When stainless steel is seen in a specification or recommendation for fastener applications, it’s most likely referring to 400-series or 300-series alloys. While both are incredibly strong and offer respectable rust resistance, there are game-changing distinctions between the two. In this article, we’ll highlight how 300 and 400 stainless steels compare in regards to composition, performance, and pricing to help you ultimately determine the best option for your next build.
What defines 300 vs 400 stainless steel series?
You may also see 400-series be referred to as martensitic stainless steel and 300-series referred to as austenitic stainless steel. The biggest difference between these groups of alloys is the chemical composition (the ratio of different elements that create the metal).
More specifically, the two groups of alloys have varying amounts of chromium and nickel.
304 stainless steel, the most common alloy for 300-series fasteners, contains around 50% more chromium than 410 stainless steel, the most common alloy for 400-series stainless steel fasteners. And while 410 stainless steel does not contain any nickel, nickel makes up around 10% of the total composition of 304 stainless steel.
While chromium and nickel are the primary differentiators of 400-series and 300-series stainless steels, molybdenum can be added to 304 stainless steel to create 316 stainless steel, making up around 2.5% of the total composition.
The important thing to remember is that both chromium and nickel work together in stainless steel to increase corrosion resistance!
How 300 series screws compare to 400 series for corrosion strength
410 stainless steel offers mild corrosion resistance thanks to its chromium content, and is commonly used in applications where the fasteners will not be exposed to constant moisture or any chemicals. An example of an application where 410 stainless steel may be used is metal wall panel attachment.
However, 304 stainless steel offers some of the best corrosion properties that are available for fasteners thanks to the amount of chromium and nickel that are in the alloy. 304 stainless steel can be used in the presence of a variety of chemicals and acids; including lower concentrations of chlorides (salt). When choosing a fastener that will regularly come in contact with moisture, chemicals, animal waste, and low concentrations of salt, 304 stainless steel is the best option!
With the addition of the molybdenum, 316 stainless steel becomes much more resistant to chlorides and harsher chemicals. When choosing a fastener that will come in contact with chemicals such as sulfuric acids and higher concentrations of salt that are present within 1km of the ocean, 316 stainless steel is the best commercially available option!
Which type of stainless steel is stronger - 300 or 400?
Because of the differences in composition, 400-series stainless steels can be heat treated to higher hardnesses while 300-series stainless steels cannot. This enables 410 stainless steel fasteners to be much harder than any 304 stainless fastener, and thus stronger. In applications where ultimate tensile or shear strength is critical, 410 stainless steel fasteners may be preferred.
How does pricing compare between 300 series stainless vs. 400?
Simply comparing raw materials, 304 stainless steel is around 50% more expensive than 410 stainless steel. In turn, this often results in most 300-series fasteners being more expensive than their 400-series counterparts. Therefore, we often direct customers towards 400 stainless steel if the anticipated exposure to corrosive elements is low. However, in scenarios in which external corrosive elements will be high, we encourage buyers to think of the long-term savings that come from fasteners with inherent resistance to rust (300-series) rather than those which will compromise the integrity of the build.
Don’t forget about galvanic corrosion when choosing a stainless steel screw
One topic that is often overlooked during fastener selection is galvanic corrosion, specifically when aluminum is used. When a fastener is being used in an application where aluminum is present, extra caution needs to be taken to limit galvanic corrosion within the connection. Galvanic corrosion is caused when dissimilar metals come in contact with an electrolyte, like water. If this is not prevented, a phenomenon called hydrogen assisted stress corrosion cracking can occur which essentially causes cracking of hardened steel, like hardened 410 stainless steel. Due to the lower hardness of 304 stainless, which may have seemed like a hindrance, actually means that it is immune to this phenomenon. Therefore, when aluminum is present in an application, 304 stainless steel is the best choice for fastener material!
Find the right stainless steel screw with SFS
We manufacture a full range of 400-series and 300-series fasteners, including the ever-popular bi-met screw. Browse our online selection or contact us to speak with a specialist about which stainless steel best fits your particular project.