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Rebar steel is used in the construction of various buildings. Vanadium (V), one of microalloying elements, is often added in the rebar steel to improve mechanical property. In order to analyse the effect of V on the microstructure and property of rebar steel, 0.043 wt.% V was added in a 20MnSi rebar steel. The base steel and V added steel were refined in a 50 kg vacuum induction furnace and rolled to plates of 14 mm thick. The mechanical properties of two steels were compared by tensile tests on a Wan-10000 tensile testing machine. The microstructure and precipitation of two steels were analysed by SEM and TEM observations. The microstructures of two steels consist of ferrite and pearlite. However, the grains of V bearing steel are finer. Moreover, fine nanoscale precipitates of V can be observed in V bearing steel. Therefore, the mechanical property of V addition rebar steel is improved by gain refinement strengthening and precipitation strengthening.

Two bearing steels, with higher Mn and Si content than GCr15, were refined in 50kg vacuum induction furnace followed by multi-pass rolling to 12mm thick flat on two-high mill. Mechanical properties and microstructures were measured and observed. The results show that higher content of Mn and Si decreases the martensite starting temperature (Ms), which is beneficial to the forming of martensite. The microstructure changes from martensite plus troostite to martensite, leading to higher hardness of steel and improvement of wear resistance. However, the band microstructure is easily formed by increase of Mn and Si, which is harmful to transverse property.

The continuous cooling transformation (CCT) curve of 12Cr2Mo1R pressure vessel steel was measured on Gleeble-1500 hot simulator. The transformation and structures were observed and analyzed. Test results show that with the addition of Cr and Mo, ferrite and perlite transformation temperature increases while bainite transformation temperature decreases, resulting in bainite zone separating from ferrite and pearlite zone. The critical cooling rate for martensite is 30 °C/s.

The heat treatment process, normalizing plus tempering, of 150 mm-thick plate of 12Cr2Mo1R pressure vessel steel was proposed according to the results of finite element simulation and static CCT curve obtained by thermal simulation experiments. After normalizing at 910 °C for 10 minutes followed by water cooling and tempering at 650 °C for 60 minutes, the microstructure at 1/4 position along the thickness direction of the thick plate consists of bainite and all the mechanical properties meet delivery requirements.

With ABAQUS software, a finite element model is built to simulate the temperature field of 150mm ultra thick plate for 12Cr2Mo1R pressure vessels during heat treatment. The simulation results show that the plate’s temperature between the surface and the core is difference during cooling process. Temperature difference is gradually increased with cooling process, then the temperature distribution of plate in the thickness direction becomes uniform. When quenching temperature is 910 °C and cooling medium is water, the microstructure at plate’s quarter in the thickness direction is bainite. Simulation results provide theoretical reference for determining heat treatment technology in industrial production of ultra thick plate.

The effects of high temperature deformation on transformed microstructure and transformation amount in a high strength bainitic steel were investigated. It indicates that isothermal bainitic transformation is promoted by high temperature deformation. The transformed bainite microstructure is also affected by high temperature deformation, i.e. deformation retards the growth of bainite sheaves, leading to shorter banitie plates. The present study is useful to further understand the effects of ausforming on bainitic transformation.

High-strength steels are usually microalloyed with niobium (Nb), titanium (Ti) and vanadium (V), individually or in combination. The reheating temperature during austenization has a significant influence on the precipitation of microalloyed steels. The purpose of the study is to investigate the effect of reheating temperature on precipitates of microalloying elements. The research results show that reheating temperature should be high enough to ensure the dissolution of carbide and nitride precipitates in order to improve the precipitation strengthening of microalloying elements during rolling and cooling. The results provide the theoretical reference for the determination of reheating technology of microalloyed steels.

Microstructure and precipitation of a Ti-Nb microalloyed high-strength steel were studied. The objective of the study is to examine the factors affecting yield strength and the effect of processing temperatures on microstructure and precipitation. The research results indicate that the dominant factors responsible for yield strength are fine ferrite grains and fine-scale carbonitride precipitatates, which are affected by processing temperatures. The influence of reheating temperature on precipitates was analyzed. Moreover, the optimum reheating temperatures is suggested for Ti-Nb microalloyed high-strength steel.