Kinetics and Microstructural Control

· Additional elements added to a steel alter the transformation curves. The C-C-T diagram for a 4340 low alloy steel is shown.
· The 4340 alloy has the composition:
Fe - 0.40 wt % C - (1.6 to 2.0 wt % )Ni - (0.4 to 0.9 wt % ) Cr - (0.2 to 0.3 wt %) Mo.
· The pearlite and bainite "noses" are now distinct and shifted to longer times than for the plane carbon steel. Bainite is formed in the C-C-T process.
· The M_S temperature is the same as for the 1080 carbon steel

From: Callister, "Materials Science & Engineering," Wiley (1994)