AISI SS 201 202 304 316 410 430 420J1 J2 J3 321 904L Cold Rolled Stainless Steel Coil Roll

Twelve grades on one page, and one of them is right

A grade list like this is a catalogue of what can be rolled, not a recommendation. The useful question is not which grades are available but which single grade fits the part, and where the others fail. Most of the cost of a wrong choice appears a year later, as staining on a roof or a crack at a weld, not on the delivery note.

The table below is the short version. The notes after it cover the three grades that are most often bought for the wrong reason.

Grade selector

321 and 904L, the two bought for the wrong reason

321 is 304 stabilised with titanium, roughly five times the carbon content of the Ti addition. Its purpose is to stop chromium carbide forming at grain boundaries in the 450 to 850 degrees C range, which is the sensitisation window where a welded 304 would corrode along the weld. If the service temperature is below 400 degrees C, 304 is cheaper and equally good. If it is above 850 degrees C, 321 is not enough and the answer is 309S or 310S. The narrow band where 321 earns its price is 400 to 600 degrees C with thermal cycling: exhaust manifolds, heat shields, furnace fixtures.

904L is a superaustenitic, 20 chromium, 25 nickel, 4.5 molybdenum, 1.5 copper. It is specified for sulfuric and phosphoric acid, for seawater cooling and for chloride stress corrosion where 316L has pitted. Two honest points: it is not a stronger alloy, its yield strength is close to 316L, so it does not solve a mechanical problem; and it costs three to four times as much, so it should be specified because the environment demands it, not as insurance.

420J1, J2 and J3 are not coil in the same sense

These three are martensitic, 12 to 14 per cent chromium with rising carbon: J1 around 0.2, J2 around 0.3, J3 around 0.4 per cent. They are supplied as hardened and tempered strip for blades, scrapers and cutlery, at 45 to 55 HRC depending on the grade. They are not soft 2B coil for deep drawing, and they cannot be bent after hardening without cracking. If you intend to blank the part and then harden it yourself, buy the annealed condition and specify the hardness you will reach, not the hardness you want to receive.

Specification

On 904L and 321, insist on PMI on every coil rather than on a sample. Both are grades where substitution is profitable and where a visual check cannot tell the difference from 304.

What a coil certificate should contain

The heat number, the chemical analysis including carbon and molybdenum, the mechanical results with the test direction, the finish and the dimensions. A certificate that lists only the grade name is a statement of intent, not a test. For 316L, check the molybdenum yourself: 2.0 to 2.5 per cent is 316L, and anything below 2.0 is not.

Frequently asked questions

Is 904L available in 0.5 mm?
Yes, but with a longer lead time and a minimum quantity. It is not a stock gauge.

Can 321 be substituted for 304?
It can, at higher cost, and it is worth it only in the 400 to 600 C band.

Do you supply 420J2 in the annealed condition?
Yes, for customers who harden after blanking.

Which grade for a coastal balustrade?
316L, and preferably a 2B or a No.4 finish that can be cleaned. 304 will tea-stain within a year.