The Research Of New Cold Working Die Steel With High Toughness And High Wear Resistance

The cold working die steel with high-carbon and high-chromium are widely used due to its high hardness and good wear resistance. But a lot of coarse net-like eutectic carbides are often located on the grain boundaries of this steel attributed to the segregation of alloy elements during the steel soldification. These carbides can play down the strength and toughness even shorten the application life of the steel. So it is a efficient method to improve the performance of the cold working die steel by breaking the net-like carbides and changing the morphology of them.In this article,RE-Nb-Ti multi-modificator is used to modify the steel and the composition of the steel is also adjusted. The HSVM,SEM,XRD,EDS and other property test experiments are used to analyze the results. It is shown that the multi-modification can effectively refine the dendritic grains of the steel. In addition,the Cr₇C₃ carbides which are plate-like and connect each other in the matrix are decreased and the morphology of those are transferred from net-like to block-like. Some particle-like M02C and NbC containing titanium and molybdenum are also formed as dispersion. At the same time, the content of oxygen and sulphur are lowered and phosphorus is transfered into the compound carbides,so the toughness of the steel is improved due to the decrease of the iron phosphide eutectic.Using the graphite pole to increase the carbon content and incorporating with multi-modification can efficiently induce the precipitation of the carbides and decrease the carbon content in matrix. Then the lath martensite can be gained after the 870℃oil-quenched and the residual austenite can be avoided. Carbides with high chromimu will be changed into hexagon by the spheroidal annealing and carbides containing niobium,titanium and molybdenum can be better spheroidal.The property test results show that the performance of the cold working die steel after multi-modification is the best when it is oil-quenched at 870℃and tempered at 600℃. The hardness is about 58.5HRC and the impact toughness can get to 50 J/cm².Moreover,the multi-modification and heat treatment can obviously improve the wear resistance without the apparent reduction of hardness.