Can Stainless Steel Rust ?

A. En19 is not a stainless steel. It is a chrome-moly low alloy steel, perhaps more widely known as AISI 4140. Nominal composition is 0.4% carbon, 1% chromium, 0.2% molybdenum, plus the usual silicon, manganese, etc, contents.

It has no greater claim to corrosion resistance than mild steel has (although it can certainly be heat treated to much higher hardness than mild steel!).

Depending on the environment and the lubrication if any, it may not be at all surprising that it corrodes.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.

A. Dear Basildon,

Stainless steels (from diff grades/series) do rust. (I welcome any comment on this statement). Literally, metals found in ore form in nature, which is very noble and resistance to environmental deterioration. Steel, a relatively 'active' element extracted from its ore. In terms of thermodynamics, this steel has absorbed much energy during the processing, extraction etc from its ore, this energy-intense element will intend flow/turn to low-energy state to achieve equilibrium with the surrounding. There are quite number of REAL literature or publication out there that explain phenomenon of SS corrosion. Many works have been done on establishing the polarisation curve of SS in acidic, salty environment SS (low grade type) will tend to corrode easily in high-chloride environment, we classified this as localised corrosion (may include intergranular, SCC, pitting and crevice corrosion). This corrosion topic alone can be explained in ASM Metals Handbook Vol. 13 'CORROSION' [affil link on Amazon], check for it. Very likely to find Cr in yr corrosion products, SS contain Cr as alloy element, only differ by its % compositions, Cr may be ranging from 12% to 27%.

Shall I conclude yr situation is a normal circumstance? say if nothing abnormal happened to the SS production. Some info to share with you. Please comment, tq.

Chee Hong, Lee
- Singapore

A. I agree with the above submissions. Stainless steel can and does rust, but its rate of rusting is much less than that for low chromium alloys. Stainless steel must contain at least 12% chromium to be classified as truly stainless. Other metals are added to enhance more specific properties of the steel.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

A. Just a note for info, some of the best stainless steel will show signs of rust if it was in contact with mild steel before it was installed, at hammer marks, rust on the skin from when it was slid across a mild steel work bench and rust from being wire brushed with a normal steel wire brush.

Bill Mashburn
- Hermiston, Oregon

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? Have you considered the possibility of fretting corrosion in your application? This can produce a rusted appearance.

John W. Harrison
diagnostics - Tarrytown, New York

A. As I understand it, there are at least two types of stainless steel -- ferritic and austenitic. Ferritic will rust in the right environment, especially if water is present.

Dave Fisher
- Northants, England

A. What makes stainless steel "stainless" is a chromium oxide passive layer. If this layer is damaged, be it as a result of the manufacturing process or some other means, the exposed metal is able to be attacked and your stainless steel will show signs of rust. The trick is to restore the passive layer as soon after manufacturing as possible, as well as limit the exposure of the material to iron contamination through the manufacturing cycle. There are various means to restore this passive layer, be it through acid treatment or electropolishing. The difficulty is finding the best process.

Tyrone Bagg
- Perth, Western Australia

A. Rust of s.s generally happen with 304, 316, 321 & 347.

FeO is an oxide encapsulated with in other oxides in the s.s and this very oxide has a property of being unstable and therefore it decomposes when the metal is cooled from high temperature ( e.g after welding) according to reaction :4Fe=Fe₃O₄+Free Fe

The fine particles of free iron in the oxide film of the HAZ then react with the moisture in the air to form a uniform "band" of rust on either side of the weld(similar s.s weld)

Mohsin Alhadad
- Libya
2005

A. Some years ago I worked for a company that built equipment for use on oil rigs. The main material used in construction was stainless steel. The most important thing to remember was that under no circumstance where tools used for works on stainless steel to be used for any other material. For example if a hacksaw blade had been used for cutting mild steel it was not allowed near the stainless steel. If it was used on stainless it was said to contaminate the material and cause a reaction in the stainless steel. even the slightest contact with ferrous metals could instigate rust. This applied to any tool, spanners, hammers any cutting tool even abrasive disks.

Jim McCormack
March 31, 2009