Flatten and twist

When you have a reasonable taper of a square section, you can beat it on the flat surface to make is more or less round, then work the round section into something with the number of sides you want. If that was four I have just led you down the garden path and you will have to work it back into square again.

A light hammer with a nice polished surface and if possible rather longitudinally well developed should do you well. A hammer with a long head holds its course a lot better than something stubby and fat, which can spin about easily.

The lower picture shows the twisted taper. You start with the fattest part as that will take more heat to twist. I have made orange blobs along the side of the bar to indicate roughly the area heated for each twist and counter twist. Six successive heats for this little section.