Stainless steel Grade 302HQ, Specification and Application

Grade 302HQ is a specialised wire grade with very wide usage for manufacture of stainless steel fasteners. The inclusion of 3% copper in the composition reduces the cold work hardening rate substantially compared to Grade 304.


302HQ is standard for manufacture of self-tapping screws and light machine screws; it is also used for some bolts, set screws, rivets and specialised fasteners. It has now totally replaced Grades 384 and 305 for cold heading applications, copper being a lower cost alternative to their high nickel contents.

The designation 302HQ is not standardised – ASTM specifications list the grade as UNS S30430, and alternative designations for the same grade include "XM-7", "304Cu" and "304HQ". The standard specification for stainless steel fasteners, ISO 3506, includes 302HQ as an acceptable composition for fastener grade “A2”; it is commonly produced in strength grades A2-70 and A2-80.

The stable austenitic structure makes 302HQ non-magnetic, even after substantial cold work, and also results in excellent toughness, even down to cryogenic temperatures.

Stainless steel Grade 302HQ Corrosion Resistance

Equal to or exceeding that of Grade 304. Subject to pitting and crevice corrosion in warm chloride environments, and to stress corrosion cracking above about 50°C. 302HQ is considered resistant to potable water with up to about 200mg/L chlorides at ambient temperatures, reducing to about 150mg/L at 60°C. Consult Atlas Technical Assistance for specific environmental recommendations.

Stainless steel Grade 302HQ Heat Resistance

Good oxidation resistance in intermittent service to 870°C and in continuous service to 925°C. Continuous use of Grade 302HQ in 425-860°C range is usually safe (free of carbide precipitation) as the grade has a very low carbon content.

Stainless steel Grade 302HQ Heat Treatment

Solution Treatment (Annealing)

Heat to 1010-1120°C and cool rapidly. This grade cannot be hardened by thermal treatment.

Stainless steel Grade 302HQ Grade Data Sheet 302HQ

Welding

Use Grade 308L rods or electrodes. Excellent weldability by all standard fusion methods, both with and without filler metals. Because of its applications this grade is not often welded. Exceptions are resistance butt welding to join wires together during wire manufacture, and when the grade is used to make stud welding fasteners. 302HQ is not specifically listed in AS 1554.6.

Stainless steel Grade 302HQ Machining

302HQ is rarely machined, because of its form and likely products. The grade always has very low sulphur content as this aids formability, but unfortunately this also reduces machinability. Machining is certainly possible.

An Improved Machinability version of Grade 302HQ is produced, having a very high machinability. This version has a slightly higher sulphur content and is also calcium treated. This Improved Machinability grade (referred to as Ugima 4567) is available only to special order, but should be considered as an option where an “18/8” type grade needs to be both heavily cold formed and extensively machined.

Stainless steel Grade 302HQ Cold Work Hardening

302HQ has the lowest work hardening rate of any of the common austenitic stainless steels. This results in a tensile strength increase of approximately 8MPa/%Ra (8MPa increase in tensile strength for each 1% reduction of area of cold work - this data from wire drawing). Even after substantial cold work this grade remains essentially non-responsive to a magnet.

For some high strength cold headed fasteners a slightly higher work hardening rate will be needed, so grade 304 or 304L (or the specialist grade 304M) will need to be used instead of 302HQ; these have work hardening rates varying between about 10 and 12.5MPa/%RA.

Stainless steel Grade 302HQ Typical Applications

All severe cold heading applications, including self-tapping screws, roofing bolts, machine screws, bolts, set screws, blind rivets.

COLLECTION OF COMMON STAINLESS STEEL GRADE

Source:


http://www.atlassteels.co.nz/documents/Atlas_Grade_datasheet_-_all_datasheets_rev_Nov_2011.pdf

Atlas Steels Technical Services Department - Copyright © Atlas Steels