D2 wear-resistant plate is a kind of high-carbon and high-chromium Laidstone type cold working die steel, which is characterized by high carbon content, many alloying elements, a large number of carbides in the steel, and has high hardness, high wear resistance, good toughness and excellent deformation resistance. But the brittleness is large, the deformation resistance is large, the forging temperature range is narrow, and the decarburization tendency is large. Therefore, the effect of quenching temperature and cooling method on the microstructure and properties of D2 wear-resistant plate was studied, and the optimum quenching process for D2 wear-resistant plate was obtained.
Obviously, the chemical composition of Si, W and Cr in the test steel is quite different from that of the standard D2 (Cr12MoVCo) wear-resistant plate, where the content of Si reaches 1.1%, while the standard D2 wear-resistant plate only contains the conventional amount of Si, and a certain amount of W is added to the test steel, while the amount of Cr is also reduced.
The bar billet was processed into several small samples of 10mm×10mm×10mm by wire cutting machine and the quenching heating test was carried out in the laboratory Muffle furnace. In order to ensure that the original structure of the sample is consistent without affecting the hardening characteristics of the quenching, all the samples used for the quenching heating test are held at 860℃ for 15min, water cooling to 400℃, immediately held at 730℃ for 60 ~ 90min, air cooling, and pre-cooling spheroidization annealing. The annealed samples were divided into 9 groups, and the quenching temperatures were 960, 980, 1000, 1020, 1040, 1060, 1080, 1100, 1120℃, respectively. The laboratory Muffle furnace is heated to the above selected quenching temperature and held for 10min to ensure the constant furnace temperature. In order to ensure the accurate and consistent temperature of the heated sample, the sample is placed in the area near the thermocouple in the furnace, held for 40min, and then taken out for quenching treatment with different heating temperatures and different cooling methods (water-cooled, oil-cooled, fog-cooled, air-cooled). The results show that:
(1) D2 wear-resistant plate with the increase of quenching temperature, different cooling methods will have a hardness peak. At 980℃ quenching, the hardness peak of the four cooling methods appeared. Under the condition of oil cooling, the second hardness peak appears at 1020℃ quenching. When fog cooling and air cooling are used, the second peak quenching occurs at about 1040 ° C.
(2) In the temperature range of 980 ~ 1040℃, the saturated carbon and alloying elements in martensite reach a moderate degree, and when the quenching cooling rate is slow, the residual austenite volume in the matrix is less, and the hardness of the sample is mainly affected by the content of carbon and alloying elements in martensite.
(3) In the 980 ~ 1040℃ temperature range, the slower the quenching cooling rate, carbon and gold elements have enough time to precipitate, the higher the quenching heating temperature, the more dissolved carbon and alloying elements, the more fine carbide precipitated by cooling, resulting in higher precipitation strengthening. The fog cooling method is used to cool the D2 wear-resistant plate without hardening cracks, which is suitable for the quenching cooling process of D2 steel.
