Forming, fabrication and joining techniques

Depending on their type and heat-treated condition, wrought stainless steels are formable and machinable. Stainless steels can also be cast or forged into shape.
Most of the available types and grades can be joined by use of appropriate 'thermal' methods including soldering, brazing and welding.

Austenitics are suitable for a wide range of applications involving flat product forming (pressing, drawing, stretch forming, spinning etc).
Although ferritics and duplex types are also useful for these forming methods, the excellent ductility and work hardening characteristic of the austenitics make them a better choice.

Formability of the austenitic types is controlled through the nickel level.
The 301 (1.4310) grade which has a 'low' nickel content, around 7% and so work hardens when cold worked, enabling it to be use for pressed 'stiffening' panels.
In contrast nickel levels of around 8.0% make the steel ideally suited to stretch forming operations, for example in the manufacture of stainless steel sinks. Higher nickel levels around 9.0% are required for deep drawing.

Martensitics are not readily formable, but are used extensively for blanking in the manufacture of cutting blades.

Most stainless steel types can be machined by conventional methods, provided allowance is made for their strength and work hardening characteristics.
Techniques involving control of feed and speed to undercut work hardening layers with good lubrication and cooling systems are usually sufficient.
Where high production volume systems are employed, machining enhanced grades may be needed.
In this respect, stainless steels are treated in similar ways to other alloy steels, sulphur additions being the traditional approach in grades like 303 (1.4305). Controlled cleanness types are now also available for enhanced machinability.

Most stainless steels can be soldered or brazed, provided care is taken in surface preparation and fluxes are selected to avoid the natural surface oxidising properties being a problem in these thermal processes.
The strength and corrosion resistance of such joints does not match the full potential of the stainless steel being joined, however.

To optimise joint strength and corrosion resistance, most stainless steels can be welded using a wide range of techniques.
The weldablity of the ferritic and duplex types is good, whilst the austenitic types are classed as excellent for welding. The lower carbon martensitics can be welded with care but grades such as the 17% Cr, 1% carbon, 440 types (1.4125) are not suitable for welding.