These machine screws are made from A4 (AISI 316 grade) stainless steel.
The most common grades are AISI 316 (A4) and AISI 304 (A2). Generally, onboard we select A4 because it has the greatest corrosion resistance. However, it is weaker than A2 which is generally selected for architectural work.
The corrosion resistance of stainless steel relies on the surface oxidation. If air is not present the oxidation can not take place. For this reason, bolts made from stainless steel passing through damp timber can be prone to severe corrosion and are best avoided.
Another problem with stainless steel is its tendency to cold weld. A bolt made of stainless steel can suddenly seize up. Don’t apply more welly, because once the threads have seized you have had it, and the fastening will need replacing.
Applying a little Lanoguard to the thread before assembly will help prevent "cold welding". Do NOT apply Lanoguard, or any grease, if you are tightening to a specific torque as the grease will affect the torque setting.