| Wear is one of the main failure forms of material. According to statistics, more than 80% of the mechanical material failure caused by wear, and more than 50% of serious accidents resulting from excessive wear and lubrication failure. Therefore, it is necessary to research and develop high-performance wear resistant steel to reduce the loss and increase the service life of equipment. Low alloy wear resistant steel as an important material, because of its low alloy content, good overall performance, flexible and cheap production, it was widely used for the manufacturing of engineering machinery, mining machinery and metallurgical machinery. In this paper, high level of low alloy wear resistant steel NM500 was studied. The composition and microstructure were designed due to the mechanical properties requirment and application condition. The relationship of the process and its microstructure, mechanical properties and three-body impact abrasive wear performance were also analyzed. At last, we development three kinds of new high performance wear resistant steel:martensitic steel with low-cost, martensitic-ferritic steel with high toughness and martensitic-nano carbides steel with high wear resistance performence. The main original works of paper are president as follows:(1) A new kind of low-cost type martensitic wear resistant steel NM500 was development by adding some Cr, B in the common carbon steel compare to the traditional wear resistante steel which adding much more Ni and Mo, even the rare ellements. The abtained mechanical properties of the development steel was:yield strength is higher than 1600MPa, Brinell hardness is higher than 500, elongation is higher than 10% and-40℃ low temperature impact is higher than 30J. The wear resistance of the development steel was also better than the same level abrasion resistant steel which produced by aboard.The continuous cooling transformation behavior, effects of hot deformation and cooling after hot deformation before the off-line heat treatment, quenching and tempering during the heat treatment on prior austenite grain size, block size, lath size and precipitation were studied, and the relationship between the process parameters and mechanical peroperties and three-body impact abrasion wear were also analyzed. The develoment steel could abtain excellent cooperation of high hardness and good toughness when the steel finish rolling at lower temperature and cooling to the bainite region, and then quenched at the temperature of 880℃ and tempering at the temperature of 170℃. The wear resistance was highest at this time.The influence of precipitates on wear resistace during lower temperatre tempering was also studied. Precipitates were firist formed the carbides of ε-FexC, and it was beneficial to the wear resistance of the steel. As the tempering temperature increased, the carbides changed to Fe3C, which will clustered at the grain boundaries and caused the adverse effect to the fracture toughness of steel, which was harmful to the wear resistance of steel.(2) In order to meet the requirements of-40℃ low temperature impact toughness, the martensitic-ferritic dual phase steel which produced by intercritical heat treatment was proposed to enhance the toughness. The abtained better toughness also could achieve the purpose of improving wear resistance.The morphology and volume fraction control of ferrite were studied for both containing 0.26% Mo and none Mo and Ni experiment steels. And the influence of them on microstructure, mechanical peroperties and three-body impact abrasive wear was also studied. The results shown that excellent low temperature toughnes and better wear resistance martensitic-ferritic dual phase steel could abtained by process control or Mo alloy addtion, such as rolling and cooling after rolling before the intercritical heat treatment to abtain acicular ferrite or bainite, then intercritical heat treatment blow the temperature of Ac3 about 10℃. At martensitic-ferritic dual phase steel, the volume fraction control of ferrite was about 3%-6%, and its -40℃ impact toughness was larger than 50J, which achieved the application requirement of cold regions.(3) To further enhance the wear resistance of the steel, the author presented the view of distribut large number of nano-carbides on lath martensite matrix. At last we achieved the microstructure of "lath martensite matrix and nano TiC or (Ti,Mo)xC", which enhanced the wear resistance of steel.By controlled rolling and cooling after rolling, we got a lot of small, dispersed nano-precipitates. During the offline heat treatment stage, we keep them not to growth and dissolution, this is the process that we abtained the co-exist of nano carbides and martensite microstructure. The continuous cooling transformation process, cooling process after rolling before offline during quenching and tempering process of the experimental micro-alloyed steel, titanium carbide, organization, and the variation of mechanical properties, three-body impact abrasive wear performance were studied. The results shown that ultra-fast cooling after rolling to 630℃ of bainite transformation range and slow cooling to room temperature at the furnace, then quenchinged at 880℃ and temperinged 180℃ for 10 min, the martensite matrix obtained the distribution of large number of nano TiC or (Ti, Mo)xC in the experimental steel, as well as’the optimum strength and toughness.(4) The abrasive wear behavior of the development low-cost type martensitic wear resistant steel, martensitic-ferritic dual phase high toughness steel and martensitic-nano carbides high wear resistance steel were studied. The wear mechanisms of the three development steel were also ananlyzed.The relative wear resistance showed that the develomment steel all exhibit excellent wear resistance. Low-cost type martensitic wear resistant steel was 1.04 times to JFE-EH500, which produced by JFE steel company, and was 1.33 times to DILLIDUR500V, which produced by Dillingen company. The martensitic-ferritic dual phase high toughness steel was 1.17 times to the low-cost type martensitic wear resistant steel. And the martensitic-nano carbides high wear resistance steel was 1.23 times to the martensitic wear resistant steel and 1.28 times to JFE-EH500 and 1.72 times to DILLIDUR500V.The abrasive wear resistance was result of both hardness and toughness when the steel was only martensite phase and martensitic-ferritic dual phase steel, only the good combined of hardness and toughness could abtain higher wear resistance. While for the martensitic-nano carbides wear resistance steel, the abrasive wear resistance was result of hardness, toughness and precipitates. Fine grain strengthening, precipitation strengthening and the high hardness of precipitates were the reasons of the high wear resistance.Based on the experimental results above, the development process has been applied successfully in Shou Steel, Nanjing Steel, Lian steel, Xiangtan Steel and Wuhan Iron and Steel Company. The products were used for the manufacturing of engineering machinery, mining machinery and metallurgical machinery. And the plates were exported to the more than ten countries and regions, such as United Kingdom, Australia. The discovers also have been award the first grade award of Jiangsu Province Science and Technology in 2012 and national key new products in 2013; In addition, the sesults of the discovers has been award the first grade of China Machinery Industry Science and Technology as part of the innovative content, which create good social and economic benefits. |
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