Machinery and tools used in the canning industry, as well as those used in catering and restaurants, must meet strict hygiene standards. Stainless steel is almost always the only choice in these sectors, thanks to its resistance to corrosion. Every alloy has its strong points and its downsides, which force manufacturers to choose wisely among the hundreds of stainless steel grades.
There is no final answer to the question “what is the best food grade alloy?” in catering and food industry. Making candy is not the same thing as making cheese: temperatures, and especially chemical compositions, are different. In food processing, the most used alloys are AISI 316 and AISI 430.
316 is an austenitic stainless steel with a high chromium and nickel content. Like most metals, it has a usable temperature range far higher than what’s required in food preparation.
This steel grade is especially suitable for food because of its high resistance to acids, alkalis, and chlorides such as table salt. Other austenitic stainless steels (i.e. 304) may develop strong pitting corrosion. 316 is not affected by this type of corrosion and is therefore suitable to most applications.
From a metallurgical point of view, AISI 316 Stainless steel is similar to 316. It has the same chromium content, but a lower percentage of nickel, making it less expensive.
Another important difference is that AISI 430 is a ferritic alloy, in other words it is a magnetic material. Ferritic alloys have a high resistance to stress corrosion cracking, which leads to failure in presence of mechanical stresses in corrosive environments.
430 stainless steel has great tolerance to organic and nitric acids and is therefore used in contact to acidic foods. It also shows good resistance to oxidation and sulfurs.
On the other hand, its lower quantity of nickel results in poor resistance to reducing acids that are found in some foods and juices.
Generally speaking, AISI 316 is the better option for machinery and containers used in canning industry and catering. Its resistance to salt and acidic foods like tomato and lemon juice make it a great solution. For less demanding applications, AISI 430 may be a less expensive (and equally valid) tradeoff.
Apart from the grade you are going to use, it’s important to choose a low surface roughness, that can be obtained with fine abrasives or electropolishing. Improving surface finish reduces the risk of cracking and corrosion and makes cleaning easier.