EFFECTS OF MN AND MO CONTENTS 1-CR STEEL POWDERS ON COMPRESSIBILITY AND TENSILE-STRENGTH OF THEIR SINTERED COMPACT

A prealloy steel powder which was Mn-less, contained 1Cr-0.3Mo and low oxygen was developed to improve compressibility of steel powder, tens ile strength and toughness of sintered compact. This newly developed s teel powder showed high compressibility of green density of 7.15Mg/m(3 ) at 690MPa of compacting pressure. This is derived from the decrease in solution hardening effect and Mn oxide on powder surface with decre ase in Mn content. The sintered compacts made from the new powder with 0.9% graphite addition gave a tensile strength of 900MPa and a Charpy absorbed energy of 17J, when compacted at 690MPa and sintered at 1150 degrees C. These values were higher by 200MPa and 3J, respectively, t han those of compacts made from a conventional 1Cr-0.3 Mo-0.7 Mn steel powder. The strength and toughness improved, respectively, because oi the production of fine pearlite structure and the decrease in Mn oxid e with decrease in Mn content.