Microstructure of Ni /WC Surface Composite Layer on Gray Iron Substrate

The surface infiltrated composite （Ni/WC） layers on gray iron substrate were fabricated through a vacuum infiltration casting technique （VICT） using Ni-based composite powder with different WC particles content as raw materials.The microstructures of surface infiltrated composite layer,the interface structures between surface composite layer and the substrate,the changes of macro-hardness with the increasing of WC content and the micro-hardness distribution are investigated.The infiltrated composite layer includes a surface composite layer and a transition layer,and the thickness of the transition layer decreases with the increasing content of WC.The thickness of transition layer with 20%WC content in the surface infiltrated composite layer was 170 μm which was the thickest for all transition layers with different WC content.The surface composite layer was mainly composed of WC,W2C,FeB and NiB,along with Ni-Cr-Fe,Ni （Cr） solid solution,Ni （Si） solid solution and Ni （Fe） solid solution.The transition layer was composed of Ni （Cr） solid solution,Ni （Fe） solid solution,Ni （Si） solid solution,Fe （Ni） solid solution and eutectic.The surface macro-hardness and micro-hardness of the infiltrated layer had been evaluated.The macro-hardness of the surface composite layer decreases with the WC content increasing,and the average macro-hardness is HRC60.The distribution of micro-hardness presents gradient change.The average micro-hardness of the infiltrated layer is about HV1000.

RESIDUAL AUSTENITE AND STRAIN-INDUCED MARTENSITE IN LASER HARDENING LAYER ON GRAY IRON

The distribution of residual austenite in the laser hardening laver on the gray cast iron and the change in the amount of residual austenite during sliding wearing have been investigated by X-ray diffractometer.The thin foils of the hardening layer worn down have been observed by electron microscopy.It was revealed that two types of martensite are strain-induced by slid- ing wearing under load of 1.72 MPa on the hardening layer of residual austenite.The strain induced martensite is profitable to improve the sliding wearing resistance.

Characterization of Dissimilar Welding between 304 Stainless Steel and Gray Iron Using Nickel Coated Electrode

This paper presents the study carried out to study the microstructure and mechanical properties of AISI 304 stainless steel and gray iron, in order to recognize the effect of welding parameters on the joint. The shielded metal arc welding technique was applied with a 3.2 mm diameter nickel coated electrode under preheating and post heat conditions at 350°C. Vickers hardness test and metallographic analysis were carried out at the heat affected zone and at the interface to determine the effect on mechanical and metallurgical characteristics. Vickers hardness differences among joint areas were directly related to microstructural changes. There are no significant differences in AISI 304 hardness, but the hardness increased at the heat affected zone and decreased at the filler metal. Grey iron hardness at the heat affected zone was even lower and more slightly superior than grey iron hardness.

Welding Effect at the Heat Affected Zone by Joining a Gray Cast Iron with Stainless Steel E308-16

Different investigations of the union of dissimilar materials such as stainless steel and different castings have been carried out, but rapid cooling immediately after welding has not been considered, in this work it was investigated how rapid cooling affects the metallurgical microstructure and consequently the mechanical properties. The effect of welding parameters on the microstructure and mechanical properties of the joint between dissimilar metals, an E-308-16 austenitic stainless steel and Gray Cast Iron was also analyzed. Gray cast iron samples (GCI) were fabricated, welded and cooled. The main welding parameters studied in this work are the welding technique and the type of filler electrodes. Flux-coated electrode E-308-16 was applied for this different joint. An experimental study was carried out for the analysis of welded joints of similar and dissimilar steels. The microstructure of the welded joints was analyzed using an optical microscope, in the base metals, heat affected zone (HAZ) and filler metal. The mechanical properties of the welded joints were evaluated by Vickers microhardness and tensile strength tests. The hardness profile showed differences in hardness between the base metals, the heat affected zone and the filler metal. The metallurgical microstructures observed along the welded areas corresponded to the profile. The hardness differences determined the effect on the mechanical and metallurgical characteristics of the welded samples as a result of the cooling rate differences. This research work is important because it allows us to analyze the possibility of reworking pieces of dissimilar materials by welding or, failing that, to determine if this may or may not be possible.

Thermal Cycling Effect on the Wear Resistance of Bionic Laser Processed Gray Iron

Thermal fatigue and wear both seriously affect the service life of some working parts. Environmental temperature will modify the surface conditions and influences the result of wear. In this research, to come close to working conditions, specimens were tested by a combination of thermal cycles and wear. Different cycles of thermal fatigue was carried out first on the gray iron specimens and subsequently wear test was performed to evaluate the effect of these thermal fatigue cycles. In this case, bionic laser processing was used to enhance the wear performance. The results indicated that bionic laser processing reduces the negative effects from thermal fatigue, such as grain fragmentation and oxidation. Because the initiation and growth of cracks as well as oxidation are suppressed in bionic processed areas. Bionic specimens exhibit high wear resistance compared with the common one. The process described can be considered as an effective method to improve the performance of gray iron in combined thermal fatigue and wear service conditions.

Research of Synthetic Rules with Mechanical Properties vs Inoculation Degree on Gray Cast Iron

To fit the special needs of gray cast iron as a new engineering material,i.e.,higher σ b and lower HB,or lower σ b and higher HB,using the method of heat analyzing and polyparameters analytic figures,the synthetic rules of carbon saturation degree,inoculation degree and mechanical properties can be exposed.The result shows that,according to the needs of the part′s mechanical properties,referring to the synthetic rules of gray cast iron,the corresponding technological measure and composition proportion can be defined,by which we will get the exact mechanical properties that could achieve the result expected completely.Thus,the casting for gray cast iron might be 'designed'from'selected'.

Characterization of Titanium-Containing Compounds in Gray Iron

Titanium produces different compounds in gray iron. In order to determine their characteristics, a scanning electron microscope, an energy dispersive X-ray spectroscopy, and an optical microscopy were used to analyze the morphology, distribution, and composition of titanium-containing compounds in metal- Iographic specimens and machined surfaces in four gray irons. The results show that the titanium-containing compounds in the gray irons are complex compounds containing V, Nb, Mn, S, and other metals, depending on the concentration of these elements in the iron. The number of titanium-containing compounds increases with increasing Ti content in the gray iron. Most of the titanium-containing compounds are located in the pearlite matrix, with some in the steadite and carbides. The results suggest that titanium-containing compounds reduce tool lifetime.

Gray Cast Iron With Directional Graphite Flakes Produced by Cylinder Covered Compression Process

A new plastic deformation process for gray cast iron named cylinder covered compression （CCC） was developed. By CCC process, gray cast iron （GCI） specimens, which are embedded in steel cylinders, were hot compressed up to 80% reduction in height without the cracking problem. It was clearly observed that the uniform distribution of directional graphite flakes appeared after more than 45 % reduction hot compression. The strength, ductility, and microhardness of GCI after 80% reduction deformation were significantly enhanced： the tensile strength varied from 117 MPa to 249 MPa, while the total elongation varied from 0 to 5.2%, and the microhardness varied from 153 HV to 217 HV. It was shown that the tensile fracture surface presented ductility characters after more than 45% reduction hot deformation.

Effect of inoculating addition on machinability of gray cast iron

Gray cast irons were inoculated with FeSi75＋RE and FeSi75＋Sr inoculants. The changes of apex angle of the drills before and after being used were used to evaluate machinability of gray cast irons. Effect of FeSi75＋RE and FeSi75＋Sr inoculants on mechanical properties, machinability and sensibility of gray cast iron used in cylinder block were investigated. Experimental results showed that gray cast iron treated with 60%FeSi75＋40% RE inoculants exhibited tensile strength consistently at about 295 MPa along with good hardness and improved metallurgical quality. While gray cast iron inoculated with 20%FeSi75＋80% Sr inoculants exhibited the best machinability, the lowest cross-section sensibility and the least microhardness difference. The tool flank wear of the drill increased correspondingly with the increase of the microhardness difference of the matrix, indicating the great effect of homogeneity of the matrix on the machinability of gray cast iron.

Effect of Power Ultrasonic on Solidification Structure of HT150 Gray Cast Iron

Power ultrasonic treatment is an efficient way to improve the solidification structure and mechanical properties of metals. The effect of 600 W power ultrasonic treatment on the solidification process and structure of HT150 gray cast iron has been studied, and the fining mechanism of power ultrasonic has been analyzed.

Optimization of Casting Process for Heat and Abrasion Resistant Large Gray Iron Castings

Numerical simulations were used to optimize the casting design and conditions for large cast iron castings for marine engines, Simulations of the mold filling and solidification sequences were used to analyze the problems of previous casting conditions with marked improvements for large cylinder liner parts, The amount and positions of chills were optimized to improve the mechanical properties and to minimize the shrinkage and micro porosity in the castings. Ultra sonic testing, penetration testing, and mechanical property testing show no defects in the castings with the productivity significantly increased.

SOLUBILITY OF NITROGEN IN MOLTEN GRAY CAST IRON

The expressions of the dependence of nitrogen solubility in molten gray cast iron on the temperature and composition of the melt were proposed under the condition of foundry practice. Three gray cast iron specimens with different compositions were examined in good agreement with the derived expression.

Analysis of Graphite Morphology of Gray Cast Iron in Pulse Magnetic Field

By self-made pulse electrical source and strong magnetic field solidification tester, the effect of strong pulse magnetic field on graphite morphology and solidification structure of gray cast iron was studied. The results show that the structure is remarkably refined after treated by pulse magnetic field, and the width of graphite flakes is decreased while the length is increased after a slight decrease. The solidification temperature and eutectic temperature are increased and the undercooling degree of eutectic transformation is decreased by magnetic field.

Different thermal fatigue behaviors between gray cast iron and vermicular graphite cast iron

The initiation and propagation of thermal fatigue cracks in gray cast iron and vemicular graphite cast iron were investigated by Uddeholm method to reveal the complex thermal fatigue behaviors of cast iron.Differences of thermal fatigue behaviors of gray cast iron and vemicular graphite cast iron were observed and analyzed.It is found that the observed differences are related to the combination of graphite morphology and the oxidization of matrix.More oxidized matrix is observed in gray cast iron due to its large specific surface area.The brittle oxidized matrix facilitates the propagation of microcracks along the oxidization layer.By contrast,the radial microcracks are formed in vermicular graphite at the edge of graphite due to fewer oxidization layers.It indicates that the thermal fatigue resistance of gray cast iron is dominated by graphite content and morphology while that of vermicular graphite cast iron strongly relates to the strength of the matrix.

Construction and analysis of dynamic solidification curves for non-equilibrium solidification process in lost-foam casting hypoeutectic gray cast iron

Most lost-foam casting processes involve non-equilibrium solidification dominated by kinetic factors, while construction of a common dynamic solidification curve is based on pure thermodynamics, not applicable for analyses and research of non-equilibrium macro-solidification processes, and the construction mode can not be applied to nonequilibrium solidification process. In this study, the construction of the dynamic solidification curve(DSC) for the nonequilibrium macro-solidification process included: a modified method to determine the start temperature of primary austenite precipitation(T_(AL)) and the start temperature of eutectic solidification(T_(ES)); double curves method to determine the temperature of the dendrite coherency point of primary austenite(T-(AC)) and the temperature of eutectic cells collision point(T_(EC)); the "technical solidus" method to determine the end temperature of eutectic reaction(T_(EN)). For this purpose, a comparative testing of the non-equilibrium solidification temperature fields in lost-foam casting and green sand mold casting hypoeutectic gray iron was carried out. The thermal analysis results were used to construct the DSCs of both these casting methods under non-equilibrium solidification conditions. The results show that the transformation rate of non-equilibrium solidification in hypoeutectic gray cast iron is greater than that of equilibrium solidification. The eutectic solidification region presents a typical mushy solidification mode. The results also indicate that the primary austenite precipitation zone of lost-foam casting is slightly larger than that of green sand casting. At the same time, the solid fraction(f_s) of the dendrite coherency points in lost-foam casting is greater than that in the green sand casting. Therefore, from these two points, lost-foam casting is more preferable for reduction of shrinkage and mechanical burntin sand tendency of the hypoeutectic gray cast iron. Due to the fact that the solidification process(from the surface to center) at primary austenite growth area in the lost-foam cylinder sample lags behind that in the green sand casting, the mushy solidification tendency of lost-foam casting is greater and the solidification time is longer.

Effect of Rare Earths and Nitrogen on Graphite Structure of Gray Cast Iron

By means of inoculating, the effects of rare earths, N and RE N joint inoculants on the content and surface morphology of graphite of high CE gray cast irons were studied The results indicate that RE, N, and especially RE N joint inoculants make the content of graphite decrease; N and RE N joint inoculants could make the surface of graphite rougher and the heads of graphite flake passive

EFFECT OF NITROGEN ON MATRIX STRUCTURE OF GRAY CAST IRON

Effect of nitrogen on matrix structure of 3 different varieties of gray cast iron,i.e., sub-eutectic Fe-C-Si,near-eutectic Fe-C-Si and Fe-C-Si-Mn,has been investigated. The eutectie colony structure of gray cast iron may be refined,the pearlite content increased and the micro-hardness of pearlite and ferrite raised with an addition of nitrogen.The influ- ence of nitrogen on the transformation temperature of the equilibrium and non-equilibrium phases,as well as,the solution of nitrogen in ferrite and cementite seem to be the major rea- sons to strengthening the matrix structure of gray cast iron.

Microstructure and high-temperature wear properties of in situ TiC composite coatings by plasma transferred arc surface alloying on gray cast iron

In this work, an in situ synthesized TiC-reinforced metal matrix composite （MMC） coating of approximately 350-400μm thickness was fabricated on a gray cast iron （GCI） substrate by plasma transferred arc （PTA） surface alloying of Ti-Fe alloy powder. Microhard- ness tests showed that the surface hardness increased approximately four-fold after the alloying treatment. The microstructure of the MMC coating was mainly composed of residual austenite, acicular martensite, and eutectic ledeburite. Scanning electron microscopy （SEM） and X-ray diffraction analyzes revealed that the in situ TiC particles, which were formed by direct reaction of Ti with carbon originally contained in the GCI, was uniformly distributed at the boundary of residual anstenite in the alloying zone. Pin-on-disc high-temperature wear tests were performed on samples both with and without the MMC coating at room temperature and at elevated temperatures （473 K and 623 K）, and the wear behavior and mechanism were investigated. The results showed that, after the PTA alloying treatment, the wear resistance of the sam- ples improved significantly. On the basis of our analysis of the composite coatings by optical microscopy, SEM with energy-dispersive X-ray spectroscopy, and microhardness measurements, we attributed this improvement of wear resistance to the transformation of the microstruc- ture and to the presence of TiC particles.

Effects of RE and N on Properties of Corrosion Resistance and Oxidation Resistance of Gray Cast Iron

By means of ladle inoculating, the effects of RE and N on the properties of corrosion resistance and oxidation resistance of gray cast iron were studied. The results show that the properties of both corrosion resistance and oxidation resistance are improved by adding suitable amount of RE, while RE and N are added as a multi inoculant, the oxidation resistance of gray cast iron is remarkably increased.

Effect of V and Sn on microstructure and mechanical properties of gray cast iron

The cylinder liner is one of the important parts of a diesel engine.Gray cast iron is the main material for manufacturing cylinder liners due to its good casting performance,convenient processing performance,good wear resistance and low cost.In the present work,the effects of vanadium(V)and tin(Sn)on the microstructure and properties of gray cast iron were studied.Results show that increasing the contents of V and Sn can not only refine the graphite,but also reduce the pearlite lamellar space.The graphite size and lamellar spacing of pearlite are firstly reduced and then increased.Pearlite quantity reaches over 98%after adding V and Sn.Adding V and Sn can promote the precipitation and solid solution strengthening of gray cast iron,so as to improve the mechanical properties.The Brinell hardness reaches the peak of 424 HB at the contents of 0.21wt.%V and 0.06wt.%Sn,and the sample containing 0.11wt.%V and 0.08wt.%Sn shows the highest compressive strength and tensile strength of 1,699 MPa and 515 MPa,respectively.The main strengthening mechanism comes from the solid solution strengthening and fine grain strengthening of V and Sn.