| China Low Activation Martensitic Steel(CLAM)is considered to be the preferred structural material for the clad of China’s fusion engineering experimental reactor due to its excellent mechanical properties,radiation resistance and mature industrial base.In order to further improve its purity and comprehensive mechanical properties,four kinds of Zr-CLAM steel(Zr0～Zr3)with different mass fraction of Zr are prepared by vacuum induction furnace.The effects of Zr and thermo-mechanical process on microstructure and properties of CLAM steel are systematically studied.The main conclusions are as follows:(1)The effect of Zr on the microstructure and properties of CLAM steel is studied.There are two types of inclusions in steel:simple inclusions(TaOx,MnS,ZrN,etc.)and composite inclusions(TaOx-ZrO2,ZrO2-MnS,TaOx-ZrN,FeZrx-ZrO2,etc.);Zr is easy to form larger sizes in steel;As the mass fraction of Zr increases,the size and number of inclusions increase significantly;The average diameter of inclusions in Zrl steel is the smallest,which is 0.79 μm,and the volume fraction is 0.018%.After quenching at 1050℃×30 min,tempering at 750℃×90 min,the yield strength of Zr0～Zr3 steel is 482.5～548.3 MPa,the tensile strength is 610.9～679.4 MPa,the elongation is 21.1%～25.7%,the impact energy at room temperature is 186.7～253.9 J,of which Zrl steel has the highest strength and impact energy.(2)The effect of heat treatment process on the structure and properties of Zr-CLAM steel is studied.Orthogonal experiment results show that the tempering temperature is the most important factor in the heat treatment process parameters(quenching temperature,quenching time,tempering temperature and tempering time)on the mechanical properties of the experimental steel(yield strength,tensile strength,Vickers hardness and room temperature impact energy).The optimal heat treatment process is 1050℃×20 min quenching+750℃×90 min tempering;the experimental steel is a tempered martensite structure with an average grain size of 18.9 μm,large amounts of precipitate are uniformly distributed in steel;The yield strength of the experimental steel is 592.1 MPa,the tensile strength is 681.4 MPa,the elongation is 25.1%,the Vickers hardness is 237.4 HV,and the impact energy 268 J.(3)The influence of TMP/T process on the microstructure and properties of Zr-CLAM steel is studied.After final rolling and air cooling at different temperatures,the experimental steels of Zr1B(final rolling at 950℃)and Zr1C(final rolling at 750℃)are both fully quenched martensite structure,and there is no austenite residue in the steel;the structure of the experimental steel after tempering is tempered martensite.As the tempering temperature increases,the yield and tensile strength of the experimental steel gradually decrease,and the elongation and impact energy gradually increase;The fracture mode of the experimental steel tempered at 690℃ is brittle fracture at room temperature,and the fracture mode of the other tempering steels is ductile fracture.760℃ tempered Zr1B and Zr1C experimental steels have excellent tensile and impact properties,with yield strengths of 597.9 and 611.8 MPa,tensile strengths of 726.8 and 730.0 MPa,elongation rates of 24.2%and 24.7%,and impact energy is 225.9 and 243.3 J at room temperature.(4)The effects of high temperature aging on microstructure,precipitates and properties of Zr-CLAM steel are studied.After quenching at 1050℃×20 min and tempering at 750℃×90 min,the microstructure of the test steel remains stable during aging at 600℃ for 1500 h.With the increase of aging time,the Laves phase with small size precipitates in the steel.After aging for 500～1500 h,the yield strength,tensile strength and elongation of the test steels are 524.4～560.7MPa,617.2～700.9MPa and 25.6%～26.3%respectively.The Laves phase of Zr1B and Zr1C steels tempered at 760℃ coarsened continuously during aging at 600℃for 1500 h.The strength of the experimental steel decreases first and then tends to be stable.The elongation increasesfirst and then decreases.After aging for 1500 h,the yield strength of Zr1B and Zr1C steels is 571.7 and 572.5 MPa,the tensile strength is 700.5 and 713.4 MPa,and the elongation is 24.5%and 25.5%. |
