Stainless Steel Fasteners

Stainless steel is a well-known steel alloy that is prized for its ability to resist corrosion and rust.  It is widely used in many industries and products – think cutlery, food processing and preparation equipment, medical instruments, marine products, refrigerators, freezers, and washing machines.  Stainless steel is also widely used to make the fasteners that hold these products together.
 
Stainless steels are a family of ferrous, or iron alloys composed of steel (iron and carbon) with a minimum of 10.5% chromium content that gives it the corrosion resistant properties it is known for.  Generally speaking, the more chromium, the better the corrosion resistance.  Chromium creates a passive surface film that is self-healing and resistant to oxidation, corrosion, and/or rust.
 
The addition of other alloying elements provide stainless steel with desirable characteristics including high strength and hardness, ductility and most notably better corrosion resistance.  After chromium, nickel is the most important additional element – the familiar 18-8 designation for stainless steel refers to the percentage of chromium and nickel, respectively, in the product.  Nickel significantly improves corrosion resistance and performance at low temperatures, and helps retain strength at high temperatures.
 
Other alloying elements include molybdenum, copper, silicon, aluminum, sulfur, selenium, tantalum, columbium, and titanium.  These additional elements can add strength, improve machinability, or further resist corrosion, for example in chlorine or acidic environments.

The most commonly used stainless steel is the non-magnetic 300 series.  This includes 304 or 18-8 stainless for standard nuts and bolts, 316 stainless for food service, marine and other wet applications and the highly formable 302HQ for screws.
 
The 400 series of stainless steel is magnetic and may be heat treated for added strength in high temperature applications.  This is often used in self drilling screws, bearings, valves, razors, utensils and medical instruments.
 
Precipitation hardening stainless steel is a process that increases the yield strength and is used mostly in aerospace, naval and marine applications.

Depending on their content and characteristics, stainless steel alloys fall into four categories as outlined in more detail below.

 

Stainless steel fasteners are used in products and equipment for industries and applications including:

  • Food Services
  • Marinas / Boats
  • Architectural Design
  • Water Treatment
  • Medical / Surgical
  • Aerospace
  • Appliances
  • Automotive / Trailer
  • Chemical
  • Railings


         

 


What are the four categories of stainless steel and their characteristics?

 
The four categories of stainless steel are austenitic, martensitic, ferritic and precipitation hardening.  Each category includes multiple series or grades of stainless steel each with their own characteristics and applications.
 

Austenitic Stainless Steel

Austenitic stainless steel, generally referred to as the 300 series, is non-magnetic with a tensile strength between 80,000 psi and 150,000 psi.  The term 18-8 (A2 for metric fasteners) stainless steel calls out the percentage of chromium, 18%, and Nickel, 8%, in the stainless steel alloy.  Other grades in the series are also an alloy of chromium and nickel with varying characteristics depending on the presence of other elements such as carbon and molybdenum.  These grades include 302, 302HQ (XM7), 303 / 303Se, 304, 304L, 305, 316 (A4 for metric fasteners), 321, 347 and 348.  Able to retain its strength at extreme temperatures with a high resistance to corrosion, austenitic stainless steel is the most commonly used type of stainless steel. 
 
Austenitic stainless as a group has better corrosion resistance than martensitic or ferritic, discussed below.  The very wide use of austenitic stainless steel for fasteners means they are readily available, and reasonably priced.


Martensitic Stainless Steel

Martensitic stainless steel is magnetic, contains 12% to 18% chromium with a tensile strength between 72,000 psi and 160,000 psi.   Heat treating will increase the tensile strength to between 180,000 psi and 250,000 psi.  Characteristics of martensitic stainless steel vary depending on the presence of other elements such as carbon and sulfur.  The most common grades are 410, 416, 420 and 431.  410 stainless steel is roughly equivalent to the strength properties of grade 5 steel.  The 400 series is somewhat corrosion resistant and is used for self-drilling screws, cutlery, razors, surgical instruments, valves, bearings and many other applications. 
Martensitic essentially trades some of the austenitic corrosion resistance and non-magnetic properties for higher strength.  Fasteners made from 400 series stainless can be coated to improve their corrosion resistant properties.

 

Ferritic Stainless Steel

Ferritic stainless steel contains chromium without nickel, has a low carbon content, and is also magnetic.  The tensile, yield and characteristics vary depending on the presence of other elements and range from 55,000 psi to 100,000 psi.  Ferritic stainless steel is less corrosion resistant and has relatively poor high temperature strength.   This family of stainless steel is less expensive due to the lack of nickel and include grades 409, 410L, 430, 439, 441, 436, 444, 445 and 447 – the most common being 430. 

Ferritic stainless is not widely used for fasteners.

 

Precipitation Hardening Grades

Precipitation hardening stainless steel contains chromium and nickel allowing for strength and corrosion resistance similar to austenitic and martensitic stainless steels.  High tensile strength is achieved through heat treatment and the addition of copper, aluminum, titanium, niobium/columbium and tantalum, molybdenum or a combination there of.  The most commonly known precipitation hardening steel, 17-4PH, also referred to as stainless steel alloy 630, contains 17% chromium, 4% nickel, 4% copper and 0.15 – 0.45% Niobium/Columbium and Tantalum.  Precipitation hardening grades of stainless steel are used for retaining rings, spring holders, chains, aerospace applications, aircraft parts, valves and gears. 

Precipitation hardening stainless steel is relatively expensive compared to 300 series, and therefore used in critical applications that specifically require its high strength and superior corrosion resistant properties. 
 

For more information on stainless steel compounds, tensile strength, yield and characteristics, see the Stainless Steel Alloy Guide link on the Technical Resource page of this website.
 

Contact AALL AMERICAN Fasteners today with your stainless steel needs!

Please contact our Certified Fastener Specialists to review your stainless steel requirements at 877-791-4426 or send your Request for Quote to us directly.

 

 
 

 
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