Several months ago, I wrote about annealing cases and some of the benefits and struggles associated with annealing brass. It is an incredibly useful tool for prolonging the life of brass and providing more accurate loads every reload. Since then, I have been asked and debated about one particular sentence I wrote in that previous article: “Brass can also be hardened by heating and rapid cooling” in relation to quenching brass immediately after annealing the neck and shoulder with a torch. Let’s take a deeper dive into this.
What exactly is brass?
While it’s no secret that some metals can be hardened by quenching, and others through work hardening, brass is a unique metal that combines copper and zinc. However, there are various types of brass. Old timers and steam fitters or stationary engineers (like myself) are very familiar with red brass. This alloy is 85% copper and 5% each of tin, zinc, and lead and is also called C83600. When the dangers of lead began to climb the lead content was replaced with bismuth.
Red brass found a home in the industrial world and featured some great benefits for the plumbing industry. Even today you can find red brass lying around at garage sales. Most people don’t know what they have and the ones that do have a steep asking price.
Gold brass has been used in instrument manufacturing for a very long time. Like red brass, it’s 85% copper and 15% zinc making it a very robust and malleable material for odd shapes and easy manipulation. The copper content brings up the value but it’s still heavily manufactured to this day. While all brass is used in instrument manufacturing, gold brass appears to be one of the most common for all types of wind instruments.
Yellow brass is what we are more familiar with in the firearms industry. It’s made from 60-70 copper and 30-40% zinc with the potential for other materials to be alloyed into it. Commonly called ‘cartridge brass,’ there’s no question as to what it’s commonly used for. It was never commonly used in industrial settings because zinc inhibited some of the inherent benefits that made red brass popular, namely conductivity and moisture resistance due to zinc degradation. Because of that, it wasn’t widely used when red brass was more commonly available than it is now.
Muntz brass is a lower copper content than all the others combined and can often be found with carbon. It’s generally marketed at 40% zinc or 60% copper and stands as a hard alternative for architectural elements. However, the majority of Muntz is now produced in China and select South American countries so the provenance is extremely difficult to verify.
Why is This Important?
Well, the different materials used in alloying metals bring some of their inherent charm to the final alloy. Conductivity and price, for example, is what has made copper a conductor of choice over gold and silver. As more metals are added into the alloy, that conductivity and inherent benefits of copper begin to diminish while new the inherent attributes of the other alloyed material present themselves more.
Likewise, zinc is an excellent resister of corrosion. Used extensively in the construction industry, galvanized materials rely on the benefits of the low-cost additive. The oxidizing effect of zinc seals damages areas regardless of being galvannealed, electrogalvanized, or mechanically galvanized. The only material that comes close to surpassing mechanically galvanized steel is anodized aluminum, but it lacks the inherent strength. Unfortunately, copper can by alloyed with aluminum, but only in small quantities. Pulling aluminum into a larger batch of molten copper can create some unintended consequences.
What Is Hardening?
Copper is known as a work hardened metal. As sheets of copper are rolled, they begin to get stronger generating a tighter atomic bond. Some materials, like low carbon steel, are also work hardened and do not harden by quenching. However, the most common material that is quench hardened is higher carbon steel, capable of being quenched in water (or more commonly oil) quickly shrinks the material creating a stronger bond called martensitic transformation.
Heat treatment is a method of hardening materials not commonly hardened via quenching or repeated heating a cooling. Stainless steel, lead, and copper can be heat treated, and in some cases quenched, and gain higher scores on the Brinell hardness index compared to non-heat treated and work hardened materials. One heat treat method both synonymous and different is ‘tempering,’ which is reheating a quenched material to reduce the brittleness inherent to the process.
Zinc Hardening:
Since yellow brass has a fairly high zinc content, it’s worth taking a look at how this effects the annealing and hardening process. Zinc itself, with minimal impurities, can be quenched and hardened at temperatures between 20-200 degrees Celsius. H.M. Gilder and G.N. Wallmark released a scientific paper is 1969 titled Thermal-Expansion Measurements of Vacancy Formation Parameters in Zinc Single Crystals in which they tested zinc between 45-410 degrees Celsius to achieve a quench hardened material. Likewise, the scientific paper titled THERMAL EXPANSION OF SINGLE CRYSTALS OF ZINC AT LOW TEMPERATURES published in the Canadian Journal of Physics in July of 1965 studied a similar phenomenon.
Zinc, in all its forms but more prominently in its pure form, is proven to harden by expanding on contracting under heat stresses combined with rapid cooling.
Hardening Brass?
Oh boy, buckle up for this one.
Brass is known to have inherent hardening capabilities similar to copper. This is absolutely true and outside of cold work hardening, heat treatment is the next best option. A micromechanical study of heat treatment induced hardening in Alpha-brass published in Atca Materialia October 2024 spoke about this in grand detail.
Alpha brass, usually containing 15% zinc content, has a particular crystalline structure that does not lend itself to quench hardening. Why? Because the content of zinc is so small that hardening is nearly immeasurable. Alpha-Beta brass has two distinct crystalline structures. Alpha-Beta structures are commonly found in brass that is 16-30% zinc. This type of brass can by minimally quench hardened but also nearly immeasurable and benefits from work hardening and heat treatment or a mixture of the two. However, Beta brass is able to be quench hardened based strictly on the crystalline structure and that is any brass that contains 31% or greater zinc content. Some sources state beta brass doesn’t begin until 40%.
The problem with quench hardening Beta brass are the structure and strength unpredictability. As voids form from the rapid expansion and contraction of zinc voids and crosshatching become more dominant. There is a lot I can discuss on this, but that is a topic for another time.
Another aspect that jewelers have been debating for some time is half annealing. Many subjective experienced have stated that quick quenching after annealing only partially anneals the brass they’re working with. Generally, jewelers’ brass is closer to 75/25 with a higher copper content than cartridge brass. If this is accurate, and I cannot find any study to support it, partial annealing of cartridge brass may be a valid concern.
The Danger that Lurks:
A common tactic to save money, which has been gaining a lot of traction since overseas brass production began, is selling Muntz brass (40% or greater zinc content and up to 15% iron/carbon) as cartridge and gilding brass. Companies that face no legal recourse are invested in defrauding their buyers and selling a brass material, or do not have the tools to proper check, inadequate for their use.
Muntz brass significantly hardens with quenching, yet there is only a 3-10% difference in the zinc content. With mass production, there are bound to be some mistakes. While one batch may be perfect the measurements may drift slightly over time and it may be enough to greatly impact the final product.
What Does This Mean for the Reloader?
In simple terms, brass can be minimally quench hardened. I write this with a big mental asterisk that emphasizes the ‘minimal.’
Brass with 30% or greater zinc content has the potential to quench harden in measurable amounts. While it may not be something that reloaders will notice, it can affect the accuracy of reloads. Consistency is key.
They main goal of annealing brass necks and shoulders is to have a consistent profile of cartridge expansion. As the brass is worked through multiple firings, the zinc and copper contained begins to work harden. Annealing is the reset button and brings brass back to a raw or virgin predictability. However, as reloaders we are not aware of the metallurgical content of our cartridges. Range brass and manufacturers are not forthcoming with the makeup of their materials often touted as ‘trade secrets.’
So, I will say it again, using a torch over water to anneal and then dunking your brass cases will harden them. That said, the caveat is: we will never know how much they have hardened based on the metallurgical composition and the copper will not harden, only the specific crystalline structures of a brass alloy will harden.
Summation:
Quenching annealed cases is a perfectly acceptable thing to do. However, I avoid it for several reasons and many are subjective. We can read all the scientific journals we want that verify high zinc content in brass does minimally harden far less than work hardened brass.
Having been in the stationary (steam) engineering field for a while, I can speak with some subjective authority on the subject as old systems pipes are routinely changed. When dealing with steam systems in particular, replacement of red brass to common yellow brass has yielded a plethora of problems resulting from the extreme thermal shock of the environment. As the red brass continues to excel nearly a century later, yellow brass continues to fail at an alarming rate and the failures present much the same way as fired hardened cartridges. Cracks and splits have cost me skin and sanity.
For our purposes of reloading, I aim for the most consistent and predictable loads which I cannot in good conscience provide providing intermittent performance variations when quenched, no matter how small. So, if your brass is truly C26000 (30% zinc) there should be no issues of hardening, no matter how small, when quenching. The big question of if it’s fully annealed remains. Perhaps it’s time to do some true, first-hand documented testing.
