Early Quenya
yaisa
noun. steel
akse
noun. steel
yakse
noun. steel
anga
noun. iron
tongo
noun. iron
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A word appearing as ᴱQ. akse “steel” in the English-Qenya Dictionary of the 1920s (PE15/77), also appearing in its partitive form aksínen “of steel” in the Early Qenya Grammar of this same period (PE14/48, 81). Based on its partitive form as well as its adjective form ᴱQ. aksína, I believe its stem form would be aksi-.
Conceptual Development: In the Qenya Lexicon of the 1910s it was ᴱQ. Y̯akse “steel” (QL/105), while in the contemporaneous Gnomish Lexicon it was {yakse >>} yaisa “steel” (GL/37).
Neo-Quenya: For purposes of Neo-Quenya I would stick with ᴺQ. axë (axi-) “steel” based on the Neo-Root ᴺ√GAK. This “steel” word does conflict with the later word Q. axë “neck” (PE17/92), but I think a stem form of axi- makes it sufficiently distinct. However, if you are uncomfortable with this, the later word tornanga “hard-iron” might also be used for “steel” (PE17/56).