Not true, the SKS and the AL-47 were design when the Soviets were still using brass. They didn't go full steel until the mid-1950s.
After doing a bit of checking, the situation is a bit more muddled and I was wondering if you had a source for your note.
As far as a quick check via the internets, I checked sources and subsequent posts and the Russians apparently did use steel for their 7.62x54r during WWII and at least the technical sources tend to agree with the ammo specialist folks that the m43 was a bimetallic copper washed case from the get go after design approval. That would indicate that the SKS and the AK would have been designed to use that cartridge. Where the confusion might be is that the Russians apparently switched to lacquer coating in the mid 50's according to those sources below from copper washed steel.
This where I got that from,
https://forums.gunboards.com/showthread.php?378246-Steel-Cased-Ammo
And, it is clear that the Russians used copper washed steel ammo during WWII for the 7.62 x 54r
https://forum.cartridgecollectors.org/t/1945-dated-soviet-7-62x54r-question/2927
Now wikipedia, tells me that the original winning design of the m43 cartridge was copper washed steel, "The 57-N-231S cartridge used a "bimetallic" (steel and
copper) case. " and their source was
https://military.wikia.org/wiki/7.62×39mm which says the same thing.
Now, what happened between the m43 cartridge during development might have had several variants but given the difficulties involved in setting up steel case production in the US, the Russians might have had something similar going on before adopting the final version. So it might very well be that the SKS was originally developed with brass cartridges but converted to steel somewhere before 1947 while the AK apparently was designed conjunctly with the steel cased ammo.
The AK files has a post with a translated Russian history of the cartridge from which most of the stuff on the internet was derived from maybe, for those that are interested.
Money quote, "Initially the 7,62 x39 cartridge manufactured only with bimetallic shell - steel clad tombac. But in 1948, owing to difficulties in obtaining the bimetal, the bulk of which is mainly supplied from the United States for lend-lease, machine sleeve chuck latunirovannoy were made of steel. Process latunirovaniya brought in German industry, was associated with the use of potent poisons. Therefore, with the development of production of bimetal with the Soviet Union in 1952, automatic liner again made from this material. Subsequently, in early 1960, the number of enterprises has been the production of steel and lacquered shells (coated with varnish green), which provided significant savings tombac. Even in our time, production of steel shells with a polymeric coating (water-polymer solution), which significantly reduced the harmful production. "
This was a computer translation by an AK files member of the original Russian Source document that is floating around. Did not want to open that puppy directly on my computer.
https://www.akfiles.com/forums/showthread.php?t=54080