Effects of thermal aging on fracture toughness and Charpy-impact strength of stainless steel pipe welds

Abstract

The degradation of fracture toughness, tensile, and Charpy-impact properties of Type 308 stainless steel (SS) pipe welds due to thermal aging has been characterized at room temperature and 290°C. Thermal aging of SS welds results in moderate decreases in Charpy-impact strength and fracture toughness. For the various welds in this study, upper-shelf energy decreased by 50-80 J/cm 2 . The decrease in fracture toughness J-R curve or J IC is relatively small. Thermal aging had little or no effect on the tensile strength of the welds. Fracture properties of SS welds are controlled by the distribution and morphology of second-phase particles. Failure occurs by the formation and growth of microvoids near hard inclusions; such processes are relatively insensitive to thermal aging. The ferrite phase has little or no effect on the fracture properties of the welds. Differences in fracture resistance of the welds arise from differences in the density and size of inclusions. Mechanical-property data from the present study are consistent with results from other investigations. The existing data have been used to establish minimum expected fracture properties for SS welds.

Effects of Thermal Aging on Material Properties, Stress Corrosion Cracking, and Fracture Toughness of AISI 316L Weld Metal

“…The general trend is that the weld metal tested at 298 K (25°C) shows the highest toughness, followed by the 561 K (288°C) air toughness, and the in situ toughness being the lowest. The fracture toughness decrease at elevated temperature is in agreement with Chopra et al [2] Furthermore, the decrease in fracture toughness at elevated temperature is also consistent with the tensile properties at elevated temperature. [19] The environmental effect on fracture toughness is significant.…”

“…Comparing this with the fractography for the in situ tested material in Figure 16, the differences are considerable: (1) The fatigue region morphology in the air-tested material exhibits ductile-striation behavior, while in the in situ case, the fatigue morphology exhibits a more crystallographic brittle striation morphology. (2) The transition between the fatigue and stretch zone region is very distinct for the air-tested material, while in the in situ case, the transition shows first a transgranular brittle zone less than 100 lm wide before the ductile stretch zone. (3) The initial crack propagation region in the stretch zone consists of featureless shear in the air-tested case, whereas it is very crystallographic in the in situ case.…”

“…THERMAL aging and consequent embrittlement are ongoing issues in cast stainless steels, [1][2][3][4] as well as duplex, [5][6][7][8][9] and high-Cr ferritic stainless steels. [10,11] Spinodal decomposition is largely responsible for the well-known ''748 K (475°C) embrittlement'' that results in drastic reductions in ductility and toughness in these materials.…”

An assessment of impact toughness of the pressure vessel steel A533-B and its 308 austenitic stainless steel weld metal

“…Thus, an increase in  y (as temperature is decreased) would lead to increasing  yy value till it surpasses that of  F , Fig. (7). In this event, it would become much easier for the material to experience brittle crack propagation rather than to exert ductile plastic deformation [9].…”

“…This means a less amount of plastic deformation for the ductile fracture processes(void growth, coalescence) of the 308 WM. In addition, the microstructure morphology of the 308 WM (vermicular delta ferrite) could also have contributed more to the coalescence process of voids [7]. This results in the consumption of a lower amount of energy in both the initiation and propagation processes of the 308 WM ductile fracture leading to a reduction in the impact toughness energy.…”