302HQ Stainless Steel (UNS S30430): The Cold-Heading Austenitic Alloy for Fasteners

Cold heading is the fastest way to mass-produce bolts, screws and special fasteners: wire is cut to length and upset into a die at high speed, then threaded by rolling. The process demands a material that flows into complex die shapes without cracking and without frequent annealing. 302HQ, standardized as UNS S30430 under ASTM A493, was designed for exactly this duty.

Its defining feature is copper: 3.0 to 4.0 percent copper in an otherwise 304-type chemistry. Copper lowers the stacking-fault energy of the austenitic matrix, which dramatically reduces the work-hardening rate. The result is a wire that deforms readily, fills the die, and keeps its ductility through repeated operations.

Chemical Composition per ASTM A493

Element	302HQ, UNS S30430 (wt%)
Carbon, max	0.03
Chromium	17.0–19.0
Nickel	8.0–10.0
Copper	3.0–4.0
Manganese, max	2.00
Silicon, max	1.00
Phosphorus, max	0.045
Sulfur, max	0.030

ASTM A493 covers wire rods and wire for cold heading and cold forging of stainless steel fasteners, and is the primary specification for 302HQ wire.

Why Copper Lowers Work Hardening, and What It Means for Heading

In standard 18-8 grades such as 304, deformation quickly transforms austenite into strain-induced martensite, which hardens the wire and eventually cracks it in the die. Copper stabilizes the austenite, postpones this transformation, and keeps the flow stress low during upsetting. The practical benefits are large head sizes in a single blow, deeper thread profiles, longer tool life, and low scrap rates in well-tuned lines.

Typical cold-heading wire for 302HQ is supplied spheroidize-annealed, with a lubricant coating suitable for the heading machine. In production, the wire must be consistent from coil to coil: variations in copper content, inclusion count or annealed hardness show up immediately as split heads or rejected threads. Mills serving the fastener industry control these parameters tightly, which is why material consistency, not just nominal composition, is part of the specification.

Fastener Standards and Mechanical Classes

Fasteners made from 302HQ are normally specified and tested to ISO 3506-1, which defines property classes A2 and A4 for austenitic stainless fasteners, or to ASTM F593 and F738 for stainless steel bolts and screws. Designers should specify the property class rather than a generic strength value; note that ASTM A574 is an alloy-steel socket-head specification and does not apply to stainless steel fasteners.

Corrosion Resistance and Limitations

In the annealed condition, 302HQ offers corrosion resistance comparable to Type 304: good in atmospheric, freshwater and mild industrial environments, with resistance to rust and staining in normal service. Like 304, it is not intended for continuous seawater immersion, high-chloride media, or strongly oxidizing chemicals, where molybdenum-bearing grades such as 316 or super-austenitic grades are required.

Procurement Specifications for 302HQ Wire

When sourcing 302HQ wire, specify the exact designation UNS S30430, the wire condition, typically spheroidize-annealed with the required surface coating, the diameter tolerance class, and the chemical limits, especially copper at 3.0-4.0 percent and carbon at 0.03 percent maximum. Request a mill test certificate with the heat number and declare the fastener standard and property class on the part drawing.

FAQ

Why is 302HQ preferred over 304 for cold heading?

304 work-hardens rapidly during upsetting and cracks in the die at high deformation levels. The copper in 302HQ suppresses work hardening, so heads and threads can be formed in one operation without intermediate annealing.

Does 302HQ have the same corrosion resistance as 304?

Essentially yes in annealed service conditions: atmospheric, freshwater and mild industrial environments. It shares 304's limitations in chlorides and seawater.

What wire condition is required for cold heading?

Spheroidize-annealed wire with a drawing lubricant, supplied to a controlled hardness range. The annealed structure makes the wire soft and uniform for upsetting.

Which standards govern 302HQ fasteners?

Material and wire: ASTM A493. Fastener properties: ISO 3506-1, with property classes A2 and A4, or ASTM F593 and F738. ASTM A574 is for alloy steel and is not applicable to stainless fasteners.

Can 302HQ fasteners be welded?

Fasteners are normally mechanically installed, not welded. The grade can be welded in principle, but 304L or 316L is preferred where welded fabrication is required.

What is the difference between 302HQ and 302?

302 carries no copper and is used for springs and general hardware. 302HQ adds 3-4 percent copper specifically to slow work hardening for cold heading, and limits carbon to 0.03 percent to preserve corrosion resistance in the formed part.