Ichihito Narita

The wear resistance without lubrication were studied experimentally for iron nitrides compound layer and high nitrogen martensite phase formed in the material surface by using industrial pure iron treated by nitriding and quenching followed by aging process. As a result both the compound layer where the generation of pores was suppressed by lowering the nitriding temperature and the high nitrogen martensite phase showed the same trend of high wear resistance. However, the pores in the compound layer decreased the wear resistance due to the acceleration of crack propagation.

<p>  The formation prcess of cast structure and ferritization prcess was investigated in spheroidal graphite cast iron containing 1.7～1.9%C, 1.4/2.0%si, and 0.2～0.3%Mn. Thermal analysis and quenching experiment revealed that the primary γ started crystallization at around 1364℃ and developed dendritically to about 88% of the specimen. Eutectic graphite crystallized in the residual liquid among dendrites and the area fraction of graphite (F_g) was about 0.4% just after eutectic solidification. F_g increased to 3.5% by the precipitation of secondary graphite during cooling to eutectoid temperature. The behaviors of Si and Mn during solidification were also clarified based on the partition coefficients of these elements to primary γ. Ferritization heat treatment was carried out on as-cast specimens with pearlite matrix by heating them at 740℃, 720℃, and 700℃ for 1h to 10h. The changes in fraction of ferrite during ferritization were examined using a series of specimens quenched during heat treatment. The higher the heating temperature, the higher was the ferritization rate. When heated at 740℃ and 720℃ for 10h, the fraction of ferrite exceeded 90%. Ferritization was retarded in the Mn-rich pearlite area where the melt finally solidified. F_g increased to 7.4% after full ferritization. The number and size of graphite nodules also increased with the precipitation of secondary graphite and ferritization treatment.</p>

The influence of V and Ta addition on solidification structure and hardness after quenching and tempering treatments was investigated for high speed steel type alloy (Fe- 1.9%C- 0.5%Mn- 4.9%Cr- 5.0%Mo- 5.0～7.2%V- 0.4～1.4%Ta). The compositions of V and Ta were systematically changed for the purpose of distributing hard MC carbides in the hypoeutectic range. EMPA and XRD analysis identified the lamellar structure as M₂C carbide containing mainly Fe and Mo, and the oval microstructure as MC carbide containing mainly V and Ta among austenite dendrite. The macrohardness of the quenched specimen gradually increased with solution treatment and increasing quenching temperature, and then decreased later. This indicates that the macrohardness of the quenched specimen depends on both the amount and hardness of the martensite matrix. All specimens which were tempered at 723K to 873K showed secondary hardening. Furthermore, hardening of the specimen was conspicuous when specimens containing large amounts of residual austenite were tempered at the optimum temperature, as seen with the increase in the hardening of Ta-contained specimen to around 900HV at the tempering temperature of 823K. These results suggest that the macrohardness of tempered specimens is governed by the amount of carbon in the austenite at quenching temperature, the degree of transformation from residual austenite to martensite, and the precipitation of secondary carbides.

当時，研究報告例が少なく，実用化のなされていなかった窒化ほう素 (BN) ケージ物質について，新規合成プロセスの開発，ナノ構造に関する基礎研究及び磁性材料としての応用を検討した．