CWI Welding Process Principles 5

Question 1

What is the primary metallurgical reason that austenitic stainless steels can experience 'sensitization' during welding?

Accepted Answer

Precipitation of chromium carbides at grain boundaries, depleting adjacent areas of chromium

Answer

When heated in the sensitization range (about 800–1600°F), carbon combines with chromium at grain boundaries to form chromium carbides, creating chromium-depleted zones susceptible to intergranular corrosion.

Question 2

Which condition is MOST likely to cause 'incomplete fusion' in a weld?

Accepted Answer

Insufficient amperage or improper electrode angle preventing the arc from melting the base metal sidewall

Answer

Incomplete fusion occurs when the weld metal fails to fuse with the base metal or adjacent weld passes, most commonly due to insufficient heat input, poor technique, or incorrect electrode angle.

Question 3

What does 'heat input' (kJ/in or kJ/mm) quantify in welding?

Accepted Answer

Energy transferred per unit length of weld, calculated from voltage, amperage, and travel speed

Answer

Heat input = (Amps × Volts × 60) / (Travel Speed in in/min), expressed in kJ/in; it governs cooling rates, grain growth, and mechanical properties of the weld and HAZ.

Question 4

In friction stir welding (FSW), the joint is made by:

Accepted Answer

A rotating non-consumable tool that generates frictional heat and mechanically intermixes the plasticized material

Answer

FSW uses a rotating shoulder-and-pin tool to generate frictional heat that plasticizes the base metal without melting it; the pin mechanically stirs the softened material to form a solid-state weld.

Question 5

When welding with an E7018 electrode, the '18' suffix designates:

Accepted Answer

A low-hydrogen coating with iron powder, usable in all positions with DCEP or AC

Answer

Per AWS A5.1, the last two digits '18' denote a low-hydrogen iron powder covering suitable for all positions with DCEP or AC, providing excellent mechanical properties and crack resistance.

CWI Practice Test

CWI Practice Test

CWI Welding Process Principles 5