If a steel has more than 10 ¾% Chromium content, it is classified as a type of Stainless Steel. There are many types (grades) of Stainless Steel, just as there are many types of corrosion. One grade of stainless steel may work well with one type of corrosion and then be terrible for service in another type of corrosion. The most common stainless grade is 304. Modify it a bit (improve) and you get 316. Enhance that a little, and you get 317. If you add Sulphur to type 304 stainless, you get 303 stainless, which is a “Free-machining grade”. Note: Generally, as you add elements to stainless steel to improve machinability, or strength, you may lessen strength and service-life.

Three hundred series grades are often referred to as; 18-8 stainless; where the 18 stands for percent of chromium content and 8 refers to the percent Nickel content. Those grades have some commonalities; grain structure of Austenite, non-magnetic, not generally responsive to thermal hardening, ability to work-harden.

Steel that has an Austenitic grain structure is not hardenable by heat treatment, but it is hardenable by cold working. Austenitic stainless grades are non-magnetic; i.e. they won’t, under general conditions, attract a magnet.
Strain-hardening, Cold-drawing, Cold-Finished, Cold-working, and Work-hardening, are all pretty much synonyms. Bang it around, Squash it, or keep bending it back and forth and it’s going to get harder; sometimes near 50RC hard.

18-8 Types of stainless steel are popular (common) for good reason. They are excellent for many applications exposed to corrosion, and they are readily available from suppliers. There are of course limitations imposed by various specific types of corrosion as well as limitations imposed by physical characteristics of the actual parts required (strength, straightness, etc). We will explore those in later posts.


-Howard Thomas, October 17th, 2022

The easier question to answer would be; who can’t use it?

A continuation of last month’s post:
Service temperatures should not exceed 750F. Any customer currently using stainless of the following types: 304L, 316L, 410, 416, 17-4ph should consider LDX, (ASSOCIATED STEEL’S ASC2250 LDX).

LDX is now made by several steel mills, to their own specific variances. In general, it is a great stainless grade for heavy maintenance applications where the grades listed immediately above are being used. It is more corrosion resistant, stronger, less apt to gall, better at resisting SCC, easier to machine and weld, than many of the commercial grades shown.

Lean Duplex work hardens. As shipped, it is generally about 28RC. The Austenitic portion of the grain structure contributes to strain hardening; it cold works as the size is drawn. As mentioned in part one; It is harder (hence stronger) than commercially available 304 and/or 316, but is still easier to machine. Duplex grades of stainless steel contain grain structures of equal parts Austenite and Ferrite. They are considered to be magnetic in their most common form.

It resists bending, (minimizes twisting), abrasive wear, resists failure due to SCC, resists galling, adds strength. It’s like the Ginsu knife of stainless steels. (Probably have to be my age to know what that means). Lean Duplex is not intended for use in applications currently requiring advanced alloy grades, such as; 2507, AL-6XN, Hastelloy C, 20cb, Ni625, etc.

The PRE (pitting resistance) is the accepted standard for determining a stainless grade’s comparable resistance to pitting and crevice corrosion. The lower the number, the less resistance.
304 is 18 316 is 24 Duplex grades are nearer to 40.
Associated Steel carries Lean Duplex (ASC2250 LDX) in two surface finishes; Fine-turned oversize (The size will make the nominal size), and Precision Polished Guaranteed Bearing Fit (Minus/minus tolerance). It is inventoried in long mill bars and may also be sold to specific required lengths.

ASC 2250 LDX offers advantage in:
Resistance to Stress Corrosion Cracking (SCC)
Resistance to Chloride pitting
Resistance to Crevice Corrosion Cracking
Elevated Strength Levels
Ease of machining
Ease of welding
Greater fatigue resistance
General corrosion resistance superior to 316L
Excellent resistance to “Thermal Shock” (low-cycle fatigue)
Excellent service to -30C

-Howard Thomas August 6th, 2021