KB58 wrote:
I had a stainless steel diving knife - it rusted.
We have a stainless steel sink strainer - it's rusted on the welds.
I welded up a stainless steel process tank for our fish pond - it has rusty welds.
Stainless can and will rust if it's been welded.
Im a retired qualified boilermaker and have spent most of my days working with stainless and building ocean going sailing yachts.
For starters, you get stainless steel and stainless steel. The best is to use the 300 series and anything from L304 upwards will not rust on terra firma and in fact on fresh water. On yachts we used L316 and after 30 years on the big blue pond no signs of rust. It goes without saying that a certain grade of SS must be welded with same or better grade electrode - regardless of Tig/Mig or arc welding.
The best way to check if you are dealing with "real" stainless is a magnetic test. SS is a non ferrous metal and not magnetic. L304 will have a very faint magnetic pull and from L310 upwards non at all.
Now try this test with your knife, kitchen sink and you will find that the magnet sticks to them like now tomorrow and that means is is still a ferrous metal.
By the way, stainless is also very tuff and if you set a pressbrake to bend a 3mm mild steel plate of a given lenght to 90 degrees, the same thickness and lenght SS will only bend to about 75 odd degrees. Same with cutting, much more muscle needed on the guillotine.
Stainless steel is also about 620lbs heavier than steel per cubic meter.