Welding multipass

Experiments were carried out on samples, made of austenitic steel with thickness from 10 to 50 mm using equipment, described above. The samples were a) multipass austenitic weld and b) base metal. 

Figure 2 a) multipass austenitic weld and b) base metal. 

Experiment was carried on samples, made of austenitic steel type 316 (18-12), with the thickness of 15 mm. The samples were in the form of a segment of a pipe with the diameter 300 mm having multipass welding. One of the variants of the sample is shown in Figure3. 

Elimination. In multipass welding, care must be exercised to remove cracks in the initial pass, before subsequent passes are applied. Pre-... 

Welded microstructures can be extremely complex and often change drastically over a very short distance. The fusion zone or weld metal is a dendritic structure that has solidified from a molten state. Bordering the fusion zone are transition, unmixed and partially melted zones, and the heat-affected zone (HAZ). These zones can be reheated and altered by subsequent weld passes, in multipass welding. For alloys with structures that depend strongly on thermal history, such as steels, the final microstructure can be extremely complex. Since welded structures are often quite susceptible to corrosion, overalloyed filler metals are often used to enhance the weld corrosion resistance. For stainless steels with sufficiently high carbon content, sensitization in the HAZ is another major problem. (Frankel)5... 

Fig. 14.36 Effects of multipass friction stir processing (FSP) welds on mechanical properties. No sig-...

Chapter 8 in this volume presents FSP of copper alloys, including NiAl bronze, an alloy frequently used to fabricate ship propellers. Data in Chapter 8 show mechanical and fatigue properties to be improved considerably by FSP. However, as shown previously for an aluminum alloy, the need may arise to friction stir process a prior-fusion repair within an NiAl bronze propeller. Thus, studies were initiated to evaluate procedures and properties for this unique combination of prior processing. Fusion welds were made at the Naval Surface Warfare Center, Carderock Division, using standard Navy weld procedures for NiAl bronze. Figure 14.43 illustrates a multipass 12.7 mm (0.5 in.) penetration fusion weld using Ampcotrode 46 weld wire of composition... 

Fig. 14.43 Micrograph illustrating a multipass 13 mm Yi in.) penetration fusion weld using Ampcotrode...

Heat-affected zone in C-Mn steel (a) hydrogen crack at root of single-run fillet weld, and (b) crack at toe of multipass fillet weld. 

Recent work indicates that for non-alloyed C-Mn weld metal, in contrast to the situation in the HAZ, the risk of weld metal hydrogen cracking can increase, particularly in multipass welds, with increasing heat input. The normally envisaged relaxation of preheat at higher heat inputs should therefore be reviewed carefully in such situations. 

Rykalin N N Calculating the parameters of the thermal cycle in the parent metal during multipass arc welding . Izvest Akad Nauk SSSR, Technical Sciences Section, No. 1 and 2, 1950, 233-48. 

The stresses in a weldment result because the contraction of the hot weld is hindered by the restraint (q.v.) of the joint. Residual stresses tend to be tensile at the weld (at the weld surface in a multipass weld) and are balanced by compressive stresses in the parent steel (or in the root regions of a multipass weld). 

Figure 4 shows the strength and impact temperature dependence of these types of welds. In multipass welding, the welded joints possess different levels of strength. 

Dong, Z.B. Wei, Y.H. (2008). Three dimensional modeling weld solidification cracks in multipass welding. Theor. Appl. Tract. Mech., Vol. 46, 156-165. 

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