Take samples from test bar 1 and carry out the experiment according to the heat treatment experimental method, and finally calibrate the heat treatment process of Bei Ma multiphase wear-resistant cast steel lining plate. It can be seen from the table that the inter cell heat treatment process in the experiment has little effect on the hardness value of the test bar of bainite Martian composite wear-resistant cast steel liner. When the test bar of bainite Martian composite wear-resistant cast steel liner is kept at 880 ° C for 2h and quenched at 300 ° C for 2H, the test bar of bainite Martian composite wear-resistant cast steel liner shows the best tensile strength and yield strength. However, when it is kept at 900 ° C for 2h, Quenched and tempered at 300 ° C for 2h, the tensile strength, yield strength, hardness and V-port impact energy of the test bar of bainite Martian composite wear-resistant cast steel liner are 1750mpa, 1480mpa, 51.2hrc and 45j, showing the best combination of strength, hardness and initial properties. Under this process, the microstructure of bainite martensite composite wear-resistant cast steel liner test bar is shown in Figure 1, which is composed of bainite, martensite and retained austenite, which meets the expected setting. It is proved that this process is still suitable for the Bei Ma multiphase wear-resistant cast steel lining plate produced this time.
Combined with the actual situation of the lining manufacturer’s workshop, the preparation process of Bei Ma multiphase wear-resistant cast steel lining plate is formulated as follows:
After fully considering the differences in heating, heat preservation and cooling between small laboratory samples and large castings in industrial production, set the heat treatment process card as shown in Figure 2, heat it to 400 ± 10 ° C (heat preservation for 2h) at a heating rate of ≤ 50 ° C / h, and then heat it to 650 ± 10 ° C (heat preservation for 3h) at a heating rate of ≤ 50 ° C / h, Then heat it to 910 ± 10 ° C at a heating rate ≤ 50 ° C / h (holding for 5H). After that, the furnace is forced to cool to room temperature, then heated to 310 ± 10 ° C at a heating rate of ≤ 50 ° C / h (holding for 8h) and air cooled to room temperature. According to the heat treatment furnace conditions and production experience of ZHY casting, the quenching holding temperature and tempering temperature are increased by 10 ° C respectively. Due to the large content of alloy elements, in order to prevent the lining plate from cracking due to large internal stress caused by rapid heating during heat treatment, an electric heating furnace that can accurately control the heating speed and temperature shall be selected during heat treatment. Two triple mounted fans are used for blowing to realize forced air cooling. During air cooling, the large opening of the lining plate faces upward and the small opening faces downward (support the lining plate with a support to ventilate the lining plate up and down and dissipate heat evenly).
The actual temperature change process of the heat treatment furnace is consistent with the heat treatment process card. Fig. 3 shows part of the heat treatment process of Bei Ma multiphase wear-resistant cast steel lining plate. It can be seen that the placement of castings during forced air cooling also meets the design requirements. The mechanical properties of test bar 2 heat treated with large liner plate are tested. The results show that the tensile strength 1342mpa, yield strength 1115mpa and impact energy 25J of Bei Ma composite wear-resistant cast steel liner plate meet the index requirements, and the hardness is 42.8hrc, which is 2.2hrc lower than the requirements, This is related to the low carbon content and the difficulty in controlling the cooling rate of large castings. After heat treatment, the Bei Ma multiphase wear-resistant cast steel lining plate is machined on a CNC machine tool. After machining, its surface is smooth and free of cracks, internal injuries and defects, which meets the assembly and use requirements of the lining plate of HP800 cone crusher.