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Stainless Steel, High Tensile, Galvanised Mild Steel: Differences in Fastener Materials

Blog | February 28th, 2018

Is there a single fastener material that satisfies every application? Stainless steel comes close. It’s a durable and corrosion resistant alloy. Doesn’t galvanised mild steel also protect fasteners from rust? We’ll concede that point, but mild steels aren’t exactly strong. No, that’s when high tensile nuts and bolts get the call to action. There are so many choices. Nevertheless, those alloy differences can help us pick the right material solution.

The Stainless Steel Outdoorsman 

Tough and durable, stainless steel fasteners are coated with a silvery finish. The chromium alloying metal gifts the hardened metal with an essential trait. Used in harsh environmental conditions, stainless steel fasteners won’t rust. Galvanised mild steel bolts include the same feature, don’t they? That’s not exactly true. Stainless metals are inherently immune to rust, but galvanised fasteners are not. Coated with a dipped zinc finish, that separate protective layer is all that stands between fastener integrity and material oxidation. If it’s scratched, it will rust.

Assessing Galvanised Mild Steel Fasteners 

Economically speaking, this softer alloy makes sense. Mild alloys work well in everyday situations. In certain construction scenarios, the hot-dipped bolts are concealed, so they’re unlikely to scratch. In plain English, they’re often used as a substitute metal, a surrogate for stainless steel, because this softer alloy is cheaper than stainless steel. However, softer steel bolt heads deform easily. Screw heads distort when they’re tightened by a high-torque tool. They lose their shape, the threads strip, and then they rust. In conclusion, mild steel fasteners suit many applications, but they’re not designed to satisfy tougher applications.

Rating the High-Tensile Candidate 

In order to comprehend the advantages we associate with this alloy, we need to understand the term. Tensile strength, sometimes referred to as Ultimate Tensile Strength (UTS), is defined as how much mechanical stress a fastener will take before it deforms. Therefore, this fastener family is built to handle excessive loads. Expect a force per unit area integer on the box or bolt head when these highly capable load handlers are utilised. By way of illustration, a high-tensile steel bolt with a grade 8.8 rating secures 50 Metric Tonnes for every 6.45-cm² of surface area. This fastener family simply won’t break when it’s under pressure.

Stainless steel is alloyed with chromium and nickel. Mild steel includes a measured quantity of carbon, but it’s not a heavily tempered material. As for that high-tensile material, it’s alloyed with manganese and other exotic metals, then it’s exposed to a precipitation hardening process. The additives and heat treatment work strengthen the alloy. By the way, high-tensile fasteners are usually zinc-plated, all the better to ensure they don’t oxidise.

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