At first glance, in comparing 304 vs 316 stainless steel, the lines between the two grades may seem fine. Each has more properties in common than not—both have very good corrosion and heat resistance, strength, and excellent welding and forming properties. In fact, 304 and 316 are two of the most popular grades of stainless steel. It’s no wonder—like all stainless steel grades—the material is easy to fabricate, clean, and maintain, and is exceptionally durable, environmentally friendly, and aesthetically pleasing.
Such material properties make stainless steel a top choice in the fabrication of parts and components for numerous applications and products. Yet the term stainless steel can be somewhat confusing. Mainly because stainless steel does not specifically define a particular type of material, but broadly defines a class of iron-based alloys that give steel corrosion-resistant properties. In essence, stainless steels are low-carbon steel that consists of a minimum of at least 10.5% chromium, which gives the material its defining characteristic and corrosion resistance. The steel can then be combined with other alloying elements such as nickel, manganese, silicon, nitrogen, titanium, molybdenum and more. However, it is the amount and variety of alloying elements used that determine the grade and type of stainless steel. There are over 100 grades of stainless steel, and 304 and 316 are but two of them.
What further differentiates 304 and 316 grades are their classification as austenitic, a type of stainless steel which refers to a specific category of stainless steel derived from the material’s crystalline microstructure. Austenitic steels—those 200 and 300 series as categorized by the AISI/SAE grade system—are the most commonly used type of stainless steels. They have relatively low levels of carbon and high levels of nickel and chromium—the latter provides a protective oxide layer to the surface of the material. The material is non-magnetic, with exceptional heat and corrosion resistance, and formability and strength. Austenitic 304 and 316 stainless steels are well regarded for their hygienic properties and are considered food, surgical or medical-grade stainless steels.
Nonetheless, as subtle as they may be, there are differences between the two 304 and 316 grades, with the one key difference that distinguishes one grade from another being the addition of molybdenum to the chemical composition of grade 316. Molybdenum enhances the material’s corrosion resistance, especially for applications in saline or chloride-exposed environments, but the addition of molybdenum to the chemical composition of 316, as well as the increase in nickel, make 316 more expensive per ounce of material than 304, with some estimates ranging upwards of 40% more in cost.
Also referred to as “18/8” in reference to its 18% chromium/8% nickel chemical composition, grade 304 is considered the most versatile and widely used of any grade of stainless steel. Its many favorable characteristics and austenitic structure make it an ideal grade for use in a wide array of industrial parts and components, chief among these are springs, nuts, bolts and screws. Far more than that, due to its innate hygienic properties, 304 stainless steel is used in the fabrication of food processing equipment, sinks and splashbacks, kitchen equipment like cutlery, flatware, and saucepans, sanitary ware, troughs, and tubing, as well as for brewery, dairy, food and pharmaceutical production equipment. Because of its strength and aesthetic appeal, and heat and corrosion resistance, 304 is also used in the fabrication of automobile parts, architectural paneling, railing and trim, heat exchangers, and parts for various marine applications.
Grade 316 stainless steel has a chemical composition of 16% chromium, 10% nickel, 2% molybdenum, and .08% carbon, and is used to fabricate parts, components, and products in applications that require exceptionally high corrosion resistance. This would include chemical processing equipment, tanks, and evaporators, valve and pump parts, marine parts, outdoor electrical enclosures, exhaust manifolds and engine parts, and heat exchangers. The hygienic properties of 316 make it ideal for use in pharmaceutical, surgical and medical applications—this includes hypodermic needles, needle caps or guards, surgical instruments, dental implants, and more.
Both 304 and 316 grades stainless steel offer very good corrosion resistance and provide the strength, durability, and heat resistance that make the materials a top choice in the fabrication of parts in components for a wide variety of products in numerous industries. Though more costly, 316 stainless steel gets an edge in applications that require a higher degree of corrosion resistance. For more information, contact James Spring and Wire Company.