The effect of thermomechanical treatment on thermal expantion and melting point of Fe-30%Ni-0.35%C alloy was investigated. The dimention changes of the ausformed martensite and the marformed martensite were decreased with increasing deformation degree in the range of $25{\sim}350^{\circ}C$ prior to reverse transformation but became larger in the range of $500{\sim}800^{\circ}C$ after the reverse transformation. The dimension change and the thermal expansion coefficient were reduced in the order of the deformed austenite, the marformed martensite and the ausformed martensite in the range of $25{\sim}800^{\circ}C$. Therefore, the ausforming treatment is more effective than the marforming treatment in improving the heat-resistance. The melting points of the deformed austenite, the ausformed martensite and the marformed martensite were lowered as either the heating rate or the degree of deformation was increased.

The elastic modulus and wear resistance in austempered ductile cast iron(ADI) are two important mechanical properties for automobile parts. Therefore, the effect of Cu, Ni, Mo and special austempering treatment such as preheated, prequenched, and step austempering treatments on elastic modulus and wear resistance has been investigated systomatically. As a result, elastic modulus and wear resistance were increased by the addition of Mo-Cu and preheated austempering treatment.

Degradation and recovery of damping capacity in a Cu-65%Mn alloy have been studied. When the alloy was isothermally aged at $400^{\circ}C$, the highest damping capacity was observed after aging for 4 hours. In case when the alloy aged at $400^{\circ}C$ for 4 hours was maintained at $100^{\circ}C$, the damping capacity gradually decreased with time. The microstructural observations showed that the formation of subdomains and ${\alpha}$-Mn precipitates are responsible for the degradation of damping capacity. When the degraded specimen was reheated at $250^{\circ}C$ for 30 minutes, the damping capacity was recovered considerably owing to the redistribution of impurity atoms, the extinction of subdomains and the release of damping sources from ${\alpha}$-Mn precipitates during the repeated transformation, fcc${\leftrightarrow}$fct.

The effects of pre-heat treatment(Q/T) on microstructure and hardness of SCM435 structural steel nitrided by micro-pulse plasma was investigated. The quenching and tempering temperatures for obtaining matrix hardness of SCM435 steel on range of HRC30 to HRC40 desired for machine parts were about $860^{\circ}C$ and $500^{\circ}C$ respectively. The case depth of SCM435 nitrided at $480^{\circ}C$ for 5 hours was independent of pre-heat treatment condition and was approximately $150{\mu}m$. However, hardness and compactness of nitrified layer on Q/T treated specimen were more heigher than annealed specimen. The case depth increased linearly with the increase of nitriding temperature, however, the hardness of nitrified layer decreased with the temperature. Phase mixture of ${\gamma}^{\prime}$-phase($Fe_4N$) and ${\varepsilon}$-phase($Fe_3N$) were detected by XRD analysis in the nitrified layer formed at optimum nitriding condition, and only single ${\gamma}^{\prime}$-phase was detected in the nitrified layer formed at higher nitriding temperature such as $540^{\circ}C$. The optimum nitriding temperature was approximately $480^{\circ}C$ which is lower than tempering temperature for preventing softening behavior of SCM435 matrix during nitriding process and the surface hardness of nitrified layer obtained by optimum preheat treatment condition was about Hv930.

The effects of chemical composition and thermal cycling on the martensitic transformation characteristics in Cu-rich, equiatomic and Zr-rich CuZr binary alloys have been studied by calorimetry. Only martensite could be indentified in equiatomic $Cu_{49.9}Zr_{50.1}$ alloy, while $Cu_{10}Zr_7$ and $CuZr_2$ intermetallic compounds as well as martensite were formed by rapid cooling from the melts in Cu-rich $Cu_{52.2}Zr_{47.5}$ alloy and Zr-rich $Cu_{48.4}Zr_{51.6}$ alloy, respectively. The $M_s$ temperature of $Cu_{49.9}Zr_{50.1}$ was $156^{\circ}C$ but those of $Cu_{52.5}Zr_{47.5}$ and $Cu_{48.4}Zr_{51.6}$ alloys, being $109^{\circ}C$ and $138^{\circ}C$, were lower than that of equiatomic $Cu_{49.9}Zr_{50.1}$ alloy. In all the alloys, the $M_s$ temperature has fallen but the $A_s$ temperature has risen, resulting in widening of the transformation hysteresis with thermal cycling. The anomalous characteristics in the transformation temperature are due to the presence of the intermetallic compounds i.e. $Cu_{10}Zr_7$ and $CuZr_2$ formed by an eutectoid reaction during thermal cycling in the temperature range between $-100^{\circ}C$ < $T_c$ < $400^{\circ}C$.

The effects of alloying elements(Mo, Cu, Ni) and austempering temperature conditions on the microstructural morphologies and mechanical properties in austempered ductile cast iron has been investigated. The austempering at $350^{\circ}C$ for 2hrs after austenitizing at $900^{\circ}C$ for 2hrs in all specimens with various alloying elements was optimum because the good combination of tensile and yield strength, hardness and impact value was obtained. The microstructures of these ADIs treated by a forementioned austempering condition are nearly a mixture type of needle and feathery bainite. Among those alloys, Mo-Cu alloyed DCI had the best optimum mechanical properties of hardness and toughness for automobile parts by austempering treatment for 2hrs at $900^{\circ}C$ followed by $350^{\circ}C$ for 2hrs.

The object of this research is to estimate the hardenability of quenched carbon steels AISI 1050. The equation of transient heat conduction was analyzed to derive cooling curve by finite element method. The effects of temperature on physical properties, metallic structures and the latent heat by phase transformation were considered. A good agreement was found between analytical and experimental results to show that the proposed numerical procedure was reliable. This procedure could be used as the detabase for optimal condition of heat treatment cycle.

The graphitization is affected by the addition of small amount of the elements, such as Si, Al, Ni, B, Cr and Mn etc. Boron is well known as the most effective element for the graphitization of cementite in high carbon steels. But a study on quantitative analysis of B effect on the graphitization is few reported. Therefore the effect of boron addition in Fe-0.65%C-1.0%Si-0.5%Mn steels on the graphitization is investigated quantitatively using hardness tester, optical microscope and scanning electron microscope, neutron induced microscopic radiography. The graphitization in high carbon steels is promoted with 0.003~0.005%B addition. But the graphitization in steels which has no boron takes long holding time at $680{\sim}720^{\circ}C$. The hardness of quenched steel containing 0.003%B is higher than that of 0.005%B added steel due to complete dissolution of fine graphites into the austenite. The 0.003%B added high carbon steel graphitized at $680^{\circ}C$ for 25hr is useful steel for the agricultural implements and automobile parts which needed a good formability and high hardness.