Effects of TIG Surface Melting and Chromium Surface Alloying on Microstructure, Hardness and Wear Resistance of ADI

Microhardness and wear resistance of different rnicrostructures formed by TIG （tungsten inert gas） surface melting and chromium surface alloying （using ferrochromium） of ADI （austempered ductile iron） were studied. Surface melting resulted in the formation of a ledeburitic structure in the melted zone, and this structure has a hardness up to 896 HV as compared to 360 HV in that of ADI. Moreover, chromium surface alloying resulted in the formation of different structures including： （1） a hypereutectic structure consisting of primary （Fe,Cr）7C3 carbides and a eutectic matrix of transformed austenite （into martensite and retained austenite）, as also （Fe,Cr）7C3 carbides, with a hardness of 1078 HV; （2） a hypoeutectic structure consisting of the same eutectic along with transformed primary austenite, with a hardness of 755 HV; and （3） a ledeburitic structure with an acicular morphology and a hardness of 896 HV. The results also indicated that surface melting reduced the wear rate of the ADI by approximately 37%. Also, chromium surface alloying yielded a superior wear behavior and reduced the wear rate of the treated specimens by about 38% and 70%, depending on the structures formed.     

Influence of Rare Earth Elements on Microstructure and Mechanical Properties of Cast High-Speed Steel Rolls

The influence of rare earth （RE） elements on the solidification process and eutectic transformation and mechanical properties of the high-V type cast, high-speed steel roll was studied. Test materials with different RE additions were prepared on a horizontal centrifugal casting machine. The solidification process, eutectic structure transformation, carbide morphology, and the elements present, were all investigated by means of differential scanning calorimetry （DSC） and scanning electron microscopy energy dispersive spectrometry （SEM-EDS）. The energy produced by crack initiation and crack extension was analyzed using a digital impact test machine. It was found that rare earth elements increased the tensile strength of the steel by inducing crystallization of earlier eutectic γ-Fe during the solidification process, which in turn increased the solidification temperature and thinned the dendritic grains. Rare earth elements with large atomic radius changed the lattice parameters of the MC carbide by forming rare earth carbides. This had the effect of dispersing longpole M C carbides to provide carbide grains, thereby, reducing the formation of the gross carbide and making more V available, to increase the secondary hardening process and improve the hardness level. The presence of rare earth elements in the steel raised the impact toughness by changing the mechanism of MC carbide formation, thereby increasing the crack initiation energy.     

Influence of Trace Alloying Elements on Corrosive Resistance of Cast Stainless Steel

18-8type austenitic stainless steel is a kind ofanti-corrosion material applied extensively.In mostcases,it must be solution-heattreated to gain goodmechanical properties and corrosive resistance.Butfor some castings with complex shape,such as thepropelle…     

Microstructure and Wear Resistance of N-Doped TiO2 Coatings Grown on Stainless Steel by Plasma Surface Alloying Technology

 N-doped TiO2 (N-TiO2) coatings were obtained by oxidation of titanium nitride coatings, which were prepared by the plasma surface alloying technique on stainless steel (SS). The microstructure of N-TiO2 coatings was characterized by X-ray diffraction (XRD), glow discharge optical emission spectrometry (GDOES), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), respectively. Ball-on-disc sliding wear was applied to test and compare the tribological behaviors of the coatings and substrate. XRD patterns showed that anatase type TiO2 existed in the coatings after oxidation. GDOES showed that the resultant coatings had a layered structure, comprising of N-TiO2 layer at the top and a diffusion-type interface. Such a hybrid coatings system showed good adhesion with the substrate. According to XPS, residual N atoms partially occupied O atom sites in the TiO2 lattice. Uniform, continuous and compact coatings were observed by SEM images of coatings after oxidation. Under a load of 7.6 N, the coefficient of friction was in the range of 0.27-0.38 for the N-TiO2/Al2O3 systems and the wear rate of the coatings was only one-fourteenth of that for untreated 316L SS. N-TiO2 coatings displayed much better wear resistance and antifriction performance than SS substrate.     

Effect of Alloying Elements on Thermal Wear of Cast Hot-Forging Die Steels

The effect of main alloying elements on thermal wear of cast hot-forging die steels was studied. The wear mechanism was discussed. The results show that alloying elements have significant influences on the thermal wear of cast hot-forging die steels. The wear rates decrease with an increase in chromium content from 3% to 4% and molybdenum content from 2% to 3%, respectively. With further increase of chromium and molybdenum contents, chromium slightly reduces the wear resistance and molybdenum severely deteriorates the wear resistance with high wear rate. Lower vanadium/carbon ratio （1.5-2.5） leads to a lower wear resistance with higher wear rate. With an increase in vanadium/carbon ratio, the wear resistance of the cast steel substantially increases. When vanadium/carbon ratio is 3, the wear rate reaches the lowest value. The predominant mechanism of thermal wear of cast hot-forging die steels are oxidation wear and fatigue delamination. The Fe2O3 and Fe3O4 or lumps of brittle wear debris are formed on the wear surface.     

Microstructure, Impact Fatigue Resistance and Impact Wear Resistance of Wear Resistant Low Cr-Si Cast Iron

Wear parts are greatly consumed in metallurgi-cal industry,fire power stations and cement works.The consumption of grinding balls and lining platesmay be the greatestunder such impactabrasive wearconditions.In China,annual consumption of ballsand plates is close to 1× 10 6 t.Therefore,develop-ing a new material for impact wear conditions is veryimportant.　　 The martensitic high chromium cast iron(WCr= 15 % ) is widely studied and used as wear resis-tance material[1— 8] ,especially for ma…     

稀土对低合金耐磨铸钢组织和性能的影响

采用扫描电镜分析,硬度测试和摩擦性能测试等手段,研究了稀土对低合金耐磨铸钢组织和性能的影响。结果表明,在低合金耐磨铸钢中添加0.15%稀土,可细化合金铸态组织,增加铸态组织中的铁素体数量,减少珠光体数量,同时可细化热处理后合金的贝氏体组织,使铁素体形态和大小分布均匀,马氏体数量减少。添加稀土后可使铸态合金硬度提高9.4%,摩擦系数由0.136 9减小为0.081 9。     

Effect of Alloying Method on Microstructure and Wear Resistance of Fe-Cr-V-B Based Alloy

The microstructure and wear behavior of Fe-Cr-V-B based alloy was investigated.Each of the specimens was characterized by metallographic techniques and hardness test.Phase analysis of alloy was performed by X-ray diffraction(XRD),scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).The results showed that the microstructure of Fe-Cr-V-B based as-cast alloy containing 8.6mass% V was composed ofα-(Fe,Cr)solid solution,VC carbides,and V_3B_4 borides,whereas the as-cast alloy containing 24.8mass% Cr was composed ofα-(Fe,Cr)solid solution and V_3B_4borides;the eutectic V_3B_4 borides mainly comprise M2B-type borides(M presents Fe and Cr).The existence of a large amount of V atoms affects the growth pattern of eutectic borides,which mainly display rod-like and grainy structure.The wear behavior of the experimental alloy has been investigated using pin-on-disk type friction and wear apparatus.The comparison of experimental results indicated that the relative wear resistance of the alloy containing 8.6mass% V after destabilization heat treatment in a conventional furnace at 1 373 K for 2hwas about six times higher than that of the high chromium(19mass%)cast iron.     

合金元素对铁素体不锈钢抗腐蚀性能的影响

通过研究Cu、Mo、Nb等合金元素对铁素体不锈钢抗腐蚀性能的影响,表明了在一定腐蚀荆条件下Cu、Mo能提高铁素体不锈钢的抗点腐蚀性能,Nb可以提高铁素体不锈钢的抗晶间腐蚀和抗大气腐蚀的性能,为开发新的铁素体不锈钢钢种提供科学依据。     

合金元素对钢筋耐腐蚀性能和机械性能的影响

通过正交试验，研究了成分为(％)：0．10～0．12C，0～0．78Cr，0．32～0．67Ni，0～0．52Mo，0～0．06V，0．30～0．36Cu低碳高强度钢筋的耐蚀性和力学性能。结果表明，Cr能显著提高钢筋的耐氯盐腐蚀性，含0．53％～0．78％Cr、0．32％～0．35％Ni的钢筋具有良好的耐蚀性；加Mo，V可显著提高钢筋的强度。     

Effect of Microstructure on Impact Fatigue Resistance and Impact Wear Resistance of Medium Cr-Si Cast Iron

 A great amount of iron grinding balls in tube mills have been consumed. Under this impact abrasive wear working condition, the failure of wear resistant alloying white irons grinding balls is mainly caused by fatigue spalling. The impact wear resistance of martensitic high chromium cast iron (Cr of 15%) is not high sometimes, but its cost is not low. Thus, medium Cr Si wear resistant cast iron is recommended. The influence of the iron on impact fatigue resistance and impact wear resistance is pronounced. Ball on ball impact fatigue test and high stress impact wear test of the grinding balls have been carried out. The results show that the impact fatigue resistance (IFR) and impact wear resistance (IWR) of medium Cr Si cast iron are superior to those of martensitic high chromium cast iron (Cr of 15%). The main reasons are that (1) the stress in medium Cr Si cast iron is released in the as cast state; (2) the matrix is fine pearlite with better toughness and plasticity; (3) the pearlite is more stable compared with a retained austenite under repeated impact load and less phase transformation can take place; (4) high silicon content improves the morphology of eutectic carbide; (5) there is no secondary carbide which results in less crack sources. All these factors are beneficial to improvement of impact fatigue spalling resistance. The eutectic carbide M7C3 is the main constituent to resist wear.     

Effect of Microstructure on Impact Wear Resistance Impact Fatigue Resistance and of Medium Cr-Si Cast Iron

A great amount of iron grinding balls in tube mills have been consumed. Under this impact abrasive wear working condition, the failure of wear resistant alloying white irons grinding balls is mainly caused by fatigue spalling. The impact wear resistance of martensitic high chromium cast iron （Cr of 15%） is not high sometimes, but its cost is not low. Thus, medium Cr-Si wear resistant cast iron is recommended. The influence of the iron on impact fatigue resistance and impact wear resistance is pronounced. Ball-on-ball impact fatigue test and high stress impact wear test of the grinding balls have been carried out. The results show that the impact fatigue resistance （IFR） and impact wear resistance （IWR） of medium Cr-Si cast iron are superior to those of martensitic high chromium cast iron （Cr of 15%）. The main reasons are that （1） the stress in medium Cr-Si cast iron is released in the as-cast state; （2） the matrix is fine pearlite with better toughness and plasticity; （3） the pearlite is more stable compared with a retained austenite under repeated impact load and less phase transformation can take place; （4） high silicon content im- proves the morphology of eutectic carbide; （5） there is no seeondary carbide which results in less crack sources. All these factors are beneficial to improvement of impact fatigue spalling resistance. The eutectic carbide M7C3 is the main constituent to resist wear.     

Effects of Alloying Elements on Hydrogen Adsorption Properties on Zirconium Surface

Metallurgical and Materials Transactions A - We theoretically investigated the effects of alloying elements Sn, Nb, Cr, Mo, Fe, Ni, and Sb, which can improve the corrosion resistance of zirconium,...     

Nb、Mo元素对X70级管线钢组织和硬度的影响

 在Formastor-Ⅱ热膨胀相变仪上,测定了3种不同化学成分的试验钢在不同冷却速度下连续冷却时的热膨胀曲线,采用热膨胀法并结合金相-硬度法绘制了试验钢连续冷却转变曲线（CCT曲线）,研究了冷却速度和化学成分对组织及硬度的影响。结果表明：添加Mo元素和高铌含量的试验钢均能在较低的冷却速度和较大的冷速范围内获得针状铁素体组织,并且试验钢的硬度随冷却速度的增大而增加。     

硅对贝氏体铸钢高应力冲击磨损性能的影响

研究了不同硅含量（0．7％－2．4％,质量分数,下同）贝氏体铸钢的抗高应力磨损性能和失效机制。结果表明：高效硅贝氏体铸钢的耐磨性能较低硅钢显提高,其磨损失重约是低硅贝氏体铸钢的1．2,这是因为硅使氏体铸钢在高应力冲击磨损下表现出不同的失效机制。低硅（0．7％）贝氏体铸钢由于韧性低、组织结构粗大及树枝晶的微区成分偏析,故材料抵抗冲击的能力很低,常在表面还未形成强烈变形层（白层）甚至变形层时,就在变形层和材料基体内产生裂纹并扩展,故低硅贝氏体铸钢的失铲方式为变形层和基体剥落机制。而硅含量为1．65－2．4％的高硅贝氏体铸钢,因脆性的渗碳体被韧性的残余奥氏体所代替,钢的韧性显提高,失效方式表现为白层的剥落机制。