Niobium-Alloyed high speed steel by powder metallurgy

A philosophy for the use of strong carbide formers like niobium in high speed steels is described. It follows the concept of independently optimizing the compositions of the matrix (for maximum secondary hardening potential) and the volume fraction of the blocky carbides (for protection against abrasive wear). Normally, the two are interdependent through the action of the solidification equilibria, but separate control becomes possible when the blocky carbides are formed by a strong carbide former such as niobium. During normal ingot solidification, such strong carbide formers would produce very large primary carbides. This can be avoided by atomization and powder metallurgical processing. In this way, a steel has been produced whose matrix composition is similar to that of AISI M2, and whose primary carbides are all of NbC type. Its composition is 1.3C, 2W, 3Mo, 1.6V, 3.2Nb (wt pct). Because of its high stability, NbC is a much more effective obstacle to grain growth than the normal high speed steel carbides, and this allows substantially higher austenitization temperatures to be used. Despite its leaner composition, the Nb-alloyed steel matches the cutting performance of AISI M2, and its secondary hardening seems to be more persistent at high temperatures.     

Quantitative metallography of high speed steels by SEM

Secondary electron imaging in SEM offers a suitable combination of contrast, resolution and speed for quantitative metallography of high speed steels. To avoid distortion of measurements by topographic effects, plane polished specimens are used in the unetched state and imaged by chemical (atomic number) contrast. The optimization of primary beam parameters and photographic contrast are discussed. It has been found that the chemical contrast of carbide phases can be substantially enhanced (and further differentiated) by coatings of ZnSe and other semiconducting substances around 60 nm thickness. Applications are exemplified by the determination of matrix compositions from the overall alloy content and the amounts of alloy elements contained in the massive carbides, and by the effect of hot work and austenitization temperature on the size distribution and volume fraction of massive carbides in Fe—6W—5 Mo—2 V (AISI M2) high speed steel.     

高速钢轧辊在棒材生产线上的应用

介绍了高速钢轧辊的特性以及优点,并通过对西林钢铁集团轧钢总厂三轧作业区全连续棒材生产线在高速钢轧辊使用过程中,使用条件、事故处理以及使用效果等方面的总结,介绍高速钢轧辊的应用前景与效益。     

The high temperature transformation of high speed steel

Low tempered hardnesses on high speed steels which had been hardened in vacuum or atmosphere furnaces and gas quenched led to a search for a reaction occurring above 1400°F and probably initiated as a result of the slower cooling rate of the gas quench. A standard TTT evaluation was carried out on Ml, M2 high carbon, M3, and M7 high speed steels, quenching from conventional hardening temperatures, into salt baths maintained at 2000° to 1500°F. Examination of these specimens indicated the presence of a reaction occurring at all temperatures investigated but having its maximum rate at 1700° to 1800°F. The reaction involved precipitation of an MoC/Mo₂C carbide at grain boundaries and within the grains, with the amount of precipitate increasing with time. The precipitation of MoC/Mo₂C is directly related to the loss in tempered hardness and apparently causes this effect by 1) reducing precipitation hardening on tempering, 2) drastically lowering retained austenite contents, and 3) reducing as-quenched hardnesses.     

烧结硬化钢高速高扭矩齿轮的开发

烧结硬化使粉末冶金零件可在一般烧结炉的冷却带进行硬化，而不需要在烧结后进行热处理。为开发用于可再充电的电动工具用的高速、高扭矩齿输，试验了掺加有2．0％Cu与0．90％石墨的预合金化粉末ATOMET 4701(0．45Mn-0．45Cr-0．9Ni-1．0Mo)。将零件生坯压制到密度6．85g／cm^3，在1120℃下于吸热性煤气气氛中烧结30min。烧结态零件(密度6．80g／cm^3)的表观硬度为37HRC。显微组织分析表明，在烧结炉冷却带充分产生了马氏体相变。随后，零件在180～210℃下回火0．5～4h。在180℃回火2h后，烧结硬化材料的力学性能与齿输齿的精度处于最佳结合状态，优于经热处理的烧结低合金钢材。     

用连续浇注外层方法生产高碳高速钢复合轧辊的性能及其应用

近年来，对钢板质量要求日益提高，同时要求提高轧钢生产率、节约能源，因而轧制技术和设备取得长足进展。与此相应，开发了一种新的复合轧辊，它的外层是高碳高速钢，心部为锻钢。它是用新的连续浇注外层方法生产的。这种新的复合轧辊提高了轧钢生产率、改善了钢板的质量。     

Solidification of M2 high speed steel

The freezing process in AISI type M2 high speed tool steel (6 pct W, 5 pct Mo, 4 pct Cr, 2 pct V, 0.8 pct C) was studied by metallographic and thermal analysis techniques. Unidirectional solidification of small laboratory melts in a modified crystal growing apparatus was employed to provide metallographic sections of known macroscopic growth direction. Also cooling curves were obtained on 40 g specimens solidified in thimble crucibles. X-ray microradiography, electron probe scanning techniques, and quantitative microanalysis of dendrites and interdendritic carbides were extensively used to supplement conventional metallography. Carbon and vanadium contents of M2 were varied in order to observe the effect of an austenite and ferrite stabilizer on the thermal analysis curves and microstructure. The nonequilibrium freezing process in M2 includes three major liquid-solid reactions: 1) Liquid → Ferrite, 1435°C; 2) Liquid + Ferrite → Austenite, 1330°C; 3) Liquid → Austenite + M₆C + MC, 1240°C. These reactions account for the as-cast structure of the commercial alloy. The addition of carbon depresses the liquidus (1) and solidus temperatures (3) and narrows the gap between the liquidus (1) and peritectic transformation (2). This gap is eliminated at > 1.39 wt pct C, where the initial freezing reaction is the crystallization of austenite. The accompanying microstructural change is the elimination of σ eutectoid dendrite cores. The addition of vanadium promotes ferrite formation by strongly depressing the peritectic reaction and thus widening the gap between the liquidus and the peritectic.     

Design of steels for high speed machining

Abstract

Historical analysis of metal cutting shows that metal removal rates have been increasing in the course of the century, predicated by the advancement in tool materials but the steel design has lagged behind. This paper examines the mechanisms of chip formation and tool wear as a function of cutting speed in metal cutting. Chemical wear is identified as the dominant mechanism of tool wear at high cutting speeds caused by temperature rise due to shear localisation in the primary and secondary shear zones of chip. Shear localisation in the primary shear zone is shown to be influenced by both microstructural parameters, i.e. matrix hardening and second phase particles, and metal cutting variables, i.e. cutting speed (strain rate) and feed (pressure). Shear localisation in the secondary shear zone is caused by the tribological conditions of seizure at the tool/chip interface. Chemical crater wear is caused by the dissolution of tool into the workpiece (chip) by diffusion mechanism and can be prevented by suppressing the tribological condition of seizure. The design of steel for high speed machining is based on engineering glassy oxide inclusions in steel, which are designed to form a viscous layer in situ at the tool/chip interface at high cutting speeds. The viscous layer lubricates the tool/chip interface and prevents the occurrence of seizure, thereby suppressing chemical crater wear. In comparison with the large volume fraction of inclusions required for promoting ductile fracture at low cutting speeds, the amount of inclusions required for lubricating the tool/chip interface is very small and is in the range that is typical of clean steel. Thermodynamic modelling is shown to be a powerful tool to engineer glassy oxide inclusions in steel     

Microstructure characteristics of spray-formed high vanadium and cobalt high speed steel

The microstructure of high vanadium and cobalt high speed steel(high-V/Co HSS) and the morphology of its carbides were analyzed by optical microscope(OM),scanning electron microscope(SEM),electron probe microanalysis(EPMA),X-ray power diffraction(XRD),atomic force microscopy(AFM) and single phase erosion(SPE).The results suggest that the as-sprayed high-V/Co HSS has fine equiaxed grains(about 20 μm in size),which were homogeneously distributed.The carbides have two classical morphologies:one is fine particles(about 2 μm in size) distributed along the grain boundaries and the other is needle-like one,distributed on the grain boundaries.There are MC carbides,M2C carbides,M6C carbides and Cr2WC2 carbides in the as-sprayed high-V/Co HSS samples,however,in the as-cast high-V/Co HSS,there are MC carbides and Cr2WC2 carbides only.The SPE results show that there are two types of MC carbides in the as-sprayed HSS:the sphere one and the particle-like one.The former is about 2 μm in size and the latter is less than 1 μm,dispersed inside the grains,quite different from the MC carbides in the as-cast HSS.According to the AFM results,the skeleton-like M6C carbides of the as-sprayed high-V/Co HSS are embedded in the matrix along the grain boundaries.It is found that there are sharp membrane pieces on the carbides.Some small bamboo-shoot-like MC carbides grow from the matrix and are dispersed inside the grain.Those larger MC carbides are spherical particles embedded at the grain boundary junctions.     

Analysis of bulging for high speed continuous casting

In order to research the temperature distribution and mechanical deformation of slab bulging during high speed continuous casting,mathematical models have been developed to analyze the thermal and mechanical behavior of the slab.The thermal history of the slab has been predicted by a two-dimensional transient finite element heat transfer model,whose results serve as the input to the stress model.The stress model has been formulated for a two-dimensional longitudinal plane.In this case,the maximum tensile strain during the bulging process is located at the solidification front just past the top of the upstream roll,which may contribute to crack formation.The maximum tensile stresses are located at the cold surface in the middle of the two back-up rolls,just at the point of the maximum bulging.Stresses near the solidification front are small because of the high temperatures which produce lower elastic modulus values.Finally,the effect of the casting speed on the bulging deformation is discussed.     

高速过滤器的改进及运行效果

对八钢公司热轧厂浊循环水工艺中的主要水处理设备高速过滤器的运行结果进行了分析。认为高速过滤器存在设计缺陷。针对高速过滤器存在的问题,对其进行了改造。改造后,其出水水质显著提高,运行效果良好。     

高速机车齿轮用钢的研制

高速机车齿轮用钢为时速250km/h以上的高速机车牵引齿轮,是高档渗碳齿轮钢,具有高强度、高耐磨性、高的塑韧性,广泛应用于各类矿山、港口等工业用减速机、高速机车牵引齿轮等方面.黑龙江省冶金研究所自开发试制以来,对该钢种进行深入的研究,不断完善工艺,采用高功率电炉+LF炉外精炼+VD真空精炼及钢锭热送、轧制或锻造、退火工艺,工艺技术先进、质量性能稳定.     

激光熔覆无碳Fe-Co-Mo高速钢涂层的组织结构与性能

用水雾化合金粉末为原料,通过同步送粉式激光熔覆技术在40Cr基材上制备无碳高速钢涂层,对涂层的显微硬度、红硬性和抗回火稳定性进行测试和分析,研究工艺参数对涂层形貌及硬度的影响。结果表明,在适宜的参数下能够在基材表面获得无宏观裂纹和气孔的无碳高速钢涂层。涂层致密度高、稀释率低,与基体呈现出良好的冶金结合。涂层熔覆态下显微硬度(HV0.2)达到700,经过600℃下1 h时效后,涂层硬度(HV0.2)明显提升至900。经过4次600℃保温1 h的时效后,涂层硬度(HV0.2)保持在800。此外在600℃保温30 h的长时间回火后,涂层仍然可以保持硬度(HV0.2)达750,相较于常规高速钢ASP2030以及热作模具钢H13具有更加出色的抗回火能力。     

基于ANSYS的高速磨削中的砂轮破坏原因的研究

应用可视化数值模拟方法,借助于大型通用有限元软件ANSYS建立砂轮回转的数学模型,对离心应力进行了仿真研究.随着磨削速度的提高,磨粒的切削作用被磨粒对工件的高速冲击作用所取代.通过输入不同的转速对比,发现砂轮孔壁处所受切向应力σt最大,径向应力很小可忽略,而在砂轮外圆处切向应力较小.随转速提高,外圆切向应力增长趋势显著,破坏趋势也愈明显,因此切向应力是破坏的主要原因.这一虚拟分析既为砂轮实际应用中出现的破坏现象所佐证,又与砂轮受力分析结果相吻合,为磨削过程的安全奠定了良好的基础.     

高速线材精轧线速度的微机检测与同步显示

本文介绍攀钢线材厂高速线材精轧线速度的微机检测与同步显示系统的硬件与软件设计思想，同时还介绍了系统的功能与技术指标。最后，给出了现场应用效果。     

高压变频调速系统的应用

目前高压变频调速技术在中国市场上有着很好的发展和应用前景。本文对高压大功率风机、水泵的节能原理进行了分析，给出了H桥串联式高压变频调速装置的方案及原理，并介绍了国产560kW，6000V高压变频调速装置的组成、技术特点和工程应用。工程应用的结果表明，该系统完全满足工艺需要，在工业节能上已达到较好的效果。     

混合机联轴器及高速轴改型

为解决烧结一期一次、二次混合机传动系统高速轴液力偶合器和减速机轴承密封维修困难的问题,通过对比分析各种联轴器的特点、性能及现场实际空间尺寸,将限矩型液力偶合器改为蛇形弹簧联轴器,加长减速机高速齿轮轴输入端的长度;并对改型后的蛇形弹簧联轴器的转矩、高速齿轮轴的强度、齿轮强度和轴承寿命等进行了校核。联轴器改型后,有效解决了因减速机端盖与原液力偶合器间距太小,液力偶合器拆装困难及无法拆除减速机轴承端盖和减速机上盖的难题,大大提高了检修效率和质量,降低了备件成本和维修费用。