Effect of Bending by Line Heating Method on Brittle-Fracture Propagation Characteristics of Steel Plates

Abstract

One of the authors has previously published the detailed procedures for plate bending by Line Heating Method, and showed its great promises for bending the steel ship hull plates. This method, which is consisted of heating and subsequently water-cooling a steel plate, has been suspected by not few concerned as possessing harmful effects on material properties. However, it was then proved by various tests such as static-tension, bending, V-notch Charpy and hardness tests or microstructure inspection, that the effect on material is as slight as that caused by press-bending in, either cold or hot state, because the heating in this process is duly controlled so as not to heat the plate beyond A-1 transformation point of steel.Recently, a number of large-scale brittle fracture tests, which is believed to have good correlation with brittle fracture of actual steel structures, has been developed. A Double-Tension test is one of the most representative of these large-scale tests, and the brittle-fracture properties of steel plates bent by Line Heating Method was investigated with this test by the present authors, the resultls of which are reported in this paper. It was revealed that the heated zone of steel plates becomes indeed more brittle than the original material, but the degree of deterioration is almost same as that caused by press-bending ; in other words, Line Heating Method can safely be used for ship hull steel plates from the viewpoint of brittle fracture.It was also found that the shear-fracture transition-temperature by Pressed-notch Charpy test is 'highly correlated with the arresting-temperature obtained by the Double-Tension test, if the applied stress is nearly as high as the yield point of the material.