Stainless Steel Types - What's the Difference?

The difference is the additives.

304 =Chromium Nickel

316 = Chromium Nickle Molybdenum

316 Stainless steel is much more resistant to corrosion then 304

For the general information and spec sheets of different stainless steel see:

http://www.sandmeyersteel.com/select-proper-grade.html

All three are Austenitic grades which are generally non-magnetic and are hardenable by cold working only; not hardenable by heat treatment.

304 is a low carbon modification of type 302 for restriction of carbide precipitation during welding. 18.00/20.00 Cr, 8.00/12.00 Ni, 0.08 C max, 2.00 Mn max, 1.00 Si max, 0.045 P max, 0.030 S max.

304L is a further modification of 304 with lower carbon (0.03 max) for the same purpose.

316 is similar to 304 but with greater corrosion resistance and higher creep strength than 304. 16.00/18.00 Cr, 10.00/14.00 Ni, 2.00/3.00 Mo. Otherwise the chemistry is identical to 304.

316L is a low carbon modification of 316 with 0.03 max C.

These are American Iron and Steel Institute (A.I.S.I.) type designations.

Refer to www.matweb.com for additional information.

The application determines selection and preference.

304 is widely available in sheet, bar, angle, etc., and easily manipulated to form all manner of mechanical support structures. 304 pipe, while available, is uncommon, as other grades of steel with a lower value may have similar corrosion resistance.

316L is widely available as pipe. Its greater corrosion resistance compared to 304 makes it attractive as a medium for carrying more aggressive fluids. It attracts a higher value-per-unit-weight, usually, than 304.

Many plastics and coatings are also suitable for aggressive fluids. Plastics and coatings going over a lower value substrate render 316L unattractive as an option for fluid handling tasks involving larger structures, like simple tanks for example, on the basis of value. Even 304 has a job competing with plastics sometimes.

For special applications, full structural pressure vessels can be fabricated in 316L, and the buyer must be ready to accept the high values involved.

ASTM A240

304

Carbon 0.08

Manganese 2.00

Phosphorus 0.045

Sulfur 0.030

Silicon 0.75

Chromium 18.00 /20.00

Nickel 8.00 /10.50

Nitrogen 0.10

316

Carbon 0.08

Manganese 2.00

Silicon 0.75

Chromium 16.00 /18.00

Nickel 10.00 /14.00

Molybdenum 2.00 /3.00

Phosphorus 0.045

Sulfur 0.030

Nitrogen 0.10

Iron Bal.

316L

Carbon 0.030

Manganese 2.00

Silicon 0.75

Chromium 16.00 /18.00

Nickel 10.00 /14.00

Molybdenum 2.00 /3.00

Phosphorus 0.045

Sulfur 0.030

Nitrogen 0.10

Iron Bal.

We use 80% 430, 20% 304, however, we have just started to use F18. Any data on this?

430

Carbon 0.12 max

Chromium 16 - 18

Iron Balance

Manganese 1 max

Phosphorus 0.04 max

Silicon 1 max

Sulphur 0.03 max

I can't Find Anything on F18 except a galvanealed (coated steal)

Another possibility is that it stands for 18% chromium any grade

Do you know which company is providing this?

Sorry! It's F18TNb, it's a replacement for 430 Ferritic, I think it's from Ugine & Alz.

From their site Here is the Spec sheet

F18TNb Has Titanium and Niobium They are not breaking down the percentage of Titanium to Niobium. (must be a trade secret)

Carbon .02

Silicon 0.5

Magnesium 0.5

Chromium 17.8

Titanium + Niobium 0.7

ASTM A240 is a heat-resisting chromium & chromium-nickel stainless steel specification only for plates, sheets, and strips.

For other stainless steel components such as pipes, tubes, flanges, fittings, structural shapes, ... etc., there are a lot of another ASTM specifications.

Thanks, Here are a few more:

http://www.key-to-steel.com/articles/art26.htm

316 CLASS E312-16 CONTAINS 2% TO 3% MOLYBDENUM TO RENDER IT AUSTENITIC TO INCREASE THE COROSION RESISTENCE TO SULFURIC ACIDS, SULFITES, CLORIDE AND CELLULOSE SOLUTIONS.

316L IS THE SAME BUT HAS A BETTER BEAD APERANCE.

Due to the characteristics mentioned above, 316L SS is also used in medical industry for implantable devices.

SS316 with its Mo content, approx 2.5%, has great resistance to corrosion respect the 304, in particular regarding pitting corrosion and in general resistance to environment with high Chlorides, eg sea water.

SS316L is the preferred choice because its lower carbon content, less than 0.03%, reduce the possibility to have problems during welding, eg carbide precipitation.

on this page u can find something more regarding SS:

http://www.corrosionist.com/materials.htm

hope this help

Vitt