Chi-Ming Lin

Effects of vanadium content on the microstructure and dry sand abrasive wear of a eutectic Cr-Fe-C hardfacing alloy

In this study, the effects of vanadium on the morphology and wear behavior of a eutectic Cr-Fe-C hardfacing alloy were discussed. The alloys tested contained different amounts of vanadium, ranging from 0 to 2.39 wt%. A fibrous V4C3 was found when the alloy contained 0.93 wt% vanadium. The addition of vanadium was found to decrease the fraction of eutectic M23C6 and increase the width of the interspaces between the eutectic cells. The DTA results revealed that V4C3 formed just before the eutectic α+M23C6 during solidification. The surface hardness was shown to increase with increasing vanadium content, which also caused the hardness deviation and wear loss to decrease; however, the addition of vanadium was not shown to affect the hardness of eutectic α+M23C6. The V4C3 could be scratched off during the wear test due to the increase in the width of the interspaces between the eutectic cells; therefore, the alloys that contained 0.93 and 2.39 wt% vanadium exhibited similar wear loss results.

Microstructure and abrasive wear properties of Fe-Cr-C hardfacing alloy cladding manufactured by Gas Tungsten Arc Welding (GTAW)

A series of Fe-Cr-C hardfacing alloys is deposited by gas tungsten arc welding and subjected to abrasive wear testing. Pure Fe with various amounts of CrC (Cr:C=4:1) powders are mixed as the fillers and used to deposit hardfacing alloys on low carbon steel. Depending on the various CrC additions to the alloy fillers, the claddings mainly contain hypoeutectic, near eutectic, or hypereutectic microstructures of austenite γ-Fe phase and (Cr,Fe)7C3 carbides on hardfacing alloys, respectively. When 30% CrC is added to the filler, the finest microstructure is achieved, which corresponds to the γ-Fe+(Cr,Fe)7C3 eutectic structure. With the addition of 35% and 40% CrC to the fillers, the results show that the cladding consists of the massive primary (Cr,Fe)7C3 as the reinforcing phase and interdendritic γ-Fe+(Cr,Fe)7C3 eutectics as the matrix. The (Cr,Fe)7C3 carbide-reinforced claddings have high hardness and excellent wear resistance under abrasive wear test conditions. Concerning the abrasive wear feature observable on the worn surface, the formation and fraction of massive primary (Cr,Fe)7C3 carbides predominates the wear resistance of hardfacing alloys. Abrasive particles result in continuous plastic grooves when the cladding has primary γ-Fe phase in a hypoeutectic structure.

The Effect of Oscillating Traverse Welding on Performance of Cr-Fe-C Hardfacing Alloys

In this study, a series of experiments involving Cr-Fe-C hardfacing alloys is conducted to evaluate the effect of oscillating traverse welding on microstructure and performance of clad alloys. The alloys are designed to exhibit hypoeutectic, eutectic, and hypereutectic morphology. The morphology of the heat-affected zone (HAZ) of the unmelted metal, the solidified remelted metal, and the fusion boundary exhibited distinct characteristics. In the hypoeutectic and the eutectic alloys, the same lamellar eutectic structure can be observed as the solidified structure, and they also showed the same evolution in the HAZ. In the hypereutectic alloy, the incomplete weld pool blending results in a eutectic morphology instead of a fully hypereutectic morphology. The hardness result reveals that, for the hypereutectic alloy, the eutectic region, instead of the HAZ, is the weak point. The wear test shows that the hypoeutectic alloy exhibits the same wear behaviors in both the remelted metal and the HAZ, and so is the hypereutectic alloy; the eutectic alloy remelted metal and the HAZ have different wear morphologies.

Characteristics of Eutectic α(Cr,Fe)-(Cr,Fe)23C6 in the Eutectic Fe-Cr-C Hardfacing Alloy

Abstract A specific eutectic (Cr,Fe)-(Cr,Fe)23C6 structure had been previously reported in the research studies of Fe-Cr-C hardfacing alloys. In this study, a close observation and discussion of the eutectic (Cr,Fe)-(Cr,Fe)23C6 were conducted. The eutectic solidification occurred when the chromium content of the alloy exceeded 35 wt pct. The eutectic structure showed a triaxial radial fishbone structure which was the so called “complex regular structure.” Lamellar costa plates showed local asymmetry at two sides of a spine. Individual costae were able to combine as one, and spines showed extra branches. Costae that were nearly parallel to the heat flow direction were longer than those that were vertical to the heat flow direction. The triaxial spines preferred to intersect at 120 deg, while the costae preferred to intersect the spine at 90 deg and 35.26 deg due to the lattice relationships. The solidified metal near the fusion boundary showed an irregular structure instead of a complex regular structure. The reason for the irregular morphology was the high growth rate near the fusion boundary.

Effect of FeO-CaO-SiO2-MgO-xAl2O3 Slags with 12.0~26.0 wt.% Al2O3 Content on Dephosphorization of Molten Steel

The purpose of this investigation is to understand the effect of FeO-CaO-SiO2-MgO-xAl2O3 slags with 12.0~26.0 wt.% Al2O3 content on dephosphorization of molten steel. The dephosphorization experiments of FeO-CaO-SiO2-MgO-xAl2O3 slags are evaluated by a heater of induction furnace at the temperature of 1823 K. The results show that the dephosphorization ability of FeO-CaO-SiO2-MgO-xAl2O3 slags significantly decreases with the increasing of Al2O3 content. The oxidative slag with 12.4 wt.% Al2O3 possesses the biggest dephosphorization ability (approximately 82.7%) in all conditions. When the Al2O3 content of oxidative slag increases from 12.4 to 25.7 wt.%, the dephosphorization ability decreases from 82.7% to 34.6%. P2O5 content of oxidative slag also decreases with the increasing of Al2O3 content. The X-ray diffraction (XRD) results reveal that the Fe-based slag with 12.4 wt.% Al2O3 contains the constituent phases of FexO and Ca2Al2SiO7. As the Al2O3 content of Fe-based slag is above 22.1 wt.%, the constituent phase of FeAl2O4 is generated. The energy-dispersive X-ray spectroscopy (ESD) results verify that the capacity of phosphorus of FeAl2O4 phase is the worst in all phases. The capacity of phosphorus for each phase is Ca2Al2SiO7 phase > FexO phase > (Fe,Mg)Al2O4 phase.

Lattice relations and solidification of the complex regular eutectic (Cr,Fe)-(Cr,Fe)23C6

The eutectic (Cr,Fe)-(Cr,Fe)23C6 showed a triaxial fishbone structure and could be categorized as a “complex regular structure”. In this study, the lattice relations of the fishbone (Cr,Fe)23C6 were examined and the solidification process was observed using a transmission electron microscope and a confocal laser scanning microscope. For one of the three fish bones in a eutectic cell, parallel (Cr,Fe)23C6 lamellas at one side of the spine had the same lattice direction, as did those in the (Cr,Fe) phase. The lattices of neighboring (Cr,Fe)23C6 and (Cr,Fe) phases were not coherent. Lamellar (Cr,Fe)23C6 on opposite sides of a spine had different lattice directions, and their lattice boundary was in the spine. By using the confocal laser scanning microscope, the solidification of lamellar eutectic structure could be observed. At the low cooling rate of 5 o C·min-1, parallel lamellas would grow thick blocks instead of thin plates. To obtain a thin lamellar eutectic structure, the cooling rate should be higher, like the rate in welding.

Effect of mechanical vibration on the residual stress of direct laser metal deposition workpiece

Mechanical vibration with different frequencies was operated during the direct laser metal deposition process in order to discuss the effects of vibration on residual stress and other characters of deposited workpiece in this study. Sub-resonance, resonance and the optimum frequency (OPF) were selected for operation. The results revealed that the residual stress of the deposited workpiece was a tensile stress. With the operation of mechanical vibration, the stress of clad workpiece decreased, and the workpiece vibrated with the OPF showed the lowest residual stress. Microstructures of all the specimens with vibration refined, and the finest structure appeared in the specimen vibrated with the OPF. The hardness result showed that the lower the residual stress was, the lower the hardness was, and a low residual stress and hardness would have advantage of subsequent process of the deposited workpiece.