烧结Cr15高铬铸铁组织与性能的研究

为研发耐磨性能优良、成本相对低廉的高铬铸铁,本文分别以亚共晶、过共晶的水雾化Cr15高铬铸铁粉末为原料,采用超固相线液相烧结工艺制备了烧结高铬铸铁(SHCCI),并对其显微组织、力学性能和冲击磨粒磨损工况下的耐磨性能进行对比研究。结果表明,烧结高铬铸铁主要由M7C3碳化物、马氏体和奥氏体组成;在亚共晶烧结高铬铸铁中,通过电解腐蚀萃取的M7C3碳化物三维形貌呈珊瑚状,沿晶界均匀分布,材料抗冲击耐磨性能优良;在过共晶烧结高铬铸铁中,优先形成的初生碳化物可能成为共晶碳化物的生长基底,形成核-壳结构的M7C3碳化物,沿晶界相互连接呈网状,严重割裂基体。亚共晶、过共晶烧结高铬铸铁的力学性能分别为:硬度HRC63.9、HRC64.3,冲击韧性7.92、3.04 J/cm^2,抗弯强度2112.65、1624.87 MPa。     

Reinforcement of Hadfield steel matrix by oriented high‐chromium cast iron bars

To attain a wear‐resistant material compatible with high hardness and high toughness, Hadfield steel matrix was reinforced by oriented high chromium cast iron bars, through inserting high chromium alloys flux‐cored welding wires into Hadfield steel melt at 1500 ± 10 °C. The obtained composites were investigated by XRD, SEM, micro‐hardness, three‐body abrasion wear and impact toughness testers. The results show that the alloy powders inside the flux‐cored welding wires can be melted by the heat capacity of Hadfield steel melt and in situ solidified into high chromium cast iron bar reinforcements tightly embedded in the matrix. The micro‐hardness of reinforcements of the water‐quenched composite is about four times higher than that of the matrix. The impact toughness of the water‐quenched composite is higher than that of the as‐cast composite and lower than that of Hadfield steel, and its fracture mechanism is very complicated and refers to brittle and ductile mixture fracture mode. The excellent impact toughness and better wear resistance of the water‐quenched composite are attributed to combine fully the advantages and avoid the drawbacks of both Hadfield steel and high chromium cast iron. Additionally, in industrial application, the pulverizer plate produced by this composite, has also better wear resistance compared to the reference Hadfield steel pulverizer plate.     

B4C包覆ZTA颗粒增强铁基复合材料制备与性能

ZTA (ZrO₂增韧Al₂O₃)陶瓷颗粒表面包覆B₄C微粉,将其制备成蜂窝状结构陶瓷预制体。采用传统重力浇注工艺将陶瓷预制体与熔融的高铬铸铁(HCCI)金属溶液进行复合,获得ZTA陶瓷颗粒增强高铬铸铁基复合材料。对复合材料中ZTA陶瓷颗粒增强相与高铬铸铁基体之间的界面及复合材料的耐磨料磨损性能进行了研究。结果表明,ZTA陶瓷颗粒与高铬铸铁界面结合处形成了明显的过渡区域,界面过渡区域的存在提高了陶瓷颗粒与金属基体的结合,从而提升了复合材料的整体稳定性能。同时,三体磨料磨损试验表明该复合材料的耐磨料磨损性能是高铬铸铁的3.5倍左右。     

高铬铸铁衬板中两种碳化物形态对耐磨性的影响

用微观组织分析、杆盘式磨损、湿磨法磨损和冲击韧性等试验手段,对高铬铸铁衬板的显微组织、力学性能和耐磨性进行了试验分析。结果表明,高铬铸铁中具有定向排列且垂直于磨损表面的碳化物形态与马氏体基体的适当配合,可提高衬板的耐磨性。     

Effect of multicomponent modifier on microstructure and mechanical properties of high Ni–Cr–Mo cast iron

Abstract

The microstructure and mechanical properties of high Ni–Cr–Mo indefinite chilled cast iron with the addition of a newly developed multicomponent modifier consisting of mixed rare earths, Si–Ca alloy and Bi–Sb alloy have been investigated through optical microscopy, X-ray diffraction and scanning electron microscopy, along with hardness, impact toughness and wear resistance measurements. After the addition of the modifier, the grain sizes of the primary austenite and eutectic carbides are found to be greatly refined, and the typically highly continuous net-like carbides become less interconnected but rather appear more blocky shaped. Such microstructure changes lead to mechanical property improvement in the cast specimen, with its hardness increased from 43 to 50 HRC, impact toughness from 6·3 to 7·8 J cm^?2 and ?20% increase in abrasive wear resistance.     

The influence of vanadium on fracture toughness and abrasion resistance in high chromium white cast irons

The influence of vanadium on wear resistance under low-stress conditions and on the dynamic fracture toughness of high chromium white cast iron was examined in both the ascast condition and after heat treatment at 500 °C. A vanadium content varying from 0.12 to 4.73% was added to a basic Fe-C-Cr alloy containing 2.9 or 19% Cr. By increasing the content of vanadium in the alloy, the structure became finer, i.e. the spacing between austenite dendrite arms and the size of massive M₇C₃ carbides was reduced. The distance between carbide particles was also reduced, while the volume fraction of eutectic M₇C₃ and V₆C₅ carbides increased. The morphology of eutectic colonies also changed. In addition, the amount of very fine M₂₃C₆ carbide particles precipitated in austenite and the degree of martensitic transformation depended on the content of vanadium in the alloy. Because this strong carbide-forming element changed the microstructure characteristics of high chromium white iron, it was expected to influence wear resistance and fracture toughness. By adding 1.19% vanadium, toughness was expected to improve by approximately 20% and wear resistance by 10%. The higher fracture toughness was attributed to strain-induced strengthening during fracture, and thereby an additional increment of energy, since very fine secondary carbide particles were present in a mainly austenitic matrix. An Fe-C-Cr-V alloy containing 3.28% V showed the highest abrasion resistance, 27% higher than a basic Fe-C-Cr alloy. A higher carbide phase volume fraction, a finer and more uniform structure, a smaller distance between M₇C₃ carbide particles and a change in the morphology of eutectic colonies were primarily responsible for improving wear resistance.     

Effect of melt treatment on microstructure and impact properties of Al-7Si and Al-7Si-2.5Cu cast alloys

The microstructures and impact toughness of Al-7Si and Al-7Si-2.5Cu cast alloys were studied after various melt treatments like grain refinement and modification. The results indicate that combined grain refined and modified Al-7Si-2.5Cu alloys have microstructures consisting of uniformly distributed α-Al grains, interdendritic network of fine eutectic silicon and fine CuAl₂ particles in the interdendritic region. These alloys exhibited improved impact toughness in as cast condition when compared to those treated by individual addition of grain refiner or modifier. The improved impact toughness of Al-7Si-2.5Cu alloys are related to breakage of the large aluminum grains and uniform distribution of eutectic silicon and fine CuAl₂ particles in the interdendritic region resulting from combined refinement and modification. This paper attempts to investigate the influence of microstructural changes in the Al-7Si and Al-7Si-2.5Cu cast alloys by grain refinement, modification and combined action of both on the impact toughness.     

Matrix microstructure effect on the abrasion wear resistance of high-chromium white cast iron

The two-body abrasion resistance of high-chromium white cast iron was investigated as a function of cast iron microstructure. Different microstructures were obtained by means of heat treatment. The chromium and carbon content were chosen in order to have different matrix microstructures (austenitic, martensitic and ferritic) with the same amount of eutectic carbide (M₇C₃). The results show that the cast iron with an austenitic matrix has the best wear resistance. The good wear resistance of this material is due to strong work hardening of the austenitic matrix resulting in a hardness which exceeds that of other structures. The effect of abrasive paper deterioration on abrasion has also been investigated.     

Microstructure and mechanical properties of Hadfield steel matrix composite reinforced with oriented high-chromium cast iron bars

To obtain a compatible material of high hardness and high toughness, Hadfield steel matrix was reinforced by oriented high-chromium cast iron bars. The mechanical behaviors of the as-cast and water-quenched composites were comparatively studied with a Hadfield steel substrate. The experimental results showed that the alloy powders inside the flux-cored welding wires could be melted by the heat capacity of Hadfield steel melt and became high-chromium cast iron bars. The impact toughness of the water-quenched composite was higher than that of the as-cast composite and lower than that of the Hadfield steel. The wear rate of the water-quenched composite was 1.23 mg/h m² at 0.3 kg and 2.93 mg/h m² at 1.2 kg, which was lower compared with those of the as-cast composite and Hadfield steel. The impact toughness and wear resistance of the water-quenched composite were related not only to the combining actions of the Hadfield steel matrix and high-chromium cast iron bars but also to the effect of heat treatment. The wear behavior of the water-quenched composite was industrially tested as pulverizer plate.     

Investigations on the Cast Boron Steel Guide Roller and Its Application in Steel Wire-Rod Mill

A new type of abrasion-resistant cast boron steel was developed based on the service conditions of the guide roller in the high-speed steel wire-rod mill. The lath martensite was its matrix and the broken Fe₂B and dispersive distributed TiB₂ were its wear resistant skeleton. The tensile strength, hardness, and impact toughness of cast boron steel quenched at 1000°C excel 750 MPa, 54 HRC, 14 J/cm², respectively. The guide roller made of this steel has high strength and wear resistance and excellent thermal fatigue resistance and it is reliable to use in the high-speed steel wire-rod mill. Its service life is 1.133 times longer than that of cast high chromium nickel alloy steel and corresponding to that of the sintered-carbide.     

Wear behavior of TiB<Subscript>2</Subscript> inoculated 20Cr–3Mo–4C high chromium white cast irons

FeTi, B₂O₃, Al, and FeW particulates, approximately 40–60 μm in size, were mixed in stoichiometric ratio and sintered at 1,200 °C. The sintered particulates were added as 5 wt% to molten high chromium white cast iron over 50 C-deg above the melting temperature, and stirred at 1,000 rpm. The samples were investigated in three groups: (1) high Cr white cast iron inoculated by the particulates sintered from Al–FeTi–B₂O₃ particulates; (2) high Cr white cast iron inoculated by the sintered particulates derived from Al–FeTi, B₂O₃, and FeW particulates; and (3) specimens of the second group that were subsequently homogenized. The microhardness of ceramic particulates was measured as 2,800–3,400 HV₁₀. The effect of sintered particulate volume fraction on the abrasive wear resistance of the high chromium white cast iron was determined. The wear resistance and hardness of the composites improved significantly as a result of particulate inoculation. The application of the homogenization heat treatment to the inoculated samples produced a microstructure having homogeneously distributed particulates.     

粉末烧结法和铸造法制备ZrO2增韧Al2O3陶瓷颗粒增强高铬铸铁基复合材料及其耐磨性能

将粒径为1~2 mm的ZrO₂增韧Al₂O₃陶瓷颗粒(ZTA_p)、高铬合金粉末和黏结剂混合真空烧结制备蜂窝状预制体,再浇注高铬铸铁液制备出ZTA_p增强高铬铸铁基复合材料。采用SEM、EDS、XRD分析复合材料的界面微观结构和物相组成,通过三体磨损试验评价复合材料的耐磨性能。结果表明,烧结高铬铸铁基体在铸造过程中发生重熔,与铸造高铬铸铁基体呈冶金结合,ZTA_p与金属基体界面结合致密,无裂纹、气孔等缺陷。复合材料三体耐磨性能达到高铬铸铁的3倍以上。将该复合材料应用于制备磨辊件,经过5 000 h服役,柱状区和复合区在磨辊半径方向上的磨损量分别为8.2 mm、5.9 mm,预计寿命可达到高铬铸铁磨辊的2倍以上。      

Rotating cylinder manufacturing method and investment casting of SiCp/AZ91HP magnesium composites

Abstract

This paper describes the rotating cylinder method for manufacturing, and investment casting for forming, composite slurry. Microstructural features, such as SiC particle distribution and grain refinement of the as cast composites, were investigated. Also the effect of SiC particle fraction and size, and process parameters on the microstructure and the mechanical properties are discussed. Attempts were made to evaluate the thermal stability of oxides against molten AZ91HP magnesium alloy. The oxides examined included CaO, CaZrO₃, and silica bonded Al₂O₃ and zircon flour. Finally, the tensile properties, hardness, and wear resistance of the as cast composites were evaluated and the results are compared with those of the as cast alloy.     

A Study of Modification of M2 Cast High Speed Steel

M2 cast high speed steel was inoculated by addition of rare earth(RE)‐Al‐N, network eutectic carbides were eliminated, matrix structures were refined and the segregation of tungsten and molybdenum elements were relieved. In the condition that the hardness did not decrease, impact toughness obviously increased. Quenching at 1180 °C and three‐times tempering at 560 °C, the hardness of M2 cast high speed steel kept 65~66HRC, impact toughness reached 21.3J/cm². Modified M2 cast high speed steel had excellent thermal fatigue resistance and high temperature wear resistance. Roll made in modified M2 cast high speed steel had excellent service effect using in slit rolling mill stand of hot rolling bar mill.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

On the structure and properties of wear- and corrosion-resistant nickel-chromium- tungsten-carbon-(silicon) alloys

In some applications, for chemical and physical reasons hard nickel-based alloys have to be used instead of cobalt-based alloys but boron must be avoided. The nickel-chromium-tungsten-carbon system with and without silicon was therefore studied in several concentration ranges at 1050°C with respect to structure, phase, hardness and corrosion and wear resistance. Alloys containing 2% carbon, 10% tungsten and more than 10% chromium are composed of a nickel solid solution and an M₇C₃ carbide in both cast and homogenized (1050°C, 180 h) conditions. On increasing the tungsten content up to 20% the M₂C carbide becomes dominant, and this is associated with a remarkable increase in the hardness of the alloys. Additions of 2% silicon do not change the M₇C₃ and M₂C carbides present. In some cases a carbon-stabilized silicide M₅Si(C) was observed. Silicon additions decrease the liquidus temperature range relatively little, but they affect particle shape and size and the grain size distribution. The relation of various chromium, tungsten and silicon contents to corrosion and wear resistance was studied. The corrosion resistance depends on the chromium content of the nickel solid solution but also on carbide formation (tungsten and carbon content). The silicon content of the nickel solid solution is important too.Because their liquidus temperature is close to 1300°C the alloys cannot be used as self-fluxing and fusing powders for flame spraying but they can be sprayed by plasma torches and they can, of course, be welded.     

Modifying high Cr–Mn cast iron with boron and rare earth–Si alloy

Abstract

By modifying 13Cr–4Mn (wt-%) white cast iron with boron and rare earth (RE)–Si complex, the carbide morphology of the iron can be changed from interconnected, coarse clusters of rods into a parallel distribution of isolated, fine rods, and the impact toughness of the iron can reach 6–7 × 10⁴ J m^?2. In a pin wear test, the relative abrasion resistance of the iron is 1·01 and in a repeated impact abrasive wear test it is 0·95, in comparison with 15Cr–3Mo cast iron. Thus, it is stated that modifying high Cr–Mn cast iron with boron and RE–Si complex is very cost effective, and has almost the same abrasion resistance, when compared with 15Cr–3Mo cast iron.

MST/957     

Investigation of quenching effect on mechanical property and abrasive wear behaviour of high boron cast steel

Abstract

The effect of quenching temperature from 900 to 1050°C on the microstructures, mechanical properties and abrasion resistance of modified high born cast steel containing 0·3 wt-%C and 3·0 wt-%B was studied by optical microscopy, scanning electron microscopy, X-ray diffraction analysis, tensile tester, impact tester, hardness tester and abrasion tester. Quenching at 900°C resulted in structures containing a small amount of pearlite. The existence of pearlite led to poor hardness and wear resistance of modified high born cast steel. Quenching at temperatures between 900 and 950°C resulted in the decrease in pearlite and the increase in hardness and abrasion resistance in comparison with 900°C quenching. The metallic matrix all transformed into the martensite quenching at 1000°C; the modified high born cast steel had high hardness, tensile strength, impact toughness and excellent abrasion resistance. The hardness, tensile strength and impact toughness of modified high born cast steel had no obvious change quenching over 1000°C. The increase in quenching temperature also led to the transformation of boride from continuous shape to isolated shape and promoted the coarsening of boride.     

Gefüge und magnetische Eigenschaften von Chromgusseisen für Mahlkugeln

Microstructure and magnetic properties of white cast irons for grinding balls Many types of cast ferrous alloys are used for applications in the grinding, crushing, mineral‐handling and earthmoving industries. The finish grinding process for cement materials uses ball mills with differently sized grinding balls. This work deals with grinding balls of high chromium white cast irons with various chemical composition. Using certains thermal treatments, the influence of parameters of microstructure on abrasive and impact wear resistance has been studied. A special test system has been adapted for the assessment of the impact properties of these alloys. Examination of the carbides were performed using a transmission electron microscope. Additional microstructural examinations were made using the Scanning electron microscope. For a nondestructive inspection of the grinding balls, the possibilities of using the magnetic characteristics for determining the structural state and mechanical properties of white cast irons are analyzed. The results showed that the hardness and the dynamic fracture toughness are important for the combined impact‐abrasion resistance. It has been established that the microstructure has a decisive influence on the magnetical properties of white cast irons.     

Influence of carbon diffusion on microstructure and wear behaviour of duplex stainless steel surface layers on lamellar grey cast iron

Surface welding with duplex stainless steel was performed to enhance the wear and corrosion properties of grey cast iron, which is used as material for applications as pump components in maritime and chemical environments. The method used for surface welding and the corresponding process parameters determine the chemical composition and microstructure, which both determine the corrosion and wear properties of the surface layer. High heat input leads to high chemical dilution and thus, reduced corrosion resistance. Slow cooling rates, which are recommended for welding of grey cast iron components, facilitate the formation of carbides in the fusion zone of the chromium‐rich duplex stainless steel surface layer. On the one hand, carbides lead to increased hardness and thus, improved wear resistance of the surface layers. On the other hand, carbides and high chemical dilution rates reduce the corrosion resistance and therefore should be avoided. Under high cooling rates, the risk of cracking in the heat affected zone of the grey cast iron increases due to martensitic phase transformations. The paper describes the correlation of process parameters, microstructure and chemical composition with a focus on carbon diffusion and carbide formation, ever considering the effect on the wear behaviour in an oscillation tribometer and under erosion‐corrosion conditions.