15CrMo (oil quenched at 910°C, tempered at 680°C) metallographic diagram

Heat Treatment Microstructure of 15CrMo Alloy Steel

15CrMo alloy steel is an alloy steel made of chromium, manganese and molybdenum elements. It has excellent strength and corrosion-resistant properties, as well as good mechanical properties up to mid-high temperatures. In order to improve the performance of 15CrMo alloy steel, a comprehensive discussion on heat treatment microstructure is introduced in this paper.

The 15CrMo alloy steel is generally hot-rolled after annealing, with high strength and good plasticity. After heat treatment, its strength and plasticity can be further improved. At first, the 15CrMo alloy steel should be heated in a furnace at 870-920℃ for about one hour. Then, it is oil quenched at 910℃ for about 40 minutes and cooled in air. This treatment can make the material obtain hypereutectoid microstructure with high strength, good plasticity and wear resistance. The hypereutectoid microstructure includes a martensite martensite (M) phase, retained austenite (A) phase and coarse pearlite (F). The martensite martensite (M) phase is distributed externally and composed of primary M and secondary M, of which the primary M is needle shaped and the secondary M is partially granular. The retained austenite (A) phase forms a needle or cup-like shape along the grain boundaries. The coarsen pearlite (F) is composed of alternate layers of ferrite and carbides, which are distributed in the middle, and there is a small amount of acicular ferrite around it.

The 15CrMo alloy steel should be tempered after quenching and cooling to obtain the best combination of mechanical properties. Tempering temperature is generally in the range of 500-680℃, and the highest strength can be obtained when the hardness is greater than HRC43. The microstructure of quenched and tempered 15CrMo alloy steel is mainly tempered sorbite, and the structure and size of tempered sorbite can be changed by quality and time of tempering. Generally, the lower the tempering temperature, the finer the tempered sorbite is; Conversely, when the tempering temperature is high, the tempering sorbite is coarse, which has a great influence on the mechanical properties. The microstructure of tempering sorbite of 15CrMo alloy steel usually contains the fine grains of proeutectoid M, pro-eutectoid F and primary M (M1). These phases and their proportion can be adjusted by controlling the tempering temperature and time.

In conclusion, heat treatment microstructure of 15CrMo alloy steel can be controlled by quenching and tempering, which is of great significance to improve its mechanical properties. Therefore, it is of great significance to study the heat treatment microstructure of 15CrMo alloy steel in order to better improve its performance.

15CrMo alloy is a kind of widely used creep-resistant alloy with stable composition and good heat resistance. It has excellent performance in high temperature environment. The metallographic structure of 15CrMo alloy after 910℃ oil quenching and 680℃ tempering can be seen in Figure 1.

Figure 1. Metallographic Structure of 15CrMo Alloy after 910℃ Oil Quenching and 680℃ Tempering

As is shown in Figure 1, several tempering colors can be seen in the metallographic structure of 15CrMo alloy. The colors of the tempering colors range from yellowish brown to darker blues and purples. The colors are arranged in a zigzag pattern, which indicates that the alloy undergoes a uniform carburization and decarburization during quenching, and thus obtains a good comprehensive performance.

The internal structure of 15CrMo alloy consists of tempered martensite and small amounts of retained austenite. Retained austenite decomposes slowly in the tempering process and forms a fine martensite martensite network structure. This structure is beneficial to the plasticity and toughness of the alloy, and makes it have excellent high temperature creep strength.

In addition, the microstructural elements of carbides and carbonitrides are also observed in the structure. The presence of these microstructural elements increases the stiffness and strength of the alloy, and also enhances its thermal stability. In conclusion, 15CrMo alloy exhibits excellent overall performance after 910℃ oil quenching and 680℃ tempering, making it an ideal material for many applications.