Why is 904L used in both SA-240 and SB-625?
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Both SA-240 and SB-625 contain 904L; their metal compositions and mechanical properties are the same. What is the difference between them? A equipment manufacturer mentioned that the former is easier to purchase while the latter is not; what affects the delivery time?
The whole issue is a bit strange; I hadn’t noticed it before. The Cr-Mo content of 904 seems to be around 25-22; it should belong to austenitic steel, so it is indeed classified under SA240. Then why is it listed under SB as well? Non-ferrous alloys?
The UNS code for 904L is N08904; its main components are those of a nickel-chromium-molybdenum alloy. This material was included in the earlier SB625 standard, but it was later removed from that standard and classified under A240. However, its chemical composition and mechanical properties remain unchanged. Therefore, it’s not easy to find 904L according to the old standard, while A240 materials are more readily available. The fact that its code is N08904 indicates that it was originally considered a nickel-based alloy. Materials starting with 8 belong to the nickel-chromium-iron alloy category and are of the solution-strengthened type. Perhaps because 904L does not belong to this category, it was removed from the relevant standards