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Professional catering and commercial kitchens, be they in restaurants, hospitals, school cafeterias, or elsewhere make abundant use of stainless steel in both their construction design and equipment choices. This includes everything from sinks and cabinets to food storage and transport equipment.
Stainless steel’s high durability and corrosion resistance make it ideal for food processing, storage, and catering, but it is also important to choose the best type of stainless steel for the purpose at hand. This will assist you in conforming to government regulations, maintaining the highest health standards, and given the proper care, in getting the longest possible life out of your equipment.
There are over 50 different grades of stainless steel on the market today, all of them being iron-based alloys with at least 10.5 percent chromium content, besides other additives. The chromium helps guard against corrosion, adds heat resistance, and makes the metal easier to form.
In food processing, there are three main types of stainless steel in common use: 304 (1.4301), 316 (1.4401 or 1.4404), and 430 (1.4016). Most plumbing and food containers in commercial kitchens is manufactured from either type 304 or 316, both considered “austenitic.” Austenitic stainless steels have 16 to 26 percent chromium and as much as 35 percent nickel content. They are valued for their high flexibility and corrosion resistance.
Stainless steel 430 is also a food grade stainless steel, though it contains only 16 to 18 percent chromium and is better used in applications where demand for corrosion resistance is only moderately high. It is suitable for splash backs, equipment housings, paneling, table tops, kitchen utensils, low-cost sinks, fasteners, flue liners, refrigeration components, baffle grease filters, and more. Due to its excellent finish, it is also often used in decorative trim.
Stainless steel 430 is “ferritic,” meaning it has good corrosion resistance; “non-hardenable,” in that it will not harden due to exposure to high temperatures; magnetic, unlike type 304 which is non-magnetic; and though with good formability, is somewhat more difficult to form or weld than stainless steel 304. Additionally, stainless steel 430 has high resistance to nitric and certain other acids, making it ideal in many situations where chemical exposure is possible.
Stainless steel 430 resists corrosion well in mild to moderate environments, and it resists oxidation at high temperatures. To optimize its corrosion resistance, its surface must be kept well polished. As a ferritic grade of stainless steel, 430 also gives high resistance to stress corrosion cracking.
We have mentioned that stainless steel 430 resists oxidation well at high temperatures. This is true when it is subjected intermittently to temperatures as high as 870°C or continuously at temperatures up to 815°C. However, as a ferritic steel, it can become brittle after long use at temperatures of even 400°C to 600°C. It can also become brittle after long exposure to sub-zero temperatures. In such cases, it may need annealing to eliminate brittleness.
Stainless steel 430 can be welded and annealed, but it is not the most weldable of stainless steel types. This means you should not weld it for use in high-impact or heavy-load situations.
Because 430 is free of all nickel and molybdenum, it is significantly less expensive than grades 304 or 316. Since, in many situations, it is more than adequate, it is therefore often preferred to its more costly counterparts.
Those purchasing stainless steel 430 material to be used in manufacturing new kitchen equipment or in repairing existing equipment should follows some basic guidelines. First, only tools exclusively reserved for stainless steel work should be used, and the work area must be made impeccably clean before beginning. Otherwise, contamination from other metals could occur, which can lead to surface discoloration and spot corrosion.
You can cold-work stainless steel 430, though it is less ductile than grade 304. On the other hand, 430 work-hardens less than does 304. If hot-working 430, the melting point of this metal is between 1425°C and 1510°C. Before forging begins, however, the whole material being worked on should first be heated uniformly to 816°C to 1038°C.
Grade 430 stainless steel is fairly easy to machine, but it is important to keep all edges sharp since dull edges exacerbate work-hardening. Cuts need to be light but sufficiently deep, chip breakers should be used, and lubrication and cooling should be applied generously.
Welding stainless steel 430 is easily accomplished by all welding methods. One should preheat the material to 150°C to 200°C and anneal at 790°C to 815°C to prevent brittleness.
Air cooling and annealing help to prevent grain growth, which can cause the surface to become rough, somewhat like an orange peel. The finish quality of grade 430 being one of its most sought-after properties, such a result would ruin the piece so affected.
As long as stainless steel 430, or any other grade of stainless steel, is used for its intended applications and not abused or misused, there should be no issue with corrosion. A smooth finish will also reduce the risk of corrosion, as well as make it easier to sanitize all surfaces.
When corrosion does occur, it can come in any of the following four forms:
1. Pitting Corrosion: This type of surface damage consists of localized pits with smooth walls. It is caused by chloride-containing solutions reacting chemically with the chromium of stainless steels. This forms chromium chloride and removes chromium from the metal’ surface, which reduces corrosion resistance. Acids, high-chloride liquids, and high temperatures all promote pitting corrosion.
2. Crevice Corrosion: When narrow crevices and other “nooks and crannies” on stainless steel kitchen equipment get filled with solutions that cannot easily exit, protective films can break down and corrosion set in. As evaporation and refilling alternately recur, the trapped solution gets stronger and stronger, speeding up the corrosion process. Gaskets, washers, sharp corners, overlaps, and flanges are frequent “targets” of crevice corrosion. Periodic disassembly and cleaning out of all areas where crevice corrosion may occur is recommended.
3. Stress Corrosion Cracking: Stainless steel 430 is highly resistant to this type of corrosion, which results in steel material actually cracking due to a combination of corrosion and applied pressure. Chloride and temperatures over 50°C usually lead to the corrosive weakening, and the normal stresses of using the equipment finish the process.
4. Inter-granular Corrosion: This type of corrosion is mostly a threat with grades 304 and 316. It is also known as “weld decay” because it occurs in bands surrounding previously welded material. As grade 430 is low in carbon and not as frequently welded, it is not as likely to suffer from this type of damage.
Stainless steel 430 is one of several much-used food grade stainless steels. Each has its own most suitable applications, and each is highly effective and durable when used and maintained according to manufacturers’ recommendations.
Grade 430 is especially valuable for its low cost, attractive finish, and better resistance to particular types of corrosion. However, it is also highly heat and corrosion resistant in general and is ideal for many types commercial kitchen and professional catering equipment.