Three different steels with the compositions given in
Table 1 were used for this work. These steels were made
in an air induction furnace and all the melts were
poured at about 1600°C, sound ingots being produced.
The ingots were then extruded to a size of about 16 mm
diameter, the extruded bars being cut into specimens of
size 10 mm10 mm8 mm for the carburizing operation.
The specimens were gas carburized in a sealed
chamber of a gas-fired gas-carburizing furnace for three
different time periods such as 1, 2, and 4 h at a constant
flow rate of 12 feet3 h1 (0.34 m3 h1) with about 15
psia (103 kPa) gas pressure and heat treated according
to the schematic diagram shown in Fig. 1. Amongst the
three steels, steel 1 is the base steel, with which the
structure and properties of the other two steels containing
Nb alone or in combination with nitrogen, were
compared.