Automotive & Transport

Transport applications split into two very different problems: hot and corrosive (exhaust) and visible and durable (trim). They use different grades, and confusing them is expensive.

What we supply

Exhaust: why 409 instead of 304

409 is a ferritic stainless with about 11% chromium and a small titanium addition. It is not as corrosion-resistant as 304, but it is cheaper, and it does not suffer from the thermal cycling problems that austenitic grades have in exhaust service. For most petrol and light diesel exhausts it is the standard choice.

Move up to 441 or 439 for higher temperature and longer life; move to 304 only where the exhaust also sees road salt or marine air, and accept the higher cost.

Trim: finish decides the grade

For visible trim, the question is what the finish has to survive. 430 is adequate indoors and on dry exterior trim; 304 is the default where the trim is handled, washed or exposed to weather. Mirror (8K) on 430 is a false economy outdoors — it will bloom.

What to specify

• Service temperature. Above roughly 700 °C continuous, grade selection changes materially.
• Forming operation. Deep-drawn parts need a suitable temper and often a softer grade than flat panels.
• Weight targets. Where mass matters more than corrosion, aluminum may beat stainless — we supply both and will say so.
• Coating or film. Laser-cut blanks often ship with film; specify whether it must survive forming.

Mistakes we see

304 for exhaust to "be safe". It costs more and can crack under severe thermal cycling where a ferritic grade would not.

Mirror finish outdoors on 430. Looks superb in the showroom, blooms within a season.

Ignoring galvanic contact. Stainless trim bolted against mild steel accelerates corrosion of the steel. Isolate or match.

Related products

• Sheet & plate — body panels, tanks, brackets
• Coil & strip — continuous roll forming and slit widths
• Aluminum range — where weight beats corrosion resistance

Send the part, the service temperature and the forming operation — we will quote the grade that survives it, not the most expensive one.