A hot-rolled steel sheet includes a specific chemical composition, and includes a microstructure represented by, in vol %: retained austenite: 2% to 30%; ferrite: 20% to 85%; bainite: 10% to 60%; pearlite: 5% or less; and martensite: 10% or less. A proportion of grains having an intragranular misorientation of 5° to 14° in all grains is 5% to 50% by area ratio, the grain being defined as an area which is surrounded by a boundary having a misorientation of 15° or more and has a circle-equivalent diameter of 0.3 μm or more.

A hot-rolled steel sheet includes a specific chemical composition, and includes a microstructure represented by, in vol %: retained austenite: 2% to 30%; ferrite: 20% to 85%; bainite: 10% to 60%; pearlite: 5% or less; and martensite: 10% or less. A proportion of grains having an intragranular misorientation of 5° to 14° in all grains is 5% to 50% by area ratio, the grain being defined as an area which is surrounded by a boundary having a misorientation of 15° or more and has a circle-equivalent diameter of 0.3 μm or more.

An apparatus line for manufacturing seamless steel pipes and tubes includes: a heating apparatus for heating a steel raw material; a piercing apparatus for piercing the heated steel raw material thus forming a hollow material; and a rolling apparatus for applying working to the hollow material to form a seamless steel pipe having a predetermined shape. A cooling apparatus is arranged on an exit side of the rolling apparatus. A heated steel raw material is worked by the rolling apparatus after being pierced by the piercing apparatus, and thereafter, using a surface temperature of a hollow piece before being cooled by the cooling apparatus as a cooling start temperature, the hollow piece is cooled to a cooling stop temperature differing by 50° C. or more from the cooling start temperature and being equal to or above 600° C. at an average cooling speed of 1.0° C./s or more in terms of an outer surface temperature.

An apparatus line for manufacturing seamless steel pipes and tubes includes: a heating apparatus for heating a steel raw material; a piercing apparatus for piercing the heated steel raw material thus forming a hollow material; and a rolling apparatus for applying working to the hollow material to form a seamless steel pipe having a predetermined shape. A cooling apparatus is arranged on an exit side of the rolling apparatus. A heated steel raw material is worked by the rolling apparatus after being pierced by the piercing apparatus, and thereafter, using a surface temperature of a hollow piece before being cooled by the cooling apparatus as a cooling start temperature, the hollow piece is cooled to a cooling stop temperature differing by 50° C. or more from the cooling start temperature and being equal to or above 600° C. at an average cooling speed of 1.0° C./s or more in terms of an outer surface temperature.

Methods of forming a high-strength metal alloy precursor by tailor-casting strips having a tailored thickness across a width of a strip material are provided. The tailor-cast strips have varying thickness throughout the width, which can then be further tailor rolled to a final required thickness profile/tailored thickness. Such tailor-casting method can be conducted by contacting a patterned surface of a casting roller or a casting block with a liquid high-strength metal alloy in a continuous casting process. The present disclosure provides methods of continuously casting a strip having varying thickness across the width allows for improved product in subsequent processing, like tailor rolling. Methods of making a high-strength metal alloy structural automotive component from a tailor-cast blank having a tailored thickness are also provided.

Methods of forming a high-strength metal alloy precursor by tailor-casting strips having a tailored thickness across a width of a strip material are provided. The tailor-cast strips have varying thickness throughout the width, which can then be further tailor rolled to a final required thickness profile/tailored thickness. Such tailor-casting method can be conducted by contacting a patterned surface of a casting roller or a casting block with a liquid high-strength metal alloy in a continuous casting process. The present disclosure provides methods of continuously casting a strip having varying thickness across the width allows for improved product in subsequent processing, like tailor rolling. Methods of making a high-strength metal alloy structural automotive component from a tailor-cast blank having a tailored thickness are also provided.

The present invention discloses a machining technology of a low-temperature high-strength-ductility high manganese steel, high manganese steel plate, and high manganese steel tube, and a high manganese steel comprises the following components in percentage by weight: Mn 30%-36%, C 0.02%-0.06%, S≦0.01%, P≦0.008% and the balance being Fe. Smelted steel ingots are subject to solution treatment and are rolled and homogenized to obtain a high manganese steel plate or are drawn to form a high manganese steel tube. The hot-rolled or cold-rolled steel plate after being hot-rolled has tremendous application value in the fields of low-temperature applications, such as the steel plate used for a low temperature pressure container.

The present invention discloses a machining technology of a low-temperature high-strength-ductility high manganese steel, high manganese steel plate, and high manganese steel tube, and a high manganese steel comprises the following components in percentage by weight: Mn 30%-36%, C 0.02%-0.06%, S≦0.01%, P≦0.008% and the balance being Fe. Smelted steel ingots are subject to solution treatment and are rolled and homogenized to obtain a high manganese steel plate or are drawn to form a high manganese steel tube. The hot-rolled or cold-rolled steel plate after being hot-rolled has tremendous application value in the fields of low-temperature applications, such as the steel plate used for a low temperature pressure container.

A high strength interstitial free low density steel and method for producing the steel.

A high strength interstitial free low density steel and method for producing the steel.