This document presents an overview of the findings of several investigations into the susceptibility of 12% chromium type 1.4003 ferritic stainless steel to heat-affected zone sensitization and intergranular stress corrosion cracking. A description of the sensitization behaviour of these steels is complicated by the partial transformation of δ-ferrite to austenite on cooling. During slow cooling or annealing below the A 1 temperature, this austenite decomposes to form desensitized ferrite and M 23 C 6 -type carbide precipitates. The rapid cooling rates associated with welding, however, prevent the transformation of austenite to ferrite at lower temperatures, and any austenite formed on cooling transforms to martensite below the M s -temperature. Four distinct modes of heat-affected zone sensitization have been identified to date. Sensitization of the martensite phase may occur on welding material inadvertently annealed above the A 1 temperature (Mode 1), or when multiple welds are positioned in such a way that the heat-affected zone of the 2 nd pass overlaps the heataffected zone of the 1 st pass (Mode 2). Rapid cooling after very low heat input welding may sensitize the ferrite phase (Mode 3), whereas very slow cooling after welding at excessively high heat input levels may lead to sensitization of the austenite phase (Mode 4). Results examining the influence of Modes 1 and 2 heat-affected zone sensitization on the incidence of intergranular stress corrosion cracking are presented.
Abstract:Compression testing of tri-isotropic (TRISO) carbon/silicon carbide-coated fuel particles between anvil materials with a wide range of hardnesses was investigated. During compression testing, the particle produces a hardness impression before it fractures. For subsequent measurements, the same position can therefore not be used.A special testing machine was designed to use the same set of anvils for testing more than one specimen. By each time positioning a particle at a slightly different position between the anvils, a large number of measurements could be made. The load required for fracture is almost independent of anvil hardness for very hard or very soft anvils. Finite element stress analysis showed that when the anvil hardness is very high, fracture occurs because of high local contact bending stresses at the point of contact.In the case of very soft anvils, a tensile stress develops along a latitudinal direction along the perimeter of the particle over a large volume in between the contact zones with the anvils. The particle then fractures by the development of cracks at right angles to the direction of the tensile stress. From the fracture load, the ability of the particle to withstand internal pressure can be assessed. The advantages of using compression testing of full particles between soft anvils without prior preparation to complement previous test methods are highlighted.
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