On 2018-08-08 14:48:54
Temper brittleness basic knowledge of two types
The first type of tempering brittleness is also known as irreversible tempering brittleness and low temperature tempering brittleness, which mainly occurs when tempering temperature is 250 ~ 400℃. (2) has nothing to do with the cooling rate after tempering; (3) the fracture is intergranular brittle fracture.
There are three views on the causes of the first type of tempering brittleness :(1) residual A transition theory; (2) carbide precipitation theory; (3) impurity segregation theory.
The first type of tempering brittleness prevention method: can not eliminate, not in this temperature range tempering, not effectively inhibit the production of this tempering brittleness alloy elements (1) to reduce the content of impurities in steel; (2) Al deoxidization or addition of Nb, V, Ti and other alloy elements to refine the grain A; (3) adding Mo, W, etc. can reduce; (4) add Cr and Si to adjust the temperature range (push to high temperature); (5) adopt isothermal quenching instead of quenching and tempering process.
The second type of temper brittleness also known as reversible temper brittleness, high temperature temper brittleness. The temperature is between 400 ℃ and 650℃, which is characterized by :(1) reversibility; (2) related to the cooling rate after tempering; After tempering and insulation, slow cooling appears, fast cooling does not appear, after the emergence of embrittlement can be re-heated after fast cooling elimination; (3) it has nothing to do with the organization state, but the embrittlement tendency of M is large; (4) tempering in the embrittlement zone, the embrittlement after tempering has nothing to do with the cooling rate; (5) the fracture is of intergranular brittleness.
Factors affecting the brittleness of the second type of tempering :(1) chemical composition (2) grain size of A (3) hardness after heat treatment.