Electroslag surfacing with liquid metal(ESSLM)is an excellent method for producing high-quality bimetallic compound rollers.The quality of each compound roller is primarily determined by the metallurgical quality of the combined interface.A GCr15/40 Cr compound roller is produced using an ESSLM non-consumable electrode electroslag heating method.The temperature and electric fields produced by the ESSLM system are calculated.As the roller core moves downward in the mold,it passes through five sections:the preheating section,the rapid heating section,the temperature homogenizing section,the bimetal fusing section and the cooling section which listed from the top to bottom of the mold,respectively.The temperature distribution and the degree of the surface temperature fluctuation in the roller core are different for each section.Near the combined interface,four layers are found from the roller core to the cladding layer:the remelting layer,the fusion layer,the interface solidification layer and the chilling layer,respectively.Among these,the fusion and interface solidification layers are the key transition zones that greatly influence the combination quality.The surface temperature of the roller core prior to cladding is mainly determined by the drawing velocity,and the thickness of the transition layer increases as the drawing velocity decreases.A transition layer that is too thick or too thin will reduce the mechanical properties at the combined interface.Therefore,the drawing velocity should be limited to a moderate range to produce a satisfactory bimetallic compound roller.
Lei RAOShuang-jun WANGJian-hua ZHAOMao-peng GENGGang DING
A comprehensive mathematical model was established and used to simulate the macro-and microstructure evolution during the production process of 5CrNiMo steel ingot by electroslag remelting(ESR)method.Along the ingot height,the macrostructure distribution characteristics changed from vertical,fine columnar grains to tilted,coarse columnar grains,and this transformation process occurred at the very beginning of ESR.In the cross section of the ingot,there were three grain morphology regions and two grain type transition regions from the outside to the center of the ingot.These regions were the fine columnar grain region,columnar competitive growth transition region,coarse columnar grain region,columnar to equiaxed grain transition(CET)region,and coarse equiaxed grain region.The influence of the remelting rate on the macrostructure and microstructure was investigated using a series of experiments and simulations.The results showed that a low remelting rate could produce a small grain growth angle(GGA);the average secondary dendrite arm spacing(SDAS)firstly decreased and then increased as the remelting rate increased.An excessively high or low remelting rate can increase the GGA and average SDAS in ingots.Thus,the remelting rate should be controlled within a suitable range to reduce composition microsegregation and microshrinkage in the ingot to produce an ESR ingot with satisfactory hot forging performance.
Lei RAOJian-hua ZHAOZhan-xi ZHAOGang DINGMao-peng GENG
The processing parameters and refining mechanism of Mg-Al alloy treated with a newly developed carbon inoculant under different conditions were investigated experimentally in this work.Results show that the finest α-Mg grain in AZ91D alloy can be obtained after processing at about 740 ℃,and the average grain size of α-Mg grain decreases from about 180.4 to 85.6 μ m by adding mass fraction w in = 1% inoculant into melt.However,no evident refinement was achieved with excessive inoculant for Mn-free Mg-9Al alloy.Scanning electron microscope(SEM) photo,energy dispersive spectroscopy(EDS) analysis on the Mn-contained intermediate phase and differential scanning calorimetry(DSC) results indicate that Mn element plays an important role in the heterogeneous nucleation of α-Mg grain.In the early stage of solidification,Al-Mn-C compound particles formed on the surface of Al4C3 nano-particles should be the potential nuclei for primary α-Mg and probably responsible for the grain refinement achieved in the carbon inoculation process.
