| Grinding balls are widely used as media in mining, building materials, chemical and other industries, the national annual consumption has exceeded 2.6 million tons, but due to working condition is constantly changing, it is urgent to upgrade performance and reduce cost. Carbidic austempered ductile iron (CADI) has broad market prospect on grinding balls for its outstanding performance advantage.The purpose of this article is to optimize the organization and heat treatment process of CADI grinding ball material by combing with its working condition and the characteristics of CADI. By using OM, SEM, XRD and other methods to study the influences of manganese, molybdenum and austempered temperature on microscopic structure and performances of CADI grinding ball material, and test the CADI grinding balls.The results showed that the microscopic structure of as-cast CADI containing pearlite, graphite nodule and carbide distributed in, the graphite spheroidizing was 2-3 grade level, graphite size reached 6-7 magnitude. The increasing content of Mn and Mo promoted the quantity of pearlite and carbide, meanwhile decreased the content of graphite nodule. After austempered, the microstructure consists of graphite nodule, needle-like ferrite, carbide and retained austenite, the increasing content of Mn and Mo promoted the quantity of carbide and retained austenite, Mo also can refine needle-like ferrite. Mn tended to dissolve out to form (Fe,Mn) 3C, Mo tended to dissolve out to form (Cr2.5Fe4.3Mo0.1) 7C3 and (Fe,Mo) 3C.When Mo content was constant, increasing Mn content, the impact toughness of CADI grinding ball material decreased; the rock hardness increased, the wear rate decreased, wear resistance increased, furrow and spalling became less, cutting marks of wear surface became shallow; the corrosion potential Ecorr increased, corrosion current Icorr decreased, corrosion resistance increased. The specimen containing 1.93wt.% Mn had good comprehensive performance, its impact toughness was 9.7J/cm2; rock hardness was 53.6HRC, the wear rate was 0.151mg·m-1; the corrosion potential Ecorr was -0.6497V, the corrosion current Icorr was 6.262x10"6 A·cm-2.When Mn content was constant, increasing Mo content, the impact toughness of CADI grinding ball material first increased and then decreased; the rock hardness increased, the wear resistance increased; the corrosion resistance increased. The specimen containing 0.43wt.% Mo had good comprehensive performance, its impact toughness was 14.6J/cm2; rock hardness was 53.4HRC, the wear rate was 0.221 mg·m-1; the corrosion potential Ecorr was -0.6016V, the corrosion current Icorr was 7.359×10-6A·cm-2.With the austempering temperature of 2# (Mn 1.93wt.%, Mo 0.29wt.%) specimen increased, the quantity of retained austenite increased, needle-like ferrite grain grew gradually, besides, the impact toughness increased, the impact fracture morphology was cleavage fracture characteristics,the rock hardness decreased, wear rate increased, wear resistance decreased, corrosion resistance increased. The specimen had good comprehensive performance when the austempering temperature was 260?, its impact toughness was 8.8J/cm2, the rock hardness was 54.7HRC, the wear rate was 0.150 mg·m-1, the corrosion potential Ecorr was -0.6491V, the corrosion current Icorr was 8.376×10-6 A·cm-2.The CADI grinding balls are made according to the results of the research, its chemical composition is C 3.3?3.8wt.%, Si 2.2?2.7 wt.%, Mn 15?2.0 wt.%, Cr 0.8?1.2 wt.%, Cu 0.4?0.8 wt.%, Mo 0.2?0.5 wt.%. Heat treatment process is made according to its size:austenitizing temperature is 900? for 1?2.5h, austempering medium is 50%KNO3+25%NaNO+25%NaNO2, austempering temperature is 250? ±20? for 1.5-3h. The suface rock hardness of ?120mm CADI grinding ball ?56HRC, average rock hardness of three consecutive points from Surface to inward ?53HRC, impact toughness?7J/cm2, ball consumption?220g/t, broken rate?0.1%, impact fatigue life?10000, which meet the request of working condition. |
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