Method of evaluating high fatigue strength material in high tensile strength steel and creation of high fatigue strength material

A method of designing a high fatigue strength metal, comprising:

• obtaining a value σB corresponding to a tensile strength of a metal in terms of MPa;
• obtaining a value Hv corresponding to a Vickers hardness of said metal;
• measuring a flaw area A of an inclusion of said metal when a fracture origin is located inside said metal;
• and
• estimating a fatigue limit σw of said metal in terms of Mpa to satisfy the equation
• σw≧3.38 A−¼.

A method of evaluating a high tensile strength structure, which method can be used in designing a high fatigue strength metal, said method comprising:

• measuring a maximum inhomogeneous elemental area B of a high fatigue strength structure after said high fatigue strength structure has been
• (i) made otherwise homogeneous by limiting the inhomogeneous elemental area, or
• (ii) minuturized by reducing a block width thereof;
• when said high fatigue strength structure has been made otherwise homogeneous by limiting the inhomogeneous elemental area, setting a distribution of a maximum-minimum range of said maximum inhomogeneous elemental area B in terms of μm within a range defined by the lines
• (a) B½=0, and
• (b) B½=0.9403y+4.571, wherein y is a standardizing parameter and a test standard area is 6.2×10−9 m2;
• and
• when said high fatigue strength structure has been miniaturized by reducing a block width thereof, setting a distribution of a maximum-minimum range of the block width d in terms of μm within a range defined by the lines
• (c) d=0, and
• (d) d=0.217y+0.701, wherein y is a standardizing parameter and a test standard area 1.0×10−10 m2.

A method of producing a high fatigue strength metal, comprising:

• designing a high fatigue strength metal by
• (i) obtaining a value σB corresponding to a tensile strength of a metal in terms of MPa;
• (ii) obtaining a value Hv corresponding to a Vickers hardness of said metal;
• and
• (iii) estimating a fatigue limit σw of said metal in terms of MPa to satisfy one of the following equations
• σw≧0.5 σB, (a)
• and
• σw≧1.6 Hv (b)
• when a fracture origin is located only at a surface of said metal, and when a square root of a flaw area contained in said metal is not greater than 45.8/σ2B or 4.47/Hv2;
• and
• evaluating a high tensile strength structure by
• (iv) measuring a maximum inhomogeneous elemental area B of a high fatigue strength structure after said high fatigue strength structure has been
• (a) made otherwise homogeneous by limiting the inhomogeneous elemental area, or
• (b) minuturized by reducing a block width thereof;
• (v) when said high fatigue strength has been made otherwise homogeneous by limiting the inhomogeneous elemental area, setting a distribution of a maximum-minimum range of said maximum inhomogeneous elemental area B in terms of μm within a range defined by the lines
• (1) B½=0, and
• (2) B½=0.9403y+4.571, wherein y is a standardizing parameter and a test standard area is 6.2×10−9 m2;
• and
• (vi) when said high fatigue strength structure has been miniaturized by reducing a block width thereof, setting a distribution of a maximum-minimum range of the block width d in terms of μm within a range defined by the lines
• (3) d=0, and
• (4) d=0.217y+0.701, wherein y is a standardizing parameter and a test standard area is 1.0×10−10 m2.

A method of producing a high fatigue strength metal, comprising:

• designing a high fatigue strength metal by
• (i) obtaining a value σB corresponding to a tensile strength of a metal in terms of MPa;
• (ii) obtaining a value Hv corresponding to a Vickers hardness of said metal;
• (iii) measuring a flaw area A of an inclusion of said metal when a fracture origin is located inside said metal;
• and
• (iv) estimating a fatigue limit σw of said metal in terms of Mpa to satisfy the equation σw≧3.38 A−¼;
• and
• evaluating a high tensile strength structure by
• (v) measuring a maximum inhomogeneous elemental area B of a high fatigue strength structure after said high fatigue strength structure has been
• (a) made otherwise homogeneous by limiting the inhomogeneous elemental area, or
• (b) minuturized by reducing a block width thereof;
• and
• (vi) when said high fatigue strength has been made otherwise homogeneous by limiting the inhomogeneous elemental area, getting a distribution of a maximum-minimum range of said maximum inhomogeneous elemental area B in terms of μm within a range defined by the lines
• (1) B½=0, and
• (2) B½=0.9403y+4.571, wherein y is a standardizing parameter and a test standard area is 6.2×10−9 m2;
• and
• (vii) when said high fatigue strength structure hag been miniaturized by reducing a block width thereof, setting a distribution of a maximum-minimum range of the block width d in terms of μm within a range defined by the lines
• (3) d=0, and
• (4) d=0.217y+0.701, wherein y is a standardizing parameter and a test standard area is 1.0×10−10 m2.

A method of producing a high fatigue strength metal, comprising:

• designing a high fatigue strength metal by
• (i) obtaining a value σB corresponding to a tensile strength of a metal in terms of MPa;
• (ii) obtaining a value Hv corresponding to a Vickers hardness of said metal;
• and
• (iii) estimating a fatigue limit σw of said metal in terms of MPa to satisfy one of the following equations
• σw≧0.5 σB, (a)
• and
• σw≧1.6 Hv (b)
• when a fracture origin is located only at a surface of said metal, and when a square root of a flaw area contained in said metal is not greater than 45.8/σ2B or 4.47/Hv2;
• and
• subjecting said metal to a heating operation in a vacuum of at least 2×10−6 Pa to temper said metal.

A high fatigue strength metal produced by:

• designing a high fatigue strength metal by
• (i) obtaining a value σB corresponding to a tensile strength of a metal in terms of MPa;
• (ii) obtaining a value Hv corresponding to a Vickers hardness of said metal;
• and
• (iii) estimating a fatigue limit σw of said metal in terms of MPa to satisfy one of the following equations
• σw≧0.5 σB, (a)
• and
• σw≧1.6 Hv (b)
• when a fracture origin is located only at a surface of said metal, and when a square root of a flaw area contained in said metal is not greater than 45.8/σ2B or 4.47/Hv2;
• and
• evaluating a high tensile strength structure by
• (iv) measuring a maximum inhomogeneous elemental area B of a high fatigue strength structure after said high fatigue strength structure has been
• (a) made otherwise homogeneous by limiting the inhomogeneous elemental area, or
• (b) minuturized by reducing a block width thereof;
• (v) when said high fatigue strength has been made otherwise homogeneous by limiting the inhomogeneous elemental area, setting a distribution of a maximum-minimum range of said maximum inhomogeneous elemental area B in terms of μm within a range defined by the lines
• (1) B½=0, and
• (2) B½=0.9403y+4.571, wherein y is a standardizing parameter and a test standard area is 6.2×10−9 m2;
• and
• (vi) when said high fatigue strength structure has been miniaturized by reducing a block width thereof, setting a distribution of a maximum-minimum range of the block width d in terms of μm within a range defined by the lines
• (3) d=0, and
• (4) d=0.217y+0.701, wherein y is a standardizing parameter and a test standard area is 1.0×10−10 m2.

A high fatigue strength metal produced by:

• designing a high fatigue strength metal by
• (i) obtaining a value σB corresponding to a tensile strength of a metal in terms of MPa;
• (ii) obtaining a value Hv corresponding to a Vickers hardness of said metal;
• (iii) measuring a flaw area A of an inclusion of said metal when fracture origin is located inside said metal;
• and
• (iv) estimating a fatigue limit σw of said metal in terms of Mpa to satisfy the equation σw≧3.38 A−¼;
• and
• evaluating a high tensile strength structure by
• (v) measuring a maximum inhomogeneous elemental area B of a high fatigue strength structure after said high fatigue strength structure has been
• (a) made otherwise homogeneous by limiting the inhomogeneous elemental area, or
• (b) minuturized by reducing a block width thereof;
• and
• (vi) when said high fatigue strength has been made otherwise homogeneous by limiting the inhomogeneous elemental area, setting a distribution of a maximum-minimum range of said maximum inhomogeneous elemental area B in terms of μm within a range defined by the lines
• (1) B½=0, and
• (2) B½=0.9403y+4.571, wherein y is a standardizing parameter and a test standard area is 6.2×10−9 m2;
• and
• (vii) when said high fatigue strength has been miniturized by reducing a block width thereof, setting a distribution of a maximum-minimum range of the block width d in terms of μm within a range defined by the lines
• (3) d=0, and
• (4) d=0.217y+0.701, wherein y is a standardizing parameter and a test standard area is 1.0×10−10 m2.