Everything you need to know about working with Stainless Steel
Everything you need to know about working with Stainless Steel
Everything you need to know about working with Stainless Steel
What is stainless steel?
Stainless steel, or inox, as it's often known, is one of the most commonly used materials in the metal-working industry. Stainless steel refers to a specific group of metal alloys renowned for their corrosion resistant properties. Specifically, steels are iron-based alloys and can only be defined as "stainless" if the Chromium content of the alloy is higher than 11% - this high chromium content not only lends the steel resistance to corrosion, but also gives the metal a higher durability under heat.
In the metal-working industry, there are four key raw states, or mill finishes, which are the standard supply for all flat stainless steel products, and form the basis for subsequent finishing processes.
1d
Hot rolled and annealed with mill scale removed. This is a coarse finish, used in applications where cosmetic appeal is not a priority. This is widely known as a "rough finish".
2d
Formed by cold rolling, heat treating and pickling, this low reflective surface is suitable for a wide range of applications where appearance is not a priority.
2b
This is a 2D finish which has been light rolled using highly polished rolls for a smooth and reflective sheen. This forms the basis for most polished and brushed surfaces.
2r
In a further step to cold rolling, the steel undergoes bright annealing under oxygen-free conditions. This produces a smooth, shiny and reflective surface.
Selecting the right mill finish
Choosing the right mill finish as a starting point for your application will greatly affect the number of additional finishing processes you will need to apply to the metal. Getting a mill finish as close as possible to your required end finish will reduce the number of mechanical or manual finishing steps needed.
There are four common mechanical finishes found today in the industry:
Mechanical Finish
Characteristics
Abrasive Mechanical Steps
Mill finish required in raw material
No.3
Also known as a linear finish, this is characterised by coarse parallel polishing lines.
Begin with 50-80 grit abrasives, then finish with finer 100-120 grits. Belts, flap wheels and Satinex wheels are most commonly used to achieve linear polishing lines
Mill finish #1, 2D or 2B
No.4 - Standard sanitary grade or high grade sanitary
This is the most common finish and is a uniform, finer version of a no.3 finish
Depending on the requirements, the final finishing can be anything from 150-230 grit, after following the steps to a no.3 finish above.
Mill finish 2B or 2D
Satin Polished
This is the smoothest of the non-reflective finishes. The average Ra should be less than 0.5 across the workpiece
The smooth surface is achieved by working up towards a 320 grit grade, or working through hard to soft density non-woven abrasives
Taken from a No.4 finish
1p/ 2p -bright buffed and bright polished
A very high quality cosmetic and reflective finish
Achieved by working with a satin-polish and applying further polishing steps
Taken from a satin finish
What is "Roughness Average"?
Measuring the surface roughness of stainless steel is a way to measure the quality of the finished piece. The surface roughness of your material plays a crucial role in the end performance of your workpiece.
A rough surface will be more susceptible to contamination and corrosion than a smoother surface. Measuring and evaluating the surface roughness is important in all applications, but is especially crucial in the medical, pharmaceutical, sanitary and food industries.
There are many ways to measure surface roughness, but the most common is roughness average (Ra). Ra is the arithmetic average of the profile heights over the evaluation length (L) - more simply, it is the average of all the miniscule peaks and troughs in the metal's surface. The graph on the right gives an example of what a roughness average reading might look like - imagine the dotted line is the visible surface of your stainless steel piece, yet under a microscope, you would actually see millions of peaks and troughs (the blue line) on what might appear to be a perfectly smooth surface to the naked eye.
Why is roughness average important?
The surface roughness will determine how the object reacts and interacts with its surrounding environment once produced. If, for example, a stainless steel piece of outdoor furniture has a rough surface (a high Ra value, meaning there are higher peaks and troughs in the surface), then contaminants in the environment will become engrained in the peaks and troughs of the surface, leading to corrosion.
A smoother surface (smaller peaks and troughs), means that there is less chance of contaminants sticking or becoming trapped in the surface.
Common Stainless Steel finishes and how to achieve them
Achieving a mirror finish with a right angle grinder
