High speed steel is high carbon, high alloy cold work die steel. Conventional quenching temperature heating, due to the dissolution of alloy carbides, the matrix of carbon content and alloying elements of high content, strength and hardness is high, but the toughness is insufficient, the use of brittle fracture prone to early failure. To improve the overall performance of high-speed steel, improve the heat treatment process is a technical key.
Shanghai Institute of Mechanical Manufacturing Technology through the W6Mo5Cr4V2 high-speed steel test, the following high-speed steel heat treatment process of the technical points.
one. Control austenitizing temperature.
Refining the grain is the only way to improve the strength of the material and improve the toughness of the material. For high speed steels and high carbon, high alloy cold work die steels can reduce the tendency of brittle cracking by appropriately reducing the quenching temperature. Because the quenching temperature is reduced, on the one hand, it can control the M6C and MC carbides into the matrix, so that the average carbon content in the austenite decreases, leading to the increase of Ms point and the reduction of the number of twin martensite after quenching. Lath martensite-based quenching organization, thereby improving the toughness of steel; the other hand, due to quenching temperature reduction, austenite grain size is refined, but also conducive to improve the toughness. The results show that when the austenitizing temperature is 1200 and 1180 ℃, the grain size is 11.5. When the austenitizing temperature is 1160 ℃, the grain size is 12, which indicates that the quenching temperature can be reduced Grain is refined. In addition, as the austenitizing temperature decreased from 1200 ℃ to 1160 ℃, the hardness of W6Mo5Cr4V2 high-speed steel decreased slightly, while the impact absorption power increased, the impact absorption energy test value increased from 4.62J to 4.96J.
Two Using graded tempering process.
The purpose of high-speed steel tempering is to obtain a stable structure by the dispersion of alloy carbides and the full transformation of retained austenite. Tempering process is the key to high redness, abrasion resistance and toughness of high speed steel. Foreign literature recommended tempering process generally tend to use two tempering method. Hierarchical tempering is also used by some domestic factories to replace the conventional three tempering process. (350 ℃ × 1 h + 560 ℃ × 1 h), the results obtained better than the conventional tempering with the strength of the toughness of the joint with the tempering process of W6Mo5Cr4V2 high-speed steel, The results show that the abrasion resistance and red hardness of W6Mo5Cr4V2 high speed steel after grade tempering are better than conventional tempering at the same austenitizing temperature. Metallographic tests show that W6Mo5Cr4V2 high speed steels after graded tempering have more uniform distribution of carburized particles and make the carbides precipitated along the twin boundaries more dispersed. The graded tempering allows the W6Mo5Cr4V2 high speed steel to have better performance than conventional tempering. This is because, when the high temperature tempering 350 ℃ grading treatment, so that the first high-speed steel precipitation of uniform distribution of carburized particles, can promote the subsequent high temperature tempering M2C alloy carbide precipitation. It is these diffused, small-distributed carbides that make the secondary hardening effect of the graded tempered high-speed steel more pronounced, resulting in higher hardness, red hardness and better wear resistance than conventional tempered high speed steels. At the same time, because the crack initiation and expansion along the twin boundaries is more difficult, but also conducive to the improvement of toughness. Performance test contrast is as follows: Hardness: graded tempering sample is 64.6 HRC, conventional tempering sample is 63.8 HRC; red hardness: graded tempering sample is 59.3 HR, conventional tempering sample is 58.6 HR.
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