The invention relates to a high strength steel with a careful selection of the normal alloying elements C, Mn, Si and Al, together with micro-element addition. This a steel with a high strength and high hole expansion ratio can be produced. The invention also relates to the method to manufacture this high strength steel.

The invention relates to a high strength steel with a careful selection of the normal alloying elements C, Mn, Si and Al, together with micro-element addition. This a steel with a high strength and high hole expansion ratio can be produced. The invention also relates to the method to manufacture this high strength steel.

Provided is a steel sheet and a method for manufacturing same, the steel sheet, which is optimized a composition and microstructure, and which can be used for automobile parts and the like, having superb bendability, and superior balance of strength and ductility and of strength and hole expansion ratio.

Disclosed are a low-silicon and low-carbon equivalent GPa grade multi-phase steel plate/steel strip and a manufacturing method therefor. The steel plate/steel strip comprises the following components in percentages by weight: 0.03-0.07% of C, 0.1-0.5% of Si, 1.7-2.0% of Mn, P<0.02%, S<0.01%, N<0.01%, 0.01-0.05% of Al, 0.4-0.7% of Cr, 0.001-0.005% of B, and 0.07-0.15% of Ti, and also comprises one or both of 0.15-0.4% of Mo or 0.02-0.08% of Nb, with the balance being Fe and other inevitable impurities; and at the same time, the steel plate/steel strip satisfies: the content of available B*>0.001, the content of available B*=B-[Ti-3.4N-1.2(C—Nb/7.8)]/22, CE<0.58, and CE=C+Mn/6+(Cr+Mo+V)/5+(Si+Ni+Cu)/15. The steel plate has a tensile strength of >980 MPa and a yield strength of >780 MPa, and the hole expansion rate satisfies: if an original hole is a punched hole, the hole expansion rate is >50%; and if the original hole is a reamed hole, the hole expansion rate is >60%. The steel plate is mainly used in the preparation of vehicle chassis and suspension system parts.

Disclosed are a low-silicon and low-carbon equivalent GPa grade multi-phase steel plate/steel strip and a manufacturing method therefor. The steel plate/steel strip comprises the following components in percentages by weight: 0.03-0.07% of C, 0.1-0.5% of Si, 1.7-2.0% of Mn, P<0.02%, S<0.01%, N<0.01%, 0.01-0.05% of Al, 0.4-0.7% of Cr, 0.001-0.005% of B, and 0.07-0.15% of Ti, and also comprises one or both of 0.15-0.4% of Mo or 0.02-0.08% of Nb, with the balance being Fe and other inevitable impurities; and at the same time, the steel plate/steel strip satisfies: the content of available B*>0.001, the content of available B*=B-[Ti-3.4N-1.2(C—Nb/7.8)]/22, CE<0.58, and CE=C+Mn/6+(Cr+Mo+V)/5+(Si+Ni+Cu)/15. The steel plate has a tensile strength of >980 MPa and a yield strength of >780 MPa, and the hole expansion rate satisfies: if an original hole is a punched hole, the hole expansion rate is >50%; and if the original hole is a reamed hole, the hole expansion rate is >60%. The steel plate is mainly used in the preparation of vehicle chassis and suspension system parts.

Disclosed are a low-cost ultra-high-strength multiphase steel plate/steel strip and its manufacturing method. Said steel plate/steel strip comprises the following components in percentage by weight: 0.03 to 0.07% of C, 0.1 to 0.5% of Si, 1.3 to 1.9% of Mn, less than or equal to 0.02% of P, less than or equal to 0.01% of S, 0.01 to 0.05% of Al, 0.2 to 0.5% of Cr, 0.07 to 0.14% of Ti, less than 0.03% of (Ni+Nb+Mo+V), and the balance being Fe and other inevitable impurities; and Mn+1.5Cr+5(Ti+Al+Cu)+10(Mo+Ni)+20(Nb+V)<3.0; Mn+2Cr+4Ti+4Nb+4V+4Mo—Si/3+2C≤3.0. The steel plate is mainly used for the manufacturing of automotive chassis and suspension system parts.

The present disclosure relates to a wear resistant steel material that is not cracked even after being cut using gas, etc., and a method of manufacturing the wear resistant steel material.

A steel sheet includes a predetermined composition satisfying Expression (1), in which the microstructure at the ¼ thickness position from the surface in the sheet thickness direction includes, by vol %, ferrite: 95% or more and a remainder of the microstructure: 5% or less, has a proportion of unrecrystallized ferrite in the ferrite of 5% or less, and a half width w and an X-ray wavelength λ at a peak of (200) plane of the ferrite satisfy Expression (2).

0.80≤{(Ti/48−N/14)+Nb/93}/(C/12)≤5.00  (1)

w×λ≥0.20  (2)

A steel sheet includes a predetermined composition satisfying Expression (1), in which the microstructure at the ¼ thickness position from the surface in the sheet thickness direction includes, by vol %, ferrite: 95% or more and a remainder of the microstructure: 5% or less, has a proportion of unrecrystallized ferrite in the ferrite of 5% or less, and a half width w and an X-ray wavelength λ at a peak of (200) plane of the ferrite satisfy Expression (2).

0.80≤{(Ti/48−N/14)+Nb/93}/(C/12)≤5.00  (1)

w×λ≥0.20  (2)

This hot-rolled steel sheet has a predetermined chemical composition, in which a metallographic structure contains, by area %, more than 92.0% and 100.0% or less of martensite and tempered martensite in total, less than 3.0% of residual austenite, and less than 5.0% of ferrite, has a ratio S.sub.60/S.sub.7, which is a ratio of a density S.sub.60 of a length of a grain boundary having a crystal misorientation of 60° to a density S.sub.7 of a length of a grain boundary having a crystal misorientation of 7° about a <110> direction, of more than 0.34 and less than 0.60, has a standard deviation of a Mn concentration of 0.60 mass % or less, and has a tensile strength of 980 MPa or more.