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.
On 2018-08-08 11:45:46
