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

Grade Overview and Designation

302HQ is the established trade designation of UNS S30430, a copper-bearing modification of the 18-8 austenitic family developed specifically for cold heading and cold forging. The intentional addition of roughly 3-4% copper lowers the work-hardening rate of the steel, so that fastener heads, shoulders and other severe upsets can be formed in one or two blows without stress-relief annealing between operations. This makes 302HQ the default material for high-volume production of stainless steel screws, bolts and rivets where die life and formability are decisive.

Designation system	Grade name	Reference standard
UNS	S30430	ASTM A493, A313, A581
Common trade name	302HQ	Wire and rod products
Similar austenitic base	18-9 (304-type)	ASTM A240 family

Chemical Composition

Typical specification limits for UNS S30430 wire are shown below. The copper content is the distinguishing element: it is not a residual impurity but an intentional alloy addition that controls the work-hardening behavior.

Element	C	Mn	P	S	Si	Cr	Ni	Cu
Limit, %	0.03 max	2.00 max	0.045 max	0.030 max	1.00 max	17.0-19.0	8.0-10.0	3.0-4.0

Mechanical Properties and Cold Heading Behavior

In the annealed soft condition, wire tensile strength is typically in the range of 520-720 MPa depending on diameter, with low hardness that permits severe upsetting. The low work-hardening rate, roughly half that of standard 304, is the decisive property for fastener production: it allows large plastic deformation per blow, extends die life and reduces the number of forming stages. After cold heading, the work hardening developed in the head and shank raises the finished fastener strength well above the annealed level, which is why fasteners produced from 302HQ meet high mechanical requirements without additional heat treatment.

Condition	Typical tensile strength, MPa	Note
Annealed wire	520-720	Soft condition for heading, depends on diameter
Cold headed fastener	650-900	Strength increases with degree of cold work

Why Copper Lowers the Work-Hardening Rate

Cold Heading Behavior

Copper in solid solution stabilizes the austenite and reduces the rate at which dislocations accumulate during plastic deformation, which is observed as a lower work-hardening exponent. In practice, a blank can be upset into a complex head geometry in a single die blow without cracking, and successive operations such as thread rolling are easier to control. The same characteristic improves the cold formability of nuts, special fasteners and small engineering components.

Annealing Response

302HQ is fully austenitic and free of ferrite in normal wire sizes, so it responds predictably to solution annealing. A full anneal near 1000-1100°C followed by rapid cooling restores the soft condition after heavy drawing, giving the fastener producer a consistent starting structure for heading.

Corrosion Resistance and Heat Treatment

In most service media, the corrosion resistance of 302HQ is comparable to that of 304: it resists atmospheric corrosion, fresh water, foodstuffs, mild chemicals and many organic media. It is not intended for chloride pitting service, where molybdenum-bearing grades such as 316 or 316L are required. The standard heat treatment is solution annealing, and the grade is non-magnetic in the annealed condition, with slight magnetism developing after severe cold work.

Typical Applications

Self-tapping screws, machine screws and cap screws

Bolts, nuts and rivets for general and automotive fastening

Fasteners for electronics, appliances and furniture

Special cold-headed and cold-formed components

Fasteners for mildly corrosive exterior service

Frequently Asked Questions

1. What is the composition of 302HQ and where is it used?

302HQ is a UNS S30430 austenitic stainless steel with about 17-19% chromium, 8-10% nickel and 3-4% copper. It is used almost exclusively for cold-headed fasteners such as screws, bolts, nuts and rivets where severe upsetting is required.

2. What is the benefit of the copper addition?

Copper lowers the work-hardening rate of the steel. This allows fastener heads to be formed in fewer blows, improves die life, reduces cracking and makes thread rolling more consistent, without sacrificing the corrosion resistance of the 18-9 austenitic base.

3. How does 302HQ compare with 304 for fasteners?

304 work-hardens rapidly, so it cracks or requires multiple anneals when forming severe head geometries. 302HQ is the preferred cold-heading grade because its low work-hardening rate permits one-blow heading of complex geometries with better die life and dimensional control.

4. What is the corrosion resistance of 302HQ?

It is comparable to 304 in atmospheric, fresh water, food and mild chemical service. It is not recommended for chloride-rich or strongly corrosive environments, where molybdenum-bearing grades such as 316 or 316L should be selected.

5. How should 302HQ wire be specified for ordering?

Specify the UNS designation S30430, the applicable standard such as ASTM A493, the wire diameter and tolerance, the condition such as annealed or cold drawn, the surface finish, and the required mechanical properties. For critical fastener applications, add the relevant fastener standard and any testing requirements such as hardness or tensile testing.