Test your knowledge: Many newly manufactured steel products have a blue sheen on their surface. Do you know how this is formed? What is its purpose?

This post was last edited by mopeizhi on 2010-2-7 at 15:08. The answer provided by this site is: Answer: It is formed through surface oxidation treatment, which improves its rust resistance. Steel undergoes surface oxidation treatment, resulting in a dense and thin layer of iron oxide protection film; this film is referred to as ‘blueing’, ‘blackening’ or ‘bluing’ depending on its color. It can improve the corrosion resistance of steel in atmospheric and mildly corrosive environments. It is usually oxidized using an oxidizing agent under acidic, alkaline, or high-temperature conditions.

This post was last edited by mopeizhi on 2010-2-7 at 15:10. It is formed through surface oxidation treatment, which improves its rust resistance. Steel undergoes surface oxidation treatment, resulting in a dense and thin layer of iron oxide protection film; this film is referred to as ‘blueing’, ‘blackening’ or ‘bluing’ depending on its color. It can improve the corrosion resistance of steel in atmospheric and mildly corrosive environments. It is usually oxidized using an oxidizing agent under acidic, alkaline, or high-temperature conditions.

This post was last edited by mopeizhi on 2010-2-7 at 15:10. I’m not sure; it should be a protective film. I don’t know what its composition is – whether it’s a deposition oxide film or an adherent film.

This post was last edited by mopeizhi on 2010-2-7 at 15:11. It is formed through surface oxidation treatment, which improves its rust resistance. Analysis: Steel undergoes surface oxidation treatment, resulting in a dense and thin layer of iron oxide protection film; it is referred to as ‘blueing’, ‘blackening’ or ‘bluing’ due to its color. It can improve the corrosion resistance of steel in atmospheric and mildly corrosive environments. It is usually oxidized using an oxidizing agent under acidic, alkaline, or high-temperature conditions.

This post was last edited by mopeizhi on 2010-2-7 at 15:14. As the temperature rises, the yield strength fy, tensile strength fu, and elastic modulus E of steel tend to decrease. However, at 250°C, the tensile strength fu of steel increases significantly; at the same time, the elongation rate δ decreases and the impact toughness worsens, resulting in brittle failure of the steel. The phenomenon in which the plasticity of steel decreases within a certain temperature range is known as \"thermal brittleness.\" Since the surface of steel often takes on a blue hue due to oxidation at 250°C, thermal brittleness in this temperature range is also referred to as \"blue brittleness.\"

This post was last edited by mopeizhi on 2010-2-7 at 15:16. It is formed through surface oxidation treatment, which improves its rust resistance. Steel undergoes surface oxidation treatment, resulting in a dense and thin layer of iron oxide protection film; this film is referred to as ‘blueing’, ‘blackening’ or ‘bluing’ depending on its color. It can improve the corrosion resistance of steel in atmospheric and mildly corrosive environments. It is usually oxidized using an oxidizing agent under acidic, alkaline, or high-temperature conditions.

This post was last edited by mopeizhi on 2010-2-7 15:20. It is formed through surface oxidation treatment, which improves its rust resistance.

This post was last edited by mopeizhi on 2010-2-7 at 15:22. The oxidation treatment of steel is also known as bluing, blackening, or boiling blackening. After oxidation treatment, a protective magnetic iron oxide is formed on the surface of the spring; this oxide film is usually blue or black, and sometimes dark brown. The function should be to protect, right?

This post was last edited by mopeizhi on 2010-2-7 15:23. Surface hardening heat treatment: Explanation of methods. Carburizing [HC]: Carburizing refers to the process of introducing carbon into the surface of low-carbon steel to turn it into high-carbon steel, followed by hardening of its surface. Although merely infiltrating carbon can harden it, the effect is not very noticeable; therefore, quenching is applied as well. In other words, the correct method involves using both carburizing and quenching processes, which is what is known as carburizing and quenching. Workpieces that have undergone carburizing and quenching are hard on the outside and soft on the inside; due to their improved wear resistance, fatigue resistance, and impact resistance, they are widely used on the surfaces of mechanical parts. 　　Nitriding [HNT] refers to a method of hardening steel by infiltrating nitrogen into its surface. Unlike carburizing, nitrogen is diffused into the steel, resulting in an increase in hardness due to the formation of iron nitride; therefore, there is no need for quenching. Parts that have been nitrided possess excellent wear and corrosion resistance, as they do not require quenching; therefore, there is no need to worry about quenching cracks or warping. The hardness after nitriding is approximately HRC 45~52. 　　High-frequency treatment ﹝HQI﹞ is a surface hardening method that uses high-frequency current for heating, thereby rapidly heating only the surface of the steel piece in a quenching process. High-frequency refers to a frequency that is higher than the commercial frequency [60Hz], which is why it is called so. For steel suitable for high-frequency quenching, S35~S45C is preferred, with a hardness of approximately HRC45~50. 　　Surface electroplating treatment: Electroplating is a widely used method in surface treatment; it is a surface technology that involves the electrical deposition of metals on metal or non-metal surfaces for purposes such as enhancing corrosion resistance, wear resistance, or providing decorative effects. Explanation of the method: Copper plating loses its luster easily when exposed to air, and its mechanical strength is not very good. It is occasionally used for mirrors and components in distribution panels, but it is rarely used as the final coating. However, nickel and chromium can adhere easily to copper, and since copper is soft and easy to polish, it is often used as an underlayer for nickel plating. Nickel plating offers wear resistance, corrosion resistance, and the ability to maintain a shiny finish. Nickel does not adhere easily to iron, so plating with copper first followed by nickel yields better results. In industry, nickel plating is roughly divided into two types: glossy nickel and matte nickel. In terms of corrosion resistance, glossy nickel is inferior, and it is usually used as a base layer for chromium plating. Chromed metals have a silver-white luster and are very hard. Chroming can be divided into two main categories: decorative and industrial, as described below: Decorative chroming: It is not applied directly to the base material; instead, it is applied over a nickel layer, with a thickness of less than 0.003 mm. Industrial chromium plating: It makes full use of chromium’s physical and chemical properties, with a highly hard chromium layer being its characteristic feature (HRC 38.8). This plating is applied to the base material to create various industrial products that are used in final engineering applications. Its specific uses include: hard chromium (h.Cr), which is used for components that require wear and heat resistance, such as tools, molds, and moving parts of machinery. Porous chromium [p.Cr] and cracked chromium: The gold-plated surface features many tiny pores and cracks in which lubricating oil can be stored. It is widely used in aircraft piston cylinders, piston rings, etc., with a thickness of over 0.1 mm. 　　Galvanizing is relatively inexpensive among various types, while gold plating offers excellent corrosion resistance; however, its drawback is that it cannot maintain its luster for long. Parts intended for corrosion protection are often treated with galvanizing, such as antennas, chains, screws, nuts, steel wires, springs, etc. It is not suitable for parts subject to wear. 　　Chemical nickel plating for steel: Also known as electroless nickel plating, this method is well-suited as a substitute for traditional electroplated nickel processes. It is used for rust and corrosion protection on various iron-based metal surfaces, and it also enhances the aesthetic appearance of these surfaces, increasing their value. 　　The principle of chemical nickel plating for steel involves using a solution-based chemical reduction reaction to form a coating on the metal surface. 　　Its main features are: the surface of the metal after treatment is smooth, it is resistant to corrosion and wear, and uniform coating can also be achieved on objects with complex shapes. The hardness can reach above HRC 51, and through heat treatment it can reach HRC 70, thus replacing hard chromium plating. The film thickness can be required to be between 5 µ and several tens of µ. It has good adhesion and can be coated on iron, steel, copper, aluminum, ABS plastic, or ceramics. The friction coefficient is only 0.03 [1/3 that of hard chromium, and the same as that of cast iron]. High cost and short solution lifespan. The advantages and disadvantages compared to electroplated nickel are as follows: Advantages: It has few pores in the coating layer and a uniform thickness; it is thin but relatively hard, and can be used on non-conductive materials. Disadvantages: Slow deposition rate, contains phosphorus-boron compounds, low melting point, and brittle. Aluminum anodizing: Aluminum items are placed in a suitable electrolyte, with the metal acting as the anode. An electric current is used to create a protective oxide layer on the surface of the aluminum. The chemical reaction involved is roughly as follows: 2Al + 3O2 → Al2O3 + energy.
Powder coating: In powder coating, resin is ground into a powdered form as the raw material. Utilizing the principle of electrostatic attraction between opposite charges, the object to be coated is given a negative charge, while the powdered coating carries a positive charge and thus adheres to the object. The coating is then baked in an oven at 200°C for 5–10 minutes, causing it to melt and stick to the object. 　　Advantages and disadvantages of powder coating: Fewer environmental pollutants and lower risk: Since powder coating does not contain organic solvents, it reduces the risk of organic solvent poisoning among operators and prevents fires. 　　Good adhesion: Since solvent-based coatings require the solvent to evaporate first during film formation, this affects the chelating effect of the polymer film on metal, whereas powder coating does not have this drawback. 　　Reduce processing time and improve production efficiency: Traditional paint coating requires a setting time to allow the solvents to evaporate fully, whereas powder coating does not need this. 　　No primer is required: Powder coatings have excellent adhesion, so no primer is needed. The thickness per application can reach over 50μ, which is 2 to 3 times that of liquid coatings (15-20μ per application for liquid coatings), thus saving spraying time. 　　Low coating loss: Since powder coatings contain no organic solvents and have a 100% solid content, the coating that does not adhere to the surface being coated can be recycled, resulting in a coating loss of less than 5%. 　　Good corrosion resistance: Since powder coatings form a hard film made of polymers, and the substrate and the coating film undergo appropriate pre-treatment along with a proper heating process, excellent corrosion resistance is achieved. 　　Easy to operate: Operators do not require extensive training. 　　Reduce storage space: It can reduce the storage space required for organic solvents. 　　The hardness of powder coating can reach 3-4H (compared to 1-2H for liquid coating). 　　Powder-coated parts are not suitable for certain organic solvent environments.

It is an oxide film that forms as a result of surface oxidation, and it serves to provide some degree of corrosion protection. When steel undergoes surface oxidation treatment, a dense and thin layer of iron oxide is formed; depending on its color, this layer is referred to as ‘blueing’, ‘blackening’ or ‘bluing’. It can improve the corrosion resistance of steel in atmospheric and mildly corrosive environments. It is usually oxidized using an oxidizing agent under acidic, alkaline, or high-temperature conditions.