Differences in hardness and microstructure between surface and area at 0.3 mm below the surface after quenching and tempering of ductile cast iron for rear planet carrier of automotive transmission have been investigated. Microstructure of ductile cast iron consisted of ferrite, pearlite, and nodular graphite. The amount of pearlite increased with going down to the half-thickness area. It was found that Cr and Mo segregated to the pearlite and the pearlite transformed to the harder martensite during quenching. The martensite was more resistant to the decomposition to ferrite and cementite during tempering because of segregation of Cr and Mo, resulting in the harder tempered martensite. Consequently, the hardness of the surface with less amount of pearlite, corresponding to the harder martensite in the quenched and tempered microstructure, was lower than that of the area at 0.3 mm below the surface.

As a basic research for developing 600 MPa yield strength reinforcing steel bars, the strengthening of 0.25 wt.% carbon steel by vanadium addition was studied. The changes of microstructure and mechanical properties were investigated for the specimen V0 (0.00 wt.% V), V1 (0.03 wt.% V) and V2 (0.06 wt.% V) processed by various heat treatments. To set the heat treatment conditions, the continuous cooling transformation (CCT) curves were drawn for austenitizing temperatures of $900^{\circ}C$ and $1100^{\circ}C$. For specimens tempered at $600^{\circ}C$ after quenching from $900^{\circ}C$ and $1100^{\circ}C$, yield strength was increased by 19 MPa and 21 MPa for 0.01 wt % V addition, and tensile strength was increased by 25 MPa and 28 MPa for 0.01 wt % V addition, respectively. Also, for 0.06 wt.% V added specimens tempered after quenching and normalized, tensile strength was increased by 50 MPa and 30 MPa for increasing austenitizing temperature of $100^{\circ}C$, respectively.

A variety of minor alloying elements such as Zr, Sr, Y, and Gd were added to Mg-3%Zn-0.5%Sn base alloy to form various fine precipitates and their effects on the microstructure, tensile properties, and sheet metal formability were investigated. Various very fine precipitates along with fine second phases were observed by the additions. It was found that Zr or Gd additive has a role to suppress the grain coarsening of alloy sheets during the hot working process. The Zr-added alloy showed the highest tensile elongation at $250^{\circ}C$ whereas the Gd-added alloy exhibited the best sheet metal forming characteristics in terms of CCV (conical cup value) and spring-back tendency.

The implant prototypes with various porosities were fabricated by Spark Plasma Sintering of atomized spherical titanium balls. The interface was observed by optical microscope. Sintering temperature and holding time were selected at the point of big change of Z-axis ratio during sintering. These experiments show that Spark Plasma Sintering of spherical titanium balls can be efficiently used to produce implants surfaced with titanium balls with various porosities in a short time less than 120 seconds by manipulating the current condition such as z-axis, temperature and balls size.