Abstract: The present invention provides a weathering steel for solid-state welding that forms an excellent weld when subjected to solid-state welding and has tensile properties equivalent or superior to those of high tensile strength steel, said steel having weathering properties superior to those of conventional weathering steel for welding, wherein the reliability of the weld is equivalent or superior to that of the parent material; and a weathering steel material for solid-state welding. Further, there is provided a solid-state welded structure that includes the weathering steel for solid-state welding according to the present invention, and a solid-state welding method for said weathering steel for solid-state welding. The weathering steel for solid-state welding having a steel composition comprises, in % by mass, C: 0.10 to 0.60% and P: more than 0.035 to 1.000%, with the remainder consisting of Fe and unavoidable impurities.

Abstract: An iron scrap having a composition comprising iron and iron-soluble elements in the sum of 100 mass %, and containing Cu, elements of the Groups IIIa, VIII, Ib, IIb, IIIb, IVb and Vb having affinity with Cu, and unavoidable impurities, is melted in an oxygen-containing atmosphere. A predetermined amount of C, and whenever necessary, a predetermined amount of at least one of Cr and Mo and/or a predetermined amount of at least one of Mn, V and Ti, are added to the molten steel. The molten iron is then separated into an Fe-enriched layer and a Cu-enriched layer under the molten state. Cu and the above elements having affinity with Cu are separated and precipitated into the Cu-enriched layer by utilizing the difference of the specific gravity between the layers. According to this method, impurity elements detrimental to the stable production of a steel material having a homogeneous property, such as Cu, Sn, etc., can be removed economically and efficiently when the iron scrap is recycled.

Abstract: The cold rolled steel sheet or galvanized steel sheet comprises by weight C: 0.0001 to 0.0026%, Si: not more than 1.2%, Mn: 0.03 to 3.0%, P: 0.015 to 0.15%, S: 0.0010 to 0.020%, Al: 0.005 to 0.1%, N: 0.0005 to 0.0080% and B: 0.0003 to 0.0030% with the balance consisting of Fe and unavoidable impurities. A process for producing the above steel sheet is also provided which comprises the steps of: performing hot roll finishing of a slab having the above chemical composition at the Ar.sub.3 transformation point or above; preferably, then cooling the hot rolled strip, within 1.5 sec after the completion of the hot rolling, to 750.degree. C. at a rate of not less than 50.degree. C./sec; coiling the strip in the temperature range of from room temperature to 750.degree. C.; cold rolling the coiled strip a reduction ratio of not less than 70%; subjecting the cold rolled strip to continuous annealing at 600.degree. to 900.degree. C.

Abstract: The present invention provides a cold-rolled steel sheet and a hot-dip galvanized steel sheet having good bake hardenability, non-aging properties at room temperature and good formability and a process for producing the same. An extra low carbon steel or an extra low carbon steel containing at least one element selected from Ti and Nb is annealed at a temperature of not lower than the AC.sub.3 transformation point to bring the structure after annealing to a structure of low-temperature transformation products. This makes it possible to provide a steel sheet that has a combination of high paint-bake hardenability and non-aging properties at room temperature and is excellent also in formability in respect of average r value (deep drawability) and elongation (punch stretchability). In particular, with respect to paint-bake hardenability, a BH property on a high level up to about 10 kgf/mm.sup.

Abstract: The present invention provides a non-aging at room temperature ferritic single-phase cold-rolled steel sheet or hot-dip galvanized steel sheet for deep drawing and having excellent fabrication embrittlement resistance and paint-bake hardenability, by heating a slab comprising, in terms of % by weight, 0.0001 to 0.0015% of C, not more than 1.2% of Si, 0.03 to 3.0% of Mn, 0.01 to 0.15% of P, 0.0010 to 0.020% of S, 0.005 to 0.1% of Al, 0.0001 to 0.0080% of N and 0.0001 to 0.0030% of B and optionally 0.1 to 3% of Cr with the balance consisting of Fe and unavoidable impurities, hot-rolling the heated slab at a finishing temperature of not lower than (Ar.sub.3 --100).degree. C., cooling the hot-rolled coil within 1 sec after the hot rolling at a rate of not less than 50.degree. C./sec from the finishing temperature to a temperature in the range of from 600.degree. to 750.degree. C.

Abstract: The present invention provides a cold rolled steel sheet and a hot dip zinc-coated cold rolled steel sheet excellent in paint bake hardenability, non-aging properties and formability, and a process for producing the same. In the present invention, an extremely low carbon steel or extremely low carbon steel containing at least one element selected from the group consisting of Ti and Nb is used as a base steel, and Mn and Cr are positively added thereto, whereby the resultant steel has a mixed structure after annealing. Accordingly, there can be obtained a steel sheet having both a high paint bake hardenability and non-aging properties, and being excellent in formability such as an average r-value (deep drawability). With regard to the paint bake hardenability, the present invention may provide a cold rolled steel sheet and a hot dip zinc-coated cold rolled steel sheet to which paint bake hardening may be optionally imparted in an amount as large as about 10 kgf/mm.sup.

Abstract: A high-strength cold-rolled steel strip or a molten zinc-plated high-strength cold-rolled steel strip which have a low yield strength, containing, by weight, of 0.0005-0.01% C, not more than 0.8% Si, more than 0.5% but not more than 3.0% Mn, 0.01-0.12%: P. 0.0010-0.015% S, 0.01-0.1% Al, 0.0005-0.0060% N, not less than 0.0001% but less than 0.005-0.1% the content of Nb being made to satisfy Nb .gtoreq.93/12 (C-0.0015), or instead of 0.005-0.1% Nb, 0.0005-0.1% Ti and 0.003-0.1% Nb, the content of Nb and the content of Ti being made satisfy, Ti.gtoreq.3.42N, and the balance Fe and incidental impurities is provided. Another steel strip or molten zinc-plated strip is provided that contains 0.2-3.0% Cr but does not require B, and includes both Ti and Nb. The method of producing such is also provided.

Abstract: A process for producing a non-aging galvanized steel sheet having good formability in a continuous galvanizing production line, which comprises heating a low carbon, Al-killed cold rolled steel sheet at a temperature not lower than a recrystallizing temperature, reducing the surface of the steel sheet thus heated in a reducing atmosphere, cooling the steel sheet to a temperature (T.sub.E) ranging from 200.degree. to 350.degree. C. from a temperature not lower than 600.degree. C. at a cooling rate not less than 30.degree. C/s, holding the steel sheet at the temperature (T.sub.E) for 0 to less than 10 seconds, reheating the steel sheet to a temperature ranging from 430.degree. to 500.degree. C. at a heating rate not less than 10.degree. C/s, immersing the steel sheet into a molten zinc bath, cooling the steel sheet thus galvanized to a temperature not higher than 370.degree. C., and subjecting the steel sheet to an overaging treatment to a temperature range from 250.degree. to 320.degree. C.