The simple difference between A2 and A4 stainless steel fasteners is that the former contains 18% chromium + 8% nickel, while the latter holds 16% chromium + 10% nickel + 2% molybdenum. Molybdenum is included to resist chloride corrosion [marine environment]. 

Fair Wind Fasteners is a retailer of corrosion-resistant fasteners and screws suitable for building boats. Remember to choose the 316 stainless bolts or the 651 silicon bronze screws because they are made from the highest quality corrosion-resistant alloys. 

What’s stainless steel?

Before moving in to understand the difference between A2 and A4 stainless steel fasteners let’s get to know stainless steel. It is an inoxydable steel alloy blended with at least 10.5% chromium. Chromium helps in resisting staining and corrosion but does not altogether stop it. It is highly corrosion-resistant graded steel. 

Carbon steel readily rusts when exposed to moisture and the atmosphere. An iron oxide rust film causes corrosion and it increases over time degrading the carbon steel product. Stainless steel has chromium, which forms a chromium oxide film that averts surface corrosion and thus saves the internal structure from getting rusted. Passive chromium film occurs only when the amount of chromium is sufficient.

There are other elements added to stainless steel to improve its properties and structure like strength, toughness, and formability. 

Metal additions are –

  • Molybdenum
  • Nickel
  • Copper
  • Titanium

Non-metal additions include –

  • Nitrogen
  • Carbon

What is an A2 stainless steel fastener?

A2 stainless steel fasteners are also popular as 18/8 or 304 stainless. A2 [304, 18/8] is austenitic steel. It is non-magnetic. Even if chromium offers resistance to oxidation and corrosion, it can stain. It is immune to sterilizing solutions, foodstuffs, dyestuffs, and the majority of organic chemicals. It is extensively used for tabletops, stoves, pots, sinks, refrigerators, the brewing sector, dairy equipment, dye tanks, pipelines, food processing plants, etc. The 304 stainless steel fasteners are easy to fabricate, clean as well as prevent product contamination. They even provide great finishes and appearances. 

What is an A4 stainless steel fastener?

A4 stainless steel fasteners are also popular as 16/10/2 or 316 stainless. A4 [316, 16/10/2] is austenitic steel. It is non-magnetic. It is suitable for every situation like A2 but has an extra advantage. It is a suitable marine solution and is referred to as marine-grade stainless steel. The 2% of molybdenum enhances corrosion resistance. The fasteners can handle harshness from industrial solvents, chemicals, and seawater salts. 

A4 has greater resistance than the A2 stainless steel alloy. Type 316 stainless steel fasteners are easy to make, weld, finish, and clean. They are even durable and regarded as more resistant solutions for handling chlorides, bromides, sulfuric acids, fatty acids, and iodides at high temperatures. 

What are the similarities between A2 and A4 stainless steel?

A2 and A4 stainless steel grades are classified as austenitic and are even called the 300 series. It means both have high resistance to chemicals but heat treatment cannot harden it. You can harden those using cold treatments. Both are non-magnetic but you can induce a little magnetism via a cold working process or even welding.