Materials, Ferrous and Non-Ferrous Metals, and Heat Effects of Welding
What this domain tests
Carbon equivalent and weldability, alloy behaviour, non-ferrous filler selection, and how the thermal cycle changes the heat-affected zone.
Core rules
- Carbon steel. Up to 2% C. As carbon and manganese rise, hardenability rises and weldability falls. Carbon equivalent: CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. CE above about 0.40 calls for preheat and controlled interpass temperature.
- Austenitic stainless. 304 (18/8) and 316 (with Mo for pitting resistance). Sensitisation occurs roughly 425–870 °C when chromium carbides precipitate at grain boundaries and leave them chromium-depleted; use L-grades or stabilised 321/347, low heat input, and interpass below 150 °C.
- Cast iron. Brittle, high carbon. Weld with preheat 300–400 °C, nickel or nickel-iron electrodes, short stringer beads and peening.
- Aluminium. Melting point 660 °C but the Al2O3 film melts near 2050 °C; thermal conductivity about five times steel and expansion about twice, so heat input and jigging matter. Match filler family: 5xxx base with 5356, 6xxx with 4043 or 5356.
- Heat-affected zone. Just outside the fusion line the metal reaches 1100–1400 °C and coarsens; further out it may harden (air-hardening steels) or soften (cold-worked or precipitation-hardened alloys).
Worked example
A steel has C 0.18, Mn 1.20, Cr 0.10, Mo 0.02, Ni 0.05, Cu 0.10. CE = 0.18 + 1.20/6 + (0.10+0.02)/5 + (0.05+0.10)/15 = 0.18 + 0.20 + 0.024 + 0.010 = 0.414. This is just above 0.40, so a preheat of about 100–150 °C and a hydrogen-controlled (basic) electrode are needed; the margin is small because the manganese term dominates the total.
Traps
Forgetting the manganese term in CE; assuming aluminium needs a higher current only because of its melting point, when the oxide film and conductivity are the real issues; ignoring interpass temperature on stainless.