超低碳深冲钢冶炼全流程中夹杂物分析

采用光学显微镜和扫描电镜对超低碳深冲钢冶炼全流程中的夹杂物进行分析。结果表明,RH精炼过程中的夹杂物由FeO转变为Al2O3类脱氧产物;中间包浇铸过程中的夹杂物以Al2O3·TiOx类夹杂为主,但受到钢包渣和中间包渣的影响;连铸过程中的夹杂物以铝钛夹杂为主,夹杂物的形成与结晶器内的卷渣紧密相关。     

高拉速连铸低碳铝镇静钢铸坯中夹杂物

针对高拉速板坯连铸生产的低碳铝镇静钢铸坯,采用Aspex自动扫描电镜对铸坯表层夹杂物进行大面积的扫描分析,得到不同拉速下夹杂物的变化规律,并探究流场和S含量对夹杂物分布的影响.结果表明：随着拉速增大,钩状坯壳的深度和长度逐渐减小.对拉速大于2 m·min^-1的铸坯,由于钩状坯壳不是很发达,铸坯表层没有发现大于200μm的夹杂物.铸坯表层尺寸介于50~200μm的夹杂物主要是由凝固坯壳所捕获,而夹杂物在凝固前沿的受力决定了夹杂物的捕获行为.随着拉速提高,凝固前沿的钢液流速增加,随着冲刷力的增加、捕获力的减少,夹杂物被捕获的数量减少.在高拉速连铸下,如果钢液中S含量较大,夹杂物受到明显的温度Marangoni力,会更容易被凝固坯壳捕获.     

Thermodynamics of carbon in liquid manganese and ferromanganese alloys

The thermodynamics of carbon in manganese and ferromanganese melts were studied to predict the refining limit of carbon during the decarburization of molten ferromanganese. The equilibrium carbon content in a Mn-C melt was determined by the C-CO equilibrium in the presence of pure solid MnO at 1673 to 1773 K. The activities of manganese and carbon in the Mn-C melt were then calculated from the experimental results, the equilibrium constant for the reaction, and the Gibbs-Duhem equation integrated by the Belton-Fruehan treatment. The standard free-energy change of carbon dissolution in the manganese melt was determined to be 41,700 — 59.6 T J/g · atom, with the standard state taken as 1 wt pct carbon in solution. The effect of iron on the activity coefficient of carbon in ferromanganese was determined by measuring the carbon solubility in Mn-Fe melts. The first- and second-order interaction parameters between carbon and iron in ferromanganese melts were determined. The activity coefficient of carbon in the ferromanganese alloy melt can be expressed as

ICP-AES法测定低碳锰铁中磷铝铜镍

研究了用ICP-AES法同时测定低碳锰铁中磷、铝、铜、镍量的分析方法.实验结果表明,该方法简便、快速、灵敏,相对标准偏差均小于5%,回收率在95%～105%之间.     

Decarburization of high carbon ferromanganese melts

The effect of oxygen/argon mixing ratio in the bottom blowing gas on the decarburization behaviour of high carbon ferromanganese melt was investigated in the temperature range of 1350 – 1550°C. Thermodynamic analysis indicates that high melt temperature and low P_CO are essential for an effective decarburization. An empirical equation for the utilization ratio of oxygen for decarburization was derived as functions of the melt temperature and the oxygen/argon mixing ratio in the refining gas. The utilization ratio of oxygen for decarburization sharply increases as the melt temperature increases and the oxygen ratio in blowing gas decreases. In oxygen refining of high carbon ferromanganese melt, it is not desirable to inject oxygen through bottom tuyères in an early stage of refining. When the melt temperature is low, the oxygen predominantly oxidizes the manganese in melt in spite of high carbon contents. The injection of oxygen/argon mixture gas is found to be an effective decarburization technique when the melt temperature is higher than 1500°C.     

Optimum condition for smelting high carbon ferromanganese

Abstract

In the present study, pilot plant experimental heats were designed and carried out to determine the optimum condition for smelting high carbon ferromanganese through investigating some parameters affecting the smelting process including Mn/Fe ratio of the blend, coke ratio, slag basicity and dolomite/limestone ratio of the flux. The results of pilot plant experimental heats showed that using Mn blend with high Mn/Fe ratio decreases the consumption of charging materials: Mn ores, coke and fluxing materials (limestone and dolomite). This means that lower amounts of Mn ores, coke and flux materials can be used for attaining the same output alloy weight by increasing the Mn/Fe ratio of the blend. Furthermore, the produced slag decreases as Mn/Fe ratio of the blend increases. The higher Mn/Fe ratio of the blend does not only reduce the input materials and the produced slag, but also improves the produced alloy quality by increasing the Mn percent and Mn/Fe ratio of the produced high carbon ferromanganese. For obtaining standard HCFeMn alloy containing minimum 75%Mn, it is necessary to use Mn blend with the Mn/Fe ratio of higher than 6·2. The added coke must be adjusted according to the material balance and stoichiometric to prevent the over-coke and minimise the highly endothermic ‘Boudouard reaction’ to attain the highest Mn recovery and metallic yield. Furthermore, the slag basicity should be optimised with flux addition to attain the highest Mn recovery and metallic yield. The optimum slag basicity for attaining the highest manganese recovery and metallic yield depends on the used formula. The slag basicity can be determined from the chemical composition of raw material mixture with taking into consideration that about 2% of silicon in the raw material mixture will be reduced and goes into metal phase. Much higher slag basicity is not recommended as this practice produces viscous slag accompanied with lower Mn recovery and metallic yield. The results also revealed the negative effect of increasing MgO/CaO ratio of slag on manganese recovery and metallic yield. The MgO/CaO ratio in the slag decreases by decreasing the dolomite/limestone ratio in the flux.     

MnO reduction in high carbon ferromanganese production: practice and theory

The SAF (submerged arc furnace) process is most widely used for industrial production of high carbon ferromanganese. Most plants use ore feed in the form of lump ore (?75 mm +6 mm), but long term supply is limited, and large quantities of ore fines are generated in ore mineral processing. Therefore development of alternative processes using ore fines (?10 mm) is important. The AlloyStream process is one such process developed to use a feed material mixture of fine ore, coal and flux. This process development provided a unique opportunity to correlate MnO reduction process theory to pilot plant production practice represented in minerlogical observations from furnace heap samples.     

空冷高硅中碳低合金钢的组织与性能

研究了高硅中碳低合金钢空冷态和空冷+回火态的显微组织和力学性能.试验钢在860℃保温0.5h奥氏体化后空冷处理,随后分别在250℃和400℃保温1h回火.结果表明:试验钢空冷后组织为贝氏体/马氏体和残余奥氏体的混合组织,硬度约为41 HRC;而250℃回火后组织变化不大,硬度明显升高,约为49 HRC,韧性明显增加,由44 J/cm2增加到66 J/cm2,抗拉强度、屈服强度和延伸率明显下降.回火温度进一步增加对力学性能影响不大.     

高碳锰铁粉与高碳铬铁粉微波升温特性对比

通过对比微波场中高碳锰铁粉和高碳铬铁粉的升温特性,分析了影响物料升温特性的因素。结果表明,微波场中高碳锰铁粉的升温效果优于高碳铬铁粉,高碳锰铁粉与高碳铬铁粉在微波场中的升温曲线均可分为2个阶段,高碳锰铁粉的平均升温速率为70.9和12.4℃·min-1,而高碳铬铁粉的平均升温速率为20.0和8.33℃·min-1;2.450GHz时,高碳铬铁粉的介电损耗较大,而高碳锰铁粉的磁损耗较大;反射损耗计算表明,高碳锰铁粉有较高的微波吸收率。     

低温贝氏体转变对中碳钢韧性的影响

摘要：沉淀硬化钢中纳米富Cu相的析出,使微应变（α）发生改变,这不仅影响力学性能,也对腐蚀性能产生作用。为了探索α对腐蚀性能和力学性能的影响规律,通过XRD谱型分析,对商用钢LJ338ESR 在300～600℃不同时间时效析出富铜纳米相后的α、硬度和电荷转移电阻（Rf）进行了研究。结果表明,300～450℃时效,8h前α值随时效时间延长而升高,8h后由于析出相与基体失去共格,α随着时效时间延长而降低;硬度与α变化相似。600℃时效,α在时效2h达到峰值,这归因于共格微应变和逆变奥氏体两种相反因素的共同影响;600℃逆变奥氏体生成,使硬度变化较小。析出相与基体保持共格时,Rf和α随时效时间的变化呈良好的反比关系,即Rf随α的增大而减小。     

Production of high carbon ferromanganese using manganese rich slag in the charge

The possibility of replacement of the high cost sinter manganese ore by manganese rich slag for the production of high carbon ferromanganese was experimentally demonstrated. The experimental heats were designed and carried out to optimize this replacement through the adjustment of different production parameters. The results of pilot plant experimental heats showed that replacement of 50% of the sinter in the blend (or 25% of the blend) by slag containing 32% Mn and operation under slag basicity 0.9 and low (MgO)/(CaO) ratio of about 0.2-0.3 are the optimum conditions to attain the highest manganese content in the produced ferromanganese, the highest manganese recovery and the highest metallic yield. The industrial application of reusing manganese slag clarified the economic efficiency of charging manganese slag up to 20-25% of the blend in reducing the production cost due to reducing the cost of manganese ores. Charging of 20-25% manganese slag reduces the cost of manganese ores and the total production cost by about 13 and 6% respectively, comparing with the conventional technology (without using manganese slag in the blend).     

Nontraditional carbon reducing agents in smelting FMn78B ferromanganese and valuable manganese slag

The smelting of FeMn78B ferromanganese (0.7% P) by a flux-free method, with the production of valuable slag (36–38% Mn), is considered in the case where some of the coke nuts are replaced by anthracene.     

奥氏体组织对低碳中锰钢冷弯性能的影响

采用冷弯直径0～60 mm,弯曲角度180°,研究了20 mm厚度低碳中锰钢的冷弯性能,冷弯后外表均无可见裂纹,判定合格。利用光学显微镜、扫描电镜、透射电镜、电子背散射衍射(EBSD)、X射线衍射仪等手段分析了显微组织,尤其是奥氏体组织在冷弯过程中对冷弯性能的影响。结果表明,冷弯前显微组织由板条马氏体和奥氏体组成,其中原始奥氏体晶界明显;冷弯直径为0 mm变形后,样品弧顶部分奥氏体的体积分数由12.3%降至1.1%,维氏硬度由295HV1增至364HV1,晶粒尺寸由4.07μm增至4.30μm。主要原因是在冷弯过程在中奥氏体组织发生塑性变形,奥氏体晶界变形消失,沿冷弯方向呈拉伸带状组织形貌,冷弯形变时奥氏体发生TRIP效应显著。     

Structure-property changes during hardening and tempering of new ultra high strength medium carbon low alloy steel

Abstract

A medium carbon low alloy steel, electroslag refined, modified AFNOR 15CDV6, has been developed for satellite launch vehicle and related applications. Conventionally processed (without electroslag refining) mostly bainitic AFNOR 15CDV6 (with 0·15 wt-% carbon and ~ 3·5 wt-% other alloying elements) has a yield strength of ~ 800 MPa. Electroslag refining, coupled with increased carbon (0·29 wt-% carbon, but no change in percentage of other alloying elements), increased the yield strength to about 1300-1400 MPa, without sacrificing ductility. The microstructure of the modified grade was martensitic. Martensite in the as hardened state was mostly in the form of laths, although ~20% plate martensite was also observed. Until 150°C tempering, no noticeable loss of tetragonality was observed, while the unit cell parameter c/a ratio dropped to almost 1 after 300°C tempering. The interesting observation at 150°C tempering was the predominant presence of fine rodlike ? carbide, which may also explain the increased yield strength. Tempering above 150°C converted the ? carbide to cementite, relatively thicker precipitates of similar morphology. At higher tempering temperatures, no evidence of spheroidisation of cementites was noted. The highest tempering temperatures of 500 and 600°C resulted in two marked changes in the microstructure: the appearance of M₂₃C₆ type (Cr, Fe and Mo bearing) carbides, and the appearance of, in some regions of the microstructure at least, a relatively 'recovered' lath structure. Misorientation among adjacent laths, nearly constant at 8-9° until 450°C tempering, increased noticeably, to 13 and 16°, after the respective tempering temperatures of 500 and 600°C.     

超塑性材料现状及新型超塑性低中碳合金钢研发

 在分析超塑性金属材料现状及发展趋势的基础上,对低中碳钢、高碳钢和双相不锈钢、奥氏体钢等钢铁材料的超塑性研究进行了归纳分析,提出了低成本量大面广低中碳合金钢将成为超塑性材料研发的一个重要方向。研究结果表明,通过科学合金化设计、精细组织调控和初步超塑性行为研究,可以获得在10－2/s应变速率和750～850 ℃下具有1 000%超塑性的低成本超塑性低中碳合金钢。这种优异超塑性性能主要归因于形成超细晶组织的合金化设计与组织调控。该研究成果打破传统低中碳钢不具有超塑性的局面,实现了可工业化超塑性能的低中碳合金钢创新发展,将推动超塑性钢材在航空航天和交通运输等领域的广泛应用。     

Textures induced by tension and deep drawing in low carbon and extra low carbon steel sheets

The texture evolution induced by tensile deformation and by deep drawing was investigated. For this purpose, the textures of 3 types of steel (rimmed, Al-killed drawing quality, and interstitial free) were measured and analyzed using the series expansion method. The results indicate that the initial texture changes drastically after a few percent of plastic strain and evolves towards a single orientation for which the <110> direction is aligned with the tensile or drawing axis. The distinct earing behaviors of the AKDQ and IF steels (i.e. 4-eared for the Al-killed and 6-eared for the interstitial free) are interpreted in terms of differences in the sharpness and homogeneity of their ND-fibres and in the influence of the {332} <110> and the partial {223} fibre.     

水口结构对连铸中低碳钢流场和温度场的影响

 为研究水口结构形状对连铸中低碳钢结晶器内流场和温度场分布的影响,采用有限容积法建立连铸圆坯三维数学模型,模拟了不同水口形状下圆铸坯的流场和温度场。结果表明,在水口浸入深度为80 mm、其他参数不变时,与直水口相比,旋流水口使钢水冲击深度降低,结晶器内涡流增强,弯月面温度和二冷区凝固率提高,且随着水口数量的增加,弯月面波高和结晶器出口温度降低;采用旋流水口并施加结晶器电磁搅拌(M EMS)时,结晶器中钢液温度升高,弯月面有卷渣行为,结晶器出口未形成凝固坯壳。在实际应用中,应避免同时使用M EMS和旋流水口,或使用旋流水口时采用低强度的M EMS。     

锰铁中锰和磷的分步测定

锰铁中锰和磷的含量是锰铁分级的主要指标,以往锰铁中锰和磷的含量测定,需要分别采用三价锰滴定法和钼蓝分光光度法,测定过程繁琐,冗长。实验采用一次取样,硝酸-氢氟酸-高氯酸溶解试样,加入过氧化氢将二氧化锰还原为锰(II)的方式制备母液,分别用EDTA滴定法测定锰铁中锰含量,磷铋钼蓝分光光度法测定锰铁中磷含量,建立了对锰铁中锰和磷的分步测定方法。对测定锰的条件进行了优化,结果表明,通过加入三乙醇胺-酒石酸钾钠溶液可掩蔽试液中的铁、铜、铝、钛;采用锰铁标准物质进行试验,结果表明,以甲基百里香酚蓝为指示剂时,测定结果和认定值相吻合,且终点变色是从蓝色变为浅红色,更易观察;加入30mL无水乙醇、25mL 80℃左右的热水可解决指示剂僵化的问题。对磷含量测定中砷和残余硅的干扰消除方法进行了探讨,结果表明,砷的干扰可以通过加入硫代硫酸钠-亚硫酸钠溶液消除,残余硅的干扰可以通过加入酒石酸钾钠溶液消除。按照实验方法测定锰铁试样中锰和磷,锰测定结果的相对标准偏差(n=8)小于0.30%,磷测定结果的相对标准偏差(n=8)小于4.0%。方法应用于锰铁标准物质中锰和磷的测定,锰测定结果的相对误差绝对值小于0.25%,磷测定结果的相对误差绝对值小于4.0%。     

Strength and fatigue properties in medium carbon duplex steels

The effect of microstructure on strength and fatigue properties has been investigated in two medium carbon alloy steels (BS 817M40 and BS 835M30) by developing dual-phase, ferritic-martensitic microstructures. Hardness-strength relationships and fatigue resistance at comparatively high strength levels were investigated by producing various microstructures. Conventional quenching and tempering, intercritical annealing and step quenching were used to vary the proportion, morphology and distribution of the ferrite and martensite phases. The results of the present study show that both hardness and strength increase with increasing proportion of martensite and/or hardness of the second phase. The relationship between hardness or strength and martensite percent is not in good agreement with a simple “law of mixtures” but is compatible with a more rapid strength increase at high martensite contents. The dual phase microstructures from the present study show superior near threshold ΔK_TH values than normal tempered martensite. The results also show a high degree of correlation between Paris equation m values and fracture toughness K_IC, showing that for high m values K_IC is low and vice versa. The present experiments show that although crack initiation resistance in dual-phase steels is excellent crack propagation rates are higher than in quenched and tempered microstructures for a given ΔK.