After quenched martensite alloy at a temperature range of 250 ~ 400 temper embrittlement of the steel, a ductile brittle transition temperature, which significantly increased. Embrittlement of steels has been unusable tempering heating method eliminated. It occurs mainly in steel alloy structural steel and high strength low alloy steel. Embrittlement of steels has intergranular fracture or fracture is intergranular and quasi-cleavage fracture mixed. Tempering causes brittleness, generally considered: (1) the cementite during tempering to flake in the prior austenite grain boundaries, resulting in the grain boundary embrittlement are closely related. (2) the elements phosphorus and other impurities in the corrugated steel sheets original austenite grain boundary segregation is also one of the reasons for tempering brittleness. Less than 0.005% phosphorus does not produce high purity steel tempering brittleness.
Phosphorus occurs when the austenite grain boundaries fire heating segregation, after quenching preserved. Phosphorus in the prior austenite grain boundary segregation and cementite during tempering at prior austenite grain boundaries, these two factors cause intergranular brittle fracture, contributed to the low incidence of temper brittleness. Steel alloying elements have a greater impact on low-temperature tempering brittleness. Promotion of impurity elements chromium and manganese and phosphorus in austenite grain boundary segregation, thereby promoting tempering brittleness, tungsten and vanadium essentially no effect on molybdenum reduce a brittle ductile transition temperature tempering steel, but not enough to suppress tempering brittleness. When silicon can be postponed tempered cementite precipitation, temperature increase its generation, it can raise the temperature tempering brittleness occurred. After the alloy quenched martensite in the temperature range of 450 ~ 600 tempering; 650 for tempering or slow cooling rate after 350 ~ 600 ; or tempering at 650 for at 350 ~ 650 temperature long-term heating, are produced in the steel embrittlement of the steel brittle if already reheated to 650 and rapid cooling can be restored toughness showed ductile brittleness temperature tempering a steel brittle transformation temperature. Toughness with sensitivity to general toughening state and embrittlement state of a brittle transition temperature difference is expressed.
Tempering brittleness more serious, intergranular fracture on the higher proportion of steel fracture. Steel elements of the role of high-temperature tempering brittleness is divided into: (1) high-temperature tempering brittleness of steel caused impurity elements such as phosphorus, tin and antimony. (2) in different forms, different levels of alloying elements that promote or slow down the high-temperature tempering brittleness. Chromium, manganese, nickel, silicon and the like from the promoting effect, and molybdenum, tungsten, titanium, etc. from the delay effect. Carbon also plays a role. General carbon steel for high temperature temper brittleness is not. Sensitive, binary contain chromium, manganese, nickel, silicon or multi-alloy steel is very sensitive to the degree of sensitivity by the type and content of alloying elements are different.
Tags: corrugated steel sheets
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