Research On Laser Surface Alloying Of Roller

The quality and lives of rolls have important effect on the efficiency of rolling production, product quality and manufacturing costs. Roll materials are deficient in our country and their prices are high, so if the roll fails due its surface wear, the whole roll will be discarded, thus causing huge waste of materials. How to improve the wear resistance of rolls matters a lot in improving economic benefits and manufacturing efficiency.In recent years, induction heating quenching, puddle welding, and thermal spraying are widely used to improve the surface wear resistance of rolls. But the bonding between the surface of roller and the coatings manufactured by these techniques is not metallurgical. Laser surface alloying can fabricate dense coatings with metallurgical bonding with substrates, thus improving the wear resistance of substrates. The aim of the present work is to get dense coatings on hot rolls by laser surface alloying, which have good wear resistance and metallurgical bonding with substrates. It can offer theoretical instructions on repair and strengthening of rolls by laser surface alloying and technical support for its further application.The substrates were 70MnV cast steel and nodular cast iron rolls. High power laser was used to carry the surface alloying experiment. Coatings with good metallurgical bonding with substrates were fabricated under optimal processing parameters. Optical microscopy (OM), scanning electron microscopy (SEM) and attached energy dispersive x-ray spectrometry (EDAX), X-ray diffract (XRD), wear tester and microhardness tester were used to analyze the microstructue, composition, phase and wear resistance of the coatings.High power laser was used to carry out the surface alloying on 70MnV cast steel roll with NiCr-Cr3C2 powders pre-deposited on it. The optimal parameters were:laser power of 4kW, laser spot diameter of 1.5mm, overlap ratio of 33.3% and scanning speed of 2.2m/min. A dense and cracks and pores free coating with uniform microstructure and metallurgical bonding with substrate could be fabricated with these parameters. The thickness was 0.4798mm and the average microhardness was 858HV, as 2.6 times higher as the substrate. High temperature wear test at 500℃showed that the wear resistance of this coating was 7.4 times higher than the cast steel roll substrate.Powder C-B-W-Cr were pre-deposited on nodular cast iron rolls before high power laser surface alloying. The optimal processing parameters were:laser power of 4kW, laser spot diameter of 1.5mm and overlap ratio of 36.7%. The thickness of this coating was 0.3670mm and average microhardness was 1201HV, which was 1.4 times higher than the substrate. Wear test results at 500℃showed that the wear resistance of the coating was 0.6 times higher than the nodular cast iron substrate.The reasons for the improvement of the mircohardness and wear resistance of the coating were as follows:there are fine microstructure, high defect concentration and high inner stress of alloying coating. There exists strengthening effect of martensite and some dispersed carbides. There exists solid solution strengthening effect of alloying elements in the coating. Furthermore, the exist of residual austenite can reduce the impact load during rolling.