A Discussion On Structural Steel Brittleness Induced By Temperature And Loading Rate And Fracture Controlment

In this paper, fracture toughness of a low alloy steel and welded joint under various temperatures has been obstained with the static J-integral test( K = 10° MPa m~1/2/s), pendulum impact(K = 105 MPam~1/2/s) and Hopkinson barimpact( K = 106 MPam~1/2/s). With comparison, it has been found that the steeland welded joint do not reveal low temperature brittlement under static, however, they reveal low temperature brittlement under dynamic. At the same time, it has been found the steel and welded joint have loading rate effect. Fracture toughness decreases with increasing loading rate and the decrease of temperature reinforces loading rate effect.The surface of fracture of the steel and welded joint has been studied by scanning electron micrography(SEM). The results show that the capacity of granular boundary is not enough to propergate fast deformation or fast propergation of crack, intergranular fracture occurs frequently, which causes brittle under high loading rate.The safety assessment of the steel and welded joint under static and dynamic have been done. The stess-critical length of crack diagrams are given, which are used to avoid brittle fracture of component including defect. On the basis of analysis of the results of fracture toughness, the temperature effect of fracture character is been discussed and a fracture characteristic analysis diagram(FCAD) is constructed. As a consequence, better effect of avoiding brittle fracture can be obtained by considering temperature, loading rate and plate thickness.