本文選題：砷 + 稀土�。� 參考：《北京科技大學(xué)》2016年博士論文

【摘要】：隨著我國(guó)鋼鐵積蓄量的迅速增加和鋼鐵使用年限的到來(lái),不遠(yuǎn)將來(lái)我國(guó)廢鋼產(chǎn)量將快速增加,終將面臨如何使用廢鋼資源的問(wèn)題。然而,廢鋼高效循環(huán)利用是個(gè)存在多年的世界難題,主要原因是廢鋼中有害殘余元素Cu、Sn、 As等的循環(huán)富集。這些殘余元素因氧勢(shì)比鐵低,在當(dāng)前的煉鋼工藝水平下很難經(jīng)濟(jì)、有效地去除。殘存于鋼中的殘余元素因易于偏析、晶界偏聚和氧化富集而影響鋼材的熱塑性、熱加工性、回火脆性和力學(xué)性能等。木文重點(diǎn)關(guān)注廢鋼循環(huán)過(guò)程中殘余元素砷的富集問(wèn)題。為消除殘余元素砷對(duì)鋼性能的有害影響、提高循環(huán)廢鋼利用效率,本文系統(tǒng)深入研究了砷在鋼中的分布規(guī)律、稀土變質(zhì)處理過(guò)程中富砷相彌散析出所需的冶金條件、砷對(duì)鋼熱塑性、高溫氧化性和力學(xué)性能的影響規(guī)律以及稀土變質(zhì)處理方法抑制或消除砷危害性的綜合效果。砷在鋼中的分布規(guī)律研究表明,低砷含量條件下,電子探針?lè)治霾⑽窗l(fā)現(xiàn)1600℃C和1200℃C下淬火的Fe-0.5wt%As合金中存在砷的凝固偏析；而透射電鏡(TEM)晶界晶內(nèi)化學(xué)成分分析表明兩試樣中砷的晶界含量高于晶內(nèi),表明砷容易發(fā)生晶界偏聚。高砷條件下,1600℃和1420℃下淬火的Fe-4wt%As和Fe-10wt%As合金中,砷會(huì)以不連續(xù)型的共晶Fe2As相形式分布于a-Fe晶間。而1200℃C下淬火的Fe-10%As合金中,砷會(huì)以連續(xù)型的共晶Fe2As相形式分布于αt-Fe晶間。此外,Fe2As相面積分?jǐn)?shù)隨著合金中As含量增加及淬火溫度降低而增加。稀土Ce變質(zhì)處理后含砷鋼中夾雜物成分分析表明,隨著Ce含量增加,Ce與As相互作用會(huì)生成不同種類的含砷稀土夾雜物。隨著Ce含量由0.037wt%增加到0.095wt%,主要類別含砷稀土夾雜物的演變規(guī)律為由心部Ce-S-O外部包裹Ce-S-As類的復(fù)合夾雜逐漸轉(zhuǎn)變?yōu)樾牟緾e-S-As外部包裹Ce-As類的復(fù)合夾雜；而當(dāng)鋼中稀土含量超過(guò)0.055wt%時(shí),也會(huì)出現(xiàn)單獨(dú)類的Ce-S-As和Ce-As夾雜物。高溫淬火實(shí)驗(yàn)結(jié)合夾雜物元素面分布分析得出Ce-As類夾雜物的生成機(jī)制為凝固過(guò)程中元素偏析發(fā)生反應(yīng)而生成,其既可以以優(yōu)先形成的稀土夾雜物為核心異質(zhì)形核生成,也可通過(guò)均質(zhì)形核直接生成。同時(shí),通過(guò)TEM電子衍射分析確定出Ce-As類夾雜物的物相結(jié)構(gòu)為面心立方的CeAs目。此外,TEM分析發(fā)現(xiàn)含砷稀土夾雜物生成后,晶界上的砷含量降至基體含量水平,這有利于抑制或消除砷晶界偏聚所引起的脆化行為。系統(tǒng)研究砷對(duì)C-Mn鋼熱塑性、高溫氧化性和力學(xué)性能的影響結(jié)果表明,對(duì)于熱塑性,無(wú)論是砷單獨(dú)存在還是銅砷共同存在時(shí),隨著砷含量增加,C-Mn鋼的熱塑性逐漸惡化。砷單獨(dú)存在情況下砷含量為0.16wt%時(shí)和銅砷共存情況下砷含量為0.075wt%時(shí),主要顯著降低了C-Mn鋼奧氏體單相區(qū)850℃-900℃溫度范圍內(nèi)的熱塑性。俄歇電子能譜儀(AES)分析表明此溫度范圍內(nèi)殘余元素砷的晶界偏聚為鋼熱塑性惡化的原因。對(duì)于高溫氧化性,砷單獨(dú)存在時(shí)加劇了晶界氧化,導(dǎo)致晶界處形成明顯的氧化粒子帶。當(dāng)氧化溫度由1000℃增加到1050℃,晶界處氧化粒子帶滲入基體的深度增加。電子探針(EPMA)分析表明氧化層/鋼基體界面處砷的最大富集量隨氧化溫度的增加呈現(xiàn)先增加后降低的趨勢(shì),在1050℃時(shí)砷的氧化富集程度最大。銅砷共同存在時(shí)銅砷的富集規(guī)律與砷單獨(dú)時(shí)相同,同樣為1050℃富銅液相侵潤(rùn)晶界現(xiàn)象最為嚴(yán)重；當(dāng)超過(guò)1100℃時(shí),富銅液相侵潤(rùn)晶界現(xiàn)象消失。能譜分析儀(EDS)結(jié)合相圖分析表明砷的存在降低了銅相的熔點(diǎn)從而促使含砷富銅相1050℃即可析出而侵潤(rùn)晶界。Gleeble熱壓縮實(shí)驗(yàn)結(jié)果表明,砷/銅砷的存在將會(huì)加劇鋼的熱裂紋敏感性,1050℃下的熱裂程度最為嚴(yán)重；而當(dāng)超過(guò)1100℃時(shí),熱裂消除。這與熱重實(shí)驗(yàn)研究的氧化富集規(guī)律結(jié)果相一致。對(duì)于力學(xué)性能,砷主要惡化C-Mn鋼的沖擊性能,尤其對(duì)低溫沖擊性能的影響更為顯著。系統(tǒng)研究稀土改善砷危害鋼熱塑性、高溫氧化性和力學(xué)性能的結(jié)果表明,對(duì)于熱塑性,添加0.016wt%-0.035wt%Ce可以改善含砷C-Mn鋼的熱塑性。隨著Ce含量由0增加到0.035wt%,含砷C-Mn鋼750℃C-950℃C溫度范圍內(nèi)的熱塑性逐漸提高。當(dāng)Ce含量超過(guò)0.027wt%時(shí),稀土Ce進(jìn)一步提升含砷C-Mn鋼熱塑性的空間不大。對(duì)于高溫氧化性,添加0.016wt%-0.035wt%的Ce均減少了氧化層與鋼基體界面處砷的富集程度,Ce含量為0.027wt%時(shí)降低效果最好。熱壓縮實(shí)驗(yàn)表明,Ce含量為0.016wt%-0.035wt%時(shí),1050℃下含砷鋼的熱裂情況完全消除。對(duì)于力學(xué)性能,添加0.016wt%Ce可以較好的改善-60℃～0℃范圍內(nèi)的沖擊韌性,而添加0.027wt%Ce因碳化物尺寸變大、大量夾雜物生成會(huì)惡化鋼的沖擊性能。因此,綜合考慮改善熱塑性、抑制表面熱裂及提高沖擊性能三個(gè)方面的效果,添加0.016wt%Ce較為合適。
[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.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG142.1

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本文編號(hào)：1843559