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Thermodynamic calculations and experiments on inclusions to be nucleation sites for intragranular ferrite in Si-Mn-Ti deoxidized steel

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Journal of University of Science and Technology Beijing 2007年第1期14卷 14-21页

作者： Xiaojun Zhuo Xinhua Wang Wanjun Wang Lee Hae-Geon Metallurgical and Ecological Engineering School University of Science and Technology Beijing Beijing 100083 China Graduate Institute of Ferrous Technology Pohang University of Science and Technology Pohang 790-784 South Korea

Microstructures and inclusions in the Si-Mn-Ti deoxidized steels after cooling in the furnace were investigated. The composition and morphology of the inclusions were analyzed using a field emission scanning electron microscope （FE-SEM） with energy dispersive X-ray spectrometry （EDS）. The kind and composition of the inclusions calculated from the thermodynamic database were in good agreement with the experimental results. There were two main kinds of inclusions formed in the Si-Mn-Ti deoxidized steels. One kind of inclusion was the manganese titanium oxide （Mn-Ti oxide）. Another kind of inclusion was the MnS inclusion with segregation points containing Ti and N. According to the thermodynamic calculation, those segregation points were TiN precipitates. The formation of intragranular ferrite （IGF） microstructures refined the grain size during the austenite-ferrite transformation. The mechanisms of IGF formation were discussed. Mn-Ti oxide inclusions with Mn-depleted zone （MDZ） were effective to be nucleation sites for IGF formation, because the MDZ increased the austenite-ferrite transformation temperature. TiN had the low misfit ratio with IGF, so the TiN precipitated on the MnS surface also promoted the formation of IGF because of decreasing interfacial energies.

关键词： Si-Mn-Ti deoxidized steel intragranular ferrite Mn-depleted zone TtN precipitation thermodynamic calculation

Ti-Deoxidized Products and Formation Mechanism of intragranular ferrite in High Grade Pipeline Steels

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Journal of Iron and Steel Research International 2010年第7期17卷 63-67页

作者： QI Jiang-hua XUE Zheng-liang WU Jie CHENG Chang-gui GAO Yun-ming Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education Wuhan University of Science and Technology Wuhan 430081 Hubei China Wuhan Iron and Steel Group Co Wuhan 430080 Hubei China

High grade pipeline steels were prepared using vacuum carbon deoxidization process combined with a final Ti-deoxidation *** microstructure of the as-cast steels was investigated by using scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.SEM observation shows that the formation of intragranular ferrite（IGF）structure is induced by fine *** selected area diffraction（SAD）patterns and elemental distribution analysis indicate that these inclusions are mainly Ti2O3 and *** is also found that Ti2O3 may act as nucleus in the formation of MnS during solidification *** spectroscopic analysis demonstrates the presence of another phase,MnTiO3,which could be formed through entrapment of Mn by *** is believed that the formation of Mn-depleted region in the inclusions and thus the formation of MnTiO3 phase will increase the Mn pickup from matrix and promote the formation of IGF during solidification of molten steel.

关键词： Ti-deoxidized product Ti2O3 intragranular ferrite Mn-depleted zone

A new step-cooling process for strength and toughness matching control of vanadium-containing railway wheels:effect of intragranular ferrite

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宝钢技术研究:英文版 2023年第3期17卷 40-48页

作者： YAO Sancheng LIU Xuehua ZHAO Hai JIANG Bo CHEN Gang XU Kang Technology Center Ma’anshan Iron and Steel Co.Ltd.Ma’anshan 243003China Technology Center Baowu Group Masteel Rail Transit Materials Technology Co.Ltd.Ma’anshan 243003China

To improve the competitive relationship between strength and toughness,the effect of low undercooling in austenite(γ)on the microstructure and mechanical properties of commercial vanadium-containing wheel steels was studied using an optical microscope(OM),a scanning electron microscope(SEM),a transmission electron microscope(TEM),and mechanical property *** results show that when the wheel steel is slightly cooled to an appropriate temperature above A c3 point for a short time after it has been austenitized at an elevated temperature,the solid-solved vanadium is pre-precipitated in the form of V(C,N)second phase semicoherent with the matrix in the originalγ*** phase hardly participates in matrix *** to the small mismatch between V(C,N)and ferrite(α),during the subsequent-cooling phase transformation stage,the pre-precipitated second phase becomes theαnucleation point,causing granular and ellipsoidal intragranular ferrite(IGF,with an average size of 4-6μm)to nucleate in the originalγ.The IGF production and strength loss increases with the increasing undercooling *** on this,Masteel Co.,*** developed a new heat-treatment step-cooling process that can promote the formation of IGF,considerably improving the level and uniformity of fracture toughness on the premise that the strength and hardness of the wheel are almost unchanged.

关键词： vanadium microalloyed railway wheel strength and toughness match low undercooling in austenite intragranular ferrite second phase step-cooling process

Banded structure control of low carbon microalloyed steel based on oxide metallurgy

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Journal of Iron and Steel Research International 2023年第11期30卷 2242-2253页

作者： Yong-kun Yang Jia-yu Zhu Xiao-ming Li Yang Wang Dong-ping Zhan School of Metallurgical Engineering Xi’an University of Architecture and TechnologyXi’an710055ShaanxiChina School of Metallurgy Northeastern UniversityShenyang110819LiaoningChina

Banded structure is a common harmful microstructure for low carbon microalloyed steel,which seriously shortens the service life of processed *** order to study the effect of oxide metallurgy on improving banded structure,the Ti-Zr deoxidized low carbon microalloyed steel that can play the oxide metallurgical role of inclusion was chosen as the research object,and the inclusion characteristics,microstructure and transverse and longitudinal mechanical properties after hot rolling were *** results showed the inclusion number density increased in all experimental steels after hot rolling,and a large number of long strip inclusions with aspect ratio greater than 3 appeared along the rolling *** addition,after hot rolling,there were element segregation bands in the experimental steels,and granular bainite bands were formed in the element enrichment ***,the intragranular ferrite generated in the cooling process destroyed the continuity of granular bainite bands,so that the microstructure anisotropy indexes of experimental steels were *** mechanical properties analysis showed that the anisotropy of performance was mainly reflected in plasticity and toughness in the experimental *** them,the difference ratio of elongation,section shrinkage and impact energy of No.2 steel was 1.69%,3.87% and 1.69%,respectively,which were less than those of No.1 steel and No.3 *** anisotropy of microstructure and mechanical properties of No.2 steel that full played the role of oxide metallurgy were improved,and the banded structure control of low carbon microalloyed steel can be realized by oxide metallurgy technology.

关键词： Low carbon microalloyed steel Hot rolling Banded structure Oxide metallurgy intragranular ferrite

Effect of titanium microalloying on microstructure and mechanical properties of vanadium microalloyed steels for hot forging

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Journal of Iron and Steel Research International 2022年第2期29卷 295-306页

作者： Fan Zhao Guo-ning He Ya-zheng Liu Zhi-hao Zhang Jian-xin Xie Beijing Laboratory of Metallic Materials and Processing for Modern Transportation Institute for Advanced Materials and TechnologyUniversity of Science and Technology BeijingBeijing100083China State Key Laboratory of Materials Processing and Die&Mould Technology Huazhong University of Science and TechnologyWuhan430074HubeiChina School of Materials Science and Engineering University of Science and Technology BeijingBeijing100083China

Effect of titanium microalloying on the microstructure and mechanical properties of vanadium microalloyed steels for hot forging was *** microalloying improves the mechanical properties mainly through refining the austenite *** the heating temperature is in the range of 1050–1300℃,the austenite grain diameter is decreased from 77–133 to 26–68μm by titanium *** the decrease in austenite grain diameter,the final microstructure is refined significantly,and the high misorientation boundaries are *** the steel is heated at 1200℃(the common hot forging temperature)and cooled slowly,titanium microalloying decreases the yield strength from 548.4 to 519.4 MPa,and the tensile strength decreases from 842.7 to 808.7 ***,the elongation increases from 19.0%to 21.4%,and the impact energy increases from 9.8 to 38.2 J.V–Ti steel has a better combination of strength,plasticity and toughness than V *** addition,the nucleation of intragranular ferrite idiomorphs is promoted by titanium microalloying,which may have a beneficial effect on the property of steels with coarse microstructure caused by the critical deformation in hot die forging.

关键词： Titanium microalloying Microalloyed steel Microstructure Mechanical property intragranular ferrite

Influence of Ce on Characteristics of Inclusions and Microstructure of Pure Iron

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Journal of Iron and Steel Research International 2011年第2期18卷 38-44页

作者： WEN Bin SONG Bo PAN Ning SHU Qi-feng HU Xiao-jun MAO Jing-hong School of Metallurgical and Ecological Engineering University of Science and Technology Beijing Beijing 100083 China Key Laboratory of Ecological and Recycling Metallurgy University of Science and Technology Beijing Beijing 100083 China School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China

The experiments on adding Ce, Mn and S to molten iron have been carried out by means of the electric furnace, and the concentration of oxygen, the evolution of inclusions and microstructures of samples are analyzed, indicating that the concentration of dissolved oxygen decreases greatly after adding Ce. The calculated thermodynamics results at 1 273 K performed on Factsage show that Ce2O2S and CeAlO3 are formed with the increase of Ce content for w（Ce）〉0. 000 2 and w（S）〈0. 000 1, while three cerium sulphides （CeS, Ce3S4 and Ce2S3 , in sequence）, MnS and Ce2 O2 S are formed with the increase of S content and the decrease of Ce content for w（Ce）〉0. 000 2 and w（S）〉 0. 000 1. These results are consistent with the SEM observations. Finally, some possible reasons are given to explain the formation of intragranular ferrite in the pure iron.

关键词： Ce inclusion intragranular ferrite deoxidation

Thermodynamic Calculation and MnS Solubility of Mn-Ti Oxide Formation in Si-Mn-Ti Deoxidized Steel

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Journal of Iron and Steel Research International 2010年第2期17卷 10-16页

作者： ZHUO Xiao-jun WANG Yuan-qi WANG Xin-hua Lee Hae-geon Technology Management Section China Minmetals Corporation Beijing 100044 China Department of Scienee and Technology Information China Iron and Steel Research Institute Group Beijing 100081 China Metallurgieal and Ecological Engineering Sehool University of Science and Technology Beijing Beijing100083 China Graduate Institute of Ferrous Teehnology Pohang University of Science and TechnologyPohang 790-784 South Korea

Mn-Ti oxides in Si-Mn-Ti deoxidized steels after cooling in the furnace were investigated. The composition and morphology of inclusions were analyzed by using FE-SEM with EDS. Mn-Ti oxides were found to be effective sites to induce intragranular ferrite formation. The thermodynamic calculation was employed to interpret the critical condition for Mn-Ti oxide formation. Mn-Ti oxide formation was controlled not only by Mn and Ti content, but also by total oxygen content in steel. When the Mn and Ti contents were around 1.5% and 0. 005% --0.01%, respectively, Mn-Ti oxide could form as the total oxygen content was 0. 001%- 0. 002 %. The experimental results were in good agreement with thermodynamic calculation results. Also, MnS solubilit：（ was examined in Mn-Ti oxide inclusion system. With an increase of MnO content in Mn-Ti oxide, MnS solubility in the oxides increased. MnS precipitation benefited from high MnO content in Mn-Ti oxide.

关键词： Si-Mn-Ti deoxided steel Mn-Ti oxide MnS intragranular ferrite thermodynamic calculation

Recent Development and Applications of V Microalloying Technology in China

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Journal of Iron and Steel Research International 2011年第S1期18卷 836-842页

作者： YANG Cai-fu,SU Hang,CHAI Feng,PAN Tao,ZHANG Yong-quan (Central Iron and Steel Research Institute,Beijing 100081,China) Cent Iron & Steel Res Inst Beijing 100081 Peoples R China

This paper reviews recent developments of V microalloying technology and its applications in HSLA ***-nitrogen in V-containing steel promotes precipitation of fine V(C,N) particles,and improves markedly precipitation strengthening effectiveness of vanadium,therefore,there is a significant saving of V addition in the same strength *** can be used effectively for ferrite grain refinement by the nucleation of intragranular ferrite promoted by VN precipitates in *** combination of intragranular ferrite (IGF) on VN particles and the recrystallization controlled rolling (RCR) technology realize the grain refinement in V-containing steel.V-N process is a cost-effective way for high strength rebars,forging steels and thin slab direct rolling strips.

关键词： V microalloying precipitation strengthening intragranular ferrite recrystallization controlled rolling