These two figures (e.g., 18/12) refer to the chromium and nickel content in flatware. I thought nickel makes flatware brighter and more durable, and that 18/12 flatware is the “best” generally available. But a website makes another claim, which doesn’t make sense to me:
“The best stainless is the 18/8 which is constructed of 18% chromium and 8% nickel content. There is also 18/10 & 18/12. This contains 10% & 12% nickel. Nickel combats stains and lends flatware a brighter silver sheen.”
What’s up?
Basically you’re correct, and the website is misleading. There may be more to it than that however.
Stainless steels are rarely so precise in composition. For example, type 304L stainless steel, which would be suitable for flatware, has a specified chromium range of 18-20% and a specified nickel range of 8-12%, and so encompasses “18-8”, “18-10” and “18-12”.
The designations “18-8”, “18-10” and “18-12” are European specifications, and the differences in their appearance and corrosion resistance are marginal. However, the higher nickel grades are slightly more formable and so might be used for manufacturing reasons.
http://www.knight-group.co.uk/Stainless_Steel/tables/Austenitic-applications.htm
Another consideration is that different types of stainless steel have different microstructures, the three most common being martensitic, ferritic and austenitic. Austenitics have the best corrosion resistance, and so the statement “The best stainless is the 18/8” may have better been stated as “the best stainless steels are the austenitic grades.”
Slight hijack…
Why would you think that 304L would be the choice for flatware? L indicates low carbon content in the steel, and I see it used for fabrications that cannot be post weld heat treated. The Heat Affected Zone (HAZ) in 304L is less prone to corrosion than it would be with straight 304.
(A HAZ is the area adjacent to a weld where the melting and resolidifying of the steel causes various elements of the steel to come out of solution with each other to varying amounts and to form different structures. A metal piece can be reheated and cooled under precise conditions to eliminate HAZ if you can fit the whole thing in a heat treating oven.)
Or am I reading too much into what you wrote?
I wouldn’t! I used the L-grade as an example because it has a fairly wide specified nickel range (wider than plain old 304), to emphasise that 18-8, 18-10 and 18-12 are nominal rather than actual compositions.
(Continued hijack:
The problem with HAZs in austenitics is called “sensitisation” or sometimes “weld decay”. It occurs when the metal has a dwell time within a high temperature range (can’t remember figures off hand) which causes the chromium and carbon to combine and form chromium carbides on the grain boundaries. This locally depletes the metal of chromium, making a non-stainless network in the HAZs. The remedial heat treatment takes the metal hot enough to re-dissolve the carbides, and then you have to fast-cool or quench it to prevent them from re-forming.)