How to care for your stainless steel appliances

This may sound silly, but even stainless steel needs love. Well, maybe not. But if you can’t give it love… at least you might want to give it care.

What is stainless steel

Stainless steel is a truly wonderful material and it is surprisingly new to the industrial world. It’s made from a very precise alloy of iron, nickel, chromium and carbon. The term alloy refers to metals made with blends of various elements such as this. What makes this steel alloy so special is its resistance to corrosion. Corrosion resistance comes from a chromium content of at least 10.5%, mixed with small amounts of molybdenum. Apparently, rust doesn’t like that mix.

Steel’s resistance to corrosion and pitting increases with higher amounts of chromium and molybdenum. Unfortunately, there are limits and some drawbacks to going too far with this. Increasing the amounts of chromium and moly too much can weaken and increase the brittleness of the metal. This means that there is no single magic bullet, or “best” alloy when it comes to stainless steel. The result is a multitude of special stainless grades. All these come with infinitely varying chromium and molybdenum ratios to address the many applications and environments they must operate in.  Choosing, or even creating the right grade of stainless steel for the job is an important and exacting metallurgical science.

In the beginning 

In 1913 Harry Brearley led a team of scientists in Sheffield, England to develop the first stainless metal alloy.  Since then, more than 250 stainless steel grades have been created to meet various needs.  Of all those grades, there are five basic types: Ferritic, Austenitic, Martensitic, Duplex and Precipitation steel.

The most exotic stainless

There is a sixth and fairly exotic family of stainless called Superalloys. As a homeowner, you can basically ignore these. Superalloys are much stronger and more durable than the others. They are also hard to make, very rare and thus come with extremely high prices. Space exploration, nuclear weapons and submarines apparently all need superalloys. I’m sure our military loves the stuff. However, homeowners needn’t care about it unless you are planning to build a DIY nuclear accelerator in the back yard.

The homeowner’s guide to common stainless grades

Here are the main grades of stainless steel that homeowners should know about:

304

This is a common grade of stainless steel that you see every day. 304 contains a minimum of 18% chromium and 8% nickel. It is ferrous (magnetic) and used in the manufacture of many mass market household appliances like refrigerator skins, BBQs and even the bodies of the Delorean automobile.

316

This is a slightly higher quality “marine” grade. 316 contains 16% chromium, 10% nickel and 2% molybdenum. Molybdenum helps resist corrosion from chloride (salt). Metal parts exposed to the ocean or other salt environments are perfect for 316 material.  316 stainless makes great food machinery, precision tools, surgical instruments and even jewelry. It is commonly built into boats and extremely durable outdoor rated appliances. The most durable BBQ’s are made with this type of stainless steel. See how to buy a BBQ.

409

This material is not attractive and does not polish well.  409 stainless is the material of choice for engine exhaust systems. It is also used in applications where corrosion resistance is desired and aesthetics are secondary.  

420

420 stainless has a higher carbon content than some and is thus stronger and harder. Flatware, cutlery, surgical and dental instruments, scissors, tapes and straight edges are all made from 420 stainless steel.

430

430 is not very hard or hardenable, but it has good aesthetics, corrosion resistance and formability. It is one of the few stainless materials that can be easily rolled into flat sheets and formed into shapes. Dishwasher interiors, chimney liners, wire lashings, auto trim and other decorative products are all made from 430 stainless steel.

440

Known as razor steel, 440 is a very hard and high grade stainless used for fine cutlery, knives and razor blades. 440 can be sharpened without losing its hardness, and is unaffected by food, acids and other corrosive materials. These characteristics make for long wearing, durable sharpness which is ideal for cutting edges. 

904L

This is an extremely high quality, non-ferrous stainless steel. It has a bright, beautiful appearance combined with good machining properties. It is used for the manufacture of one the most sought-after wristwatches in the world, the Rolex Stainless Steel Daytona. Critical parts for top-secret US military machinery and submarines are made from 904 L stainless. Unfortunately I can’t tell you about those.

General care

When first manufactured stainless steel is ultra tough, but contamination can adversely affect its surface during later fabrication. Debris, dirt residue like free iron, grease and machining oils can all collect on the surface. These are usually microscopic and can go unseen to the human eye. These pollutants weaken the metals resistance to surface corrosion and make it more susceptible to degradation. This microscopic contamination can allow stainless steel to corrode and explains why some low-cost products will develop “rust spotting”.

Passivation

A process called “passivation” or pickling can return some corroded stainless steel surfaces back to original specifications. Passivation aggressively removes the contaminants from the surface and neutralizes any unwanted electrical charges. It then washes the material in a protective bath, and coats it with a sealer. The process is labor intensive, but it purifies and protects the surface of the stainless steel and allows the metal to protect itself. Years ago I developed a good formula for the passivation of high-quality outdoor stainless steel railings and other materials. We use it at HPS frequently for our clients with homes exposed to marine environments. If you are interested in the “pickling” process, the recipe for it can be found here.

Cleaning

Do not scrub stainless steel with an abrasive. Appliances with stainless steel have a very uniform, machine applied finish. It is surprisingly easy to scratch. Any use of an abrasive will mess up the machine marks and permanently ruin the finish. Simply clean stainless steel with mild detergent, water and a soft cloth. 

Also, never, ever use steel wool to clean stainless material. Its abrasiveness will ruin the machine finish and also embed microscopic particles of iron onto the surface. These particles will begin rusting almost immediately and destroy the finish. As tough as stainless steel is, the cosmetics are delicate. If you scratch or mar the surface, you may have to replace the part. Refrigerator and dishwasher fronts are often the victims of damage thanks to kids or overzealous housekeepers. It is possible to replace the damaged front “skins” on some of these appliances, but it can be expensive. Perhaps it would be better to just place a magnetic reminder over the damage. It should say “Don’t scratch me!”

Nothing is sadder for a homeowner than to see expensive and gorgeous materials that have been left to corrode in the elements.  Stainless steel finishes are a good example. Most homeowners don’t know the basics of caring for these nice finishes and if you happen to live in a corrosive environment or close to the ocean, it really really can take a toll.

Here is a process we use at HPS Palo Alto, Inc. to clean, polish and passivate exterior stainless steel architectural finishes. This is a time and labor extensive process but is quite effective at returning weathered stainless back to original glory. This treatment should also be a mandatory specification for new stainless steel products and installations. Let your designer or architect know.

Material needed:

• Scotch Brite pads
• Wichinox paste
• Phosphoric acid (available in bulk from some commercial nursery suppliers)
• Baking soda
• Distilled water
• Denatured alcohol
• Molecular surface sealer (Everbrite Protectaclear)
• Dust free absorbent cloth for drying and application of alcohol.

Warning!

Do not use this process on stainless steel sheet material with a factory machined finish. Always test first on an area that is least exposed to be sure that it meets with your aesthetic needs.

The stainless steel passivation process

Step 1

First wash and scrub the metal with regular tap water and a Scotch Brite pad. This will remove dirt, dust, bird droppings and any accumulated surface residue.

Step 2

Next vigorously scrub the entire surfaces with fresh pads along with a mix of 2 parts phosphoric acid and 10 parts distilled water. Scrub the length of the metal parts and go with the “grain” not across it.  Continue to scrub and polish the metal until all rust and corrosion has been satisfactorily removed. Do this in small sections at a time in order to not miss any spots. Heavily corroded and hard to access areas may need to be done several times.

Step 3

During the first step, apply Wichinox paste to any welds in the work area while the acid mix is still wet on the metal. The welds are the worst areas and the paste help to give the phosphoric acid longer to work its magic. Rinse off the acid mix from the rest of the work but leave the weld areas with paste for at least 15 minutes before rinsing.

Step 4

Mix baking soda and distilled water together in a ratio of about a box of soda to 5 gallons of water. Carefully wash all surfaces of the metal with the baking soda/water mix. This will completely neutralize any of the acid that may be left from the previous step. Scrub the welds if necessary with this mix using a clean toothbrush to remove all the paste. Rinse with a fresh batch of distilled water when done and allow to air dry.

Step 5

Wipe all metal surfaces with denatured alcohol and let dry. This removes all residue from prior steps including fingerprints, dust, oils, grease etc. and leaves the surface clean and ready for the sealer.

Step 6

When the surface is completely dry from the above step, and the appearance of the metal surface is completely satisfactory, then apply two coats of Everbrite Protectaclear sealer waiting 1 hour between coats.

Note:

The sealer is a wafer thin molecular protectant and it is completely invisible. It will last in harsh conditions and direct sun for about 2 years and keep the steel looking new and shiny. After two years the sealer will begin to break down and the steel will again be exposed and vulnerable to corrosion. The manufacturer recommends that the metal be washed again and a new coat of sealer applied every year. This way the bare steel is never again exposed to corrosion. The wash and re-coating process is much faster than the initial treatment.

Summary

If you like your expensive metal trim looking like new, this is the only reliable and lasting way to accomplish it.

Halting Stainless Steel Corrosion

Yes stainless steel can rust?

It may come as a surprise, but stainless steel is not really stainless. In fact, stainless steel can to some degree both rust and corrode. To help you understand better, this post is all about the care required for halting stainless steel corrosion.

What is stainless steel

Stainless steel is a very precise alloy (blend) of iron, nickel, chromium and carbon. What makes this alloy of steel so corrosion resistant is a chromium content of at least 10.5% with a small amount of molybdenum. The corrosion and pitting resistance increases with higher amounts of chromium and molybdenum. Unfortunately, increasing those amounts too much can also affect the strength and brittleness of the metal. The result is numerous special grades of stainless steel all with varying chromium and molybdenum ratios for the diverse environments that must be endured.  Choosing the right grade of stainless steel for the job is important.

Grades of stainless steel

Over the years more than 250 grades of stainless steel have been developed. Of those, there are only five basic types.  Ferritic, Austenitic, Martensitic, Duplex and Precipitation. There is a sixth type called Superalloys. Superalloys are much stronger and more durable than the other steels. They are also rare and come with extremely high prices. Made for submarines and other exotic uses, I’m sure our military loves Superalloys. Homeowners could care less about most of these.

Here are the grades that homeowners need to know about:

304 Most common grade, magnetic, appliances, BBQs

316 Marine grade, food and surgical stainless steel, jewelry grade (except Rolex), marine exposed appliances and BBQ’s

409 Low cost, stainless auto exhausts

420 Low cost, mass market cutlery grade

430 Auto trim, decorative material

440 High grade, cutlery steel, razor blades

904L Rolex Stainless Steel Daytona watches

Passivation

When a stainless steel part is machined and fabricated various contaminants and abrasive particles can permeate the surface of the metal. Debris, dirt residue such as free iron, grease and machining oils all can become embedded in the surface. These can be microscopic and often go unseen to the human eye. These contaminants weaken the metals resistance to corrosion and make it more susceptible to degradation. It is this contamination that allows stainless steel to corrode.

The passivation process (sometimes called pickling) can return the stainless steel surface back to its original specifications. It does this by aggressively removing the contaminants from the surface, neutralizing the electrical charge and then submerging the part into a protective bath. The process essentially improves, purifies and protects the surface of the part. The restored surface allows the metal to perform as designed to protect itself.

It is important to note that passivation does not change the original outward appearance of the base metal.  I have developed a low cost formula if you are interested in optimally protecting your stainless steel. Register with this site and send an email request. We will forward it to you. 

Summary

The passivation of stainless steel material is a process performed to make a surface passive or less reactive. A surface film is created that causes it to lose its chemical reactivity. Stainless steel is already known as being corrosion-resistant, however the passivation process strengthens its’ natural coating by improving the exterior surface of the material. Stainless steel passivation purges the stainless steel of the oxygen absorbed by the metal surface, creating a monomolecular oxide film. Passivation results in a highly desired, low corrosion surface on the metal.

Advantages of Passivation

• • Improved Corrosion Resistance
  • Uniform, Smooth Appearance & Finish
  • Deburring (Polished Surface)
  • Cleanliness
  • Improved & Extended Life of Product

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