Phosphor Bronze: Its Properties and Characteristics

Phosphor Bronze, also known as tin bronze, is alloys made up of copper, tin and phosphorous and known for its strength, low coefficient of friction and toughness. The phosphor bronze contains between 0.5 and 11% tin and 0.01 to 0.35 % phosphorous. The addition of tin increases the resistance to corrosion and strength of the alloy. The phosphorous increases the resistance to wear and stiffness of the alloy. The phosphor bronze has superb spring qualities, resistance to high fatigue and corrosion, excellent formability and solderability. They are basically used for electrical products, corrosion resistant bellows, diaphragms, and spring washers. The phosphor bronze has to grades UNS C50100 through C54200. Leaded phosphor bronze combines good strength and resistance to fatigue, corrosion and wears along with good machinability.

Copper alone is not suitable for use in connectors because it is not elastic enough and loses its strength when held at the operating temperature of most electrical switchgear. Therefore Copper, in the form of an alloy has to be strengthened without unnecessary loss of electrical conductivity.

To remove oxygen Phosphorus is added to molten copper. The product of this deoxidation- Phosphorus pentoxide, is readily removed from the melt during the refining process. Any excess phosphorus goes into solution in the copper, where it provides some strengthening when the copper is cast and worked to a sheet. But phosphorus in solution reduces electrical conductivity dramatically. As little as 0.25% phosphorus will reduce conductivity to only 30% IACS, (International Annealed Copper Standard for the pure metal).  During the hot rolling stage of sheet production, too much phosphorus also causes problems. It is, therefore, a challenge, to maintain the amount of phosphorus at an optimal value to remove oxygen but keep it low enough to enable the material to be worked down to a sheet and still retain a relatively high electrical conductivity.

To strengthen the alloys Tin is added to conventional phosphor bronze. Like phosphorus, tin goes into solution in the molten copper and remains in solution in the solidified alloy. The maximum tin concentration that can be retained in solid solution is about 16%.

The tin content in this alloy determines the corrosion resistance and also gives it strength. Tin in solution produces two conflicting effects. Due to solid-solution strengthening, it increases the strength of the copper significantly. But the more the content of tin in solid solution the lower is the electrical conductivity. Fortunately, the effect of tin on electrical conductivity is less severe than in the case of phosphorus, and 1% of tin only reduces the conductivity to 60% International Annealed Copper Standard (IACS). Again, there has to be a balance, which depends on the cost of the material and the properties required.  If the tin content is above 2.5% the alloy becomes too expensive to process; if the content of tin below 1.5% the alloy lacks strength and the ability to retain strength at its operating temperature.

Hence, conventional phosphor bronze is a compromise, with optimum additions of phosphorus and tin to give as high strength as possible coupled with a relatively high electrical conductivity.

Properties and Characteristics

• Strength and resilience – phosphor bronze is an alloy which is resistant to fatigue. It holds up exceptionally well to wear. The inclusion of tin is what gives Phosphor bronze its added strength.
• Corrosion resistance – phosphor bronze is typically used in applications where it will have exposure to corrosive chemicals and/or physical elements.
• Electrical conductivity – the use of Phosphor bronze in electrical components is perhaps its most well-known application.
• Excellent elasticity – the fine grain size of this alloy enables the material to have a greater degree of spring back.

Features and Uses of Stainless Steel 316 Round Bars

Stainless steel 316 round bars are also known as UNS S31600 grade bars. It is chromium, nickel and austenitic SS build to provide enhanced resistance in moderately corrosive environments. These are often used in process streams containing halides and chlorides. It has some amount of molybdenum improved general corrosion and chloride pitting resistance. These bars provide higher stress to rupture, tensile strength and higher creep strength at hoist temperature too. It's common practice for 316 grade to dual certified. It has a lower carbon composition with the addition of nitrogen enable to meet the mechanical properties.

Stainless steel 316 round bars resist atmospheric corrosion in moderately oxidizing and reducing environments. These bars also resist corrosion in polluted salty waters. This grade has outstanding resistance to intergranular corrosion in welded condition too. These possess excellent strength and down the toughness at cryogenic environments. When these are annealed becomes non-magnetic in nature. However, it becomes slightly magnetic in nature when these are cold worked or welded.

These are easily weldable and processed by standard shop fabrication process. In most applications, this alloy has superior corrosion resistance to other conventional grades. In the cyclic mild environments, these are not corroded. Once exclusion, it is highly oxidizing such as nitric acid where it contains molybdenum content. These bars perform well in sulfur-containing environments that are encountered in paper processing industries. Alloy 316 can be utilized in higher concentration temperature up to 38 degrees C. These have good resistance to pitting in acetic and phosphoric acids. These perform well in 20% boiling phosphoric acids.

This grade is non-toxic and bio-compatible makes it ideal for food and pharmaceutical process industries. It is utilized to handle fatty acids and hot organic acids that lower product contamination.

Stainless steel 316 round bars performs well in fresh water even that contain a high level of chlorides. The higher composition of molybdenum content makes it superior pitting resistance to traditional grades in the application, including chloride solutions, particularly in adverse environments. For instance, the corrosion resistance level will be roughly equal to reducing climates. However, in a mild environment, it has sufficient resistance that causes intergranular corrosion of welds in the heat affected zone that is due to its lower carbon amount.

SS round bars are formed with hot or cold forging methods. The hot working temperature ranges between 927 to 1204 degree C. To achieve maximum corrosion resistance it is annealed at 1038 degree C and rapidly quenched with water or air. These bars are quite ductile and form easily. The cold working method will enhance its hardness and strength. These are easily weldable by most standard process. Post-welding heat treatment is not required. 316 bars are subjected to work hardening during manufacturing that leads in chip breaking. The best machining results are gained by slower feeds, speeds, lubrication and powerful tool.

Fabricated stainless steel 316 round bars are undergone with several testing for the maximum factor of safety. Some of those are buckling or crushing test, destructive/nondestructive test, mechanical test and more.