Smelting steel is referring to the act of - just what it means - smelting steel. It requires a higher level of heat to smelt steel than it does iron.
Today, steel is one of the most common materials in the world, with more than 1.3 billion tons produced annally. I mean, annually.
Smelting steel is often found in MMORPGs usually in the fantasy genre. It is possible to smelt steel in Minecraft and also in RuneScape, requiring level 30 to do so.
Lastly, "smelting steel" is also a slang term for sexual intercourse between two guys because it's more refined than "smelting iron." This bit of slang is very uncommon but is sometimes used by teenagers to avoid having to say 'sex.'
1. Smelting steel is a long process and creates excellent building material.
Guy1: Smelting steel is a good way to make cash in RS, I just made 1k of them and turned them into cannonballs! I made 400k cash, dude!
Guy 2: Lmfao, 400k sucks. Bot frost dragons and then you'll make some real money.
Guy 1: Where's everybody else?
Guy 2: Well, Jess couldn't come to the meeting because at Sea World and you-know-who is too busy smelting steel with Joey.
Guy 1: WHAT!