Phosphorus in Steels

Phosphorus in Steels  Phosphorus (P) (atomic number 15 and atomic weight 30.974) has density of 1.82 gm/cc. It has a melting point of 44.1 deg C and boiling point of 280 deg C. The iron (Fe) – P phase diagram is shown in Fig 1. Fig 1 Fe- P phase diagram P is normally considered an undesirable impurity in steels. It is present in varying concentrations in iron ore, is retained in hot metal, but is eliminated early in the steelmaking process. P oxidizes readily and is removed from steel as P2O5, which is taken up by the oxidizing slag, before the oxidation of carbon takes place. Carryover of any P2O5 containing oxidizing slag can result in P reversion to the steel in subsequent steelmaking operations. In normal commercial steels, residual P content is usually  at a level of 0.05 % max, but concentrations as low as 0.005 % are not unusual. P is readily removed only in basic steelmaking processes. Acidic processes must therefore begin with low P raw materials. It was the ability to remove this element that led to the widespread adoption of the steelmaking by the basic open hearth, electric arc furnace, basic Bessemer converter and subsequently basic oxygen furnace (BOF) processes. P is sometimes added intentionally to the steel to improve strength, machinability and atmospheric corrosion resistance. P is added to the steel in the form of ferro-phosphorus (Fe-P), containing 23 % to 26 % P. Fe-P fines are usually briquetted, after using a binder. Fe-P is capable of oxidizing the residual silicon to silica, thus enabling it to float out to the ladle slag during steel making. The intent is to reduce the concentration of residual siliceous inclusions, which are detrimental to machinability. Fe-P is normally added to the...

Metal Coatings of Steels Sep18

Metal Coatings of Steels...

Metal Coatings of Steels  Metallic coated steels are defined as a steel substrates coated with a layer of zinc, Zn/Al (zinc/aluminum) alloy, Zn/Si (zinc/silicon) alloy, or pure Al etc. The schematic arrangements of metal coating structure with and without passivation is shown in Fig 1, Fig 1 Metal coating structure with and without passivation  Metal coatings of steels enhance the life and the performance of the steels. They provide the most effective and economical way of protecting steels against corrosion. Metal coated steels offer unique combination of properties which include high strength, formability, light weight, corrosion resistance, aesthetics, recyclability and low cost. There are several processes for metal coating of steels as given below. The hot dip coating process, whereby the steel strip is immersed in a bath of molten metal. The composition of the molten metal (Zn, Zn/Al, Al/Si, or pure Al etc.) determines the nature of the metal coating. The electro-galvanizing process, in which metal is deposited electrolytically on the cold steel strip. Coating under vacuum, such as PVD (physical vapour deposition), CVD (chemical vapour deposition) etc. Hot dip coating processes are the most popular processes for the metal coating of steel strips. Normally continuous coating lines are employed for the production of the metal coated steel products. Metallic coated steels produced in continuous coating lines have experienced a remarkable growth and continues to be used in increasingly varied new fields. This is due to their outstanding economic, technological and environmental advantages. .The wide range of metallic coated steel products available today meets the requirements of all sectors. The following are the parameters which govern the choice of the metal coated steel material. Quality or grade of the steel substrate Type of metal coating Mass or thickness of the metal coating Surface...

Colour Coating of Steels Sep14

Colour Coating of Steels...

Colour Coating of Steels  Colour coating is a term used to describe the application of a decorative and/or protective organic coating to steel substrate supplied in coil form. Colour coated steel is also called as pre-painted steel. Colour coatings are paint coatings and are specialty products, which are used to give the steel a long term protection under a broad range of corrosive conditions, extending from atmospheric exposure to full immersion in strongly corrosive solutions. A colour coating provides little strength to the substrate steel, yet it protects the steel so that its strength and integrity can be maintained. Colour coating of steel is a continuous and highly automated industrial process for efficiently coating of coils of steel. In this process of application of colour coating, the substrate steel gets protective and decorative coating. This process of colour coating is also called a duplex coating. The process of colour coating of steel according to EN 10169:2010 is a ‘process in which an organic coating material is applied on rolled metal strip in a continuous process which includes cleaning, if necessary, and chemical pre-treatment of the metal surface and either one side or two side, single or multiple application of (liquid) paints or coating powders which are subsequently cured or / and laminating with permanent plastic films’. The first colour coating line was started in Europe during 1940s. It became immediately very popular due to its basic inherent advantages which are given below. Higher productivity A highly sophisticated and computerized controlled coating application Environmental benefits and energy saving More consistent properties of the coated sheets Lesser wastage of coating material Colour coating usually refers to the application of liquid paint coat over the substrate in an automatic, continuous process after pre-treatment. The pre-painted colour coated steel is a...