砷对钢性能的影响及稀土的改善作用研究

发布时间：2018-05-04 15:37

本文选题：砷 + 稀土　；参考：《北京科技大学》2016年博士论文

【摘要】：随着我国钢铁积蓄量的迅速增加和钢铁使用年限的到来,不远将来我国废钢产量将快速增加,终将面临如何使用废钢资源的问题。然而,废钢高效循环利用是个存在多年的世界难题,主要原因是废钢中有害残余元素Cu、Sn、 As等的循环富集。这些残余元素因氧势比铁低,在当前的炼钢工艺水平下很难经济、有效地去除。残存于钢中的残余元素因易于偏析、晶界偏聚和氧化富集而影响钢材的热塑性、热加工性、回火脆性和力学性能等。木文重点关注废钢循环过程中残余元素砷的富集问题。为消除残余元素砷对钢性能的有害影响、提高循环废钢利用效率,本文系统深入研究了砷在钢中的分布规律、稀土变质处理过程中富砷相弥散析出所需的冶金条件、砷对钢热塑性、高温氧化性和力学性能的影响规律以及稀土变质处理方法抑制或消除砷危害性的综合效果。砷在钢中的分布规律研究表明,低砷含量条件下,电子探针分析并未发现1600℃C和1200℃C下淬火的Fe-0.5wt%As合金中存在砷的凝固偏析；而透射电镜(TEM)晶界晶内化学成分分析表明两试样中砷的晶界含量高于晶内,表明砷容易发生晶界偏聚。高砷条件下,1600℃和1420℃下淬火的Fe-4wt%As和Fe-10wt%As合金中,砷会以不连续型的共晶Fe2As相形式分布于a-Fe晶间。而1200℃C下淬火的Fe-10%As合金中,砷会以连续型的共晶Fe2As相形式分布于αt-Fe晶间。此外,Fe2As相面积分数随着合金中As含量增加及淬火温度降低而增加。稀土Ce变质处理后含砷钢中夹杂物成分分析表明,随着Ce含量增加,Ce与As相互作用会生成不同种类的含砷稀土夹杂物。随着Ce含量由0.037wt%增加到0.095wt%,主要类别含砷稀土夹杂物的演变规律为由心部Ce-S-O外部包裹Ce-S-As类的复合夹杂逐渐转变为心部Ce-S-As外部包裹Ce-As类的复合夹杂；而当钢中稀土含量超过0.055wt%时,也会出现单独类的Ce-S-As和Ce-As夹杂物。高温淬火实验结合夹杂物元素面分布分析得出Ce-As类夹杂物的生成机制为凝固过程中元素偏析发生反应而生成,其既可以以优先形成的稀土夹杂物为核心异质形核生成,也可通过均质形核直接生成。同时,通过TEM电子衍射分析确定出Ce-As类夹杂物的物相结构为面心立方的CeAs目。此外,TEM分析发现含砷稀土夹杂物生成后,晶界上的砷含量降至基体含量水平,这有利于抑制或消除砷晶界偏聚所引起的脆化行为。系统研究砷对C-Mn钢热塑性、高温氧化性和力学性能的影响结果表明,对于热塑性,无论是砷单独存在还是铜砷共同存在时,随着砷含量增加,C-Mn钢的热塑性逐渐恶化。砷单独存在情况下砷含量为0.16wt%时和铜砷共存情况下砷含量为0.075wt%时,主要显著降低了C-Mn钢奥氏体单相区850℃-900℃温度范围内的热塑性。俄歇电子能谱仪(AES)分析表明此温度范围内残余元素砷的晶界偏聚为钢热塑性恶化的原因。对于高温氧化性,砷单独存在时加剧了晶界氧化,导致晶界处形成明显的氧化粒子带。当氧化温度由1000℃增加到1050℃,晶界处氧化粒子带渗入基体的深度增加。电子探针(EPMA)分析表明氧化层/钢基体界面处砷的最大富集量随氧化温度的增加呈现先增加后降低的趋势,在1050℃时砷的氧化富集程度最大。铜砷共同存在时铜砷的富集规律与砷单独时相同,同样为1050℃富铜液相侵润晶界现象最为严重；当超过1100℃时,富铜液相侵润晶界现象消失。能谱分析仪(EDS)结合相图分析表明砷的存在降低了铜相的熔点从而促使含砷富铜相1050℃即可析出而侵润晶界。Gleeble热压缩实验结果表明,砷/铜砷的存在将会加剧钢的热裂纹敏感性,1050℃下的热裂程度最为严重；而当超过1100℃时,热裂消除。这与热重实验研究的氧化富集规律结果相一致。对于力学性能,砷主要恶化C-Mn钢的冲击性能,尤其对低温冲击性能的影响更为显著。系统研究稀土改善砷危害钢热塑性、高温氧化性和力学性能的结果表明,对于热塑性,添加0.016wt%-0.035wt%Ce可以改善含砷C-Mn钢的热塑性。随着Ce含量由0增加到0.035wt%,含砷C-Mn钢750℃C-950℃C温度范围内的热塑性逐渐提高。当Ce含量超过0.027wt%时,稀土Ce进一步提升含砷C-Mn钢热塑性的空间不大。对于高温氧化性,添加0.016wt%-0.035wt%的Ce均减少了氧化层与钢基体界面处砷的富集程度,Ce含量为0.027wt%时降低效果最好。热压缩实验表明,Ce含量为0.016wt%-0.035wt%时,1050℃下含砷钢的热裂情况完全消除。对于力学性能,添加0.016wt%Ce可以较好的改善-60℃～0℃范围内的冲击韧性,而添加0.027wt%Ce因碳化物尺寸变大、大量夹杂物生成会恶化钢的冲击性能。因此,综合考虑改善热塑性、抑制表面热裂及提高冲击性能三个方面的效果,添加0.016wt%Ce较为合适。
[Abstract]:With the rapid increase in the amount of steel accumulation and the arrival of steel service years in China, the production of scrap steel will increase rapidly in the near future and will eventually face the problem of how to use the waste steel. However, the high efficiency recycling of scrap steel is a world problem for many years, the main reason is the cyclic enrichment of the harmful residual elements in the scrap steel Cu, Sn, As and so on. These residual elements are lower than iron and are difficult to be economically and effectively removed at the current level of steelmaking process. The residual elements remaining in the steel will affect the thermal plasticity, thermal processing, tempering brittleness and mechanical properties of the steel due to easy segregation, grain boundary segregation and oxidation enrichment. In order to eliminate the harmful effects of arsenic on the properties of steel and improve the utilization efficiency of recycled steel, this paper systematically studied the distribution of arsenic in steel, the metallurgical conditions needed for the dispersion and precipitation of arsenic rich phase in the process of rare earth modification, the influence of arsenic on the thermal plasticity of steel, the oxidation and mechanical properties of high temperature and the dilute effect of arsenic. The distribution law of arsenic in steel shows that, under the condition of low arsenic content, the electron probe analysis did not find the solidification segregation of arsenic in the Fe-0.5wt%As alloy quenched at 1600 C and 1200 C C; and the analysis of the intragranular chemical composition of the grain boundary of the transmission electron microscope (TEM) showed that two samples were found. The grain boundary content of the intermediate arsenic is higher than that in the crystal, indicating that the arsenic is prone to grain boundary segregation. In the Fe-4wt%As and Fe-10wt%As alloys quenched at 1600 and 1420 C under high arsenic conditions, arsenic will be distributed between the a-Fe crystals in the form of discontinuous eutectic Fe2As phase, and arsenic in the Fe-10%As alloy quenched at 1200 C at C will be distributed in the form of continuous eutectic Fe2As phase. In addition, the area fraction of Fe2As phase increases with the increase of As content in the alloy and the decrease of quenching temperature. The analysis of inclusions in arsenic bearing steel after the modification of rare earth Ce shows that with the increase of Ce content, the interaction of Ce and As will produce various kinds of arsenic containing rare earth inclusions. As Ce content increases from 0.037wt% to 0.095wt%, the content of Ce is increased from 0.037wt% to 0.095wt%. The evolution of the inclusions containing arsenic and rare earth inclusions is transformed from the complex inclusion of the Ce-S-As class in the outer core of the heart Ce-S-O to the complex inclusions of the Ce-As class outside the heart Ce-S-As, while the Ce-S-As and Ce-As inclusions of a single class will appear when the rare earth content in the steel is more than 0.055wt%. The distribution analysis shows that the formation mechanism of Ce-As inclusions is generated by the reaction of element segregation during solidification, which can not only be generated by the rare earth inclusions formed as the core heterostructure, but also by the homogeneous nucleation. At the same time, the phase structure of the Ce-As inclusions is determined by the TEM electron diffraction analysis. In addition, the TEM analysis found that the arsenic content in the grain boundary was reduced to the level of the matrix content after the formation of arsenic containing rare earth inclusions, which was beneficial to inhibiting or eliminating the embrittlement of the arsenic grain boundary segregation. The results of the systematic study of the effects of arsenic on the thermal plasticity, high temperature oxidation and mechanical properties of C-Mn steel showed that the thermal plasticity, whether it was arsenic single, was the result of CeAs. The thermal plasticity of C-Mn steel gradually deteriorates with the presence of copper and arsenic in the presence of arsenic and arsenic. When arsenic content is 0.16wt% and arsenic content is 0.075wt% under the presence of arsenic in the presence of arsenic, the thermal plasticity in the temperature range of C-Mn steel austenite 850 C at -900 C is significantly reduced. Auger electron spectroscopy (AES) The analysis shows that the grain boundary segregation of the residual arsenic in the temperature range is the cause of the deterioration of the steel thermal plastic. As for the high temperature oxidation, the grain boundary oxidation is aggravated when the arsenic is alone, leading to the formation of the obvious oxide particles at the grain boundary. When the oxidation temperature increases from 1000 to 1050, the depth of the oxide particles with the grain boundary is increased. The probe (EPMA) analysis shows that the maximum concentration of arsenic at the oxidation layer / steel substrate increases first and then decreases with the increase of the oxidation temperature. The concentration of arsenic is the largest at 1050 C. The enrichment of copper and arsenic is the same as that of arsenic when copper and arsenic is common, which is the same as the most serious phenomenon of the grain boundary of the rich copper liquid at 1050 C. The crystallization of the rich copper liquid vanishes at more than 1100 degrees. The energy spectrum analyzer (EDS) analysis shows that the presence of arsenic reduces the melting point of the copper phase and precipitates the precipitation of the arsenic rich copper phase at 1050 C, and the.Gleeble thermal compression test results of the infiltration grain boundary show that the presence of arsenic / copper and arsenic will increase the thermal crack sensitivity of steel, 1050 The thermal crack is the most serious at the degree of temperature, and the thermal cracking is eliminated when more than 1100 degrees centigrade. This is in accordance with the results of the oxidation enrichment of the thermogravimetric experiment. As for the mechanical properties, the impact properties of the C-Mn steel are mainly deteriorated, especially the impact on the low temperature impact. The results of sexual and mechanical properties show that for thermoplastic, adding 0.016wt%-0.035wt%Ce can improve the thermal plasticity of arsenic bearing C-Mn steel. With the increase of Ce content from 0 to 0.035wt%, the thermal plasticity of arsenic containing C-Mn steel at C-950 C C temperature range is increased gradually. When Ce content exceeds 0.027wt%, rare earth Ce further improves the thermal plasticity of arsenic containing C-Mn steel. For high temperature oxidation, adding 0.016wt%-0.035wt% Ce reduces the concentration of arsenic at the interface between the oxidation layer and the steel matrix. When the content of Ce is 0.027wt%, it is best to reduce the effect. The thermal compression experiment shows that when the content of Ce is 0.016wt%-0.035wt%, the thermal cracking situation of the arsenic bearing steel at 1050 C is completely eliminated. For mechanical properties, the addition of 0.016wt%Ce is added. The impact toughness in the range of -60 C to 0 C can be improved well, and the addition of 0.027wt%Ce will deteriorate the impact properties of the steel because of the larger size of the carbide and the formation of a large number of inclusions. Therefore, it is more suitable to add the effect of improving the thermal plasticity, inhibiting the surface thermal cracking and improving the impact performance of the three aspects. The addition of 0.016wt%Ce is more suitable.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG142.1

【参考文献】