Welding and Metal Working Flashcards

When performing GTAW (TIG) welding on 304 stainless steel, carbide precipitation (sensitization) is most likely to occur in the heat-affected zone when the metal is held between which temperature range?

Answer: 800°F – 1,500°F (427°C – 816°C)

Sensitization in austenitic stainless steels like 304 occurs when chromium carbides precipitate at grain boundaries in the 800°F–1,500°F (427°C–816°C) range, depleting the surrounding zones of chromium and making them susceptible to intergranular corrosion. This is why low-carbon grades (304L) or stabilized grades (321, 347) are preferred in corrosive service.

A welder is joining two pieces of HSLA (high-strength low-alloy) steel with a carbon equivalent (CE) of 0.48. According to standard preheat guidelines, what is the PRIMARY risk if adequate preheat is NOT applied?

Answer: Hydrogen-induced cracking (cold cracking) in the HAZ

A carbon equivalent of 0.48 indicates a hardenable steel that requires preheat to slow the cooling rate. Without adequate preheat, diffusible hydrogen from the welding process becomes trapped in the hardened martensite of the HAZ, leading to hydrogen-induced (cold) cracking hours or even days after welding. Hot cracking is a solidification issue unrelated to CE; nitrogen porosity and lamellar tearing have different root causes.

During SMAW, a welder notices consistent 'wagon tracks' (two parallel linear indications) appearing on radiographic examination of completed welds. What is the MOST likely cause?

Answer: Slag entrapment from incomplete removal between passes

Wagon tracks on radiographs are a classic signature of inter-pass slag entrapment, where slag from a previous pass was not completely removed before depositing the next bead. The trapped slag appears as two parallel linear indications following the edges of the underlying bead. Tungsten inclusions are specific to GTAW; centerline cracks appear as single linear indications; toe fusion issues typically appear as single irregular lines.

A machinist is measuring the outside diameter of a steel shaft using an outside micrometer and obtains a reading of 1.278 inches. After comparing with a calibrated gauge block, the micrometer consistently reads 0.003 inches high. The shaft's ACTUAL diameter is:

Answer: 1.275 inches

If the micrometer reads 0.003 inches HIGH (over-reads), the actual measurement is the reading minus the error: 1.278 − 0.003 = 1.275 inches. This is a systematic zero error. Confusing the direction of correction is a common error — if the instrument reads high, the true value is lower than indicated.

In flux-cored arc welding (FCAW), a welder switches from DCEP (electrode positive) to DCEN (electrode negative) while using a gas-shielded flux-cored wire. What is the MOST likely result?

Answer: Erratic arc behavior, poor fusion, and excessive spatter

Gas-shielded FCAW wires (E70T-1, E71T-1, etc.) are specifically designed for DCEP. Switching to DCEN disrupts the arc characteristics established by the flux chemistry, resulting in an unstable arc, poor penetration, excessive spatter, and degraded weld quality. Self-shielded wires (E71T-11) are designed for DCEN, but the two types are NOT interchangeable in polarity.

When cutting aluminum alloy plate using an oxy-fuel torch, a technician finds the process is ineffective compared to cutting mild steel. The FUNDAMENTAL reason aluminum cannot be efficiently cut with a standard oxy-fuel cutting torch is:

Answer: Aluminum oxide (Al₂O₃) melts at a higher temperature than aluminum itself, forming a refractory barrier

The oxy-fuel cutting process relies on iron oxidizing (burning) at a temperature below the melting point of steel — the oxide runs away as liquid slag. Aluminum fails this criterion because Al₂O₃ (alumina) has a melting point of approximately 3,720°F (2,049°C), which is far above aluminum's melting point of 1,221°F (660°C). The oxide skin solidifies and shields the base metal before cutting can occur. This is why aluminum must be cut by plasma, laser, saw, or chemical methods instead.