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A3 axle vacuum heat treatment process

As one of the important running parts of railway vehicles, axles have been used under alternating stress conditions for a long time, and the stress conditions are complex, and their quality status is closely related to the safety of railway transportation. With the rapid development of high-speed rail and heavy-haul freight, only by continuously improving the quality of axle products can we meet the new demands of various railway vehicles.

This level of axles has the same performance requirements as EA4T axles for EMUs, but there are obvious differences in the composition system. Its Mn content is high. In the process of smelting and continuous casting, it is easy to cause segregation of chemical components in the direction of the section of the billet, resulting in macrosegregation. There is a serious impact on the uniformity of axle organization and performance. In addition, the axle steel of this material has high high temperature hot brittleness and general hardenability, and is prone to quench cracking during the quenching process. Relevant studies have shown that the composition segregation leads to the low content of C, Mn and other elements in the microscopic local area of the axle, the hardenability of the steel will be deteriorated, and proeutectoid ferrite will appear during the quenching process; Body is the main reason for reducing the plastic toughness, and also has a negative impact on the fatigue performance of the axle.

The problem to be solved

In view of the situation in the prior art that the A3 material axle has poor hardenability and low strength and toughness, the overall performance is poor. By properly increasing the content of carbon and manganese in the axle composition, it is used to strengthen and increase the hardenability of the axle, and at the same time add an appropriate amount of chromium and nickel to improve the strength and toughness of the axle; and by strictly controlling the heating in several heat treatment steps The temperature and holding time make the final axle have high strength and toughness resistance, avoiding the generation of quenching cracks, and the overall structure is uniform and the strength and toughness are well matched.

Technical solutions

In order to solve the above problems, the following technical solutions are adopted.

An A3 axle steel, comprising the following components by mass percentage: carbon 0.34-0.37%, silicon 0.25-0.40%, manganese 1.40-1.50%, phosphorus≤0.020 %, sulfur≤0.015%, chromium 0.20～0.30%, nickel 0.13～0.20%, copper≤0.30%, molybdenum≤0.40%, vanadium 0.035～0. 045%, aluminum 0.015-0.040%, and the rest are iron and inevitable impurities.

It is made of the above-mentioned axle steel.

The vacuum heat treatment process method of A3 axle includes the following steps:

1.Forging heating: heating the axle, the heating time of the axle at a temperature greater than 1100°C T=aL, where a is the soaking time coefficient, taking 1.0 ~ 1.2min/mm; L is the section edge of the axle long;

2.Pretreatment: in step 1, after the axle is cooled to room temperature, it is heated in a pretreatment furnace, the heating temperature is 880 ° C ~ 910 ° C, and the holding time T ′=1.05D+10 (CE-0.67% ), out of the furnace for cooling; where D is the maximum cross-sectional diameter of the axle; CE is the carbon equivalent;

3.Vacuum quenching: after the second step, heat it in a quenching furnace, and the heating temperature is 850°C to 870°C.

Time T′′=KD, cooling out of the furnace; among them, K is the heating time coefficient, and the value is 1.0～1.2min/mm;

4.Vacuum tempering: after step 3, put it into the tempering furnace for heating, the heating temperature is 630°C ~ 650°C, and the temperature is kept warm.

The time is 1.5 times the holding time of the quenching step, and the furnace is cooled to room temperature.

The cooling method in the steps 2 and 4 is air cooling, and the cooling method in the step 3 is water cooling.

In described step 2, cool with the speed of average 10 ℃/min, in step 3, cool with the speed of average 10～12 ℃/s, in step 4, cool with the speed of average 5 ℃/min.

In step 2, the axle surface temperature after cooling is lower than 250°C, and in step 3, the axle surface temperature after cooling is lower than 100°C.

A temperature display is provided outside the furnace and at the corresponding places of the heating zone and the heat preservation zone. In the step 1, the target temperature for firing is 1170-1200°C, and the final forging temperature is not lower than 860°C.

The use of the vacuum heat treatment process method can significantly improve the hardenability of the material axle, avoid quenching cracking of the forgings, and solve the technical problem of uneven structure and performance of the axle after heat treatment caused by the segregation of the axle components, so that the axle can reach the mechanical properties. In the case of the index, it has a larger toughness allowance, finer grains and no residual ferrite, and its organization is tempered sorbite and bainite complex structure, which has good strength and toughness; The axle as a whole has high mechanical properties and uniform structure and properties, which can replace EA4T and become the axle steel for subways and high-speed EMUs.

Selection of vacuum heat treatment equipment: The vacuum furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.