Method of providing superplastic steel and of producing articles by deformation thereof

Claim 1

A method as defined in claim 1, in which the steel is a carbon standard steel having a carbon content in the range up to about 1 percent, and said rapid heating is effected at a rate of at least about 50* F. per second from a temperature substantially below any value for transformation of alpha iron in the steel.

Claim 4

A method of establishing a condition of high ductility, that provides deformability at a strain rate greater than 0.1 per minute, in a steel which is of normally ferritic compositional character and has a carbon or alloy content such that as exhibited by the equilibrium phase diagram for said compositional character there is an alpha-gamma-transition temperature value capable of providing temporary microstructural instability, comprising cold reducing a quantity of said steel by at least about 70 percent and thereafter, without annealing said cold reduced steel, rapidly heating a body of said non-annealed, cold reduced steel, at a rate of at least about 10* F. per second, to the aforesaid temperature value and holding the body at said value for providing said high ductility in said body during an interval of microstructural instability while transformation occurs in the steel from alpha iron at least partially to gamma iron.

Claim 6

A method of establishing a condition of high ductility, that provides deformability at a high strain rate, in a steel of normally ferritic composition having a carbon content providing a hypoeutectoid character such that said steel exhibits a phase field, in a range of elevated temperature values, which at equilibrium contains both ferrite and austenite, comprising subjecting a body of said steel to rapid heating, at a rate of at least about 20* F. per second, to a temperature in the aforesaid range, the rapidity of said heating and the selection of said temperature being such that after reaching and upon being held at such temperature the steel undergoes microstructural instability which does not substantially terminate before the end of an interval of at least several seconds at said temperature, and thereupon holding the body at said temperature for providing said high ductility therein during occurrence of said microstructural instability while phase transformation is occurring in the steel.

Claim 8

A method of establishing a condition of high ductility, that provides deformability at a high strain rate, in a steel of normally ferritic composition having a carbon content providing a hypoeutectoid character such that said steel exhibits a phase field, in a range of elevated temperature values, which at equilibrium contains both ferrite and austenite, comprising subjecting An essentially non-annealed, cold-reduced body of said steel, which has been cold reduced by at least 70 percent without subsequent annealing, to rapid heating, at a rate of at least about 20* F. per second, to a temperature in the aforesaid range, the rapidity of said heating and the selection of said temperature being such that substantial recrystallization of the cold-reduced steel occurs only after approaching said temperature, and such that after approaching such temperature the steel experiences microstructural instability which does not substantially terminate before the end of an interval of at least several seconds at said temperature, and thereupon holding the body at said temperature for providing said high ductility therein during occurrence of said microstructural instability while phase transformation and recrystallization are occurring in the steel.

Claim 12

A method of establishing a condition of high ductility in a selected steel and of deforming said steel while characterized by said condition, said steel being of normally ferritic compositional character and having a carbon content such that as exhibited by the equilibrium phase diagram for said compositional character there is an alpha-gamma transition temperature value where upon heating to and holding at such value microstructural instability can be temporarily attained, comprising: subjecting a body of said steel to rapid heating, at a rate of at least about 10* F. per second, to the aforesaid temperature value, the rapidity of said heating and the selection of said temperature value being such that after reaching and being held at such value the steel undergoes temporary, phase-transforming, microstructural instability, creating said condition of high ductility permitting deformation at a strain rate of at least about 10 per minute, in an interval of sufficient duration to permit deformation at a strain rate not greater than about 1,000 per minute; and while holding the body at said temperature value, subjecting the body to deformation under stress to a selected extent, by applying said stress during an interval which substantially coincides with at least part of said first mentioned interval, so that said deformation is effected while the body is in a condition of high ductility.

Claim 16

A method of establishing a condition of high ductility in a selected steel and of deforming said steel while characterized by said condition, said steel being of such normally ferritic composition and carbon content that it exhibits a phase field, over a determinable elEvated temperature range in the course of transformation between ferrite and austenite, which at equilibrium contains both ferrite and austenite, comprising: subjecting a body of said steel to rapid heating, at a rate of at least about 20* F. per second, to a temperature selected in the aforesaid range, the rapidity of said heating and the selection of said temperature being such that after reaching and upon being held at said selected temperature the steel undergoes ductility-enhancing microstructural instability over an interval long enough to permit large deformation by stress in such interval; and while holding the body at said selected temperature, applying stress to the body within said interval to deform it to a selected extent.