Study On Thermal Deformation Behavior And Microstructure Property Of 700Mpa Anchor Steel

High strength anchor steel has the features of high-strength,corrosion resistance and good comprehensive mechanical properties,and is widely used in the support of coal roadways and bridge tunnels.The development of strength anchor steel with high strength and comprehensive mechanical properties is of great economic and social benefits as the mining depth of the coal industry increases and ordinary strength anchor steel materials can no longer fulfill the corresponding needs.China is already at the advanced level in the world in terms of high strength anchor steel category and strength level,but there are few systematic researches concerning the basic theories of microstructure control,production technology and strengthening mechanism of anchor steel.In this thesis,the characteristics of hot deformation,the process of controlled rolling and cooling and the strengthening mechanism of 700MPa high strength anchor steel are studied,which can serve as a guideline for industrial production and has some theoretical significance.The core research work and results of the paper are as follows:（1）In this paper,single-pass thermal compression trials were conducted on the 700MPa high strength anchor steel manufactured by a firm using a Gleeble-3800 thermal simulation tester,and the thermal deformation behavior of700 MPa anchor steel affected by temperature and strain rate were analyzed.Constitutive model,thermal working diagram and critical conditions for dynamic recrystallization were constructed.（2）The equilibrium and non-equilibrium transformation phase diagrams of experimental steel,as well as the continuous cooling transformation rules and isothermal transformation rules of undercooled austenite,were calculated using JMat Pro software,as well as the experimental determination of CCT curve is carried out.Experimental steel in the 0.1～1℃/s cooling rate between the organization of the ferrite and pearlite complex phase organization.The phase transformation points of the experimental steel are measured as A_c1=705℃,A_c3=810℃,M_f=150℃,M_s=290℃.（3）The microstructure of this anchor steel was systematically observed and the strengthening mechanism of the experimental steel was further systematically clarified based on the classical alloy strengthening theory.In addition,the microstructure of the anchor steel consists of ferrite and pearlite dual-phase structure.The ferrite is fine and equiaxed,while the pearlite is distributed in long strip-like layers.The volume fraction of pearlite in the microstructure is about 43%and a large number of nano-sized V（C,N）particles with dispersive distribution less than 20nm are precipitated from the ferritic matrix.In addition,the yield strength of the anchor steel is about 734 MPa and the tensile strength is about 936 MPa,with post-break elongation of approximately 15.1%and the yield ratio is about 0.78.The strengthening mechanism of the anchor steel is the synergistic effect of solid solution strengthening,fine grain strengthening,dislocation strengthening and precipitation strengthening,where the strength contributions induced by grain refining strengthening and solid solution strengthening accounted for about 73%of the total strength.