Heat-affected zone material

Comparison between ARTndj for heat-affected-zone materials and A/ 7iMDTfor base metals from Japanese PWR surveillance results (Soneda et al, 2007). 

Fracture toughness requirements for Reactor Coolant Pressure Boundary components are established in accordance with the ASME Boiler and Pressure Vessel Code, Section III. Fracture toughness testing of base, weld and heat affected zone materials will be conducted in accordance with the ASME Code. Data from these tests will be available after the required testing has been performed and may be examined upon request at the appropriate manufacturing facility. 

Thus, the metallurgy of welds, comprising the weld metal and surrounding heat-affected zone, is influenced not only by the composition of the materials involved, but also by the welding process, the specific procedures for applying the process, and the heat-transfer characteristics (deterrnined by material, mass, and geometry) of the welded joint (9—12). 

AU other carbon steel, low-intermediate, and high-aUoy steels, ferritic steels Base metal Deposited weld metal and heat-affected zone (See Note 1) 2. Except when conchtions conform to Note 2, the material shall be heat-treated to control its microstructure by a method appropriate to the material as outlined in the specification applicable to the product form and then impact-tested. (See Note 1.) Deposited weld metal and heat-affected zone shall be impact-tested. 

Any tests and associated acceptance criteria which are part of the welding-procedure qualification for filler materials and heat-affected zone need not he repeated. 

Corrosive chemicals and external exposure can cause tank failure. Materials of construction should be chosen so that they are compatible with the chemicals and exposure involved. Welding reduces the corrosion resistance of many alloys, leading to localized attack at the heat-affected zones. This may be prevented by the use of the proper alloys and weld materials, in some cases combined with annealing heat treatment. 

The weld was riddled with mildly undercut, gaping pits. Attack was confined to fused and heat-affected zones, with a pronounced lateral or circumferential propagation (as in Fig. 6.10). The resulting perforation at the external surface was quite small. Pits were filled with deposits, friable oxides, and other corrosion products. Black plugs embedded in material filling the gaping pit contained high concentrations of iron sulfide. Bulk deposits contained about 90% iron oxide. Carbonaceous material was not detected. 

There is no guarantee that crack-free joints will automatically be obtained when fabricating weldable metals. This is a result of the fact that weldability is not a specific material property but a combination of the properties of the parent metals, filler metal (if used) and various other factors (Table 9.7) . The consequence of the average structural material possessing imperfect weldability is to produce a situation where defects may arise in the weld deposit or heat-affected zone (Table 9.8 and Fig. 9.27). 

Concern about hydrogen damage has lead to much debate regarding limits for protection potentials of high-alloy steels. However, it is thought that under normal seawater service and cathodic protection conditions, these materials will not be adversely affected provided that the microstructure has at least 40% austenite present . This latter point is of particular importance to welds and their heat affected zone where careful control of heat input is necessary to maintain a favourable microstructure. 

A listed material may be used at any temperature not lower than the minimum shown in the tables in Appendix IX, provided that the base metal, weld deposits, and heat affected zone (HAZ) are qualified as required by the applicable entry in Column A of Table GR-2.1.2(b)(2). 

Weld metal across the weld, with notch in the weld metal notch axis shall be normal to material surface, with one face of specimen S 1.5 mm (Vj6 in.) from the material surface Heat affected zone (HAZ) across the weld and long enough to locate notch in the HAZ after etching notch axis shall be approximately normal to material surface and shall include as much as possible of the HAZ in the fracture... 

NOTE For chromium-nickel materials, extreme discoloration of the weld deposit or heat affected zone shall not be allowed. Acceptable coloration includes light straw, light blue, or hueing. 

Joining is another problem. Fusion welding in inert atmospheres often develops recrystallized structures in the heat-affected zones, so that welded pans lose strength and are embrittled. Special joining techniques being used In help overcome these deficiencies include electron-beam and solid-phase welding, and the development of special brazing materials. 

From an engineering standpoint, the ability to weld stainless steels with relative ease is a major advantage to their usefulness. Weld deposits, because they are cast structures, are subject to discussion regarding corrosion resistance similar to the cast materials. The chemistry of a weld deposit is likely to exhibit segregation and, depending on the alloy and the welding technique employed, may develop deleterious secondary phases in either the weld or heat-affected zone. 

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