Basic knowledge of brass

I have also been working with brass recently. It seems that although it is a very ancient alloy, there are still many areas where improvements can be made. For example, there is no standardized specification for lead-free free-cutting brass to this day. Additionally, the zinc equivalent factor for brass remains a somewhat ambiguous concept in my opinion

Thank you for sharing. I hadn’t paid much attention to brass before; after reading everyone’s posts, I feel like I understand it better now.

A bit more on brass: Brass is an alloy composed of copper and zinc. Brass that consists only of copper and zinc is called ordinary brass. Alloys composed of two or more elements are called special brasses. Copper alloys composed of lead, tin, manganese, nickel, lead, iron, and silicon. Brass has good wear resistance. Special brass, also known as advanced brass, features high strength, high hardness, and strong resistance to chemical corrosion. Moreover, its mechanical properties in machining are also superior to those of brass materials. Seamless copper tubes drawn from brass are soft and possess strong wear resistance. Brass seamless tubes can be used in heat exchangers and condensers, low-temperature pipelines, and submarine transmission pipes. Manufacturing sheet metal, strips, bars, tubes, cast parts, etc. It contains 62% to 68% copper, has good plasticity, and is used in manufacturing pressure-resistant equipment. 　　Depending on the types of alloying elements present in brass, it is divided into ordinary brass and special brass. Brass used for pressure processing is called wrought brass. 　　1. Plain brass 　　(1) Microstructure of plain brass at room temperature: Plain brass is a binary copper-zinc alloy, and its zinc content varies over a wide range; as a result, its microstructure at room temperature also differs significantly. According to the Cu-Zn binary phase diagram (Figure 6), there are three types of microstructures for brass at room temperature: brass with a zinc content of 35% or less, whose microstructure at room temperature consists of a single-phase α solid solution, and is known as α-brass ； Brass with a zinc content in the range of 36% to 46% has a microstructure consisting of two phases, (α+β), at room temperature; such brass is known as (α+β) brass (two-phase brass) ； Brass with a zinc content of over 46%–50% has a microstructure that consists solely of the β phase at room temperature, and is known as β-brass. 　　(2) Formability α-phase brass (ranging from H96 to H65) possesses good plasticity and can withstand cold and hot working. However, it is prone to intermediate-temperature brittleness during hot working such as forging; the specific temperature range for this phenomenon varies depending on the zinc content, generally falling between 200 and 700°C. Therefore, the temperature during hot processing should be above 700°C. The reason for the intermediate-temperature brittleness zone in single-phase α brass is mainly the presence of two ordered compounds, Cu3Zn and Cu9Zn, within the α-phase region of the Cu-Zn alloy system; during heating at intermediate and low temperatures, these compounds undergo ordered transformations, which renders the alloy brittle ； Furthermore, trace amounts of harmful impurities such as lead and bismuth present in the alloy form low-melting eutectic films with copper and are distributed at the grain boundaries, causing intergranular fracture during heat treatment. Practice has shown that the addition of trace amounts of cerium can effectively eliminate medium-temperature brittleness. 　　Two-phase brasses (from H63 to H59) have, in their alloy structure, not only an α phase with good plasticity but also a β solid solution based on the electronic compound CuZn. The β phase exhibits high plasticity at high temperatures, whereas the β′ phase (ordered solid solution) is hard and brittle at low temperatures. Therefore, (α+β) brass should be forged in the hot state. β-brass with a zinc content of over 46%–50% is too hard and brittle in its properties to be processed under pressure. 　　(3) Mechanical properties: In brass, the mechanical properties vary depending on the zinc content; Figure 7 shows the curves depicting how these mechanical properties change with varying zinc contents. For α-brass, as the zinc content increases, both σb and δ increase continuously. For (α+β) brass, the room-temperature strength increases continuously until the zinc content reaches about 45%. If the zinc content is increased further, the strength drops sharply due to the appearance of the more brittle r-phase (a solid solution based on the Cu5Zn8 compound) in the alloy structure. The room-temperature plasticity of (α+β) brass always decreases as the zinc content increases. Therefore, copper-zinc alloys with a zinc content exceeding 45% have no practical value. 　　Plain brass has a very wide range of applications, such as water tank straps, supply and drainage pipes, medals, bellows, coiled tubes, condenser tubes, cartridge cases, as well as various complexly shaped stamped parts and small hardware items. As the zinc content increases from H63 to H59, all of them can withstand hot working well, and are commonly used in various mechanical and electrical components, stamped parts, and musical instruments. 　　2. Special brass: In order to improve the corrosion resistance, strength, hardness, and machinability of brass, small amounts of elements such as tin, aluminum, manganese, iron, silicon, nickel, and lead are added to copper-zinc alloys – generally 1% to 2%, in some cases 3% to 4%, and in very rare cases 5% to 6%. This results in ternary, quaternary, or even pentagonal alloys, which are known as complex brasses or special brasses. 　　(1) The microstructure of complex brass with a zinc equivalent factor can be determined based on the \"zinc equivalent factor\" of the elements added to the brass. Because adding a small amount of other alloying elements to copper-zinc alloys usually only shifts the α/（α+β） phase region in the Cu-Zn phase diagram to the left or to the right. Therefore, the microstructure of special brass generally corresponds to that of ordinary brass with an increased or decreased zinc content. For example, the microstructure resulting from adding 1% silicon to a Cu-Zn alloy is equivalent to the microstructure of an alloy with 10% more zinc in the Cu-Zn alloy. Therefore, the “zinc equivalent” of silicon is 10. Silicon has the highest \"zinc equivalent factor,\" which causes the α/（α+β）phase boundary in the Cu-Zn system to shift significantly toward the copper side, thereby greatly reducing the α-phase region. The “zinc equivalent factor” for nickel is negative, which expands the α-phase region. 　　(2) Properties of special brasses: The α and β phases in special brasses are complex multicomponent solid solutions, which confer a high degree of strengthening, whereas the α and β phases in ordinary brasses are simple Cu-Zn solid solutions, resulting in a lower degree of strengthening. Although the zinc equivalent is similar, the properties of multi-component solid solutions differ from those of simple binary solid solutions. Therefore, minor multi-element strengthening is a way to improve the properties of alloys. 　　(3) Microstructure and pressure processing properties of several commonly used specially deformed brasses Lead brass: Lead is actually insoluble in brass and exists as free particles distributed at the grain boundaries. Lead brass exists in two forms based on its microstructure: α and (α+β). Due to the significant harmful effects of lead, α-lead brass has very low plasticity at high temperatures; therefore, it can only be processed through cold deformation or hot extrusion. (α+β) lead brass exhibits good plasticity at high temperatures, allowing it to be forged. 　　Tin brass: Adding tin to brass significantly improves the alloy’s heat resistance, particularly its resistance to seawater corrosion; hence, tin brass is also known as \"navy brass\". 　　Tin can dissolve into copper-based solid solutions, providing solid solution strengthening. However, as the tin content increases, a brittle r-phase (a CuZnSn compound) appears in the alloy, which hinders its plastic deformation; therefore, the tin content in tin brass is generally kept within the range of 0.5% to 1.5%. 　　Commonly used tin brass includes HSn70-1, HSn62-1, HSn60-1, etc. The former is an α alloy with high plasticity, which can be processed by cold and hot pressing. The latter two grades of alloy have a (α+β) two-phase structure, with a small amount of r phase often present; their plasticity at room temperature is low, and they can only be deformed in the hot state. 　　Manganese brass: Manganese has a high solubility in solid brass. Adding 1% to 4% manganese to brass can significantly improve the strength and corrosion resistance of the alloy, without reducing its ductility. 　　Manganese brass has an (α+β) microstructure; the commonly used grade is HMn58-2, which exhibits excellent formability both in the cold and hot states. 　　Iron brass: In iron brass, iron precipitates as particles of iron-rich phases, which serve as nuclei to refine the grain structure and prevent the growth of recrystallized grains, thereby improving the mechanical and process properties of the alloy. The iron content in iron brass is usually below 1.5%, and its microstructure is (α+β). It possesses high strength and toughness, good plasticity at high temperatures, and can also be deformed at low temperatures. The commonly used grade is Hfe59-1-1. 　　Nickel brass: Nickel and copper can form a continuous solid solution, significantly expanding the α-phase region. Adding nickel to brass significantly improves its corrosion resistance in atmospheric and seawater environments. Nickel can also raise the recrystallization temperature of brass, promoting the formation of finer grains. 　　HNi65-5 nickel brass has a single-phase α structure. It exhibits good plasticity at room temperature and can also be deformed at high temperatures; however, the content of impurities such as lead must be strictly controlled, as otherwise it will severely degrade the hot working properties of the alloy. 　　Chemical composition of brass: 1) Ordinary brass It is an alloy composed of copper and zinc. 　　When the zinc content is less than 39%, zinc can dissolve in copper to form a single-phase structure denoted as single-phase brass; it has good ductility and is suitable for cold and hot pressing processes. 　　When the zinc content is greater than 39%, there is a single-phase alpha phase as well as a copper-zinc based beta solid solution; this is known as duplex brass. Phase beta reduces plasticity while increasing tensile strength, making it suitable only for hot pressure processing. If the zinc content is increased further, the tensile strength decreases, rendering it unsuitable for use. The designation is expressed as “H + number”, where H denotes brass and the number indicates the percentage of copper by mass. 　　For example, H68 indicates a brass with 68% copper content and 32% zinc content; for cast brass, the letter “Z” is added before the code, such as ZH62. Meanwhile, Zcuzn38 denotes cast brass with 38% zinc content and the remaining amount being copper. 　　H90 and H80 are single-phase and have a golden color; hence they are also referred to as gold. They are used in coatings, decorations, medals, and so on. 　　H68 and H59 are types of duplex brass, which are widely used in structural components for electrical devices, such as bolts, nuts, washers, springs, etc. 　　Generally, single-phase brass is used for cold deformation processing, while dual-phase brass is used for hot deformation processing. 　　2) Special brass: Multicomponent alloys formed by adding other alloying elements to ordinary brass are called brass. Commonly added elements include lead, tin, aluminum, etc.; accordingly, they can be referred to as lead brass, tin brass, and aluminum brass. The purpose of adding alloying elements. The main goal is to increase tensile strength and improve workability. The code is expressed as “H + symbol of the main additive element (other than zinc) + mass percentage of copper + mass percentage of the main additive element + mass percentage of other elements”. 　　For example, HPb59-1 indicates that the mass fraction of copper is 59%, the mass fraction of lead, which is the main additive element, is 1%, and the remainder is zinc; it is thus a lead brass. 　　The earliest use of brass for coin casting in our country began during the Jiajing period of the Ming dynasty. Chalcopyrite The term “yellow brass” first appeared in the work \"Shen Yi Jing • Zhong Huang Jing\", written by Dong Fang Shuo during the Western Han Dynasty: \"To the northwest there is a palace, whose walls are made of yellow brass; it is called the Palace of the Earthly Emperor.\" ” 　　It remains to be determined what copper alloy this “brass” refers to. The \"Treatise on Food and Goods\" in the \"New Book of Tang\" also uses the terms \"brass\" and \"copper alloy,\" referring respectively to the color of the ore and the product obtained after smelting; these are not the copper-tin alloys and copper-zinc alloys used today. Hong Zikui of the Song dynasty wrote in his \"Ode to Daye\" that \"it is brass; the mines have distinct names, and there are many types of raw materials in the mountains,\" referring to pure copper produced through smelting methods. 　　The term \"brass\" specifically refers to a copper-zinc alloy, and its use dates back to the Ming Dynasty; records of it can be found in the \"Ming Hui Dian\": \"According to the regulations during the Jiajing era, for 6 million Tongbao coins, 47,272 pounds of two-type brass were required…\" ”Through the analysis of the composition of copper coins from the Ming dynasty, it was found that brass, as referred to in the \"Ming Hui Dian\" as the material used for coin casting, actually appeared much later than other types of copper alloys, due to the difficulty in obtaining zinc, a metal component of brass. 　　Zinc oxide can be rapidly reduced to metallic zinc only at high temperatures of 950°C to 1000°C, whereas liquid zinc boils at 906°C; therefore, the metallic zinc obtained through reduction exists in vapor form. During cooling, the reaction reverses: vapor zinc is reoxidized to zinc oxide by carbon dioxide in the furnace; therefore, a special condensation device is required to obtain metallic zinc. This is why the use of zinc metal came much later than that of copper, lead, tin, and iron, and it is also one of the reasons why brass coins appeared late. 　　However, brass sheets and brass tubes with a zinc content of over 20% have been unearthed at the Jiangzhai Yangshao Culture site, and two types of brass cones have also been found in the strata of the Longshan Culture at Sanlihe in Jiaoxian, Shandong. Obviously, the appearance of these brass artifacts does not mean that people possessed the technology to smelt brass in prehistoric times; rather, it was an accidental discovery resulting from the use of copper-zinc sulfide ores. 　　The zinc content in bronzes from the Shang and Zhou dynasties was very low, generally on the order of 10 to the minus z. Among the coins from the Western Han and Xin Mang dynasties, there were some copper-zinc brass coins; in some of these coins, the zinc content reached 7%. However, this does not indicate that brass coins were first created during the Western Han and Xin Mang periods. Because these copper-zinc alloys are extremely rare phenomena, their zinc content is generally much lower than the 15% to 40% zinc content found in true brass. Therefore, we believe that these zinc-containing copper coins were produced during the Han Dynasty when copper-zinc symbiotic ores were used for coin casting in the mountains. Surveys of relevant mines have revealed that areas such as Changwei, Yantai, and Linyi in Shandong, as well as Hubei, possess copper-zinc sulfide deposits rich in these resources, which results in the copper obtained through smelting containing a small amount of zinc. By the Tang Dynasty, the standardization of coin-making materials ensured that the zinc content in the coins minted remained constant.

I have just started working in non-ferrous metal smelting; please give me your guidance. What equipment is used to smelt scrap brass and brass slag into brass ingots? Can a crucible be used?