Effect of TMCP process on the microstructure and mechanical property of an ultra low carbon Nb treated HSLA steel

摘要

The effect of thermomechanical control processes (TMCP)on the microstructure and mechanical property evolution of an ultra low carbon high strength low alloy steel containing 0.04% Nb has been investigated.The results showed that the microstructure consisted of a large amount of acicular ferrite and bainite and a small amount of strain induced fine ferrite distributed at the prior austenite grain boundaries when the samples were held for 0 s and 50 s after 50% compressive deformation at 850°C.When holding time increased from 500 s to 1000 s,the microstructure grew and the recrystallization occurred.The amount of the polygonal ferrite increased considerably.The hardness tests showed that when holding time ranged in 0-50 s the hardness dropped slightly and when holding time ranged from 50 s to 1000 s the hardness decreased remarkably.