脉冲电流对过共晶灰口铸铁凝固组织的影响

采用储能电容为1200uF的脉冲电源，在不同的充电电压下，对过共晶灰口铸铁进行电脉冲处理。结果表明：脉冲电流能够明显细化和改善过共晶灰口铸铁的凝固组织，使石墨由粗大的长片状变为小块状或小片状，石墨的分布更加均匀，而且尖角钝化甚至呈近似球形。脉冲电压的升高和脉冲频率的增大都有利于过共晶灰口铸铁凝固组织的细化和改善。     

Nb合金化对高Cr铸铁轧辊组织的影响

微合金化是细化高Cr铸铁轧辊的凝固组织、提高轧辊的性能和使用寿命重要手段。研究了Nb微合金化对高Cr铸铁轧辊组织和硬度的影响,并采用Thermo-Calc软件分析了Nb对高Cr铸铁凝固组织的细化机制,结果表明,Nb合金化能够显著细化高Cr铸铁的轧辊的凝固组织,提高轧辊的硬度。Nb微合金化对高Cr铸铁的组织改善作用取决于MC型碳化物析出温度及其对奥氏体和共晶M₇C₃碳化物的形核的促进作用。当Nb质量分数为0.5%时,高Cr铸铁轧辊硬度最大;进一步提高Nb含量能显著细化高Cr铸铁轧辊组织,但使硬度降低。     

高铬铸铁中不同初生相在不同凹槽半径过流冷却体中的形貌演变

采用过流冷却体法制备高铬铸铁半固态浆料,研究高铬铸铁中不同初生相在不同凹槽半径过流冷却体中的形貌演变。结果表明:采用过流冷却体法细化高铬铸铁半固态浆料组织是行之有效的方法。呈树枝状长大的初生奥氏体的细化在凹槽半径较小的冷却体中以熔断为主,在凹槽半径较大的冷却体中以扭折为主。呈杆状长大的初生M7C3型碳化物在冷却体中的细化以破碎、折断、劈裂为主,在凹槽半径较小的冷却体中较凹槽半径较大的冷却体中易形成包裹层较厚的杆状碳化物,且较难被破碎和折断。     

多元合金化对共晶31Cr高铬铸铁碳化物的影响

采用多元合金化处理共晶31Cr高铬铸铁,借助金相显微镜、扫描电镜、AXIOS（PW4400）型X荧光及Leica图像分析仪对金相组织、成分、碳化物尺寸及形貌进行分析。结果表明,经多元合金化后,碳化物尺寸细化、形貌改善,碳化物形状因子K先增大后减小,粒度因子D先减小后增大;确定了最佳成分,其碳化物的形状因子K=0.83,...     

钨合金白口铸铁共晶碳化物团球化的研究

针对钨合金白口铸铁脆性大,应用于承受冲击载荷的工况下安全性差,使用范围受到严格限制,探讨了碱金属元素钾、钠对钨合金白口铸铁组织和性能的影响。结果表明:钨合金白口铸铁经钾、钠处理后,共晶碳化物由网状分布变为团块状甚至团球状分布,碳化物明显细化,分布均匀性增大,分析了共晶碳化物团球化的机理。碳化物形态的改善,导致钨合金白口铸铁的冲击韧性和抗冲击磨损能力明显提高。     

低合金白口铸铁共晶碳化物团球化工艺的研究

低合金白口铸铁是一种耐磨性能优良的铸铁材料,但其组织中共晶碳化物呈连续网状分布,削弱了基体的连续性,导致铸铁脆性过大。我们探讨了复合变质处理和热变形处理对共晶碳化物团球化的影响,同时还研究了共晶碳化物团球化对低合金白口铸铁机械性能和耐磨性的影响,结果表明,共晶碳化物团球化有利于白口铸铁韧性和耐磨性的大幅度提高。     

耐磨高铬白口铸铁

耐磨高铬铸铁的耐磨性取决于共晶碳化物和金属基体。碳化物的数量、形态和组织结构直接影响到耐磨性和韧性。而碳化物和金属基体首先是由其化学成份决定的,所以必须合理设计其化学元素的含量。1.成份设计1.1 铬和碳含量铬和碳是耐磨高铬铸铁的最主要成份,它们的作用是在铸铁内生成(FeCr)7 C 3,根据 Fe—Cr—C 系相图一般所应用的高铬铸铁均处于奥氏体相区,其共晶组织为奥氏体和 M7C3,因为铁素体太软不能硬化故应避免产生铁素体相,M3 C 和过量初生 M7 C3时脆性太大故也不希望。     

钼含量对高铬铸铁堆焊层组织及耐磨性的影响

高铬铸铁堆焊层因其较高的耐磨性而广泛应用于各种大型工业设备的内部衬板,研究发现Mo系碳化物可为初生碳化物的生成提供形核点从而细化组织,但Mo元素除了提供形核点外是否对组织存在别的作用仍尚待研究。为了研究Mo含量对高铬铸铁堆焊层组织与性能的影响,设计了一种含Mo超高碳高铬堆焊耐磨板,利用XRD、SEM分析了Mo元素对堆焊层组织、相组成以及磨损后堆焊层表面和纵截面的影响,利用EDS分析了元素在各相中的分配情况,并进一步利用硬度和干砂磨料磨损试验,研究了Mo合金化对高铬高碳堆焊层硬度和耐磨性的影响。结果表明,Fe-Cr-Mo-C合金堆焊层组织主要由γ相、M₇C₃(M=Fe、Cr)组成。随着Mo含量的提高,堆焊层内初生碳化物含量降低,奥氏体含量增加,单个初生碳化物尺寸先减小后增大;初生碳化物硬度增加,堆焊层宏观硬度先增加后降低;磨损后初生碳化物截断裂纹减少,剥落逐渐减少,其中30Mo试样出现了共晶碳化物的剥落。加入0.13%Mo后磨损失重减少了13.6%,加入0.30%Mo后磨损失重增加了20.0%。这是因为Mo原子的加入会提高初生碳化物的硬度,但是...     

轧钢轧辊中的溶质浓度与碳化物形成

选择碳化物及其形成可控制轧钢轧辊的质量和服役寿命，因此，研究了高速钢型铸铁和M硬铸铁凝固过程中石墨和碳化物的形成和显微偏析，高速钢型铸铁的结晶过程顺序为初生奥氏体（γ），γ＋MC和γ＋M2C共晶。另一方面，在Ni硬铸铁中，无论含强碳化物形成元素，如Cr，通过控制Ni和si的成分，在形成初生γ和γ＋M3C共晶后，结晶出共晶石墨片，当γ＋碳化物共晶生长时，根据残余液体和共晶体之间的分配系数，溶质元素在共晶体的残余液体中或富集或贫乏。可对两种铸铁用Scheil—Guhirer公式和计算的相图来评价凝固过程中碳化物形成元素成分的变化，利用这些参数预计石墨形成倾向性及熔融Ni冷硬铸铁中C的溶解彦极限。     

高综合性能亚共晶高铬铸铁的烧结制备

以气雾化粉末为原料,采用液相烧结(LPS)制备亚共晶高铬铸铁(HCCIs),系统研究烧结工艺参数对致密化行为、显微组织演变和力学性能的影响规律。研究结果表明,采用LPS可以获得相对致密度达99%以上的制品,但合适的烧结温度范围很窄;XRD分析表明烧结亚共晶高铬铸铁由M7C3型碳化物、马氏体和奥氏体构成;金相分析显示烧结样晶粒细小,碳化物为一次晶杆状,且分布均匀。随烧结温度升高和保温时间延长,晶粒和碳化物均逐步粗化,其中温度的影响更加显著;而强度和冲击韧性则呈现先升高后降低的变化规律。优化的烧结工艺下高铬铸铁的力学性能为：硬度HRC65,抗弯强度1199 MPa,冲击韧性4.6 J/cm2。并提出了一个烧结高铬铸铁中碳化物形态演变的生长模型。     

Influence of Electric-Current Pulse Treatment on the Formation of Regular Eutectic Morphology in an Al-Si Eutectic Alloy

This article describes the influence of an electric current pulse (ECP) on the microstructure of an Al-Si eutectic alloy during directional solidification. Experimental results demonstrate that the ECP has a significant effect on the microstructure of the directionally solidified Al-Si eutectic alloy. Application of ECP can increase the number and area percentage of the complex regular structure (CRS). Furthermore, the area of single CRS increases first and then declines with the increase of the ECP density. Analysis results suggest that the change of the CRS is a result of the forced convection caused by Lorentz force and change of temperature gradient induced by the ECP. The growth process of the CRS is discussed.     

Correlation of microstructure with the wear resistance and fracture toughness of duocast materials composed of high-chromium white cast iron and low-chromium steel

The objective of this study is to investigate the correlation of microstructure with wear resistance and fracture toughness in duocast materials that consisted of a high-chromium white cast iron and a low-chromium steel as the wear-resistant and ductile parts, respectively. Different shapes, sizes, volume fractions, and distributions of M₇C₃ carbides were employed in the wear-resistant part by changing the amount of chromium and molybdenum. In the alloys containing a large amount of chromium, a number of large hexagonal-shaped primary carbides and fine eutectic carbides were formed. These large primary carbides were so hard and brittle that they easily fractured or fell off from the matrix, thereby deteriorating the wear resistance and fracture toughness. In the alloys containing a smaller amount of chromium, however, a network structure of eutectic carbides having a lower hardness than the primary carbides was developed well along solidification cell boundaries and led to the improvement of both wear resistance and toughness. The addition of molybdenum also helped enhance the wear resistance by forming additional M₂C carbides without losing the fracture toughness. Under the duocasting conditions used in the present study, the appropriate compositions for wear resistance and fracture toughness were 17 to 18 pct chromium and 2 to 3 pct molybdenum.     

Solidification and solid-state transformation mechanisms in Si alloyed high-chromium white cast irons

Chromium white cast irons are widely used in environments where severe abrasion resistance is a dominant requirement. To improve the wear resistance of these commercially important irons, the United States Bureau of Mines and CSIRO Australia are studying their solidification and solid-state transformation kinetics. A ternary Fe-Cr-C iron with 17.8 wt pct (pct) Cr and 3.0 pct C was compared with commercially available irons of similar Cr and C contents with Si contents between 1.6 and 2.2 pct. The irons were solidified and cooled at rates of 0.03 and 0.17 K · s^-1 to 873 K. Differential thermal analysis (DTA) showed that Si depresses the eutectic reaction temperature and suggests that is has no effect upon the volume of eutectic carbides formed during solidification. Microprobe analysis revealed that austenite dendrites within the Si alloyed irons cooled at 0.03 and 0.17 K·s^-1 had C and Cr contents that were lower than those of dendrites within the ternary alloy cooled at the same cooling rate and a Si alloyed iron that was water quenched from the eutectic temperature. These lower values were shown by image analysis to be the result of both solid-state growth (coarsening) of the eutectic carbides and some secondary carbide formation. Hardness measurements in the as-cast condition and after soaking in liquid nitrogen suggest an increase in the martensite start temperature as the Si content was increased. It is concluded that Si’s effect on increasing the size and volume fraction of eutectic carbides and increasing the matrix hardness should lead to improved wear resistance over regular high-chromium white cast irons.     

Influence of industrial tempering on the composition of complex cast iron

The chemical composition of the metallic base and carbides in complex cast iron is investigated in the laboratory. The iron is studied before and after heat treatment in industrial conditions. The redistribution of elements in the metallic base and in eutectic and secondary carbides is determined.     

稀土变质铸铁中石墨—奥氏体共晶的生长方式

用Ｂｒｉｄｇｍ ａｎ 定向凝固技术制取了稀土变质共晶铸铁不同石墨形态时的液－固平界面试样。观察结果表明,稀土变质铸铁共晶凝固过程中,石墨相不论形态如何均为领先相;石墨与奥氏体共晶有共生生长和离异生长两种生长方式。在共生生长情况下,奥氏体紧贴石墨片两侧协同生长,形成锯齿状的液－固界面结构;在离异生长情况下,石墨相单独在液相中析出并充分长大,随后被奥氏体包围,液－固界面形态主要取决于奥氏体－液相界面的稳定性。分析表明,稀土在石墨－液相界面的富集是导致石墨－奥氏体共晶离异生长的主要原因。     

高速钢M2中共晶碳化物M_2C的性质和形态

采用砂型和金属型铸造制备M2高速钢铸锭,研究了共晶碳化物M2C性质和形态随冷却速度的变化规律。结果表明,冷速加快,促进共晶M2C由平直片层状变为弯曲棒状,并使碳化物中合金元素含量降低,基体合金含量升高。不同形态M2C热分解性质差异较为明显:片层状M2C分解产生的MC多分布在碳化物内部,形成大量M6C+MC复合碳化物;棒状M2C起始分解温度低于片层状M2C,MC多形成于碳化物和基体界面处,高温加热时易与M6C分离,使复合碳化物数量减少。共晶M2C热分解性质的差异与冷速不同引起的合金元素分布变化有关。     

Effect of RE Modification and Heat Treatment on Impact Fatigue Property of a Wear Resistant White Cast Iron

Withhigherhardnessandbetterwearresistance ,whitecastironscanbeusedaswearresistantpartsinmanyfields .Inpractice ,thewearresistantpartsareoftenrequiredtobesubjectedtogrindingofabrasivesandrepeatedimpactaction .Therefore ,fatiguecracksareliabletobegeneratedo…     

变质处理高碳高速钢导板的研究

导板是线材轧机的关键备件，要求有优良的耐磨性，抗断裂性，抗粘钢性和热冲击抗力，常用高镍镍钢导板和高铬铸铁导板满足不了上述要求，使用寿命短，更换频繁，降低了轧机作业率，增大了工人劳动强度，高速钢具有硬度高，红硬性好和耐磨性好等特点，但铸造高速钢脆性大，通过调整高速钢成分和采用RE－Mg-Ti复合变质处理，可改变共晶碳化物的形态和分布，使高速钢冲击韧性大幅度提高，变质处理高速钢导板使用中不粘钢，不断裂，耐磨性明显优于普通导板。     

Eutectic growth: A modification of the Jackson and Hunt theory

The Jackson and Hunt theory of eutectic growth is modified in order to get a better understanding of the physical mechanisms driving the solidification process. The density difference between the eutectic phases is taken into account when calculating the diffusion field, and the isothermal interface coupling condition is replaced by an equilibrium criterion for the three-phase junction. Although the problem can be solved in the general case, a simpler solution is derived for the case of nearly isothermal interface, which differs from that of Jackson and Hunt only by a corrective factor reflecting the density differences between the phases, the correction being quite large in the case of cast iron. The volume fractions of the eutectic phases are shown to be adjusted by the movement of the three-phase junctions. The boundary layer composition, which depends on this mechanism, is shown to be responsible for the well-known occurrence of austenite halos surrounding the primary graphites in cast iron. The curvature undercooling is written as the ratio of the volumetric interface energy contained in the eutectic microstructure to an average volumetric entropy of melting, which allows a quantitative evaluation of the effect of an anistropy in the α/β interface energy. Reliable values of the relevant physical constants are provided for several important eutectic alloys.     

喷射成形含铌M3型高速钢的组织和耐磨性

采用喷射成形技术制备了M3型高速钢和以Nb替代V的M3型高速钢.利用扫描电镜、X射线衍射、差示扫描量热仪和金相显微镜研究了Nb对M3型高速钢组织的影响.喷射成形能有效消除宏观偏析,细化组织.以Nb代V,提高了MC型碳化物开始析出温度,大量MC相先于共晶反应析出,呈独立的近球形分布于晶界,同时其尺寸减小.由于消耗大量C,抑制了共晶反应,M₂C片层数量减少且厚度变薄,其在热变形过程中更易于分解,进一步增加了组织均匀性.低温低载荷时含铌的M3型高速钢抗磨损性能显著优于M3高速钢,温度升高到500℃时磨损机制逐渐以氧化磨损为主,两合金的抗磨损性能差距减小,主要原因是大量呈弥散球形分布的含铌MC型碳化物能有效提高高速钢的磨粒磨损抗性,而其对抗氧化性能并无明显作用.