Plastically deformed hardened steel parts and method of forming same

Claim 1

A METHOD OF MAKING PLASTICALLY DEFORMED METAL PARTS FROM THROUGH HARDENED STEEL SHEET STOCK COMPRISING THE STEPS OF: DECARBURIZING BOTH MAJOR SURCFACE OF A THROUGH HARDENING STEEL SHEET ABOUT 0.01 INCH-0L08 INCH IN THICKNESS TO PRODUCE A SHARPLY DEFINED ZONE OF FERRITE ON EACH OF SAID SHEET MAJOR SURFACES, WITH AN ABRUPT CHANGE IN CARBON CONCENTRATION TO AN UNDECARBURIZED CENTRAL CORE OF THROUGH HARDENING STEEL THEREBETWEEN, CONTINUING SAID DECARBURIZATION UNTIL SAID FERRITE ZONES EXPAND IN THICKNESS TO ABOUT 5 PERCENT-20 PERCENT OF THE THICKNESS OF SAID SHEET, WHILE MAINTAINING AT LEAST THE OUTER 90 PERCENT OF THE OUTER THICKNESS OF SAID ZONES AT A CARBON CONCENTRATION BELOW ABOUT 0.01 PERCENT BY WEIGHT, AUSTENITIZING SAID SHEET WITHOUT INDUCING MIGRATION OF CARBON FROM SAID CENTRAL CORE INTO SAID DECRARBURIZED ZONES THAT SIGNIFICANTLY ALTERS SAID ABRUPT CHANGE IN CARBON CONCENTRATION, RAPIDLY COOLING SAID AUSTENITIZED DECARBURIZED SHEET TO THROUGH HARDEN SAID CENTRAL CORE TO A HARDNESS OF AT LEAST ABOUT 40 RC BEFORE MIGRATION OF CARBON FROM SAID CENTRAL CORE INTO SAID DECARBURIZED ZONES CAN SIGNIFICANTLY ALTER SAID ABRUPT CHANGE IN CARBON CONTENT BETWEEN SAID FERRITE ZONES AND SAID CENTRAL CORE, AND PLASTICALLY DEFORMING SAID SHEET INTO A DESIRED SHAPE.

Claim 2

A METHOD OF MAKING PLASTICALLY DEFORMED METAL PARTS FROM THROUGH HARDENED STEEL SHEET STOCK COMPRISING THE STEPS OF: DECARBURIZING BOTH MAJOR SURCFACE OF A THROUGH HARDENING STEEL SHEET ABOUT 0.01 INCH-0L08 INCH IN THICKNESS TO PRODUCE A SHARPLY DEFINED ZONE OF FERRITE ON EACH OF SAID SHEET MAJOR SURFACES, WITH AN ABRUPT CHANGE IN CARBON CONCENTRATION TO AN UNDECARBURIZED CENTRAL CORE OF THROUGH HARDENING STEEL THEREBETWEEN, CONTINUING SAID DECARBURIZATION UNTIL SAID FERRITE ZONES EXPAND IN THICKNESS TO ABOUT 5 PERCENT-20 PERCENT OF THE THICKNESS OF SAID SHEET, WHILE MAINTAINING AT LEAST THE OUTER 90 PERCENT OF THE OUTER THICKNESS OF SAID ZONES AT A CARBON CONCENTRATION BELOW ABOUT 0.01 PERCENT BY WEIGHT, AUSTENITIZING SAID SHEET WITHOUT INDUCING MIGRATION OF CARBON FROM SAID CENTRAL CORE INTO SAID DECRARBURIZED ZONES THAT SIGNIFICANTLY ALTERS SAID ABRUPT CHANGE IN CARBON CONCENTRATION, RAPIDLY COOLING SAID AUSTENITIZED DECARBURIZED SHEET TO THROUGH HARDEN SAID CENTRAL CORE TO A HARDNESS OF AT LEAST ABOUT 40 RC BEFORE MIGRATION OF CARBON FROM SAID CENTRAL CORE INTO SAID DECARBURIZED ZONES CAN SIGNIFICANTLY ALTER SAID ABRUPT CHANGE IN CARBON CONTENT BETWEEN SAID FERRITE ZONES AND SAID CENTRAL CORE, AND PLASTICALLY DEFORMING SAID SHEET INTO A DESIRED SHAPE.

Claim 3

A method of making plastically deformed metal parts from through hardened steel sheet stock comprising the steps of: decarburizing both major surfaces of a through hardening steel sheet 0.01 inch - 0.08 inch in thickness by heating said sheet at a temperature within 50*F. of the A1 temperature of said sheet in a dry disassociated ammonia atmosphere consisting essentially of nitrogen and about 3 percent - 5 percent by volume hydrogen to obtain an abrupt change in carbon concentration in said sheet below said surfaces, continuing said decarburization for a sufficient duration to produce a scale-free decarburized zone contiguous each of said major surfaces and a substantially undecarburized central core therebetween, in which the decarburized surface zones have a thickness approximately 5 percent - 20 percent of the sheet thickness and at least the outermost 90 percent of the thickness of each of said zones has a residual carbon concentration below about 0.01 percent by weight that increases formability of said sheet, heating said sheet in a protective atmosphere to a temperature between the A1 and A3 temperature of said sheet to austenitize said central core but not induce rapid carbon migration from it into said decarburized zones thickness, rapidly cooling said austenitized decarburized sheet before carbon migration from said central core into said outermost zone thickness can increase said carbon concentration above about 0.0l percent by weight and significantly decrease the abruptness of said change in carbon concentration between said surface zones and said central core, so as to produce a hardened central core that has a thickness about 60 percent -90 percent of the thickness of the sheet and a hardness of at least about 40 Rc, and plastically deforming said sheet into a desired shape having at least one radius of curvature beyond the formability of said sheet if its entire thickness were of the same hardness as said central core.

Claim 4

A method of making plastically deformed metal parts from through hardened steel sheet stock comprising the steps of: decarburizing both major surfaces of a through hardening steel sheet 0.01 inch - 0.08 inch in thickness by heating said sheet at a temperature within 50*F. of the A1 temperature of said sheet in a dry disassociated ammonia atmosphere consisting essentially of nitrogen and about 3 percent - 5 percent by volume hydrogen to obtain an abrupt change in carbon concentration in said sheet below said surfaces, continuing said decarburization for a sufficient duration to produce a scale-free decarburized zone contiguous each of said major surfaces and a substantially undecarburized central core therebetween, in which the decarburized surface zones have a thickness approximately 5 percent - 20 percent of the sheet thickness and at least the outermost 90 percent of the thickness of each of said zones has a residual carbon concentration below about 0.01 percent by weight that increases formability of said sheet, heating said sheet in a protective atmosphere to a temperature between the A1 and A3 temperature of said sheet to austenitize said central core but not induce rapid carbon migration from it into said decarburized zones thickness, rapidly cooling said austenitized decarburized sheet before carbon migration from said central core into said outermost zone thickness can increase said carbon concentration above about 0.0l percent by weight and significantly decrease the abruptness of said change in carbon concentration between said surface zones and said central core, so as to produce a hardened central core that has a thickness about 60 percent -90 percent of the thickness of the sheet and a hardness of at least about 40 Rc, and plastically deforming said sheet into a desired shape having at least one radius of curvature beyond the formability of said sheet if its entire thickness were of the same hardness as said central core.

Claim 5

A method of making plastically deformed metal parts from through hardened plain carbon steel sheet stock comprising the steps of: decarburizing both major surfaces of a through hardening plain carbon steel sheet 0.05 inch - 0.08 inch in thickness by heating said sheet at a temperature of 1,300* - 1400*F. in a disassociated ammonia atmosphere consisting essentially of nitrogen and about 3 percent - 5 percent by volume hydrogen and having a dew point less than about 0*F. to obtain an abrupt change in carbon concentration in said sheet below said surfaces, continuing said decarburization for a sufficient duration to produce a scale-free decarburized zone contiguous each of said major surfaces and a substantially undecarburized central core therebetween, in which the decarburized surface zones have a thickness approximately 10 percent - 20 percent Of the sheet thickness and at least the outermost 90 percent of the thickness of each of said zones thickness has a residual carbon concentration below about 0.01 percent by weight that increases formability of said sheet, heating said sheet in a protective atmosphere to a temperature of about 1,550* - 1,600*F. to austenitize said central core but not induce rapid carbon migration movement from it into said decarburized zones, rapidly cooling said austenitized decarburized sheet before carbon migration from said central core into said outermost zone thickness can increase said carbon concentration above about 0.01 percent by weight and significantly decrease the abruptness of said change in carbon concentration between said surface zones and said central core, so as to produce a hardened central core that has a thickness of about 60 percent - 80 percent of the thickness of the sheet and a hardness of at least about 40 Rc, and plastically deforming said sheet into a desired shape having at least one radius of curvature beyond the formability of said sheet if its entire thickness were of the same hardness as said central core.

Claim 6

A method of making plastically deformed metal parts from through hardened plain carbon steel sheet stock comprising the steps of: decarburizing both major surfaces of a through hardening plain carbon steel sheet 0.05 inch - 0.08 inch in thickness by heating said sheet at a temperature of 1,300* - 1400*F. in a disassociated ammonia atmosphere consisting essentially of nitrogen and about 3 percent - 5 percent by volume hydrogen and having a dew point less than about 0*F. to obtain an abrupt change in carbon concentration in said sheet below said surfaces, continuing said decarburization for a sufficient duration to produce a scale-free decarburized zone contiguous each of said major surfaces and a substantially undecarburized central core therebetween, in which the decarburized surface zones have a thickness approximately 10 percent - 20 percent Of the sheet thickness and at least the outermost 90 percent of the thickness of each of said zones thickness has a residual carbon concentration below about 0.01 percent by weight that increases formability of said sheet, heating said sheet in a protective atmosphere to a temperature of about 1,550* - 1,600*F. to austenitize said central core but not induce rapid carbon migration movement from it into said decarburized zones, rapidly cooling said austenitized decarburized sheet before carbon migration from said central core into said outermost zone thickness can increase said carbon concentration above about 0.01 percent by weight and significantly decrease the abruptness of said change in carbon concentration between said surface zones and said central core, so as to produce a hardened central core that has a thickness of about 60 percent - 80 percent of the thickness of the sheet and a hardness of at least about 40 Rc, and plastically deforming said sheet into a desired shape having at least one radius of curvature beyond the formability of said sheet if its entire thickness were of the same hardness as said central core.