Microstructure and abrasive wear properties of Hi-C medium chromium wear resistant alloy steels after heat treatment （2）
1.1 Heat treatment process
Five quenching temperatures were designed: 860 ° C, 900 ° C, 940 ° C, 980 ° C, 1020 ° C, according to the phase composition calculation of wear-resistant alloy steel at different temperatures by JmatPro and the phase diagram analysis of Fe-C-Cr ternary alloy in longitudinal section.
The heat treatment process is high-temperature annealing at 1000 °C + quenching at different temperatures (air cooling) + low-temperature tempering at 220 °C.
1.2 Abrasive wear
The wear behavior of alloy steel was characterized by abrasive wear. Fig. a is a schematic diagram of the test machine. Two specimens are respectively installed on the fixture of the manipulator. The specimen size is shown in fig. lb. The wear surface is in contact with the track. The load applied to the specimen is controlled by an additional code, and the sample is pressed into the circular rail with which the friction pair is formed to make a uniform circular motion; at the same time, the scraper fixed on the rotating shaft will continuously scrape the abrasive to the track in order to wear the sample—the abrasive enters between the specimen and the rail through the trapezoidal cross-section. With the relative motion of the specimen and the rail, the abrasive rotates and slides between the specimen and the rail, showing the phenomenon of three-body abrasive wear. The abrasive in this paper is quartz sand, the quantity of the abrasive in each test is 7 kgs, and the abrasive will be ground small in the course of wear. In order to keep the same test conditions of each sample, the abrasive is replaced when the sample is replaced; the test load is 30n, the spindle speed is 30r/min, the pre-grinding time was 20 min. The specimens were worn for 1 h, 5 times altogether, and each wear’s mass loss was recorded.
The hardness (HRC) of alloy steel was tested by Rockwell hardness tester, the impact toughness was tested by pendulum impact tester, and the phase composition of alloy steel was determined by Smartlab X-ray diffractometer (XRD), the scanning range of XRD was 20 ° ~ 100 °. The microstructure of the alloy steel after Om and SEM observed heat treatment, and SEM observed the wear surface morphology.
2.1 Mechanical property
The as-cast hardness of medium chromium alloy steel is HRC32, and the hardness is improved obviously after heat treatment, as shown in Fig. 2. Fig. 2a shows the mechanical properties of 1 # alloy steel after annealing, quenching at different temperatures, and low-temperature tempering. The diagram shows that the hardness is about HRC58 when the quenching temperature is 860-980 °C and decreases to HRC54.5 when the quenching temperature reaches 1020 °C. The impact toughness of alloy steel quenched at 900 °C and 940 °C is relatively poor, and that quenched at 860 °C, 980 °C, and 1020 °C is relatively good, and the best one is 4.4 J at 980 °C. Based on the hardness and impact toughness, 1000 °C annealing + 980 °C quenching + 220 °C tempering was used for the subsequent heat treatment of medium chromium alloy steel with different C content. As shown in Fig. 2b, the impact toughness and hardness of 2 # (1.0% C) medium chromium alloy steel increased significantly compared with 1 # (1.1% C). But the impact toughness and hardness of 3 # (0.9% C) medium chromium alloy steel changed little compared with 2#(1.0%C)