A steel for forging mechanical parts including of the following elements 0.04%≤C≤0.28%; 1.2%≤Mn≤2.2%; 0.3%≤Si≤1.2%; 0.5%≤Cr≤1.5%; 0.01%≤Ni≤1%; 0%≤S≤0.06%; 0%≤P≤0.02%; 0%≤N≤0.015%; 0%≤Al≤0.1%; 0.03%≤Mo≤0.5%; 0%≤Cu≤0.5%; 0.04%≤Nb≤0.15%; 0.01%≤Ti≤0.1%; 0%≤V≤0.5%; 0.0015%≤B≤0.004%; the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel having microstructure including in area fraction, 55% to 85% of Martensite, 20% to 45% of Auto-tempered Martensite, 0 to 10% Residual Austenite and, wherein cumulated amounts of Auto-tempered martensite and martensite is at least 90%.

A steel for forging mechanical parts including of the following elements 0.04%≤C≤0.28%; 1.2%≤Mn≤2.2%; 0.3%≤Si≤1.2%; 0.5%≤Cr≤1.5%; 0.01%≤Ni≤1%; 0%≤S≤0.06%; 0%≤P≤0.02%; 0%≤N≤0.015%; 0%≤Al≤0.1%; 0.03%≤Mo≤0.5%; 0%≤Cu≤0.5%; 0.04%≤Nb≤0.15%; 0.01%≤Ti≤0.1%; 0%≤V≤0.5%; 0.0015%≤B≤0.004%; the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel having microstructure including in area fraction, 55% to 85% of Martensite, 20% to 45% of Auto-tempered Martensite, 0 to 10% Residual Austenite and, wherein cumulated amounts of Auto-tempered martensite and martensite is at least 90%.

A 780 MPa-grade ultra-high reaming steel having high surface quality and high performance stability, and a manufacturing method therefor. The ultra-high reaming steel comprises the following components in percentage by weight: 0.03-0.08% of C, Si≤0.2%, 0.5-2.0% of Mn, P≤0.02%, S≤0.003%, 0.01-0.08% of Al, N≤0.004%, 0.05-0.20% of Ti, 0.1-0.5% of Mo, Mg≤0.005%, O≤0.0030%, and the remainder being Fe and other inevitable impurities. The ultra-high reaming steel of the present invention achieves matching between good structure homogeneity and performance homogeneity and excellent strength, plasticity, and ultra-high reaming rate; the ultra-high reaming steel has yield strength greater than or equal to 750 MPa, tensile strength greater than or equal to 780 MPa, an elongation A50 greater than or equal to 15%, and a reaming rate greater than or equal to 70%; moreover, appearance of red iron scales on the surface of a steel plate can be avoided, thereby improving the surface quality of pickled high-strength steel; the ultra-high reaming steel can satisfy user requirements well, and can be applied to parts of passenger vehicle chassis components such as a control arm and an auxiliary frame, which require high strength and thinning.

A 780 MPa-grade ultra-high reaming steel having high surface quality and high performance stability, and a manufacturing method therefor. The ultra-high reaming steel comprises the following components in percentage by weight: 0.03-0.08% of C, Si≤0.2%, 0.5-2.0% of Mn, P≤0.02%, S≤0.003%, 0.01-0.08% of Al, N≤0.004%, 0.05-0.20% of Ti, 0.1-0.5% of Mo, Mg≤0.005%, O≤0.0030%, and the remainder being Fe and other inevitable impurities. The ultra-high reaming steel of the present invention achieves matching between good structure homogeneity and performance homogeneity and excellent strength, plasticity, and ultra-high reaming rate; the ultra-high reaming steel has yield strength greater than or equal to 750 MPa, tensile strength greater than or equal to 780 MPa, an elongation A50 greater than or equal to 15%, and a reaming rate greater than or equal to 70%; moreover, appearance of red iron scales on the surface of a steel plate can be avoided, thereby improving the surface quality of pickled high-strength steel; the ultra-high reaming steel can satisfy user requirements well, and can be applied to parts of passenger vehicle chassis components such as a control arm and an auxiliary frame, which require high strength and thinning.

A 980 MPa-grade full-bainite ultra-high hole expansion steel and a manufacturing method therefor. The hole expansion steel has the following chemical compositions in percentage by weight: 0.05-0.10% of C, Si≤2.0%, 1.0-2.0% of Mn, P≤0.02%, S≤0.003%, 0.02-0.08% of Al, N≤0.004%, 0.1-0.5% of Mo, 0.01-0.05% of Ti, O≤0.0030%, the remainder being Fe, and other inevitable impurities. The ultra-high hole expansion steel in the present invention has yield strength ≥800 MPa, tensile strength ≥980 MPa, and a hole expansion rate up to 60% or more, and can be applied in the parts of chassis components such as a control arm and an auxiliary frame, which require high strength thinning and complex forming, of passenger vehicles.

A 980 MPa-grade full-bainite ultra-high hole expansion steel and a manufacturing method therefor. The hole expansion steel has the following chemical compositions in percentage by weight: 0.05-0.10% of C, Si≤2.0%, 1.0-2.0% of Mn, P≤0.02%, S≤0.003%, 0.02-0.08% of Al, N≤0.004%, 0.1-0.5% of Mo, 0.01-0.05% of Ti, O≤0.0030%, the remainder being Fe, and other inevitable impurities. The ultra-high hole expansion steel in the present invention has yield strength ≥800 MPa, tensile strength ≥980 MPa, and a hole expansion rate up to 60% or more, and can be applied in the parts of chassis components such as a control arm and an auxiliary frame, which require high strength thinning and complex forming, of passenger vehicles.

Disclosed are a 980 MPa-grade bainite high hole expansion steel and a manufacturing method therefor. The steel contains the following chemical components in percentages by weight: 0.05-0.10% of C, 0.5-2.0% of Si, 1.0-2.0% of Mn, P≤0.02%, S≤0.003%, 0.02-0.08% of Al, N≤0.004%, Mo≥0.1%, 0.01-0.05% of Ti, Cr≤0.5%, B≤0.002%, O≤0.0030%, and the balance of Fe and other inevitable impurities. The high hole expansion steel of the present invention has a yield strength of ≥800 MPa and a tensile strength of ≥980 MPa, has a good elongation rate (the transverse A.sub.50 being ≥11%) and hole expansion performance (the hole expansion ratio being ≥40%), and can be applied to a position on a chassis part of a passenger car, such as a control arm and a vice frame, where high strength and thinning are required.

Disclosed are a 980 MPa-grade bainite high hole expansion steel and a manufacturing method therefor. The steel contains the following chemical components in percentages by weight: 0.05-0.10% of C, 0.5-2.0% of Si, 1.0-2.0% of Mn, P≤0.02%, S≤0.003%, 0.02-0.08% of Al, N≤0.004%, Mo≥0.1%, 0.01-0.05% of Ti, Cr≤0.5%, B≤0.002%, O≤0.0030%, and the balance of Fe and other inevitable impurities. The high hole expansion steel of the present invention has a yield strength of ≥800 MPa and a tensile strength of ≥980 MPa, has a good elongation rate (the transverse A.sub.50 being ≥11%) and hole expansion performance (the hole expansion ratio being ≥40%), and can be applied to a position on a chassis part of a passenger car, such as a control arm and a vice frame, where high strength and thinning are required.

A low-carbon martensitic high hole expansion steel with a tensile strength above 980 MPa, and a manufacturing method therefor, the weight percentage of the chemical components thereof being: C 0.03-0.10%, Si 0.5-2.0%, Mn 1.0-2.0%, P≤0.02%, S≤0.003%, Al 0.02-0.08%, N≤0.004%, Mo 0.1-0.5%, Ti 0.01-0.05%, and O≤0.0030%, and the remainder being Fe and other inevitable impurities. The high hole expansion steel of the present invention has a yield strength of ≥800 MPa and tensile strength of ≥980 MPa, a lateral extension rate A50≥8%, and a hole expansion ratio of ≥30%, passes cold bending performance tests (d≤4a, 180°), and can be used for passenger car chassis parts that require high strength and thinning such as control arms and sub-frames.

A low-carbon martensitic high hole expansion steel with a tensile strength above 980 MPa, and a manufacturing method therefor, the weight percentage of the chemical components thereof being: C 0.03-0.10%, Si 0.5-2.0%, Mn 1.0-2.0%, P≤0.02%, S≤0.003%, Al 0.02-0.08%, N≤0.004%, Mo 0.1-0.5%, Ti 0.01-0.05%, and O≤0.0030%, and the remainder being Fe and other inevitable impurities. The high hole expansion steel of the present invention has a yield strength of ≥800 MPa and tensile strength of ≥980 MPa, a lateral extension rate A50≥8%, and a hole expansion ratio of ≥30%, passes cold bending performance tests (d≤4a, 180°), and can be used for passenger car chassis parts that require high strength and thinning such as control arms and sub-frames.