Seamless Steel Pipe High Brittleness

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 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. Reduce the high-temperature tempering brittleness measures are: (1) high-temperature tempering oil after rapid cooling or cold water to suppress impurity elements in the grain boundary segregation; (2) the use of steels containing molybdenum, molybdenum content increased when the steel 0.7%, the tempering embrittlement tendency is greatly reduced, which exceed this limit molybdenum steel formed a special carbide-rich, lower molybdenum content in the matrix, but the steel embrittlement tendency to increase; (3) reduce the impurity elements in steel content; (4) component of long-term work in the high-temperature tempering embrittlement Area, plus molybdenum is also difficult to prevent embrittlement, only lower impurity elements in steel to improve the purity of steel and composite aluminum and rare earth elements complemented alloying, can effectively prevent tempering brittleness. Original organization tempered steel has a significant difference in the sensitivity of the high-temperature tempering steel brittle. Tempering of martensite tempering brittleness tissue sensitivity of the largest organizations bainitic tempering followed pearlite. The nature of high-temperature tempering steel brittle, generally considered to be phosphorus, tin, antimony, arsenic and other impurities segregate prior austenite grain boundaries, resulting in the grain boundary embrittlement results. And manganese, nickel, chromium and other alloying elements and said impurity element of grain boundary segregation to promote and increase the impurity element concentration embrittlement. And molybdenum, in contrast, phosphorus and other impurities have a strong interaction, can produce precipitates in the grain and hinder grain boundary segregation of phosphorus, reduce the temperature temper brittleness of rare earth elements and molybdenum have a similar effect. Titanium to more effectively promote the precipitation of phosphorus and other impurities in the crystal, thus weakening the grain boundary segregation of impurity elements slowed the high-temperature tempering brittleness.