Guide
What causes season cracking in machined brass parts, and when does a drawing need a stress-relief anneal?
Season cracking is stress corrosion cracking of brass: a part that carries residual stress from forming or machining cracks when it meets a corrosive agent, classically ammonia, even though no load is applied. It shows up as cracks in fittings, stems and nuts that sat in storage or were assembled without incident, and it depends on how the part was made as well as on the alloy. This guide covers what in a turned-part route adds the stress, how to tell it from other failures, and how to word a stress-relief anneal and a test without inventing numbers.
By Saola Manufacturing engineering team · Published · Updated
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What is season cracking in brass, and why does it happen?
Season cracking is cracking of brass under the combined action of residual tensile stress and a corrosive environment, most often ammonia. The part does not need to be loaded; the stress is locked in by the way it was made.
The name comes from the early cases. A 2019 paper in Materials Research recounts that the effect was termed season cracking because it occurred during the rainy season, in cartridge cases used by the British Army in India, and attributes it to ammonia from decaying organic matter in damp air. A 1945 review for the American Institute of Mining and Metallurgical Engineers says the causes are not fully understood, but that corrosion combined with stress, residual or applied, appears to drive it, with ammonia the most commonly implicated agent (see the AIME paper).
The same 2019 study found that cracking in brass was most severe in ammonia vapor, and it reported both intergranular and transgranular cracks depending on the corrosion films, pH and residual stress. It also named slip dissolution and dezincification as the underlying mechanisms, which is why the cracks can resemble a corrosion failure. The 1945 review adds that the copper-zinc ratio and the structure produced by mechanical working both affect susceptibility.
Which operations in a turned brass route add residual stress?
Operations that cold work the surface: drawing of the bar, heavy knurling, thread rolling, stamping of marks, press fits and crimping. That is our reading of the sources, which tie cracking to residual stress from forming and working.
The 2019 study ties residual stress to manufacturing: extrusion with non-uniform flow can leave it, and cold working such as cutting, hammering or stamping letters produced stresses that drove cracks at edges, stamped letters and sample tips. That is the evidence in the literature; the table below is our engineering reading of how the same mechanism applies to a turned-part route.
| Operation | Why it can add stress | Drawing or RFQ action |
|---|---|---|
| Cold-drawn bar | Drawing leaves the bar surface in tension unless it is relieved | Ask the mill whether the temper is stress relieved; state the temper on the drawing |
| Heavy knurling | Surface displacement cold works the material | Accept a lighter pattern, or anneal after knurling |
| Thread rolling | Plastic flow at the root of the thread | Anneal after rolling if the part sees ammonia or amine exposure |
| Stamped part marking | Cold-worked, notched surface; cracks start at stamped letters | Prefer laser or etched marks, or place marks in low-stress zones |
| Press fit or crimped joint | Hoop stress stays in service | Specify the interference and test the assembly condition |
| Straightening | Bending beyond yield leaves tensile stress on one side | Avoid or relieve after straightening |
How do you tell season cracking from dezincification and other failures?
Season cracking appears as cracks at the highest-stress locations, often after a delay in storage or service. Dezincification is selective loss of zinc and has its own guide.
Look at where the cracks sit. In the 2019 study they started at edges, stamped letters and sharp features where cold work concentrated stress. A crack that follows a rolled thread root, a press-fit shoulder or a crimp line points the same way, and a part that cracked in the box before use points to a stored residual stress and an ammonia source nearby (cleaning products, animal housing, fertilizers). Those sources are our examples, not findings from the cited papers.
Because dezincification is named as one of the mechanisms in the cracking study, the two failures can overlap. Our guide to dezincification and DZR brass covers the dezincification-resistant alloys, which address zinc loss but are not a stress-relief substitute. For tarnish and surface corrosion without cracks see brass tarnish and corrosion; for the stainless equivalent see stress corrosion cracking in stainless.
Which standard tests detect residual stress in brass: B858 or B154?
ASTM B858 uses an ammonia vapor atmosphere and ASTM B154 uses a mercurous nitrate solution. Both are accelerated tests for residual stress in wrought copper alloy products, and B154 itself points to B858 as the option that avoids mercury.
The B858 scope says the method determines the presence of residual stresses in wrought copper alloy products, is suitable only for alloys known to be susceptible, and has a severity that depends on the pH of the solution, with four atmospheres tied to risk levels. The pH is set by the product specification or by agreement between supplier and purchaser. The store page does not give the exposure time or the temperature, so those belong to the standard text.
The B154 scope describes an accelerated test for residual stresses that could cause failure in storage or service by stress corrosion cracking, and its notes call the method historically reliable but not promoted because of the hazards of mercury. Both standards say they are not intended for assemblies or parts under applied stress, and results from such a use are for information only and not a cause for rejection. That limit matters for press-fit parts: the tests suit mill products and unassembled parts.
When does a drawing need a stress-relief anneal?
Ask for one when the part is brass, carries cold-worked features, and may meet ammonia, amines or damp organic atmospheres in storage or service. Without those three conditions, an anneal adds cost and a temper change for no benefit.
Check three questions in order. First, does the route cold work the part after the last stress relief, through knurling, rolled threads, marking or straightening? Second, is there a plausible ammonia source in service or storage? Third, would a crack matter, as in a pressure-containing or sealing part? If all three are yes, specify the anneal after the last cold-working step and ask for the test below.
A stress-relief anneal can soften cold-worked material, so the drawing should state the final temper or hardness that the part must keep. Heat treatment of this kind is arranged through partner plants we manage and is not part of the CNC turning at our lead CNC plant, which means the sequence of turning, anneal, final features and inspection has to be agreed at quote stage.
How do you word the anneal and the test in an RFQ without inventing numbers?
Name the step, the position in the route and the record, and leave the time and temperature to the alloy supplier’s recommendation or the product standard. Then name the test, the pH atmosphere and the acceptance rule.
A workable note reads: “Stress relieve after final cold-working operation per alloy supplier recommendation; record furnace temperature and time on the traveler. Residual stress test per ASTM B858, atmosphere and pH as agreed in the purchase order; no cracking after exposure.” The brackets that matter are the agreed atmosphere and the sample basis, both set between buyer and supplier.
Keep expectations modest. Because B858 and B154 are not for assemblies under applied stress, an assembly can be tested for information but not rejected on the result. If a pressed or crimped joint is the real concern, the controls are the interference and the stress relief before assembly, and the drawing should say so.
Frequently asked
Is season cracking only caused by ammonia?
Ammonia is the most commonly implicated agent, according to the 1945 review, but the review treats the causes as not fully understood. Do not assume ammonia is the only source.
Does lead-free brass avoid season cracking?
Lead content is not the variable in the sources cited here. The sources point to residual stress and the corrosive environment, so alloy changes need separate evidence.
Can a dezincification-resistant brass crack by season cracking?
The cracking study names dezincification as one of the mechanisms, but residual stress is the driver, and a DZR alloy does not remove stress. Treat the two questions separately.
Which test should I specify, B858 or B154?
B858 avoids mercury and B154 says so itself. Name the test, the atmosphere and the sample basis in the purchase order.
Does a stress-relief anneal change the part?
It can soften cold-worked material, so state the temper or hardness the finished part must keep and have the supplier confirm the sequence at quote.
Sources
- ASTM B858-06, Ammonia Vapor Test for Determining Susceptibility to Stress Corrosion Cracking in Copper Alloys, ASTM International, 2006 (reapproved 2024 per the store listing)
- ASTM B154-16, Mercurous Nitrate Test for Copper Alloys, ASTM International, 2016 (reapproved 2022 per the store listing)
- Observations of Corrosion Product Formation and Stress Corrosion Cracking on Brass Samples Exposed to Ammonia Environments, Materials Research, vol. 22, no. 1, 2019
- Season Cracking of Brass, American Institute of Mining and Metallurgical Engineers, 1945