Effect of rare earth addition on continuous heating transformation of a high speed steel for rolls

The effect of rare earth(RE) on continuous heating transformation of a high speed steel for rolls was investigated by using differ-ential scanning calorimetry(DSC) with combination of microstructure analysis.Determination of the Ac1 and Ac3,the starting temperature of carbide dissolution and melting upon heating,the enthalpy change for the α→γ transformation and overall carbide dissolution were also es-tablished.It was found that RE could reduce the volume fraction of large eutectic carbides and the chrysanthemum-like eutectic colonies but could not change the phase composition.RE made a little change to Ac1,but the variation in Ac3 and enthalpy for the α→γ followed an in-creasing pattern as the RE addition increased.The start temperatures of carbides dissolution increased with increase of RE addition,which may be associated with the influences of RE on the morphology of carbides,but the overall enthalpy change of carbides dissolution decreases as the RE addition increased.Moreover,the start temperature of melting also increased with increasing RE addition.     

Influence of rare earth elements on solidification behavior of a high speed steel for roll using differential scanning calorimetry

The influence of rare earths(RE) on solidification behavior of a high speed steel for roll was investigated by using differential scanning calorimetry(DSC) in combination of microstructure analysis.It was found that the sequence of solidification was L→γ,L→γ+MC,L→γ+M2C,L→γ+M6C,respectively.The start temperature and the latent heat liberated by unit mass of L→γ and L→γ+MC increased with increase of RE addition,indicating that RE could trigger the crystallization of the primary γ and the MC carbide more effectively.The promoting effect of RE on the heterogeneous nucleation was believed to be an important cause of this effect.Grain refinement,discontinuous network of eutectic carbides and disperse and finer MC were observed in the samples with RE addition,moreover,RES could act as the heterogeneous nucleus of the MC.RE addition was favorable for stable M6C at the expense of the metastable M2C.     

Effect of Rare Earth Elements on Quenching Crack Resistance of Steel 9Cr2Mo

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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.     

Effect of rare earth elements on the thermal cracking resistance of high speed steel rolls

The effect of rare earth elements on the thermal cracking resistance of high speed steel (HSS) rolls was investigated. Laser rapid heating was used for thermal fatigue experiments. Thermal cracks and microstructure were observed using metalloscopy and scanning electron microscopy. The results showed that thermal cracks initiated from the interface between the matrix and eutectic carbides (including M6C and M7C3 type carbides),and propagated along the interface between the two phases. MC type carbides enriched with vanadium could prevent the propagation of thermal cracks. The presence of rare earth elements decreased the quantity of big eutectic carbides,and proportionally increased spherical and rod-shaped MC type carbide content. HSS0 (0.00% RE) had approximately three times the thermal cracking density of HSS3 (0.12 wt.% RE). Rare earth elements were shown to significantly improve the microstructure and thermal cracking resistance of HSS rolls.     

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。     

Effect of Rare Earth Element on Formation and Propagation of Thermal Fatigue Crack in Low-Chromium Semi-Steel

The formation and growth of thermal fatigue crack in low chromium semi steel were investigated by means of optical microscope and scanning electron microscope, and the function of RE in low-chromium semi steel was analyzed. The results show that the thermal fatigue cracks are mainly generated at eutectic carbides, and the cracks not only grow and spread but also join each other. RE can improve the eutectic carbide‘s morphology, inhibit the generation and propagation of thermal fatigue cracks, and therefore promote the activation energy for the crack‘s propagation, which is especially more noticeable in case of the RE modification in combination with heat treatment. The mathematical model of the crack propagation is put forward.     

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。     

Influence of Rare Earth on Property of Low Chromium Semi-Steel

Itisnoticeablethatthelowchromiumsemi steelhashighhardnessandabrasionresistance[1] .However,thematerialhaslowductility ,owingtothereticulatedistributionofcarbide ,whichrestrictsitsapplications .Therefore ,itisnecessarytoim provethecomprehensivepropertiesforpotentialap plications .Thecomprehensive propertiesoflowchromiumsemi steelcanbeimprovedbyaddingrareearths (RE)becauseREcanchangethemorphologyofcarbideandnon metallicinclusions ,refinegrainsize,purifyandstrengthen grainboundaryandsoon[2 -5] …     

Effect of Heat Treatment on Microstructure of Modified Cast AISI D3 Cold Work Tool Steel

 High chromium high carbon AISI D3 steel is used as cold-work tools and dies in industry. Microstructure of this wrought steel usually consists of chromium carbides homogenously dispersed in a ferritic or martensitic matrix. On the other hand, a eutectic network consisting of chromium carbide and austenite forms in a cast D3 steel, at the end of solidification due to the segregation of carbon and chromium. This heterogeneous microstructure gives rise to the reduced mechanical properties such as toughness, impact strength, and tensile strength. In this research, modified AISI D3 steel was developed by replacing part of Cr with Nb and Ti, in which chromium carbide was partially replaced with MC carbides. The cast samples produced by investment casting were heat treated at different conditions. The microstructures of the samples were studied by light and scanning electron microscope attached with EDS analyzer. To determine the optimized homogenizing process, the effects of homogenizing treatment on the microstructure and the morphology of carbides were also studied.     

Effect of rare earth oxides on the morphology of carbides in hardfacing metal of high chromium cast iron

The flux cored wires with different amounts of rare earth (RE) oxides additions for hardfacing (harden-face-welding) the workpieces of high chromium cast iron were studied in this work.The morphology of carbides in hardfacing metal was observed,and the type of the carbides was determined by optical microscopy,scanning electron microscopy (SEM),energy dispersive spectrometer (EDS) and X-ray diffraction (XRD).Based on the data of effect of RE on carbides morphology,the refined reason for carbide by RE oxide was discussed with the misfit theory.The results showed that,the microstructure of hardfacing metal was composed of martensite,residual austenite and M7C3 carbides.With the increasing amount of RE oxide additions,the volume fraction and roundness of the carbides were increased,however,the area and perimeter of carbides were decreased.It indicated that carbides in hardfacing metal could be refined and spheroidized by adding RE oxides in flux cored wires.     

Effect of Rare Earth Elements on Isothermal Transformation and Microstructures in 20Mn Steel

The effect of rare earth elements on the isothermal transformation and microstructures in 20Mn steel is in-vestigated by means of metallography and dilatometry.Rare earth elements decrease both the incubation periodof pro-eutectoid ferrite and the rate of pearlitic transformation.In addition,rare earth elements play a role ofreducing needle-like ferrite and the amount of pearlite,densifing the lamellar space of pearlite and enhcingsegregation of carbide in granular bainite.It is suggested that rare earth elements may decrease the interfacialenergy of grain boundary and interphase,hinder the diffusion of carbon atoms and form rare earth carbides withhigh melting point which reduce the carbon content in austenite.     

3Cr2W8V热作模具钢的稀土合金处理

采用15tEAF冶炼,25tLF精炼,740kg铸锭锻制成Φ110mm的3Cr2W8V钢材。在LF精炼后期,钢中氧含量为29×10^-6,加入0.048%RE合金(%:21~24RE,44Si,3Mn,5Ca,3Ti,余Fe)进行稀土合金处理,稀土元素的回收率为30.78%。检验结果表明,进行稀土处理能够有效地改善3Cr2W8V模具钢共晶碳化物偏析,并显著减少P、Pb、Sn、As、Sb等有害元素在晶界的偏析。     

Effect of Rare Earth Elements on Carbide Morphology and Phase Transformation Dynamics of High Ni-Cr Alloy Cast Iron

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Influence of Cerium on Solidification Microstructure of M2 High Speed Steel

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Effect of Rare Earth on Microstructures and Properties of High Speed Steel With High Carbon Content

The effects of rare earth （RE） on the microstructures and properties of high carbon high speed steel （HCHSS） were investigated. The results show that when suitable RE is added to the HCHSS, the effect of RE on the austenite and eutectic carbides is obvious. The austenite grain and coarse eutectic structure are refined, and flake carbides in the eutectic structures become short and fine. After heat treatment, most of the eutectic carbides are spheroidized and distributed in a uniform manner. The hardness and red hardness of modified HCHSS are slightly increased; impact toughness is greatly increased by 37.81% and reaches 10.17 J/cm^2. The mechanism by which RE improves the structures and properties of HCHSS is also analyzed.     

Phase precipitation and segregation behavior of nickel based superalloy GH4151

The element segregation behavior, as cast microstructure characteristics and precipitation phase types of GH4151 alloy were studied by electron probe microanalysis (EPMA), field emission scanning electron microscopy (SEM) and differential thermal analysis (DTA), and the solidification process of the alloy was discussed. During the solidification of GH4151 alloy, element W is segregated to the dendrite cores, elements Mo, Nb and Ti are segregated to the interdendritic regions, and elements Co, Cr, Al are not segregated, elements Nb and Ti are biased more heavily. The core of GH4151 ingot is coarse equiaxed grains, whose main precipitated phases include γ′, MC carbide, η phase, (γ+γ′) eutectic phase and Laves phase. At the end of solidification, low temperature brittle phases such as η phase, (γ+γ′) eutectic phase and Laves phase are formed, which enlarge the solidification range and increase the hot cracking sensitivity of the alloy.     

镍基高温合金GH4151的偏析及相析出行为

摘要：利用电子探针(EPMA)、场发射扫描电镜（SEM）及差热分析（DTA）研究了GH4151合金的元素偏析行为、铸态组织特征以及析出相种类,并对合金凝固过程进行讨论。结果表明：GH4151合金凝固过程中,W元素偏聚于枝晶干,Mo、Nb、Ti元素偏聚于枝晶间,Co、Cr、Al元素几乎不发生偏析,Nb、Ti元素偏析较重。GH4151铸锭心部为粗大的等轴晶,主要析出相包括强化相γ′相、一次碳化物、η相、（γ+γ′）共晶相以及Laves相,其中枝晶间分布的η相、（γ+γ′）共晶相和Laves相为低温脆性相在凝固末期形成,扩大了合金的凝固区间,从而导致合金热裂敏感性增加。     

Influence of rare earths on eutectic carbides in AISI M2 high speed steel

The effect of rare earths on the morphology and microstructure of eutectic carbides in M2 high speed steel was studied. The results showed that rare earths promoted the formation of fishbone-like M6C eutectic carbides, compared to plate-like M2C carbides in ingots without modification. The formation of M6C was expected to be caused by rare earth inclusions which acted effectively as the substrate for nucleation of M6C carbides during solidification. M2C and M6C eutectic carbides exhibited different stability during heating. M2C eutectic carbides were much less stable than M6C carbides, and decomposed at high temperatures, favoring the spheroidization and refinement of carbides in high speed steels.     

H13钢中一次碳化物的特征及控制进展

首先结合H13钢的成分特点肯定了H13钢优异的材料性能,随后总结了一次碳化物与H13钢使用寿命之间的关系。进一步系统地论述和研究了H13钢中一次碳化物的特征,包括二维和三维形貌、热稳定性、析出机理等。最后对比了4种H13钢中一次碳化物的控制手段,包括成分优化、冷速控制、Mg处理和稀土处理。相关论述和研究工作能够对钢中一次碳化物的合理优化起到一定的启发作用。