Research on non-metallic inclusions in high-speed wheel steel
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摘要: 为评估高速车轮钢中包裹类夹杂物的包裹状态，利用扫描电镜和ASPEX型自动扫描电镜对高速车轮钢中核壳结构包裹类非金属夹杂物进行分析研究，包括核壳结构包裹类非金属夹杂物形貌、成分，包括核和壳、包裹类夹杂物和基体界面的成分，统计分析了核和壳的尺寸。研究表明，核壳结构包裹类非金属夹杂物一般呈椭圆形，长度主要分布在1～10 μm，包裹外壳主要成分为塑性的MnS夹杂，包裹厚度不均匀，一般为0～2.26 μm。被包裹的核以脆性夹杂物Al2O3为主，核的尺寸较小，一般为0.31～1.43 μm。从夹杂物核心到外壳存在成分梯度，推断包裹夹杂物外层MnS和Al2O3间为化学结合。采用JMatPro热力学软件计算，结果表明，S和Mn尤其是S含量的增加可以提高MnS的析出温度，有助于形成MnS包裹Al2O3的核壳类非金属夹杂物，从而改善高速车轮钢的疲劳性能。Abstract: In order to reduce the adverse effects of brittle Al2O3 inclusions on the fatigue properties of high-speed wheel steels, plastic inclusions are usually used to wrap the brittle inclusions. In order to evaluate the wrapping state of wrapped inclusions in high-speed wheel steel, scanning electron microscope and ASPEX automatic scanning electron microscope are used to analyze and study the wrapped non-metallic inclusions in core-shell structure of high-speed wheel steel, including core-shell structure wrapped non-metallic inclusions. The morphology and composition of metal inclusions, including the core and shell, the composition of the inclusions and the matrix interface, were analyzed. And the size of the core and shell had been statistically measured. It is found out that core-shell structured non-metallic inclusions are generally elliptical with a length of 1～10 μm. The main component of the coating shell is plastic MnS inclusions. The thickness of the coating is typical around 0～2.26 μm. The wrapped core is dominated by brittle inclusions Al2O3, and the size of the core is small, generally 0.31～1.43 μm. There is a composition gradient from the core of the inclusion to the outer shell. It is inferred that the outer layer of the inclusion is chemically bonded between MnS and Al2O3. The calculation results using JMatPro thermodynamics software show that the increase of S and Mn content can increase the precipitation temperature of MnS, help to form core-shell non-metallic inclusions of MnS wrapped Al2O3, thereby improve the fatigue performance of high-speed wheel steel.
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图 1 高速车轮钢中包裹类非金属夹杂物形貌
Figure 1. The morphology of wrapped non-metallic inclusions in high-speed wheel steel
图 2 高速车轮钢包裹类夹杂物EDS面分析图像
Figure 2. EDS surface analysis image of high-speed wheel steel-wrapped inclusions
图 3 高速车轮钢包裹类夹杂物扫描电镜形貌及能谱照片
Figure 3. SEM image and energy spectrum photos of inclusions in high-speed wheel steel
图 5 高速车轮钢包裹类非金属夹杂物壳及被包裹Al2O3核长宽分布
Figure 5. High-speed wheel steel-coated non-metallic inclusion shell and the length and width distribution of the coated Al2O3 core
图 6 高速车轮钢包裹类非金属夹杂物包裹厚度分布
Figure 6. Thickness distribution diagram of non-metallic inclusions wrapped in high-speed wheel steel
图 7 高速车轮钢凝固过程中非金属夹杂物的析出行为
Figure 7. Precipitation behavior of non-metallic inclusions during solidification of high-speed wheel steel
图 8 S含量对高速车轮钢MnS析出温度的影响
Figure 8. Effect of S content on the precipitation temperature of MnS in high-speed wheel steel
图 9 Mn含量对高速车轮钢MnS析出温度的影响
Figure 9. Effect of Mn content on precipitation temperature of MnS in high-speed wheel steel
表 1 高速车轮钢的主要化学成分
Table 1. Main chemical compositions of high-speed wheel steel
% C Si Mn Mo Ni V Cr Cu S P Al O N 0.2～0.3 1.2～1.5 1.91 0.5 0.2～0.28 0.03～0.12 0.03 0.09 <0.006 0.019 <0.04 <0.001 <0.005 
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表 2 不同长度的各类夹杂物数量占总夹杂物数量的比例
Table 2. The proportion of the number of various types of inclusions of different lengths to the total number of inclusions
夹杂物类型 占比/% 1～5 μm 5～10 μm 10～15 μm 15～20 μm >20 μm 合计 氧化物 0.4 0.7 1.3 0.0 0.2 1.6 MnS 32.9 27.6 11.3 3.7 0.4 75.9 氧化物-MnS复合 12.8 7.0 2.0 0.5 0.2 22.5 合计 46.1 35.3 14.6 4.2 0.8 100
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