Improving the Dimensional Stability and Mechanical Properties of AISI 316L + B Sinters by Si3N4 Addition

Abstract

The following paper describes a new and effective method to obtain high-density sinters with simultaneously decreased distortions, produced by one press and sinter operation. This effect was achieved through the induced disappearance of the eutectic liquid phase. The study was carried out on AISI 316L stainless steel powder that was mixed with elemental boron and silicon nitride. Boron was used as a sintering process activator. The scientific novelty of this publication consists of the use of a silicon nitride as a solid-state nitrogen carrier that was intended to change the borides’ morphology by binding boron. Based on the thermodynamic calculations, 20 blends of various compositions were tested for physical properties, porosity, microstructure, and mechanical properties. Moreover, phase compositions for selected samples were analyzed. It was shown that the addition of silicon nitride as a nitrogen carrier decreases the boron-based eutectic phase volume and both increases the mechanical properties and decreases after-sintering distortions. An explanation of the observed phenomena was also proposed.

Improved Mechanical and Corrosion Properties of Powder Metallurgy Austenitic, Ferritic, and Martensitic Stainless Steels by Liquid Phase Sintering

“…Based on the above results, it is clear that B and Cr elements tended to jointly concentrate at the boride in the eutectic area, and other elements, including Fe, Ni, or C, were mainly distributed in the matrix. Such Cr segregation in the boride has been found in several B-alloyed PM stainless steels and alloy steels [ 3 , 12 , 15 , 18 ]. However, C atoms could be rich or deficient in the boride according to the crystal structures of boride [ 17 ].…”

“…Several techniques, such as warm compaction, double-press double-sintering, powder forging, and spark plasma sintering can decrease the porosity, though these techniques greatly raise the production cost [ 4 , 5 , 6 , 7 , 8 ]. Liquid phase sintering (LPS) is an economical technique to facilitate the sintering densification of PM materials by adding specific alloying elements for liquid generation without obviously increasing the cost [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. For PM steel, boron (B) is an effective alloying element for LPS due to an Fe–B eutectic reaction [ 11 , 12 , 13 , 14 , 15 , 16 ].…”

“…Liquid phase sintering (LPS) is an economical technique to facilitate the sintering densification of PM materials by adding specific alloying elements for liquid generation without obviously increasing the cost [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. For PM steel, boron (B) is an effective alloying element for LPS due to an Fe–B eutectic reaction [ 11 , 12 , 13 , 14 , 15 , 16 ].…”

The Microstructure of Fe-Based Laminated Metal Composite Produced by Powder Metallurgy

“…Powder metallurgy (PM) is a cost-effective process for manufacturing nearly net-shaped metallic materials, particularly Fe-based alloys, in mass production, one that has been widely investigated [ 11 , 12 , 13 , 14 , 15 ]. However, the use of PM technology to fabricate LMCs has been rare to date in industry.…”

In Situ Formation of TiB2 in Fe-B System with Titanium Addition and Its Influence on Phase Composition, Sintering Process and Mechanical Properties

“…Moreover, it is possible to obtain a material whose properties have lesser decrease in ductility and impact toughness as the boron content increases compared with similar boron-containing cast/wrought borated stainless steels. The application of boron in powder metallurgy as addition to ferrous alloys has been of interest to numerous researchers over the last years [3][4][5][6][7][8][9][10][11][12]. The main cause of this interest is the eutectic reaction between iron and boron, resulting in the appearance of a liquid phase which efficiently improves mass transport by intensifying a diffusion process [7].…”