Embrittlement of Precision Steel Pipe

Brittle tempering temperature range based on precision tubes can be divided into low and high temperature temper brittleness temper brittleness.

After tempering brittleness precision tube alloy steel quenched martensite at a temperature range of 250 ~ 400 ℃ tempered steel embrittlement which a brittle ductile transition temperature increased significantly. It occurs mainly in steel alloy structural steel and low-alloy high strength precision tubes. Already brittle fracture precision tubes is intergranular fracture or quasi-cleavage and intergranular fracture mixed. Cause tempering brittleness, generally considered: (1) and cementite during tempering to a sheet in the original austenite grain boundaries, causing grain boundary embrittlement are closely related. (2) impurity elements such as phosphorus in austenite grain boundary segregation is also one of the reasons tempering brittleness. Phosphorus less than 0.005% high purity precision tubes do not produce low-temperature tempering brittleness. Phosphorus occurs in the austenite grain boundaries when the fire heating segregation after quenching preserved. Phosphorus in austenite grain boundary segregation and cementite during tempering in the former austenite grain boundaries, these two factors caused the intergranular brittle fracture, contributed to tempering brittleness occurs.

Precision tube alloying elements have a greater impact on the low-temperature tempering brittleness. Chromium and manganese promote segregation of impurity elements such as phosphorus in the austenite grain boundaries, thus contributing to tempering brittleness, tungsten and vanadium had essentially no effect, molybdenum deteriorate the toughness of a brittle transition temperature tempering precision tubes, but not enough inhibition tempering brittleness. When silicon can postpone tempered cementite precipitation, which generates a temperature increase, it is possible to improve the precision tubes tempering temperature brittleness occurred.