Structure property relationship of high boron cast alloy steel

In this work, the effect of different boron (0.5-5%) additions to a hypoeutectoid steel alloy containing 0.48%C, 0.43%Si, 1.02%Mn and 11.15%Cr by weight on microstructure, hardness, wear resistance and toughness has been researched. For the B content of 0.5%, 1.5%, 2.0%, 3.0%, 4.0%and 5.0%by weight of the samples designed to contain boron in different ratios, Fe-B additions were made in equal proportions in the furnace, in the crucible and during the pouring of the liquid alloy into "Y" block molds produced using silica sand with alpha-set resin binder. The samples, which were austenitized at a temperature of 1050 ºC for 60 minutes, were subjected to isothermal heat treatment in a salt bath at a temperature of 390 ºC for 3 different periods (24 hours, 96 hours and 168 hours). Microstructure (optical microscope, scanning electron microscope, scanning electron microscope with elemental analysis, x-ray diffraction) and mechanical properties (macro/micro hardness, wear resistance and impact thoughness) of untreated and heat treated samples were determined. The following conclusions were obtained in this study; The eutectic phase consisting of a mixture of network boride and boron carbides (Fe2B and (Cr, Fe)7(C, B)5) with martensite in the microstructure was observed in boron added alloy. As the amount of boron additions increased, the volume ratio of boride and carbides increased. Samples containing 3.10%and 4.75%boron by weight, 60%and 69%carbide / boride volume ratios, respectively, took the matrix position. Carbides and borides formed in microstructure with boron additions have fishbone shape and network distribution in castings containing up to 2.05%boron, while at higher boron contents they have turned into rod/needle shape and exhibited an irregular distribution. As the boron content of the alloy increased, macrohardness and wear resistance increased, but the toughness decreased. The matrix microstructure of the samples containing varying amounts of boron and martensitic matrix did not change by isothermal heat treatment. Isothermal heat treatments increased the macrohardness and toughness values of alloys up to 3.10 wt%boron content, but did not have a remarkable effect on wear resistance.