A method for ultra-refinement of martensitic structure of steel for die-casting mold

Abstract

The invention relates to a martensite tissue ultra-refining method of steel for a die-casting die. The method comprises the steps that (1) an ultra-refined forging is subjected to vacuum heat treatment and heat preservation, then is subjected to gas quenching, so that the temperature of the surface of the forging is reduced to 255-275 DEG C, the forging is kept at the temperature for 105-130 s, and thus the temperature difference between the surface and the core part of the forging is controlled to be 50-80 DEG C; (2) heat preservation is carried out under the protection atmosphere condition of 360-400 DEG C; (3) heat preservation is carried out at the temperature of 550-600 DEG C, and then the forging is subjected to oil quenching to room temperature; and (4) 1-3 times of de-stress tempering treatments are carried out till the hardness meets the requirements. The method is simple, easy to operate, and is particularly suitable for large-specification die steel; and the heat treatment period is shortened, the impact toughness is improved by 12%-20% under the conventional die casting requirement hardness condition, the service life of the die-casting die can be prolonged, and the hardness requirement of the high-performance die-casting die steel for aluminum alloy automobile part die-casting is met.

Description

technical field [0001] The invention belongs to metal heat treatment technology, in particular to a heat treatment method for steel for die-casting molds, especially a method for ultra-refining the martensite structure of steel for die-casting molds. Background technique [0002] AISI H13 (4Cr5MoSiV1) is currently the most widely used type of hot work die steel, which can be used for die casting dies, hot stamping dies, hot forging dies and extrusion dies. The hardness of H13 steel is generally ≥ 50HRC; as a die-casting mold steel, the generally accepted hardness is 44-48HRC. [0003] Martensite (martensite) is a name for the structure of ferrous metal materials. It is a supersaturated solid solution of carbon in α-Fe, which is formed by rapid cooling (quenching) of austenite. Martensitic stainless steel is a class of stainless steel whose properties can be adjusted by heat treatment (quenching, tempering). When the austenite reaches the martensite transformation temperatu...

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Problems solved by technology

[0013] The ultra-refinement of the microstructure of the invention patent is only aimed at the control of carbide precipitation. It adopts the method of high-temperature homogenization combined with isothermal spheroidization to refine and spheroidize alloy carbides, and does not consider the fineness of quenched martensite lath. However, high-temperature homogenization will bring grains and subsequent coarser martensitic laths, so this technology is still limited in improving the thermal fatigue resistance of steel for die-casting molds

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