Only manganese steel (used mainly by Commonwealth countries, the USA and after 1923, France) is non magnetic. Great War German helmets are made or nickle or nickle-chrome steel alloy, Second World War helmets were made of nickle-chrome-molybdenum, or later when some of these metals became scarce, nickle-silicon. Look at the Irish M27, it's non-magnetic but weighs only 1 kg compared to 1.25 kg for an equivalent German Stahlhelm. That's because Vickers used manganese steel, which has to be cold-pressed, and for such a deep-draw helmet had to use a thinner gauge of steel than the Germans did - hence most surviving M27s have more than their share of dents.
Roger
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