Beryllium Copper Alloys vs Steel: Which Metal Works Harder?
While some steel alloys have a distinct cost advantage over beryllium copper, the latter is superior to steel in terms of corrosion resistance, thermal and electrical conductivity and non-sparking features.
Always on the search for materials possessing just the right combination of properties for demanding applications, specifiers and corrosion engineers evaluate materials such as beryllium copper alloys as a superior alternative to steel.
What is Beryllium Copper?
Beryllium copper (BeCu) alloys, often called beryllium bronze, contains copper, beryllium and other elements in some cases. The remarkable features of this alloy make it an ideal choice for specific applications requiring high strength, hardness, superior electrical conductivity, non-sparking qualities, corrosion resistance and other characteristics.
Beryllium copper is a well-known high performance metallic alloy. The mere addition of 2% beryllium to copper produces an alloy that is almost 600% stronger than copper alone. It combines the favorable features of copper alloys with high tensile strength. Additionally, it can be hardened or softened by simple heat treatment processes. It has some mechanical properties that are similar to strong alloy steels.
Beryllium copper has the highest tensile strength and hardness among all of the copper alloys. The strength of heat-treated beryllium copper alloys is comparable to the strength of some steel alloys; however, steel is inferior to beryllium copper in respect of corrosion resistance and thermal conductivity and electrical conductivity. (For information on other metals, see the Guide to Corrosion-Resistant Metals.)
In the oil & gas and coal mining industries, where non-sparking properties are needed, tools made from beryllium copper are preferred over steel tools.
Certain proprietary products have been developed that possess the high strength, hardness and corrosion resistance required for ceramic casting and investment casting applications. The special alloy beryllium copper 165C, with high corrosion resistance, has been developed for saltwater immersion service.
Distinguishing Features of Beryllium Copper
The main features of beryllium copper include:
- Machinability and formability
- Creep resistance
- Superior corrosion resistance
- Ease of formation of strips, wires and low weight miniaturized components
- The ability to form stampings of complicated geometrical shapes with accurate measurements
- High ductility
- Superior electrical conductivity
- Good thermal conductivity
- Fatigue resistance
- High elastic limit
- Dimensional stability
- Biofouling resistance
- Work hardening and age hardening features
- Minimal risk of hydrogen embrittlement and stress corrosion cracking (SCC)
However, beryllium compounds such as oxides are considered toxic if accidentally inhaled, so safety measures may be needed during production, handling and use of BeCu alloys.
Because beryllium metal itself is brittle, it is used in very small proportions (e.g., 1.5 to 3 percent) in beryllium copper as an alloying element. Applications requiring higher hardness contain a higher proportion of beryllium, whereas springs with medium hardness use a lower proportion of beryllium. Beryllium copper alloys with less than one percent beryllium and a slightly higher proportion of cobalt (slightly more than 2%), are preferred for high electrical conductivity applications.
Corrosion Resistance and Mechanical Properties of Beryllium Copper
Beryllium copper has a higher corrosion resistance than steels typically used for springs and other pressure sensitive devices in the normal environmental condition. Studies also confirm that beryllium copper has superior corrosion resistance compared to stainless steel in seawater. (To learn more about stainless steel, read An Introduction to Stainless Steels.) However, beryllium copper should not come in contact with acetylene or sulfur compounds as these will react with this alloy.
Heat treated cold worked beryllium copper forgings have a tensile strength of 50-55 tons/square-inch with a percent elongation of 10 percent. By comparison, the tensile strength of mild steel is 25 tons/square-inch (50000 psi). Beryllium copper wires have a tensile strength of 150000 - 230,000 psi and wires of comparable steel grade ASTM A 229, class 1 have a tensile strength of 165000 - 293000 psi.
Beryllium copper alloys are not prone to stress corrosion cracking (caused by chlorides) or hydrogen embrittlement. Beryllium copper was used to manufacture the connectors for undersea transatlantic communication cables between the United States and Europe.
Conductivity of Beryllium Copper Alloys
The electrical conductivity of low-beryllium BeCu can vary between 45% IACS to 52% IACS (highest value reached when heat treatment is performed to achieve optimum electrical conductivity; optimum electrical resistivity achieved in this case corresponds to 3.3 to 3.6 micro ohms). Electrical conductivity of normal BeCu alloy is in the range of 32 to 38 percent of IACS. (Note: IACS is the International Annealed Copper Standard.)
The thermal conductivity of beryllium copper 25 alloy is 105 watts/kelvin/meter, whereas for carbon steel it is 45 watts/kelvin/meter and for stainless steel it is 15 watts/kelvin/meter. In general, beryllium copper alloys have 3 to 5 times superior thermal conductivity compared to that of tool steels.
Applications for Beryllium Copper
A study of beryllium copper alloys classifies the applications of beryllium copper alloys into the following categories:
- Based on high strength as well as elasticity: pressure sensitive high precision instruments, diaphragms, springs
- Based on high conductivity, good corrosion resistance and strength: electrodes and holders for resistance welding
- Based on hardness as well as strength: dies used for forging metals and for deep drawing of metals
- Based on non-sparking features and hardness: hazardous applications requiring non-sparking implements and tools
Category 1 Applications
An advantage of using beryllium copper metal alloys for springs and pressure sensitive precision appliances and instruments is the ease of working the metal into complicated geometrical shapes before hardening and tempering them later. Because the conductivity of this alloy is much higher than other varieties of steel, as because of its elasticity and nonmagnetic features, beryllium copper is also preferred in electric measuring instruments. This copper alloy is also used to make clock hairsprings.
Category 2 Applications
Electrode holders and electrodes used for resistance welding must have hardness and strength to withstand the tendency to deform at higher temperature and must have high electrical and thermal conductivity features. Proprietary beryllium copper alloys developed through research include low beryllium copper containing cobalt and silver. Similarly, low beryllium copper with high heat transfer features is used for making fuel oil and gas burners.
While welding with beryllium copper rods, the operators must ensure that they do not inhale the fumes because beryllium fumes are hazardous and considered carcinogenic. Precautions are needed when processing beryllium copper, such as when gas cutting, soldering, brazing, polishing, finishing, blasting, grinding, machining, or sawing because beryllium fumes and dust can be hazardous for operators.
Category 3 Applications
The advantages of using beryllium copper in deep drawing dies and forging dies is the ease of manufacturing by precision casting, machining and hardening in a subsequent process. The superior wear resistance and higher thermal conductivity ensure that operation cycles are shortened, particularly in plastic molding, as compared to the operating cycle of steel dies of comparable dimensions.
Category 4 Applications
Beryllium copper alloys are used to make non-sparking safety tools suitable for hazardous locations such as aerodromes, oil & gas installations, coal mines, facilities that produce and use ammunition and explosives, and factories distributing, storing and using flammable oils and gases.
The general list of safety tools made from beryllium copper include screwdrivers, pliers, hacksaw blades, scissors, shovels, hammers, spanners, chisels, knives, shears and scrapers. These tools may be cast, rolled or forged. Tools used for steel cutting retain their cutting edge, hence longevity and efficiency is ensured. (Related reading: The Use of Vinyl Coatings for Tools and Small Metal Parts.)
In hazardous locations, tools made of steel can produce sparks due to tiny ferrous particles flying out and the heat generated at the moment of impact. These particles oxidize instantly, thus prompting the automatic ignition of flammable materials. If beryllium copper alloy tools are used, the particles produced by an impact with solids such as concrete do not oxidize instantly and the spark hazard is minimized. Although there is a remote possibility of iron particles being oxidized during the impact of beryllium copper tools against ferrous solids, the risk is much lower if normal precautions are taken.
Other Notable Applications for BeCu Alloys
Beryllium copper alloys are used in cryogenic applications because they consistently retain thermal conductivity and mechanical strength at lower temperatures. The valve seats of four–stroke internal combustion engines with coated titanium valves are now made of beryllium copper alloys because the heat dissipation rate is superior to the dissipation rate of valve seats made from ferrous metals. (Related reading: Understanding Ferrous and Non-Ferrous Metals: Understanding These Key Differences.)
Miniaturized components are being developed for computer electronics and mobile phones due to the alloy's electrical and thermal conductivity, ease of miniaturization and superior strength.
Other applications include undersea cable connectors and high quality professional percussion instruments. Triangles and tambourines made of beryllium copper alloy emit a consistent resonance as well as a high quality tone.
Because beryllium copper is nonmagnetic, it is used for magnetometers in directional drilling and measure while drilling (MWD) tools. Because ferrous parts can interfere with the magnetic resonance imaging (MRI) process, parts made of a non-ferrous metal such as beryllium copper are an obvious choice.
While some steel alloys have a distinct cost advantage over beryllium copper, the latter is superior to steel in terms of corrosion resistance, thermal and electrical conductivity and non-sparking features. After heat treatment, beryllium copper equals some of the alloy steels in terms of strength and hardness.
Non-sparking features make these alloys appropriate for tools meant for explosion-prone facilities such as coal mines and oil rigs.
Beryllium copper alloys have a smaller modulus of elasticity, and hence cause greater deflection than steel spring for similar loads. Due to superior thermal and electrical conductivity, beryllium copper alloys are preferred for use as electrodes and holders in resistance welding. Easy formability and accuracy of shaping gives a distinct advantage to beryllium copper.
The biggest disadvantage is toxic beryllium dust and fumes; hence safety measures must be in place when working with these alloys in certain situations.