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Lawrence Cho Seok Jae Lee Myung Soo Kim Young Ha Kim Bruno C. De Cooman 《Metallurgical and Materials Transactions A》2013,44(1):362-371
The selective oxidation and reactive wetting of intercritically annealed Si-bearing CMnSi transformation-induced plasticity steels were investigated by high-resolution transmission electron microscopy. In a N2 + 10 pct H2 gas atmosphere with a dew point (DP) ranging from 213 K to 278 K (?60 °C to 5 °C), a continuous layer of selective oxides was formed on the surface. Annealing in a higher DP gas atmosphere resulted in a thinner layer of external oxidation and a greater depth of internal oxidation. The hot dipping was carried out in a Zn bath containing 0.22 mass pct Al, and the bath temperature was 733 K (460 °C). Coarse and discontinuous Fe2Al5?x Zn x grains and Fe-Zn intermetallics (?? and ??) were observed at the steel/coating interface after the hot dip galvanizing (HDG) of panels were annealed in a low DP atmosphere 213 K (?60 °C). The Fe-Zn intermetallics were formed both in areas where the Fe2Al5?x Zn x inhibition layer had not been formed and on top of non-stoichiometric Fe-Al-Zn crystals. Poor wetting was observed on panels annealed in a low DP atmosphere because of the formation of thick film-type oxides on the surface. After annealing in higher DP gas atmospheres, i.e., 263 K and 278 K (?10 °C and 5 °C), a continuous and fine-grained Fe2Al5?x Zn x layer was formed. No Fe-Zn intermetallics were formed. The small grain size of the inhibition layer was attributed to the nucleation of the Fe2Al5?x Zn x grains on small ferrite sub-surface grains and the presence of granular surface oxides. A high DP atmosphere can therefore significantly contribute to the decrease of Zn-coating defects on CMnSi TRIP steels processed in HDG lines. 相似文献
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A transformation induced plasticity (TRIP)-assisted steel with 0.2 pct C, 1.5 pct Mn, and 1.5 pct Al was successfully galvanized
using a thermal cycle previously shown to produce an excellent combination of strength and ductility. The steel surface chemistry
and oxide morphology were determined as a function of process atmosphere oxygen partial pressure. For the 220 K (–53 °C) dew
point (dp) + 20 pct H2 atmosphere, the oxide morphology was a mixture of films and nodules. For the 243 K (–30 °C) dp + 5 pct H2 atmosphere, nodules of MnO were found primarily at grain boundaries. For the 278 K (+5 °C) dp + 5 pct H2 atmosphere, nodules of metallic Fe were found on the surface as a result of alloy element internal oxidation. The steel surface
chemistry and oxide morphology were then related to the reactive wetting behavior during continuous hot dip galvanizing. Good
wetting was obtained using the two lower oxygen partial pressure process atmospheres [220 K dp and 243 K dp (–53 °C dp and
–30 °C dp)]. An increase in the number of bare spots was observed when using the higher oxygen partial pressure process atmosphere
(+5 °C dp) due to the increased thickness of localized oxide films. 相似文献
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Lawrence Cho Geun Su Jung Bruno C. De Cooman 《Metallurgical and Materials Transactions A》2014,45(11):5158-5172
The selective oxidation of a CMnSi transformation-induced plasticity (TRIP) steel during intercritical annealing (IA) in a N2 + 10 pct H2 gas atmosphere with a dew point (DP) in the range from 213 K to 278 K (?60 °C to +5 °C) was investigated by transmission electron microscopy. The decarburization during IA resulted in a fully ferritic matrix at the TRIP steel surface. Annealing in high DP gas atmospheres resulted in a reduction of the oxide layer thickness at the surface and an increase of the depth of the subsurface internal oxidation. The experimental results were compared to the calculations of the DP for the transition from internal to external oxidation based on the Wagner model. The evolution of the surface oxide composition during annealing was analyzed thermodynamically by means of the chemical potential diagram for the surface oxides. In the high DP atmosphere conditions, mainly, Mn-rich xMnO·SiO2 (1 < x < 2) oxides were formed at the surface, while Si-rich xMnO·SiO2 (x < 1) oxides were formed by internal oxidation. The use of a high DP gas atmosphere is therefore advantageous to induce internal selective oxidation and reduce the amount of surface oxides. It also leads to the formation of Mn-rich xMnO·SiO2 (1 < x < 2) oxides. 相似文献
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Lawrence Cho Myung Soo Kim Young Ha Kim Bruno C. De Cooman 《Metallurgical and Materials Transactions A》2013,44(11):5081-5095
The Fe-Zn reaction occurring during the galvannealing of a Si-bearing transformation-induced plasticity (TRIP) steel was investigated by field-emission electron probe microanalysis and field-emission transmission electron microscopy. The galvannealing was simulated after hot dipping in a Zn bath containing 0.13 mass pct Al at 733 K (460 °C). The galvannealing temperature was in the range of 813 K to 843 K (540 °C to 570 °C). The kinetics and mechanism of the galvannealing reaction were strongly influenced by the gas atmosphere dew point (DP). After the galvannealing of a panel annealed in a N2+10 pct H2 gas atmosphere with low DPs [213 K and 243 K (?60 °C and ?30 °C)], the coating layer consisted of δ (FeZn10) and η (Zn) phase crystals. The Mn-Si compound oxides formed during intercritical annealing were present mostly at the steel/coating interface after the galvannealing. Galvannealing of a panel annealed in higher DP [263 K and 273 K, and 278 K (?10 °C, 0 °C, and +5 °C)] gas atmospheres resulted in a coating layer consisting of δ and Г (Fe3Zn10) phase crystals, and a thin layer of Г 1 (Fe11Zn40) phase crystals at the steel/coating interface. The Mn-Si oxides were distributed homogeneously throughout the galvannealed (GA) coating layer. When the surface oxide layer thickness on panels annealed in a high DP gas atmosphere was reduced, the Fe content at the GA coating surface increased. Annealing in a higher DP gas atmosphere improved the coating quality of the GA panels because a thinner layer of oxides was formed. A high DP atmosphere can therefore significantly contribute to the suppression of Zn-alloy coating defects on CMnSi TRIP steel processed in hot dip galvanizing lines. 相似文献
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对改良森吉米尔法镀锌线热镀锌钢板产生漏镀现象的原因进行了详细分析,通过控制无氧化段的氧化、还原炉和喷冷段的露点及正确使用耐火材料等措施,有效控制了热镀锌钢板漏镀缺陷,使钢板漏镀率从1.3%降低到0.3% 相似文献
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析出硬化型热强钢中合金元素的作用机制 总被引:4,自引:0,他引:4
采用X射线衍射和透射电镜等手段,对高温下析出硬化型热强钢中合金元素的再分配行为及其作用机制进行了分析和探讨,并和用余氏理论分析了该钢的价电子结构,阐述了高温下钴的作用机制。结果表明:在700℃的高温下,钢中的合金元素会逐渐析出并形成碳化物等析出相;在700℃下保持600h后,钢中全部的钼、钨、碳及部分的铬、微量的钴和钒等脱溶析出,形成μ相、Layes相、MC、M23C6和M6C等析出相,产生析出强化作用。而大部分的钴、铬和少量的钒保留在基体中起固溶强化作用。价电子结构计算结果表明,钴增强了基体晶格的键合力,同时也提高了回火抗力。 相似文献
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新设备新工艺在热镀锌机组上的应用 总被引:1,自引:0,他引:1
汽车工业是21世纪的支柱产业之一.随着中国加入WTO和世界经济一体化速度的加快,国内汽车市场成为国际竞争舞台,作为高级轿车外板主要原材料之一的热镀锌板以其良好的性价比越来越受到汽车行业的青睐.通过宝钢现有热镀锌机组与国外同类热镀锌机组的对比,简要介绍一些新设备、新工艺在现代热镀锌机组上的应用,主要包括前清洗、退火炉、镀锌段和平整段. 相似文献
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合金化热镀锌钢板镀层性能的工艺因素分析 总被引:4,自引:0,他引:4
热镀锌钢板锌层合金化过程中,热镀锌过程形成的合金层和合金经工艺影响Fe-Zn金属阐化合物生长行为,同此而改变镀层抗粉化性能。简述了钢板化学成分、热镀和锌层合金化条件对锌层合金化工艺的影响因素。 相似文献
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Mohammad Emami Hamid Reza Shahverdi Shigenari Hayashi Mohammad Javad Torkamany 《Metallurgical and Materials Transactions A》2013,44(7):3176-3184
In the present study, a two-step surface treatment was employed to produce an iron-rich aluminide surface layer on 9Cr1Mo steel. In the first step, the steel specimen was immersed in a 1073 K (800 °C) aluminizing bath for 90 seconds to obtain an Al-rich iron aluminide/Al double layer. Then, the aluminum-rich layer and some portion of the substrate material underneath were melted using a pulsed Nd:YAG laser with different pulse energies in the range of 4 to 8 J. The surface and cross section of the alloyed layers were studied using optical microscopy, scanning electron microscopy, an electron microprobe, and X-ray diffraction analyses. The results showed that after laser remelting of the hot dipped aluminized steel at a pulse energy of 7 J, an integrated layer of FeAl replaced the primary layer. 相似文献
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DUAN Han-qiao YAN Xiang WEI Bo-kang LIN Han-tong 《钢铁研究学报(英文版)》2005,12(5):52-57
18-8type austenitic stainless steel is a kind ofanti-corrosion material applied extensively.In mostcases,it must be solution-heattreated to gain goodmechanical properties and corrosive resistance.Butfor some castings with complex shape,such as thepropelle… 相似文献
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针对热镀锌钢卷外圈产生白锈状腐蚀现象,分析出其产生原因为钝化膜厚度较薄、PMT温度过低以及包装时钢卷与环境温差较大,通过优化钝化烘干工艺,降低卷取与包装温度等措施,消除了钢卷外圈白锈缺陷,保证了产品质量。 相似文献
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介绍了汽车用超深冲热镀锌钢带DC54D+Z、DC56D+Z的研发机理,开发过程中化学成分、热连轧关键工艺参数、冷轧和连续退火工艺的设计及控制。大批量生产实践表明:产品化学成分稳定,具有优良的力学性能、冲压成形性能、焊接性能、耐腐蚀性能,产品广泛应用于汽车的各种覆盖件及零部件。 相似文献