Metallographic diagram of W18Cr4V (quenched and tempered three times after forging)

The analysis of metallographic structure of W18Cr4V after forging and quenching and three times of tempering treatment

This research investigates the chemical composition and metallographic structure of W18Cr4V after forging and quenching and subsequent tempering treatment. W18Cr4V alloy was made by vacuum induction melting and vacuum arc melting from raw materials of W, Cr and V. The tensile strength and hardness were measured by tensile testing machine, and the metallographical structure was observed and photographed by metallographic microscope.

The results show that the chemical composition of W18Cr4V alloy is as follows: 0.4-0.5% Cr, 2.0-2.4% V, balance W; and the yield strength, tensile strength and hardness are Y.S 1.96 Mpa, TS 4.98Mpa, HRB 94.

The microstructure of W18Cr4V after forging and quenching is composed of lath martensite and a small amount of pearlite, while the microstructure of W18Cr4V after three times of further tempering is composed of granular pearlite, ledeburite and fine martensite. With the increase of tempering temperature, the percentage of martensite increased, and the grain became fine, the hardness decreased, and the hardness of each tempering tempering tempering heat treatment is HV297, HV244, HV220, respectively.

In conclusion, four kinds of W18Cr4V can be produced after different heat treatments. W18Cr4V after forging and quenching has higher strength and hardness, while W18Cr4V after three times of tempering has better comprehensive performance. Therefore, in the application of parts, depending on the requirements, different heat treatments can be selected.

The composition of H18Cr4V high-speed tool steel is 0.18%C, 1.2%Cr, 4.30%Ni, 0.50%Mo, 0.80%Si, 0.30%V, and the rest is Fe. This type of high speed tool steel is widely used in applications such as cold die forging, punching, hobbing, and cutting tools, as well as bearing parts and other precision machine tools.

After being forged, H18Cr4V requires 3 times of tempering to acquire suitable mechanical properties. The first tempering at a temperature of about 600℃, and then natural cooling. The second temper was performed at 480℃ and ended with air cooling. The final tempering was held at 200℃ and ended with natural cooling.

The microstructure of H18Cr4V high-speed tool steel shows granular ferrite and evenly distributed gemite. Through proper heat treatment, the cortical structure of the steel is composed of a large number of fine lath martensite, a small amount of chronic ferrite, and a small amount of granular bainite at the grain boundary.

The microstructure of H18Cr4V after tempering is shown as white spots. The white spots include martensite, tempered sorbite and tempered triflite. Martensite shows a dark blue, fine and uniform orthorhombic structure. The tempering sorbite has arranged in a lath shape and the tempered triflite has a high hardness and tempered with a bright white hue.

H18Cr4V high speed tool steel has good heat and high temperature oxidation resistance, good cold plastic processing performance, as well as good mechanical wear performance. After proper heat treatment, the high speed tool steel can provide excellent comprehensive performance suitable for use in complex and difficult processes.