A hot-rolled steel bar or wire rod consisting of C: 0.1 to 0.3%, Si: 0.05 to 1.5%, Mn: 0.4 to 2.0%, S: 0.003 to 0.05%, Cr: 0.5 to 3.0%, Al: 0.02 to 0.05%, and N: 0.010 to 0.025%, the balance being Fe and impurities, and the impurities containing P: 0.025% or less, Ti: 0.003% or less, and O: 0.002% or less, wherein the structure thereof is composed of a ferrite-pearlite structure, ferrite-pearlite-bainite structure, or ferrite-bainite structure; the standard deviation of ferrite fractions at the time when randomly selected 15 viewing fields of a transverse cross section are observed and measured with the area per one viewing field being 62,500 μm 2 is 0.10 or less; and in a region from the surface to one-fifth of the radius and a region from the center to one-fifth of the radius in the transverse cross section, the amount of Al precipitating as AlN is 0.005% or less, and the density in terms of the number of AlN having a diameter of 100 nm or larger is 5/100 μm 2 or less. In the hot-rolled steel bar or wire rod, even if hot forging is performed in various temperature ranges, austenite grains can be stably prevented from being coarsened at the time of heating for carburization.

Hot-rolled steel bar or wire rod

Device for cutting a protective layer away from a material roll of web-formed material, comprising a rotation device which rotates the roll. The rotation device includes at least two rotatable carrier rollers, on which the material roll is supported and is rotated. In this way the protective layer on the material roll is cut away from the roll during a cutting operation by a cutting tool device. This contacts the roll during its rotation. The rotatable carrier rollers form lifting and carrying devices on a mobile load carrier in order to support the material roll whilst rotating it during the cutting operation and in order to transport the material roll to and, respectively, from a chosen place for the cutting operation.

Device for cutting a protective layer away from a material roll

The present invention relates to an ultra-high-strength steel bar and to a method for manufacturing same, wherein the steel bar comprises: C: 0.05 to 0.45 wt %, Si: 0.10 to 0.35 wt %, Mn: 0.1 to 0.85 wt %, Cr: 0.6 to 1.20 wt %, Mo: 0.05 to 0.35 wt %, with the remainder being Fe and other impurities. The method for manufacturing the steel bar involves twice performing a process of reheating and rough-milling billets for the steel bar comprising the above-described alloy composition so as to reduce the prior-austenite grain size, and performing intermediate roll-milling and finishing roll-milling to manufacture steel bars and cooling the steel bars with water to a temperature of 400 to 600°C through a Tempcore process such that a fine ferrite structure is formed at a center layer. The method of the present invention involves forming a martensite structure, serving as a hardening layer, at a surface layer, by means of the alloy design, heat treatment, rolling ratio control, Tempcore process, etc., and enables the center layer to have a fine ferrite structure, thereby producing an ultra-high-strength steel bar which has a yield strength of 800MPa or higher, a tensile strength of 900 MPa or higher, and an elongation percentage of 10% or higher, and which satisfies 180° bending test. The steel bar of the present invention can be combined with high-strength concrete to be effectively used as a main bar or a shear-reinforcing bar in a building structure.

Ultra-high-strength steel bar and method for manufacturing same

The present invention provides a steel wire rod or bar which exhibits good cold deformability even though it does not undergo spheroidizing annealing after hot rolling. The steel wire rod or bar with good cold deformability is characterized in that its ferrite structure contains no less than 25 nitride and carbide particles in a mixed state or composite state per 25 μm on average in a sectional area three-fourths of the diameter within the circumference of the rod or bar. Such nitride and carbide precipitates contribute to the reduction of flow stress at temperatures raised by heat generation at the time of cold deforming.

Steel wire rod or bar with good cold deformability and machine parts made thereof

The invention relates to a production method of HRB400 (Rockwell Hardness) deformed steel bar. The method is characterized in that the chemical component of the deformed steel bar comprises 0.21-0.25wt% of carbon, 0.65-0.80wt% of silicon, 1.20-1.40wt% of manganese, less than or equal to 0.045wt% of phosphorus, and less than or equal to 0.045wt% of sulphur. The method comprises the following steps of: controlling the carbon and phosphorus contents of molten steel at the finish point of a converter and the tapping temperature as follows: C is greater than or equal to 0.06wt%, P is less than or equal to 0.030wt% and the tapping temperature at 1620-1644 DEG C; controlling the addition of calcium carbide in LF (Low Frequency) refinery within 50-100kg; controlling the degree of superheat in casting production at 30 DEG C, 5 DEG C plus or minus, controlling the pulling rate at 2.2-2.4m/min; controlling the rolling temperature of reinforcing steel bars with diameters of 8mm, 12mm and 14mm at 970-1000 DEG C, controlling the finishing inlet temperature at 940-960 DEG C; and opening the Stelmor cooling line protective hoods completely. The method has the advantages that the deformed steel bar produced by the method is stable in performance and reasonable in cost.

Production method of HRB400 (Rockwell Hardness) deformed steel bar

PURPOSE: To obtain the titled steel products without requiring a tempering treatment entailing hardening and tempering after reheating by subjecting a specifically composed steel to quick cooling under prescribed conditions then to direct hardening after hot rolling and subjecting the steel to self tempering under prescribed conditions by the heat internally retained therein. CONSTITUTION: The ingot contg., by weight, 0.20W0.60% C, 0.10W0.35% Si, 0.30W1.80% Mn, and if necessary ≥1 kinds among ≤1.50% Cr, ≤0.30% Mo and ≤0.005% S and consisting of the balance iron is hot rolled. The steel is quickly cooled from A 3 WA 3 +150°C down to the temp. above 50°C and below the M s point after the end of said rolling to provide the internally retained heat in such a manner that the surface temp. attains 100W600°C to effect the self tempering. The rolled steel products, more particularly, rolled steel bars, which consist essentially of the tempered martensite structure in the surface layer part and tempered martensite and bainite or supercooled ferrite pearlite structure in the central part and are much improved in the strength and toughness are thus obtd. COPYRIGHT: (C)1987,JPO&Japio

Production of hot rolled steel products having high strength and high toughness

PURPOSE:To obtain the titled steel only through rolling by regulating the Al and N contents in a steel having a specified composition, conditions during the hot rolling of the steel and the amount of AlN precipitated after the rolling and by specifying the grain size of ferrite. CONSTITUTION:A steel contg., by weight, 0.05-0.35% C, =30% finish working rate so as to regulate the amount of AlN precipitated in the rolled material to <=40ppm and the ferrite grain size number to 11.0-9.0.

Production of steel having superior cold workability and preventing coarsening of grain during carburization heating

PURPOSE:To manufacture fine grain rolled steel stock having a superior mechanical property similar to that after normalizing without requiring normalizing after rolling, by applying hot rolling and heat treatment under specified conditions to low or medium carbon steel or alloy steel contg. specified small quantities of Al and N. CONSTITUTION:Steel slab of low and medium carbon steel or alloy steel contg. by weight 0.10-0.60% C, 0.10-0.35% Si, 0.30-1.80% Mn, 0.010-0.045% Al, 0.007-0.020% N, (Al/N weight ratio >1.6) of further 0.015-0.10% Nb or singly or composedly one kind or more among <1.5% Cr, <0.3% Mo, 0.050-0.30% V is heated to 750-950 deg.C and hot rolled. In this case, the plate is cooled to Ms point - 850 deg.C from 850-1,000 deg.C before finish rolling, and finish rolling is ended at 700-850 deg.C. Steel stock contg. fine AlN, having uniform and fine ferrite and pearlite structure and superior mechanical property can be manufacture without requiring normalizing after rolling.

Manufacture of fine grain steel

PURPOSE:To produce a steel bar having a fine ferrite/pearlite structure uniform over the section by cooling the billet of a low-and middle-carbon low-alloy steel having a specific compsn. down to a specific range prior to finish rolling and specifying the end temp. of the finish rolling. CONSTITUTION:The billet consisting, by weight %, 0.10-0.60% C, 0.10-0.35% Si, 0.30-1.80% Mn, 0.010-0.045% Al, and the balance Fe and inevitable impurities is heated to 750-950 deg.C and is hot rolled. The billet is cooled from 850-1,000 deg.C down to the temp. below 850 deg.C and higher than the M3 point prior to the finish rolling at this time. The end temp. of the finish rolling is specified to 700-850 deg.C. 0.015-0.100% Nb is incorporated at need into this steel compsn. and further, >=1 kinds among <=1.5% Cr, <=0.3% Mo, and 0.050-0.300% V are incorporated therein. The fine-grained steel having the ferrite/pearlite structure which is uniform and fine in both the front layer part and the inside is thereby obtd.

Production of fine grain steel

PURPOSE:To enable machining as it is after induction hardening by subjecting a middle-carbon steel to rapid cooling and direct hardening right after hot working at a specific temp. then stopping the cooling and allowing the steel to make self-annealing so that the surface layer part is converted to sorbite structure. CONSTITUTION:The middle-carbon steel contg. 0.35-0.60wt.% C is smelted and is hot worked at the finishing temp. specified to an A3 point-A3 point +200 deg.C range. Steel bars, etc., which are cooled to form uniform austenite immediately after the hot working is thereafter directly hardened at >=50 deg.C/sec cooling rate. The cooling is thereafter stopped and the steel material are allowed to make self-annealing in an about 600-200 deg.C range by the heat possessed by the steel materials. The steel bars which are converted to the sorbite structure in the surface layer part down to at least 2mm depth from the surface and to ferrite pearite structure in the inside layer part are thereby obtd. These steel bars do not required a tempering treatment and can be produced into machine parts by induction hardening as they are, then by machining such as turning.

Wada Yukio

Papers

Production of hot rolled steel products having high strength and high toughness

Production of steel having superior cold workability and preventing coarsening of grain during carburization heating

Manufacture of fine grain steel

Production of fine grain steel

Production of mechanical parts to be machined after induction hardening