Welding
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Austenitic filler materials can be use to join any combination when welding dissimilar stainless steels. Is it correct? Why?
Austenitic SS is a ductile joint that can deform without cracking. Why? Note that austenitic (alpha phase) is a FCC structure.
Welding austenitic stainless steels to carbon steels, austenitic SS filler metal should be used. Is it correct? Why?
"Buttering" with austenitic SS the surface of carbon steels to prevent or minimize cracking. The low carbon electrodes should be avoided. Why?
A "constant-voltage DC machine" is used for submerged arc welding. Why?
Some welders use this type without criterion.
Arc blow is indicated by this welding defects: undercut, high penetration, surface porosity, wavy bead and wide bead irregular in width. The back-step technique may eliminate this defects. Why?
Back step procedure may eliminate magnetic forces during welding.
What the difference between "crater crack" and "hot crack" of a weld bead?
Sometimes no difference.
Why carburizing oxyacetylene flame is used for the welding of aluminum alloys and high-carbon steels?
This type of flame is reducing.
In general, carbon and alloy steels with higher strength levels are more difficult to weld. Why? Explain this.
Consider hydrogen cracking and reheat cracking.
The continuous cooling transformation diagrams for welding are often not available. Similar diagrams for heat treating have been used as an approximation. It is correct? Explain why or why not.
The welding cooling rate is different.
The first weld bead tends to have a higher dilution ratio (%) and a higher C content than subsequent beads .Why?
Consider the formation of brittle phase and cracking of the weld metal.
Low-carbon stainless steels AISI 304L and 316L are less susceptible to weld decay. Explain why.
Observe carbide precipitation
Severe residual stresses can be present in austenitic stainless steels after welding. Explain why or why not.
Consider welding thermal cycles.
The sensitization of ferritic steels (AISI 430 and 446) is different from that of unstabilized austenitic stainless steels. Explai why.
Consider thermal cycles.
Martensitic stainless steels with higher C contents are rather susceptible to underbead cracking when hydrogen is present during welding. Explain why.
Consider residual stresses.
Heat-affected zone: the portion of the base metal which not been melted, but whose mechanical properties and microestructure have been altered by the stresses of welding. Explain why or why not.
Observe heating effect during welding
Backhand welding is a technique wherein the welding gun is directed toward the progress of welding. Is it correct?
Observe backhand and forehand welding procedures.
In arc welding, "crater" is a depression at the termination of the weld bead. Why the defect "crater crack"?
Consider welding techniques and procedures.
Consider the use of straight polarity (electrode "-") with automatic welding to increase melting rate. Why?
Observe the heat generated between "-" and "+" polarity.
Steels with a C range of 0,15 to 0,30% can be welded without preheating, post heating or special electrodes (MMA). Explain why or why not.
Observe thin sections of base metals (~6mm).
During solidification of the weld metal (base metal C steels), sulfur may form bubbles which reduce the resistance of the weld. Explain why or why not.
Consider hydrogen during welding.
Welding machines are paralleled (connecting the output of 2 or more machines) when power sources of sufficient welding are not available. Is it correct?
Consider the total available output at rated duty cycle.