Fracture Toughness in of Welded Low Alloy Steels

Abstract

With reference to the particular aspect of the heat-affected zone, the fracture toughness of a welded low alloy steel has been examined. Test specimens have been prepared from a multiple-pass welded plate of 25 mm full thickness. The welding has been carried out under the heat input of 20 KJ/cm and interpass temperature 150°C. The hardness survey along the fusion boundary in heat-affected zone has shown that the hardness attains to the maximum value at the vicinity of the toe of weld. For this reason, the most critical feature of specimen machining has been concerned with the preparation and the location of the slit. The unusual shallow slits, such as 1 mm slit depth, have been also made. Furthermore, the tip of all the slits with various slit depth has been located in the heat-affected zone adjacent to the fusion line. Fracture testing has been carried out in four point bending over a wide temperature range.
Results of the present studies are summerized as follows.
(1) A typical result obtained at low temperature reveals that the plastic deformation near slit tip just before fracture decreases with decreasing slit depth. Especially, the plastic deformation and nominal fracture stress in the case of the most shallow slit exhibit remarkably low value.
(2) Fracture toughness value decreases with decreasing slit depth. The feature of the low fracture toughness with reference to the slit depth is remarkable at low temperature. For example, the fracture toughness value in 1 mm slit depth specimen at -133°C is only 23 kgmm^-3/2 and this value is about 1/10 of the value in the case of the slit depth of 12.5 mm.
(3) In assessment of the fracture toughness in welded low alloy steel, the special attention should be paid to the location of the tip of the slit and its depth.
(4) It is revealed that there may be the risk of low stress level fracture even though the depth of the surface defect in the welded low alloy steel is shallow.