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The effect of the sixth element(M = Co, In, Sn), as a substitution for Ni in Cu_(47)Ti_(33)Zr_(11)(Ni, M)_8Si₁ alloys, on the glass forming ability was examined using thermal analysis, X-ray diffractometry and TEM. Partial substitution of Ni with 2 at% In and Sn in Cu_(47)Ti_(33)Zr_(11)Ni_8Si₁ alloy enhanced the glass-forming ability. The maximum diameter for single amorphous phase formation in Cu_(47)Ti_(33)Zr_(11)Ni_8Sn₂Si₁ alloy by injection casting was 6 ㎜. Both amorphous alloys prepared by melt spinning and injection casting showed similar crystallization process during continuous heating in DSC. Co-relationship between variation of critical diameter for formation of an amorphous phase and that of parameters suggested to reflect glass-forming ability such as ΔT^*_m, T_(rg), ΔT_x, T_m-T_x, K parameter was examined.

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An investigation was made to determine the effects of Mn content and annealing conditions on the formation of the low temperature transformation products in ultra low carbon interstitial free steels. With increasing the Mn content, yield and tensile strengths increased, but yield ratio decreased. The Mn was found to be effective to decrease the yield point elongation, causing continuous yielding in 3% Mn steel. Low temperature transformation ferrites such as quasi-polygonal ferrite, granular bainitic ferrite, and bainitic ferrite more easily formed with higher Mn content, higer annealing temperature, longer annealing time, and faster cooling rate. Polygonal ferrite grain was readily identified in the light microscope and was characterized by the polyhedral and equiaxed shape while quasi-polygonal ferrite showed the irregular changeful grain boundaries. It was found that both granular bainitic and bainitic ferrites revealed some etching evidence of substructures in the light microscope.

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Transformation behaviors, microstructures and shape memory characteristics of thermo-mechanically treated and aged Ti-Ni-Si alloys were investigated by means of differential scanning calorimetry, electrical resistivity measurements, X-ray diffraction, transmission electron microscopy, constant load thermal cycling tests and tensile tests. In a thermo-mechanically treated Ti-48Ni-2Si alloy, two stage transformation behavior, i.e., the B2→R→B19` was observed on cooling and the critical stress for slip deformation increased to 696 ㎫. Stress dependence of the martensitic transformation start temperature(Ms) in this alloy was very small(0.199 K/㎫) as compared to Ti-rich Ti-Ni alloys(0.313 K/㎫). Two stage transformation, i.e., the B2→R→B19` occurred in an aged Ti-50Ni-2Si alloy while the solution treated alloy did not show martensitic transformation behavior. The difference in transformation behavior was attributed to the precipitation of Ti₃Ni₄. Stress dependence of Ms in an aged Ti-50Ni-2Si alloy(0.285 K/㎫) was smaller than that(0.360 K/㎫) in Ni-rich Ti-Ni alloys.

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Thin films of 55Ti-(45-x)Ni-xCu(x = 0, 5, 10, 20 at.%) compositions were fabricated by d.c. magnetron sputtering method. Deposited films were annealed at 973 K for 3.6 ks to induce crystallization. The phase transformation behaviors of these thin films were investigated by differential scanning calorimetry and X-ray diffraction. Shape memory characteristics were studied by thermal cycling test under a constant load. As-sputtered films contained a mixture of amorphous and very fine(=15 ㎚) Ti₂Ni phase. Crystallization temperature(Tc) decreases from 774 K to 747 K with increasing Cu-content from 0 at.% to 20 at.%. Two-stage transformation behavior, i.e., the B2→R→B19`, was observed in a 55Ti-45Ni(at.%) alloy thin film. The B2→B19` transformation occurred in a 55Ti-40Ni-5Cu(at.%) alloy film, while the B2→B19 transformation occurred in 55Ti-35Ni-l0Cu(at.%) and 55Ti-30Ni-20Cu(at.%) alloy films. The stress dependence of transformation temperature(dT/dσ) of 55Ti-40Ni-5Cu(at.%) and 55Ti-35Ni-10Cu(at.%) thin films were 0.015 K/㎫ and 0.016 K/㎫, respectively. They were very small as compared to those of 50Ti-45Ni-5Cu(at.%) and 50Ti-40Ni-10Cu(at.%) alloys.

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Inferior drawability of AISI4135 steel rod is sometimes due to the presence of hard constituents such as bainite and martensite in the microstructure of as-hot rolled state. The amount of hard phases can be minimized by controlled rolling, thus refining the austenite grains, which, in turn, shift the CCT diagram towards shorter times. For the same cooling rate, the austenite to ferrite-plus-pearlite transformation is accordingly enhanced. In conducting numerous hot torsion tests, equations describing the recrystallization behavior of AISI4135 steel during hot deformation were developed in order to find the best condition for grain refinement. Austenite grain sizes predicted by the equations are in good agreement with data from commercial rod rolling.

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The cracking occurring during strip casting of an AISI 304 stainless steel was microstructurally examined, and then methods to prevent it were suggested. Detailed microstructural analyses of the cracked regions showed that the cracks were mostly deep, sharp, and longitudinal ones parallel to the casting direction. They initiated at the root of dendrites, and propagated along the segregated liquid films between primary dendrites, indicating that they were typical solidification cracks. This cracking phenomenon was closely related with the unhomogeneous solidification of cast strips represented by depressions, i.e., uneven and somewhat concave areas on the strip surface. The depressions, which were inevitable in flat rolls due to the presence of the gas gap between a roll and a cast strip, were distributed fine and evenly all over the cast strip by artificially providing homogeneous roughness on the roll surface, and then the number and size of cracks were considerably reduced. In addition, the nitrogen gas atmosphere which had excellent solubility and wettability in the melt, was successfully used to prevent the cracking because the thickness of the gas gap was minimized.

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To study reoxidation of molten steel in contact with Al₂O₃-MgO castables in the teeming ladle, the crucibles made of castables were reacted with Al, Si-Al and Al-Ti killed steels in an inert gas for 30, 60, 90 and 120 minutes at 1600±10℃. The samples from crucibles were cut into thin and polished sections to be observed under optical microscope. Steels were chemically analyzed. The main results could be summarized as follows: (1) As Al₂O₃ and MgO would form a very stable spinel (MgAl₂O₄), they do not react with any component in the molten steel. Al₂O₃-MgO castables are confirmed to be excellent as refractories in contact with molten steel in the teeming ladle. (2) SiO₂, added as the mineralizes in the castables plays a role as the source of oxygen to the molten steel, oxidizing [Al], [Ti], [C] and [Mn] and thus forming oxide inclusions. Therefore, it exerts a harmful influence upon steel cleanliness. (3) The manganese in the melt reacted with SiO₂ in the refractory to form manganese oxide, which resulted in excessive wear of refractory by complexing Al₂O₃ and SiO₂ in the refractories. (4) The deepest altered zone is observed in the case of using Al-Ti killed steel probably due to the formation of a relatively low-melting compound of TiO₂and Al₂O₃.

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