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Untreated Valve |
Mechanical Polishing |
Electropolishing |
Finished Valve |
Why treat stainless steel surfaces?
In order to obtain desirable aesthetic and technically functional surfaces finishes on stainless steel the following processes are carried out:
Mechanical
Chemical
Electro-chemical
Stainless Steel or Not?
As referred to in the Stainless Steel section the name “Corrosion Resistant Steel” would be a more appropriate name used for this group of materials. The stainless steel section details methods in which the materials are formed, alloying elements and applications. In particular, the methods of fabrication, manipulation and induced heat treatment greatly affect the material in its performance, especially when referring to the supplier technical data for any specific material, many of which are surface properties.
When heat or stress is put upon a material surface the characteristics of that surface is often changed and therefore the properties and performance of the material are change, usually reducing the performance below the desired levels as required when specifying a particular grade.
Materials are chosen for their specific performance data, which is often critical to the application of the end product. Therefore should this performance be reduced than the product may not be “fit for its purpose”. In this section we try to show you how these changes are made within the manipulation, fabrication and welding processes. Manipulation & Fabrication
By bending, forming, pressing, drilling and cutting we are introducing cold working, tearing, shearing and stress that change the surface properties of the surface. Care must be taken not to cut the material too quickly, inducing too much heat and not to over manipulated through fabrication techniques.
Welding & Heat Treatment
When welding and heat treatment takes place many things occur in the structure of the material, depending on the temperature achieved through the process. The material local to the weld site is taken into the full melting stage and the surface is oxidised, forming a scale depending on the atmosphere or shielding method. These surface oxides do not have the surface properties of the base materiel and subject to attack and corrosion. Often non metallic elements within the alloy do not fully re-dissolve back into the base material. A remarkable loss of the original properties may be encountered by this process.
We must remember that most of the materials within the group none as “Stainless Steel” contain at least 70% iron and therefore surface oxides containing iron readily corrode within most atmospheres. These oxides should be removed by methods that do not induce further complications.