Niobium-containing steel for motor train unit axle and production method and heat processing technology thereof

Abstract

The invention relates to niobium-containing steel for a motor train unit axle and a production method and heat processing technology thereof. The niobium-containing steel is prepared from, by weight, 0.24-0.30% of C, 0.20-0.40% of Si, 0.70-1.00% of Mn, 0.90-1.20% of Cr, 0.70-1.30% of Ni, 0.20-0.30% of Mo, 0.10-0.60% of Cu, 0.01-0.04% of Zr, 0.015-0.050% of Nb, 0.001-0.005% of Ca, 0.0040-0.0060% of [N] and 0.015-0.045% of Als, and the balance Fe and unavoidable impurities, the weight percentage of P, the weight percentage of S and the weight percentage of T[O] are smaller than or equal to 0.010, 0.008 and 0.0015 respectively. The steel tissue includes tempered sorbite and a small amount of lower bainite, wherein the content of the tempered sorbite on the near surface of the axle is 100%, and the content of the tempered sorbite at the 1 / 2 radius position of the axle is 80-90%. Plasticity and tenacity of the niobium-containing steel are obviously higher than those of commercial steel, the fatigue limit is remarkably higher than that of commercial steel, and the niobium-containing steel is good in strength and tenacity match and excellent in fatigue resistance.

Description

technical field [0001] The invention relates to the field of alloy steel, in particular to alloy steel for tensile strength 750-900MPa, yield strength ≥ 600MPa, -40°C KV 2 ≥150J, and require high-speed EMU axle steel with excellent fatigue resistance and its heat treatment process. 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 reliabil...

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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