High-strength and high-toughness bainitic steel rail and its on-line controlled cooling process

Abstract

The invention provides a high-strength high-toughness bainite steel rail and an online controlled rolling technology thereof. The online controlled rolling technology comprises the following steps of: when the finish rolling temperature of the bainite steel rail is 850-930 DEG C, performing online controlled cooling on the steel rail; the controlled cooling on the steel rail is performed through the following stages of: first stage: when the finish rolling temperature is 360-390 DEG C, setting the cooling speed to be larger than 0.4 DEG C / s, performing accelerated cooling on the steel rail with residual heat till the temperature of the tread center of a rail head reaches 360-390 DEG C, and stopping cooling; second stage: when the temperature changes from 360-390 DEG C to 180-210 DEG C, setting the cooling speed to be 0.07-0.2 DEG C / s; and third stage: when the temperature changes from 180-210 DEG C to the straightening temperature, performing natural air cooling. The online controlled rolling technology is made according to the phase change law of bainite, is simple and practicable, and is applicable to industrial production. The bainite steel rail prepared by the online controlled rolling technology has the advantages that the microscopic structure is refined, the content of martensite is low, residual austenite is stable, and the mechanical property of the bainite steel rail is excellent.

Description

technical field [0001] The invention relates to the technical field of railway rail production, in particular to a high-strength and high-toughness bainite rail and an online controlled cooling process thereof. Background technique [0002] The rapid development of China's railways requires all rail manufacturers to continuously improve the quality of the rails, expecting the rails to obtain a higher level of wear resistance and plasticity. The pearlitic rails that are commonly used at present have basically exerted their strength and toughness due to their composition and organizational structure. to the limit, and the impact toughness and fracture toughness are also low. The bainite rail has good strength, plasticity, impact toughness, wear resistance, and rolling contact fatigue resistance, and is favored by countries all over the world. [0003] Since the 1980s, many countries in the world, including my country, have carried out the research and development of bainitic ...

AI Technical Summary

Problems solved by technology

[0005] The patent application with the publication number CN103243275B provides a method for preparing a bainite / martensite / austenite composite high-strength steel for rails. The metallographic structure contains a large amount of martensite, and the bainite volume fraction is only 20-50%, if the residual stress of the rail after straightening is large, it is easy to cause the rail to crack during use, and in order to stabilize the structure of this multi-phase steel and eliminate the residual stress, the rail should be kept at 200-350°C for 6-60 Hours of tempering stabilization treatment, and a small amount of unstable retained austenite may undergo martensitic transformation, resulting in performance fluctuations

[0006] The patent application with the publication number CN101921971A provides bainite steel for curved and heavy-duty rails and bainite rails and their production methods. In order to stabilize the performance of the rails, reheating and cooling are required, which is time-consuming and energy-consuming.

[0007] The patent applications with publication numbers CN103160736A, CN102021481A, and CN102534403A all provide heat treatment methods for bainite rails, only emphasizing that the rails are finally cooled to 350-200° C. with a wider cooling rate range after final rolling, and then air-cooled to room temperature. If the speed range is too wide, it does not avoid the temperature range where upper bainite or coarse M / A islands may appear in rail cooling, resulting in multi-phase composition and phase content uncertainty in bainite rails, which will lead to poor performance. Stablize

[0008] The patent application with publication number CN103966520A provides a bainitic steel rail containing trace carbides and its production method. Although the rail is cooled to 220-240°C after rolling, the rail is placed in a tempering furnace at 300-350°C Medium tempering 4-6h, using the method of online + offline simultaneously, long working hours, low production efficiency, increasing the difficulty of industrial mass production

[0009] The above-mentioned patent involves the following technical problems in the heat treatment of bainitic rails: it is difficult to match the microstructure and strength and toughness of bainitic rails, the online heat treatment cooling control does not reasonably match the cooling speed and range, and does not avoid the possibility of bainitic rail cooling. The temperature range of celite or coarse M / A islands, and the complex heat treatment process are not conducive to large-scale and stable industrial production

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