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High wear-resistant cast iron heat treatment process charact
Pubdate date:2019-10-17Views:0
In order to further improve the performance of the wear-resistant cast iron material, we can use the relevant heat treatment process to improve, and the heat-resistant process of the high wear-resistant cast iron can improve the characteristics. The Chinese standard parts network is analyzed according to the specific understanding as follows:

1. Stress-relieving annealing wear-resistant cast iron and alloy cast iron have effect force and tissue stress during heating, cooling and phase transformation due to uneven wall thickness of the casting. In addition, large parts are subject to residual stresses after machining, and all these internal stresses must be eliminated. The stress-free annealing usually has a heating temperature of 500 to 550 ° C for 2 to 8 hours, and then furnace cooling (gray iron) or air cooling (ball iron). This process can eliminate 90~95% of the internal stress of the casting, but the cast iron structure does not change. If the temperature exceeds 550 ° C or the holding time is too long, it will cause graphitization, which will reduce the strength and hardness of the casting.

2. When the high-temperature graphitized and annealed castings of the white hole of the casting are cooled, the white layer is often produced at the surface layer and the thin section. The white mouth tissue is hard and brittle, has poor processing properties, and is easily peeled off. Therefore, annealing (or normalizing) must be used to eliminate white-mouth tissue. The annealing process is: heating to 550-950 ° C for 2 to 5 h, followed by furnace cooling to 500-550 ° C and then air cooling. During high temperature insulation, the high cementite and eutectic cementite are decomposed into graphite and A, and the secondary cementite and eutectoid cementite are also decomposed during the subsequent cold protection process, and the graphitization process takes place. Due to the decomposition of the cementite, the hardness is lowered, thereby improving the machinability.

3. The purpose of the normalizing iron of the ductile iron is to obtain the pearlite matrix structure, and to refine the grains and uniformly structure to improve the mechanical properties of the casting. Sometimes normalizing is also the preparation of the surface quenching of the ductile iron, the normalizing of the high temperature normalizing and the low temperature normalizing. The high temperature normalizing temperature generally does not exceed 950~980 °C, and the low temperature normalizing is generally heated to a common folding temperature range of 820~860 °C. After normalizing, four people are usually required to eliminate the internal stress generated during normalizing.

4. Quenching and tempering of ductile iron In order to improve the mechanical properties of ductile iron, the casting is generally heated to 30~50 °C above Afc1 (Afc1 represents the final temperature of A when heated), and is quenched into oil after heat preservation to obtain martensite structure. . In order to properly reduce the residual stress after quenching, tempering should be carried out after quenching. The low-temperature tempering structure is tempered Markov and residual bainite plus spheroidal graphite. This type of tissue has good abrasion resistance and is used for parts requiring high wear resistance and high strength. The medium temperature tempering temperature is 350-500 ° C. After tempering, the structure is tempered troostite plus spheroidal graphite, which is suitable for thick parts requiring good wear resistance, stability and elasticity. The high temperature tempering temperature is 500-60D °C. After tempering, the structure is tempered Soxhlet for adding spherical graphite, which has a combination of toughness and strength.
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