The heat treatment furnace tends to produce more serious dendrite segregation on steel castings produced by casting method, resulting in uneven structure and large residual internal stress. Therefore, steel castings, especially alloy steel castings, usually have to undergo heat treatment and supply by heat treatment.
(1) Matters needing attention in the application of heat treatment of steel castings
(1) Cast steel heat treatment and chemical composition of the same forged steel pieces or rolled pieces are not the same, the heating temperature should be slightly higher than the same composition of forged steel pieces or rolled pieces (can be slightly higher than 20℃ or so), the austenitizing heat preservation question should also be appropriately extended.
The choice of heat treatment method for steel castings is closely related to its material characteristics.
A. The heat treatment methods of carbon steel castings are annealing, normalizing, normalizing ten-tempering and so on.
B. Heat treatment methods for medium and low alloy steel castings are as follows: annealing, normal, isothermal normalizing, double normalizing, normalizing + tempering, quenching + tempering, etc. Among them, double normalizing can be adopted. The purpose of the first normalizing is to evenly organize through diffusion, which needs to be carried out at a higher temperature [Ac3+(100-160)℃]. The second normalizing process was to refine the tissue at a normal normalizing temperature [Ac3+(40 ~ 60)℃].
C. The heat treatment method of high manganese steel castings is water toughening.
D. The heat treatment methods for corrosion-resistant stainless steel castings are annealing, normalizing + tempering, quenching + tempering, homogenizing + quenching + tempering, annealing + quenching + tempering, solid solution treatment + aging treatment, etc.
E. Heat treatment for heat resistant steel castings is normalizing + tempering, etc.
F. The heat treatment methods for steel castings of working die are annealing, quenching, quenching + tempering, normalizing + tempering, annealing + normalizing + tempering, solid solution treatment, solid solution treatment + aging treatment, etc.
G. The heat treatment methods for low temperature steel castings are normalizing, quenching, normalizing + tempering, quenching + tempering, etc.
(3) the heat treatment of steel castings should be in order to ensure that there is no deformation and cracking under the premise of heating as fast as possible, in order to improve the production capacity. The heating rate depends mainly on the following points.
A. The chemical composition of steel castings. The higher the carbon content of steel casting, the worse the thermal conductivity and the lower the allowable heating rate. The heating rate of alloy steel castings is generally lower than that of carbon steel castings.
B. Section size of steel castings. The larger the section of the steel casting, the greater the temperature difference between the inner and outer layers, and the greater the thermal stress caused, so the heating rate should be slower.
C. Shape characteristics of steel castings. The more complex the shape of the steel castings and the greater the difference in section thickness, the slower the heating rate will be.
(2) The common methods of heat treatment of steel castings and their main purposes and application scope mainly focus on the differences in process.
On 2018-08-08 11:45:46
