Full Introduction of Brass Materials for Brass Valves in China

Brass is a basic metal material for brass valves, from this article you will learn more about brass in terms of history, main performance, main classifications, compositions, heat treatment.

So far, the earliest copper products found in the world are mainly in West Asia, such as the Jawi Chemi area of ​​Iraq. Copper ornaments were found, dating from about 10,000 BC to 9,000 BC; Ali in western Iran ·Bronze ornaments have also been found in Kashgar, dating from 9000 BC to 7000 BC; copper needles and copper cones were unearthed at the Chayoni site in southern Turkey, dating from about 8000 BC. These copper products are all made of natural red copper, not copper obtained by smelting ores.

From the use of pure copper, to the smelting of copper ore to obtain pure copper, to the smelting of bronze alloys, mankind has gone through a long period of groping, which is like using copper to create a sparkling time and space in a magical world. tunnel.

The earliest smelted copper in the world was discovered in Shaanxi, China. In 1973, a semi-circular brass sheet and a brass tube were discovered in the Jiangzhai Cultural Site in Lintong, Shaanxi, dating to around 4700 BC. It is worth pointing out that recently at Shanghai Light Source, using X-ray fluorescence surface scanning analysis, it was found that there are significant differences in the zinc content in different areas of the Jiangzhai brass sheet, while the lead element is scattered in dots. Its characteristics are similar to those prepared by solid-state reduction. Brass is exactly the same, which proves that the ancestors used hot forging or solid reduction to smelt metals when they used natural metal and invented metal for casting.

From about 1230 AD, brass products have been popular in Europe for about 300 years because they are much cheaper than large sculptures. The bronze statue of Archbishop Wilp, which began in 1231, is the earliest known bronze statue made of brass. The process of casting brass products is as follows: first mix the crushed zinc ore and charcoal with the copper block to heat to combine the zinc and copper, then heat to melt the alloy, and then pour the copper liquid into the casting mold. The earliest brassware in Britain was imported, mainly from Tours. The client can order a complete tombstone from Tourne which has been installed in a beautiful floor or marble base. The way to make a bronze tombstone is to first cast the bronze statue, usually the silhouette of the surrounding canopy, and then place it in a prefabricated stone slab, and use a knife to carve out the details of the person on the bronze statue. 

Chemical performance

Ordinary brass is a binary alloy of copper and zinc, and its zinc content varies widely, so its room temperature structure is also very different. According to the Cu-Zn binary state diagram, there are three types of brass at room temperature: brass with a zinc content of 35% or less, and the microstructure at room temperature is composed of a single-phase α solid solution, called α brass; containing zinc For brass with a content of 36%～46%, the microstructure at room temperature consists of (α+β) two phases, called (α+β) brass (two-phase brass); the zinc content exceeds 46 %～50% brass, the microstructure at room temperature is only composed of β phase, which is called β brass.

Pressure processing performance

α single-phase brass (from H96 to H65) has good plasticity and can withstand hot and cold processing, but α single-phase brass is prone to medium temperature brittleness during hot working such as forging, and its specific temperature range varies with the Zn content. The change is generally between 200 and 700°C. Therefore, the temperature during thermal processing should be higher than 700°C. The reason for the formation of the medium-temperature brittle zone in single-phase alpha brass is mainly due to the existence of two ordered compounds, Cu3Zn and Cu9Zn, in the alpha phase zone of the Cu-Zn alloy system. The orderly transformation occurs when heated at medium and low temperatures, which makes the alloy brittle; , There are trace amounts of lead and bismuth harmful impurities in the alloy and copper to form a low-melting eutectic film distributed on the grain boundary, causing intergranular fracture during thermal processing. Practice has shown that adding a small amount of cerium can effectively eliminate medium temperature brittleness.

In two-phase brass (from H63 to H59), in addition to the α phase with good plasticity, the β solid solution based on the electronic compound CuZn also appears in the alloy structure. The β phase has high plasticity at high temperature, while the β'phase (ordered solid solution) at low temperature is hard and brittle. Therefore (α+β) brass should be forged in hot state. Beta brass with a zinc content of more than 46%-50% cannot be press-processed due to its hard and brittle properties.

Mechanical properties

Due to the different zinc content in brass, the mechanical properties are also different, and the mechanical properties of brass vary with the zinc content. For alpha brass, as the zinc content increases, both σb and δ continue to increase. For (α+β) brass, the room temperature strength continues to increase before the zinc content increases to about 45%. If the zinc content is further increased, the more brittle r-phase (a solid solution based on Cu5Zn8 compound) appears in the alloy structure, and the strength is drastically reduced. (Α+β) The room temperature plasticity of brass always decreases with the increase of zinc content. Therefore, a copper-zinc alloy with a zinc content of more than 45% has no practical value.

Ordinary brass has a wide range of uses, such as water tank belts, water supply and drainage pipes, medals, bellows, serpentine tubes, condenser tubes, bullet casings and various complex shaped punching products, small hardware parts, etc. As the zinc content increases from H63 to H59, they can withstand hot processing well, and are mostly used in various parts of machinery and electrical appliances, stamping parts and musical instruments.

In order to improve the corrosion resistance, strength, hardness and machinability of brass, a small amount is added to the copper-zinc alloy (generally 1% to 2%, a few up to 3% to 4%, and very few up to 5% to 6 %) Tin, aluminum, manganese, iron, silicon, nickel, lead and other elements form ternary, quaternary, and even five-element alloys, which are complex brass, also known as special brass.

Zinc equivalent coefficient

The structure of complex brass can be calculated based on the "zinc equivalent coefficient" of elements added to brass. Because a small amount of other alloying elements are added to the copper-zinc alloy, it is usually only to move the α/(α+β) phase region in the Cu-Zn state diagram to the left or right. Therefore, the structure of special brass is usually equivalent to that of ordinary brass with increased or decreased zinc content. For example, adding 1% silicon to the Cu-Zn alloy is equivalent to adding 10% zinc to the Cu-Zn alloy. So the "zinc equivalent" of silicon is 10. The "zinc equivalent coefficient" of silicon is the largest, causing the α/(α+β) phase boundary in the Cu-Zn system to move significantly to the copper side, that is, the α phase region is strongly reduced. The "zinc equivalent coefficient" of nickel is negative, that is, the α phase region is expanded.

The α and β phases in special brass are multi-element complex solid solutions with greater strengthening effects, while the α and β phases in ordinary brass are simple Cu-Zn solid solutions with low strengthening effects. Although the zinc equivalent is equivalent, the properties of multi-component solid solutions and simple binary solid solutions are different. Therefore, a small amount of multi-element strengthening is a way to improve the properties of the alloy.

Lead brass

Lead is actually insoluble in brass and is distributed on the grain boundaries in the state of free particles. According to its organization, lead brass has two types: α and (α+β). Due to the harmful effects of lead, alpha-lead brass has very low high temperature plasticity, so it can only be cold deformed or hot extruded. (α+β) Lead brass has good plasticity at high temperature and can be forged. Lead brass is the most used material for brass valves, such as brass ball valves, brass gate valves, brass angle valves, brass fittings and so on.

Tin brass

Adding tin to brass can significantly improve the heat resistance of the alloy, especially the ability to resist seawater corrosion, so tin brass is called "navy brass".

Tin can dissolve into the copper-based solid solution to play a solid solution strengthening effect. But with the increase of tin content, brittle r-phase (CuZnSn compound) will appear in the alloy, which is not conducive to the plastic deformation of the alloy, so the tin content of tin brass is generally in the range of 0.5% to 1.5%.

Commonly used tin brasses are HSn70-1, HSn62-1, HSn60-1 and so on. The former is an alpha alloy with high plasticity and can be processed under cold and hot pressure. The alloys of the latter two grades have (α+β) two-phase structure, and a small amount of r-phase is often present, and the plasticity at room temperature is not high, and it can only be deformed in the hot state.

Manganese Brass

Manganese has greater solubility in solid brass. Adding 1% to 4% of manganese to brass can significantly increase the strength and corrosion resistance of the alloy without reducing its plasticity.

Manganese brass has a (α+β) structure, and HMn58-2 is commonly used, and its pressure processing performance under cold and hot conditions is quite good.

Purity measurement

The purity of brass can be measured by Archimedes principle, the volume and mass of the sample can be measured, and then the ratio of copper contained in brass can be calculated based on the density of copper and the density of zinc.

Ordinary brass

It is an alloy composed of copper and zinc.

When the zinc content is less than 35%, zinc can be dissolved in copper to form a single-phase α, called single-phase brass, which has good plasticity and is suitable for cold, hot, and pressurized processing.

When the zinc content is 36%~46%, there are α single phase and β solid solution based on copper and zinc, called dual-phase brass. β phase reduces the plasticity of brass and increases the tensile strength, which is only suitable for Hot pressure processing.

If you continue to increase the mass fraction of zinc, the tensile strength will decrease and there will be no use value.

The code name is represented by "H + number", H represents brass, and the number represents the mass fraction of copper.

For example, H68 means brass with a copper content of 68% and a zinc content of 32%. For cast brass, add "Z" before the code, such as ZH62.

For example, CuZn38 represents a cast brass with a zinc content of 38% and the balance being copper.

H90 and H80 belong to single-phase brass, golden yellow.

H59 is a two-phase brass, which is widely used in structural parts of electrical appliances, such as bolts, nuts, washers, springs, etc.

In general, single-phase brass is used for cold deformation processing, and dual-phase brass is used for hot deformation processing.

Special brass

The multi-element alloy formed by adding other alloying elements to ordinary brass is called special brass. Commonly added elements include lead, tin, aluminum, etc., which can be called lead brass, tin brass, and aluminum brass accordingly. The purpose of adding alloying elements. Mainly to improve the tensile strength and improve the processability.

Code: It means "H + the symbol of the main element (except zinc) + the mass fraction of copper + the mass fraction of the main element + the mass fraction of other elements".

For example: HPb59-1 means that the mass fraction of copper is 59%, the mass fraction of lead containing the main element is 1%, and the balance is lead brass with zinc.

Thermal processing temperature is 750～830℃; annealing temperature is 520～650℃; low temperature annealing temperature to eliminate internal stress is 260～270℃.

Environmental protection brass C26000 C2600 has excellent plasticity, high strength, good machinability, welding, good corrosion resistance, very suitable for brass valves, heat exchanger, pipe, machinery, electronic parts.

Specifications (mm): Specifications: thickness: 0.01-2.0mm, width: 2-600mm;

Hardness: O, 1/2H, 3/4H, H, EH, SH, etc.;

Applicable standards: GB, JISH, DIN, ASTM, EN;

Specialty: Excellent cutting performance, suitable for high-precision parts processed by automatic lathes and CNC lathes.

Brass is an common and important metal that closely related to humans, second only to aluminum in the consumption of non-ferrous metal materials in China.  Brass is widely used for brass valves, water pipes, brass fittings for air conditioners and radiators., machinery manufacturing, construction industry, national defense industry and other fields.