Heat treatment process of niobium-containing steel for axles of motor train unit

Abstract

The invention relates to a heat treatment process of niobium-containing steel for axles of a motor train unit. The heat treatment process comprises the following steps of firstly, primary quenching: heating the niobium-containing steel for the axles of the motor train unit to be 870 to 900DEG C, calculating the heating and heat preservation time of the temperature section according to 1.5 to 2.0min / mm, and subsequently cooling; secondly, secondary quenching: heating the niobium-containing steel for the axles of the motor train unit to be 850 to 880DEG C, calculating the heating and heat preservation time of the temperature section according to 1.5 to 2.0min / mm, and subsequently cooling; and thirdly, tempering: heating the niobium-containing steel for the axles of the motor train unit to be 620 to 680DEG C, calculating the heating and heat preservation time of the temperature section according to 2 to 2.5min / mm, and subsequently cooling. The steel for the axles obtains excellent fatigue damage resistance and lower cost while high strength is obtained.

Description

technical field [0001] The invention relates to the field of alloy steel, in particular to a steel alloy suitable for tensile strength 800-950MPa, yield strength ≥ 650MPa, and -40°C KV 2 ≥150J, and require high-speed EMU axle steel heat treatment process with excellent fatigue resistance. Background technique [0002] The axle is one of the most important moving and load-bearing parts in various vehicles related to safety. Since the vehicle bearings are subject to dynamic loads, the stress state is relatively complex, such as bending load, torsional load, bending-torsion composite load, and is subject to certain impacts, especially for high-speed EMU axles, and its stress state is more complicated. Therefore, high-speed EMU axles may break due to fatigue, bending, torsion, or tensile stress during service, and fatigue fracture is a common form of high-speed axle fracture. In order to ensure the safe operation of vehicles, the axles of high-speed EMUs must have sufficient r...

AI Technical Summary

Problems solved by technology

For example, the anti-fatigue failure axle steel in Chinese patent application 201110417295.9 still adopts the idea of ​​high C content of traditional medium carbon axle steel, and the C content (0.42-0.45%) is relatively high, which makes the toughness of the steel poor and cannot meet the requirements of EMU axles. Requirements for toughness, and the range of improvement in fatigue resistance is limited

A new type of alloy steel for hollow axles in Chinese patent application 201210384581.4, although the carbon content is low, it has good strength and toughness, but the fatigue strength is still low

The EMU axles imported from Europe are mainly made of quenched and tempered alloy steel EA4T. Although the chemical composition and mechanical performance requirements are given, the key heat treatment process parameters are not given. What is more important is the alloy in the steel that affects hardenability. The element content is low, which makes it difficult for the internal structure (ferrite that is not allowed to exist) and performance (low strength, toughness and fatigue performance of the proximal part) of the large-scale EMU axle to meet the standard requirements.

These are all limited in practical application, and more importantly, the range of improvement in fatigue resistance of axle steel is limited, which affects its popularization and application.

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