EFFECT OF STRAIN RATE ON HOT DUCTILITY OF LOW CARBON STEEL

Abstract

Tensile strength and reduction of area for low carbon steel (LC) were measured. The experiment was performed in the high temperature region of stabile austenite at strain rates of 1 x 10-3 s-1 and 1 x10-2 s-1 usinga thermo-mechanical simulator GLEEBLE 1500. Tensile tests were carried out at test temperatures of 1000 - 1300 °C after heating to the solution temperature of 1350 °C.
The change of strain rate did not influence the strength values more significantly; however, it had effect on high temperature plastic properties at temperatures under solidification and also around 1100°C.The low ductility at 1100°C for the higher strain rates was caused probably by deformation induced precipitation of Al based particles along the prior austenite grain boundaries. It led to intergranular fracture, brought into effect by cleavage mechanism. The ratio of Mn/S is an important factor in LC steel, influencing the hot ductility. At low rates of Mn/S ≤ 20, there is a high probability of embrittlement in the stable austenite region. However, the higher ratio of Mn/S and low sulphur content, as it was in the tested steel, cannot warrant sufficient hot ductility in the stabile austenite region, and this way it excludes cracking during continuous casting. The plasticity also depends on the strain rate used. The low strain rate of 1 x 10- 3 s-1 can eliminate the embrittlement in the tested low carbon steel with Al and N2 content of 0.049 % and 0.0068 %, respectively.