Stainless Steel Fabrication – Grades of Steel
Stainless steel fabrication is done for making a range of products like automobile parts, medical equipment and instruments, frames, furniture items, grills, railings, brackets, panels, sinks, utensils, bathroom and kitchen accessories, lab equipment, many other products and welding of pipelines for industrial and other applications.
The stainless steel used for fabrication has different grades. All grades of Stainless Steel (SS) possess different mechanical properties that allow only a few selected grades easier to fabricate. Most commonly used grades are 316 L and 304 L.
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The austenitic stainless steel grades have the ability to be fabricated using all the standard fabrication processes. The common austenitic SS has high ductility and can be bent, folded, cold and hot forged, spun, deep drawn and roll formed. Austenitic SS work hardens very rapidly; as such the operations require more force and heavier machines. Grades 301, 302 and 304 can be cold drawn. But, higher tensile properties are mostly limited to thin sheets and fine wire sizes. With the increase in the size, the material gets work-hardened. In some forming operations, it may be necessary to soften the parts by annealing for further processing.
Free-machining Grade 303 is preferred for making machined parts . 430F and 416 are other free-machining grades.
The stainless steel raw material for fabrication is available in different shapes and sizes including sheets, plates, flats, wires, rods, rounds and solid profiled sections and hollow round , rectangular and square tubes.
Fabrication of different products includes the production of their parts employing different processes such as cutting, bending, shearing, welding, grinding, polishing and assembling. The cutting can be done with a chisel and hammer or shears manually or with metal saws, power hacksaw, shears, press brakes, and using gas cutting, gas welding cutters, oxy-fuel, plasma torches and laser cutting equipment etc.
The stainless steel wires, rods sheets and pipes are formed into different shapes in cold condition with bending and forming jigs on different machines. Both manual labor and machines are used for fabrication work. Rolling machines are used to form round shapes from the plates. You may need to straighten the warped metal also.
A number of parts are manufactured using power presses for use in fabrication. Power presses are mostly used for making parts from sheets and plates by cutting, piercing, blanking, bending, forming and drawing operations .
A few round shaped parts may be manufactured on lathe machines by the turning and further machining operations. Drilling is a very common operation in fabrication work. Finally, the parts produced by various operations are assembled together by fabricators to make sub-assemblies and final products. In fabrication most of the assembly work involves welding. Different types of welding done for stainless steel fabrication are Gas Tungsten Arc, Plasma Arc, Shielded Metal Arc, Gas Metal Arc, Flux Cored Arc (MIG), Submerged Arc, and Electric Resistance Welding.
A few parts are also joined by brazing and soldering as a well. The parts are assembled using binding, fasteners and rivets besides welding process.
The weldabilities of the different grades of stainless steel considerably varies. Nearly all grades can be welded. The austenitic grades can be easily welded. Special welding electrodes are used for welding of SS. Mostly, the common welding methods can be employed. A complete range of different welding consumables is easily available for use with standard equipment.
It is recommended to make use of special-alloyed austenitic welding electrodes to weld together different grades of SS, or with other materials.
It is also possible to solder all grades of SS with a lead-tin soft solder. However, leaded solder is not to be used in food processing or serving products. Soldered joints are weaker and can be used only where low mechanical strength is needed. Where welding cannot be done, brazing can give stronger joint using silver.