Steel Hardening Methods

Company develops affordable compound liner-clad pipe range

Industrial large-diameter-pipe producer Erndtebrücker Eisenwerk (EEW) has, in a recent project with its research and devel- opment (R&D) team, been working on producing a new economic type of clad pipe, the compound liner-clad (CLC) steel pipe.

It is undertaking the project in conjuction with global synthetic and formulated polymer systems supplier Huntsman Advanced Materials and its distributors in Germany, Bodo Möller Chemie.

The idea behind the CLC pipe was to produce a budget-priced product providing additional technical advantages to simple liner-clad pipes, while serving to close the quality gap between metallurgically bonded clad pipes and liner pipes.

It was decided that the company’s standard facilities for pipe production would be used to create a composite plate compounded out of a carbon manganese (CMn) steel plate and a corrosion-resistant alloy (CRA) sheet, bonded together with a high-performance epoxy.

The challenge lay in identifying an epoxy adhesive that could enable the cladding of steel plates with all commonly used grades of CRA sheets, prior to forming and welding the heavy composite-clad plates into pipes.

EEW followed the principles of lean engineering in selecting single package system epoxy adhesives to include in a series of rigorous tests designed to assess differences in break strength and elasticity.

After the company has assembled the composites for testing, the adhesives were hardened in a hot press at 180 °C and differences in the resistance to shear and tensile forces were observed. For most of the products, disbonding occurred with some of the composite samples showing significant signs of breakage.

However, one of the adhesives, the Araldite AV 4600 emerged as the preferred adhesive, because of its ability to form a strong and durable joint without any signs of disbonding and displaying the highest shear strength values of all products tested.

“The stress in compound cladding often reaches maximum levels owing to bending or shear force. A bonding solution that helps enhance performance and prevents issues such as inner buckling of the pipe is critical,” says EEW R&D leader Markus Bockelmann . “Araldite AV 4600 proved to be ideal for this application in providing the strength needed to withstand both bending in production and the shear and tensile stresses that the pipe would be subject to in offshore applications,” he says.

Case Hardening - Methods to Harden a Steel Body - Heat Treatment's ...

It is very important to harden the steel body after it is annealed and Case Hardening is one of the methods to harden a steel body. The process which is used while Case Hardening is to add Carbon to the outer surface of the steel body and this means that the inner core is left untouched and the steel body retains its properties like flexibility, malleability and ductility. Case Hardening is a method which is used for steel bodies which are less in Carbon content. It is less difficult than tempering and other methods of hardening a steel body.

Let’s take a look at the procedure. The steel is heated till it is red hot. First it is heated on one part of the steel body and it is concentric on that particular part so that the hardening takes place quickly. In the next stage the steel body is covered with carbon and then kept in a brazen hearth. After this the steel is removed from the brazing hearth with the help of a blacksmith’s tong and then the whole case is kept in as a hardening compound being allowed to cool off. The outer covering of the compound is high in Carbon.

Stage three of Case Hardening involves heating the steel body one more time until it takes a red colour and then once again removed from the brazing hearth and kept in cool distilled water. Now, the steel body will have a hard outer covering and a soft interior which is flexible, malleable and ductile. If you want to increase the hardening of the steel body then you will have to repeat this process again and again so that the case gets hardened even better.      

Case Hardening is also known as Surface Hardening and the material’s surface is inducted with different materials by which a thin layer of a harder alloy is formed and as it takes a final shape then process of hardening is also increased till it is given a pattern welding and this technique is also discussed with modern armour. For example a revolver showcases different shapes and colours of Case Hardening and the shine provided is also due to Case Hardening.

There are different types of Case Hardening that takes place at different levels. Say for example Flame and induction harden Carburizing, Nitriding, Cyaniding, Carbonitriding and Ferritic Nitro Carburizing. Flame and induction hardening is a process in which the surface of the steel body is heated to high temperatures by keeping the steel body under the influence of a flame and then finally cooled rapidly using cold water. This process creates a layering of Martensite on the surface of the steel body. This generally involves a Carbon layering of about 0.4 to 0.6 % and then hardened with Flame and induction hardening process. Now, this process is used to make a shackle of a lock, mechanical surfaces, and hard gear mesh surfaces which will give a longer service life and also maintain its durability and toughness.

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