Based on ferro based superalloy K273 and heat resistant steel ZG40Cr24, test alloys were cast by intermediate frequency induction furnace with non-oxidation method by alloying of aluminium and silicon. The oxidation resistance at 1100°C for 500 hours of test alloys was carried out according to oxidation weight gain method. Experimental results show that the scale exfoliation resistance of K273 and ZG40Cr24 is reinforced greatly by Al2O3 and SiO2. The scale exfoliation weight gain rate at 1100°C descends from 1.2681g.m-2.h-1 to zero, reaching complete exfoliation resistance for ZG40Cr24 test alloy. Because of 1.5<PBR(Al2O3⁄Fe)<2 and the growing of Al2O3 and SiO2 from out side of scale-scale/oxygen interface, the composite scale grows intact and compact without accumulation of growing stress.

The effects of titanium modification, which was added along with the pouring liquid in ladles, on the shrinkage porosity and cavity of cast steel ZG45 smelted in intermediate frequency induction furnace were studied. The metal liquid fluidity was measured by casting spiral samples. 0.2 wt.% titanium modification achieved the highest fluidity for steel liquid. Proper content of titanium could effectively increase the volume of concentrated shrinkage cavity, and restrain the forming of shrinkage porosity. By scanning electron microscope (SEM) and energy disperse spectroscope (EDS) analysis, it was found that TiC, acting as heterogeneous nuclei, could refine the structure grains, diminish the strong dendrite, and increase the fluidity and feeding capacity of steel liquid. However, overdoes titanium modification easily caused mass oxide TiO2, which kept solid phases with high meting point in metal liquid to increase its viscosity and decrease the fluidity. Meanwhile, these solid state titanium compounds enlarged the composition supercooling, so the metal liquid changed from sequential solidification to simultaneous solidification, resulting in inadequate metal liquid feeding, less oncentrated shrinkage cavity and serious shrinkage porosity.

The affecting laws of boron and silicon on structure and properties of Fe-based superalloy were studied by analyses of scanning electron microscope (SEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Proper content of boron could not only purify the matrix and restrain the polymerizing and growing of carbides effectively, but also promote the forming of secondary precipitate of borides, which dispersed in form of micro particles to strengthen grain boundaries and enhance the heat strength for Fe-based superalloy. Boron was an adverse element to high temperature oxidation resistance. Silicon could toughen the matrix by solid solution strengthening. Overfed silicon in alloys caused great dropping of strength and toughness. The component of SiO2 endowed the oxide scale with flat and compact structure, fine and even grains, and few exfoliating. The optimum contents of boron and silicon in Fe-based superalloy are 0.02wt.% and 1.5wt.% respectively by comprehensive consideration of high temperature mechanical properties and oxidation resistance.

The affecting law of nickel on structure and properties of ferro superalloy, which was cast by intermediate frequency induction furnace, were studied by orthogonal experimental method. The tensile strength and oxidation weight gain rate at 1000°C were tested. The matrix microstructure and scale morphologies and composition were studied using scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. It was found that the high temperature tensile strength went up with the increase of nickel by the forming of high temperature strengthening phase of γ’. After 100 hours aging at 1000°C, γ’ phase separated in blocks. Certain content of nickel improved the high temperature oxidation resistance of test alloys, but excess of it caused the higher oxidation weight gain rate and loose structure oxide scales with holes and exfoliating. In considering of high temperature tensile strength and oxidation resistance, the ideal content of nickel in ferro superalloy should be 9wt.%, with which at 1000°C the tensile strength of test alloys mostly exceeded 70MPa, and the average oxidation weight gain rate was only 0.55g.m-2.h-1, reaching the strong oxidation resistance. Such scale was compounded by Cr2O3 and Fe(Ni)Cr2O4 with compact structure, fine and even oxide grains.

Proper content of titanium, microalloying in steel ZG200-400 smelted in intermediate frequency induction furnace, could effectively increase the volume of concentrated shrinkage cavity, and restrain the forming of shrinkage porosity. The concentrated shrinkage cavity was analyzed quantitatively by stuffing wet gluten and draining water method. The maximal cavity arrived at 0.18wt.% titanium microalloying. By scanning electron microscope (SEM) and energy disperse spectroscope (EDS) analysis, it was found that TiC, acting as heterogeneous nuclei, could refine the structure grains, diminish the strong dendrites, and increase the fluidity and feeding capacity of steel liquid. However, overdoes titanium microalloying easily caused mass nitrides or oxides, which kept solid phases with high meting point in metal liquid to increase its viscosity, decrease the fluidity and enlarged the composition supercooling. So the metal liquid, with poor feeding, left more shrinkage porosity, less concentrated shrinkage cavity in solidification.