Abstract: A high-strength steel sheet comprises carbon: 0.06 to 0.25 mass %, Si: 0.5 to 3.5 mass % and Mn: 0.7 to 4 mass %. Its mother structure is ferrite, its second phase structure comprises martensite and the residual austenite and the second phase structure measured by image analysis has an area fraction of 25 % or less based on the total structure. The steel sheet satisfies the following requirements (1) to (3): (1) the volume fraction (Vt&ggr;hd R) of the residual austenite is 5 % or more; (2) the ratio (SF&ggr;R/Vt&ggr;R) of the area fraction (SF&ggr;R) of the residual austenite within ferrite to Vt&ggr;R is 0.65 or more; and (3) the ratio [&agr;2/(&agr;1+&ggr;R)] of the space factor (&agr;2) of martensite to the second phase structure (&agr;1+&ggr;R) is 0.25 to 0.60. The steel sheet has excellent balance between strength and local elongation, and a low yield ratio.

Abstract: A hot-dip galvanized steel sheet composed of a basis steel sheet containing Si in an amount of 0.05-2.5 mass % and Mn in an amount of 0.2-3 mass % and a hot-dip galvanized zinc layer formed on the surface thereof, wherein said hot-dip galvanized zinc layer is formed in such a way that there is an Si—Mn enriched phase which is found, by observation under a scanning electron microscope or a transmission electron microscope, in the vicinity of the interface in a region no shorter than 50 &mgr;m in the cross section perpendicular to the interface between the basis steel sheet and the hot-dip galvanized zinc layer, said Si—Mn enriched phase containing more than twice as much Si and/or Mn as the basis steel sheet and extending over a length no more than 80% of the length of the interface observed. This hot-dip galvanized steel sheet is free of bare spots even in the case where the basis steel sheet contains Si and Mn in a comparatively large amount and hence is liable to suffering bare spots.

Abstract: Disclosed herein are a high-carbon steel wire having high strength and superior in resistance to longitudinal cracking, a steel for said high-carbons steel wire, and a process for producing said steel. The high-carbon steel wire is characterized in that the essential components are C (0.65-1.2 wt %), Si (0.1-2.0 wt %), Mn (0.2-2.0 wt %), and Fe, the main phase is pearlite, and the ferrite area ratio is less than 0.40 % in the surface layer up to a depth of 50 &mgr;m from the surface. The high-carbon steel may further contain B (0.0003-0.0050 wt %), Ti (less than 0.030 wt %), and N (less than 0.0050 wt %), with the amount of B, Ti, and N satisfying the following equation 0.03≦B/(Ti/3.43−N)≦5.0 The resulting steel wire produced in the usual way contains ferrite in an amount less than 0.40 wt % in its surface layer. This low ferrite content is responsible for good resistance to longitudinal cracking because ferrite causes longitudinal cracking to start from it.

Abstract: A P- and Ti-added galvannealed steel sheet superior in ductility, and a process for production thereof. It is made of a cold-rolled steel sheet and has alloyed hot-dip galvanizing on the surface thereof, said cold-rolled steel sheet having the chemical composition (in terms of wt %) of C: less than 0.010%, Si: no more than 0.5%, Mn: 1.0˜3.0%, P: no more than 0.20%, S: no more than 0.01%, Al: 0.005˜0.10%, N: no more than 0.0050%, Ti/48−(C/12+N/14+S/32): 0.0003˜0.0018 with the remainder being chiefly Fe, and said cold-rolled steel sheet being characterized by &rgr;1≦107 and &rgr;2≦5×105, where &rgr;1 is the number of precipitates whose particle diameter (D) is in the range of 10 nm≦D<100 nm and &rgr;2 is the number of precipitates whose particle diameter (D) is in the range of 100 nm≦D.

Abstract: A hot-dip galvanized steel sheet which is produced from a cold-rolled steel sheet, as a base steel sheet, consisting essentially of C: 0.010-0.06 wt %, Si: no more than 0.5 wt %, Mn: no less than 0.5 wt % and less than 2.0 wt %, P: no more than 0.20 wt %, S: no more than 0.01 wt %, Al: 0.005-0.10 wt %, N: no more than 0.005 wt %, Cr: no more than 1.0 wt %, Mn+1.3Cr: 1.9-2.3 wt %, Fe: remainder, and having a structure composed of ferrite and a second phase containing martensite, said second phase in the structure accounting for no more than 20% in terms of area and martensite in the second phase accounting for no less than 50%, and which has a zinc-plated layer formed on the surface thereof by hot-dip galvanizing or hot-dip galvannealing. A process for production of said hot-dip galvanized steel sheet. This steel sheet has a composite structure containing martensite and yet it has a low strength (no higher than 500 MPa) and also has good strength-ductility balance.

Abstract: A hot-dip galvanized steel sheet composed of a basis steel sheet containing Si in an amount of 0.05-2.5 mass % and Mn in an amount of 0.2-3 mass % and a hot-dip galvanized zinc layer formed on the surface thereof, wherein said hot-dip galvanized zinc layer is formed in such a way that there is an Si-Mn enriched phase which is found, by observation under a scanning electron microscope or a transmission electron microscope, in the vicinity of the interface in a region no shorter than 50 &mgr;m in the cross section perpendicular to the interface between the basis steel sheet and the hot-dip galvanized zinc layer, said Si-Mn enriched phase containing more than twice as much Si and/or Mn as the basis steel sheet and extending over a length no more than 80% of the length of the interface observed. This hot-dip galvanized steel sheet is free of bare spots even in the case where the basis steel sheet contains Si and Mn in a comparatively large amount and hence is liable to suffering bare spots.

Abstract: A steel wire is composed mainly of fine pearlite and/or coarse pearlite, where the lamellar cementite in the pearlite is amorphous or amorphous-like. Alternatively, the wire may be composed mainly of bainite, where the cementite in the bainite is amorphous or amorphous-like. To manufacture the steel wire, a starting steel product is subjected repeatedly to patenting and cold drawing, and then subjected to final drawing at a true strain of 2.0 or above while cooling. The steel wire is higher in strength and toughness than wire whose lamellar cementite consists of nano crystals. The steel wire does not suffer any delamination when subjected to torsion.