431 – Heat Vision!

Superboy uses his heat vision for the first time in Superboy #5, September 1949
Superboy uses his heat vision for the first time in Superboy #5, September 1949

In Superboy #5 (Sept 1949), for the first time, Superboy concentrates his x-ray vision into heat vision to melt a bullet. The bullet was meant for a girl named Lucy from Borgonia, who is a top athlete visiting Smallville. She ends up helping Superboy and being dubbed Supergirl:

The first character to be named Supergirl in Superboy #5, September 1949
The first character to be named Supergirl in Superboy #5, September 1949