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.

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 production method for a high-strength steel sheet having a tensile strength TS of 780 MPa or more is provided. The production method comprises: heating a steel slab having a predetermined chemical composition; hotrolling the steel slab; coiling the hot-rolled sheet; subjecting the hot-rolled sheet to pickling treatment; holding the hot-rolled sheet in a pre-determined temperature range for predetermined time; cold rolling the hot-rolled sheet to obtain a cold-rolled sheet; subjecting the cold-rolled sheet to first annealing treatment; cooling the cold-rolled sheet at a pre-determined average cooling rate; cooling the cold-rolled sheet to room temperature; reheating the clod-rolled sheet to perform second annealing treatment; cooling the cold-rolled sheet at a first average cooling rate; cooling the cold-rolled sheet at a second average cooling rate; reheating the cold-rolled sheet to a predetermined reheating temperature range; and holding the cold-rolled sheet in the reheating temperature range.

A steel sheet has a composition comprising 0.060%≤C≤0.085%, 1.8%≤Mn≤2.0%, 0.4%≤Cr≤0.6%, 0.1%≤Si≤0.5%, 0.010%≤Nb≤0.025%, 3.42N≤Ti≤0.035%, 0≤Mo≤0.030%, 0.020%≤Al≤0.060%, 0.0012%≤B≤0.0030%, S≤0.005%, P≤0.050%, 0.002%≤N≤0.007% and optionally 0.0005%≤Ca≤0.005%, the remainder of the composition being iron and unavoidable impurities. The microstructure consists of 34% to 80% bainite, 10% to 16% martensite, and 10% to 50% of ferrite. The surface fraction of unrecrystallized ferrite, with respect to the whole structure, is of less than 30%. The martensite consists of self-tempered martensite and fresh martensite, the surface fraction of self-tempered martensite being comprised between 4% and 10%.

A steel sheet includes a predetermined composition, in which a microstructure at a ¼ thickness position from a surface in a sheet thickness direction includes, by vol %, ferrite: 80% or more, martensite: 2% or less, and residual austenite: 2% or less, a proportion of unrecrystallized ferrite in the ferrite of 5% or less, and in the microstructure of the steel sheet stretched by 10% at the ¼ thickness position from the surface in the sheet thickness direction, a number density of voids having a maximum diameter of 1.0 μm or more is 1.0×10.sup.9 pieces/m.sup.2 or less.

A hot stamped component, includes: a base material; and a Zn-based plating layer provided in contact with the base material as an upper layer of the base material and containing Zn and Ni. A region of the Zn-based plating layer on a base material side is a Fe—Zn solid solution containing Ni, and two or more twins exist in 10 crystal grains of the Fe—Zn solid solution containing Ni adjacent to an interface between the base material and the Zn-based plating layer.

Functionally graded materials may comprise a graded volume extending between a tungsten-based structure and a steel-based structure, where the graded volume comprises a plurality of additively manufactured layers. At least one of the plurality of additively manufactured layers may comprise a ternary element selected from vanadium and chromium. Some of the additively manufactured layers may further comprise aluminum.

A method of manufacturing steel strip including the steps of: casting molten steel into slabs; reheating the slabs at 1150° C. or more for 1 hour or more; hot rolling the steel into a strip, preferably with an average F1 slab entry temperature above 1000° C.; coiling the hot rolled steel strip; batch annealing the steel strip: at an intercritical temperature (i.e. between Ac1 and Ac3), preferably below 700° C.; in non-oxidising and non-nitrogenated atmosphere; total annealing time at least 5 hours, preferably at least 10 hours to get Mn enrichment in austenite such that Mn content is at least 1.25 times bulk Mn content of the steel and C enrichment such that C content is at least 1.2 times bulk C content of the steel; cooling the steel after batch annealing in air, forced air or water quench.

Provided is a high-strength steel sheet having high impact resistance. The steel sheet includes: by weight %, carbon (C): 0.05% to 0.14%, silicon (Si): 0.01% to 1.0%, manganese (Mn): 1.5% to 2.5%, aluminum (Al): 0.01% to 0.1%, chromium (Cr): 0.005% to 1.0%, phosphorus (P): 0.001% to 0.05%, sulfur (S): 0.001% to 0.01%, nitrogen (N): 0.001% to 0.01%, niobium (Nb): 0.005% to 0.06%, titanium (Ti): 0.005% to 0.11%, and the balance of iron (Fe) and inevitable impurities. The steel sheet has a microstructure comprising ferrite and bainite in a total area fraction of 90% or more. The steel sheet has a value of 0.05 to 1.0 as a shear texture ({110}<112>, {112}<111>) area ratio of a center region (ranging deeper than 1/10t to ½t in a thickness direction, t refers to thickness (mm)) and a surface region (ranging from a surface to 1/10t in the thickness direction).

[Problem] To provide: a roll-bonded body which is able to be suppressed in waviness in the surface; and a method for producing this roll-bonded body. [Solution] A roll-bonded body according to the present invention is obtained by bonding a first metal layer and a second metal layer with each other by means of rolling, and is characterized in that the surface of the first metal layer has an arithmetic average waviness (Wa.sub.1) 0.01-0.96 and a maximum waviness height (Wz.sub.1) of 0.2-5.0 μm.