Welding
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Welding machines to be paralleled must operate on the same input volts and frequency. Explain why.
Observe improper paralleling.
Is it essential to ground welding machines? Explain why or why not.
Observe arc unstable and safety precautions.
Hydrogen embrittlement of steels may occur during arc welding in moist atmosphere. Explain why.
Consider air humidity.
Is it possible the elimination of electric interferences during Tig and Mig/Mag welding? Explain why or why not.
Consider power plant.
Ferritic stainless steel filler metals are often used to avoid underbead cracking in martensitic stainless steel after welding. Is it correct? Explain why.
Observe stainless steel austenitic and ferritic.
Postweld heat treatment can be used to stress-relieve the weld before it cools to room temperature. Explain why.
Observe austenite transformation.
Martensitic stainless steel with higher C contents (0,25 to 0,30%) are rather susceptible to "underbead crack" when hydrogen is present during welding. Explain why.
Observe hydrogen diffusivity (austenite and martensite).
In welding, the use of laser beam significantly reduces the distortion of the workpiece and the thermally induced stresses. Explain why.
Consider a very small total heat input per unit length of weld.
During laser beam welding vacuum systems are required to protect the weld bead. Is it correct?
Observe laser reflection and dispersion.
In aluminum welding, a laser beam can be reflect by its smooth surface and lose portion of total energy. Explain why.
Observe surface brightness and opaque coatings.
When arc blow is a problem in submerged-arc welding, do you expect to minimize it by using DC or AC welding?
Observe AC cycles.
Why preheating during low alloy steels welding? And posheating?
To avoid martensite transformation during welding cycles
What is the basic difference between welded beads and brazed beads?
The first one melts the base metal; the brazed beads do not.
Is there diffusion zone in welded beads?
The zone between welded beads and the base metal
Suppose the base metal steel AISI 8630. It is necessary some preheating cycle before and during welding (MMA, mig/mag, tig)?
The low alloy steels ever need preheating cycles to avoid brittle phases - bainite and martensite.
What is the definition of "hot cracking" and "cold cracking"?
Wrong welding thermal cycles and procedures (MMA, tig, mig/mag).
Does hydrogen induced cracking occur in welded sheet joints?
Hydrogen fragility affects many welded joints. Why?
Lamellar tearing promotes irreparable defects. Does it occur during or after low carbon steel sheets welding?
Aligned inclusions cause lamellar tearing
Arc blow is one welding defect among others. What type? Mechanical, Electrical or metallurgical defect?
Arc blow causes many welding defects.