Steels continued carbide precipitation

Edm] Edmonds, D.V., The Strengthening of an C-Fe-V Low-Alloy Steel by Carbide Precipitation during Continuous Cooling from the Austenitic Condition , Metallurg. Trans., A, 4(11), 2527-2533 (1973) (Morphology, Phase Relations, Experimental, Meehan. Prop., 19)... 

One final test was conducted on a heat treated sample to elucidate the effect of heat treatment and sensitization on the fracture behavior of this steel. A CF sample was heated for 24 hours at 650°C to see if the fracture mode would continue to change with an even larger amount of carbide precipitation. Note in Figure 15-a this heavily sensitized steel has a fracture appearance that is completely dominated by small microvoids associated with carbides. The bimodal distribution of microvoids like those in Figure 7 has been eliminated. In fact, the fracture appearance is remarkably similar to that of the tritium-exposed-and-aged steels albeit at a different magnification (Figure 15-b). It appears that carbides in the microstructure affect the fracture mode in a similar manner as the decay helium bubbles but on a different scale. 

An example of weld effects is shown in Fig. 6. Four different 18Cr-8Ni stainless steel panels were joined by welding and were then immersed in a solution of nitric-hydrofluoric acids. This solution produces rapid attack on grain boundaries containing chromium-rich carbide precipitates, which are surrounded by chromium-depleted zones. The attack is similar to that shown in Fig. 3. Dislodgement of grains in the weld-decay zones leads to the formation of grooves on both sides of the panel of Type 304 (about 0.06 % C) steel that are parallel, but not adjacent to the weld bead. If immersion had been continued, the panel would have dropped off from the assembly. 

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