改性HP40合金碳化物析出规律的热力学计算

利用Thermo-Calc热力学计算软件和与之相应的铁基合金数据库,计算了改性HP40合金中可能析出的平衡相及铌、钛和钨成分改变时对碳化物析出规律的影响,并计算了碳化物的平衡化学成分,以期为发展高稳定性的改性HP40合金提供理论依据。结果表明:铌和钛是MC型碳化物的主要形成元素。随着铌和钛含量的提高,MC型碳化物的最大析出量增加,M₂₃C₆型和M₇C₃型碳化物的最大析出量减少,MC型和M₂₃C₆型碳化物的开始析出温度升高。钨元素在高温时主要分布在γ基体中,在服役温度下长期时效,钨从γ基体向M₂₃C₆型碳化物不断偏聚。随着钨含量的提高,M₇C₃型碳化物的最大析出量减少,M₂₃C₆型碳化物的开始析出温度及M₇C₃相向M₂₃C₆相转变的温度均显著升高。     

Fe-Cr-Mo-W-V系热作模具钢高温热稳定性机理研究

采用硬度和扫描组织评价方法分析了三种Fe-Cr-Mo-W-V热作模具钢(DM、H21和H13)在580~650℃下的热稳定性,研究结果表明DM钢较H21、H13钢具有高的热稳定性。同时,通过测定三种钢的连续加热曲线并结合透射电镜组织,研究了高温热稳保温过程中存在的重要碳化物的类型。为了揭示Fe-Cr-Mo-W-V钢的热稳定机理,计算了三种钢由M2C型碳化物形成阶段向MC型碳化物形成阶段转变的临界点激活能,其值为163.9~204.1kJ/mol,表明M2C、MC型碳化物的形成不仅受体扩散影响,而且与位错管道扩散激活能相关,DM钢具有最高临界激活能,其值高达204.1kJ/mol。进一步对比三种钢中的价电子结构差异,得出最高热稳定性的DM钢具有最佳价电子结构。     

Si对9Cr型铁素体/马氏体钢析出相和力学性能的影响

研究了Si含量对9Cr型铁素体马氏体(F/M)钢析出相和力学性能的影响。结果表明：在不同Si含量的9Cr型F/M钢中析出相均为M₂₃C₆、MX和Laves相，Si能促进Laves相和M₂₃C₆型碳化物的析出。Si含量为0.9%～1.2%的这种钢其拉伸强度和延伸率略有降低，冲击性能维持稳定；Si含量为1.2%～1.8%时，Si的固溶强化和析出相的沉淀强化使钢的拉伸强度提高。但是，随着Si含量的进一步提高Laves相和M₂₃C₆型碳化物大量析出，使其冲击功显著衰退。     

表面激光强化对汽车模具钢H13组织与性能的影响

采用表面激光熔覆和激光冲击强化的方法对汽车模具钢进行表面强化处理,研究了M2高速钢粉末含量(粉末成分:Fe104 75%～100%,M2粉末0～25%,质量分数)对熔覆层显微组织、物相组成和耐磨性能的影响,并探讨了激光冲击强化对熔覆层耐磨性能的影响。结果表明:除未添加M2粉末的M0试样熔覆层中的ɑ-Fe、γ-Fe、M₂₃C₆和M₇C₃相外,添加M2高速钢合金粉末后的熔覆层中还出现了硬度更高的MC、M₂C和M₆C相;M2高速钢粉末含量的提升有助于细化复合熔覆层的组织,而熔覆层与基体仍然保持着良好的冶金结合。添加不同含量M2高速钢合金粉末的复合熔覆层的硬度都高于M0试样,且加入15%M2高速钢合金粉末的熔覆层的平均摩擦系数和磨损率小于M0熔覆层。     

高淬低回复合冷处理工艺对DC53钢组织性能的影响

基于1 040℃淬火+200℃回火复合冷处理工艺，研究高淬低回热处理复合冷处理工艺对DC53钢组织性能的影响。结果表明：冷处理温度未改变物相析出种类，物相由马氏体、奥氏体、(Cr_2.5Fe_4.3Mo_0.1)C₃和(Cr, Fe)₇C₃型碳化物组成，温度诱发的马氏体择优取向、晶格畸变或层错逐步增强，-196℃时最为剧烈。当-11℃冷处理时驱动力不足碳化物析出较少；-80℃时碳化物析出量最多，以M₇C₃型碳化物为主；-196℃时碳原子扩散动力学不足而固溶于马氏体中。-80℃条件下试样组成相配合最佳，其硬度值59.6 HRC,冲击吸收功9.2 J,较未冷处理的试样硬度提升近5%,韧性提升1.875倍；冲刷腐蚀磨损性能随温度的降低而先升后降，冲刷腐蚀18 h后磨损率为7.65 mg/cm²,相对性能提升近17%。     

球磨转速对含钆ODS钢中M23C6析出的影响研究

以“结构/屏蔽一体化”为研发目标的含钆ODS合金具有较优的中子屏蔽性能与高温力学性能，可作为小型模块化铅冷快堆中子屏蔽材料的研发方向之一。在机械合金化-放电等离子体烧结工艺制备含钆ODS-316L钢的研究中发现，球磨转速影响材料的析出相种类，如在220 r/min低球磨转速下，ODS-316L钢中仅存在纳米尺寸的Gd-Si-O析出相，而在300 r/min高球磨转速下，除纳米尺寸的Gd-Si-O析出相外，材料内还分布着大量百纳米尺寸的片层堆叠状M₂₃C₆型碳化物，且M₂₃C₆内同样存在纳米含钆氧化物颗粒。高球磨转速使球磨粉内元素的偏析与内应力的累积促进了M₂₃C₆的形核，随后的粉末烧结温度则为M₂₃C₆的生长提供了驱动力。此研究可为粉末冶金含钆ODS-316L钢的微观组织调控奠定一定的实验与理论基础。     

TiCp/Cr15高铬铸铁复合材料的制备与性能

以TiC_p粉末和水雾化Cr15高铬铸铁粉末为原料,采用粉末冶金液相烧结技术制备TiC_p增强高铬铸铁复合材料。研究了TiC_p含量对高铬铸铁的物相组成、显微组织和力学性能的影响。研究结果表明,全致密的TiC_p增强高铬铸铁基体复合材料的构成相为TiC、M₇C₃型碳化物、马氏体和少量奥氏体;随着TiC_p添加量增大,金属基体逐步呈孤岛状,并在其中析出越来越多的M₇C₃型碳化物,同时TiC_p逐步呈连续网状分布;同时,其硬度稳步提升,而抗弯强度和冲击韧性降低。当TiC_p添加量为20wt%时烧结态复合材料具有最佳综合力学性能。此时硬度为HRC 66.8 ,冲击韧性为6.86 J/cm2,抗弯强度为1 343.10 MPa。当TiC_p添加量为25wt%时硬度达到最大值HRC 67.20 。      

具有近室温磁热效应的Fe71Mo9P13C7块体非晶态合金

通过Fluxing提纯处理和J-Quenching快速凝固技术相结合的方法成功制备出临界尺寸为1.3 mm的Fe₇₁Mo₉P₁₃C₇块体非晶态合金棒,并对其热力学性能、磁性能和磁热性能进行了研究。结果显示,Fe₇₁Mo₉P₁₃C₇块体非晶态合金的饱和磁化强度为0.55 T;在5 T外加磁场下的最大等温磁熵变值为2.57 J/（kg·K）,制冷能力为305.57 J kg。重要的是Fe₇₁Mo₉P₁₃C₇块体非晶态合金的居里温度为355 K,接近室温,因此有望成为室温磁制冷工质的候选材料。     

45钢表面Ni/WC复合熔覆层的形成机制

采用真空熔覆技术在45钢表面制备Ni +WC复合熔覆层并进行阶段性取样,研究镍基复合涂层的形成机制。结果表明：在45钢表面生成与基体冶金熔合、WC硬质颗粒分布均匀的Ni基复合熔覆层。整个熔覆层由4 mm厚的复合层、1 mm厚的过渡层、20 μm厚的扩散熔合区以及250 μm厚的扩散影响区组成。复合层区由WC和分解形成的富W复相碳化物包围在Ni颗粒周围组成;复合熔覆层的主要组成相有γ-Ni固溶体、Cr₇C₃、Ni_2.9Cr_0.7Fe_0.36、Cr₂₃C₆、Ni₃Fe、Ni₃Si、Ni₃B、W₂C以及C等;真空熔覆过程包括：镍基合金颗粒达到熔点(900℃)前升温阶段颗粒间微烧结颈的形成、升温达到熔点(1020℃)开始的镍基合金颗粒熔融以及保温阶段(1060℃)的熔合扩散与WC颗粒微区位置的调整。     

Cr8Nb3CSiMnTi系堆焊合金的组织及耐磨性研究

为解决中铬合金耐磨性不足的问题，采用“复合粉粒+H08A实心焊丝”埋弧焊方法制备Cr8Nb3CSiMnTi系中铬耐磨合金，借助X射线衍射仪(XRD)、扫描电镜(SEM)及附属能谱仪(EDS)等手段，研究了碳含量对该合金组织和耐磨性的影响。结果表明：中铬堆焊合金的基体由α-Fe构成，硬质相包括(Fe, Cr)₇C₃、(Fe, Cr)₃C碳化物和(Nb, Ti)C等相；随着碳含量升高，α-Fe固溶的铬含量持续减小，沿晶(Fe, Cr)₇C₃型碳化物数量增多，形态从孤立状依次改变为树枝状、定向聚集态等，与(Nb, Ti)C相的间距随之减小。湿砂橡胶轮式磨损试验结果显示，随碳含量提高，堆焊合金的耐磨性先显著改善然后降低，这主要与沿晶碳化物(Fe, Cr)₇C₃数量提高以及其与(Nb, Ti)C相的间隔距离改变有关；堆焊合金的韧性则先持续下降，然后上升，这不仅决定于基体数量，而且与沿晶碳化物的形态及其分布有关；其磨损机制包括显微切削和剥落，以显...     

TEM study on precipitation and transformation of secondary carbides in 16Cr–1Mo–1Cu white iron subjected to subcritical treatment

High chromium white irons solidify with a substantially austenitic matrix supersaturated with chromium and carbon. The subcritical heat treatment can destabilize the austenite by precipitating chromium-rich secondary carbides and other special carbides. In the as-cast condition the eutectic carbides are (Fe,Cr)₇C₃ and (Fe_4.3Cr_2.5Mo_0.1)C₃. The initial secondary carbide precipitated is (Fe,Cr)₂₃C₆ after heat-treating at 853 K for 10 h. There are MoC, Fe₂MoC and -carbide precipitating, and (Fe,Cr)₂₃C₆ transforms to M₃C after 16 h at 853 K. The -carbide and (Fe,Cr)₂₃C₆ accomplish transformation to M₃C and the matrix changes from martensitic to pearlitic after 22 h at 853 K. Thereby, in the subcritical heat treatment process, the initial secondary carbide precipitated is (Fe,Cr)₂₃C₆, followed by -carbide, MoC and Fe₂MoC. In addition, there are two in situ transformations from (Fe,Cr)₂₃C₆ and -carbide to M₃C carbides.     

Microstructural characterization of high-carbon ferrochromium

Light optical and scanning electron microscopy techniques were used for high-carbon ferrochromium microstructural analysis. Different microstructures were observed for industrially and laboratory-produced ferroalloys. Primary carbides of M₇C₃ with chromium ferrite were found in the industrially produced, slowly solidified, and cooled ferroalloy, while primary M₇C₃ carbides accompanied a eutectic mixture of M₇C₃ carbides and chromium ferrite in the laboratory-melted and in the water-solidified and water-cooled materials. Different microstructural arrangements are directly related to the friability properties of this material, which characterizes its resistance to abrasion on handling and impact. In ferrochromium upgraded by carbon content reduction, the eutectic M₇C₃ hexagonal carbides are partly replaced by M₂₃C₆ dendritic carbides. The presence of dendritic carbides in the ferrochromium eutectic microstructure can be interpreted as a proof of a lower carbon content, raising the commercial value of the ferroalloy. The hexagonal M₇C₃ carbides exhibited a central hollow along the longitudinal axis, and on metallographic samples they looked like screw nuts. A model of the solidification mechanism for such crystals is proposed.     

Microstructural transformations of heat affected zones in duplex steel welded joints

The influence of the welding thermal conditions exemplified by heat input and heat treatment after welding on the structure of the heat affected zone (HAZ) UNS S31803 has been analysed. The post weld treatment was used to create the precisely defined thermal conditions for the decomposition of primary phases in the HAZ, by a multi-layer welding thermal cycle stimulation. Detailed analyses of the microstructure and chemical composition of the phases in the different post welded conditions were performed by scanning electron microscopy (SEM) combined with energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM). Three types of secondary precipitates have been observed: secondary austenite (γ₂), carbides: M₂₃C₆ and M₇C₃. The dependence of the secondary austenite volume fraction and morphology in the HAZ on thermal cycle have been interpreted. The eutectoid decomposition of the primary phases in the analysed thermal conditions was confirmed.     

Electron microscopy and hardness study of a semi-solid processed 27 wt%Cr cast iron

A semi-solid processed 27 wt%Cr cast iron was studied by electron microscopy and its microstructure was related to the hardness. In the as-cast condition, the primary proeutectic austenite was round in shape while the eutectic M₇C₃ carbide was found as radiating clusters mixed with directional clusters. Growth in the [0 0 1]M₇C₃ with planar faces of {0 2 0}M₇C₃ and was usually observed with an encapsulated core of austenite. Destabilisation heat treatment followed by air cooling led to a precipitation of secondary M₂₃C₆ carbide and a transformation of the primary austenite to martensite in the semi-solid processed iron. Precipitation behaviour is comparable to that observed in the destabilisation of conventional cast iron. However, the nucleation of secondary M₂₃C₆ carbide on the eutectic M₇C₃ carbide was observed for the first time. Tempering after destabilisation led to further precipitation of carbide within the tempered martensite in the eutectic structure. The maximum hardness was obtained after destabilisation and tempering heat treatment due to the precipitation of secondary carbides within the martensite matrix and a possible reduction in the retained austenite.     

Precracking structures in a creep-fatigued low-carbon Cr---Mo steel

A grain boundary phenomenon observed, after metallographic polishing and etching, in a 1Cr-0.5Mo steel is shown to be due to the selective etching of the boundaries. The phenomenon is a feature only of material that has been subjected to strain-controlled fatigue cycles incorporating a dwell time at peak tensile stress (creep fatigue) and is largely confined to boundaries whose orientation is approximately normal to the direction of the principal tensile stress. The structural feature responsible has not been identified, although it has been established that it is not a physical discontinuity, such as a void cavity or a decohered carbide particle. The phenomenon develops concurrently with the precipitation of M₃C and M₇C₃ carbides at the boundaries, which also is a feature of creep fatigue, and develops at the interface between these particles and the ferrite matrix as well as at the ferrite grain boundaries themselves. It seems to have been initiated in a very thin layer at these interfaces, perhaps in a layer only of the order of atom layers in thickness.     

The effect of niobium on the microstructure of ferritic stainless steel

The effect of different amounts of Nb and of homogenization on the ferritic stainless steels containing 17–18 wt.% Cr was investigated with scanning electron microscopy (SEM), optical microscopy, energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and differential thermal analysis (DTA). It was observed that M₂₃C₆, NbC and sigma phase formed in these steels. In addition, the formation of Nb₂C was observed in the sample containing 3.0 wt.% Nb. While the amount of Nb increased from 0.5 to 3.0 wt.% Nb, the microhardness of the matrix and the amount of M₂₃C₆ decreased and the toughness of the samples increased. After homogenization, the increase in the toughness of the samples containing 1.5–3.0 wt.%Nb was considerable and impressive.     

淬火温度对含铜5Cr15MoV马氏体不锈钢性能的影响

将含铜5Cr15MoV马氏体不锈钢在不同温度热处理并使用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射(XRD)、透射电子显微镜(TEM)、硬度测试和电化学测试等手段对其表征,研究了淬火温度对其组织、硬度以及耐蚀性能的影响.结果 表明,铜元素的添加提高了材料中残余奥氏体的体积分数,而使其硬度降低.淬火后钢中的...     

A Metallographic Study of the High-Temperature Decomposition of Austenite in Alloy Steels Containing Mo and Cr

Optical and electron microscopy have been used to study the complex microstructures developed during the isothermal decomposition of austenite above 550°C in Fe-4Mo-0.2C and Fe-10Cr-0.4C alloy steels. As the transformation temperature is decreased, the decomposition products change from the disordered growth of nodular alloy pearlites to blocky ferrite structures containing fine dispersions of alloy carbide, and finally to acicular ferrite structures also containing alloy carbide. The branched M₆C and M₂₃C₆ of the high-temperature pearlite is replaced by Mo₂C and M₇C₃ with a fibrous or lath morphology in the lower temperature structures. The decomposition microstructures are explained in terms of a model which takes account of the growth of particular alloy carbides at the interfaces of ferrite allotriomorphs, where the growth mechanism, and hence the morphology, is sensitive to transformation temperature.     

High speed steel produced by spray forming

In this paper, ASP2030 (A30) high speed steel (HSS) was produced by spray forming and the microstructure was studied by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The spray formed A30 (SF A30) steel exhibited a very uniform and fine microstructure consisting of martensite, retained austenite and uniformly distributed network carbides. Microstructure refining can be explained in terms of the rapid solidification of spray forming. M₂C, MC and M₆C type carbides were found in the as-sprayed A30 HSS by XRD and TEM. A uniform distribution of carbides was obtained after forging and annealing. The microstructure properties of SF A30 steel indicate that spray forming can be considered as a cost-effective route for the production of A30 steels and other highly alloyed steels.     

Recrystallization in a directionally solidified cobalt-base superalloy

The recrystallization behavior in a range of annealing temperature from 1020 to 1280 °C in a directionally solidified cobalt-base superalloy was studied. Local recrystallization first appeared at 1040 °C. The recrystallized volume increased rapidly as increasing the annealing temperature. Pinning effect of all carbides (M₂₃C₆, M₇C₃ and MC) was observed and large amount of twin formed at low annealing temperature. The size of the recrystallized grains increased significantly at high annealing temperatures accompanied with the sharp decrease of twin. The effect of annealing temperature and the role of carbide and twin on the development of the recrystallization were discussed.