Development Of The Electrode For Part Surfacing Repair Of MC5Cold Working Roll

In order to increase the service life of roll, the method of surfacing has been used for rollrepairing. Due to its flexibility and convenience, manual arc welding has already been the best choicefor part surfacing repair of cold working roll. At present, MC5steel is widely applied formanufacturing cold working roll because of its outstanding mechanical performance. Therefore, highhardness, high cracking resistance, high strength and toughness are desired by the deposited metal.The species of the domestic surfacing electrodes of medium and high carbon alloy steel are lesscompared with similar foreign products. In addition, these domestic surfacing electrodes are difficultto meet the performance requirements from MC5cold working roll for their unsatisfactory usingeffect. Consequently, it is imperative to explore the surfacing electrode with high hardness, excellentwear resistance and fine cracking resistance.According to phase transition strength, precipitation strength, solution strength and grain-refiningstrength of metallic material, the effect of content changes of alloy elements (Cr, W, Mo and V) onmicrostructure and mechanical properties of deposited metal was investigated by means of orthogonaldesign. Through data processing of the orthogonal test, the optimized contents of alloy elements havebeen ascertained: C~0.55%, W~4%, V~1.0%and Mo~2.5%. Moreover, the alloy elements can besorted in descending order as C, W, Mo, V by the impact on mechanical properties of deposited metal.Based on the results of the orthogonal test and further adjustment of the content of alloy elements, anew kind of surfacing metal formula of CrWMoV alloy series has been developed. The crackingresistance of new CrWMoV alloy series is improved. However, the crackings in weld bead are foundin rigid constraint test. It is revealed by scan electronic microscope that there are a few hot crackingsalong eutectic grain boundary in the microstructures of deposited metal of the new CrWMoV alloyseries. And the hot crackings are thought to be related with the iron alloy crystallizing point intervalwidening.In terms of the characteristics of new alloy series adopted in this paper and the microalloytechnology, yttrium oxide was added into the coating to increase cracking resistance. The effect ofyttrium oxide addition on microstructure, hardness and impact toughness of deposited metal wasstudied. The mechanism of effect of yttrium oxide on microstructure and mechanical properties ofdeposited metal was also discussed. It is concluded that when the addition amount of yttrium oxide is3%, the impact toughness of deposited metal can be increased by65%compared with the yttrium oxide doped with0%, but the hardness be reduced by0.6HRC. At this time, the microstructures ofhigh hardness deposited metal are mixtures of martensites, a small amount of residual austenite anddispersed carbide particles.The holding time fixed as4h, the effect of temper temperature on microstructure and mechanicalproperties of deposited metal has been researched. Meanwhile, the relation between the growthvelocity of precipitated carbides and temper temperature was identified. With two different heattreatment procedures compared, the final heat treatment process of deposited metal for part surfacingrepair of MC5cold working roll after welding was determined.The electrode developed in this paper was used for surfacing simulation experiment, MC5substrates was prepared for surfacing purposes, and the thickness of the deposited metal wascontrolled to20mm. The hardness of deposited metal of the electrode developed in this paper is59.3HRC and its impact value is7.6J. The mechanical properties of the designed electrode are superior toD322whose hardness and impact value are58.7HRC and5.7J respectively on the market. And itshould be pointed out that the electrode D322has been successfully applied to surfacing a few kindsof cold dies and cutting tools. As a result, the designed electrode can meet the part cold surfacingrequirement of MC5cold working roll and it will have high application value.