Research On Alternative Domestic Materials And Manufacturing Process Of Rock Drilling Tools

Drill bit tools had been widely applied to the infrastructure constructionsuch as the energy exploitation, water conservancy and subway transportation.With the rapid development of economy, more and more market of the shankwas in demand. The quality requirement was higher and higher. The product mixof the drilling tools were unreasonable in China. Because there is a seriouscontradiction between excess capacity of the low-end products and dependenceon import of the high-end product. Compared with the developed industrialcountries, such as Sweden, British, American and Japan, gaps are wide on manyaspects such as properties, quality and specifications.The microstructure and mechanical properties of imported shank productswere investigated by using component analysis. Different domestic materialswere chosen for heat treatment experiment. And the effects of heat treatmentprocesses and parameters on mechanical properties of40CrNiMo and65Mnsteel were analyzed．The optimum heat treatment process was proved by aseries of refinement experiments. The main contents and conclusions wereshown below.(1)The results of chemical composition analysis show that this importedproduct is made of SNCM439steel. The microstructure is composed of withthe surface carburizing+thermal refining is fine tempered sorbite+carbide.Mechanical properties testing results show that the product has goodcomprehensive mechanical properties.(2)40CrNiMo and65Mn were chosen to replace the imported products.The results show that40CrNiMo after normalizing+high tempering+tempering heat treatment have the optimal performance. Adding hightemperature normalizing+tempering heat treatment in advance, the hereditaryof austenitic organization can be effectively blocked to prevent grain growth.After dealing with the two plans in this paper, the strength and toughness of65Mn has a big gap with imported products.(3)Different normalizing temperature (830℃,860℃,880℃,900℃and 930℃)experiments were conducted on40CrNiMo. With the increase ofnormalizing heating temperature, the grain refined firstly. The degree of grainrefinement is the largest at880℃. When the temperature was over900℃, theaustenitic grain was raised obviously. Normalizing sample of880℃fordifferent quenching temperature (770℃,790℃,830℃,860℃,890℃)experiment, the quenching heating temperature is higher, the quenchinghardness value is bigger. But when quenching at890℃, austenitic grainbegan to grow up obviously. the sample afer quenching at860℃for differenttempering temperature (550℃,580℃,600℃,630℃) experiment, Strengthtoughness value with the rise of temperature decreased obviously, shockabsorption function value increased gradually with break elongation andreduction of area.600℃tempering,40CrNiMoA has the best strongtoughness.(4)The property of40CrNiMo steel tempered had reached the standard ofimported products. The optimum heat treatment process was proved to benormalizing at880℃+tempering at high-temperature650℃,and thantempering at600℃after oil quenching at860℃.