加热工艺对轴承钢连铸坯液析碳化物溶解行为的影响

Influence of heating process on dissolve behavior of liquation carbide in casting bearing steel

利用DICTRA软件及金相法对GCr15轴承钢连铸坯中的液析碳化物在加热工艺中的溶解与扩散机理进行研究,并针对常规加热工艺存在的问题,提出加热工艺的设计思路：第一阶段在液析严重区域连铸坯的固相线温度以下进行加热,加热过程中仅发生液析碳化物的溶解,令C元素快速扩散,同时该区域固相线温度逐渐升高;第二阶段在1200～1280℃的高温区进行加热,由于第一阶段中液析严重区域连铸坯的固相线温度升高,此时很难再有液相增加,可保证Cr元素快速扩散,最终令液析碳化物快速溶解扩散。根据DICTRA软件对加热工艺的模拟计算结果,设计加热工艺为＂1100℃加热1 h后1250℃加热1 h＂。以该工艺对试样进行加热试验,液析碳化物级别由4.0级降低至0.5级,结果证明了该加热工艺的可行性。

Solution and diffusion of liquation carbide in the casting piece of GCr15 bearing steel during heated at different temperatures were studied by DICTRA and metallographic observation methods. In view of problems on normal heating process, a two-step heating process was designed：in the first step, carrying out a temperature rise to a temperature region lower than the solidus temperature of the central area of the casting piece, only the eutectoid cementite in liquation carbide melted and C existed in carbide is made a quick diffusion in the steel, simultaneously the solidus temperature of the central segregation part of the casting piece goes up; in the second step, the heating temperature of the casting piece is carried out at 1200-1280 ℃ , it becomes difficult to produce the liquid phase due to the solidus temperature of the central part of the casting piece being raised in the first step, the diffusion disappearance of Cr can be carried out in short time, making the liquation carbide diffuse efficiently. According to the result of the calculation on the two-step heating process by DICTRA, the final two-step heating process was designed to ＂heating at 1100 ℃ for 1 h and at 1250 ℃ for 1 h＇. The sample of the casing piece of GCrl5 bearing steel with liquation carbide is carried out by the two-step heating process. The experimental results indicate that the level of the liquation carbide deteriorates from 4.0 to O. 5, showing the feasibility of the idea of the two-step beating process.