Study On Strengthening And Toughening Treatment Process,Structure And Properties Of 23CrNi₃Mo Drill Rod

23CrNi₃Mo steel is a low-alloy structural steel,which is widely used in the drill rod component of rock drilling tools because of its good toughness and hardenability.When used as a drill rod member,it is subjected to high-strength pressure,torsion,tensile,bending stress and high-frequency impact.Therefore,the steel member should have extremely high toughness.The strength of the drill rod member currently used is basically satisfactory,but The impact toughness is seriously insufficient,causing early breakage during use and causing serious economic losses.In this paper,the lower bainite heat treatment process of 23CrNi₃ Mo steel drill rod is studied.The morphology and effect on the properties of 23CrNi₃ Mo steel bainite are explored.The factors affecting the toughness of 23CrNi₃ Mo drill rod are studied.Concluded as follow:(1)Considering the comprehensive influence of the strengthening and toughening design process,the optimum toughening combination process of 23CrNi₃ Mo steel is 920 °C austenitizing + 240 °C isothermal 24 h.(2)The morphology of bainite structure under different heat treatment processes was studied by optical metallography,scanning electron microscopy and transmission electron microscopy.The interface type,interface transformation and new phase growth of the new phase in the solid phase transformation of the steel were made.Preliminary theoretical analysis.The research indicates that the isothermal temperature of 350°C after the heating of steel austenite is the boundary temperature of upper and lower bainite transformation of 23CrNi₃ Mo steel,and the lower bainite structure of typical lath is formed below 350°C.The irregular island shape and granularity are above 350°C.Typically the bainite morphology.(3)After the isothermal treatment at 240 °C near the lower limit of lower bainite transformation,the bainite structure is the smallest,and with the increase of isothermal time,sub-structures such as lower bainite strip breakage and dispersed carbide precipitation appear,resulting in significant material.strengthen.(4)Based on the phase transformation and microstructure study,the hardness and tensile and impact tests were used to test and verify the toughness obtained under various bainite heat treatment processes of the steel,combined with the lower bainite morphology.According to the research results of the influence of the toughness of the drill rod,the optimum process of the bainite heat treatment under the 23CrNi₃ Mo drill rod is as follows: austenitizing temperature 920 ° C,isothermal temperature 240 ° C,isothermal time 24 h,the process is strong.The highest toughness is: tensile strength ?b=1090MPa,yield strength ?0.2=998.7MPa,room temperature impact toughness ak=100J/cm2,and section expansion ratio is 81.36%,which is higher than the yield strength and toughness of the original heat treatment process.9% and 20%,that is,have higher yield ratio and better impact toughness.This is an important achievement of this research and has great application prospects.(5)Analysis and research show that the impact fracture type of the steel is ductile fracture under the lower bainite heat treatment process,and the fracture mechanism is ductile fracture dominated by microporous aggregation;while the impact fracture type is solution under the upper bainite heat treatment process.Rational brittle fracture.Fine crystal,solid solution,precipitation,dispersion and substructure strengthening,coherent strengthening are the main strengthening and toughening methods of the steel,in which fine grain strengthening takes into account the improvement of strength and toughness.