Temper brittleness test, temper brittleness evaluation, temper brittleness test step cold test, step cold impact test temper brittleness, temper brittleness detection mechanism
Tianjin Rong Da Testing Co., Ltd. contact: Wang Jingfu
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Telephone: 022-23892103
Temper brittleness is a phenomenon that occurs after tempering of quenched steel. Quenching steel in tempering, with the increase of tempering temperature, the hardness decreased, the toughness increases, but the relation curve of the tempering temperature and the impact toughness of many steel has appeared in the two valleys, one at 200~400 DEG C, another at 450~650 DEG C. With the increase of tempering temperature, the impact toughness is decreased, and the temper brittleness can be divided into the first kind of temper brittleness and the second kind of temper brittleness.
Temper embrittlement, temper brittleness can be divided into the first type of temper brittleness and the second kind of temper brittleness.
The first kind of temper brittleness, also known as irreversible temper brittleness, low temperature temper brittleness, mainly occurs in the tempering temperature of 250 ~ 400 degrees Celsius, characteristics:
1, there is no reversibility.
2, and the cooling rate after tempering;
3, the fracture is intergranular brittle fracture. There are three reasons for this phenomenon:
1) residual A transformation theory
2) carbide precipitation theory
3) impurity segregation theory. It can not be eliminated, not in the range of temperature tempering, alloy elements can effectively suppress the temper brittleness, but weakened, such as reducing the content of impurity elements in steel; deoxidized with Al or adding Nb, V, Ti and other alloy elements A grain; adding Mo, W can be reduced; adding Cr Si, adjust the temperature range (to high temperature); isothermal quenching and tempering process of hardening.
Second types of temper brittleness, also known as reversible temper brittleness, high temperature temper brittleness. The temperature occurred in 650 ~ 400 degrees Celsius, the characteristics of:
(1) with reversibility;
(2) the cooling rate after tempering, tempering heat preservation, slow cooling, fast cold does not appear, the embrittlement can be re heated after the rapid cooling elimination.
(3) tempering in the embrittlement region, and the embrittlement after tempering has nothing to do with the cooling rate;
(4) the fracture is intergranular brittle fracture.
Factors that affect the second types of temper brittleness are:
1) chemical composition
2) A grain size
3) hardness after heat treatment.
And the mechanism:
(1) in the temper brittleness, Ni, Cr, Sb, Sn, P and so on all to the original A grain boundary segregation, are concentrated in the 2~3 atomic thickness of grain boundary, temper brittleness increases with the increase of impurity element.
(2) the partial segregation of alloying elements and impurity elements was not found in the quenched and tempered without embrittlement.
(3) the alloying element Mo can restrain the segregation of impurity element to the A grain boundary, and it is not biased.
Prevention of the second types of temper brittleness:
(1) increase the purity of steel;
(2) adding appropriate amount of beneficial alloying elements;
(3) the small size and simple shape parts, using the method of quick cooling after tempering;
(4) the quench (A1~A3): grain refinement, reduce segregation. After heating for A+F (F for thin strip), impurities will be enriched in F, and the ability of F dissolved impurity elements is larger, can inhibit the impurity element to the A grain boundary segregation;
(5) by using high temperature deformation and heat treatment, the grain refinement, increase the grain boundary area, reduce the concentration of impurity elements