Guoyong Liu

Effect of heating rate on microstructural evolution and mechanical properties of cold-rolled quenching and partitioning steel

Quenching and partitioning (Q&P) processes were performed using initial heating rates ranging from 0.5 to 300 K s−1 with either one step or two steps in the intercritical annealing stage. Increasing the heating rate strongly affected the recrystallisation of ferrite and spheroidisation of pearlite. The nucleation and growth mechanisms of austenite under various heating rates were discussed, and the characteristics of retained austenite in each annealed sample were evaluated. Tensile tests demonstrated that the mechanical properties of Q&P steel increased with increasing heating rate. The poor mechanical properties of the slowly heated samples are suggested to result from the linable distribution of martensite.

Flow Uniformity of Roller-Type Quenching Machine

Three-dimensional finite element flow field model of spraying pipe of roller-type quenching machine is built. The flow field with different structural parameters is computed. After grouping the nozzles, the spraying uniformity is analyzed under the conditions of different water inlet pipe diameter, different water inlet pipe distance, nozzle diameter and nozzle distance. And the spraying intensity absolute deviation and relative deviation are computed under different conditions. The effect of different structural parameters on cooling uniformity is obtained. The results provide theoretical basis for improving production quality and optimizing cooling device design.

Water–air online quenching process of 3Cr2Mo steel based on numerical simulation

A three-dimensional finite element model was established to investigate the water–air online quenching process of 3Cr2Mo steel with 130-mm thickness. The temperature, metallographic structure and stress–strain fields of the steel were calculated under single-pass continuous quenching, multi-pass continuous quenching and multi-pass interrupted quenching (MPIQ) processes. The results show that the three quenching processes can avoid the pearlite appearance, and MPIQ process could be more effective to decrease the brittleness of steel. Besides, MPIQ process is able to reduce stress–strain, minimise deformation and avoid cracking problem. The hardness and the metallographic structure were tested after MPIQ process and tempering. After tempering, the metallographic structures were all tempered sorbite, and the hardness difference of the whole steel was less than 3HRC with no cracks. It can draw the conclusion that the MPIQ process is a suitable quenching process for 3Cr2Mo steel.

Study on online prehardening process of large 3Cr2Mo die steel

Abstract The thermal parameters of 3Cr2Mo plastic die steel were tested, and a two-dimensional finite element model was established in this paper. The temperature fields of 3Cr2Mo plastic die steel with the thickness 120 mm were calculated and analysed under three different quenching processes. The results showed that for the third process, the cooling velocity was faster when the temperature was >500°C, which was not in the bainite and martensite transformation zone. In addition, the fast cooling rate effectively avoided the pearlite appearance. When the temperature was <500°C, the cooling velocity under the third cooing process was slower, which alleviated the big transformation stress. The hardness and the microstructures were tested after the third cooling process and tempering. The microstructures after tempering were all tempered sorbite, and the tempering hardness difference was ≤3 HRC. The study provided references for 3Cr2Mo large plastic die steel online prehardening process formulation and optimisation.