Yefeng Bao

A New Type of Submerged-Arc Flux-Cored Wire Used for Hardfacing Continuous Casting Rolls

It is expected that the welding hardfacing of continuous casting rolls has better welding performance and higher wear resistance. A new type of submerged-arc hardfacing flux-cored wire has been developed through nitrogen replacing part of carbon and addition of the nitrogen-fixing elements of niobium and titanium. And microstructure, degree of hardness and high-temperature wear resistance of its deposited metal samples were also investigated. It is found that the microstructure is martensite, residual austenite and carbonitride precipitates. As a result, the hardfacing metal with homogeneous distribution of very fine carbonitride particles had high hardness and excellent wear-resisting property during high-temperature wear, which could significantly extend the service life of continuous casting rolls.

Effect of C/N Concentration Fluctuation on Formation of Plasma Electrolytic Carbonitriding Coating on Q235

The plasma electrolytic carbonitriding (PEC/N) on the Q235 steel was investigated in an aqueous solution containing monoethanolamine and KCl in a very short period of time. The microdischarge characteristics of the voltage/current on the Q235 were observed using real-time imaging during the PEC/N. The microstructure and element distribution of the carbonitriding layer were examined using scanning electron microscope (SEM) equipped with energy dispersive spectroscope (EDS). The effect of microdischarge on roughness, thickness and microhardness was evaluated. The formation of the carbonitriding layer was discussed. Research shows that it is similar in the microstructure and properties between the plasma electrolytic carbonitriding and the traditional gas carbonitriding. The formation of the carbonitriding layer results from the carbon and nitrogen fluctuation in PEC/N process. The microhardness and thickness can be up to HV 779 and 0.360 mm in 180 s, respectively, which is close to the results of the gas carbonitriding in the microhardness. Therefore, the plasma electrolytic carbonitriding has a potential to substitute the gas carbonitriding.

Formation mechanism of titanium and niobium carbides in hardfacing alloy

The most effective carbide-forming elements titanium and niobium were added into hardfacing alloy. Formation and composition of carbides in the hardfacing alloy were investigated by means of optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and energy-dispersive spectrometer (EDS). Hardness and impact toughness of the hardfacing alloy were measured. The thermodynamics and formation mechanism of carbides were also discussed. It is found that the carbides consist of TiC and NbC which are able to form directly from welding pool during the welding process. The formation mechanism of carbides involves nucleation of TiC followed by epitaxial precipitation of NbC on the surface of TiC. The formation of titanium and niobium carbides can obviously refine the microstructure and deplete the carbon in the matrix. The microstructure transforms to well-distributed carbides and a tough martensite matrix, contributing to a good combination of high hardness and high toughness in the hardfacing alloy.

An experimental study on contact resistance of coated galvanized steel sheet

A contact resistance measurement system was developed based on a four-wire contact resistance measurement method. A series of experiments were conducted on four kinds of coated galvanized steel sheets using the contact resistance measurement system at different pressures and temperatures. The results showed that pressure and temperature had great effect on contact resistance. The contact resistance was not stable during the initial period when the pressure was changeless and subsequently decreased with the increase of pressure. The contact resistance did not always decline with the temperature at low temperatures because of the joint effects of the electrical and mechanical properties of base metal and the films. However, the contact resistance decreased when the temperature rose within a certain temperature range.

Effect of Titanium Content on Microstructure and Wear Resistance of Hardfacing Alloy

The hardfacing alloys with different concentrations of titanium were deposited on carbon steel substrates by shielded metal arc welding, and the effect of titanium content on the microstructure characteristics of the hardfacing alloys was investigated. The wear resistance test of the hardfacing alloys was carried out by using a slurry rubber wheel abrasion test machine, and the wear behaviour was also studied. The results indicate that the addition of titanium can effectively promote the precipitation of the complex carbides of Nb and Ti due to the prior precipitation of titanium carbide which acts as nucleation sites for complex carbides. With the increase of titanium content, the wear resistance of the hardfacing alloys is increased gradually resulting from the refinement of microstructure and dispersive distribution of fine carbide precipitates. And the wear mechanism is mainly minimum plastic deformation with interrupted grooves due to the strengthening and protecting effects of carbide precipitates.

Microstructure and wear property of Fe–Cr13–C hardfacing alloy reinforced by WC particles

Tungsten as the most effective carbide-forming element was added in the Fe–Cr13–C hardfacing alloy to precipitate WC particles. Optical microscope (OM), scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS) were used to investigate the microstructures of the hardfacing alloy. The wear resistance was tested through a slurry rubber wheel abrasion test machine, and the wear behavior was also studied. The results indicate that the microstructures of the hardfacing alloy consist of lath martensite, residual austenite and WC particles. The wear resistance can be significantly improved through the addition of tungsten element being provided by the precipitation of WC particles. And the predominant wear mechanism was microcutting with shallow grooves and spalling.