FOR INTERNAL USE ONLY
5.1
CARBON EQUIVALENT (CE) & WELDABILITY
Depth of hardening is not a relevant concept in a welding situation, but we are interested in the hardness produced at a given cooling rate or the critical cooling rate to produce a given hardness in the HAZ of a weld. There are several models that have been developed to calculate hardenability from a welding process. The simplest model is one in which the effects of individual alloying elements are added together (a linear model) to produce a carbon equivalent (CE) which in turn relates to a critical cooling rate to produce a given hardness. Figure 35 shows a reasonable correlation between the CE plotted against critical cooling rate from 540째C to give a hardness of 350Hv in the HAZ.
Figure 34
Linear Correlation of CE and Cooling Rate for a Fixed HAZ Hardness
Another linear model has been used to predict the hardness of the HAZ for different cooling rates in low alloy steels and is illustrated in Figure 36.
Hv@50deg/sec
1400
Hv@100deg/sec
1200
Hv@200deg/sec Hv@500deg/sec
Hv
1000 800 600 400 200 0 0.62 WELDING AND COATING METALLURGY2
0.72
0.82 CE
0.92
1.02 28 of 69