Al对M2高速钢铸态组织的影响

试验M2高速钢(%:0.85C、5.92W、4.74Mo、3.86Cr、1.81V)由25 kg真空感应炉熔炼,并用砂型铸造成锭。研究了0～1.3%Al对钢铸态组织的影响。结果表明,加入0.6%Al,可细化共晶莱氏体网,改善碳化物分布;加入过量Al(1.3%),初生晶粒内部出现大量由δ铁素体通过共析转变产生的针状碳化物。Al促进M₂C共晶碳化物形态由弯曲棒状变为平直片层状,并提高其合金元素含量。与片层状M₂C相比,棒状M₂C在高温易分解成短棒状或球状碳化物,有利改善碳化物形态。     

M2/FeV机械合金化及烧结过程中的碳化物形态转变

对水雾化M2高速钢粉和FeV合金粉末进行混合高能球磨,制备V含量(质量分数,下同)为8%的M2高速钢/Fe V合金化粉末,研究机械合金化过程中粉末形貌的变化与显微组织结构演化,并在球磨48 h的粉末配碳至目标碳含量(质量分数)2.2%,研究真空烧结过程中的碳化物形态转变。结果表明,随球磨时间延长,粉末颗粒细化速率逐渐降低,球磨28 h后粉末粒度趋于稳定,D_(50)为15μm左右。球磨过程中Fe V颗粒先嵌入到M2的基体相α-Fe中,然后固溶进入基体,V元素逐步均匀分散于基体相α-Fe和M_6C型碳化物中;M_6C发生细化并呈流线形分布,含量逐渐减少,MC颗粒有一定的细化但仍维持粒状形态,含量基本不变。烧结过程中合金元素先脱溶,析出大量粒状M_6C与MC型碳化物,随烧结温度升高,M_6C颗粒长大的同时含量减少,温度过高时M_6C呈针片状;1 180℃之前MC颗粒长大不明显,1 210℃时MC颗粒异常粗大并呈芯环结构。1 180℃下烧结可获得优良组织,其孔隙度为0.8%,M_6C与MC的平均尺寸分别约为1μm和0.3μm。     

W6Mo5Cr4V2高速钢连铸坯碳化物的研究——高速钢连铸坯内部质量研究之二

W6Mo5Cr4V2高速钢连铸坯退火后的主要碳化物为M_6C、MC、M_(23)C_6、M_7C_3及M_2C。碳化物总量为金属量的15—19％,其中M_6C MC约占碳化物总量的80％以上,M_(23)C_6 M_7C_3占13％左右,M_2C极微。碳化物在铸坯中分布极不均匀,从边沿到中心碳化物聚集程度有增加的趋势,在靠近中心的V形及中心偏析区内,碳化物聚集最严重。铸坯中出现的典型共晶碳化物形貌为片层状及羽毛状,遍及整个铸坯,约占95％左右,在铸坯中部元素富集的偏析区内,出现了鱼骨状及蜂窝状的共晶碳化物,前者为高钨的共晶碳化物,而后者为高钒、高钨、钼的共晶碳化物,估计是VC及M_2C共晶碳化物的混合体。减少偏析的措施均能减轻碳化物的聚集。文中提出了改进工艺的措施。     

含Hf和Ta新型镍基高温合金粉末中碳化物相

对含Hf和Ta新型镍基高温合金FGH98Ⅰ等离子旋转电极(PREP)雾化原始和不同温度下预热处理粉末中的碳化物相进行了研究.结果表明:原始粉末中MC′型碳化物可分为两类,一类为富Ti、Ta和Nb,另一类为含Ta、Hf和Zr.两类碳化物均含有一定量非碳化物形成元素Co和Ni及中等强碳化物形成元素Cr和Mo,并以块状、粒状分布于枝晶或胞晶间;随着预热处理温度升高,粉末中富Ti、Ta和Nb的MC′型碳化物转变为MC型碳化物,且其所含Ti、Ta和Nb的总量增大;含Ta、Hf和Zr的MC′型碳化物发生分解和转变,析出稳定的M23C6、M6C和MC型碳化物,M23C6碳化物的析出和溶解温度为950℃和1150℃,M23C6和M6C碳化物共存温度为1000～1100℃.另外,粉末中微量元素Hf和Ta主要以碳化物和γ′相参与碳化物反应.     

K445高温合金的微观组织特征研究

研究了K445高温合金微观组织特征.结果表明,K445铸态合金的主要组织为γ基体、粗大的γ'相、花辩状的γ+γ'共晶组织以及晶界上和晶内的MC碳化物;经过热处理后的K445合金的主要组织的形貌和分布有较大改变,成分偏析程度减轻,粗大的γ'相变得细小而弥散,在晶界上及晶内都分布着一定数量的M23C6及少量的MC碳化物.     

M2高速钢大尺寸碳化物的形貌特征及析出机理

主要研究成品及锻造后M2高速钢碳化物种类和析出机理,为大尺寸碳化物控制提供理论依据。采用扫描电镜和能谱仪观测成品及锻造后M2高速钢中碳化物形貌、成分和分布;采用Thermo-Calc热力学软件计算M2高速钢的平衡析出相和Scheil凝固过程。结果表明,成品M2高速钢棒材中大尺寸碳化物网状分布包括MC、M6C、M2C碳化物及其复合碳化物;锻造后高速钢中出现带状碳化物和粗大碳化物堆积现象。平衡条件下,MC和M6C碳化物的析出温度分别为1 294和1 288℃,高于1 220℃奥氏体化温度;Scheil凝固时,MC、M6C和M2C碳化物依次析出。采用热处理及锻造难以消除M2高速钢中大尺寸碳化物,控制钢液凝固过程中碳化物的析出有重要意义。     

高合金钢Vanadis4凝固过程及组织

通过激光扫描共焦显微镜、X射线衍射、扫描电镜、电子探针、微区成分能谱分析和差示扫描量热法,研究了高合金Vanadis4(V4)模具钢(%:1.5C、8.0Cr、1.5Mo、4.0V)的凝固过程及其微观组织。结果表明,V4钢基体为马氏体和残余奥氏体,基体中碳化物主要为MC与M₇C₃型。杆状、棒状或团块状VC分布在晶界。该钢在凝固时,首先发生结晶过程L→γ从液相中析出初生γ相,随着γ相不断析出,剩余液相中合金元素含量不断富集,达到共晶成分后将先后发生L→γ+MC与L→γ+M₇C₃共晶反应。     

钒对高速钢铸态碳化物的影响

本文运用扫描电镜及图像分析仪系统研究了钒(0～4％)对高速钢共晶碳化物形态及数量的影响,着重分析了钒影响共晶碳化物的机制。结果表明:钒不仅有利于碳化物(MC)的形成,而且明显抑制碳化物(M_6C)的形成,促使碳化物(M_2C)的形成。钒对共晶碳化物总量及形态的影响在不同钨钼配比的钢中有所不同。增钒使共晶碳化物明显粗化。     

气体雾化快凝W9高速钢粉末的组织特征

研究了颗粒粒度不同的气体雾化W9Mo3Cr4V高速钢粉末的组织、形貌及结构.结果表明:粉末由铁素体和奥氏体基体和分布在周围的MC及M2C型碳化物组成,基体组织为等轴晶及树枝晶,碳化物在空间上呈连续网状或树枝状分布;粉末中相的含量与粉末粒度相关,随高速钢粉末粒度减小,组织中的铁素体和MC型碳化物含量增加,奥氏体和M2C型碳化物含量减少.     

镍基高温合金GH4738的凝固偏析和碳化物析出行为

高温合金铸锭凝固过程内部各区域散热条件不同,冷却速率存在明显差异。采用差示扫描量热分析(DSC)、高温共聚焦显微镜(HT-CLSM)原位观察和定向凝固(DS)的方法,研究了宽冷速范围下GH4738合金的凝固偏析和碳化物析出行为。结果表明, GH4738合金的凝固顺序为L→γ+L,L→γ+L+MC,L→γ+MC+η+(γ+γ′),其中MC型碳化物、η相和(γ+γ′)共晶相为合金凝固过程中的主要偏析产物;Ti、Mo元素是合金的主要枝晶间偏析元素;提高冷却速率能有效降低凝固前沿残余液相中的溶质富集程度;铸态组织中的的碳化物主要为富Ti的MC型碳化物(TiC、Ti(N)C)和以TiN或Al₂O₃为核心的MC型复合碳化物(Al₂O₃-TiC、TiN-TiC);随着冷却速率降低,碳化物平均尺寸增大,体积分数减小,形貌由小块状向长条状、汉字状和大块状演变。     

Growth crystallography and lamellar to rod transition in directionally solidified Nb-Nb2C eutectic composites

The crystallographic relationship displayed by the niobium and niobium carbide <Nb₂C> phases in an aligned eutectic sample with a lamellar carbide morphology is lamellar interface ∥ {110}_NB ∥ (001)_{Nb 2C} growth direction ∥<112>_NB ∥ [010]Nb₂C or [1-20]_{Nb 2}C and for the rod-like carbide morphology rod interface (major axis) ∥{110}_Nb ∥ (001)_{Nb 2}C growth direction 11(H2)Nb II l010]Nb.,c or [210]NB₂C. The transition in morphology of the carbide phase is discussed in terms of the relative volume fraction of the phases, growth rate, and orientation relationships. The carbide morphology is influenced by the growth rate and carbon content. For constant growth rate increasing the volume fraction of the carbide phase favors the lamellar morphology. At low growth rates the lamellar morphology is favored, and at high growth rates the rod-like morphology is favored. Growth crystallography has no direct influence on the transition in carbide morphology.     

A New Approach for Refining Carbide Dimensions in M42 Super Hard High-speed Steel

Obtaining small carbides is crucial but difficult for high-speed steels.A new approach for refining carbide dimensions in M42 super hard high-speed steel by increasing cooling rate and spheroidizing treatment was proposed. The morphologies and properties of eutectic carbides formed at different cooling rates were investigated by means of scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS),X-ray diffraction (XRD),transmis-sion electron microscopy (TEM),electron back-scattered diffraction (EBSD)and differential scanning calorimeter (DSC).The results show that eutectic carbides change from a lamellar shape into a curved-rod shape as cooling rate increases.Despite different morphologies,the two carbides are both of M2 C type with a hexagonal close-packed structure and display a single crystal orientation in one eutectic colony.The morphology of M2 C mainly depends on the growing process of eutectic carbides,which is strongly influenced by cooling rate.Compared with lamellar car-bides,M2 C carbides with curved-rod shapes are less stable,and decompose into M6 C and MC at lower temperatures. They are more inclined to spheroidize during heating,which ultimately and distinguishably refines the carbide dimen-sions.As small carbides are much easier to dissolve into matrices during austenization,the process described herein improves the supersaturation of alloying elements in martensite,which leads to an increment of hardness in M42 steel.     

冷却速率对M2高速工具钢铸锭凝固组织的影响

试验M2钢(/%:0.81C,0.31Si,0.33Mn,4.01Cr,4.57Mo,5.71W,1.77V)由实验室25 kg高频真空感应炉熔炼,并浇铸成横截面50 mm×100 mm钢锭。研究了水冷铜模和铸铁模浇铸的M2钢的低倍组织、晶粒尺寸和碳化物分布。结果表明,快速冷却可有效控制和消除M2钢铸锭中的柱状晶,随着冷却速率增大,M2钢铸锭部分气泡上浮不完全,但中心缩孔显著减小,晶粒更细小且分布更均匀,碳化物更加弥散且细小;铸铁模锭边缘和中心部分的晶粒尺寸分别为40~57μm用和55~62μm,而水冷铜模锭边缘和中心部分的晶粒尺寸分别为30~40μm和50μm。     

水冷铜模与砂模铸造M2钢显微组织对比

采用实验室25 kg高频真空感应炉熔炼M2钢,并用水冷铜模和砂模均浇铸为横截面100 mm×50 mm的M2钢铸锭,研究冷却速度对M2钢二次枝晶间距、渗透率、碳化物和晶粒尺寸及分布的影响.研究结果表明:M2钢凝固过程中,快的冷却速度能有效减小二次枝晶间距、渗透率、晶粒和网状碳化物的尺寸,同时可以改善晶粒和网状碳化物的分布和均匀性;砂模和水冷铜模M2钢铸锭的平均二次枝晶间距分别为42.5μm和21.6μm,平均冷却速度为1.06 K·s-1和12.50 K·s-1,平均渗透率分别为0.13μm2和0.035μm2.快的冷却速度能有效减轻中心碳偏析程度,砂模和水冷铜模模铸的M2钢铸锭中心碳化物面积分数分别为0.46和0.30,且其较各自的平均值分别增大38.7%和2.2%;水冷铜模铸锭平均晶粒尺寸（43.1μm）较砂模铸锭的平均晶粒尺寸（72.6μm）减小约40.7%,铸锭中心晶粒尺寸减小43.2%,且水冷铜模铸锭的晶粒尺寸较砂模铸锭均匀.文中获得了M2钢凝固过程中晶粒尺寸与冷却速度的关系式.      

Growth of niobium-niobium carbide (Nb2C) eutectic and hypereutectic composites by zone melting

Growth from the melt of niobium-niobium carbide (Nb-Nb₂C) composites at the eutectic and off the eutectic composition by electron beam floating zone melting and freezing was studied. Composite growth has been successfully achieved for the eutectic composition and for compositions up to four atomic percent above the eutectic. The volume fraction of the carbide phase was increased from 26 to 33 pct by growing off the eutectic composition. The alignment and morphology of the carbide phase are influenced primarily by growth rate and composition. The carbide morphology may be either rod-like or plate-like. For a given composition, rod morphology is favored at higher growth rates. For constant growth rate, the plate-like morphology is promoted by increasing carbon content. The transition from plate to rod morphology is gradual. Lamellar and inter-rod spacings vary from 1 to 6 microns for growth rates varying from 5 to 90 microns per second. Variation of lamellar spacing with freezing rate,R, produces a straight line (on a log-log plot) in agreement with a relationship of the form {fx2309-1} = constant, withn = 0.8. For alloys four at. pct above the eutectic, primary Nb₂C dendrites nucleate and grow ahead of the still well aligned two phase solid plus liquid interface.     

Growth crystallography and lamellar to rod transition in directionally solidified Nb-Nb2C eutectic composites

The crystallographic relationship displayed by the niobium and niobium carbide <Nb₂C> phases in an aligned eutectic sample with a lamellar carbide morphology is lamellar interface ∥ {110}_NB ∥ (001)_{Nb 2C} growth direction ∥<112>_NB ∥ [010]Nb₂C or [1-20]_{Nb 2}C and for the rod-like carbide morphology rod interface (major axis) ∥{110}_Nb ∥ (001)_{Nb 2}C growth direction 11(H2)Nb II l010]Nb.,c or [210]NB₂C.     

The effect of lamellar morphology on tensile and high-cycle fatigue behavior of orthorhombic Ti-22Al-27Nb alloy

The room-temperature tensile and high-cycle fatigue (HCF) behavior of orthorhombic Ti-22Al-27Nb alloy with varying lamellar morphology was investigated. Varying lamellar morphology was produced by changing the cooling rate after annealing in the single B2 phase region. A slower cooling rate of 0.003 K/s, for example, resulted in several large packets or colonies of similarly aligned O-phase lamellae and a nearly continuous massive α ₂ phase at the prior B2 grain boundaries, while a faster cooling rate of 0.1 K/s led to the refinement of colony sizes and the O-phase lamellae. The interface of O-phase lamellae and B2 phases was semicoherent. Water quenching produced a very fine tweed-like microstructure with a thin continuous O phase at the prior B2 grain boundaries. The 0.2 pct yield stress, tensile strength, and HCF strength increased with increasing cooling rate. For example, the tensile strength and HCF strength at 10⁷ cycles of 0.003 and 0.1 K/s-cooled were 774 and 450 MPa, and 945 and 620 MPa, respectively. Since the fatigue ratio, which is the ratio of HCF strength at 10⁷ cycles to tensile strength, did not show a constant value, but instead increased with increasing cooling rate, part of the fatigue improvement was the result of improved resistance to fatigue associated with the microstructural refinement of the lamellar morphology. Fatigue failure occurred by the subsurface initiation, and every initiation site was found to contain a flat facet. Concurrent observation of the fatigue initiation facet and the underlying microstructure revealed that the fatigue crack initiated in a shear mode across the colony, irrespective of colony size, indicating that the size of the initiation facet corresponded to that of the colony. Therefore, the colony size is likely a major controlling factor in determining the degree of fatigue improvement due to the microstructural refinement of lamellar morphology. For the water-quenched specimens, fatigue crack initiation appeared to be associated with shear cracking along the boundary between the continuous grain boundary O phase and the adjacent prior B2 grain.     

Phosphorous Enrichment in Molten Adjusted Converter Slag： Part I Effect of Adjusting Technological Conditions

 The effects of adjusting technological conditions on the phosphorous enrichment of adjusted converter slag were investigated. The results showed that the phosphorus could be effectively enriched to 2CaO·SiO2 and 2CaO·SiO2-3CaO·P2O5 solid solution (SS, namely phosphorus-rich phase) to be formed with the decreasing of basicity and cooling rate. Moreover, the morphology of the phosphorus-rich phase changed from granular for the original converter slag with higher basicity to the coexistence of granular shape and rod-like for the adjusted slag with lower basicity. P2O5 content in phosphorus-rich phase exceeded 30% while the basicity was 13 at the cooling rate of 10 ℃/min.     

Effect of Ultra-Fast Cooling on Microstructure of Large Section Bars of Bearing Steel

The ultra-fast cooling technology of large section bars and the microstructure for different cooling patterns were studied by optical microscope, transmission electron microscope and energy spectrometer. The results indicated that the large section bars were passed through the zone of secondary carbide precipitation quickly by ultra-fast cooling technology (UFC) at instantaneous cooling rate of about 200 ℃/s and the finishing cooling temperature was higher than M,. The lamellar spacing of pearlite decreased and the microhardness increased with decreasing the re-reddening temperature. The precipitation of network carbide was restrained when rereddening temperature was 690 ℃. And fine laminated pearlite was obtained through transformation of pseudopearlition that induced the reduction of the diameter of pearlite grain and refinement of the lamellar spacing of pearlite, so ideal microstructures of promoting spheroidizing annealing were obtained.