A simple route for preparation of TRIP-assisted Si-Mn steel with excellent performance using direct strip casting

The complex producing procedures and high energy-consuming limit the large-scale production and application of advanced high-strength steels(AHSSs).In this study,the direct strip casting(DSC)technology with unique sub-rapid solidification characteristics and cost advantages was applied to the production of low-alloy Si-Mn steel with the help of quenching&partitioning(Q&P)concept to address these issues.Compared this method with the conventional compact strip production(CSP)process,the initial microstructure formed under different solidification conditions and the influence of heat treatment processes on the final mechanical properties were in-vestigated.The results show that the initial structure of the DSC sample is a dual-phase structure composed of fine lath martensite and bainite,while the initial structure of the CSP sample consists of pearlite and ferrite.The volume fraction and carbon content of retained austenite(RA)in DSC samples are usually higher than those in CSP samples after the same Q&P treatment.DSC samples typically demonstrate better comprehensive mechanical properties than the CSP sample.The DSC sample partitioned at 300℃ for 300 s(DSC-Pt300)achieves the best comprehensive mechanical properties,with yield strength(YS)of 1282 MPa,ultimate tensile strength(UTS)of 1501 MPa,total elongation(TE)of 21.5%,and product of strength and elongation(PSE)as high as 32.3 GPa·%.These results indicate that the excellent mechanical properties in low-alloy Si-Mn steel can be obtained through a simple process(DSC-Q&P),which also demonstrates the superiority of DSC technology in manufacturing AHSSs.

Effect of phosphorus content on interfacial heat transfer and film deposition behavior during the high-temperature simulation of strip casting

The interfacial wettability and heat transfer behavior are crucial in the strip casting of high phosphorus-containing steel.A hightemperature simulation of strip casting was conducted using the droplet solidification technique with the aims to reveal the effects of phosphorus content on interfacial wettability,deposited film,and interfacial heat transfer behavior.Results showed that when the phosphorus content increased from 0.014wt%to 0.406wt%,the mushy zone enlarged,the complete solidification temperature delayed from1518.3 to 1459.4℃,the final contact angle decreased from 118.4°to 102.8°,indicating improved interfacial contact,and the maximum heat flux increased from 6.9 to 9.2 MW/m2.Increasing the phosphorus content from 0.081wt%to 0.406wt%also accelerated the film deposition rate from 1.57 to 1.73μm per test,resulting in a thickened naturally deposited film with increased thermal resistance that advanced the transition point of heat transfer from the fifth experiment to the third experiment.

Wetting behavior of CaO-Al_(2)O_(3)-based mold flux with various BaO and MgO contents on the steel substrate

The Interfacial phenomena in mold have a great impact on the smooth operation of continuous casting process and the quality of the casting product.In this paper,the wetting behavior of CaO-Al_(2)O_(3)-based mold flux with different BaO and MgO contents was studied.The results showed that the contact angle between molten flux and interstitial free(IF)steel substrate increased from 62.4°to 74.5°with the increase of BaO content from 3 wt%to 7 wt%,while it decreased from 62.4°to 51.3°with the increase of MgO content from 3 wt%to 7 wt%.The interfacial tension also increased from 1630.3 to 1740.8 mN/m when the BaO content increased,but it reduced from 1630.3 to 1539.7 mN/m with the addition of MgO.The changes of contact angle and interfacial tension were mainly due to the fact that the bridging oxygen(O^(0)) at the interface was broken into non-bridging oxygen(O^(-)) and free oxygen(O_(2-)) by MgO.However,more O^(-) and O_(2-) connected into O^(0) when BaO was added,since the charge compensation effect of BaO was so stronger that it offset the effect of providing O_(2-).

基于界面固相反应的软磁复合铁芯成分定制策略及磁性能优化研究

因具有高饱和磁化强度、高磁导率和相对较低的磁芯损耗等优异性能,软磁复合铁芯被认为是最具发展潜力的电磁转换器件。但软磁复合铁芯的能量损耗和导磁性作为保证电磁器件有效运行的关键性能参数,却往往呈制约关系。因此,通过调控粉末基体与包覆层分布特征,增加软磁复合铁芯内部的铁磁填充因子,实现绝缘层的原位包覆,有助于达到同时限制能量损耗和提高导磁性的目的。本工作设计了一种新的界面固相反应策略,首先通过水热法将乙酸钙均匀地包覆在Fe-Si-Al软磁合金粉末表面,再利用热压烧结制备Fe-Si-Al基软磁复合铁芯,研究了烧结温度和包覆层相变对制备的软磁复合铁芯形貌、微观结构和磁性能的影响。结果表明,通过水热法乙酸钙被成功包覆在Fe-Si-Al合金粉末表面,形成了以Fe-Si-Al合金粉末为核、乙酸钙为壳的核壳异质结构;烧结温度的提高消除了软磁复合铁芯内部的孔隙,促使绝缘层发生从乙酸钙到碳酸钙再到Al_(2)O_(3)·SiO_(2)·CaSiO_(3)的转变,最终为软磁复合铁芯提供了高质量的复合绝缘层;在850℃下高温烧结制备的软磁复合铁芯绝缘包覆层致密均匀,磁稀释效应被降到最低,在10 mT、100 kHz时拥有最高的磁导率(67.2)、最低的损耗(9.24×10^(-5)kW/cm^(3))和相对更高的饱和磁化强度(129.0 emu/g),综合性能最优,为制约传统软磁材料中导磁性与损耗间的反向关系提供了解决方案。因此,基于有机盐类化合物热分解氧化的绝缘包覆方法有望成为基于界面固相反应工程的软磁复合铁芯性能优化策略的重要补充。