| Cold treatment processes materials below 0?,which can improve the microstructure and optimize the performance of materials,using cold processing equipment with alcohol or liquid nitrogen as refrigerant.Wear resistant steel ball is used for milling medium in a ball mill,it is widely used in mining,electricity,building materials and other industries,and it is easy to wear and tear,and widely used at home and abroad.Wear resistant steel ball is formed by the rolling of high-carbon low-alloy steel,it has a high carbon content,suitable alloying elements,rare types of inclusions,so it has high hardness,good harden-ability and wear resistance.Performance of steel ball unstable,it easy to crack,and its life is not ideal.The chemical composition and the metallurgical quality of steel billet and high carbon low alloy B3 steel rolling ball was researched reasonably selection of materials;Cold processing technology and traditional heat treatment technology with a reasonable convergence,optimizing heat treatment process of steel ball,which can improve the hardness,wear resistance,and use of performance stability.It has an important significance to improve the quality of our wearable steel ball.This paper describes the present situation of the development of cold processing technology and high-carbon low-alloy steel ball at home and abroad.Design of quenching,tempering and cooling process of B3 steel ball specimens,and comparative analysis of the change of microstructure and properties of steel ball specimens under the three treatment methods.These three methods are hardening,quenching and tempering,quenching and tempering and cold treatment.The Rockwell hardness test hardness,the Pendulum impact testing machine test impact toughness;the microstructure analysis by optical microscope,the microstructure and impact specimens were analyzed by scanning electron microscope.X ray phase analysis was used to determine content of residual austenite microstructure changes of steel ball specimens before and after cold treatment.the change of martensite,residual austenite forms and contents was researched influence on properties of steel ball specimens.The main conclusions are follows:B3 steel ball specimen is heated to 1250?×10min and cooled to 850?in the furnace,and then quenched with water,225?×175min tempered,which receives a great deal of lath martensite and a certain amount of retained austenite,its hardness and toughness values are 58.0HRC,39.05 J/cm~2.B3 steel ball specimen is quenched below 800?×10min,austenitizing less,the main microstructure is Pearlite,which has low hardness and high impact toughness.When steel ball specimen is heated to 850?×10min quenching,its austenitized incompletely,resulting in dissolution of cementite is not sufficient,insufficient high-temperature austenite,inhomogeneity,while obtaining lath martensite,upper bainite,lower bainite and a small amount of residual austenite.Its toughness is 18.38 J/cm~2.Due to the presence of Cr,Si and other alloying elements in B3 steel ball specimens,after quenching and tempering which tissues contain retained austenite volume fraction of about 9.5%.Through cold treatment process,steel ball in the microstructure will transform from retained austenite to martensite,as well as precipitating fine granular carbide,resulting in martensite transformation hardening and a second phase precipitation strengthening.This two enhancement patterns are superimposed,enabling steel ball higher hardness,while also maintaining a certain degree of toughness.B3 steel ball specimen is heated to 1250?×10min and cooled to 850?in the furnace,and then quenched with water,225?×175min tempered,-80?cold treatment 4h.Through the process,the volume fraction of retained austenite fell 4percent,and its hardness value is 60.8HRC,its toughness is 23.74J/cm~2.Low impact toughness specimens contain large size,irregularly shaped metallic inclusions,their main types are globular sulfides and oxides. |
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