Computer simulation of core filling process of cast high speed steel roll

Core filling process of cast high speed steel roll was simulated.Ductile iron was used as core material.The influences of filling parameters,such as core filling time and core filling temperature,on the filling process were investigated.Based on the simulated results,optimal core filling parameters were determined.The predicted temperature fields show that the temperature at the roll shoulder is the lowest during the core filling process and usually causes binding defects there.Method for solving this problem was presented.

Experimental research on electromagnetic continuous casting high-speed steel composite roll

A high speed steel composite roll billet was fabricated, which is regular in shape, smooth in surface, slight in trace, compact in internal structure, free of slag inclusion, shrinkage cavity, cracks and other flaws, and good in macro quality of junction surface using a vertical continuous casting machine. The interface zone microstructure of bimetallic in billet of high speed steel composite roll was analyzed by metallurgical microscope(OM), X-ray diffractmeter(XRD), scanning electron microscopy(SEM) and energy-dispersive X-ray analysis(EDS). The results indicate that the microstructure of roll billet is composed of chilled solidified layer, dendrite zone, interfacial zone of bimetal and core material zone. The microstructure of outer shell material is composed of martensite + bainite + residual austenite + some small labyrinth-shape, small-short lath-shape, or dollop-shape eutectic carbides. The microstructure of core material is slice-shape pearlite and a little ferrite along boundary of cells. The interface region microstructure of bimetallic composite roll consists of diffusion region, chilled solidified layer and columnar grain region.

Effect of quenching temperature on structure and properties of centrifugal casting high speed steel roll

The critical points and time-temperature-transformation(TTT)curves of the isothermal transformation diagrams for a high-speed steel casting on a horizontal centrifugal casting machine had been determined experimentally in the study.The effects of quenching temperature on the microstructures and properties of centrifugal casting high speed steel(HSS)roll has been investigated using scanning electron microscopy(SEM), light optical microscopy(LOM)and X-ray diffraction(XRD)as well as using tensile,impact,and hardness tests. The results show that the HSS roll has excellent hardenability and its matrix structure can be transformed into the martensite after being quenched in the sodium silicate solution.The retained austenite in the quenching structure increases and the hardness decreases when the quenching temperature exceeds 1,040℃.The tensile strength and impact toughness of HSS roll increase once the quenching temperature is raised from 980℃to 1,040℃. However,the tensile strength and impact toughness have no significant change when the quenching temperature exceeds 1,040℃.The HSS roll quenched at 1,040℃exhibits excellent comprehensive mechanical properties.

Effect of rare earth elements on the thermal cracking resistance of high speed steel rolls

The effect of rare earth elements on the thermal cracking resistance of high speed steel （HSS） rolls was investigated. Laser rapid heating was used for thermal fatigue experiments. Thermal cracks and microstructure were observed using metalloscopy and scanning electron microscopy. The results showed that thermal cracks initiated from the interface between the matrix and eutectic carbides （including M6C and M7C3 type carbides）,and propagated along the interface between the two phases. MC type carbides enriched with vanadium could prevent the propagation of thermal cracks. The presence of rare earth elements decreased the quantity of big eutectic carbides,and proportionally increased spherical and rod-shaped MC type carbide content. HSS0 （0.00% RE） had approximately three times the thermal cracking density of HSS3 （0.12 wt.% RE）. Rare earth elements were shown to significantly improve the microstructure and thermal cracking resistance of HSS rolls.

Effect of rare earth addition on continuous heating transformation of a high speed steel for rolls

The effect of rare earth（RE） on continuous heating transformation of a high speed steel for rolls was investigated by using differ-ential scanning calorimetry（DSC） with combination of microstructure analysis.Determination of the Ac1 and Ac3,the starting temperature of carbide dissolution and melting upon heating,the enthalpy change for the α→γ transformation and overall carbide dissolution were also es-tablished.It was found that RE could reduce the volume fraction of large eutectic carbides and the chrysanthemum-like eutectic colonies but could not change the phase composition.RE made a little change to Ac1,but the variation in Ac3 and enthalpy for the α→γ followed an in-creasing pattern as the RE addition increased.The start temperatures of carbides dissolution increased with increase of RE addition,which may be associated with the influences of RE on the morphology of carbides,but the overall enthalpy change of carbides dissolution decreases as the RE addition increased.Moreover,the start temperature of melting also increased with increasing RE addition.

Influence of rare earth elements on solidification behavior of a high speed steel for roll using differential scanning calorimetry

The influence of rare earths（RE） on solidification behavior of a high speed steel for roll was investigated by using differential scanning calorimetry（DSC） in combination of microstructure analysis.It was found that the sequence of solidification was L→γ,L→γ＋MC,L→γ＋M2C,L→γ＋M6C,respectively.The start temperature and the latent heat liberated by unit mass of L→γ and L→γ＋MC increased with increase of RE addition,indicating that RE could trigger the crystallization of the primary γ and the MC carbide more effectively.The promoting effect of RE on the heterogeneous nucleation was believed to be an important cause of this effect.Grain refinement,discontinuous network of eutectic carbides and disperse and finer MC were observed in the samples with RE addition,moreover,RES could act as the heterogeneous nucleus of the MC.RE addition was favorable for stable M6C at the expense of the metastable M2C.