The process of forming black iron oxide to ferrous metals and other types of materials is often called black oxide. The black oxide process is a chemical conversion coating for ferrous materials, stainless steel, copper and copper-based alloys, zinc, powdered metals, and silver solder. This process is done to add corrosion resistance, enhance appearance, and minimise light reflection.
Unlike nickel or zinc electroplating, the black oxide is not deposited on the surface of the substrate. Instead, a chemical reaction is generated between the iron on the ferrous metal surface and the oxidizing salts that are present in the black oxide solution. The generated chemical reaction results in the formation of magnetite, a black iron oxide, on the surface of the coated material.
The Black Oxide Processes
The black oxide chemical conversion can be done through the hot process or cold process.
The hot process starts by fixturing, which is the hanging of individual parts from a wire, placing them in baskets, or putting them in a tumbler. After fixturing, the parts will be cleaned by submerging them in an alkaline bath and then rinsing them in clean water. For blackening ferrous materials, they must be placed in a bath of propriety blackening solution that contains sodium hydroxide, nitrates, and nitrites. This solution converts the material surface into magnetite. The proprietary blackening bath is not applied when applying hot black oxide for stainless steel parts.
The cleaning and rinsing of materials must be done in warm baths, up to 160°F. The blackening, on the other hand, must have temperatures ranging from 265°F to 285°F. The final step in the hot process is the application of oil to heated parts. To avoid corrosion, the oil seals the black finish by sinking into the porous layer of the black oxide.
Cold black oxide is only introduced since it reduces hazards and saves energy. With the cold process, a compound called copper selenium is applied to the materials at room temperature. This process is contrary to the hot process wherein the parts are subjected to numerous chemicals at high temperatures. The final step in the cold oxide process also deals with the application of oil to parts for added corrosion resistance.
While cold black oxide can offer better productivity and convenience for in-hose blackening, its coating property tends to rub off easier and offers less abrasion resistance. Hot blackening, on the other hand, is known to be cost-effective, provides superior coverage, and offers enhanced corrosion resistance.
Applications of Black Oxide
The blackening process of materials is typically used in industries that revolve around retail, automotive, electrical, home, garden, gearing, and firearms. Some products and tools that are processed with black oxide include store displays, fixtures, oil filter cans, hood fasteners, nuts, washers, wire strippers, cutters, clipping tools, small gears, electrical switches, gun components, and shotgun shell magazines. With the black oxide process, you can easily get products and tools that have a remarkable surface look and have enhanced corrosion resistance property. To know more about black oxide, feel free to contact us now at Alpha Detroit Heat Treatment.
Case hardening is a process of reinforcing the surface of some types of soft metal, making them more durable and tough. This process forms a thin layer of durable metal coating that allows the metal underneath to remain soft. One type of case hardening is carburization, which involves introducing steel items to carbon atoms.
The Essence of Carburization
Carburization is a process that transforms a specific type of metal like iron or steel into a highly carbonized metal. The transformation is done by exposing and heating the soft type of metal to a carbon-dense atmosphere such as charcoal or carbon monoxide. Once the carbon atoms have attached to the surface of the involved metal, it will ultimately develop improved hardness and strength.
The temperature and duration of the whole carburization process typically determines the overall strength acquired by the soft metal. A metal that is exposed to longer carburizing times and higher temperatures generally has a higher concentration of carbon. When this metal is quickly cooled by quenching, its outer surface becomes hard and resistant to wear, while the core will remain soft and tough.
Types of Carburization Process
To date, there are four different types of carburization that are used in metal manufacturing industries.
Benefits of Carburization
The process of carburization can be advantageous for steel materials. For one, the whole carburization process can make the steels more durable. The formation of a very hard exterior out of this process allows the steel alloys to deal with immense physical trauma without damaging their soft interior. Speaking of the soft interior, the process of carburization can maintain this core part. The presence of this metal part allows the metals to be easily manipulated into different shapes. Lastly, steels that are carburized are much affordable than other types of steel.
The carburization in heat treatment allows the metal to gain a surface that is difficult to get damaged. It also maintains important properties of metal even with the presence of an outer protective layer. If you want to know more about this process, you can always ask us at Alpha Detroit Heat Treatment.
A heat treatment does far more than just change the physical appearance of metals. It also can modify the properties of them to reach the intended goal. This type of treatment involves heating and cooling the metals at the right temperatures to alter their microstructure. How long the treatment requires depends upon the size of the project as well as the type of metal. We will discuss how heat treatments modify the metal properties as well as the different types of these treatments in the following.
The Main Goals of Heat Treatment for Metals
• Increases the hardness and or strength of the metal to make it more durable. It will be additionally resistant to cracks, chips and breaks as a result.
• Softens the chosen metals to increase their workability. This helps to form them into the right shape more effectively. Regardless of how you are moulding the metals into shape, the heating and cooling processes of these treatments can help produce the ideal outcome.
• Heat treatments stabilise the physical and mechanical characteristics of the metal to ensure that they will stand up to a number of environmental and work conditions.
• Lowers the amount of magnetism that a metal has, especially in the case of iron, cobalt and nickel.
• Reduces that amount of residual stress that a fabrication process can inflict on metals. Less damage and waste happen when this stress is lowered.
• Heat treatments ensure the dimensional stability of metal as well in certain circumstances.
• Helps the metals to become resistant to electrical current so that they can be used in a variety of situations involving electricity.
Metals Differ in Their Response to Heat Treatments
Since each metal has a unique chemical composition, metals respond differently to heat treatments regardless of the method that is utilised. Alterations of their structural and physical properties happen when they reach their ideal temperature. Also, their composition will determine the method of heat treatment as well as the time it takes and the rate of cooling that is necessary.
Examples of the Types of Heat Treatment
• Age Hardening uses a low-temperature to perform the heat treatment to strengthen metals.
• Solution Heat Treatment heats metal to the right temperature and then holds it there until the alloy elements turn to a solid state. The metal is then quenched to cool it.
• Precipitation Hardening is a combination of the solution heat treatment, age hardening and quenching and is for increasing the hardness or strength of an alloy.
• Annealing softens the metals by heating them to the correct temperature and then, cooling them slowly to accomplish the desired result.
Ensure that the metals you wish to modify receive the right heat treatment to accomplish your goal. Also, turn to the professionals if you do not have any experience with these treatments to ensure ideal results.
Various properties of metals experience change when they go through a heat treatment. Some changes make the metals more resilient or resistant while others allow them to be reshaped. Even though modern technology has created new methods for this type of treatment, blacksmiths many years ago used to accomplish similar goals by heating and cooling metals for horseshoes, wagon parts and more. To learn additional facts about how heat treatments affect the characteristics of metals, read the following details.
The Effects of Heating Metals
1. Thermal Expansion
As metals are heated, their volume, surface and length will expand. The term for these actions is thermal expansion. Each metal will have a different rate of expansion when exposed to the heat.
2. Structural Alterations
Another effect that heat treatments have on metals is that the structure of them will go through a transformation. This is due to the fact that heat displaces the allotrope atoms in metals and causes them to reform in a different configuration. For this reason, this action is called the allotropic phase transformation. It not only can change the structural shape of the metal, but it also can alter its strength, ductility and hardness of it.
3. Makes the Metals Resistant to Electrical Current
A heat treatment can effectively make a metal have a certain level of electrical resistance. The reason that this happens is that when metals are heated, their electrons can absorb addition energy and makes them move faster than normal.
4. Reduces a Metal’s Magnetism
Magnetic metals such as nickel, cobalt and iron can lose some of their magnetism by undergoing a heat treatment. In some cases, they are no longer magnetic at all.
Types of Heat Treatments
All heat treatments involve heating and cooling metals to change them in some fashion. The most popular reasons for performing these treatments is to increase a metal’s toughness, hardness, strength, corrosion or electrical resistance, and ductility. The following are the most common methods for performing these treatments:
• Annealing softens the metal through heating to make it workable and to increase its ductility. The metal is heated to the appropriate temperature to alter its microstructure and then, it is slow-cooled. It also increases the metal’s electrical conductivity.
• Hardening improves the mechanical properties of steel and other alloys. During this process the metal is heated to a high enough temperature to dissolve a portion of the carbon in it, prior to the appropriate quenching medium being applied. Hardening can increase wear resistance and strength but can also increase brittleness at times, so it is not recommended for some engineering applications.
• Normalising is used on alloys to provide them with a uniform composition and grain.
• Tempering is used on steel to improve its ductility. Steel that does not undergo this process is extremely hard but too brittle to use in many applications.
While there are many other details to learn about how heat treatments affect the properties of metals, the above information gives you a start on your education about this topic. Ensure that your metals receive the appropriate heat method to achieve your purposes.
Black oxide is a conversion coating that is suitable for ferrous metals along with copper-based alloys, copper, zinc, stainless steel, silver solder and powdered metals. It accomplishes this through a chemical reaction since it is made of caustic oxidisers and additives. Also, it gives items a lustrous, black appearance and provides some corrosion protection. On top of all this, it offers other advantages such as anti-galling properties, smut-free finishes and dimensional stability.
Examples of Items That Benefit From a Black Oxide Coating
A wide assortment of items can benefit from being coated with black oxide, including such ones as:
• Assorted components ranging from parts to nuts and bolts
• Architectural pieces
• Tools
• Surgical instruments
Types of Processes to Apply Black Oxide
While you can achieve a black oxide coating through the hot-temperature, mid-temperature and cold-temperature processes, the first two are the most popular since they bond better to the various metals and offer improved abrasion-resistance. For the rest of this information, we will be discussing only the first two processes.
How the Hot-Temperature and Mid-Temperature Black Oxide Processes Differ
The hot-temperature method uses a temperature of 140.556-degrees C to produce a finish with black oxide iron magnetite or Fe3O4, and it will blacken a wide range of metals. The mid-temperature method accomplishes its task at temperatures ranging from 107.222-degrees C to 123.889-degrees C to coat various items with Fe3O4. The following are some other differences between these two processes:
• Hot process takes about 10 to 20 minutes while the mid-temperature one requires 30 to 45 minutes to blacken metals
• A glossy blue-black colour is achieved with the hot process, and the mid-temperature method produces a glossy black finish
• The hot method produces less sludge than the mid-temperature method does
• Mid-temperature process produces fewer fumes than the hot-temperature method
• The hot method produces a finish that is longer lasting than that of a mid-temperature method, even when the components are exposed to flexing
It is important to note that both methods create finishes that resist corrosion and abrasion. Matte finishes are possible upon request.
Which Process Is Right for Your Purposes?
Select the process that provide your workpieces the ideal finish for the conditions that they will face. Also, consider the alloy, steel or other metal in your components or other elements that need the black oxide coating.
Benefits of the Black Oxide Coating
To finish, read about the advantages of this coating in the following:
• More economical than other types of protective coatings
• All methods for applying black oxide can be performed in large batches of small components or items
• No significant dimensional changes
• Black oxide can conform to military standards