| A small amount of rare earth metals(REM) was added in melts of 5Cr hot working tool steel in order to investigate the changes in cleanliness, shape control of nonmetallic inclusions, and mechanical properties in comparison with those of typical hot working tool steel. The important results obtained are summarized as follows. 1) REM addition in 5Cr hot working tool steel resulted in significant decreases in final oxygen and sulfur, and total nonmetallic inclusions content. 2) RE-complex inclusions in the form of fine globular less than 3㎛ were composed of RE-oxysulfide surrounded by RE-sulfide. 3) Impact toughness, machinability, and chipability were improved by REM addition, owing to the refining of prior austenite grain size and insoluble carbide, and RE-complex inclusions. |
|
