温度对红土矿球团直接还原的影响

在还原时间90min、氧化钙配比10%、复合剂配比11%、还原碳配比5%的条件下制成球团进行焙烧、磁选。考察球团还原过程温度的变化对球团产生镍铁颗粒金属化率和镍品位的影响。结果表明:还原的最佳温度1 200～1 250℃,此温度下镍的金属化率达到89%以上、铁的金属化率85%以上。镍的品位达到5%。     

红土镍矿高料层碳热还原试验

 红土镍矿是生产镍铁合金的主要原料之一,其碳热还原后的镍铁金属颗粒尺寸对后期磁选分离至关重要。基于此,进行了红土镍矿在高料层条件下的碳热还原试验研究,考察了还原温度、时间及添加剂CaO等对还原后镍铁金属颗粒尺寸的影响规律和作用机理。试验结果表明,在配碳量C/O(质量比)为1.0、还原温度为1400 ℃、还原时间为45 min的条件下,还原效果最佳,还原后大于40 μm的金属颗粒约占70%,最大颗粒约为100 μm。对该还原条件下得到的金属化球团进行磁选分离可得到镍铁合金,基本可以将金属镍回收。研究结果可为红土镍矿碳热还原工艺的应用提供操作参数和理论依据。     

钒钛铁精矿非自然碱度含碳球团高温固态还原试验

为了研究钒钛铁精矿非自然碱度含碳球团高温固态还原规律,以钒钛铁精矿为原料,在实验室条件下,探索了还原温度、还原时间、碱度和配煤比对钒钛铁精矿非自然碱度含碳球团高温固态还原的影响,采用X射线衍射仪测定了金属化球团的物相组成。研究结果表明,适当提高还原温度、延长还原时间、提高碱度和配煤比均可促使球团的金属化率提高;对于钒钛铁精矿金属化球团物相组成,在还原温度高于1 400℃时,金属化球团中出现大量碳氮化钛,碱度的提高有利于抑制还原产物中碳氮化钛的生成,配煤比的增加促进了碳氮化钛的生成。从后续熔分工序对钒钛铁精矿金属化球团质量要求的角度来说,高温固态还原的适宜条件,还原温度为1 350℃,碱度为1.0,还原时间为30 min,配煤比为1.3,在此条件下,球团的金属化率为93.72%,金属化球团碳质量分数为6.08%,主要物相为黑钛石和金属铁。     

低镁钒钛磁铁矿的还原机理

为开发利用辽宁朝阳地区低镁钒钛磁铁矿资源,本文以石墨粉为还原剂,研究还原温度、碳氧比等因素对内配碳球团还原过程的影响,并采用X射线衍射(XRD)和扫描电镜(SEM)等分析方法对还原机理进行分析.研究结果表明,低镁钒钛磁铁矿与攀西地区钒钛磁铁矿相比,易于还原.当还原温度超过1 150℃时,球团均能快速进行反应;配碳比增加有利于反应分数的提高.随着反应时间的延长,球团内部先后出现浮氏体、新生钛铁矿和FeTi2O5等过渡相,还原产生的金属铁从矿物颗粒外表面到内部依次析出,金属铁相不断增加并聚集长大,球团内部新生相界面逐渐清晰.     

内配碳对氧化球团冶金性能的影响

适量的内配碳可以改善赤铁矿球团预热和焙烧性能较差的问题,为进一步阐述内配碳对氧化球团冶金性能的影响,以赤铁矿为主要原料,研究不同内配碳熔剂性球团的显微结构与冶金性能。结果表明:内配碳质量分数增加至1.2%时,球团内Fe_2O_3晶粒进一步长大,孔隙变圆且孔隙率下降,可以显著提高熔剂性球团的抗压强度,以Fe_2O_3再结晶键连接的固结形式有利于降低球团的还原膨胀率,相应的还原球团中的金属铁晶须明显变短变粗且呈板状形式发展。此外,内配碳质量分数的增加对软化性能相对不利,而控制内配碳质量分数在1.2%之内有利于其滴落性能的提高,对还原度影响较小。     

台车连续炉生产镍铁金属化球团的实验研究

介绍了一种利用台车连续炉,以红土镍矿为原料,煤粉为还原剂,生产镍铁金属化球团的方法。通过对正交实验结果分析,得到可用于实际生产的工艺参数。工业实验结果表明,内配碳量是影响球团金属化率的最重要因素,但过多内配碳量带来的残余灰分会降低产品球团的品位,因此以碳氧比1．3为宜;采用一定的盖碳保护措施可以有效防止球团氧化,抑制球团金属化率的降低;考虑成本因素,流程时间不宜过长,球团在还原段的时问以24h为宜。     

红土镍矿深度还原-磁选富集镍铁实验研究

采用深度还原-磁选工艺,以煤粉为还原剂,添加氧化钙作助溶剂,在微熔化,不完全造渣的条件下,将矿石中镍和铁的氧化物还原成金属镍铁,然后经磁选方法使金属镍铁在磁性产品中得到富集.结果表明,深度还原最佳工艺条件为:还原温度1 300℃,还原时间60 min,配煤过剩倍数2.在此工艺条件下得到镍、铁质量分数分别为5.01%,22.46%的镍铁产品,镍、铁回收率分别为96.05%,79.69%.对深度还原过程研究表明,还原物料中镍和铁以金属合金颗粒形式存在,高温有利于镍铁金属相凝聚,适当延长还原反应时间有利于镍铁颗粒的还原和聚集长大,进而有利于磁选富集.     

白云鄂博铁精矿配碳球团还原特性研究

以白云鄂博铁精矿配碳球团和某外矿铁精矿配碳球团为研究对象,在950~1 100℃下进行等温还原试验。经相同条件还原后,对比两种球团的还原度及球团体积变化得到白云鄂博铁精矿配碳球团的还原特性。发现在相同条件下,白云鄂博铁精矿配碳球团的还原度均大于某外矿铁精矿配碳球团,但两者差值随还原温度的升高而减小;球团收缩率及球团表面开裂程度均随还原温度的升高而增大,且白云鄂博铁精矿配碳球团的球团收缩率大于某外矿铁精矿配碳球团。     

台车连续炉生产低P、S镍铁精矿的实践

以低品位红土镍矿为原料,利用台车连续炉工艺生产镍铁金属化球团。通过正交实验研究了配碳量、还原时间及不同熔剂对金属化球团磁选后精矿中P、S含量的影响,结果表明:熔剂是影响精矿中P含量的最主要因素,配碳量是影响S含量的最主要因素。综合考虑精矿中的P、S含量,结合成本及效益,得到最佳工艺条件:内配碳量(C/O)为1.3,还原时间为24 h,采用CaO作为熔剂。     

含碳球团的还原熔分行为

通过高温电阻炉对含碳球团还原熔分的行为进行热态模拟研究,考察温度、配碳比、化学成分等因素对球团还原熔分的影响程度.结果表明,温度、配碳比和球团传热方向上的尺寸是控制球团还原熔分的关键;化学成分对还原速率影响不明显,但是通过改变渣的组成可对渣铁熔分起促进或抑制作用.     

A two-stage thermal upgrading process for nickeliferous limonitic laterite ores

Sulphide ore deposits are becoming increasingly less viable as a source of nickel, driving recent interest in the development of nickel laterite deposits. The difficulties with the current methods of nickel metal production from these oxide ores arise mainly from the inability to produce a concentrate analogous to that obtained in the flotation of sulphide ores, resulting in high production costs. In this work, a two-stage reduction and thermal growth process is proposed for the treatment of the nickeliferous limonitic laterite ores to produce a ferronickel product, recoverable by magnetic separation. An initial reduction roast of the ore with 6% coal and 4% sulphur additions at 600°C for 1?h, followed by particle growth for 1?h at 1000°C, produced a ferronickel concentrate with a nickel grade of 4% and a nickel recovery of 93·2%. The impact of particle growth temperature and retention time at temperature on the ferronickel particle size was also studied. For the control conditions, typical ferronickel particles produced were 10–20?μm in size. The particle size did not significantly change at temperatures higher than 1200°C or for retention times beyond 60?min.     

Austenite Grain Growth Behavior of X80 Pipeline Steel in Heating Process

Through changing soaking temperature and soaking time,austenite grain growth behavior of X80 pipeline steel under different heating conditions was studied. Relationships of average grain size to soaking temperature and time were obtained respectively. The results show that the prior austenite grains grow with the increase of soaking temperature and time. When soaking temperature is lower than 1180℃,austenite grain size and growth rate are small; when it higher than 1200℃,austenite grains grow rapidly and abnormal grain growth appears. For soaking at 1180℃,austenite grain growth rate is initially high and then decreases when soaking time exceeds 1h.     

钒钛磁铁矿含碳球团还原的影响因素

通过单因素实验考察了还原温度、还原时间及碳氧摩尔比(n_C/n_O)对钒钛磁铁矿含碳球团还原的影响,结合扫描电镜照片解释了钒钛磁铁矿的还原机理.实验结果表明,适当升高还原温度、延长还原时间及增加碳氧摩尔比均可以促进钒钛磁铁矿的还原,并且金属化率随还原温度的升高先急剧升高而后趋于平缓,随着还原时间的延长及碳氧摩尔比的增加而先升高后降低,而残碳量随着反应的进行不断降低.当还原温度为1350℃,还原时间为30 min,碳氧摩尔比为1.2时,球团的金属化率达到最大值.通过扫描电镜照片可以看出,球团在还原过程中形成了铁连晶,并且在不同的还原条件下铁连晶的大小及形态不同.      

Effects of Ti and Nb on the Grain Refinement and Mechanical Properties of AISI 4145 Steel

In this study, we investigated the effects of Ti and Nb additions on the grain size of prior austenite and mechanical properties such as yield strength, yield ratio, and impact toughness in quenched and tempered AISI 4145 steel. It was found that the grain size of prior austenite directly influenced the mechanical properties. Thermodynamic calculations were carried out to find the characteristics of the precipitates such as dissolution temperature of precipitates, the average size of precipitate particles, precipitate fraction, and mean distance among precipitate particles, quantitatively. A specimen with low Ti content had a smaller Ti/N ratio than the stoichiometric ratio of 3.42 and showed an effective inhibition of grain growth of prior austenite, whereas a specimen with high Ti content showed a little effect to prevent the austenite grain growth compared with a Ti-free sample. Based on the thermodynamic simulation, the (Nb, Ti) (C, N) complex was precipitated and contributed to the inhibition of austenite grain growth, resulting in not only higher yield strength and yield strength/tensile strength ratio but also improved toughness.     

镍沉降渣深度还原过程中的相变特征

通过化学成分、光学显微镜、X射线衍射、扫描电镜能谱分析等测试手段,分析了镍沉降渣矿物成分和嵌布特点和沉降渣深度还原过程中物相的转变特征,结果表明,渣的物相由铁镁橄榄石和玻璃质组成.渣中主要有用成分铜镍铁硫化物嵌布粒度微细,分布无规律,回收困难.经深度还原,沉降渣逐渐转变为镁黄长石、含镍金属铁、辉石、钙霞石、钠闪石、石英等新的矿物成分,加热至1300℃,还原产物物相组成稳定,镁黄长石和含镍金属铁相对含量最高.还原时间也是影响还原效果重要因素,含镍金属铁相对含量随还原时间的增加而增长,120 min时相对含量最高.热力学分析表明,镍沉降渣深度还原过程中主要发生的反应为铁镁橄榄石与氧化钙作用生成镁黄长石和FeO,FeO被C和CO还原为金属铁.金属硫化物与CaO和C通过氧化还原作用,生成的金属铜和镍溶于金属铁中,产生的CaS与硅酸盐一起析出.      

微波加热配碳还原分解铁酸锌的工艺及机理研究

研究了利用微波配碳还原焙烧分解铁酸锌的工艺及机理。利用碳气化控制、化学控制及扩散控制模型研究了样品中铁酸锌分解的动力学行为,并考察了微波功率、反应温度、配碳比和粒度对铁酸锌分解率的影响。结果表明,样品的微波加热碳热还原试验的控制步骤为碳气化控制,活化能为39.21kJ/mol,在微波加热温度850℃、C/ZnFe2O4质量比为1∶4、粒径74～89μm、微波功率1.8kW、加热时间60min的条件下,铁酸锌的分解率达到90%。     

Part II. The creep behavior of Ti-Al-Nb O+bcc orthorhombic alloys

The intermediate-temperature (650 °C to 760 °C) creep behavior of orthorhombic (O)+bcc alloys containing 50 at. pct Ti was studied. Ti-25A1-25Nb, Ti-23Al-27Nb, and Ti-12Al-38Nb ingots were processed and heat treated to obtain a wide variety of microstructures. Creep deformation mechanisms and the effects of grain size, phase volume fraction, tension vs compression and aging on creep rates were examined. Unaged microstructures, which transformed during the creep experiments, exhibited larger primary creep strains than transformed microstructures, which were crept after long-term aging. The deformation observations and calculated creep exponents and activation energies suggested that separate creep mechanisms, dependent on the applied stress level, were dominating the secondary creep behavior. Coble creep characteristics, including relatively low activation energies and dislocation densities as well as stress exponents close to unity, were exhibited at low applied stresses. Experiments on fiducially marked specimens indicated that grain-boundary sliding was occurring for intermediate applied stresses. In this regime, the minimum creep rates were proportional to the applied stress squared and inversely proportional to the grain size. Dislocation-controlled creep characteristics, including stress exponents of greater than or equal to 3.5 and relatively high activation energies and dislocation densities, were exhibited at high stresses. Overall, the minimum creep rates were dependent on microstructure and stress. Within the low-to-intermediate stress regimes, subtransus processed and heat-treated microstructures, which contained much finer grain sizes than supertransus microstructures, exhibited the poorest creep resistance. The influence of grain size was not as significant within the high-stress regime. It is shown that for low-to-intermediate stress levels, grain size is the dominant microstructural feature influencing the creep behavior of O+bcc alloys.     

Nb(C,N)溶解对高铌奥氏体晶粒长大行为的影响

为了定量研究铌对高铌钢加热过程奥氏体晶粒长大的影响，采用化学溶解过滤分离及电感耦合等离子光谱测定不同加热温度两种试验钢固溶铌质量分数，并对比研究了奥氏体晶粒长大行为。结果表明，在低温条件下，低铌钢固溶铌质量分数高于高铌钢；随加热温度升高，高铌钢固溶铌质量分数快速增加，但即使在1 300 ℃时，铌也不能完成固溶，少量铌存在于(Ti,Nb)(N,C)析出相中；奥氏体晶粒快速长大的温度与固溶铌质量分数快速增加的温度有关。随铌质量分数由0.082%增加到0.120%，奥氏体晶粒快速长大的临界温度由1 050升高到1 150 ℃。高铌钢在1 150～1 250 ℃加热温度范围内，奥氏体晶粒尺寸小于100 μm。     

中锰马氏体NM500钢奥氏体晶粒长大行为

 中锰马氏体耐磨钢是一种新型的低成本高性能耐磨钢,揭示钢中奥氏体晶粒长大行为,并建立精确的预测模型,对其组织和性能的调控至关重要。利用Gleeble-3500型热模拟试验机、金相显微镜和透射电子显微镜等设备,系统研究了中锰马氏体NM500钢在不同加热温度和保温时间下的奥氏体晶粒长大行为,探讨了微合金第二相对奥氏体晶粒长大行为的影响。研究结果表明,加热温度对试验钢中奥氏体晶粒长大的影响明显大于保温时间,且试验钢中奥氏体晶粒长大行为受基体中V(C,N)粒子析出行为的影响,其可分为两个阶段。当加热温度小于950 ℃时,试验钢中存在大量未溶的纳米级球状和短棒状V(C,N)粒子,能够有效地钉扎奥氏体晶界,奥氏体晶粒长大缓慢;但当加热温度不低于950 ℃时,试验钢中V(C,N)粒子大量溶解和粗化。其中,加热温度为950 ℃、保温时间为60 min时,试验钢中V(C,N)粒子的体积分数仅为0.041%,平均粒径增大至45.78 nm。其对奥氏体晶粒的钉扎作用显著减低,且随着温度升高,原子扩散速度加快,奥氏体晶粒快速长大。基于Beck模型,建立了试验钢中奥氏体晶粒等温长大动力学模型,计算得到低温及高温阶段试验钢中奥氏体晶粒长大表观激活能分别为66.561 kg/mol和170.416 kJ/mol,且奥氏体晶粒的理论计算值与实测结果吻合较好。