Welding and Metal Working Flashcards

When welding high-strength low-alloy (HSLA) steel with a hydrogen-bearing electrode, what is the primary metallurgical risk if preheat is omitted on thick sections?

Answer: Hydrogen-induced cold cracking in the heat-affected zone

HSLA steels are susceptible to hydrogen-induced cold cracking (also called delayed cracking or hydrogen embrittlement) in the HAZ. Hydrogen diffuses into the hardened martensite formed during rapid cooling. Preheat slows the cooling rate and allows hydrogen to diffuse out before cracking initiates. Hot tearing and porosity are different phenomena unrelated to hydrogen diffusion in this context.

A welder is performing a multipass SMAW weld on 1-inch carbon steel plate in the flat position. After the second pass, visible slag inclusions are found embedded in the weld. What is the MOST likely root cause?

Answer: Inadequate slag removal and undercutting left by the previous bead

Slag inclusions in multipass welds are most commonly caused by incomplete removal of slag from a previous pass combined with undercut or irregular bead profiles that trap slag during the next pass. The new molten metal flows over entrapped slag rather than flushing it out. While electrode angle can also contribute, inadequate interpass cleaning is the primary culprit in multipass scenarios.

In gas tungsten arc welding (GTAW), a welder switches from DCEN to AC current when welding aluminum. Which specific AC characteristic is responsible for removing the refractory aluminum oxide layer during the weld?

Answer: The electrode-positive half-cycle, during which electrons bombard the base metal surface

During the electrode-positive (reverse polarity) half-cycle of AC, electrons flow FROM the base metal TO the electrode. This electron bombardment causes cathodic cleaning — it breaks up and disperses the aluminum oxide layer, which melts at roughly 2037°C (far above aluminum's 660°C melting point). The electrode-negative half-cycle provides the deeper penetration and heat. HF is for arc starting/stabilization, not oxide removal.

A carbon steel shaft is being repaired by hard-facing with a cobalt-based (Stellite) overlay. After welding, the overlay cracks upon cooling to room temperature. Which factor MOST likely caused this cracking?

Answer: Insufficient preheat allowed thermal contraction stresses to exceed the overlay's low ductility

Cobalt-based hard-facing alloys are extremely hard but have very low ductility and high coefficients of thermal expansion mismatch compared to carbon steel. Without adequate preheat (and controlled interpass and post-weld slow cooling), the steep thermal gradient causes contraction stresses that exceed the overlay's tensile ductility, causing cracking. While dilution is a concern for performance, cracking on cooling is primarily a thermal-stress/ductility issue.

During plasma arc cutting (PAC) of stainless steel, the operator notices a significant increase in dross adherence and a rougher-than-normal cut surface. The gas pressures and amperage are correctly set. What is the MOST probable cause?

Answer: The plasma gas nozzle orifice has eroded, distorting the plasma column geometry

Nozzle orifice erosion is a common but often overlooked cause of cut quality degradation. As the orifice enlarges and distorts from wear or double-arcing, the plasma column loses its tight, focused geometry. This reduces energy density, widens the kerf, and causes incomplete melting at the bottom of the cut — resulting in dross that solidifies and adheres. Other parameters being correct makes consumable wear the primary suspect.

A Ramsay mechanical aptitude test question shows two gears meshing: Gear A has 48 teeth and Gear B has 16 teeth. If Gear A is the driver turning at 150 RPM, and Gear B drives a pulley of 8-inch diameter, what is the surface speed (in feet per minute) at the rim of the pulley driven by Gear B?

Answer: Approximately 942 FPM

Step 1 — Gear ratio: 48/16 = 3:1, so Gear B turns at 150 × 3 = 450 RPM. Step 2 — Pulley circumference: π × diameter = π × 8 in = 25.13 in = 25.13/12 ft = 2.094 ft. Step 3 — Surface speed: 450 RPM × 2.094 ft = 942.5 FPM ≈ 942 FPM. The other choices correspond to errors such as forgetting the gear ratio (150 RPM × 2.094 ≈ 314 FPM) or doubling incorrectly.