Epic simile, also known as Homeric simile, is a comparison of something using similes that have many lines, not just a couple of words. Here, the use of the epic simile in this excerpt helps the reader understand how hot the spear actually is.
The narrator mentions screeching steam while making a sword, or something like that, when you put a hot piece of metal into water to cool it down, there is a high pitched sound followed by steam.