Abstract A method of hardening hypereutectoid steels having less than about 10 percent total alloy content is described which results in a structure with an ultra-fine grain size (finer than ASTM No. 10) and a natural dispersion of very small excess carbides. The process includes high temperature solid solution of the carbide phase present in the material, controlled cooling through a selected area of the time-temperature-transformation for the material to form pearlite (a ferrite and carbide lamellar structure) and cementite, reheating to austenitize the material, and finally, quenching to produce a structure with an ultra-fine grain and a natural dispersion of very small excess carbides that results in an improvement of fatigue life and an increase in compressive yield strength.
A METHOD OF PRODUCING A CASE HAVING A STRUCTURE WITH AN ULTRA-FINE GRAIN SIZE FREE FROM MICROCRACKS WITH VERY SMALL WELL DISPERSED EXCESS CARBIDES ON CARBURIZED STEEL COMPRISING THE STEP OF: CARBURIZING AT A TEMPERATURE NOT EXCEEDING THE SOLIDUS, QUENCING QUICKLY INTO A SUITABLE LIQUID QUENCH MEDIUM TO THE APPROXIMATELY TEMPERATURE RANGE OF 900* TO 1333*F TO PRODUCE PEARLITE, AND, WHEN THE PEARLITE, TRANSFORMATION IS COMPLETE, RAPIDLY HEATING THROUGH THE A1,3 AND ACM TEMPERATURE RANGE OF THE EQUILIBRIUM DIAGRAM OF THE CARBURIZED CASE TO THE AUSTENITIZING TEMPERATURE FOR THE MATERIAL FOR A CONTROLLED TIME ONLY SUFFICIENT TO CONVERT THE CARBIDE LAMELLAE WITHIN THE PEARLITE INTO VERY SMALL EXCESS CARBIDES AND TRANSFORM THE FERRITE TO AUSTENITE, AND, QUENCHING TO HARDEN THE CASE.
Claim 2
Independent Claim
121 words
A METHOD OF PRODUCING A CASE HAVING A STRUCTURE WITH AN ULTRA-FINE GRAIN SIZE FREE FROM MICROCRACKS WITH VERY SMALL WELL DISPERSED EXCESS CARBIDES ON CARBURIZED STEEL COMPRISING THE STEP OF: CARBURIZING AT A TEMPERATURE NOT EXCEEDING THE SOLIDUS, QUENCING QUICKLY INTO A SUITABLE LIQUID QUENCH MEDIUM TO THE APPROXIMATELY TEMPERATURE RANGE OF 900* TO 1333*F TO PRODUCE PEARLITE, AND, WHEN THE PEARLITE, TRANSFORMATION IS COMPLETE, RAPIDLY HEATING THROUGH THE A1,3 AND ACM TEMPERATURE RANGE OF THE EQUILIBRIUM DIAGRAM OF THE CARBURIZED CASE TO THE AUSTENITIZING TEMPERATURE FOR THE MATERIAL FOR A CONTROLLED TIME ONLY SUFFICIENT TO CONVERT THE CARBIDE LAMELLAE WITHIN THE PEARLITE INTO VERY SMALL EXCESS CARBIDES AND TRANSFORM THE FERRITE TO AUSTENITE, AND, QUENCHING TO HARDEN THE CASE.