Today, stainless steel is generally divided into four distinct families:
1. Austenitic
This family is the most popular and widely used around the world. It often includes chromium and nickel. Some grades also include manganese and molybdenum. They are particularly versatile and are renowned for displaying excellent strength and malleability. Popular grades of austenitic stainless steel include 303, 304, 316, 310, and 321 grades.
2. FerriticDue to its lower nickel content, this is one of the most cost-effective families available. Containing anywhere between 10.5% and 30% chromium, ferritic stainless steels usually have low carbon consistencies of not more than 0.1%. Ferritic stainless steels are magnetic and are primarily chosen for their resistance to temperature oxidation and stress corrosion cracking. Common grades of ferritic stainless steel include 409 and 430 grades.
3. Duplex
This family includes many of the most recent and proprietary alloys created. Duplex stainless steel combines the austenitic with the ferritic, resulting in a metal that is stronger than both: this higher strength can lead to considerable weight reductions. Its excellent resistance to corrosion, even in demanding environments, makes it perfect for use in marine applications. Common duplex alloys include 318L, LDX 2101, LDX 2304, 2507, and 4501 (Also known as 25CR super duplex) grades.
4. Martensitic & Precipitation Hardening
Structurally similar to ferritic stainless steel but with an elevated carbon content (up to 1.2%), martensitic stainless steel can be hardened to a large degree.While it's the least common of the four major stainless steel families, martensitic and precipitation hardening steels are popular in applications requiring a precise, hardened edge. They are especially useful for creating medical tools and surgical instruments. Common grades of martensitic and precipitation hardening steels include 410 and 420 grades.
Let's dive into stainless steel as it relates to food. There are essentially two grades of stainless steel that can be used for food processing. They are 316 and 430. Here are their differences and comparisons according to MarlinWire...
Food Grade Stainless Steel 316
Grade 316 stainless is an austenitic stainless steel alloy with a high chromium and nickel content. Like many steel alloys, it has a continuous use temperature several times higher than most food-making processes will ever require (more than 800°C, or 1472°F).
What makes the grade 316 alloy an ideal food grade steel sheet material is the fact that it has a high resistance to acids, alkalis, and chlorides (such as salt). Other austenitic stainless steels, such as grade 304 SS, can experience severe pitting corrosion when exposed to salt, which is often present in food products.
316 makes for great food grade stainless steel containers for nearly any food application.
Grade 430 Stainless Steel and Food
As an alloy, stainless steel 430 food grade metal is very similar to grade 316 stainless. It has the same chromium content as 316, but only a fraction of the nickel content, which makes it a more affordable alternative for some food makers.
Another major difference between 430 and 316 stainless steel is that grade 430 SS is a ferritic alloy, meaning that it’s magnetic by default. Ferritic alloys like 430 SS also have extraordinary resistance to stress corrosion cracking (the growth of crack formations that can cause a sudden failure in corrosive environments).
430 SS has a strong resistance to nitric & organic acids and is often used for applications where prolonged contact with mildly acidic compounds is a concern. The alloy also boasts resistance to sulfur and oxidation.
However, because of the low nickel content, this alloy is not as resistant to some dilute reducing acids as grade 316 stainless steel would be.
So which is Best for Food-Safe Applications?
Overall, grade 316 is usually the better choice when making food-grade stainless steel containers. 316 SS is more chemically resistant in a variety of applications, especially when dealing with salt and stronger acidic compounds such as lemon or tomato juice.
However, 430 is a good, lower-cost alternative for food makers that need a moderately resistant, food-grade steel sheet for their manufacturing process.
It’s important to note that the resistance properties of both alloys can be enhanced via electropolishing. This process not only improves the oxide layer that protects the steel; but also removes microscopic peaks and valleys on the alloy’s surface, making it harder for food to stick to the steel and easier to clean.
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