热作模具钢DM的高温稳定性和热疲劳性能

研究了热作模具钢DM的高温稳定性和热疲劳性能。结果表明,DM钢在620℃热稳保温过程中马氏体板条内的薄片状M₃C型碳化物逐渐向条块状M₇C₃型碳化物转变,在板条的边界生成M₇C₃、M₂₃C₆型碳化物。DM钢的短循环周次热疲劳性能受控于位错重排和湮灭,长循环周次热疲劳性能受控于碳化物的粗化程度。DM钢中M₃C、M₇C₃、M₆C型碳化物的生成自由能分别为27765.5 J/mol、3841.5 J/mol、-7138.1 J/mol,表明在热稳保温与热疲劳试验过程中碳化物的演变机理一致,发生了M3C→M7C3→M6C类型演变。     

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.     

Microstructure characteristics of Ni-based WC composite coatings by laser induction hybrid rapid cladding

To avoid low cladding rate and cracks of cladding layer, laser induction hybrid rapid cladding (LIHRC) has been put forward in the paper. The microstructure characteristics of Ni-based WC composite coatings at the different laser scanning speed were investigated. For low laser scanning speed, the growth of γ-nickel was characterized by coarse columnar dendrites and eutectics, blocky W₂C + Fe₃W₃C carbides, and bar-like (W, Cr, Ni)₂₃C₆ carbides were formed. With increasing laser scanning speed, the growth of γ-nickel presented the fine dendrites and eutectics, the only blocky mixed carbides were precipitated and identified as W₂C + FeW₃C + W₆C_2.54 carbides. With further increasing laser scanning speed, the growth of γ-nickel was characterized by cellular crystals and eutectics, the only blocky carbides were identified as W₂C + W₆C_2.54. Moreover, experimental results showed that the efficiency of LIHRC was increased much four times higher than that of laser cladding without preheating, ceramic–metal composite coatings detected were free of cracks and had a good metallurgical bonding with substrate.     

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.     

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.     

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.     

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.     

Effect of tempering temperature on Z-phase formation and creep strength in 9Cr–1Mo–V–Nb–N steel

The effect of the tempering temperature on Z-phase formation and creep strength in 9Cr–1Mo–V–Nb–N steel was examined with particular attention to the precipitation sequence of MX, M₂X, and Z-phase during creep exposure. Tempering at a lower temperature provided a high dislocation density and a fine lath structure. Tempering at 953, 1003, and 1038 K provided [M₂₃C₆, M₂X, NbX], [M₂₃C₆, M₂X, NbX, VX], and [M₂₃C₆, NbX, VX] phases, respectively. The creep strength of steel tempered at 953 K was the highest among the steels studied, even in the long term. No large decrease in creep strength was observed in steel tempered at 953 K. The Z-phase was observed after long-term creep in steel tempered at 1003 or 1038 K. In steel tempered at 953 K, a VX rather than a Z-phase formed during creep, and this was accompanied by consumption of M₂X. Retardation of the Z-phase formation can retard the creep strength degradation in steel tempered at 953 K.     

Inconel 600合金中不同类型晶界处铬的浓度

应用TEM、EDS和EBSD等技术研究了Inconel 600合金在715℃时效过程中不同类型晶界处碳化物的结构、形貌和晶界附近Cr浓度的分布。结果表明,不同类型晶界处碳化物的结构和形貌有较大的不同：在Σ3_c晶界析出的碳化物很少,在Σ3_i晶界析出不规则形状的M₂₃C₆碳化物,在Σ9晶界析出较大的M₂₃C₆碳化物颗粒,在Σ27晶界随机析出粗大的M₇C₃碳化物颗粒。富Cr碳化物在晶界的析出使晶界附近贫铬,在相同的时效条件下晶界的Σ值越高其附近贫铬越严重。随着时效时间的延长各晶界附近贫铬区的宽度不同程度地增大,时效15 h贫铬区的深度最大,时效50 h后深度不同程度地减小。     

WC-氧化石墨烯/Ni复合熔覆层的制备及形成机制

采用真空熔覆技术制备了WC-氧化石墨烯(GO)/Ni复合熔覆层,运用扫描电镜、能谱仪、X射线衍射仪观察并分析在不同温度下熔覆层内显微形貌的变化与物相组成。结果表明:在ZG45表面制备了组织致密、与基体形成良好冶金熔合的WC-GO/Ni复合熔覆层;熔覆层的微观结构组成从表面至基体依次是约1.5 mm厚的复合层、360 μm左右的过渡层、50 μm左右的扩散熔合层和100 μm左右的扩散影响层,其主要组成相有Cr₇C₃、FeNi₃、WC、Cr₂₃C₆、Ni₃Si、C、Fe₇W₆、γ-Ni固溶体等,FeNi₃、Fe₇W₆分散在冶金熔合带,扩散影响区主要组织为珠光体;复合区的物相尺寸小于界面区的物相尺寸,熔覆层形成过程中复合区的金属颗粒变化先于界面区,凝固时熔化不完全的颗粒表面长出团簇物(Cr₇C₃/Cr₂₃C₆),随着保温长大逐渐变成针状物镶嵌在Ni基固溶体中。      

Synthesis of Aluminium-Cementite Metal Matrix Composite by Mechanical Alloying

Cementite powder was prepared from elemental iron and graphite powder by mechanical alloying (MA) in a specially built dual-drive planetary mill. The phase evolution, particle-size distribution, and morphology of particles were studied during 40 hours grinding period. X-ray diffraction (XRD) shows formation of cementite and other iron carbides along with elemental iron after milling, whereas after annealing only cementite is present. Initially particle size increases with milling due to ductility of iron powder and then reduces with further milling.

Al-cementite composite was synthesized by mixing cementite with Al powders, and then by hot pressing or cold compaction and sintering. XRD analysis of Al-Fe₃C composite shows Fe₃C, FeAl, Al, and other iron carbides along with Al₄C₃ after sintering. Scanning electron microscope (SEM) micrograph of hot-pressed samples shows excellent compatibilility between Al matrix and cementite particles.     

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...     

Assessment of material thermal history in elevated temperature components

The extraction replica technique provides a valuable nondestructive metallographic tool both for monitoring microstructural changes caused by material aging and for quantitatively assessing the thermal history of material in components operating in creep regime. It has been, in fact, verified that the chemical composition of carbides collected on replicas is correlated both to temperature and to time of exposure of the material. In this report, the infield application of the replica technique is described, focusing on the quantitative evaluation of exposure temperature of a 21/4Cr1Mo steel. The validity of the technique has also been verified for 9–12% Cr ferritic steels after long-term creep exposure in laboratory tests; also in this case, on the basis of the available data, a correlation between the Cr/Fe ratio in M₂₃C₆ carbide and the Larson-Miller parameter appears promising.     

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.     

Characterization of mechanically alloyed ternary Fe–Ti–Al powders

The effects of Ti-substitution for Fe in the Fe₃Al system on the mechanical alloying process were investigated. For this purpose, blended elemental powders with the following nominal compositions (at.%): Fe₇₅Al₂₅, Fe₇₀Ti₅Al₂₅, Fe₆₅Ti₁₀Al₂₅, Fe₆₀Ti₁₅Al₂₅, were mechanically alloyed in a high energy attritor-type ball milling system for up to 100 h. The structural evolution in these powders was characterized by scanning electron microscopy, differential thermal analysis and X-ray diffraction techniques. It was found that elemental powders were progressively transformed into nanocrystalline solid solutions during mechanical alloying. The addition of Ti in the powders shortened the milling time for solid solution formation. With increasing Ti content, the grain size of the solid solutions decreased, but the lattice parameter increased. Upon heating, the milled powders were transformed into ordered (Fe,Ti)₃Al intermetallic compounds in an extended range of temperature (from 350 to 500°C). Ti addition enhanced the occurrence of DO₃ ordering in heated powders.     

具有固-液转变的磁性Fe3O4纳米流体的制备、结构及性能

Fe3O4纳米粒子与离子型改性剂N,N-二癸基-N-甲基-N-三甲氧基硅正丙基氯化铵进行接枝反应,再采用反离子脂肪醇聚氧乙烯醚磺酸盐的长链阴离子交换Cl-,在Fe3O4纳米粒子表面得到具有阴、阳离子双电层结构的表面处理层,制备出了无溶剂Fe3O4纳米流体。分析结果表明,表面处理鏖已成功地接枝在Fe3O4纳米粒子表面,改...     

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.     

高质量水系钠离子电池正极Fe4[Fe(CN)6]3的合成及其电化学性能

采用水热法合成高质量的Fe₄[Fe(CN)₆]₃(HQ-FeHCF)纳米材料, 并对材料进行X射线衍射(XRD), 扫描电子显微镜(SEM), 透射电子显微镜(TEM)和热重分析测试(TGA)等表征。结果表明：Fe₄[Fe(CN)₆]₃呈规则立方体, 颗粒大小约500 nm, 属面心立方结构。Fe₄[Fe(CN)₆]₃在NaClO₄-H₂O-聚乙二醇电解液中1C、2C、5C、10C、20C、30C和40C的容量分别为124、118、105、94、83、74和64 mAh·g ^-1, 表现出优异的倍率性能; 以5C倍率循环500次, 容量保持率接近100%, 表现出极佳的循环稳定性。以Fe₄[Fe(CN)₆]₃和磷酸钛钠分别为正负极的全电池工作电压高达1.9 V, 能量密度可达126 Wh·kg ^-1; 以5C倍率恒流充放电测试140次后全电池容量保持率为92%, 且库伦效率始终接近100%。     

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 。      

Microstructure and mechanical properties of high boron white cast iron

In this paper, high boron white cast iron, a new kind of wear-resistant white cast iron was developed, and its microstructure and mechanical properties were studied. The results indicate that the high boron white cast iron comprises a dendritic matrix and an interdendritic eutectic boride in as-cast condition. The distribution of eutectic boride with a chemical formula of M₂B (M represents Cr, Fe or Mn) and with a microhardness of HV2010 is much like that of carbide in high chromium white cast iron. The matrix includes martensite and a small amount of pearlite. After quenching in air, the matrix changes to martensite, but the morphology of boride remains almost unchanged. In the course of austenitizing, a secondary precipitation with the size of about 1 μm appears, but when tempered at different temperature, another secondary precipitation with the size of several tens of nanometers is found. Both secondary precipitations, which all forms by means of equilibrium segregation of boron, have a chemical formula of M₂₃(C,B)₆. Compared with high chromium white cast iron, the hardness of high boron white cast iron is almost similar, but the toughness is increased a lot, which attributes to the change of matrix from high carbon martensite in the high chromium white cast iron to low carbon martensite in the high boron white cast iron. Moreover, the high boron white cast iron has a good hardenability.