Comparison of Microstructure and Mechanical Behavior of the Ferritic Stainless Steels ASTM 430 Stabilized with Niobium and ASTM 439 Stabilized with Niobium and Titanium

The use of Ferritic Stainless Steels has become indispensable due its lower cost and the possibility to replace austenitic stainless steels in many applications. In this study, cold rolled sheets of two stabilized ferritic stainless steels with 85% thickness reduction were annealed by applying a heating rate of 24 oC/s and a soaking time of 24 s. The niobium stabilized ferritic stainless steel type ASTM 430 (430Nb) was annealed at 880 oC while the niobium and titanium bi-stabilized steel ASTM 439 was annealed at 925 oC. The annealed samples were tensile tested and due to the smaller grain size, steel 430Nb, showed a higher yield stress and a higher total elongation. Concerning drawability the steel ASTM 439 presented a better performance with higher average R-value, lower planar anisotropy coefficient and a greater value for Limit Drawing Ratio (LDR). These results are explained in terms of the differences in size and volume fraction of precipitates between the two steels.