The effect of chromium addition on the strain ageing and recrystallisation behaviour of low carbon steel

The strain ageing and recrystallisation behaviour of conventional low carbon A06 steel was compared with those containing varying amounts of chromium (0.26, 0.52 and 0.74 wt.%). The results show that the A06 steel undergoes four stages of strain ageing: (i) the pinning by solute atoms of dislocations generated during pre-strain, (ii) the generation of fresh dislocations from grain boundaries, (iii) the onset of precipitation and, (iv) the inhibition of dislocation generation from grain boundaries due to pinning by carbon segregation. On the other hand, the chromium containing steels only exhibit the fIrst three stages of strain ageing. An approximately twofold reduction in the rate of strain ageing was observed in the 0.74Cr steel as compared to the A06 steel. The above is directly attributed to the reduction of carbon concentration in ferrite due to the enrichment of iron carbides by chromium and to the formation of alloy carbides which slows their dissolution upon coiling. The addition of chromium signifIcantly delays the recrystallisation process and affects the morphology of the recrystallised grains by reSUlting in larger aspect ratios than A06 steel