Effects of cooling manner on Laves phase precipitation and mechanical properties of Al modified super ferritic stainless steels

Abstract

The solution treating and cooling experiments were conducted to study the microstructure and mechanical properties of Al modified super ferritic stainless steels with various cooling methods. The results demonstrated that the grain was characterized by the stratified distribution. The grain coarsened gradually with the decrease in cooling rate. And the surface grain coarsened obviously, Nb (C, N) particles were precipitated in the samples in different cooling manners. However, the Laves phase was distributed both at the grain boundaries and in the grains in the furnace-cooled specimen, and the area fraction of Laves phase increased significantly with the increase of Al content. With the cooling rate decreased, the yield strength, ultimate tensile strength and Vickers hardness of the Al-free samples increased, while the elongation decreased, and the furnace-cooled specimens showed brittle fracture during the tensile test. The addition of Al also increased yield strength, ultimate tensile strength and Vickers hardness and deteriorated plasticity of samples with different cooling manners. Meanwhile, the plasticity of furnace-cooled samples was more sensitive to addition of Al than water-quenched and air-cooled specimens. The analysis results showed that the plastic deterioration of furnace-cooled samples was mainly related to the coarsening of Laves phase at grain boundaries. Hence, the precipitation of large size Laves phase at grain boundaries should be inhibited in the process of industrial production.

Keywords

• Super-ferritic stainless steel
• Al additions
• Cooling manner
• Laves phase
• Grain size
• Mechanical properties