Austenitic stainless steel weld metal

Delong W. T., Ferrite in austenitic stainless steel weld metal. Weld. Res. Suppl. 53 (1974), 273s —286s... 

Ironically, their reasoning that the hardened, heat-affected zone of the 5-Cr steel would have ductile, austenitic stainless steel weld metal on one side of it and ductile, 5-Cr steel parent metal on the other, is equally valid in the rejected case where the weld met is carbon steel. 

Ino] Inoue, H., Koseki, T., Ohkita, S., Tanaka, T., Effect of Solidification on Subsequent Ferrite-to-Austenite Massive Transformation in an Austenitic Stainless Steel Weld Metal , ISIJ Int., 35 (10), 1248-1257 (1995) (Calculation, Experimental, Morphology, Phase Diagram, Phase Relations, 23)... 

Figure 8. SANS-scan over 08H18N10T austenite stainless steel welded and base metal forward cross section I0i (per cm3) for large defects Rgl 20nm, colour scale in units of cm"1. Right and left pieces are base metal and joint metal in between (coupled triangles).

Hardness, Impact Strength. Microhardness profiles on sections from explosion-bonded materials show the effect of strain hardening on the metals in the composite (see Hardness). Figure 8 Ulustrates the effect of cladding a strain-hardening austenitic stainless steel to a carbon steel. The austenitic stainless steel is hardened adjacent to the weld interface by explosion welding, whereas the carbon steel is not hardened to a great extent. 

Austenitic stainless steel 3(3. If (1) the carbon content by analysis is greater than 0.10 percent or (2) the material is not in the solution-heat-treated conchtion, then impact testing is required for design temperatures below-29 C (-20 F). See Note 2. ib. When materials are fabricated or assembled by wel(hng, the deposited weld metal shall be impact-tested for design temperature below —29 C (—20 F) unless cou(htious conform to Note 2. 3. The material shall be impact-tested. See Note 2. 

A somewhat similar phenomenon is knife-line attack which may be observed after welding titanium or niobium stabilised austenitic stainless steels. In this case there is a very narrow band of severe intergranular attack along the interface between the parent metal and the fusion zone. During welding, the parent metal immediately adjacent to the fusion zone is heated to just below the melting point and both chromium carbides and niobium or titanium carbides dissolve completely. On cooling rapidly, the conditions are such that when relatively thin sections are welded, neither chromium carbide nor niobium or titanium carbide have time to precipitate. If the weld is now... 

The electrochemical examination of fusion joints between nine pairs of dissimilar metal couples in seawater showed that in most cases the HAZ was anodic to the weld metals" . Prasad Rao and Prasanna Kumarundertook electrochemical studies of austenitic stainless steel claddings to find that heat input and 5Fe content significantly affected the anodic polarisation behaviour under active corrosion conditions whilst Herbsleb and Stoffelo found that two-phased weld claddings of the 24Cr-13Ni type were susceptible to inter-granular attack (IGA) as a result of sensitisation after heat treatment at 600°C /pa was unaffected by heat input. 

Knife-line Attack severe highly localised attack (resembling a sharp cut into the metal) extending only a few grains away from the fusion line of a weld in a stabilised austenitic stainless steel, which occurs when the metal comes into contact with hot nitric acid and is due to the precipitation of chromium carbides. 

The selection of materials for high-temperature applications is discussed by Day (1979). At low temperatures, less than 10°C, metals that are normally ductile can fail in a brittle manner. Serious disasters have occurred through the failure of welded carbon steel vessels at low temperatures. The phenomenon of brittle failure is associated with the crystalline structure of metals. Metals with a body-centred-cubic (bcc) lattice are more liable to brittle failure than those with a face-centred-cubic (fee) or hexagonal lattice. For low-temperature equipment, such as cryogenic plant and liquefied-gas storages, austenitic stainless steel (fee) or aluminium alloys (hex) should be specified see Wigley (1978). 

A SANS investigation is finally reported, carried out on a sample cut out from a plate of base metal (100 mm, 08H18N10T austenite stainless steel, SU standard) and welded by the wire (3 mm in diameter, steel 04H19N18M3) in electric arc using flux 48-OF-6. 

Heat-affected zone (HAZ) is the volume of parent metal in which the mechanical properties and/or the microstructure have been changed by the heat of welding or thermal cutting. For most welds in carbon and low-alloy steels, the HAZ is a band, usually about 1/8 in. (3 mm) wide, adjacent to the fusion line of the weld. In austenitic stainless steels, a narrow, secondary HAZ may be generated some distance from the fusion line as illustrated in Figure 21.4. 

In rare cases, a relatively small area near the weld will be an anode to the relatively large cathodic surface area of the parent metal. In moderately corrosive media, this zone may corrode much faster than either the weld metal or the parent metal. Postweld heat treatment is usually helpful. In some instances, normalizing (or even solution annealing in the case of an austenitic stainless steel) the weldment is necessary, a measure that can cause significant distortion problems. In most cases, the weld metal, HAZ, and parent metal do not have significant galvanic differences. 

Aluminum, copper, and other face-centered cubic metals and alloys (such as the austenitic stainless steels and nickel-base alloys) do not become brittle at low temperatures, except if heavily cold worked. Most such alloys are exempt from impact testing for design temperatures down to -320°F (-195°C). Some types, such as Type 304, are exempt down to 25°F (-255°C). The exemption temperatures for weld metals and HAZs are usually higher than those for the parent metal. 

Austenitic stainless steels are often susceptible to sigma-phase embrittlement after extended exposure at 1050°F to 1700°F (565°C to 925°C). Occurrence depends primarily on the temperature and the presence of ferrite. While Type 304 SS can develop sigma-phase embrittlement, it is more common in austenitic products that contain small amounts of ferrite. Examples include austenitic weld metal and castings. 

Fracture toughness (J-integral) results for a solid-state inertia weld (IW) and gas-tungsten arc (GTA) fusion weld in the austenitic stainless steel 21Cr-6Ni-9Mn (adapted from Somerday ef al. [28]). Results are shown for the hydrogen-exposed and non-exposed conditions. Data for the base metal are included for comparison. 

Often the very engineers who insist on post-weld heat-treatment with carbon steel or low-alloy weld metals would be willing to omit the post-weld heat treatment if an austenitic stainless steel electrode, particularly type 309 (25-Cr, 12-Ni) were used. 

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