Mechanical Characteristics Of The Gdl, High Strength And Toughness-1 Of New Materials

The fracture toughness of new tiny deformation steel(GDL-l) are studied in the paper. The effect of heat treatment technology, microstructure and subunits to fracture toughness of bainitic steel is researched..The results show that the fracture toughness of new tiny deformation steel(GDL-l) is the best after air-cooling and tempering at 250℃-300℃.σ_0.2 =1043.55—1047.32 MPα,σ_b = 1158.06—1167.8MPα,δ(%)=13.25～14.8,Ψ(%)=58.24—59.56, A_KV =97-120.5J, HRC42—43, J_IV=0.1415—0.1513MP.m, K_IC=173—179(Mp.ml/2), the crystalline grain grade is 8—9.The optical microscope and scanning electron microscope shows that microstructure of the fracture toughness of new tiny deformation steel(GDL-l) was a mixed structure which is composed of bunchy bainite, Granular Bainite, martensite and a little retained austenite. The retained austenitic film separates bunchy bainite into extra-fine subunits and improves the micro-ductility of the steel.The X-ray stress analyzer shows that more retained austenitic content and stability can improve fracture toughness when that retained austenitic of air cooling is between 5%-8% and oil quenching is between l%-4%.D_iC=d_i/nδ_c compound parameter which means effective grain size of the effective distortion before crack tip is adopted to illuminate the reason why fracture toughness of the new material is better. Because effective grain size is microcosmic structure parameter which include the width of bainite and subplates , the width size of subplate is between 0.2～0.9μm , the width size of subcell is between 30～250nm. Pellicle retained austenitic which exist between ultrafine bainite structure and subplates lead to higher toughness and ductility of crack tip'frontiers. Profile metallography analysis proves that passivating radius of curvature of crack tip in air-cooling is above 30μm .crack propagation is flexura . otherwise passivating radius of curvature of crack tip in oil quenching is in 20μm. crack propagation is more flat. Which explain that ultrafme subplates and the Pellicle retained austenitic of good ductility increaseδ_c apparently .which exist between ultrafine bainite structure and ultrafine subplates increaseδ_c apparently . the good fracture toughness is gained .