稀土元素对低碳钢中奥氏体-铁素体相变动力学的影响

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Effects of rare earth elements on inclusions and impact toughness of high-carbon chromium bearing steel

[J]. J. Mater. Sci. Technol., 2019, 35(7): 1298

High-carbon chromium bearing steels with different rare earth (RE) contents were prepared to investigate the effects of RE on inclusions and impact toughness by different techniques. The results showed that RE addition could modify irregular Al2O3 and MnS into regular RE inclusions. With the increase of RE content, the reaction sequence of RE and potential inclusion forming elements should be O, S, As, P and C successively. RE inclusions containing C might precipitate in molten steel and solid state, but the precipitation temperature was significantly higher than that of carbides in high-carbon chromium bearing steel. For experimental bearing steels, the volume fraction of inclusions increased steadily with the increase of RE content, but smaller and more dispersed inclusions could be obtained by 0.018% RE content compared with bearing steel without RE, whereas the continuous increase of RE content led to an increasing trend for inclusion size and a gradual deterioration for inclusion distribution. RE addition could improve the transverse impact toughness and isotropy of bearing steel, and for modified high-carbon chromium bearing steel by RE alloying, the increase of RE content continuously increased both transverse and longitudinal impact toughness until excessive RE addition.

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Z H

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, et al.

Effects of rare earth on microstructure and impact toughness of low alloy Cr-Mo-V steels for hydrogenation reactor vessels

[J]. J. Mater. Sci. Technol., 2020, 45: 1

The effects of rare earth (RE) on the microstructure and impact toughness of low alloy Cr-Mo-V bainitic steels have been investigated where the steels have RE content of 0 to 0.048 wt.%. The results indicate that the normalized microstructures of the steels are typical granular bainite (GB) composed primarily of bainitic ferrite and martensite and/or austenite (M-A) constituents. The M-A constituents are transformed into ferrite and carbides and/or agglomerated carbides after tempering at 700 °C for 4 h. The addition of RE decreases the onset temperature of bainitic transformation and results in the formation of finer bainitic ferrite, and reduces the amount of carbon-rich M-A constituents. For the normalized and tempered samples, the ductile-to-brittle transition temperature (DBTT) decreases with increasing RE content to a critical value of 0.012 wt.%. Lower DBTT and higher upper shelf energy are attributed to the decreased effective grain size and lower amount of coarse agglomerated carbides from the decomposition of massive M-A constituents. However, the addition of RE in excess of 0.012 wt.% leads to a substantial increase in the volume fraction of large-sized inclusions, which are extremely detrimental to the impact toughness.

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W M

, Liu

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, Zhang

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, et al.

Effect of rare earth addition on microstructure, mechanical property and nitriding performance of a medium carbon steel

[J]. Chin. J. Mater. RES., 2021, 35(1): 72

Effect of rare earth microalloying on the microstructure and mechanical property of a medium carbon steel have been investigated, focusing on the influence of rare earth on the formed surface layer after nitriding heat treatment. The results indicate that by adding rare earth elements into the test steel: the original inclusions of long strips of MnS and the coarse Al2O3 convert into the small spherical inclusions of complex rare earth sulfur oxide; the ferrite volume content is reduced,while more finer lamellar pearlites are formed; the impact energy increases by 126% and the plasticity increases by 10%. After nitriding heat treatment, it is found that the addition of rare earth elements can significantly improve the surface hardness and nitride case depth, as well as improving the vein-like structure of the nitriding layer.

桂伟民, 刘义, 张晓田等.

稀土元素对中碳钢组织、力学性能和渗氮的影响

[J]. 材料研究学报, 2021, 35(1): 72

在一种中碳钢中通过添加微量稀土元素，研究稀土微合金化对钢的微观组织、力学性能以及在渗氮热处理条件下对渗层的影响。结果表明，添加稀土后，长条状的MnS夹杂和粗大块状的Al<sub>2</sub>O<sub>3</sub>转变成小球状的稀土硫氧化物夹杂；铁素体的含量降低，并促进细小片层结构的珠光体形成；冲击性能提升126%以及塑性提高10%；渗氮处理后，添加稀土能显著提高表面硬度和加深有效硬化层深，明显改善表面渗层的脉状组织。

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DOI PMID

Intra-granular Acicular Ferrite (IAF), as one of the most well-known desirable microstructure of ferrite with a chaotic crystallographic orientation, can not only refine the microstructure and retard the propagation of cleavage crack but also provide excellent combination of strength and toughness in steel. The effect of adding cerium on microstructure and controlling proper cerium-based inclusions in order to improve properties in low-carbon commercial steel (SS400) were investigated. The type of inclusions can be controlled by changing S/O ratio and Ce content. Without Ce modification, MnS is a dominate inclusion. After adding Ce, the stable inclusion phases change from AlCeO to CeOS. The optimum amount of cerium, 0.0235 wt.%, lead in proper grain refinement and formation of cerium oxide, oxy-sulfide and sulfide inclusions. Having a high amount of cerium results in increasing the number of inclusions significantly as a result it cannot be effective enough and the inclusions will act like barriers for others. It is found that the inclusions with a size of about 4∼7 μm can serve as heterogeneous nucleation sites for AF formation. Thermodynamic calculations have been applied to predict the inclusion formation in this molten steel as well, which show a good agreement with experimental one.

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原位观察稀土镧对低合金高强度钢焊接热影响区晶粒细化的影响

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