Materials and weldability
Carbon steel, stainless, aluminium, cast iron, copper, titanium — how each behaves and what to weld it with.
Every material has one dominant problem, and the procedure is built around it. Stainless: heat, because it conducts badly and expands more — and sensitisation if it sits too long in the wrong temperature range. Aluminium: the oxide film, which melts at three times the temperature of the metal underneath. Cast iron: carbon, ten times what weldable steel carries. Dissimilar joints: dilution, because the weld is a third alloy made of both parents plus the filler.
Knowing which problem you are dealing with is most of the work. The rest — filler, gas, preheat — follows from it, and where a number is needed the calculators supply it.
- Welding stainless steel Which filler and gas to pick for austenitic stainless, how to avoid sensitisation, and what to do about distortion and oxide colour.
- Welding aluminium Why aluminium behaves differently: the oxide film, heat conduction, AC balance in TIG and the wire feeding problems in MIG.
- Welding cast iron Why cast iron cracks when welded, when to preheat and when to weld cold, and which electrodes actually hold a repair together.
- Welding dissimilar steels Joining stainless to carbon steel and other mismatched pairs: filler choice, dilution and the Schaeffler diagram used in practice.
Frequently asked questions
Why is stainless welded with a non-matching filler?
Because 308L on 304 leaves a few per cent of delta ferrite in the deposit, and that ferrite is what prevents solidification cracking. A perfectly matching fully austenitic weld would crack more, not less.
Can aluminium be welded with an ordinary MIG set?
With difficulty. You need pure argon, a U-groove roll, a PTFE liner and a very short torch — and even then the soft wire buckles. For more than occasional work, a spool gun or push-pull torch is the real answer. TIG on aluminium additionally needs AC output.
Is cast iron worth welding at all?
Often yes, with nickel electrodes, low current, short runs and peening. What a cold repair will not give you is a machinable joint — the heat-affected zone comes out harder than the cutter. For that you need the full preheat-and-slow-cool route, which needs a furnace.