There are a diverse range of stainless steel fasteners like stainless steel bolts and nuts offering different levels of corrosion resistance and strength. They are used for corrosive industrial and seawater environments, equipment, structural and architectural applications. These products can be used for all stainless steel designs and for joining other metals such as copper, aluminum, carbon steel, and zinc.

The specification of a specific fastener grade should be based on the required corrosion resistance, strength and materials that will be fastened. The fastener should have equivalent or higher corrosion resistance than the most corrosion resistant of the metal(s) being fastened.

Manufacturing Methods:

Stainless steel fasteners (stainless steel bolts) can be manufactured by either machining or cold heading. Machining is the oldest method of fastener production, and it is still specified for very large diameters and small production runs.

Cold heading is the more common production method. It transforms wire into the desired shapes by applying enough pressure to cause the metal to plastically deform into the die and punch cavities without preheating the material. Larger production runs of galvanized bolts, screws, nails and rivets are made by cold heading, but special custom runs can also be made by this method. Cold heading can significantly increase the strength of 300-series types stainless steel fasteners (stainless steel bolts).

ASTM Standards:

The ASTM International standards for fastener materials and specific products (bolts, nuts, screws, and studs) are provided in the following table. There are standards for both general use and for specialized high temperature, high pressure, and cryogenic applications.

Types of Bolts And Nuts

·          Bolt: Hex Bolt, Flange Bolt, Carrage Bolt, High tensile Bolt , Carriage Bolts,

·          Nut: Cold Forged Nut, Turned Nut, Weld Nut, Flange Nut, Castle Nut, Dome Nut

ASTM Standard

Title

A 193/A 193 M

Alloy-steel and stainless steel bolting materials for high temperature or high pressure service and other special purpose applications

A 194/A 194M

Carbon and alloy steel nuts for bolts for high pressure or high temperature service or both (includes stainless steel)

A 962/A 962M

Common requirements for fasteners or fastener materials, or both, intended for use at any temperature from cryogenic to the creep range

F 593

Stainless steel bolts, hex cap screws and studs

F 594

Specification for stainless steel nuts

F 738M

Stainless steel metric bolts, screws and studs, metric

F 788/F 788M

Surface discontinuities of bolts, screws, and studs, inch and metric

F 836M

Specification for stainless steel metric nuts

F 837/837M

Specification for stainless steel socket head cap screws

F 879/879M

Stainless steel socket button and flat countersink head cap screws

F 880/880M

Specification for stainless steel socket set screws

 

Galling:

Fastener thread galling or cold welding can occur with stainless steel, aluminum, titanium and other alloys which self-generate a protective oxide surface film for corrosion protection. In applications where disassembly will not occur and any loosening of fasteners is structurally undesirable, it may be an advantage.

In applications like equipment, easy fastener removal for repairs is important and galling should be avoided. Several precautions can be taken to avoid this problem with stainless steel.

  • Slow down the installation RPM speed
  • Lubricate the internal or external threads with products containing molybdenum disulfide, mica, graphite or talc or a suitable proprietary pressure wax
  • Use different stainless steel grades with different hardness levels for the bolt and nut
  • Make sure that the threads are as smooth as possible

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