The heat treatment process of quenching between Ac1 ~ Ac3 is called sub-temperature quenching. Sub-temperature quenching can improve the impact properties of the material. For working conditions that require high toughness, this is a relatively excellent quenching process. Because of the The low heating temperature shortens the heating time and improves production efficiency, so it is widely used. The cylinder material 30CrMnSi wear-resistant plate used in high-end hydraulic supports uses a sub-temperature quenching process to obtain the best combination of hardness and toughness.
The test material is an outsourced 30CrMnSi hot-rolled wear-resistant plate. The sample is analyzed with a spectrum analyzer. The chemical composition (mass fraction, %) of the 30CrMnSi wear-resistant plate is 0.31C, 0.99Mn, 1.02Cr, 1 .03Si, 0.028S, 0.032P, balance Fe. Use DK7740 wire-cut electric discharge machine to cut the material into 15mm × 15mm × 15mm cube specimens. Use an HRC-150A hardness tester to measure the hardness. Measure three times and take the average value; in accordance with GB/T229-2007 "Charpy Pendulum of Metal Materials". According to the provisions of "Hammer Impact Test Method", the material was processed into a 10mm×10mm×55mm U-shaped notch impact specimen, and the JB-300 impact testing machine was used to measure the impact absorbed energy; the OLYMPUS GX51 metallographic microscope was used to observe the microstructure; JEM-2100 transmission electron microscope was used to observe the tissue morphology.
In order to study the hardness and impact properties of different quenching processes of 30CrMnSi wear-resistant plates, two heat treatment processes were selected for research. The first process is a conventional quenching process, the quenching temperature is 910°C, and the tempering temperature is selected according to 230, 330, 430, 530, and 630°C. The second process is 910°C quenching + 630°C tempering + 810°C sub-temperature quenching. After 810°C sub-temperature quenching, the tempering temperature is selected according to 230, 330, 430, 530 and 630°C. Research indicates:
(1) After conventional quenching at 910℃, the microstructure of 30CrMnSi wear-resistant plate is martensite + retained austenite. After quenching at 910℃ + tempering at 630℃ + sub-temperature quenching at 810℃, the microstructure is fine. Lath martensite + ferrite + retained austenite.
(2) In the range of 230~630℃, as the tempering temperature increases, the hardness of conventional quenching and sub-temperature quenching gradually decreases. When tempered at 630℃, both conventional quenching and sub-temperature quenching have minimum hardness values of 24 and 22HRC.
(3) In the range of 230~630℃, as the tempering temperature increases, the impact absorption energy curve of conventional quenching takes on a "W" shape; while the impact absorption energy of sub-temperature quenching increases with the increase of tempering temperature. While increasing monotonically, when tempered at 630°C, it has the highest impact absorption energy of 119J, obtaining the best combination of hardness and toughness.
