| The conical pick is the main consumable component for coal mining,roadway excavation and road milling.Due to the harsh working conditions,the short service life of conical pick seriously affects the efficiency of the equipment and increases the production cost of the enterprise.The failure form of conical pick is wear,fracture and loss of tooth tip,which is mainly caused by their insufficient quality characteristics.Therefore,how to regulate and optimize the quality characteristics of conical pick has become an important research direction.Currently,the improvement of material microstructure by cryogenic treatment(CT)and magnetic treatment is a hot topic of research.Based on this,this paper combines and superimposes these two processes and proposes an electromagnetic coupled cryogenic treatment(ECT)process to improve the quality characteristics of conical pick by improving the microstructure of the material.The object of this paper is the conical pick used in roadheading machines,and the main research is as follows:(1)According to process parameters affecting the quality characteristics of conical pick,the characteristics of CT process and magnetic treatment process,the key parameters of ECT are determined as cryogenic temperature,cryogenic time,magnetization intensity and magnetization time.The key quality characteristics of conical pick are wear resistance,impact toughness,hardness and shear strength.According to the model of multi-parameter and multi-characteristics,the experimental design method of response surface method was developed and multi-objective optimization was performed using NSGA-Ⅱ genetic algorithm.Based on COMSOL multiphysics simulation software,the finite element analysis model of ECT process test device was established.The coupling effect between electromagnetic field and temperature field parameters was analyzed.The ECT test device was designed and manufactured to achieve the test requirements of high magnetization intensity and adjustable magnetization parameters.(2)According to the characteristics of the structure composition,material selection and brazing connection of dissimilar materials,the ECT process parameters of tooth body,tooth tip and brazing material of conical pick were studied respectively.By analyzing the results of quality characteristics,a model based on the regulation between process parameters and quality characteristics was established.Multi-objective optimization results of the quality characteristics were derived based on the principle of focusing on material wear resistance.Compared with the conventional heat treatment(HT),the wear resistance,impact toughness and Rockwell hardness of the tooth body after ECT were increased by 32.06%,9.23% and 2.07%,respectively.The wear resistance,impact toughness and Vickers hardness of the tooth tip after ECT were increased by 35.75%,11.39% and 10.44%,respectively.The shear strength of the brazed interface after ECT was increased by 31.92%.(3)Shear fractures at the brazed interface,frictional wear and impact fractures of the tooth body and tooth tip of conical pick were analyzed.The wear mechanism,impact fracture and shear fracture morphological characteristics were obtained.Microscopic tests such as TEM,EBSD,SEM and XRD were used to study the strengthening mechanism of the conical pick material.The increase in martensite,carbide precipitation,the increase inε-Co phase,and the increase in dislocations improved the hardness and strength of the material,and finally enhanced the wear resistance of the material.The increased β-Cu(s.s)phase and the grain refinement improved the toughness and strength.The appearance of the dendritic organization and the relief of tensile stresses inhibited the crack extension and finally improved the shear strength of the material.(4)On the basis of research on quality characteristics regulation of conical pick materials,the optimal process scheme of the integral conical pick was obtained.The influence law of ECT on the quality characteristics of the integral conical pick was studied.Compared with HT,the verified values of impact toughness,wear resistance and shear strength of conical pick after ECT were increased by 5.24%,30.77%,29.43%,respectively.The verified values of impact toughness and Vickers hardness of tooth tip after ECT were increased by 10.73% and 9.13%.The verified value of Rockwell hardness of the tooth body after ECT was increased by 1.91%.The results are in good agreement with the results for each material,indicating that the final derived ECT process is effective and can be applied to the manufacturing process of conical pick. |
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