The Study On The Microstructure And Properties Of Cast Wear-resistant Materials For Impeller Breaker Hammer

With the development of society and economy, more and more materials have been becoming necessities, such as ore,cement,coal and so on. A lot of materials need to be broken in the process of handling, at the same time, wear-resistant materials have been used enormously. At the present, there are many types of equipment which are used to break crude materials, such as impeller breaker,jaw crusher,hammer mill and roll breaker and so on. It is the hammer that is the easiest to be abraded and consumed in shattering process.Hammer, which is in the state of high-speed rotation, violently collides with materials, and the materials are broken into different kinds of grain size. So,the work condition is very awful when the hammer is in a high-impact,high-stress abrasion state. Rock,metal ores and other hard objects are usually broken by the hammer which is used out quickly because of abrasion and need to be replaced with a new hammer. In addition, production process will be paused because the hammer could be broken due to high impact force.In recent years, science and technology workers at home and abroad have been conducting a lot of researches on enhancing the strength and toughness and been receiving many harvests. But, there still are many difficulties about enhancing capability of the materials of hammer.impeller breaker is being widely used because its many merits,such as, simple structure,high broken ratio,lower power consumption,discharging uniform,strong adaptability to different types of materials,operation and maintenance convenience, and so on. In this paper, based on the hammer of impeller breaker, we quest for the ways to enhance the capability of the materials of hammer.Based on researches about alloy wear-resistant materials in recent years, we select five kinds of materials from all wear-resistant materials which are composed of alloy wear-resistant steel and alloy wear-resistant iron. The five kinds of materials are as follow : medium- chromium alloy steel,high-chromium alloy steel,high-siliconbainite steel,Ni-Mo alloy iron,Cr-Mo-Cu alloy iron. We hope to receive a kind of material to replace of the material that is being used by many factories.Many wear-resistant materials that are prepared by directly casting methods have inevitably deficiencies,for instance, large casting structure , non-homogeneous component and larger residual stress. In order to erase these deficiencies, the casting materials must be heat-treated by different methods. At the same time, because different abrasion mechanism, it is necessity that the samples have high-hardness,good plasticity and toughness to enhance its operational life span in the actual process of service. And different hardness,plasticity and toughness of wear-resistant materials are needed under different working conditions. These mechanical properties could be good match if the sample is heat-treated.Different samples are used with different heat treatment. We use same heat treatment for the three former kinds of samples, as follow:Firstly, No.1,No.2 and No.3 are heated to 900℃and held with 1 hour, dry quenching, and tempered with 250℃and held with 1 hour;Secondly, No.1,No.2 and No.3 are heated to 930℃and held with 1 hour, dry quenching, and tempered with 250℃and held with 1 hour;Thirdly, No.1,No.2 and No.3 are heated to 960℃and held with 1 hour, dry quenching, and tempered with 250℃and held with 1 hour;We use same heat treatment for the two latter kinds of samples, as follow:Firstly, No.4 and No.5 are heated to 910℃and held with 2 hours, oil quenching, and tempered with 230℃and held with 2 hours;Secondly, No.4 and No.5 are heated to 910℃and held with 2 hours, isothermal quenching (the temperature is about 150℃), and tempered with 230℃and held with 2 hours.In this paper, we have compared microstructure with different samples, tested the mechanical properties and wear resistance of different samples.1,comparing microstructure with different samples:(1) The metallurgical structures which were ferrite equiaxed structure and a little grid-pearlite were transformed into tempered martensite and carbonide, after medium-chromium alloy steel was heated to 900℃,930℃,960℃and held with 1 hour, dry quenching, and tempered with 250℃and held with 1 hour. But,after the sample was heat-treated , the crystal grains have become bigger and more uneven than cast structure, grain boundary have become more obvious.(2) The metallurgical structures which were a great lot of pearlite and continuous grid-carbonide were transformed into tempered martensite+ granular bainite+ retained austenite+ intermittent grid-carbonide, after high-chromium alloy steel was heated to 900℃,930℃,960℃and held with 1 hour, dry quenching, and tempered with 250℃and held with 1 hour. It is useful for enhancing impact ductility after heat treatment because continuous grid-carbonide was transformed into intermittent grid-carbonide.(3) The metallurgical structures which were needle-like white bainite ferrite and retained austenite were transformed into the board strips bainite and retained austenite among the gap of matrix, after high-silicon bainite steel was heated to 900℃,930℃,960℃and held with 1 hour, dry quenching, and tempered with 250℃and held with 1 hour.(4) The metallurgical structures which were flake guaphite+ retained austenite+ martensite were transformed into martensite+ bainite+ retained austenite,after Ni-Mo grey cast iron was heated to 910℃and held with 2 hours, oil quenching, and tempered with 230℃and held with 2 hours. The metallurgical structures which were flake guaphite+ retained austenite+ martensite were transformed into tempered martensite +lower bainite+"white–bright zone", after it was heated to 910℃and held with 2 hours, isothermal quenching, and tempered with 230℃and held with 2 hours.(5) The metallurgical structures which were pearlite and grid-carbonide were transformed into tempered martensite+carbonide+ a little iron phosphide eutectic after Cr-Mo-Cu grey cast iron was heated to 910℃and held with 2 hours, oil quenching, and tempered with 230℃and held with 2 hours. The metallurgical structures which were pearlite and grid-carbonide were transformed into martensite+ lower bainite+ massive carbonide.2,The samples heat treated can be tested with hardness tester and toughness detector, the results are as follow:(1)The hardness results show: The hardness of medium-chromium alloy steel decreased;The tempering hardness of high-chromium alloy steel,which was HRC55.9,was better than cast hardness HRC36.3 and increased 53.9%;Before and after heat treatment, the hardness of high-silicon bainite steel changed litter; after heat treatment, the hardness of Ni-Mo grey cast iron can attain HRC62.6 and the hardness heat tof Cr-Mo-Cu grey cast iron can attain HRC 62.1.(2) the results of impact ductility show:After the high-chromium alloy steel was heated to930℃and held with 1 hour, dry quenching, and tempered with 250℃and held with 1 hour, its impact ductility is 15.16J/cm2,which was nearly double than the impact ductility of material of active hammerhead. Because of its high impact ductility, it can prevent the fault caused by fractured hammerhead in the actual production process.3,The samples of high-chromium alloy steel and Cr-Mo-Cu grey cast iron were tested with abrasion tester. The results show the abradability of two kinds of material was better than the material of active hammerhead. Under the positive pressure with 15N, wearing capacity of high-chromium alloy steel was 0.0122g which was less than 0.0166g that was the value of wearing capacity of active hammerhead. Wearing capacity of Cr-Mo-Cu grey cast iron was 0.0129g which was less than 0.0166g that was the value of wearing capacity of active hammerhead.Based on the above three factors, we choose the high-chromium alloy steel to replace of the material of active hammerhead, because the heat treated high-chromium alloy steel had high-hardness,high-impact ductility and good wear-resisting property.So, we choose high-chromium alloy steel and heat treatment process were high-chromium alloy steel was heated to930℃and held with 1 hour, dry quenching, and tempered with 250℃and held with 1 hour.