H13 Tool Steel Heat Treatment Technology
H13 tool steel after heat treatment to obtain excellent performance, such as high strength, red hardness and high impact toughness. From the analytical H13 steel chemical composition start the selection of high-temperature ball annealing, quenching and tempering made secondary instructions provided process data, and gives five production practice experience gained in the conclusion.
H13 steel is widely used internationally a hot die steel, because it has a good impact toughness at high temperatures, wear resistance, ductility, hot hardness and applied die casting, forging die and extrusion die manufacturing. This article describes a heat treatment process H13 steel after forging change.
1, The chemical composition of the steel
H13 steel is the American National Standard ANSI steel, the equivalent of China GB / T1299 4Cr5MoSiV1. H13 steel in Cr, Mo, Si, V and other alloying elements , shown in Table 1, except Si element does not form carbides, Cr, Mo, V three elements will combine to form special carbides with carbon, these special carbide will improve the steel tempering resistance.
Chemical composition Table 1 H13 tool steel.
Influence of Cr: Cr with carbon to form special carbide, chromium carbide as a solid solution in austenite can increase over the stability of supercooled austenite. When it is dissolved in the tempered martensite contribute to enhancing its ability to promote secondary hardening effect, more Cr main purpose is to raise H13 steel hardenability, high temperature strength and high temperature oxidation resistance .
Influence of Mo: Mo is a carbide-forming elements, in H13 steel can improve the steel tempering stability and wear resistance.
Influence of Si: increase steel strength, hardness and resistance to tempering, heat treatment furnace at the same time weaken the oxidizing atmosphere.
Effect of V: The lower thermal sensitivity of steel to improve stability of steel tempering and secondary hardening effect, the vanadium carbide particle dispersed can greatly improve the wear resistance of steel.
2, The heat treatment process selection
2.1, The critical point
The heat treatment temperature, cooling method depends on the critical transition point of steel and isothermal transformation diagram. 1) H13 steel critical point: Ac1,850 ~ 885 ℃, Ac3: 910 ℃. 2) cooling transition critical point: Ar1,700 ℃; Ar3,820 ℃; Ms, 335 ℃. 3) austenitizing temperature: 1 010 ℃.
In order to H13 steel forgings eliminate stress, improve the organization, grain refinement, lower hardness, ease of machining, the need for annealing. H13 alloy elements more change when heated slowly, it can not and should be used with conventional annealing temperature ball annealing, the alloy carbides form a uniform granular material, to give a fine granular pearlite. High temperature ball annealing temperature should be slightly higher than the heating temperature of Ac1 critical point of steel, were kept at the same temperature, is conducive to retain undissolved carbide particles, the cooling process, these dots can become granular structure of nuclei, guaranteed uniform fine granular structure.
Cooling ball annealing in Ar transformation point should be in the region isothermal treatment, prompting the formation of fine granular pearlite and carbide aggregation of fine particles contribute to reduce hardness, ease of machining.
H13 steel has good hardenability, of less than 150 mm thick parts oil quenching to achieve a uniform hardness. But because the steel contains Mn, Si element prone to oxidation and decarbonization. In the production practice, the proposed salt bath, controlled atmosphere heat treatment, vacuum heat treatment can also be used for anti-covering or coating decarbonization protection.
Select 1 030 ℃ quenching temperature can be obtained hardness 54 ~ 55 HRC, 1 040 ℃ grain begins to grow. It is recommended heat treatment temperature range 1 030 ~ 1 040 ℃. Special attention should also be released when the pre-cooling to Ac3 above 20 ~ 30 ℃ (950 ~ 980 ℃) in order to reduce stress concentrations, thus avoiding cracking.
In order to eliminate stress and improve the toughness of H13 forging at high temperatures must be tempering. The use of H13 steel alloying elements good resistance to tempering and secondary hardening effect, using secondary tempering can improve die life. Tempering temperature (580 ± 20) ℃ obtain hardness 47 ~ 52 HRC. Organization after tempering is tempered martensite and a small amount of granular carbide.
H13 steel after heat treatment has a good red hardness, high-temperature toughness and thermal fatigue resistance. To ensure the quality of heat treatment, production should pay attention to the following points:
1) Inspection of raw materials: the need to make the macro defect inspection, to discover such as slag, center shrinkage, folding, surface cracks and other defects.
2) After forging Forging should slow furnace cooling or cold, and timely annealing.
3) The H13 steel is easy to oxidation and decarbonization, so die blanks allowance should be increased after the soft spot in order to avoid hardening.
4) After the mold rework must be low-temperature annealing in order to avoid re-quench cracking.
5) during heat treatment operations should be strictly in accordance with operating instructions.