Must of the really high quality alloy steels are what is called vacuum degassed. The 'heat' (what a batch of steel is called) is first melted in an electric furnace. Once the chemistry is gotten to an acceptable level it is tapped out into a special ladle at a very high temperature, somewhere close to 3100 degrees. It has to be that hot because the next step. The special ladle has a machined surface that sits on top of a large O-ring at the top of a large sealed tank. In the tank is another ladle to catch the finished steel. The tank has been sealed and almost all the air has been pulled out of it creating as close to a total vacuum as possible. The steel is then poured out of the bottom of the ladle, through the vacuum into the final ladle. While the final pour is happening, additional alloying stock is added to get the chemistry to the proper level. The vacuum causes the stream to flare and any dissolved gases to be pulled out thus creating a very clean, fine grained steel.
Back in a prior career I used to work for US Steel in a steel producing shop. We made some fancy steels and some tie plate stuff too. It just depended on what the Production Planning department wanted. All the 41xx, 51xx, and 86xx steels were degased. The fanciest steel we made was HY80 that was used for Trident submarine hulls. We also made about 4 kinds of stainless.