Silicon effect on sintered and tempered Fe-Mo-Si-C steel microstructure and mechanical property

Silicon carbide was employed as a source of silicon and carbon to produce sintered silicon steels, offering the advantages of silicon addition. This work explored the effects of low SiC contents of 1.0 and 2.0 wt.% on as-sintered and as-tempered microstructures and mechanical properties of sintered silicon steels. The experimental sintered steels were produced from mixtures of pre-alloyed Fe-1.50Mo and SiC powder. The mixtures were compacted to tensile bars, sintered at 1553 K for 2.7 ks, and cooled at 9.0 K/s with N2. Sintered specimens were tempered at 873 K and held for different times. The microstructures and mechanical properties of the sintered and tempered specimens were characterized. It was revealed that the sintered silicon-bearing steels showed low temperature phase transformations under cooling at 9.0 K/s. The sintered steel produced by 1.0 wt.% SiC addition had degenerate upper bainite microstructure and its tempered microstructure was upper bainite. The sintered steel produced by 2.0 wt.% SiC addition had a microstructure consisting of bainitic-ferrite plates, martensite plates, and austenite blocks. Its tempered microstructure was upper bainite. The tempered microstructures resembled those of sintered Si-free Fe-Mo-C steels. Tempered specimens exhibited tensile strength higher but elongation lower than sintered ones attributed to carbide precipitation strengthening.