| The service condition of rock drill rod member is strict,23CrNi3Mo steel is widely used in drilling rod components of rock drilling tools because of its good strength and toughness.In use,it is found that although the strength of the members is basically satisfied,the impact toughness is insufficient,resulting in early fracture in the service process and a sharp decline in service life.In response to this problem,the composite toughening mechanism of the steel is proposed,that is,the structure toughening(the matrix structure is composed of pure toughness bainite lamellar structure,no brittle structure such as martensite or unstable residual austenite)+high The density,nanometer size and stable new phase/coherent phase interface between the parent phases form stable toughening,and apply this principle to obtain excellent toughening performance.This paper is devoted to improving the strength and toughness of the steel used for the component.The work focuses on(1)the development of the optimal heat treatment process of 23CrNi3Mo steel rod members;(2)test and analysis of mechanical properties and microstructure of materials;(3)reveal the strengthening and toughening mechanism and influencing factors of the steel used for the component.Based on the above work,this paper obtains the rock drill rod member which can meet the engineering service conditions and has excellent performance.The thesis draws the following main conclusions:(1)The best strengthening and toughening process for 23CrNi3Mo steel brazing rod members is 920℃austenitizing+240℃isothermal for 24h.The drill rod obtained by this process has the highest strength and toughness,namely tensile strength=1090MPa,yield strength=998.7 MPa,room temperature impact toughness=100 J/cm~2,which are respectively higher than the yield strength and toughness of the company’s original process.It is increased by 9%and 20%,the yield ratio is higher,and the impact fracture type is ductile fracture,and the fracture mechanism is micro ductile aggregate-based ductile fracture.This is an important result of this research,and has great application prospects;(2)Using metallographic,SEM,and TEM tools to study the morphological characteristics of microstructures under different heat treatment processes,and preliminary studies on the interface types,interface transformations,and new phase growth of new phases in solid phase transformation under the best heat treatment process for steel theoretical analysis.It was found that the bainite structure was the finest after isothermal treatment at the lower limit temperature of the lower bainite transformation at 240℃,and with the increase of the isothermal time,substructures such as broken bainite flakes and the precipitation of disperse coherent carbides appeared,leading to further material Significant strengthening and toughening,that is,refinement of lower bainite flakes,carbon supersaturated solid solution,coherent dispersion precipitation,and substructure strengthening are the four main strengthening and toughening methods of the steel,which constitute the steel with excellent strength and toughness. |
