The invention relates to a steel sheet skin-pass rolled with a deterministic surface structure, and to a method for producing it.

A hot-press formed product can be achieved which has regions corresponding to a shock resistant portion and an energy absorption portion within a single formed product without applying a welding method and achieves the balance of high strength and elongation with a high level according to each region by means of having a first forming region exhibiting a metal structure containing martensite: 80-97 area % and retained austenite: 3-20 area % respectively, the remaining structure being 5 area % or less, and a second forming region exhibiting a metal structure containing annealed martensite or annealed bainite: 30-97 area %, martensite as quenched: 0-67 area %, and retained austenite: 3-20 area %.

A steel for wheel contains, in mass %, C: 0.65 to 0.84%, Si: 0.4 to 1.0%, Mn: 0.50 to 1.40%, Cr: 0.02 to 0.13%, S: 0.04% or less and V: 0.02 to 0.12%, wherein Fn1 expressed by formula (1) is 32 to 43, and Fn2 expressed by formula (2) is 25 or less, the balance being Fe and impurities. P, Cu and Ni as impurities are P: 0.05% or less, Cu: 0.20% or less and Ni: 0.20% or less:
Fn1=2.7+29.5'C+2.9'Si+6.9'Mn+10.8'Cr+30.3'Mo+44.3'V   (1)
Fn2=exp(0.76)'exp(0.05'C)'exp(1.35'Si)'exp(0.38'Mn)'exp(0.77'Cr)'exp(3.0'Mo)'exp(4.6'V)  (2).
The steel has excellent properties for use as a wheel.

A hot press-forming method includes a forming step that clamps a steel sheet heated to a temperature not less than an austenite transformation temperature and press-forms the steel sheet into a desired shape by causing a forming concave of a die and a convex of a punch to be close to each other. A formed portion has side and top portions that merge. The side portion rises up from an inner circumferential edge of a flange portion having been clamped by the die and the blank holder. A cooling step cools a region of the steel sheet after the heating step has been completed and before the forming step is completed. The particular region is along an inter-edge area formed between an opening circumferential edge of the forming concave and a top circumferential edge of the forming convex before the forming step is completed.

A method of performing a localized post weld heat treatment on a weld seam in a thin wall metallic body may include attaching thermocouples to the outside surface of the weld seam and covering the weld seam with a thermal insulating blanket. Cooling bands are attached to the outside of the body on both sides of the weld seam. An inert atmosphere enclosure with inlet and exhaust ports is fitted over the weld seam, thermal insulating blanket, and cooling bands. A power supply and control system for an induction coil or coils situated in close proximity to the weld seam are actuated and the weld seam is subjected to a heat treatment without thermally affecting regions of the metallic body adjacent to the weld seam and external to the cooling bands.

A tool for manufacturing hot formed structural components having locally different microstructures and mechanical properties, the tool comprising upper and lower mating dies, each die being formed by two or more die blocks (10) comprising one or more working surfaces (34) that in use face the structural component to be formed and one or more supporting blocks, the upper and lower dies comprising die blocks are adapted to operate at different temperatures corresponding to zones of the structural component to be formed having locally different microstructures and mechanical properties, the die blocks including one or more warm die blocks adapted to operate at a higher temperature, and one or more cold die blocks adapted to operate at a lower temperature, and wherein at least one of the warm die blocks is an electrically conductive die block which is electrically connected to a current source configured to provide a DC current through the die block to control the temperature of the die block. Furthermore, a method for manufacturing hot formed structural components is also provided.

A waterwall panel welding apparatus is provided. The apparatus includes an inlet assembly, a welding assembly, an outlet assembly, and a heating system. The inlet assembly is for receiving a plurality of tubes. The welding assembly is for receiving the tubes from the inlet assembly and for allowing the tubes to be welded together to form a waterwall panel. The outlet assembly is for receiving the waterwall panel from the welding assembly. The heating system heats the tubes and operates via magnetic induction.

A hot-stamping formed body has a predetermined chemical composition and a microstructure including, by area ratio, 90% to 100% of martensite and 0% to 10% of a remainder in the microstructure. In the microstructure, a region in which an average GAIQ value in a unit grain is 60,000 or more is 30 area % or more, and a number density of carbides having a circle equivalent diameter of 0.20 μm or more is 50/mm.sup.2 or less.

A press-hardened shaped metal sheet has at least two adjacent zones having different sheet thicknesses and different strengths such that one of the zones is press-hardened and the other zone is non-hardened or only slightly hardened. A transition zone, which is simultaneously designed as a thickness transition zone and as a strength transition zone, is located between the zones. The press-hardened shaped metal sheet is preferably a pillar reinforcement for a motor vehicle body.

A method for manufacturing a high-strength cold-rolled steel sheet includes a temperature distribution forming step of forming a temperature distribution in a width direction of a steel sheet such that a temperature of the steel sheet increases from an end of the steel sheet in the width direction toward a center part of the steel sheet in the width direction, and a water quenching step of performing water quenching treatment on the steel sheet by immersing, in cooling water, the steel sheet on which the temperature distribution is formed in the width direction.