Interface characteristics and wear resistance of Ni-B_(4)C plated ZTA reinforced high chromium cast iron composite

A chemical composite plating of Ni-B_(4)C was used to prepare the surface-modified zirconia toughened alumina(ZTA)ceramic particles.The ceramic preforms were prepared by the plated ZTA and sodium silicate solution binder,followed by casting infiltration to prepare the ZTA particles reinforced high chromium cast iron(HCCI)composites.The result reveals that a distinct interface layer forms at the ZTA/HCCI interface,which consists of phases of ZrB_(2),FeB,Fe_(2)B,and NaSiO_(4).The interfacial wettability between ZTA and HCCI is improved by the diffusion and reaction of Ni and B_(4)C.The wear test reveals that the Ni-B_(4)C plated ZTA particles can effectively improve the wear resistance of the ZTA/HCCI composite,and the wear rate of the composite is decreased to 11.6%of HCCI.

STUDY ON THE STRUCTURE AND PROPERTIES OF HIGH CHROMIUM WHITE CAST IRON AND ITS TEMPERING STANDARD

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Effect of Manganese on As-Cast Microstructure and Hardening Behavior of High Chromium White Cast Iron

The effect of manganese on the as-cast structure and hardening behavior of high chromium white cast iron subjected to sub-critical treatment was studied.The results indicate that the fraction of retained austenite and the manganese distribution in as-cast alloys are controlled by manganese content.The manganese distribution in as-cast alloys is not homogeneous.The manganese content in carbide is higher than that in matrix.Whether the secondary hardening occurs or not and the peak hardness of secondary hardening is controlled by manganese content in retained austenite in as-cast structure.Higher manganese content can cause more retained austenite.The secondary hardening occurs in sub-critical treating process if the fraction of retained austenite is high.

Effects of RE,V,Ti and B composite modification on the microstructure and properties of high chromium cast iron containing 3% molybdenum

The effects of RE, V, Ti and B on the microstructure and properties of high chromium cast iron containing 3% molybdenum under as-cast and heat treatment conditions were investigated with the method of comparing experiments. The results show that with the increase of RE content, the primary austenite of high chromium cast iron is obviously refined. The morphology of carbide is changed from netlike and lath to small multiangular isolated blocks or massive blocks, the isolated degree of carbide is improved obviously, and the size is significantly refined. The addition of V and B into high chromium cast iron can refine the microstmcture, reduce coarse columnar crystals and make the carbide smaller and uniform. Through composite modification with RE, V, Ti and B, the hardness, wear resistance and impact toughness of high chromium cast iron are increased conspicuously. After heat treatment, the hardness of high chromium iron is increased significantly, but the toughness and wear resistance do not show great improvement.

Optimizing hardenability of high chromium white cast iron

The formulas proposed by J. Dodd and J. L. Parks for calculating the hardenability of high-Cr white cast iron under continuous cooling condition was recommended. For broader application, some supplements were made to the formula. Through tests on the half-cooling time of typical castings, the compositions of ideal alloys were precisely designed using the Dodd’s formula. Hardness testing of heat-treated castings showed that the designed compositions were correct. The application of castings demonstrated excellent abrasion resistance.

Effect of Cryogenic Treatment on Property of 14Cr2Mn2V High Chromium Cast Iron Subjected to Subcritical Treatment

Effect of cryogenic treatment on the microstructure, hardening behavior and abrasion resistance of 14Cr2Mn2V high chromium cast iron （HCCI） subjected to subcritical treatment was investigated. The results show that cryogenic treatment after subcritical treatment can obviously improve the hardness and abrasion resistance of HCCI because abundant retained austenite is transformed into martensite and fine secondary carbides E（Fe, Cr）23 C6 ] precipitate. The amount of martensite and precipitated secondary carbide in HCCI experiencing subcritical treatment followed by cryogenic treatment was more than that experiencing the subcritical treatment followed by air cooling. When the abrasion resistance of HCCI reaches the maximum, its microstructure contains about 15 % retained austenite. Cryogenic treatment can further reduce the austenite content but the retained austenite cannot be transformed in to martensite completely.

High Cr white cast iron/carbon steel bimetal liner by lost foam casting with liquid-liquid composite process

Liners in wet ball mill for mineral processing industry must bear abrasive wear and corrosive wear, and consequently,the service life of the liner made from traditional materials,such as Hadfield steel and alloyed steels,is typically less than ten months.Bimetal liner,made from high Cr white cast iron and carbon steel,has been successfully developed by using liquid-liquid composite lost foam casting process.The microstructure and interface of the composite were analyzed using optical microscope,SEM,EDX and XRD.Micrographs indicate that the boundary of bimetal combination regions is staggered like dogtooth,two liquid metals are not mixed,and the interface presents excellent metallurgical bonding state.After heat treatment,the composite liner specimens have shown excellent properties,including hardness>61 HRC,fracture toughnessα k >16.5 J·cm-2 and bending strength >1,600 MPa.Wear comparison was made between the bimetal composite liner and alloyed steel liner in an industrial hematite ball mill of WISCO,and the results of eight-month test in wet grinding environment have proved that the service life of the bimetal composite liner is three times as long as that of the alloyed steel liner.

Effects of Rare Earths and Al on Structure and Performance of High Chromium Cast Iron Containing Wolfram

Effects of RE and Al on the structure, impact toughness, hardness, and wear resistance of high chromium cast iron containing wolfram were investigated. The results show that without modification the volume fraction of austenite is high and the carbide appears to be thick lath and the grain size is relatively large; proper modification using RE combined with Al can reduce volume fraction of residual austenite in the as-cast structure obviously, refine grain size of primary austenite notably, and make the morphology of carbide changing from thick lath to thin lath, rosette, and feather-like modification can also increase hardness, wear resistance and impact toughness of cast iron.

Effect of Ti-V-Nb-Mo addition on microstructure of high chromium cast iron

The effects of trace additions of multi-alloying elements(Ti,Nb,V,Mo)on carbides precipitation and as- cast microstructure of eutectic high chromium cast iron containing 2.85wt.%C and 31.0wt.%Cr were investigated from thermodynamic and kinetic considerations.The thermodynamic calculations show that Ti and Nb exist in the multi-alloying system in the forms of TiC and NbC.The formation of VC during the solidification is not feasible from the thermodynamic consideration.XRD analysis shows that the V exists in alloy compounds(VCr2C2,VCrFe8).The first precipitated high melting point particles(TiC,NbC)can act as the heterogeneous substrate of M7C3 carbides, which results in significant refinement of the M7C3 carbides.After the addition of alloying elements,C atom diffusion is hindered due to the strong affinities of the strong carbide forming elements for carbon,which decreases the growth rate of carbides.The combined roles of the increase of nucleation rate and the decrease of carbides growth rate lead to the finer microstructure.

Microstructure and wear resistance of highchromium cast iron containing niobium

In the paper, the effect of niobium addition on the microstructure, mechanical properties and wear resistance of high chromium cast iron has been studied. The results show that the microstructure of the heattreated alloys is composed of M7C3 and M23C6 types primary carbide, eutectic carbide, secondary carbide and a matrix of martensite and retained austenite. NbC particles appear both inside and on the edge of the primary carbides. The hardness of the studied alloys maintains around 66 HRC, not significantly affected by the Nb content within the selected range of 0.48%-0.74%. The impact toughness of the alloys increases with increasing niobium content. The wear resistance of the specimens presents little variation in spite of the increase of Nb content under a light load of 40 N. However, when heavier loads of 70 and 100 N are applied, the wear resistance increases with increasing Nb content.

Effect of vibration frequency on microstructure and performance of high chromium cast iron prepared by lost foam casting

In the present research, high chromium cast irons(HCCIs) were prepared using the lost foam casting(LFC) process. To improve the wear resistance of the high chromium cast irons(HCCIs), mechanical vibration was employed during the solidification of the HCCIs. The effects of vibration frequency on the microstructure and performance of the HCCIs under as-cast, as-quenched and as-tempered conditions were investigated. The results indicated that the microstructures of the LFC-produced HCCIs were refined due to the introduction of mechanical vibration, and the hardness was improved compared to that of the alloy without vibration. However, only a slight improvement in hardness was found in spite of the increase of vibration frequency. In contrast, the impact toughness of the as-tempered HCCIs increased with an increase in the vibration frequency. In addition, the wear resistance of the HCCIs was improved as a result of the introduction of vibration and increased with an increase in the vibration frequency.

SPHERICAL MICROSTRUCTURE FORMATION OF THE SEMI-SOLID HIGH CHROMIUM CAST IRON Cr20Mo2

The nondendritic semi-solid slurry preparation of high chromium cast iron Cr20Mo2 has been studied in this paper. The experiments show that the proeutectic austenitic particles are more spherical under a larger stirring power condition, even if the stirring time is shorter, while the proeutectic austenitic particles are not very much spherical under a smaller stirring power condition and some proeutectic austenitic dendrites also exist, even if the stirring time is very long. The experiments also show that when stirred for 5-6 minutes under the test condition, the semi-solid slurry with 40vol.%-50vol.% solid fraction and spherical proeutectic austenite in the size of 50-80μm can be obtained.

Effect of surface Cr/C infiltration on microstructure,mechanical properties and wear resistance of high chromium cast iron

A new type of high chromium cast iron(HCCI)was prepared,and its microstructure,mechanical properties,and abrasion resistance were investigated systematically.Results showed that after surface carburizing and chromizing,the microstructure of HCCI mainly consists of martensite,boride(M_(2)B),and carbide(M_(7)C_(3)),accompanied with a large amount of secondary precipitations M_(23)C_(6).Moreover,the morphology and hardness of the carbide and boride in HCCI change little,while the volume fraction of carbide and boride increases from 16.23%to 23.16%.This effectively increases the surface hardness of HCCI from 64.53±0.50 HRC to 66.58±0.50 HRC,with the result that the surface of HCCI possesses a better abrasion resistance compared to the center position.Furthermore,the wear mechanism of HCCI changes from micro-plowing to micro-cutting with the increase of surface hardness.

Effect of tempering temperature on microstructure and mechanical properties of high boron white cast iron

The effect of different tempering temperatures on the microstructure and mechanical properties of airquenched high boron white cast iron was studied.The results indicate that the high boron white cast iron comprises dendritic matrix and inter-dendritic M 2 B boride;and the matrix comprises martensite and pearlite.After quenching in the air,the matrix is changed into lath martensite;but only 1-μm-size second phase exists in the matrix.After tempering,another second phase of several tens of nanometers is found in the matrix,and the size and quantity increase with an increase in tempering temperature.The two kinds of second precipitation phase with different sizes in the matrix have the same chemical formula,but their forming stages are different.The precipitation phase with larger size forms during the austenitizing process,while the precipitation phase with smaller size forms during the tempering process.When tempered at different temperatures after quenching,the hardness decreases with an increase in the tempering temperature,but it increases a little at 450 ℃ due to the precipitation strengthening effect of the second phase,and it decreases greatly due to the martensite decomposition above 450 ℃.The impact toughness increases a little when tempered below 300 ℃,but it then decreases continuously owing to the increase in size and quantity of the secondary precipitate above 300 ℃.Considered comprehensively,the optimum tempering temperature is suggested at 300 ℃ to obtain a good combination of hardness and toughness.

Use of electron microscopy on microstructure characterization of high chromium cast irons

The physical metallurgy underlying the development of cast microstructures in abrasion resistant high chromium cast irons, and their structural modification by thermal treatments is relatively complex. Structural characterisation via electron microscopy therefore has a key role to play in furthering our understanding of the phase transformations that control the microstructures and hence the service performances of these irons as wear parts. This paper shows how both scanning and especially transmission electron microscopy can provide valuable information on the nature of eutectic and secondary carbides and on the matrix structures in these irons. Particular attention is given to current characterisation research on conventionally cast 30%Cr irons that are used for applications involving corrosive wear e.g. slurry pumps and on a semi-solid cast 27%Cr iron that has a potential for applications in industry.

On the Comparison of Microstructure Characteristics and Mechanical Properties of High Chromium White Iron with the Hadfield Austenitic Manganese Steel

In this study, high chromium white iron (HC-Wi) alloy and the Hadfield steel were studied. The microstructure of this high-chromium iron was studied using Metallurgical optical microscopy (OM) and compared to the Hadfield steel. The hardness and unnotched charpy impact strength of the HC-Wi alloy and Hadfield steel were examined at ambient temperature in the as-cast and heat-treated conditions. A pin-on-disc test at linear speed of 1.18 m/s and a 10 N normal load was employed to evaluate the wear behavior of both steel samples. Microstructural results showed that varying the carbon level in HC-Wi alloys can affect the chromium carbide morphology and its distribution in the austenite matrix which leads to considerable changes of the mechanical properties. Abrasion test showed that HC-Wi alloys have superior wear resistance, about three times of the Hadfield steel.

Effect of RE Complex Inoculation on the Fatigue Wear Behaviours of High Chromium Cast Iron

Inoculation of high chromium cast iron is made by RE complex inoculant. Influence of inoculating on rolling fatigue wear characteristics of high chromium cast iron is investigated. The experimental resutls indicate that high chromium cast iron inoculated by RE complex inoculation is improved in structure and properties, i. e. fatigue wear sevice life is prolonged and relative wear resistance is increased greatly.

Influences of copper on solidification structure and hardening behavior of high chromium cast irons

The influences of copper on microstructure and the hardening behavior of high chromium cast irons subjected to sub-critical treatment were investigated. The results show that the microstructure of the as-cast high chromium cast irons consists of retained austenite, martensite and M7C3 type eutectic carbide. When copper is added into high chromium cast irons, austenite and carbide contents are increased. The increased addition of copper content from 0% to 1.84% leads to the increase of austenite and carbide from 15.9% and 20.0% to 61.0% and 35.5%, respectively. In the process of sub-critical treatment, the retained austenite in the matrix can be precipitated into secondary carbides and then transforms into martensite in cooling process, which causes the secondary hardening of the alloy under sub-critical treatment. High chromium cast irons containing copper in sub-critical treatment appear the second hardening curve peak due to the precipitation of copper from supersaturated matrix.

RESEARCH AND APPLICATION OF AS-CAST WEAR RESISTANCE HIGH CHROMIUM CAST IRON

The influence of alloy elements, such as boron and silicon, on the microstructure and properties of as cast high chromium cast iron is studied. The results show that boron and silicon have a great effect on the mechanical properties and the wear resistance. Through proper addition of boron and silicon, the properties of as cast high chromium cast iron can be improved effectively. Through analyzing the distribution of elements by scanning electron microscope, it has been shown that the addition of boron and silicon lowers the mass fraction of chromium saturated in as cast austenite, and makes it unstable and liable to be transformed into martensite. The as cast high chromium cast iron with proper content of boron and silicon is suitable for the manufacture of lining for asphalt concrete mixer and its wear resistance is 14 times that of lining made of low alloy white cast iron.

OXIDATION BEHAVIOUR OF HIGH Cr CAST IRON

The oxidation behaviour of high Cr Cast iron was investigated at 950 and 800℃ in terms of Cr content in matrix and the amount of carbide.The morphology and types of oxide films and the microstructure of subsurface were also examined.The main conclusions are:1)The original chromium content in the matrix determines the type of oxide film and it is an important factor for the oxidation resistance of high chromium cast iron;2) The oxidation resistance improves with increasing carbide content at 950℃ because of the decomposition of the carbide,while the decompsition of the carbide do not take place at 800℃ so the oxidation resisteance do not improve with increasing carbide volume.