【作者】 李平；

【导师】 魏伯康； 蔡启舟；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2006， 博士

【摘要】 湿法炼锌料浆介质中含有SiO2等固相颗粒、稀H2SO4及Cl–、F–、Zn2+、Fe3+等杂质离子,料浆泵遭受严重的液固两相流冲刷腐蚀,特别是叶轮的快速损坏使工厂频繁停机检修、更换备件,导致生产效率降低,生产成本增加,给工厂带来巨大的经济损失。虽然工厂在改进料浆泵叶轮结构和叶轮材料采用铜合金、钛合金等高性能金属材料、工程塑料和陶瓷材料等方面作了大量工作,但这一难题一直没有得到很好的解决。到目前为止,有关湿法炼锌料浆介质中材料冲刷腐蚀行为的研究报道极少,因此,开展此领域中冲刷腐蚀的研究极为迫切。本论文以湿法炼锌料浆介质为背景,对三种不锈钢材料的冲刷腐蚀机理和影响因素等展开了系统而深入的研究,以期为料浆泵叶轮的合理选材提供理论依据,同时研究结果对于耐冲刷腐蚀材料的开发以及丰富摩擦学理论将具有重要意义。论文首先对料浆泵叶轮进行失效分析,同时采用电化学方法和旋转圆盘冲刷腐蚀试验装置对湿法炼锌过程的腐蚀性及叶轮不同部位冲刷作用的动力学特性进行了模拟研究。结果表明,现采用的奥氏体不锈钢(0Cr25Ni18Mo)叶轮的失效是腐蚀和机械冲刷共同作用的结果,其中冲刷作用占主导地位;叶轮材料的硬度低、抗冲刷磨损性能差是导致其快速损坏的主要原因。料浆的流速和固体颗粒的浓度,即颗粒的冲击动量对叶轮不同部位损坏程度有重要影响,叶轮外缘由于流速大且固体颗粒浓度高,冲击动量大,因而冲刷腐蚀失重速率大,叶轮中心处附近由于流速小且固体颗粒浓度小,冲击动量小,因而冲蚀失重速率小。电化学分析表明,增大介质中的SO42-、Cl-、F-浓度,使叶轮材料的维钝电流密度ip和致钝电流密度ipp增大、钝化区间缩小、腐蚀速度加大,当SO42-、Cl-、F-同时存在时,对叶轮材料的腐蚀有强烈协同促进作用,从而增大叶轮材料的冲刷腐蚀失重率;而Zn2+、Fe3+、Cd2+等阳离子使材料的腐蚀电位正移,维钝电流密度ip降低、促进材料钝化,对材料的腐蚀有抑制效应,降低试验材料的腐蚀分量,从而使冲刷腐蚀失重率减小。研究结果对耐冲刷腐蚀材料的开发和理论研究都具有重要参考价值。对常用耐蚀或耐磨材料的冲刷腐蚀研究表明,在湿法炼锌介质中,选用传统的耐蚀或耐磨材料作为料浆泵叶轮无法保证其较长服役寿命。而具有一定耐蚀性和一定抗变形或耐磨能力的不锈钢系列材料有可能成为未来耐冲刷腐蚀的首选,初步筛选出了较适合于此介质环境下的3种候选材料:含氮双相不锈钢、17-4PH沉淀硬化不锈钢和σ相强化奥氏体不锈钢。对含氮双相不锈钢的研究结果表明,在模拟湿法炼锌料浆介质中,在试验氮量范围内,随含氮量增加,腐蚀电流密度逐渐减小、钝化区逐渐增大,双相钢的纯腐蚀速率(Vc)逐渐减小。但纯冲刷速率(Ve)和整个材料流失速率(Vt)并未随含氮量的增加而减小,当含氮量在0.1%～0.3%时,钢中奥氏体相(γ)含量为30%～70%、其余为铁素体相(α),两相比例比较适当,其Ve和Vt较低,双相钢有较好的抗冲刷腐蚀性能,当两相含量相当时,其Ve和Vt最低,双相钢的抗冲刷腐蚀性能最好。硬度不是双相钢抗冲刷腐蚀性能的决定因素,形变强化能力才对其起决定作用。对17-4PH沉淀硬化不锈钢的研究表明, 460℃时效处理时,钢中析出大量弥散分布的富铜相,硬度最高,在模拟试验料浆介质环境下,抗冲刷腐蚀性能最好。与失效叶轮相比,硫酸浓度对17-4PH钢的冲刷腐蚀失重速率的影响显著,当硫酸浓度低时, 17-4PH钢的抗冲刷腐蚀性能比失效叶轮好,当硫酸浓度高时,抗冲刷腐蚀性能比失效叶轮差。对σ相强化奥氏体不锈钢的研究表明,σ相硬度高、在软的奥氏体基体中起到骨架作用,耐磨性得到提高,同时σ相中主要耐蚀合金元素含量高,与基体的电极电位差小,耐蚀性良好,因而具有优良的抗冲刷腐蚀性能。时效处理后析出的细针片状σ相,在软的基体上弥散分布,对钢进一步强化,而基体中的主要耐蚀合金元素的含量没有明显降低,耐蚀性仍很好,因而抗冲刷腐蚀性能得到进一步提高。在模拟湿法炼锌料浆介质中,σ相强化奥氏体不锈钢材料的冲刷腐蚀失重速率比失效叶轮材料相比降低了57%。系统研究了主要环境参数对σ相强化奥氏体不锈钢和失效叶轮材料冲刷腐蚀行为的影响。结果表明VE-C与υ之间满足指数关系:VE-C = k1·υn1 ,在试验条件下,n1值在1~2.5之间,与通常气固冲蚀的速度指数2~5要小; SiO2固体颗粒浓度在5%和20%附近时,VE-C增大的幅度显著;VE-C随SiO2粒度Dp增大呈近似线性关系增大;在料浆H2SO4浓度较低时,材料的耐冲刷腐蚀性能主要取决于材料的抗冲刷磨损性能,当H2SO4浓度较高时,材料的耐冲刷腐蚀性能除取决于材料的抗冲刷磨损性能外,还与其耐腐蚀性,尤其是冲刷与腐蚀交互作用的失重速率(Vs)的大小有关。将研究结果绘制出了流速-SiO2颗粒尺寸、流速-SiO2颗粒浓度和流速-H2SO4浓度的材料流失机制图,可以对工况条件变化时材料的流失情况作出预测。通过三种研究不锈钢与失效叶轮材料冲刷腐蚀对比试验表明,在湿法炼锌料浆介质中,σ相强化奥氏体不锈钢材料的抗冲刷腐蚀性能最好,明显高于现使用叶轮材料。因此,利用弱阴极第二相强化是开发料浆泵叶轮等过流部件材料,延长其使用寿命的一种有效途径。更多还原

【Abstract】 The slurry pumps are suffered from serious erosion-corrosion (E-C) in liquid-solid two-phase flow of zinc hydrometallurgy slurry containing solid particles such as silica , and diluted sulfuric acid as well as the impurities of Cl–、F–、Zn2+、Fe3+ and so on. Especially due to the rapid damages of the impellers, the plant is forced to stop production frequently so as to repair or replace spare parts. It results in decrease of productive efficiency and increase of production cost, together with the huge economic loss. Although many efforts were made such as improving the configurations and replacing the materials of the impellers, in which better performance metallic materials such as copper alloy and titanium alloy, engineering plastic and ceramic material were used, the difficult problem has not been still satisfactorily solved. By now ,there are few research reports on E-C behavior of the materials used in zinc hydrometallurgy environment, therefore the basic research on it is urgent. In this thesis, three kinds of stainless steels were selected as research object and zinc hydrometallurgy slurry as medium, systemic researches were carried out on E-C mechanism and effect factors and so on, the purpose is to provide a guide for rational selection of the impeller materials of slurry pump. At the same time the research results should be of benefit not only to the development of E-C resistant materials, but also to the richness of tribology theory.Failure analysis of the impeller of slurry pump was firstly carried out, at the same time corrosion behavior of slurry ions composition and dynamics characteristic of erosion action at different position of the impeller were simulated by using electrochemical method and rotating disc E-C apparatus. The results showed that the failure of austenite stainless steel (0Cr25Ni18Mo) impeller used in zinc hydrometallurgy environment was due to the interaction of corrosion and erosion-wear, erosion-wear was dominating, low hardness of the impeller material namely poor wear resistance was main reason that resulted in rapid damage of it. Moreover erosion damage of the impeller at different place depended on flow velocity of the slurry and concentration of solid particles, i.e. the momentum of particles. Erosion rate in the margin of the impeller was higher because of higher flow velocity and bigger particles concentration ,namely bigger impact momentum, while erosion rate near the center of the impeller was lower because of lower flow velocity and smaller particles concentration,namely smaller impact momentum.The results of electrochemical analysis showed that with the increase of acidic ions such as SO42-,Cl-, F- in the slurry , the critical passivation current density ip or ipp of stainless steel was increased and passive potential range was shortened , therefore corrosive mass loss rate and E-C mass loss rate of the material were increased; While with the increase of the cations such as Zn2+ and Fe3+ in the slurry, passivation current density ip was decreased and passive potential range was widened, therefore corrosion mass loss rate and E-C mass loss rate of the material were reduced. The conclusion should be of benefit not only to the development of E-C resistant materials, but also to the richness of E-C research.The research results on the simulated tests of the several corrosion resistant or wear resistant materials showed that under the condition of zinc hydrometallurgy selecting the traditional materials as that of the impellers of slurry pumps couldn’t ensure longer service life. But stainless steel series materials possessing certain corrosion resistance and good deformation resistance or wear resistance should be likely to become the first selection of the impeller materials. Three kinds of candidate materials, i.e. nitrogen-containing duplex stainless steel (DSS), 17-4PH precipitation-hardening stainless steel (17-4PH) and austenite stainless steel strengthened byσphase were screened out as three kinds of candidate materials of the impeller from the simulated test.The research results on nitrogen-containing DSS showed that in the simulated slurry corrosion current density ic of the tested materials was decreased and passive potential range was enlarged, and pure corrosion rate (Vc) was decreased with the increase of N content. While pure erosion rate (Ve) and total E-C rate (Vt) weren’t decreased with the increase of N content in the studied the range of N content. DSSs containing nitrogen contents from 0.1% to 0.3% had the microstructures of austenite (γ) contents from 30% to 70% and ferrite (α), the ratio ofγandαwas appropriate, their Ve and Vt were lower, their E-C resistant performance were more excellent, moreover Ve and Vt of DSS containing the microstructure of nearly equal content ofγandαwere lowest, therefore its E-C resistant performance is most excellent. Hardness of DSS is not be the determinant factor, deformation strengthening ability is just a key factor on E-C resistance.The research results on 17-4PH steel showed that under the simulated slurry medium owing to dispersive precipitate of a number of Cu-rich particle aged at 460℃,the hardness of the material was highest and its E-C resistance was most excellent. Effect of corrosion factor on E-C rate was more remarkably compared with failure impeller material. When sulfuric acid concentration was lower, 17-4PH steel showed better E-C resistance than that of failure impeller, while sulfuric acid concentration was higher, its E-C resistance was poorer than that of failure impeller.The research results on austenite stainless steel strengthened byσphase showed that they exhibited better wear resistance due to the protecting action ofσphase on soft matrix as well as excellent corrosion resistance owing to higher main corrosion-resistant alloy element inσphase and little difference of electrode voltage with austenite matrix, therefore they showed excellent E-C resistance. The steels aged had been reinforced further owing to the dispersive precipitate of fine needle and flakeσphase in the matrix, at the same time it held good corrosion resistance due to the slight decrease of main corrosion resistant elements in the matrix, therefore E-C resistance of the improved materials had been significantly promoted. 57% of E-C rate of the improved materials was decreased compared with that of failure impeller in the simulated zinc hydrometallurgy slurry.The systemic research of main environmental parameters on E-C behavior of austenite stainless steel strengthened byσphase and failure impeller was performed. The results showed that under the test condition, flow velocity (υ) dependency of E-C rate (VE-C) was as follows: VE-C = K1·υn1 ,n1 in the test was between 1 and 2.5, n1 is smaller than velocity exponent (2～5) of general gas-solid E-C. VE-C was markedly increased with the concentration of silica(Cp) of about 5% or 20%. VE-C was approximately linerly increased with the increase of granularity of silica (Dp). When sulphuric acid concentration (Ca) was lower, E-C resistances of the tested materials mainly depended on erosion resistance, while Ca was higher, E-C resistances depended on not only erosion resistance but also corrosion resistance, especially synergistic rate (Vs) between erosion and corrosion besides erosion resistance. Material loss mechanism maps of flow velocity-silica granularity, flow velocity-silica particles concentration and flow velocity-sulphuric acid concentration are drawn by the research results,thereby material loss trend could be forecasted by them when the condition change of the material occurs.E-C test result of three kinds of stainless steels and failure impeller material confirmed that under the zinc hydrometallurgy slurry, E-C resistance of austenite stainless steel strengthened byσphase was most excellent, much more excellent than the impeller material used now. It should be an effective approach to develop the material of flow-handling component of slurry pump such as the impeller and prolong its service life to make use of such method that the material is strengthened by second phase with weak cathode.更多还原