Tempering and deformation prevention

Temper
According to the different performance requirements of the workpiece and the tempering temperature, the tempering can be divided into the following types:

(1) Low temperature tempering (150-250 degrees)

The structure obtained by low temperature tempering is tempered martensite. Its purpose is to reduce the internal stress and brittleness of quenched steel while maintaining the high hardness and high wear resistance of the quenched steel, so as to avoid cracking or premature damage during use. It is mainly used for various high-carbon cutting tools, measuring tools, cold punching dies, rolling bearings and carburized parts, etc. The hardness after tempering is generally HRC58-64.

(2) Medium temperature tempering (250-500 degrees)

The structure obtained by tempering at medium temperature is tempered troostite. Its purpose is to obtain high yield strength, elastic limit and high toughness. Therefore, it is mainly used for the treatment of various springs and hot work molds, and the hardness after tempering is generally HRC35-50.

(3) High temperature tempering (500-650 degrees)

The structure obtained by high temperature tempering is tempered sorbite. Traditionally, the heat treatment combining quenching and high temperature tempering is called quenching and tempering treatment, and its purpose is to obtain comprehensive mechanical properties with good strength, hardness, plasticity and toughness. Therefore, it is widely used in important structural parts of automobiles, tractors, machine tools, etc., such as connecting rods, bolts, gears and shafts. The hardness after tempering is generally HB200-330.

Deformation prevention

The causes of deformation of precision and complex molds are often complicated, but we only need to grasp the law of deformation, analyze the causes, and adopt different methods to prevent the deformation of molds, which can be reduced and controlled. Generally speaking, the following methods can be used to prevent heat treatment deformation of precision and complex molds.

(1) Reasonable selection of materials. For precision and complex molds, micro-deformation die steels with good materials (such as air-quenched steel) should be selected. For die steels with severe carbide segregation, reasonable forging and quenching and tempering heat treatment should be performed. For larger and unforgeable die steels, solid solution double Refine the heat treatment.

(2) The mold structure design should be reasonable, the thickness should not be too large, and the shape should be symmetrical. For the larger deformed mold, the deformation law should be mastered and the machining allowance should be reserved. For large, precise and complex molds, a combined structure can be used.

(3) Pre-heat treatment of precision and complex molds is required to eliminate residual stress generated during machining.

(4) Reasonably select the heating temperature and control the heating speed. For precision and complex molds, slow heating, preheating and other balanced heating methods can be adopted to reduce the heat treatment deformation of the mold.

(5) On the premise of ensuring the hardness of the mold, try to use the pre-cooling, hierarchical cooling quenching or warm quenching process.

(6) For precision and complex molds, when conditions permit, try to use vacuum heating and quenching and cryogenic treatment after quenching.

(7) For some sophisticated molds, pre-heat treatment, aging heat treatment, and tempering and nitriding heat treatment can be used to control the accuracy of the mold.

(8) When repairing mold blisters, pores, wear and other defects, use cold welders and other repair equipment with low thermal impact to avoid deformation during the repair process.

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