Carbide refinement in M42 high speed steel by rare earth metals and spheroidizing treatment

The influence of rare earth metals and heat treatment on the microstructure and performance of M42 steel has been investigated by means of an optical microscope OM scanning electron microscope SEM energy dispersive spectroscopy EDS transmission electron microscope TEM electron back-scatter diffraction EBSD and X-ray diffraction XRD . The results show that M2 C is the prevailing type of eutectic carbides in M42 steel. After modification with rare earth metals M2 C eutectic carbides change from the ordered lamellar structure into a circular structure.Despite different morphologies the two carbides present the same characteristics of microstructure and growth orientation.Compared with lamellar carbides M2 C carbides with the circular structure are much easier to decompose and spheroidize after heating which remarkably refines the carbide dimensions.The refined carbides improve the supersaturation of alloying elements in martensite and increase the hardness of M42 steel by 1.5 HRC.

New Spheroidizing Technique of Ultra-High Carbon Steel With Aluminum Addition

A new spheroidizing process of ultra-high carbon steel （UHCS） containing C 1.55%, Cr 1.45%, and Al 1.5% in mass percent has been proposed. The effect of processing parameters on the microstructure was analyzed. The UHCS produced by this new process has a microstructure with recrystallized ferrite matrix and fine and uniform carbide particles. After this spheroidizing, the UHCS exhibits good mechanical properties at ambient temperature, for example σb= 1 100 MPa, σs =915 MPa, δ=8% and high ratio of σs/σb.

DEFORMATION AND STRENGTHENING OF COLD-DRAWN STEEL WIRES

It was shown by the study of TEM that the fine lamellar pearlite becomes a ductile phase dur- ing cold drawing.There exist many ledges to emit dislocations at Fe_3C/Fe interface.It is one of the reasons that high density of dislocations emerges at the Fe_3C/Fe interface. Furthermore,there are some evidences to support that dislocation cuts through Fe_3C.There- fore,it is necessary to consider the contribution of cementite being sheared strengthening.

Spheroidization and Ostwald Growth of Carbide in Isothermal Process of Hot-Deformed High Carbon Chromium Cast Steel

In isothermal spheroidizing process,the spheroidization and growth of the carbide formed in hot-deformed high-carbon chromium cast steel at high temperature were investigated.The results showed that the spheroidizing growth of carbide proceeds in such a way that the bigger carbide particles swallow the smaller ones,and the short rhabdoid carbides dissolve and are spheroidized by itself.When the samples were held at 720℃ for more than 3 h,the spheroidization is not obvious.The feature of the process is the size increment and the amount decrement of carbide particles.The empirical equation for growth rate of carbides was obtained.The volume fraction of carbides keeps constant.The growth process agrees well with Ostwald Ripening Law.

Spheroidization process in large-deformed high-carbon steel

In this study,the spheroidization process of large-deformed steel under various conditions was researched.Steel with a high carbon content （1.0％ C） was first treated thermomechanically using multipass rolling.Then it underwent spheroidization treatments at different heating temperatures,using various heating times and cooling rates.Spheroidization processes with a lower heating temperature,shorter heating time,or faster cooling rate than those of the traditional process all showed good results,indicating that the spheroidization process was promoted significantly by the large deformation process.Grain refinement and fragmentation of cementite,along with the large deformation process,promoted this spheroidization process.

On-line spheroidization process of medium-carbon low-alloyed cold heading steel

Conventionally manufactured 35CrMo cold heading steel must undergo spheroidization annealing before the cold heading process In this paper, different types of deformation processes with various controlled cooling periods were operated to achieve on-line spheroidal cementite using the Gleeble-3500 simulation technique. According to the measured dynamic ferrite transformation temperature （Ad3）, the deformation could be divided into two types： low temperature deformation at 810 and 780℃; ＂deformation-induced ferrite transformation＂ （DIFT） deformation at 750 and 720℃. Compared with the low temperature deformation, the DIFT deformation followed by accelerated cooling to 680℃ is beneficial for the formation of spheroidal cementite. Samples subjected to both the low-temperature deformation and DIFT deformation can obtain granular bainite by accelerated cooling to 640℃; the latter may contribute to the formation of a fine dispersion of secondary constituents. Granular bainite can transform into globular pearlite rapidly during subcritical annealing, and the more the disperse phase, the more homogeneously distributed globular cementite can be obtained.

桥梁缆索用87MnSi钢线材微观组织演变对力学性能的影响

针对桥梁缆索用87MnSi钢线材的异常断裂现象,对其盘条和生产工艺过程中钢丝的微观组织和力学性能演变规律进行系统分析。结果表明,盘条组织由珠光体和少量的先共析铁素体组成,且渗碳体片层随机分布。冷拉拔后,渗碳体片层发生扭转弯曲或减薄纤维化,且部分渗碳体发生破碎溶解,溶解量为1.40%(占比9.69%)。热镀锌后,溶解的渗碳体发生球化。盘条(329.8HV)在冷拉拔-热镀锌-稳定化处理过程中的显微硬度呈现先增大(450.2HV)后减小(447.9HV)再增大(469.6HV)的变化趋势;冷拉拔过程中溶解的渗碳体使得钢丝硬度值上升至468.3HV,而热镀锌过程渗碳体的球化,导致硬度值下降至439.8HV,并恶化拉伸性能。当边部的渗碳体球化程度明显时,使得钢丝内外组织和力学性能存在较大差异,并在稳定化处理过程中因受力不均匀而导致断裂。

SCM435冷镦钢的球化退火工艺

为获得球状珠光体以改善冷镦性能,对SCM435冷镦钢进行了亚温退火和亚温退火加两相区温度退火,前者为700℃保温4 h炉冷至580℃空冷,后者为700℃保温3.5 h,再升温至745℃保温0.5 h炉冷至580℃空冷。检测了退火后钢的显微组织、力学性能和冷镦性能。结果表明:经两种工艺球化退火后,SCM435钢的显微组织均为铁素体和球状珠光体,与热轧态相比断后伸长率和断面收缩率均提高、抗拉强度降低;经两种工艺球化退火的SCM435钢均能进行大变形率冷镦而不开裂。

H13模具钢电子束选区熔化热行为的模拟研究

为了提高H13模具钢在电子束选区熔化技术过程中成型件的表面质量,并探明其成型过程缺陷问题的原因,文章基于离散元法建立了随机分布的金属粉末床模型,对熔体的热流体动力学行为进行数值模拟。单道结果表明,当电子束功率从600 W提高到1 080 W,扫描速度为1.5 m/s时,单道熔池平均深度从15.2μm增加到49.2μm,单道熔池宽度从79.2μm增加到140.1μm,同时发现电子束功率为960 W,单熔道形貌表面质量最好。双道结果表明,Z型扫描路径会导致熔道的一端形貌粗糙,S型扫描路径熔道内易形成热量累积现象。当电子束能量较低时,会出现球化效应和单道不平直现象。当电子束能量较高时,熔道易出现热量累积现象,影响后续的熔道形貌和尺寸。

球化退火冷却速率对SR19热作模具钢组织和硬度的影响

利用DEFORM软件模拟得到大尺寸(200 mm×800 mm×2 000 mm)SR19热作模具钢在退火降温过程中不同深度位置的温度场,根据降温曲线设计该钢小尺寸试样的球化退火工艺,如下:将试样加热至860℃保温2 h,分别以不同速率(15,30,45,60℃·h^(-1))缓冷至740℃保温4 h,再炉冷至500℃后空冷至室温。分析了冷却速率对试样组织和硬度的影响。结果表明:随着冷却速率增大,试样中的先共析铁素体含量和碳化物分布均匀程度均先减小后增大,球化率先保持平稳后快速下降,退火硬度先减小后增大;当冷却速率为45℃·h-1时得到的显微组织最佳,碳化物分布均匀,球化率较高,先共析铁素体含量较少且出现了硬度的回落。先共析铁素体产生的原因主要是退火过程中冷却速率的控制不当导致奥氏体优先转变为铁素体并保留在最终组织中。

SCM435冷镦钢连续冷却过程中的组织转变及球化退火

利用Gleeble-3800热模拟试验机测定了SCM435冷镦钢的热膨胀曲线。通过金相分析和硬度试验获得了钢的动态连续冷却转变曲线。研究了原始显微组织对钢球化退火效果的影响。结果表明:以小于0.5℃/s的速率冷却后,SCM435钢的组织主要为铁素体和珠光体,以1℃/s及以上速率冷却后组织为贝氏体和马氏体以及少量铁素体,以3℃/s及以上速率冷却后组织为马氏体和贝氏体,以15℃/s及以上速率冷却后组织全部为马氏体。采用相同工艺球化退火时,马氏体和贝氏体的球化效果优于珠光体和铁素体。通过优化轧制工艺试制的原组织为贝氏体和马氏体的SCM435钢盘条球化退火后,组织中碳化物分布均匀,球化效果好,球化退火时间明显缩短。

含硼冷镦钢10B33冷镦开裂原因分析

含硼冷镦钢10B33冷镦锻打带法兰面六角螺栓时出现法兰面开裂。对冷镦开裂不同形貌的螺栓、未开裂螺栓、拉拔精丝及母材盘条分别进行检验。结果表明:法兰面圆周上存在多处碎裂,较大裂口呈现斜向45°开裂形貌的冷镦螺栓是由于球化退火工艺不良,法兰界面存在较多未完全球化的珠光体团,球状珠光体弥散不完全,材料塑性不足引起的切应力开裂;法兰圆周单一竖直开裂形貌的冷镦螺栓,由于铸坯近角部存在卷渣缺陷,轧制成盘条后缺陷无法消除,带有缺陷盘条拉拔制成的精丝冷镦时卷渣缺陷扩展造成开裂。

热处理工艺对Cr5型热作模具钢的组织性能影响研究

对Cr5型热作模具钢的扩散退火工艺和球化退火工艺进行相关研究,探讨各个工艺的保温时间对其碳化物的影响规律。根据TTT图制定热处理方案,改善组织的带状偏析;探究球化退火过程中,随着等温时间的延长,碳化物以未溶碳化物为核心逐渐长大,使显微组织分布得更加均匀;阐述相关组织形貌及转变机理,经验证,与显微组织分析的结果是相一致的。

罩式炉GCr15钢丝球化退火工艺研究

对比分析了GCr15轴承钢普通球化退火工艺和改进球化退火工艺处理后的金相组织和硬度。结果表明,GCr15轴承钢采用改进球化退火工艺处理后比普通球化退火处理后硬度值低6 HBW,金相组织级别波动小,经0.2~0.3 mm拉拔减径后,成品材料硬度满足要求。改进球化退火工艺采用氢气作为保护气氛,材料无附加脱碳;采用快速加热方式,工艺周期缩短2 h,材料金相组织和硬度均匀性较改进前明显提高;生产效率提高,经济效益显著。

超高压蒸汽管道开裂失效分析与预防策略

石油化工企业高压蒸汽管道多采用耐热低合金钢材料,由于长期在高温、高压条件下服役,其微观组织易发生珠光体球化及石墨化等现象,导致材料的力学性能降低,引发开裂泄漏事故。选择炼化企业四个超高压蒸汽管道开裂失效典型案例,开展服役条件、材质成分、力学性能及微观组织等方面的对比分析,探究管道的失效原因;从服役条件、日常检测与排查、预防策略等方面提出针对性措施,抑制低合金钢材料珠光体球化及石墨化现象,减少腐蚀泄漏问题的发生。为炼化企业超高压蒸汽管道的安全稳定运行提供参考。

Effect of Al on Microstructures and Mechanical Properties of the Ultrahigh Carbon Steels

In this research, we tried to find a simple processing method to break up the network carbides in ultrahigh carbon steels (UHCS). Our results revealed that Al addition was favorable to the decrease in the proeutectoid carbides, the pearlite-colony size and the pearlitic interlamellar spacing of the forged microstructures, and that a fully-pearlitic structure was obtained in the UHCS containing 1.6 wt pct Al. The quenching-and-tempering process resulted in fine microstructure in those steels. On the other hand, the strength of the UHCSs increased with the increase of the Al content, and the highest strength was obtained at the UHCS with 1.6 wt pct Al. The UHCSs with Al contents higher than 1.3 wt pct showed a high tensile strength of more than δb=1000 MPa and good ductility of higher than δ5=10% at ambient temperature.

Investigation into microstructure of spray formed V4 cold working mould steel and its roiling and annealing

The material selected for this work was the spray formed Vanadis4 high alloy cold working mould steel （abbreviated to V4 steel）. Its microstructure, hot rolling process, and annealing treatment have been investigated. Observed from the optical and electron microscopes, the as-sprayed V4 steel had the finer microstructure of uniform and equiaxial grains ,while after hot rolling for densification and spheroidized annealing, the V4 steel obtained an excellent spheroidized structure that is favorable to subsequent quenching and tempering treatment. The spheroidized structure and level of annealed hardness of the V4 steel are almost the same as expensive imported powder metallurgy the V4 steel. It is difficult to produce V4 steel with the conventional ingot metallurgical technique, so the multi-step and high-cost powder metallurgy method is generally used at present. Compared to the powder metallurgy technique, using the spray forming technique to produce the V4 steel has obvious advantages and potential market competitiveness in reducing production costs, simplifying working process, and shortening the production cycle.

Characteristic of Near-surface Microstructure and Its Effects on the Torsion Performance of Cold Drawn Pearlitic Steel Wires for Bridge Cables

The characteristic of near-surface microstructure and its effects on the torsion performance of cold-drawn pearlitic steel wires for bridge cables were investigated by focused ion beam-scanning electron microscope,transmission electron microscopy and differential scanning calorimetry.The samples with similar tensile strength before and after hot-dip galvanizing process are,respectively,characterized as delaminated and non-delaminated in torsion test which indicates that the tensile strength is independent of the toughness value(i e,reduction area and torsion ability).It is interesting to find that there exists submicron granular ferrite on near-surface of the wires,which can be attributed to dislocation rearrangement and sub-grains rotation during cold drawing and hot-dip galvanizing process.And their distribution can suggest homogeneousness of deformation degree to a certain extent:the closer to the surface of their distribution,the more homogeneous deformation of the wires.There is a close relationship between the thermal stability of the cementite layer and distribution of granular ferrite:differential scanning calorimetry(DSC)analysis shows that the sample is accompanied by submicron granular ferrite which is located closer to the surface has higher thermal stability under galvanizing temperature(450°C).A new mechanism of the torsion delamination of pearlitic steel wires is discussed in terms of the thermal stability of the cementite layer and distribution of granular ferrite.

Effect of hot-rolling deformation on the microstructure of pearlite of eutectoid steel

The effect of austenite deformation on the pearlite microstructure of eutectoid steel w as investigated by hot uniaxial compression tests using a Gleeble 1500 thermo-mechanical simulator. The results show ed that the deformation of the austenite phase accelerated the transformation of pearlite,leading to a smaller colony size and a smaller interlamellar space of pearlite; meanw hile,the orientation of pearlite lamellae became more heterogeneous,and the lamellar thickness decreased. Larger strain of austenite w as observed to accelerate the spheroidization process of carbides w ithin pearlite colonies.

亚温球化退火工艺对热轧态65Mn钢组织及性能影响

主要研究了亚温球化退火工艺对热轧态65Mn钢的组织及性能的影响,通过模拟不同退火温度、保温时间、冷却速率等条件,得到热轧态65Mn钢组织及性能的变化规律,为优化65Mn钢罩式退火工艺提供参考。结果表明,当温度低于相变点温度时,退火温度越高,热轧态65Mn钢球化效果越好;随着保温时间的延长,片状珠光体逐渐趋于球化,720℃保温12 h后,继续延长保温时间对球化效果影响不大;另外,在相同的加热温度和保温时间下,冷却速率对热轧态65Mn退火后的组织及性能无明显影响。