On the correlation among ultra-fast quenching, retained ferrite content and strengthening mechanism in PC steel bars

Prestressed Concrete (PC) steel bars made of 30MnSi are widely used in various prestressed components. This paper compared the hot-rolled, cold-drawn, quenched and tempered samples of PC steel bars, observed the microstructure evolution and hardness changes of steel bars in various processes, and studied the austenitizing process and mechanical properties at different quenching temperatures. The results show that there is a small amount of residual ribbon ferrite in the tempered microstructure, and the hardness of the quenched and tempered microstructure fluctuates locally, which may be related to the inhibition of ferrite recrystallization by rapid heating and the heterogeneity of carbon during austenitizing. With the increase of quenching temperature, the residual ferrite content decreases, and the tensile strength, hardness and yield ratio increase, while the plasticity decreases.