🟡 BRASS
Heat Treating Brass: Annealing, Stress Relief, and Preventing Season Cracking in C360 and C260
Brass behaves like copper in one critical respect, it cannot be hardened by heat treatment, but it adds a failure mode copper doesn't have: stress-corrosion cracking, also called season cracking, where residual tensile stress plus a trace of ammonia splits the part open over time. That single risk is the main reason buyers stress-relieve brass, and it shapes how every cold-formed brass part should be processed.
ISO 9001ISO 14001AS9100
Season Cracking: The Stress-Corrosion Failure That Drives Brass Stress Relief
Brass is susceptible to stress-corrosion cracking when three things coexist: tensile residual stress (almost always from cold forming, drawing, or machining), a susceptible alloy (higher-zinc brasses like C260 cartridge brass are most vulnerable), and a trace of a specific corrodent, classically ammonia or amines but also sometimes moisture. The cracks are intergranular and can appear weeks or months after the part is made, sitting on a shelf, hence the historical name season cracking, discovered when cartridge cases stored in horse stables (ammonia from manure) split spontaneously.
The defense is a low-temperature stress-relief anneal, typically 450 to 575F for an hour, which removes enough residual stress to stop crack initiation without significantly softening the cold-worked part or growing the grain. This is routinely specified after deep drawing, heavy machining, or bending of high-zinc brasses, and it is the single most important heat treatment decision for brass that will be cold formed and then exposed to the environment.
For buyers, the rule is: if a brass part is cold worked and the zinc content is moderate to high, specify a stress relief, especially for parts that may see ammonia, marine, or humid service. Skipping it is how you get field failures that look like the metal was defective when it was actually the missing thermal step.
Full Annealing and Why Brass Tempers Come From Cold Work
Like pure copper, brass strengthens through cold work, not heat treatment, there is no age-hardening or quench response because brass has no useful phase precipitation in these grades. Full annealing heats brass into the recrystallization range, roughly 800 to 1400F depending on alloy and prior cold work, to grow new strain-free grains and return the part to a soft, formable condition. C260 cartridge brass anneals easily and is annealed between deep-drawing passes precisely because it work-hardens fast and needs softening to continue forming.
Grain size control is a real concern in annealing brass for forming. Anneal too hot or too long and the grains grow coarse, producing an orange-peel surface and poor formability, anneal too cold and you don't fully recrystallize. Brass mills control anneal temperature and time tightly to hit a target grain size (often quoted in millimeters, like 0.035 mm) that balances formability and surface finish.
The practical point: brass is ordered to a temper that reflects cold-work level, and annealing resets it to soft for further forming or for applications needing maximum ductility. You do not heat-treat brass to make it harder.
Frequently Asked Questions
No, common brasses like C360 free-cutting, C260 cartridge, and naval brass cannot be hardened by heat treatment. They are copper-zinc alloys with no age-hardening precipitation reaction and no quench-hardening phase transformation, so there is no thermal route to increase their strength. Brass gains hardness and strength only through cold working, drawing, rolling, bending, or peening, which is why brass is sold in tempers like soft, half-hard, and full-hard that describe the amount of cold work, not a heat-treated condition. Heat treating brass actually softens it: full annealing in the 800 to 1400F range recrystallizes the grains and returns the metal to a dead-soft, ductile state for further forming. The one heat treatment that does not soften brass much is a low-temperature stress relief around 450 to 575F, but its purpose is to remove residual stress and prevent stress-corrosion cracking, not to harden. If you need a hardenable copper-base alloy, you would specify beryllium copper or an aluminum bronze, which can be heat treated to high strength, rather than trying to harden ordinary brass.
Season cracking is the historical name for stress-corrosion cracking in brass, and it requires three conditions together: tensile residual stress, usually locked in by cold forming, drawing, or machining; a susceptible alloy, with higher-zinc brasses like C260 cartridge brass most at risk; and exposure to a specific corrodent, classically ammonia or amine vapors, sometimes just moisture. When all three are present, intergranular cracks initiate and propagate over time, often appearing weeks or months after the part was made while it sits in storage or service, which is where the name season cracking comes from. The fix is a low-temperature stress-relief anneal, typically 450 to 575F for about an hour, which relaxes the residual tensile stress that drives crack initiation without significantly softening the cold-worked part or coarsening the grain. This treatment is routinely specified after deep drawing, heavy bending, or aggressive machining of moderate-to-high zinc brass, particularly for parts that may encounter ammonia, marine, or humid environments. Skipping the stress relief on a cold-formed high-zinc brass part is a common cause of field failures that get misdiagnosed as defective material.
Grain size control during annealing directly governs how well brass forms afterward and how its surface looks. When you anneal brass to soften it for further forming, the recrystallized grain size depends on the anneal temperature, time, and the amount of prior cold work. If you anneal too hot or too long, the grains grow coarse, and coarse-grained brass develops an orange-peel surface texture when it is subsequently formed, because individual large grains deform visibly, ruining cosmetic finish and reducing formability and dimensional control. If you anneal too cold or too briefly, the metal does not fully recrystallize and stays partly hard, so it cannot be drawn or bent as far without cracking. Brass mills target a specific grain size, often quoted in millimeters such as 0.015 to 0.050 mm, chosen to balance deep-drawability against surface finish, fine grain for smooth surfaces and tight features, slightly coarser grain for maximum drawability. This is why an anneal spec for forming-grade brass like C260 cartridge brass calls out a grain-size requirement, not just a temperature, the grain size is the property that actually matters to the downstream forming operation.
Brass annealing and stress relief are inexpensive heat treatments because the temperatures are moderate and the cycles are short. Stress relief at 450 to 575F typically runs $0.50 to $2.00 per pound at production volume with lot minimums of $125 to $350, and full annealing runs a similar range, slightly higher if a protective atmosphere is needed to keep the surface bright. Lead times are generally fast, 2 to 6 business days, limited mainly by furnace batching since the cycle itself is an hour or two. Bright annealing in a controlled or inert atmosphere to prevent surface oxidation, important for decorative, plated, or precision parts, adds cost and a bit of lead time. For high-volume screw-machine work in C360, stress relief is often skipped entirely when the parts are simple turned components with low residual stress, while deep-drawn C260 and high-zinc parts headed for ammonia or marine service almost always justify the stress relief. The biggest cost lever is whether you need atmosphere control for surface cleanliness and grain-size verification, which adds inspection overhead. Expedited turnaround is readily available at a small premium given the short cycles.
Last updated: July 2026
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