2.3. Pressure carburizing procedure
For the PC process, only the thermo-mechanically treated specimens
were used. Upon the same sample preparation methods as in
conventional carburizing, the specimens were arranged inside a
clamp, as shown in Fig. 1b. It can be seen that the carburizing powders
were filled completely within the center hole of the clamp. An
initial pressure of 74 MPa was applied on the specimens by tightening
the screws and nuts of the clamp using a torque wrench. The pressure
was applied in order to superplastically deform the surface
asperities of the material. Both processes were performed in a tube
furnace under a controlled atmospheric condition at a temperature
of 1223 K for 4 h. Finally, the specimens were air-cooled to room
temperature.