Laser engraving stainless steel removes important protective layers. In fact, any method of digging a mark on a surface (deep or shallow) will remove this layer.
This thin protective layer consists of chromium oxide. Chromium oxide is naturally formed when chromium reacts with oxygen. This process is an ideal form of oxidation known as passivation. The resulting layer prevents corrosion by preventing oxygen from reaching the steel below.
When this layer is removed, the oxygen causes a chemical reaction on the bare steel. This reaction is called oxidation. The result is rust, which creates weak points that gradually destroy the material. This happens when you mark stainless steel by laser engraving or laser etching.
Note that laser etching and annealing of stainless steel are sometimes used interchangeably.
Stainless steel must be laser annealed, not engraved
To create marks such as logos or Data Matrix codes on stainless steel, you need to rely on a technique that does not remove the chromium oxide layer from the surface.
For such needs, there is only one technique to leave permanent marks directly on stainless steel. This technique is laser annealing and can be done using a metal laser marking machine.
Laser annealing chemically modifies the steel beneath the chromium oxide layer. For this, the surface is heated until it temporarily melts. During this brief time span (milliseconds), oxygen moves below the surface. This produces the desired and controlled form of oxidation subsurface.
what's the result? As the surface cools and solidifies, the surface color changes due to oxidation. This color is usually black, although many colors can be achieved. The resulting marks are beautiful, colorful and permanent.
Most importantly, no material is removed from the surface (as opposed to laser engraving, which ablates material). This means that the protective layer is not affected and your parts will not rust.
