Study On Surfacing Technology For 9Cr2Mo Cold Midst-Roller And Its Application In Engineering

Cold midst-rollers are main parts of cold rolling mill, and they are liable to be consumed. So repairing or re-manufacturing cold mist-rollers with submerged arc surfacing processes will have good economic and social benefits. Now the solid and cored wires as submerged arc surfacing materials are widely used on a global scale. Flux-cored wires, as a kind of high-tech surfacing product, are of many advantages in surfacing, such as good flexibility in adjusting chemical composition, high welding quality, low cost, 1-3 times longer service life and 20-40percent lower cost than the ordinary roller etc. Therefore Cr-Mo-W-V-Ni system flux-cored wires are selected in hardfacing for cold midst-rollers made of 9Cr2Mo steel.The high internal stresses between the roller and the surfacing layer may induce cracking, In order to avoid hot cracking during surfacing, a kind of transition flux-cored wire named YD404L-4 is used, and meanwhile, another kind of surfacing flux-cored wire named YD551-4 is selected according to the requirements of cold midst-rollers.There are many factors that influence the properties of surfacing metal, for instance the type of flux-cored wire, the selection of welding conditions and the administration of welding processes. Otherwise, welding defects may appear in surfacing layer. So causations of defects in submerged arc surfacing are analyzed, and measurements for avoiding them are supplied in this paper.The composition of surfacing metal, flux, process variables and heat-treating condition are the main factors influencing the characteristics of surfacing layer. By means of experiments, HJ 107 as an optimistic flux and the corresponding welding parameters have been selected for the two flux-cored wires above. Under the condition, the excellent welding process behavior, good weld formation and the higher alloy transition coefficient can be acquired, and mechanical properties of surfacing metal are excellent, which meet the requirements of cold mist-roller working.The technologies developed in this paper have passed through the medium-term testing in Cold Rolling Firm of Pan Gang Group. Practical employments have proved that the cold midst-rollers repaired satisfied the working need, and have been approbated and accepted by users. The hardness of surfacing layer is 55-58 HRC, the fluctuating range of which is no more than ±2.0HRC. There are not cold and hot cracks in surfacing layer during and after welding. The resistance to wear and the impacttoughness are good. The flux-cored wires above, with high hardness, high resistance to crack and wear, are new in China.