A New Method to Recycle Stainless–Steel Duplex UNS S31803 Chips

Abstract

Due to the increased consumption of raw materials, energy, and the waste it generates, recycling has become very important and fundamental for the environment and the industrial sector. The production of duplex stainless-steel powders with the addition of vanadium carbide in the high energy mechanical milling process is a new method for recycling materials for the manufacture of components in the industrial sector. This study aims to reuse the chips from the duplex stainless-steel UNS S31803 by powder metallurgy with the addition of Vanadium carbide (VC). The mechanical milling was performed using a planetary ball mill for 50 h at a milling speed of 350 rpm and a ball-to-powder weight ratio of 20:1, and the addition of 3 wt % of VC. The material submitted to milling with an addition of carbide has a particle size of less than 140 µm. After milling, the sample went through a stress relief treatment performed at 1050 • C for 1 h and the isostatic compaction process loaded with 300 MPa. The sintered powders and material was characterized by scanning electron microscopy, X-ray diffraction, and micro-hardness tests. The milling process with an addition of 3% VC produced a particle size smaller than the initial chip size. The measurement of micrometric sizes obtained was between 26 and 132 µm. The sintered material had a measurement of porosity evaluated at 15%. The obtained density of the material was 84% compared to the initial density of the material as stainless-steel duplex UNS S31803. The value of the microhardness measurement was 232 HV. The material submitted for grinding presented the formation of a martensitic structure and after the thermal treatment, the presence of ferrite and austenite phases was observed. Thus, in conclusion, this study demonstrates the efficacy in the production of a metal-ceramic composite using a new method to recycle stainless-steel duplex UNS S31803 chips.

Recent Advancements in Material Waste Recycling: Conventional, Direct Conversion, and Additive Manufacturing Techniques

“…Metal chips can be recycled by turning them into powders by using processes like milling, gas atomization, and electrolytic decomposition. A high-end ball milling process using vanadium carbides has been studied by Mendonça et al [281][282][283] for recycling stainless steel chips (Figure 26).…”

Producing Metal Powder from Machining Chips Using Ball Milling Process: A Review

“…This study also demonstrated that increasing the reinforcing concentration results in a decrease in average particle size. In contrast, another study demonstrated that the sintered composite has a lower hardness than the as-received alloy and that the porosity of the sintered composite is to blame for the failure [ 169 ].…”

From Machining Chips to Raw Material for Powder Metallurgy—A Review

“…This study also presented that: the increase in the reinforcement concentration results in the reduction of average particle size. However, a similar study shows that the hardness of the sintered composite was smaller than the as-received alloy, and the failure was attributed to the porosity of sintered composite [ 37 ]. Other researchers also exhibited a significant effect on the fragmentation of particles in the presence of reinforcements, d = 80 µm in Ti 6 Al 4 V powder and 4 µm in Ti 6 Al 4 V-10 wt.% nanoalumina [ 27 ].…”