| Title |
Effect of microstructure on the Fracture Toughness of ferrite - Martensite - Bainite Steels |
| Authors |
변택상(Thak Sang Byun); 김인섭(In Sup Kim) |
| Abstract |
The effect of microstructure on the fracture toughness of ferrite-martensite bainite steels was investigated with Fe-0.11C 1.64Mn-0.78Si composition. One inch compact tension specimens (1T-CTSs) were machined from hot rolled plates. The microstructure of ferrite-martensite-bainite was introduced to the specimens by the heat treatment of inter critical annealing at 800˚C and isothermal holding at 350C Holding at 350 C increased volume fraction of bainite. while decreased that of martensite, and refined martensite particles. Single specimen unloading compliance method was used in fracture test to obtain J-resistance (J-R) curve and to determine the fracture toughness(J_(IC)). Introduction of bainite to the ferrite-martensite steel1 improved the fracture toughness due to the deformation of bainite which relaxed the stress concentration on the interface of ferrite and martensite. Observation of fractgraphs through the scanning electron microscope (SEM) identified the fracture mechanism of ferrite- martensite-bainite steels as dimple nucleation and crack growth by decohesion of ferrite matrix and second phase particles and by mi crovoid coalescence. |