Effect of Final Rolling Temperature on Microstructure, Mechanical Properties, and Strengthening Mechanism of High-Strength Ti – Zr Composite Microalloyed Steels

Abstract

The effect of the final rolling temperature during the thermomechanical treatment process on the microstructure and mechanical properties of high-strength Ti – Zr composite microalloyed steel plate was studied using TEM, SEM, EBSD, optical microscopy and tensile tests. It has been shown that the final microstructure of Ti – Zr composite microalloyed steel with isothermal exposure at 600°C consists of polygonal ferrite and acicular ferrite when the final rolling temperature is in the range of 1000 – 850°C. Adecrease in the final rolling temperature promotes the formation of acicular ferrite in the steel structure, the average ferrite grain size is refined, and the uniformity of the structure increases. As a result, the yield strength and tensile strength of the steel increase with a slight change in elongation. It has been established that with a decrease in the final rolling temperature, the recrystallization of deformed austenite is inhibited, resulting in an increase in dislocation density, promoting strain-induced precipitation in the austenite of (Ti, Zr)C, and reducing the number of fine TiC precipitates in the ferrite. The quantitative analysis of strengthening mechanisms shows that the changes in final rolling temperature mainly affect the contribution of fine grain strengthening, dislocation strengthening, and precipitation strengthening to strength.