Stellite alloys are a group or a range of cobalt-chromium alloys. They are designed to be resistant to wear and corrosion. These alloys may also have some portions of tungsten or molybdenum and some small but critical amounts of carbon. Stellite is a trademarked name of Deloro Stellite Company supplying Stellite alloys like Stellite3, Stellite 6, Stellite 12 and Stellite 21. Deloro Stellite Company also supplies other products like casting, machinery, welding, coating, knives and many others. The alloy was invented in the early 1900s by American metallurgist Elwood Haynes as a proper substitute for easily staining silverware.
The CAS Registry Number for Stellite alloys is 12638-07-2.
There are many types of Stellite alloys composed of varying quantities of cobalt, chromium, molybdenum, tungsten, iron, nickel, boron, aluminum, carbon, manganese, phosphorus, silicon, titanium and sulfur in different proportions. Most Stellite alloy compositions contain at least four to six of the listed elements.
Stellite Chemical Formula
Stellite alloys do not have any specific chemical formula as various types of alloys are formed by combining a number of elements in different proportions. The various types of Stellite alloys are represented by using numbers, such as Stellite 1, Stellite 6K and Stellite 706.
Types of Stellite
A special form of Stellite known as Talonite is manufactured by hot-rolling and hardening a specific alloy combination. Talonite combines the properties of hardness, machinability and wear resistance. It is important to note that not all types of Stellite alloys can be processed to create Talonite.
Stellite alloys are non-magnetic alloys which are highly resistant to corrosion. A range of different alloy compositions are prepared by combining different elements in varying proportions and the properties of an individual alloy composition might vary from an alloy of a different composition. Different alloy compositions are used for different purposes and valued for their functional flexibility. The alloy Stellite 100 is mostly used nowadays for cutting tools as it is very hard and is capable of maintaining a great cutting edge even when exposed to high temperatures. The alloy is also resistant to processes such as hardening and annealing that might result from excessive heat. Other Stellite alloys are manufactured to combine the properties of corrosion resistance, wear resistance and the ability to tolerate extreme temperatures.
Stellite alloys can be characterized as having great hardness and toughness. They are also normally highly resistant to corrosion. The extreme harness of these alloys frequently makes it difficult to work with them and so anything made from these alloys are normally very expensive. Usually, Stellite parts are precisely cast to avoid any need of further excessive machining. Stellite alloys are more frequently machined by grinding instead of cutting. These alloys usually have very high melting points resulting from the combined content of cobalt and chromium.
The various uses of Stellite alloys are discussed below:
- Stellite alloys are used in the process of hardfacing.
- They are also applied in the manufacturing of saw teeth and acid-resistant machine parts.
- The invention of Stellite alloys greatly improvised the manufacturing of poppet valves as well as the valve seats for valves. These alloys revolutionized the exhaust valves of internal combustion engines. The interval between maintenance of the valves and re-grinding of the valve seats was lengthened to a significant degree by reducing the erosion of the valves from hot gases.
- The first third of M60 machine gun barrels (starting from the chamber) and the M2HB machine gun are lined with Stellite. Stellite alloys were also used to make the shoulders and locking lugs of Voere Titan II rifles.
- Stellite alloys are also frequently used to make the cast structure used for dental prosthesis.
- During early 1980s, experiments were conducted in United Kingdom to see if precision-cast Stellite alloys could be used to create artificial hip joints as well as other bone replacements.
- Stellite alloys have been used to manufacture turning tools for lathes. Stellite alloys have greater cutting abilities compared to carbon steel tools as well as some high speed steel tools. They are especially capable of cutting difficult materials like stainless steel. Improvements in tipped tools over the years have greatly reduced the use of Stellite alloys in lathes.
Stellite alloys are normally very stable materials. However, they can react with oxidizing agents and mineral acids to form explosive hydrogen gas which can cause fire hazards.
Under normal circumstances, handling of Stellite alloys hardly poses any risk of health hazards. However, machining or welding with these alloys can produce dust, fumes and small particles of component alloy elements. These particles can pose a serious threat to human health when they enter the body in excess of maximum exposure limits.
Inhalation: Inhaling particles of Stellite alloy generated from grinding, welding or similar processes can cause asthma and metal flume fever. Component materials like boron, chromium, cobalt, copper, manganese, molybdenum, nickel and vanadium are respiratory irritants.
Ingestion: Stellite particles normally do not enter the human body through ingestion. However in some cases a person’s hands, clothing or foods and drinks can get contaminated with dusts from Stellite alloy materials and the particles may enter the body through activities such as smoking, eating, drinking and nail biting. Ingesting Stellite particles can cause vomiting, diarrhea, nausea and abdominal pain.
Skin: Irritation, sensitization or allergic dermatitis can occur from the some of the components of Stellite alloys. When the skin comes in contact with vanadium, copper and nickel, it may result in dermatitis. Exposure of the skin to cobalt might cause allergic skin reactions and dermatitis. Skin exposed to manganese might suffer from excessive sweating. Vanadium and boron exposure causes skin irritation.
Eyes: If the eyes get contaminated by coming in contact with soiled fingers or airborne particles, it might result in irritation or abrasion of the eyes. Particles of Stellite materials can cause irritation of the eyes resulting from mechanical abrasion. Severe allergic conjunctivitis and eye irritation might result when dusts of cobalt enter the eyes. Irritation may also be caused by dusts of copper.
Chronic health effects
Chronic health effects resulting from Stellite alloys are difficult to detect as these alloys are made up of several elements. Effects of chronic inhalation include pulmonary fibrosis, chronic obstructive lung disease, rhinitis and bronchitis. Chronic occupational exposure to dusts of cobalt results in goiter, bloody urine and polycythemia.
Some elements of Stellite alloys have been recognized as carcinogenic substances by The International Agency for Research on Cancer (IARC). Exposure to nickel and nickel compounds, cobalt and cobalt compounds and hexavalent chromium can greatly increase the risk of cancer among workers dealing with these alloys.
Medical Symptoms Aggravated By Exposure
Individuals already having sensitivity to certain elements and are prone to develop allergic reactions to metals like nickel, copper, chrome and cobalt might possibly encounter dermatitis and skin rashes. Persons already suffering from impaired pulmonary function can develop airway diseases and health conditions such as emphysema, asthma and chronic bronchitis, etc. when excessive concentrations of alloy fumes or dusts are inhaled. If any of these health conditions are already present, the inhalation of Stellite alloy particles can aggravate the symptoms. If a person is already suffering from prior damages to the Circulatory, Neurologic (nervous), Renal (kidney) or Hematogic (blood) systems, proper examinations or screening should be conducted for appropriate diagnosis of these patients. They should also be prohibited from entering areas contaminated by dusts of Stellite alloys.
Ventilation: The area should be well ventilated to minimize contamination of dust, fume and particles. Air exposure of materials should be kept below the recommended limits of exposure.
Respiratory: If the room is not properly ventilated and the exposure levels of alloy dust is not maintained below the exposure limits, adequate respiratory protection needs to be used by the working personnel. The respirators should be NIOSH-approved and have a proper air purifying filter.
Skin: Rubber or leather gloves should be used while dealing with Stellite alloys to avoid skin contact and for preventing metal abrasions and cuts. Unnecessary and risky skin contact can be easily avoided by using protective coveralls.
Eye: Safety goggles or glasses should be worn while entering a contaminated area.
First Aid Measures
Inhalation: The victim suffering from breathing difficulty due to inhalation of dust particles and fumes should be removed to an area of fresh air. A physician needs to be consulted if the breathing still does not improve.
Ingestion: The victim should drink plenty of water and try to vomit. A doctor should be consulted for ensuring further safety.
Skin: The infected area should be washed nicely with plenty of water. The victim should take a shower if possible. Contaminated clothing should be removed. Medical attention is required if irritation of skin persists.
Eye: The eyes should be washed well with ample amounts of water. A doctor needs to be consulted if eye irritation persists. While working with powders and dusts of Stellite alloys, a person should not wear contact lenses.
Recommended Monitoring Procedures
Environmental Surveillance: Air samples should be taken from the industrial working area for regularly checking the levels of air contamination.
Medical Surveillance: The workers should regularly go through a thorough health check up. Tests like chest x-rays, lung tests and routine physical examinations should be conducted on regular intervals to ensure safety of the workers.
Waste Disposal: Wastes of Stellite alloys should be disposed of by following the relevant Local, Provincial and Federal regulations regarding waste management.
Harmful effects of Stellite Usage in Nuclear power plants
Stellite alloys should not be used in nuclear power plants as cobalt can be changed to Cobalt-60 in nuclear reactors, which is a harmful radioisotope having a half life of five years and releases strong gamma radiation.
Stellite alloys are often a first choice in many industrial applications and functions. They are highly valued for their high resistivity to corrosion and weariness and hardness.