Material Identification, Selection, and Preparation
What this domain tests
Identification questions check whether you can name an alloy from its designation, trace it to a mill test report, and prepare it so the weld or cut will not fail from contamination or hydrogen.
Designations that matter
- Carbon steel: ASTM A36 at about 250 MPa yield, CSA G40.21 300W and 350W, ASTM A572 Gr. 50 at 345 MPa, A992 for wide-flange shapes.
- Weathering steel: ASTM A588 or CSA 350A, often used unpainted.
- Quenched and tempered: ASTM A514 at about 690 MPa yield, with high hardenability and hydrogen cracking risk, so preheat and low-hydrogen consumables per WPS.
- Stainless: 304/304L and 316/316L austenitic, plus duplex 2205. L grades resist sensitization; 316 has molybdenum for chloride service.
- Aluminum: 5052-H32 for formability, 6061-T6 for strength; heat-treatable alloys lose strength in the heat-affected zone.
Identification and traceability
The mill test report ties heat number, chemistry, and mechanical properties to the material. Transfer the heat number to cut pieces when the specification requires traceability. Field checks:
- Spark test: carbon steel throws long bushy yellow-orange sparks; stainless gives short red-orange sparks; cast iron gives short red sparks.
- Magnet: ferritic and martensitic steels are strongly magnetic; 304 and 316 are not, though cold work can make them slightly magnetic; 200-series stainless is magnetic.
- Colour codes on bar ends and hardness files support identification, but never replace the MTR.
Storage and preparation
Keep stainless away from carbon: dedicated brushes, wheels, and tables, because carbon contamination rusts stainless. Store aluminum dry and keep it from galvanic contact with steel. Low-hydrogen electrodes such as E7018 go into a holding oven at about 120 C after opening.
Before welding, clean at least 25 mm each side to bare metal, since mill scale, oil, paint, and moisture all feed porosity and hydrogen. Bevel to the WPS angle, with a 60 degree included V being 30 degrees per side, with the specified root face and gap. Degrease before grinding, never after, and never use chlorinated solvents, because UV light decomposes them into toxic gas.
Worked example
A bar is non-magnetic, gives short red sparks, and files moderately. That fits an austenitic stainless such as 304. Confirm with the MTR or a chemical test before welding, then use a new stainless brush, a wheel reserved for stainless, and a matching 308L filler.
Traps
- Trusting a magnet to prove stainless.
- Grinding stainless with a carbon steel wheel.
- Using brake cleaner before welding.
- Forgetting L-grade selection for welded 304.
- Welding over mill scale at the root.