Microstructural Evolution of Bassar Steel during Forging Process

Forging was used by smiths to make products such as kitchenware, hand tools, edged weapons and jewelry. Kabiye smiths in Togo (West Africa) used hammer and anvil to produce traditional objects onto desired shape and size. Long time ago, only Bassar steel was used as a raw material. Nowadays, the steel parts resulting from metal recovery were widely used as raw materials due to their low cost and easy availability. But the final users prefer forged objects produced with Bassar steel. However, microstructure evolution of Bassar steel during traditional Kabiye forging process and its influence on mechanical properties of forged products remains an outstanding issue. The present study investigated the microstructural evolution of the Bassar Steel during the traditional Kabiye forging process at laboratory scale. Some pieces of Bassar steels ingots were subjected to a series of annealing followed by hot rolling in the laboratory. To follow microstructure evolution, samples were taken at different stages: after cold rolling, the first annealing-rolling, the first annealing-rolling-annealing, the fifth annealing-rolling and finally the fifth annealing-rolling-annealing. The microstructure and mechanical properties of the last annealing-rolling-annealing sample were then compared to the traditional forged one. The results showed that the repeated cycles of annealing-rolling operations progressively homogenize the microstructure of the sample. The brittle cementite phase present in the BS pearlite phase is the key element that allows the forging operation to be effective. The last annealing-rolling-annealing yielded equiaxial grain structure similar to the traditional forged one. However, the size and distributions of inclusions were different from one sample to another. Both samples had similar mechanical properties except for the ductility. The laboratory annealed-rolled sample showed very low ductility compared to traditional forged one.