Optimization of milling parameters for the synthesis of nano-structured duplex and ferritic stainless steel powders by high energy planetary milling

• Duplex and ferritic stainless steel powders were prepared by DDPM for 10 h.
• Effects of PCA, BPR and milling speed were studied successfully.
• Increase in BPR from 6:1 to 12:1 enhances phase transformation from α-Fe to γ-Fe.
• PCA like SA can decrease the particle size but the shape of the powder is irregular.
• Higher mill speed gives highly refined and spherical stainless steel powders.

Nano-structured duplex and ferritic stainless steel powders were prepared by high energy planetary milling of elemental Fe, Cr and Ni powders. Here, we have studied the effect of process control agent (PCA) such as stearic acid (SA), effect of ball to powder weight ratio (BPR 6:1and 12:1) and milling speed (64% and 75% critical speed) during planetary milling of elemental Fe–18Cr–13Ni (duplex) and Fe–17Cr–1Ni (ferritic) powders for 10 h in a dual drive planetary mill (DDPM). We have found that all these milling parameters have great influence in tuning the final particle morphology, size and phase evolution during milling. It was found that addition of PCA, a BPR of 12:1 and 75% critical speed is more effective in reducing particle size and formation of duplex and ferritic stainless steel after 10 h milling of elemental powder compositions than their counterparts. The particle size of duplex and ferritic stainless steel milled in the presence of SA for 10 h is found to be 13 and 14 μm, whereas the particle size is 20 and 16 μm without SA respectively. The particle size of powder milled at 12:1 BPR is lower than powder milled at 6:1 BPR because of more impact energy induced by balls on powders and it is found to be 10 and 12 μm respectively for duplex and ferrite in presence of SA. The median particle size of duplex and ferritic stainless steel milled at 75% critical speed is found to be 3.5 and 2.4 μm respectively.

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