Precision Seamless Steel Pipe Produces A brittle Tempering Temperature Range

Precision seamless steel tubes produce a brittle tempering temperature range that can be classified into low temperature temper brittleness and high temperature temper brittleness. Precision tube low temperature temper brittleness After quenching the martensitic structure, the alloy steel is tempered in the temperature range of 250~400 °C to embrittle the steel, and the toughness-brittle transition temperature is obviously increased.

The brittle steel tube can no longer be eliminated by the method of low temperature tempering heating, so it is also called %26ldquo; irreversible temper brittleness%26rdquo;. It mainly occurs in steels such as alloy structural steels and low-alloy ultra-high-strength precision tubes. The fracture of the embrittled precision tube is a fracture along the crystal fracture or along the crystal and quasi-cleavage.

The reason for the low temperature temper brittleness is generally believed to be: (1) It is closely related to the cementite embrittlement caused by the flaking of the cementite at the low temperature tempering in the flaky form of the prior austenite grain boundary. (2) Segregation of impurity elements such as phosphorus in the prior austenite grain boundaries is also one of the causes of low temperature temper brittleness.

High-purity precision tubes containing less than 0.005% phosphorus do not produce low-temperature temper brittleness. The austenite grain boundary segregation occurs when phosphorus is heated by fire, and remains after quenching. Phosphorus precipitates at the prior austenite grain boundary during the austenite grain boundary segregation and cementite tempering. These two factors cause brittle fracture along the crystal, which contributes to the occurrence of low temperature temper brittleness.

The alloying elements in the precision tube have a great influence on the low temperature temper brittleness. Chromium and manganese promote the segregation of impurity elements such as phosphorus at the austenite grain boundary, thereby promoting low temperature temper brittleness. Tungsten and vanadium have essentially no effect. Molybdenum reduces the toughness-brittle transition temperature of low temperature tempered precision tubes, but it is not enough. Inhibition of low temperature temper brittleness.

Silicon can delay the precipitation of cementite during tempering and increase the temperature of its formation, so it can increase the temperature at which the low temperature temper brittleness of the precision tube occurs.

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