Steel article having high hardness and improved toughness and pr

Details Steel article having high hardness and improved toughness and pr Steel article having high hardness and improved toughness and pr

1997-11-25

1999-06-08

Yee, Deborah

Metal treatment

Process of modifying or maintaining internal physical...

Carburizing or nitriding using externally supplied carbon or...

148233, 148319, C22C 3802, C23C 822

Patent

active

059102233

ABSTRACT:
A steel article is formed of a steel material containing from about 0.08 to about 0.35 carbon and is characterized by having a plurality of carbides dispersed on at least one pre-selected surface area of the article, with the surface carbides being dispersed within a predominantly lower bainitic matrix. A method for forming the steel article having high hardness and higher toughness includes carburizing the article at a temperature and for a period of time, in an atmosphere having a carbon potential, sufficient to form carbides and austenite on at least one preselected surface of the article, and then quenching the carburized article to a temperature below the Ar.sub.1 temperature and above the M.sub.s temperature of the steel material for a time sufficient to transform a major portion of the austenite in the preselected surface area microstructure to lower bainite. The steel article has an equivalent Knoop 500 gram maximum particle hardness of at least 900 and a Charpy unnotched, room temperature toughness of at least 50 Joules, thereby providing an article having both high hardness and improved toughness properties.

REFERENCES:
patent: 4921025 (1990-05-01), Tipton et al.
patent: 5536335 (1996-07-01), Burris

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