Posted: Sep 27, 2007
Contrary to popular belief, stainless steel is susceptible to rusting if it is not properly maintained.
This Buyer’s Guide will discuss the common types of stainless steel used in food service and the best way to care for your investment.
To be classified as stainless steel, the metal alloy has to contain iron and must contain at least 10.5% chromium. Other alloying elements are added to increase the corrosion resistance, improve the fabrication properties, increase the high temperature performance, improve the machining characteristics, etc., which is why there are so many grades.
Common “metallurgical” structures (or classes)
Each has different characteristics and has been created for different applications.
1. Austenitic stainless steel (300 series) has high ductility and consists of both chromium (15 to 30%) and nickel (6 to 20%). Austenitic is also called 18-8, consisting of 18% chromium and 8% nickel, of which 304 and 316 are the major grades. A typical composition of 18% chromium and 10% nickel, commonly known as 18/10 stainless is often used in flatware. View a work table with 304 series.
Benefits: Excellent corrosion resistance; Non-magnetic; Good high and low temperature mechanical properties; Can be polished to a bright mirror finish.
2. Ferritic stainless steel (400 series) is the structure that results when just chromium is added to iron with limited carbon content. 409 (primarily used for automotive exhausts) and 430 (machining) are the most common grades. View a prep table top with 430 stainless steel top.
Benefits: Good corrosion resistance; Magnetic; Limited temperature use; Can be polished.
3. Martensitic stainless steel is the structure that results when chromium (12 to 17%) and carbon (around 0.15%) is added to iron. This structure can be “heat treated” to high hardness levels and is sometimes called “hardenable stainless” 400 series of which 410, 420 and 440 (very high carbon levels between 0.60 and 1.20 %) are the most common.
Benefits: Some adequate corrosion resistance; Hardenable by heat treatment; Magnetic; Somewhat limited temperature use.
What reduces rust in stainless steel?
A 12-30% chromium content of the steel allows the formation of a rough, adherent, invisible, corrosion-resisting chromium oxide film on the steel surface. As long as the film is intact and not broken or contaminated, the metal remains protected and stain less. If damaged mechanically or chemically, this film is self-healing, providing that oxygen, even in very small amounts, is present. The corrosion resistance and other useful properties of the steel are enhanced by increased chromium content and the addition of other elements such as molybdenum, nickel and nitrogen.
Enemies of Stainless Steel
Common foodservice occurrances that can break down the chromium oxide film and allow corrosion to occur.
1. Mechanical abrasion caused by steel pads, wire brushes and scrapers. Use these with care.
2. Hard Water and Mineral Deposits may leave spots, and when heated leave deposits behind that if left to sit, will break down the passive layer and rust stainless steel. Other deposits from food preparation and service must be properly removed.
3. Chlorides, particularly household and industrial cleaners.
4. Metal-to-metal contact between dissimilar metals.
Steps to prevent stainless steel rust
1. Use non-abrasive tools when cleaning stainless steel products. Soft cloths and plastic scouring pads will not harm steel’s passive layer. Stainless steel pads also can be used but the scrubbing motion must be in the direction of the manufacturers’ polishing marks.
2. Clean with the polish lines or “grain.” When visible lines are present, always scrub in a motion parallel to the lines. When the grain cannot be seen, play it safe and use a soft cloth or plastic scouring pad.
3. Use alkaline, alkaline chlorinated or non-chloride containing cleaners. While many traditional cleaners are loaded with chlorides, the industry is providing an ever-increasing choice of non-chloride cleaners. If you are not sure of chloride content in the cleaner used, contact your cleaner supplier. If your present cleaner contains chlorides, ask your supplier if they have an alternative. Avoid cleaners containing quaternary salts; it also can attack stainless steel and cause pitting and rusting.
4. Treat your water. Though this is not always practical, softening hard water can reduce deposits. There are filters that can be installed in faucets to remove distasteful and corrosive elements. To insure proper water treatment, call a treatment specialist.
5. Keep your food equipment clean. Use alkaline, alkaline chlorinated or non-chloride cleaners at recommended strength. Clean frequently to avoid build-up of hard, stubborn stains. If you boil water in stainless steel equipment, remember the single most likely cause of damage is chlorides in the water. Heating cleaners that contain chlorides have a similar effect.
6. Rinse and Wipe. If chlorinated cleaners are used, rinse and wipe equipment and supplies dry immediately. The sooner you wipe off standing water, especially when it contains cleaning agents, the better. Avoid the use of oily rags or greasy cloths when wiping the surface. After wiping equipment down, allow it to air dry; oxygen helps maintain the stainless steel’s protective film.
7. Never use hydrochloric acid (muriatic acid) on stainless steel.
Recommended cleaners for specific situations
Stainless steel needs to be cleaned for aesthetic considerations and to preserve corrosion resistance. Stainless steel actually thrives with frequent cleaning, and, unlike some other materials, it is impossible to “wear out” stainless steel by excessive cleaning. The effect of surface/pattern roughness, grain/pattern orientation, and designs that allow for maximum rain cleaning (exterior applications) should be considered when selected from the methods below.
Fingerprints & smears
Stubborn Stains &
Grease & Fatty Acids, Blood,
Burnt-on or Baked-on Foods
Grease and Oil
Warm Water, Soap, Ammonia, Detergent
3M Stainless Steel Cleaner and Polish,
Arcal 20, Lac-O-Nu, Lumin Wash,
O’Cedar Cream Polish, Stainless Shine
3M Stainless Steel Cleaner and Polish, Allchem Concentrated Cleaner, Samae, Twinkle, Cameo Copper Cleaner, Liquid
Nu Steel, Copper’s or Revere Stainless
Steel Cleaner, Household Cleaners, Lumin Cleaner, Zud Restoro, Sta-Clean, Highlite, Allen Polish, Penny-Brite, Copper-Brite
Scotch-Brite Power Pad 2001, Easy-Off,
De-Grease-It, 4% to 6% hot solution of
agents such as tri-sodium polyphosphate,
5% to 15% caustic soda solution
Any good commercial detergent or caustic cleaner.
Apply with soft cloth or sponge.
Can be used on all finishes.
Provides barrier film to minimize fingerprints.
Can be used on all finishes.
Rub lightly using damp cloth in direction of polish lines or grain.
Excellent removal on all finishes. Particularly useful where rubbing is not practical.
Apply with sponge or soft cloth in direction of polish lines.
Based on information supplied by the Stainless Steel Information Center.