Abstract: There are provided an excellent cold-workability exhibiting high-strength steel wire or steel bar, or high-strength shaped article and a process for producing them. In particular, there is provided a process comprising carrying out hot working at 350 to 800° C. of a steel ingot, cast slab, steel slab or steel semifinished product having a C content of not greater than the solid solution limit of carbon of ferrite phase at Ael point and not greater than 0.010 mass % and being free of any cementite, or having a C content of >0.01 to 0.45 mass % to thereby obtain a material whose average crystal grain diameter in a cross section perpendicular to the longitudinal direction is ?3 ?m, and thereafter carrying out cold working of the material to thereby attain formation of a ferrite structure whose average crystal grain diameter in a cross section perpendicular to the longitudinal direction is ?500 nm.

Abstract: A tough high strength heavy wall steel material having superior weldability is provided, said steel material has a diameter or a side 5 mm or more in length, and comprises oxides 1 ?m or less in particle diameter homogeneously dispersed at a dispersion density in a range of from 10,000 to 100,000 particles/mm2 and uniform ferrite grains 2 ?m or less in grain diameter formed over the entire plane making a right angle with respect to the rolling direction.

Abstract: A method of rolling with a flattened-shaped caliber in a 1st pass and subsequently roiling with a square-shaped caliber in a 2nd pass In a caliber rolling of two or more continuous passes. The rolling is performed with a caliber which sets the ratio of the minor axis (2A01) of a 1st pass flattened to a material opposite side dimension (2A0) to A01/A0?0.75 and the ratio of a 2nd pass vertical diagonal dimension 2As1 to the major axis 2B1 of a material after the 1st pass to As1/B1?0.75 to introduce the large strain into the material. Thus, the effect of the distribution of strain introduced into the material in the 1st pass on the distribution of strain and the shape of the next pass is made clear so that the large strain can be introduced into the entire cross sectional are of the material, particularly at the center of the material.

Abstract: A multi-directional warm-rolling method for manufacturing an ultrafine grain steel material with an ultrafine grain structure of 3 ?m or smaller in average grain size. When roiling of two passes or more is performed for a steel material in the rolling temperature range of 350 to 800° C., a rolling by an oval shape caliber and a rolling by the other shape caliber an performed at leas one time so that a large amount of strain can be introduced into the material by a simple means with less section reduction ratio and less number of passes. Steel materials having the ultrafine grain structure and excellent strength and ductility can be manufactured by this method.

Abstract: The invention presents a new warm control rolling method, in consideration of processing heat generation, as a method of stably manufacturing ultrafine crystal steel of 3 microns to 1 micron or less, without any limitation in pass interval or strain speed, being a rolling method of manufacturing steel mainly composed of fine ferrite particle texture with average ferrite grain size of 3 ?m or less, in which, in the rolling process of one pass or more wherein the rolling temperature range is a temperature region of 350° C. to 800° C., the material temperature upon start of rolling of each rolling process does not exceed the maximum temperature of 800° C., and the material temperature during rolling and right after final rolling (within 1 second) is not lower than 350° C., temperature Tx-out right after rolling in each rolling process (within 1 second) is not higher than the temperature that is higher than rolling entry temperature Tx-in by 100° C.

Abstract: A formed product, characterized in that it is produced by using, as a material, a steel having an ultra fine structure comprising ferrite grains having an average grain diameter of 3 ?m or less and by a method comprising only a forming step and including none of refining steps; and a method for producting the above formed product with ease. The formed product contains no alloying element and has been subjected to no refining step, and has been imparted with high strength and high toughness by the above ultra fine structure.

Abstract: A tough high strength heavy wall steel material having superior weldability is provided, said steel material has a diameter or a side 5 mm or more in length, and comprises oxides 1 ?m or less in particle diameter homogeneously dispersed at a dispersion density in a range of from 10,000 to 100,000 particles/mm2 and uniform ferrite grains 2 ?m or less in grain diameter formed over the entire plane making a right angle with respect to the rolling direction.

Abstract: A tough high strength heavy wall steel material having superior weldability is provided, said steel material has a diameter or a side 5 mm or more in length, and comprises oxides 1 &mgr;m or less in particle diameter homogeneously dispersed at a dispersion density in a range of from 10,000 to 100,000 particles/mm2 and uniform ferrite grains 2 &mgr;m or less in grain diameter formed over the entire plane making a right angle with respect to the rolling direction.

Abstract: A fine ferrite-based steel is disclosed, wherein at least 60% of the ferrite grain boundary is a large angle grain boundary of at least 15°, and the mean ferrite grain size is not more than 2.5 &mgr;m. The fine ferrite-based steel of the invention has a high strength and a long fatigue life.

Abstract: A method of producing a ultra fine grain steel made of ferrite having a mean grain size of not larger that 3 &mgr;m as the base phase, after ingoting raw materials, by austenitizing the ingot by heating it to a temperature of at least an Ac 3 point, then, applying compression working of a reduction ratio of at least 50% at a temperature of from an Ae 3 point or lower to an Ar 3 point −150° C., or at a temperature of at least 550° C., and thereafter, cooling, wherein the strain rate as compression working is in the range of from 0.001 to 10/second.

Abstract: A tough high strength heavy wall steel material having superior weldability is provided, said steel material has a diameter or a side 5 mm or more in length, and comprises oxides 1 &mgr;m or less in particle diameter homogeneously dispersed at a dispersion density in a range of from 10,000 to 100,000 particles/mm2 and uniform ferrite grains 2 &mgr;m or less in grain diameter formed over the entire plane making a right angle with respect to the rolling direction.

Abstract: A fine ferrite-based steel is disclosed, wherein at least 60% of the ferrite grain boundary is a large angle grain boundary of at least 15°, and the mean ferrite grain size is not more than 2.5 &mgr;m. The fine ferrite-based steel of the invention has a high strength and a long fatigue life.

Abstract: The invention according to the present application provides a high strength solidification body by solidifying a starting metallic powder of iron and the like by means of plastic working using hydrostatic pressing, which is, for instance, a high strength high toughness steel material and the like having a superfine texture comprising a crystalline texture consisting of grains 5 &mgr;m or less in average diameter, or preferably, 3 &mgr;m or less in average diameter. Furthermore, the present invention provides a steel material included in the high strength solidification body, which contains oxide grain 0.2 &mgr;m or less in diameter at a volume ratio of from 0.5 to 60%.

Abstract: A high strength phosphorus-containing steel having fine texture free from the problem of embrittlement by positively using the presence of P, which is a carbon steel having an average ferritic grain diameter of 3 &mgr;m or less and containing from 0.04 to 0.1% by mass of P, wherein the volume fraction of P segregated in the grain boundary accounts for 0.3 or less in case the grain boundary is covered by a P layer 1 nm in thickness.

Abstract: The invention provides an ultra-fine grain steel comprising fine ferrite grains as oriented at random and surrounded by large angle grain boundaries. The steel comprises fine ferrite grains having a mean grain size of not larger and 3.0 &mgr;m and surrounded by large angle grain boundaries having an misorientation not smaller than 15°.

Abstract: In carbon steel, oxides with grain diameter of 1 .mu.m or less and with grain spacing of 6 .mu.m or less are dispersed to suppress growth of .gamma. grains by heating at .gamma. region temperature.