Effect of Tempering Temperature on Microstructure and Mechanical Properties of Cr-Mo Steel Lining Plate

    
    The lining plate is mainly installed in the inner wall of the steel container. In order to reduce the cost of the container, the lining plates are usually made of Cr-Mo steel. However, due to the demanding requirements of the production process, the mechanical properties of the lining plate must be improved after heat treatment. The most common and popular heat treatment method of lining plate is tempering. It is the purpose of this paper to investigate the effects of tempering temperature on the microstructure and mechanical properties of Cr-Mo steel lining plates.
    
    The experimental specimens used in this research were prepared from 6Cr-7Mo-1C (wt%) Cr-Mo steel. The specimens were austenitized at 980℃-1000℃ for 10min, quenched to room temperature with oil, then solution annealed at 860℃ for 8min, and finally tempered at different temperatures between 400℃-600℃. The microstructure and mechanical properties of the specimens were examined by metallurgical microscope and universal testing machine.
    
    Figure 1 shows the broken surfaces of the specimens tempered at 400℃, 500℃ and 600℃, respectively. It can be seen that the specimens tempered at 600℃ were broken by distortion of the pearlite structure and a large number of martensite crystals were found on its broken surfaces. On the other hand, the tempered specimens at 400℃ and 500℃ failed due to its broken martensite crystals.
    
    In order to further study the effect of tempering temperature on the microstructure of lining plates, the microstructure morphology of specimens after tempering at differnt temperatures is shown in Figure 2. The specimens tempered at 600℃ exhibited a dominant network granular structure of proeutectoid ferrite and pearlite, the specimens tempered at 500℃ and 400℃ exhibited a mixture of martensite, proeutectoid ferrite and pearlite.
    
    Figure 3 shows the results of tensile test of specimens tempered at different temperatures. It can be seen that the 0.2%, 0.5% and 1% proof strengths of the specimen tempered at 600℃ were higher than those of 400℃ and 500℃, while the elongation % were lower. These results indicate the effect of tempering temperature on the mechanical properties of Cr-Mo steel lining plates.
    
    In conclusion, this paper has investigated the effect of tempering temperature on the microstructure and mechanical properties of Cr-Mo steel lining plate. It is found that the specimens tempered at 600℃ exhibited a dominant network granular structure of proeutectoid ferrite and pearlite, while the specimens tempered at 500℃ and 400℃ exhibited a mixture of martensite, proeutectoid ferrite and pearlite. Furthermore, when tempering temperature increases, the 0.2%, 0.5% and 1% proof strength increased, while the elongation % decreased. Therefore, it is necessary to adjust the tempering temperature to obtain the desired mechanical properties of the lining plate.

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