Influencing factors of heat treatment of powder metallurgy materials
Nov 06, 2022
Influencing factors of heat treatment of powder metallurgy materials
What are the factors influencing the heat treatment of powder metallurgy materials? It is understood that the pores generated in the sintering process of powder metallurgy materials are their inherent characteristics, but also have a great impact on the heat treatment, especially the relationship between the change of porosity and heat treatment. Therefore, the alloy elements added to improve the compactness and grain size will also have a certain impact on the heat treatment. What are the main factors affecting these? Zhongwei Precision Powder Metallurgy Factory tells you:
1. Effect of porosity on heat treatment process
During the heat treatment of powder metallurgy materials, the rapid cooling can inhibit the diffusion of austenite into other structures, so as to obtain martensite. The existence of pores has a great impact on the heat dissipation of materials. Through the thermal conductivity formula: thermal conductivity=theoretical thermal conductivity of metal × (1-2 × Porosity)/100
It can be seen that the hardenability decreases with the increase of porosity. On the other hand, porosity also affects the density of the material, and the effect on the surface hardness and hardening depth of the material after heat treatment is related to the density, reducing the surface hardness of the material. Moreover, because of the existence of pores, salt water cannot be used as the medium during quenching to avoid corrosion caused by salt residue. Therefore, general heat treatment is carried out in vacuum or gas medium.
2. Effect of porosity on surface hardening depth during heat treatment
The heat treatment effect of powder metallurgy materials is related to the density, permeability (hardenability), thermal conductivity and electrical resistance of the materials. The porosity is the biggest cause of these factors. When the porosity exceeds 8%, the gas will rapidly penetrate through the pores. When carburizing and hardening, the effect of surface hardening will be reduced by increasing the carburizing depth. Moreover, if the carburizing gas penetrates too fast, soft spots will be produced during quenching, which will reduce the surface hardness and make the material brittle and deformed.
3. Effect of alloy content and type on powder metallurgy heat treatment
Copper and nickel are common alloy elements, and their content and type will affect the heat treatment effect. The hardening depth of heat treatment increases with the increase of copper content and carbon content, and decreases when it reaches a certain content; The stiffness of nickel alloy is higher than that of copper alloy, but the inhomogeneity of nickel content will lead to the inhomogeneity of austenite structure.
4. Effect of high temperature sintering
Although high temperature sintering can obtain the best alloying effect and promote densification, different sintering temperatures, especially at low temperatures, will lead to a decrease in heat treatment sensitivity (alloy in solid solution decreases) and mechanical properties. Therefore, good heat treatment effect can be obtained by using high temperature sintering with sufficient reduction atmosphere.
These are the factors that affect the heat treatment of powder metallurgy materials. Do you know about them? It has to be said that the heat treatment process of powder metallurgy materials is really a complex process, which is related to porosity, alloy type, alloy element content and sintering temperature. If you want to know more about powder metallurgy technology, please continue to pay attention to the dynamic update of zhongwei precision powder metallurgy manufacturers.
