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High wear resistant cast iron heat treatment process characteristics

by:BoQiao Machinery     2020-11-18
In order to further improve the performance of wear resistant cast iron material we can use the heat treatment process of ascension, heat treatment process is its high wear resistant cast iron can improve what characteristic, analyzes the Chinese standard network according to the specific as follows: 1, eliminating stress annealing wear-resistant cast iron, alloy cast iron because of casting wall thickness is not uniform, in the heating, cooling and the phase change process, force and organizational stress can produce effect. Another large parts after machining the internal residual stress, and also all the internal stress must be eliminated. To stress annealing usually heating temperature is 500 ~ 550 ℃ heat preservation time is 2 ~ 8 h, then the furnace cooling ( Gray iron) Or air cooling ( Ductile iron) 。 Using this new process can eliminate stress in the casting of 90 ~ 95%, but cast iron group does not change. If the temperature over 550 ℃ or holding time is too long, it will cause the graphitization, reduce casting strength and hardness. 2, eliminating casting chilling of casting high temperature graphitizing annealing cooling, surface and thin section, tend to produce white. White tissue hard and brittle, poor processing performance, easy peeling off. So must adopt annealing ( Or normalizing) The method to eliminate white tissue. Annealing: heating to 550 - 950 ℃ heat preservation 2 ~ 5 h, then the furnace cooling to 500 - 550 ℃ from air cooling. During the high temperature thermal insulation, high cementite and the decomposition of eutectic cementite to graphite and A, in the subsequent secondary cementite in the process of cold protection and eutectoid cementite decomposition, graphitization process. As a result of the cementite decomposition, resulting in a decline in hardness, so as to improve the cutting processability. 3 iron, ductile iron is the fireball is the purpose of normalizing for pearlite matrix organization, and refine the grain size, smooth texture, in order to improve the mechanical properties of the castings. Sometimes normalizing is ductile iron surface quenching in organizational preparation, normalizing points high temperature normalizing and low temperature normalizing. High temperature normalizing temperature is generally not more than 950 ~ 980 ℃, low temperature heat is burning to fold the temperature range 820 ~ 860 ℃. After normalizing general four people still need to deal with, in order to eliminate internal stress produced when normalizing. 4, ductile iron of quenching and tempering in order to improve the mechanical properties of ductile iron castings commonly heated to Afc1 above 30 ~ 50 ℃ ( Afc1 represents A formation during heating temperature) the end of , heat preservation after quenching in oil, martensite structure. In order to reduce the residual stress after quenching, appropriate general tempering after quenching and low temperature tempering organization for tempering martensite with residual bainite nodular graphite more. This organization good abrasion resistance, used for high wear resistance, high strength of the parts. Medium temperature tempering temperature is 350 - After 500 ℃ tempering for tempered troostite and spheroidal graphite, applicable to require good abrasion resistance, has certain stability and elastic thick pieces. High temperature tempering temperature is 500 - D 60 ℃, the organization for tempering soxhlet after tempering and spheroidal graphite, toughness and strength combined with good comprehensive performance.
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