A Vacuum Grading Gas Quenching Method for Thin-walled D6ac Ultra-High Strength Steel Shell

Abstract

The invention provides a vacuum step gas quenching method of a D6AC ultra-high strength steel thin-walled shell. The vacuum step gas quenching method of the D6AC ultra-high strength steel thin-walledshell comprises the steps of heating D6AC ultra-high strength steel to 900 degrees centigrade under a vacuum degree of 6.7x10<-2> Pa in two steps; cooling the D6AC ultra-high strength steel to 50 degrees centigrade under the atmosphere of 2 bar high-purity nitrogen in four steps; and discharging the D6AC ultra-high strength steel out of a furnace to be cooled by air. According to the vacuum step gas quenching method of the D6AC ultra-high strength steel thin-walled shell, by using a vacuum step gas quenching method, decarburization in heat treatment can be prevented, the mechanical performancecan be improved, deformation can be reduced, and meanwhile, the high-purity nitrogen is adopted to replace quenching oil, and the high-purity nitrogen is extracted from the air, and therefore, the production of the high-purity nitrogen is convenient, and the high-purity nitrogen is clean and pollution-free.

Description

technical field [0001] The invention relates to a quenching method. Background technique [0002] After quenching and tempering, the microstructure of D6AC ultra-high-strength steel is sorbite. It has high yield ratio, good ductility and notch toughness. It can still maintain high strength at high temperatures. It is mainly used in solid rocket motor casings and booster housing, etc. Solid rocket motor casings and booster casings are thin-walled long tubes. After heat treatment, the requirements for dimensional accuracy and mechanical properties of the casing are high. After conventional heat treatment, large thermal stress and tissue stress are generated. These stresses lead to thin The wall shell is deformed greatly or micro-cracks appear, which affects the dimensional accuracy and stability of the shell. However, when using austenitic alloys for staged cooling and quenching, the temperature cannot be automatically adjusted when the austenite alloys are kept warm, and th...

AI Technical Summary

Problems solved by technology

Solid rocket motor casings and booster casings are thin-walled long tubes. After heat treatment, the requirements for dimensional accuracy and mechanical properties of the casing are high. After conventional heat treatment, large thermal stress and tissue stress are generated. These stresses lead to thin Large deformation of the wall shell or micro cracks appear, which affects the dimensional accuracy and stability of the shell

However, when using austenitic alloys for staged cooling and quenching, the temperature cannot be automatically adjusted when the austenite alloys are kept warm, and the operation is difficult. Moreover, the graded quenching process can only classify the austenite alloys, and cannot change the transformation from high temperature to pearlite. and martensite stage transformation, it is impossible to reduce thermal stress and structural stress in stages, and when the thin-walled shell is cooled in the air atmosphere, the temperature is not uniform

At the same time, there is a problem of decarburization when the thin-walled shell is heated in the air atmosphere, which affects the mechanical properties of the material

In addition, the pollution caused by oil quenching is large, which cannot meet the requirements of green environmental protection

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