Stainless fasteners: property class, galling and grade
Fastener failure is almost always a specification failure. Property class and galling are where it usually goes wrong.
Stainless steel fasteners cover any threaded or fixing product made from stainless — bolts, nuts, screws, washers, studs, threaded bar, rivets and pins. They are specified for corrosion resistance, appearance and, in some grades, strength.
Property class is not the grade
A stainless fastener is designated by a property class under ISO 3506, such as A2-70 or A4-80. The letter and number identify the material group — A2 is broadly 304, A4 broadly 316 — and the two-digit figure is one tenth of the tensile strength in MPa. A4-80 is therefore 316-group material at 800 MPa.
| Class | Material group | Tensile MPa | Typical use |
|---|---|---|---|
| A2-70 | 304 group | 700 | General purpose, indoor and sheltered |
| A2-80 | 304 group | 800 | Higher strength, non-chloride |
| A4-70 | 316 group | 700 | Marine, chemical, coastal |
| A4-80 | 316 group | 800 | Marine structural |
Scroll the table horizontally to see all columns.
Galling is the failure nobody plans for
Austenitic stainless fasteners are prone to galling — the thread surfaces cold-weld under pressure during tightening, seizing the fastener so it can be neither tightened nor removed. It is not a material defect; it is a consequence of the passive film being stripped and clean metal being pressed against clean metal.
- Slow the installation speed — galling is aggravated by fast driving
- Use an anti-seize compound on the threads
- Pair dissimilar grades where possible, for instance an A4 bolt with an A2 nut
- Keep threads clean; grit initiates it
- Avoid re-using a fastener that has already been torqued
Choosing the grade
For indoor and general work, A2 is adequate and cheaper. For anything coastal, marine, chemical or exposed to de-icing salt, specify A4. Where strength is the governing requirement rather than corrosion, 17-4 PH offers tensile strengths above 1300 MPa, though with corrosion resistance only comparable to 304.
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The full text, as first published by Rajgranth Metals & Alloys.
The Ultimate Guide to Stainless Steel Fasteners: Types, Uses, and Benefits
Date : June 15, 2024
What is mean by Stainless Steel Fasteners?
Stainless steel fasteners mean any number of related products manufactured out of stainless steel that are used to assemble or join two or more materials. These components include screws, bolts, nuts, rivets, pin, washers, and any other similar items that may be used to fasten two products together. The most significant property of stainless-steel fasteners that defines them is the presence of a chromium content of not less than 10. Naturally, stainless steel fasteners do not corrode. This property makes them quite appropriate to be used in places that tend to be exposed to moisture, chemicals, and extreme changes in temperature.
Stainless steel fasteners are a form of stainless-steel material that has been formed into a particular shape which is used for assembling material or holding material together. This is due to the fact that chromium, an integral part of the stainless steel, makes substances which cause corrosion, rust or staining, practically harmless. These fasteners can be used frequently in areas that demand strength and endurance and environmental applications including construction, automobile industry, marine and industrial uses.
Types of Stainless Steel Fasteners
Bolts and Screws:
Bolts and screws comprise the major category of SS fasteners, and they are widely used in a number of applications. Bolts carry a nut with them in order to be fixed while screws cut their own threads in the surface they are screwed into. Some of the classifications on the head style are hex head, socket head, and the flat head.
- ✓ Hex Head Bolts : Ideal for heavy-duty applications due to their high tensile strength.
- ✓ Socket Head Cap Screws : Used in applications requiring a clean and flush finish.
- ✓ Flat Head Screws : Perfect for situations where a smooth surface finish is essential.
Nuts:
Nuts are internally threaded fasteners that pair with bolts to hold components together.
Common types include:
- ✓ Hex Nuts : The most commonly used, suitable for general-purpose fastening.
- ✓ Lock Nuts : Designed to resist loosening under vibrations and torque.
- ✓ Wing Nuts : Allow for manual adjustment and removal, useful in applications where frequent disassembly is required.
Washers:
Washers serve as a buffer between the fastener and the material being fastened, distributing the load and preventing damage. Types include:
- ✓ Flat Washers : Provide a larger bearing surface to prevent wear.
- ✓ Spring Washers : Offer a degree of flexibility and shock absorption.
- ✓ Sealing Washers : Incorporate a seal to prevent leaks in applications involving fluids.
Rivets:
Rivets are permanent fasteners used to join materials together. Unlike bolts and screws, rivets do not require threads. Types of rivets include:
- ✓ Blind Rivets : They can be installed from one side of the workpiece, making them ideal for applications where access is limited.
- ✓ Solid Rivets : Provide high strength and are commonly used in structural applications.
- ✓ Tubular Rivets : Hollow, allowing for a lighter assembly, and used in non-structural applications.
Pins:
Pins such as cotter pins and dowel pins are used to align or secure components. They are critical in applications requiring precise alignment and retention.
Uses of Stainless Steel Fasteners
Industry applications of stainless-steel fasteners include consumer products, automotive, plumbing, construction, and medical industries.
Construction
Stainless steel fasteners such as screws and bolts are widely used in the construction industry because they can easily withstand various environmental challenges. They are applied to construction frameworks, bridges, and even the shells of buildings.
Automotive
In automotive industry itself, these fasteners provide the structural reinforcement on the vehicle assemblies. These metals are incorporated in engine, transmission, and other structural parts where rigidity against vibratory stress is essential.
Marine
Marine generic environment challenges for example are the aggression of salt water solution, which corrodes most of the ordinary metals very fast. Screw fasteners are rustproof since stainless steel is not alive to rust and therefore can be sued on boats, docks or any other offshore constructions.
Aerospace
Aerospace applications require solutions that could lead and bear load and operate under extremely high temperatures. Aerospace fasteners are built with stainless steel materials in their assemblies mainly for safety and performance when put under extreme conditions.
Manufacturing
In manufacturing, stainless steel fasteners are applied in machines and equipment that is meant to run for a long duration and with much pressure. This is especially so because of their length of service and durability that assists in reducing both times lost and the need to fix or replace the equipment.
Benefits of Stainless Steel Fasteners
Recyclabilityp
Stainless steel fasteners are fully recyclable and, therefore, can be described as an environmentally friendly option. The employment of stainless steel fasteners as part of company sustainability strategies entails considering the possible detracting factors in relation to waste and consumable resources.
Corrosion Resistance
One of the best benefits of stainless steel fasteners is that they are resistant to corrosion and this is one factor that makes them preferable to other types of fasteners. This property is extremely significant in areas that receive exposure to humidity, chemical and saline environments. To enhance the Rust resistance in it the chromium content of steel audully forms a thin layer of chromium oxide to cut off the Rust formation.
Strength and Durability
Fastener made of stainless steel are able to handle the most challenging work due to their strength and lasting qualities. In materials, they can carry high stress and substantial loads without getting deformed or even fracturing hence preferred mainly in special applications.
Low Maintenance
The longevity and resistance to corrosion and wear mean that stainless steel fasteners require minimal maintenance. This benefit translates into cost savings over the lifespan of the application.
Conclusion
Stainless steel fasteners are unbeatable for a whole range of applications across such industries thanks to several admitted advantages such as: Once you are aware of the various types, usage and advantages of the following fasteners, you will be in a sound position to make the best choice when it comes to adding value to any of your projects.
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