Interrupted normalization heat treatment process
AssigneeNational Forge Company
InventorsAshok K. Khare, Michael Scott
Life of this patent
Estimating the term…
Abstract
An interrupted normalization heat treatment process for ferritic alloy steel that includes the steps of rapidly cooling at least the outer surfaces of the steel from a temperature above the Ac.sub.3, temperature to a temperature below the Ar.sub.1, temperature and during subsequent air cooling to room temperature reheating the outside surfaces of the ferritic alloy steel back above the Ar.sub.1, temperature by bleed back heat from the steel, tempering the air cooled workpiece, and forming an as interrupting normalized workpiece having substantially bainitic structures.
Claims8
A heat treating process for a ferritic alloy steel, comprising the steps of:
- (a) heating the steel to a temperature above the Ac.sub.3 temperature and maintaining the steel at that temperature until the steel microstructure has transformed substantially to austenite;
- (b) rapidly cooling the steel in a cooling medium so that at least outer surfaces of the steel are at a temperature below the Ar.sub.1 temperature at which bainite colonies form in the austenite;
- (c) removing the steel from the cooling medium after at least the outer surfaces of the steel are at a temperature below the Ar.sub.1 temperature;
- (d) reheating the outer surfaces of the steel to a temperature at least above the Ar.sub.1 temperature with bleed back heat from the steel;
- (e) air cooling the steel to room temperature during and after step (d);
- and
- (f) tempering the steel after step (e).
A heat treating process for large section, large mass ferritic alloy steel workpieces, comprising the steps of:
- (a) heating a workpiece to a temperature above the Ac.sub.3 temperature and maintaining the workpiece at that temperature until the workpiece microstructure has transformed substantially to austenite;
- (b) rapidly cooling the workpiece in a cooling medium so that at least outer surfaces of the steel are at a temperature below the Ar.sub.1 temperature;
- (c) removing the workpiece from the cooling medium after at least the outer surfaces of the steel are at a temperature below the Ar.sub.1 temperature at which bainite colonies form in the austenite;
- (d) reheating the outer surfaces of the workpiece to a temperature at least above the Ar.sub.1 temperature with bleed back heat from the workpiece;
- (e) air cooling the workpiece to room temperature during and after step (d);
- and
- (f) tempering the workpiece after step (e).
Dependencies are inferred from the claim text.