Our Defender® stainless steel bird spikes are available in both 304 and 316 grade stainless steel so we are often asked what the difference is between these grades. It can be hard to explain the pros and cons of each so we have put together a definitive answer for you, but do bear with us while we go right back to basics.
What is Steel?
Steel is an alloy made of carbon and iron which has good strength and fracture properties when compared to iron on its own.
What is Stainless Steel?
Adding a minimum of 10% chromium to low-carbon steel is what creates stainless steel. The chromium oxidises in oxygen to create a rough, thin, invisible film on the surface which in turn creates a barrier against corrosion and additional oxidisation, it can also self-heal if damaged either mechanically or chemically! Magic!
Different grades of stainless steel have various degrees of strength, corrosion resistance, high and low-temperature performance, hardness, ductility (ability to be stretched or drawn into a thin wire) and wear. The microstructure (the way molecules are bonded together and can only seen under a microscope) is what impacts its grade and mechanical properties. There are 5 types of steel microstructure; ferrite, pearlite, martensite, cementite and austenite.
What is corrosion?
When iron combines with oxygen and water, a flaky red oxide forms, commonly known as rust. Steel and iron are both susceptible to this type of corrosion particularly with in coastal areas where sodium chloride is present in the air. Pitting is a localised type of corrosion that creates shallow holes or crevices on the surface.
What type of steel is used in Defender® Bird Spike manufacture?
We use austenitic stainless steel 300 series for our bird spikes, it’s the commonest class. It is characterised by microstructure which is a cubic structure. The two types of stainless steel we manufacture our spikes in are type 304 and type 316. These types are non-magnetic, can be hardened through cold-working, (not heat treatment) and because of the added chromium and nickel, they have super corrosion-resistant properties.
Comparing 304-grade and 316-grade stainless steel
Type 304
Also known as 304 Grade, it is the most common and versatile austenitic stainless steel. As it has high levels of chromium and nickel it has excellent corrosion resistance, strength and fabric-ability. Its particular resistance to the atmosphere and pollutants makes it ideal for outside applications, for example in bird spikes! It also has excellent heat resistance.
304 grade is a ductile metal meaning good machinability properties and can be formed into complex shapes and sizes without losing strength. Ideal for bird spike pins.
Type 316
Also known as 316 Marine Grade, it is the second most commonly used stainless steel after 304. Alongside the chromium, this grade has higher levels of nickel than 304 and added molybdenum. This is the perfect combo to provide increased corrosion resistance. The molybdenum specifically controls pit-type corrosion which exposure to sodium chloride (salt) phosphoric and acetic acids causes. It is often referred to as marine grade due to its suitability for use in saltwater environments. Molybdenum is an extremely hard element that increases the toughness and strength of 316 which gives it super heat and wear resistance.
The addition of other alloys further enhances its resistance properties. Its austenitic microstructure retains toughness over a wide range of temperatures. This is why it is used in highly corrosive environments such as chemical plants and marine coastal areas.