependence of yield strength, ultimate tensile strength, strength coefficient, strain-hardening component and true stress-strain curves on pre-straining effect are available from the ball indentation test, and they are validated with the standard mechanical test results. It is found that the increment of the pre-straining effect results in an increment of the yield strength and ultimate tensile strength values, while strength coefficient and strain-hardening component values are decreased. The existence of Luders bands in the conventional stress-strain curves is also revealed in ball indentation test by the presence of the Luders strain surrounding the indentation profile. In the conventional test it is found that the amount of Luders bands is decreasing with increasing pre-strain. Similarly, Luders strain as well as pile-up/sink-in of materials surrounding the indentation decrease as the pre-straining increases. It is found that ball indentation technique can be effectively used to determine the minute changes of mechanical properties due to introducing small amount of pre-straining.