The precision tube to produce brittle tempering temperature range
According to the precision tube to produce brittle tempering temperature range, can be divided into low temperature temper brittleness and high temperature temper brittleness.
The ductile brittle transition temperature is obviously increased when the martensite structure is obtained by quenching the brittle alloy steel with low temperature tempering at low temperature tempering at 250 ~ 400 ℃. Has been brittle precision tube can no longer use low temperature tempering heating method to eliminate, it is also known as "irreversible brittleness brittle". It mainly occurs in alloy steel and low alloy ultra-high strength precision pipe and other steel.
The fractures of the brittle precision tubes are along the crystal fracture or along the crystal and quasi-cleavage mixed fracture.
(1) Cementite in the low temperature tempering with flaky in the original austenite grain boundary precipitation, resulting in grain boundary embrittlement is closely related.
(2) Impurity elements such as phosphorus in the original austenite grain boundary segregation is also caused by low temperature tempering brittle one of the reasons. Phosphorus less than 0.005% of the high purity precision tube does not produce low temperature temper brittleness. Phosphorus in the fire when the austenite grain boundary segregation occurs, after quenching retained. Phosphorus in the original austenite grain boundary segregation and cementite tempering in the original austenite grain boundary precipitation, these two factors caused by crisp fragmentation along the grain, contributed to the occurrence of low temperature temper brittleness.
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