High strength wire rod excellent in drawability and method of producing same

A high strength wire rod having a high reduction of area, comprising:

• at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Al:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities,
• wherein a tensile strength (MPa) of the wire rod is specified by the following formula,
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450],
• wherein, in a portion from a surface to a depth of 100 μm of the at least one portion, an area fraction of a non-pearlite structure is approximately at most 10%, and the balance is composed of a pearlite structure, and
• where the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along grain boundaries of a prior austenite.

A high strength wire rod having a high reduction of area, comprising:

• at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Al:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities,
• wherein a tensile strength (MPa) of the at least one portion is specified by the following formula,
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450],
• wherein, in a section from a surface to a central portion of the at least one portion, an area fraction of a non-pearlite structure is approximately at most 5%, and the balance is composed of a pearlite structure, and
• where the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along a grain boundaries of a prior austenite.

A high strength wire rod having a high reduction of area, comprising:

• at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Ti:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities,
• wherein a tensile strength (MPa) of the wire rod is specified by the following formula,
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450], and
• wherein in the at least one portion from a surface to a depth of 100 μm, an area fraction of a non-pearlite structure is approximately at most 10%, and the balance is composed of a pearlite structure, and
• wherein the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along grain boundaries of a prior austenite.

A high strength wire rod having a high reduction of area, comprising:

• at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Ti:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities,
• wherein a tensile strength (MPa) of the wire rod is specified by the following formula:
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450],
• wherein, in the at least one section from a surface to a central portion thereof, an area fraction of a non-pearlite structure is approximately at most 5%, and the balance is composed of a pearlite structure, and
• wherein the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along grain boundaries of a prior austenite.

A method of producing a wire rod, comprising:

• hot-rolling steel in a form of a billet comprising at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Al:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities, wherein a tensile strength (MPa) of the wire rod is specified by the following formula,
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450],
• wherein, in a portion from a surface to a depth of 100 μm of the at least one portion, an area fraction of a non-pearlite structure is approximately at most 10%, and the balance is composed of a pearlite structure, and
• where the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along grain boundaries of a prior austenite;
• coiling the rolled steel at a temperature of approximately 800 to 950° C.;
• and patent-treating the steel,
• wherein the patent-treating procedure is performed by at least one of (i) directly dipping the steel in a molten salt of approximately 480 to 650° C. within a particular period after the coiling step and subsequent to the hot-rolling step, or (ii) by cooling the steel to a temperature of about 200° C. or less by at least one of molten-salt cooling, Stelmore cooling, or natural-air cooling re-austenitizing the steel at a temperature of approximately 950° C. or more, and dipping the steel in a molten lead of approximately 480 to 650° C., the predetermined period being defined by the following particular formula:
• predetermined period=0.0013×(Tr−815)2+7×(B content−0.0003)/(N content−Ti content/3.41−B content+0.0003), and
• wherein the predetermined period is about 40 seconds that can be a period usable in the method if a value of (N content−Ti content/3.41−B content+0.0003) is zero or smaller, or if a value of the predetermined period is determined by the particular formula to be greater than 40 seconds.

A method of producing a wire rod, comprising:

• hot-rolling steel in a form of a billet comprising at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Al:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities, wherein a tensile strength (MPa) of the at least one portion is specified by the following formula,
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450],
• wherein, in a section from a surface to a central portion of the at least one portion, an area fraction of a non-pearlite structure is approximately at most 5%, and the balance is composed of a pearlite structure, and where the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along a grain boundaries of a prior austenite;
• coiling the rolled steel at a temperature of approximately 800 to 950° C.;
• and patent-treating the steel,
• wherein the patent-treating procedure is performed by at least one of (i) directly dipping the steel in a molten salt of approximately 480 to 650° C. within a particular period after the coiling step and subsequent to the hot-rolling step, or (ii) by cooling the steel to a temperature of about 200° C. or less by at least one of molten-salt cooling, Stelmore cooling, or natural-air cooling re-austenitizing the steel at a temperature of approximately 950° C. or more, and dipping the steel in a molten lead of approximately 480 to 650° C., the predetermined period being defined by the following particular formula:
• predetermined period=0.0013×(Tr−815)2+7×(B content−0.0003)/(N content−Ti content/3.41−B content+0.0003), and
• wherein the predetermined period is about 40 seconds that can be a period usable in the method if a value of (N content−Ti content/3.41−B content+0.0003) is zero or smaller, or if a value of the predetermined period is determined by the particular formula to be greater than 40 seconds.

A method of producing a wire rod, comprising:

• hot-rolling steel in a form of a billet comprising at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Ti:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities, wherein a tensile strength (MPa) of the wire rod is specified by the following formula,
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450], and
• wherein in the at least one portion from a surface to a depth of 100 μm, an area fraction of a non-pearlite structure is approximately at most 10%, and the balance is composed of a pearlite structure, and
• wherein the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along grain boundaries of a prior austenite;
• coiling the rolled steel at a temperature of approximately 800 to 950° C.;
• and patent-treating the steel,
• wherein the patent-treating procedure is performed by at least one of (i) directly dipping the steel in a molten salt of approximately 480 to 650° C. within a particular period after the coiling step and subsequent to the hot-rolling step, or (ii) by cooling the steel to a temperature of about 200° C. or less by at least one of molten-salt cooling, Stelmore cooling, or natural-air cooling re-austenitizing the steel at a temperature of approximately 950° C. or more, and dipping the steel in a molten lead of approximately 480 to 650° C., the predetermined period being defined by the following particular formula:
• predetermined period=0.0013×(Tr−815)2+7×(B content−0.0003)/(N content−Ti content/3.41−B content+0.0003), and
• wherein the predetermined period is about 40 seconds that can be a period usable in the method if a value of (N content−Ti content/3.41−B content+0.0003) is zero or smaller, or if a value of the predetermined period is determined by the particular formula to be greater than 40 seconds.

A method of producing a wire rod, comprising:

• hot-rolling steel in a form of a billet comprising at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Ti:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities, wherein a tensile strength (MPa) of the wire rod is specified by the following formula:
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450],
• wherein, in the at least one section from a surface to a central portion thereof, an area fraction of a non-pearlite structure is approximately at most 5%, and the balance is composed of a pearlite structure, and
• wherein the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along grain boundaries of a prior austenite;
• coiling the rolled steel at a temperature of approximately 800 to 950° C.;
• and patent-treating the steel,
• wherein the patent-treating procedure is performed by at least one of (i) directly dipping the steel in a molten salt of approximately 480 to 650° C. within a particular period after the coiling step and subsequent to the hot-rolling step, or (ii) by cooling the steel to a temperature of about 200° C. or less by at least one of molten-salt cooling, Stelmore cooling, or natural-air cooling re-austenitizing the steel at a temperature of approximately 950° C. or more, and dipping the steel in a molten lead of approximately 480 to 650° C., the predetermined period being defined by the following particular formula:
• predetermined period=0.0013×(Tr−815)2+7×(B content−0.0003)/(N content−Ti content/3.41−B content+0.0003), and
• wherein the predetermined period is about 40 seconds that can be a period usable in the method if a value of (N content−Ti content/3.41−B content+0.0003) is zero or smaller, or if a value of the predetermined period is determined by the particular formula to be greater than 40 seconds.

A method of producing a wire rod, comprising:

• hot-rolling steel in a form of a billet comprising at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Al:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities, wherein a tensile strength (MPa) of the wire rod is specified by the following formula,
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450],
• wherein, in a portion from a surface to a depth of 100 μm of the at least one portion, an area fraction of a non-pearlite structure is approximately at most 10%, and the balance is composed of a pearlite structure, and
• where the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along grain boundaries of a prior austenite;
• directly after the hot-rolling step, coiling the rolled steel at a temperature of approximately 800 to 950° C.;
• cooling the steel within a range of approximately 15 to 150° C./sec to a particular range 480 to 650° C. within a predetermined period after the cooling-coiling step subsequent to the hot-rolling, and
• patent-treatment of the steel at the particular range, wherein the predetermined period is defined by the following particular formula:
• predetermined period=0.0013×(Tr−815)2+7×(B content−0.0003)/(N content−Tr content/3.41−B content+0.0003),
• wherein the predetermined period of approximately 40 seconds is selectable as a period usable in the method if a value of (N content−Ti content/3.41−B content+0.0003) is zero or smaller, or if a value of the predetermined period is determined by the predetermined formula to be is greater than approximately 40 seconds.

A method of producing a wire rod, comprising:

• hot-rolling steel in a form of a billet comprising at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Al:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities, wherein a tensile strength (MPa) of the at least one portion is specified by the following formula,
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450],
• wherein, in a section from a surface to a central portion of the at least one portion, an area fraction of a non-pearlite structure is approximately at most 5%, and the balance is composed of a pearlite structure, and
• where the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along a grain boundaries of a prior austenite;
• directly after the hot-rolling step, coiling the rolled steel at a temperature of approximately 800 to 950° C.;
• cooling the steel within a range of approximately 15 to 150° C./sec to a particular range 480 to 650° C. within a predetermined period after the cooling-coiling step subsequent to the hot-rolling, and
• patent-treatment of the steel at the particular range, wherein the predetermined period is defined by the following particular formula:
• predetermined period=0.0013×(Tr−815)2+7×(B content−0.0003)/(N content−Tr content/3.41−B content+0.0003),
• wherein the predetermined period of approximately 40 seconds is selectable as a period usable in the method if a value of (N content−Ti content/3.41−B content+0.0003) is zero or smaller, or if a value of the predetermined period is determined by the predetermined formula to be is greater than approximately 40 seconds.

A method of producing a wire rod, comprising:

• hot-rolling steel in a form of a billet comprising at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Ti:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities, wherein a tensile strength (MPa) of the wire rod is specified by the following formula,
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450], and
• wherein in the at least one portion from a surface to a depth of 100 μm, an area fraction of a non-pearlite structure is approximately at most 10%, and the balance is composed of a pearlite structure, and
• wherein the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along grain boundaries of a prior austenite;
• directly after the hot-rolling step, coiling the rolled steel at a temperature of approximately 800 to 950° C.;
• cooling the steel within a range of approximately 15 to 150° C./sec to a particular range 480 to 650° C. within a predetermined period after the cooling-coiling step subsequent to the hot-rolling, and
• patent-treatment of the steel at the particular range, wherein the predetermined period is defined by the following particular formula:
• predetermined period=0.0013×(Tr−815)2+7×(B content−0.0003)/(N content−Tr content/3.41−B content+0.0003),
• wherein the predetermined period of approximately 40 seconds is selectable as a period usable in the method if a value of (N content−Ti content/3.41−B content+0.0003) is zero or smaller, or if a value of the predetermined period is determined by the predetermined formula to be is greater than approximately 40 seconds.

A method of producing a wire rod, comprising:

• hot-rolling steel in a form of a billet comprising at least one portion which has approximately, in mass %, C:
• 0.7 to 1.2%, Si:
• 0.35 to 1.5%, Mn:
• 0.1 to 1.0%, N:
• 0.001 to 0.006%, Ti:
• 0.005 to 0.1%, B:
• 0.0004 to 0.0060%,
• wherein a solid-solubilized amount of B is approximately, by mass %, at least 0.0002%, and the balance consisting of Fe and unavoidable impurities, wherein a tensile strength (MPa) of the wire rod is specified by the following formula:
• TS≧[1000×C content (%)−10×wire-diameter (mm)+450],
• wherein, in the at least one section from a surface to a central portion thereof, an area fraction of a non-pearlite structure is approximately at most 5%, and the balance is composed of a pearlite structure, and
• wherein the non-pearlite structure is composed of at least one of a pro-eutectoid ferrite, a degenerate-pearlite or a bainite generating along grain boundaries of a prior austenite;
• directly after the hot-rolling step, coiling the rolled steel at a temperature of approximately 800 to 950° C.;
• cooling the steel within a range of approximately 15 to 150° C./sec to a particular range 480 to 650° C. within a predetermined period after the cooling-coiling step subsequent to the hot-rolling, and
• patent-treatment of the steel at the particular range, wherein the predetermined period is defined by the following particular formula:
• predetermined period=0.0013×(Tr−815)2+7×(B content−0.0003)/(N content−Tr content/3.41−B content+0.0003),
• wherein the predetermined period of approximately 40 seconds is selectable as a period usable in the method if a value of (N content−Ti content/3.41−B content+0.0003) is zero or smaller, or if a value of the predetermined period is determined by the predetermined formula to be is greater than approximately 40 seconds.