Abstract: A workpiece is made of a steel body and has a hard material coating thereon. The surface which receives the hard material coating is enriched with at least one of C, N, B, O, S or Si. A transition zone between the enriched surface area and the hard material coating has a non-diminishing content of the at least one element.

Abstract: (Object) IF-based, continuously cast slab essentially freed from defects such as surface defects, difficult production and poor strength, etc. of the product that the IF-based sheet steels have; sheet steels and a process for producing the same are provided.(Structure) A continuously cast slab of extremely low carbon steel comprising not more than 1.5% by mass of Si, not more than 2.0% by mass of Mn, not ore than 0.15% by mass of P, 0.01-0.15% by mass of Al, and not more than 0.0050% by mass of N, where the surface layer further contains 0.01-0.08% by mass of C existing as a cementite and the inner layer further contains not more than 0.0050% by mass of C, and at least one of 0.02-0.10% by mass of Ti, 0.01-0.10% by mass of Nb, 0.02-0.10% by mass of V and 0.03-0.10% by mass of Zr, the carbon existing substantially as carbides of these elements, preferably both the surface layer and the inner layer further contain 0.0001-0.

Abstract: A process for the thermochemical treatment of thin-walled structural elements made of steel comprising enriching an edge zone of a thin-walled structural element with nitrogen and carbon at 590.degree. to 700.degree. C. to harden the edge zone whereby an intermediate layer (3) is formed in the diffusion zone (2), said intermediate layer comprising 1 to 3% by weight of nitrogen and at most 0.8% by weight of carbon and cooling the said thin-walled structural element under an inert atmosphere at a rate of 50.degree. to 100.degree. C. per minute to room temperature to form a nitrogen austenite and/or braunite phase between the connection layer (1) and the basic structure (4) with increased fatigue strength.

Abstract: One of component parts of an inner race, an outer race and rolling elements of a rolling bearing is composed of a bearing material that is prepared by working a high-speed steel, carburizing or carbonitriding the wrought steel in a temperature range from 800.degree. C. to less than 1200.degree. C. and subsequently hardening and tempering the carburized or carbonitrided steel, the steel composing of 0.2 wt %.ltoreq.C.ltoreq.2.3 wt %, Si.ltoreq.1.0 wt %, Mn.ltoreq.1.0 wt %, 2.0 wt %.ltoreq.Cr.ltoreq.7.0 wt %, 1.5 wt %.ltoreq.W.ltoreq.22.0 wt %, Mo.ltoreq.10.0 wt %, 0.5.ltoreq.V.ltoreq.6.0 wt %, Co.ltoreq.18.0 wt %, the balance Fe and incidental impurities. By carburizing or carbonitriding the steel at low temperatures less than 1,200.degree. C.

Abstract: A toroidal-type continuously variable transmission provides an input side disk disposed on an input shaft, an output side disk disposed on an output shaft, and a power roller for transmitting motive power of the input shaft to the output shaft while engaging both the input side disk and the output side disk, in which the input side disk, the output side disk, and the power roller made of a material are subjected to either a carburizing and grinding process or to a carbonitriding and grinding process so that effective carburized depths of the input side disk, the output side disk, and the power roller are limited to a range between 2.0 mm and 4.0 mm. The toroidal-type continuously variable transmission is capable of improving not only the rolling contact lives of the traction surfaces of the input and output side disks as well as the traction surfaces of the power rollers, but also the fatigue fracture lives of the input and output side disks and power rollers.

Abstract: A coated wear resistant steel article has a basic carburized low silicon steel article of preselected properties including carbides isotropically exposed and having an elevation greater than material adjacent said carbides of said carburized surface and a coating material having a hardness greater than about 1200 Kg/mm covering the material adjacent said carbides of said carburized surface. In another aspect, the coating material is absent and the surface is modified by ion implantation.

Abstract: A camshaft made of cast iron containing at least one element selected from the group consisting of Bi, Te, Se, As, Sb and Sn in a total amount of 0.0001 to 0.1 weight %, preferably, 0.001 to 0.1 weight %. The cast iron may further contain at least one element selected from the group consisting of Ni, Cu and Co, in an amount of 0.2 to 5.0 weight %. Furthermore, in the camshaft of the present invention, a carbide area ratio at the sliding surface of the cam lobe portion is not less than 40%, the chilled carbide has an average grain diameter of not more than 15 .mu.m, and the sliding surface of the cam lobe portion has a hardness of not less than HRC 53.

Abstract: A process for forming a low silicon rapid-carburizing wear resistant steel article includes selecting an article formed of a steel material having less than about 0.05% silicon by weight, and carburizing the article for a preselected time and temperature to form an austenitic surface and attain a carburized case depth which is at least 5% greater than the carburized case depth of a similar article formed from a steel material having a range of about 0.09% to about 0.25% silicon by weight and being carburized at substantially same conditions of time and temperature. After quenching, the as-carburized surface transforms into a microstructure of martensite and retained austenite, being substantially free of intergranular oxides. A low silicon rapid-carburizing wear resistant steel article formed according to the present invention is particularly useful for making gears, couplings, shafts, bearings, and similar articles subjected to a combination of high bending loads, surface wear and contact fatigue.

Abstract: There is disclosed herein a steel alloy bearing having an inner race, an outer race and rolling elements comprising: at least one of said elements being made of alloy steel which constitutes from 10.0 to 18.0 wt % chromium and 0.05 to 0.30 wt % carbon, 0.10% to 2.0 wt % molybdenum, 0.15 to 1.0 wt % silicon, 0.20 to 1.5 wt % manganese, 0.8 to 1.2 wt % tungsten, 0.20 to 0.30 wt % vanadium, 0.2 to 1.0 wt % of nickel, and the remainder of said steel alloy being iron; and said at least one element having been carburized in a carbon atmosphere containing from 0.25 to about 0.40 % carbon potential.

Abstract: A slide surface construction is formed of an aggregate of Fe crystals having a body-centered cubic structure. The aggregate includes {222} oriented Fe crystals with their {222} planes by Miller indices oriented toward a slide surface. The content S of the {222} oriented Fe crystals is in a range represented by S.gtoreq.20%, preferably in a range represented by S.gtoreq.40%. The {222} oriented Fe crystals form a trigonal pyramid shape on the slide surface, which provides good oil retention for the slide surface construction. Thus, the slide surface construction exhibits an excellent seizure resistance.

Abstract: A case carburizable stainless steel alloy intended to be used at operating temperatures up to 700.degree. F. The alloy is able to achieve and maintain a high surface hardness when carburized and heat treated and combines high fracture toughness, hot hardness, metal-to-metal wear resistance and corrosion resistance while retaining core ductility and strength. The alloy consists essentially of (in weight percent) 0.1 to 0.25% carbon, 0 to 1% silicon, 0 to 1% manganese, 13 to 19% chromium, 1.75 to 5.25% nickel, 3 to 5% molybdenum, 0.25 to 1.25% vanadium, 5 to 14% cobalt, 0.01 to 0.1% niobium; 0 to 0.02% boron; and the balance iron and incidental impurities. The alloy is particularly suited for use in bearing applications and also in cams, shafts, gears, bolts and like articles exposed to elevated temperatures and corrosive atmospheres.

Abstract: An object of this invention is to provide a rolling bearing which is long enough in serve life even when it is applied with a lubricant mixed with foreign matters, simply by quenching or by carbonitriding it for a short period of time, and which can be formed at a relatively low manufacturing cost. A rolling bearing is formed as follows: The quantities of elements such as C, Si, Mn, Cr and Mo forming a bearing alloy steel, and the quantity of retained austenite are adjusted to be in predetermined ranges, and the steel is quenched and tempered or carbonitrided so that its hardness is in the following range:-2.2.times.(.gamma..sub.R vol %)+810.ltoreq.Hv.ltoreq.-2.2.times.(.gamma..sub.

Abstract: A rolling bearing is disclosed, which comprises an inner ring, an outer ring, and rolling elements each composed of an alloy steel which are, after being subjected to a carburizing treatment or a carbonitriding treatment, subjected to quench-hardening and tempering or is subjected to quench-hardening or tempering, wherein the alloy steel contains from 0.10 to 1.00% by weight C, from 0.50 to 3.00% by weight Cr, from 0.15 to 1.00% by weight Si, from 0.2 to 1.50% by weight Mn, and rest being Fe and unavoidably intermixed impurities, the average amount of the retained austenite of at least the inner ring in the inner ring and the outer ring is not more than 4% by volume and the average amount of the retained austenite of the rolling elements is from 20 to 30% by volume.

Abstract: Method for the treatment of alloy steels and refractory metals such as Ti, Zr and Nb, especially for depassivation and subsequent thermochemical surface treatment in a process chamber (1, 2) under the action of pressure and temperature, wherein, in a first process step, a first gas or gas mixture from the group N.sub.2, H.sub.2 or NH.sub.3 is admitted for the depassivation into a process chamber (1), a pressure greater than 1 bar a and a temperature between 100.degree. C. and 1,000.degree. C. is established in the chamber (1), and in a second process step a second gas or gas mixture from the group of N-, C- or B-containing gases is admitted into a process chamber (1, 2) for the thermochemical surface treatment, and a temperature between 100.degree. C. and 1,000.degree. C. at a pressure greater than or equal to 1 bar a is established.

Abstract: The present invention provides a steel sheet for press working that exhibits excellent stiffness and satisfactory press workability. The steel sheet for press working includes: a composition of C+N+B=0.007 to 1.0 wt % in a region from the surface of the steel sheet to a position of 5% of the thickness in a direction of the thickness in at least either of the surface layers; a pole intensity of [{321}+{211}]/{100}.gtoreq.1.2 in a vertical direction to the sheet surface realized at a 3% thickness position in the direction of the thickness from the surface; and a composition of C+N+B=0.010 wt % less than in the central portion 40% except for two 30% portions of the two surface layers in the direction of the thickness.

Abstract: A bearing component is prepared from a carburazing steel and having a surface hardness of 63 to 67 in terms of Rockwell hardness C and a surface retained austenite content of at least 20% to less than 25%. The bearing component is produced by a process including the step of carburizing and quenching a bearing component workpiece prepared from a carburizing steel and machined to a predetermined shape, the step of subjecting the resulting workpiece to a preliminary tempering treatment, the step of subjecting the tempered workpiece to a sub-zero treatment and the step of subjecting the treated workpiece to a main tempering treatment. Further, the bearing component is produced by another process including the step of carburizing and quenching a bearing component workpiece prepared from a carburizing steel and machined to a predetermined shape, the step of subjecting the resulting workpiece to a secondary hardening treatment and the step of subjecting the hardened workpiece to a main tempering treatment.

Abstract: A high tensile steel sheet excelling in workability and stretch flanging formability, which is of a composite texture composed of a ferrite phase and a 2nd phase selected from the group consisting of martensite, bainite, pearlite, retained austenite and cold-transformed ferrite, wherein the volume fraction of the 2nd phase is not less than about 1.3 times higher at an outer region of the steel sheet than the volume fraction of the 2nd phase in a central region of the sheet thickness.

Abstract: A rolling member used as an outer race, inner race, a ball or roller of a bearing contains a metal flow in the structure formed by plastic working (fold forging). The angle of metal flow determined by a tangent line of the metal flow and the axis of rotation of the rolling member is 10.degree. or larger to improve the service line against rolling fatigue.

Abstract: In a process for forming a solid lubricating film on an iron-base substrate, an organic material having a vapor pressure of 10.sup.-4 Torr or less at room temperature is deposited on an iron-base alloy substrate in a vacuum atmosphere in a vacuum degree of 10.sup.-4 Torr or more, and simultaneously ions of a metal element having a chemical affinity to carbon is irradiated on the iron-base alloy substrate at a dose of 1.times.10.sup.16 ions/cm.sup.2 or more, the ions having an energy of 5 keV or more. Accordingly, the iron-base substrate is coated with a solid lubricating film which includes an atom mixture layer including carbide of the metal element and alloy of iron and the metal element and a carbon layer including amorphous carbon. Hence, the solid lubricating film has an excellent lubricating property as well as a high adhesion property to the iron-base substrate. Namely, the excellent lubricating property will last for a long period of time.

Abstract: A boron steel consisting of 0.18% to 0.35% C, 0.06% to 0.15%, Si, 0.50% to 1.00% Mn, 0.40% to 0.90% Cr, 0.01% to 0.05%, Al, 0.01% to 0.04% Ti, no more than 0.012% N, no more than 0.003% O, 0.0005% to 0.0030% B, and the balance Fe and impurities contained inevitably in manufacturing the steel, all percentages being based on the weight of the steel. The ratio of Ti to N is 3.4 to 6.0. The boron steel has an improvement in the reduction of heat-treatment distortion, surface oxidation in carburization and material cost, and also has superior hardenability, mechanical strength and fatigue strength.

Abstract: Cold-rolled steel sheets or hot-dip galvanized steel sheets for deep drawing which have excellent resistance to cold-work embrittlement, containing, all by mass, 0.01% or less C, 0.2% or less Si, 0.05-1.0% Mn, 0.10% or less P, 0.02% or less S, 0.005-0.08% sol.Al, and 0.006% or less N, containing Ti (%) and/or NB (%) solely or in combination within the range in which a relationship between the effective amount of Ti (hereinafter referred to as Ti*) defined by the following formula (1) and the amounts of Nb and C satisfies the following formula (2), and further containing 0.003% or less B when required.Ti*=total Ti-{(48/32).times.S+(48/14).times.N}TM (1)1.ltoreq.(Ti*/48+Nb/93)/(C/12).ltoreq.4.5 (2)And the balance of Fe and inevitable impurities, the steel sheets have a concentration gradient as a result of carburizing.

Abstract: A rolling contact parts steel has C: 0.2-0.6 wt%; Si: 0.3-2.0 wt%; Cr: 0.5-2.5 wt%; Mn: 1.7 wt% or less; O: 12 ppm or less; and the balance of Fe and an inevitable impurity. The steel produces a fine carbide without the need for a separate heat treatment. The dimensioal stability at high temperature of the steel is superior. A rolling bearing has at least one of the races and the rolling element thereof made of the steel, the steel being carburized or carbonitrided, then quenched and then, finally, tempered. The one of the races and the rolling element will not soften at a high temperature.

Abstract: A rotary output shaft for a vehicle starter motor having a planet gear speed reducing device is formed by forging a steel blank to form a product having a shape similar to the rotary output shaft but having slightly larger outer dimensions, by subjecting a planet gear carrier portion 7c of the forged entire product to copper plating to prevent carburization, by subjecting the product to a carburizing treatment, and by finishing the locally carburized portion of the product.

Abstract: A rolling contact element steel has C: 0.2-0.6 wt %; Si: 0.5-2.0 wt %; Cr: 5.0-8.0 wt %; Mo: 3.0 wt % or less; Mn: 1.6 wt % or less; O: 12 ppm or less; and the balance of Fe and an inevitable impurity. A rolling bearing made of this steel will not soften even at high temperature. The dimensional stability at high temperature and wear-resistance of the steel are superior. The steel can produce a fine carbide without the need for a separate heat treatment. A rolling bearing has at least one of the races and the rolling element made of the steel, the steel being carburized or carbonitrided, then quenched and finally high-temperature tempered.

Abstract: A method for improving the wear characteristics and corrosion resistance of a metal surface having the basic steps of:A. case hardening the metal surface by placing the metal in a fluidized bed and exposing it to a first atmosphere of nitrogen, ammonia and natural gas at a temperature between about 750.degree. F. and about 1200.degree. F. for a period between about 1 and about 5 hours, followed by exposure to a second atmosphere containing nitrogen and water at a temperature between about 750.degree. F. and about 1200.degree. F.;B. coating the metal with an aqueous coating composition consisting essentially of a polymeric additive and water; andC. allowing the coating composition retained on the metal to cure for a period between about 2 and about 48 hours.

Abstract: This invention provides a case hardening steel alloy and articles made therefrom which, when case hardened and heat treated, have high case hardness, corrosion resistance, high temperature capability and metal-to-metal wear resistance and high core ductility, impact toughness and fracture toughness. The alloy contains about 0.05-0.1 w/o C, 0.04 w/o max. N, 1.5 w/o max. Mn, 1 w/o max. Si, 11-15 w/o Cr, 1-3 w/o Mo, 1.5-3.5 w/o Ni, 3-8 w/o Co, 0.1-1 w/o V, and the balance Fe. In a preferred embodiment, the alloy is balanced according to Equation 1 (Eq.1) so that:______________________________________ 3(w/o Cr) + 6(w/o Si) + 2.5 (w/o Mo) + 6(w/o V) - 25(w/o C + N) - 6(w/o Ni) - 2(w/o Mn) - 2(w/o Co) - 21 .ltoreq. 0.

Abstract: A steel having good wear resistance which contains 0.55-1.10% of C, up to 2.0% of Si, up to 2.0% of Mn, 12.0-25.0% of Cr and particularly suitable as a material for piston rings or rocker arms. Further addition of 0.05-1.10% of Al to the above steel gives a steel improved in properties for spheroidization of carbides and uniformization of carbide particle size, leading to further enhancement of wear resistance. If required 0.20-2.0% of Ni may be added to the steels, whereby corrosion resistance, toughness and hardenability are improved. An addition of at least one of 0.2-3.0% of Mo, 0.1-1.5% of V and 0.05-0.70% of Nb to the steels improves high-temperature strength and surface hardness. The steel is surface treated by gas nitriding of the like in a surface area for sliding contact with an opponent member.

Abstract: A rolling bearing having an inner ring, outer ring and rolling element, at least one of these elements being made of one of the following first, second or third medium-carbon manganese steels. The first medium-carbon manganese steel includes C: 0.4 to 0.7 wt. %, Si: 0.15 to 1.2 wt. %, Mn: 1.2 to 1.7 wt. %, Al: 200 to 300 ppm, Ti: up to 40 ppm, N: 100 to 200 ppm, S: up to 80 ppm, O: 9 ppm and the balance of Fe. The second steel includes at least one of Nb: 0.03 to 0.08 wt. % and V: 0.1 to 0.15 wt. % in addition to the elements of the first medium-carbon manganese steel. The third medium-carbon manganese steel includes at least one of Nb: 0.03 to 0.08 wt. % and V: 0.1 to 0.15 wt. % instead of Al and N and includes the other elements of the first medium-carbon manganese steel. Each medium-carbon manganese steel is subject to carburizing or carbo-nitriding so as to include a case with a 25 to 45 vol. % retained austenite.

Abstract: A process for forming a carburized steel article includes carburizing a steel material containing not more than 0.10% silicon and less than 1.1% chromium to form an austenitic surface matrix having a high density of carbides dispersed therein. After quenching, the carburized steel article is characterized by an outer surface having a high ratio of carbides and is substantially free of intergranular oxides. As a result of preventing undesirable surface oxide formations and simultaneously providing a beneficial surface carbide structure, the bending fatigue strength, wear properties, and contact fatigue strength of articles such as gears, shafts, bearings and couplings are greatly enhanced.

Abstract: In a process for case-hardening rolling bearing elements of low-alloy nickeliferous steel, the rolling bearing elements are carburized in a dissociating carburizing gas, cooled down, heated to hardening temperature, austenitized in the carburized layer and, lastly, quenched.So that no brittleness of the rolling bearing elements takes place upon carburization due to dissociated hydrogen, the bearing elements are cooled from carburizing heat down to about 300.degree. C. in agitated inert gas and then held at this temperature, so that sufficient dissociated hydrogen escapes from the carburized layer of the rolling bearing elements. Subsequent heating of the said elements to hardening temperature or to intermediate annealing temperature is advantageously effected after holding at 300.degree. C.

Abstract: A rolling bearing, comprising an inner race, an outer race and rolling members which roll therebetween, at least one of the inner and outer races being subjected to carburizing and heating treatment, is characterized in that:the one race comprises a carbon steel containing 0.1 to 0.7 wt. % of carbon, with the residual austenite content on the track surface layer being 20 to 45 vol. % and the rolling members comprise a carbon steel containing 0.7 to 1.1 wt. % of carbon having carbonitriding and heating treatment applied on the surface layer, with the residual austenite content in such surface layer being 20 to 45 vol. % and the carbonitride in such surface being 3 to 15 vol. %.In another form of the bearing, the rolling members may comprise a carbon steel containing 0.1 to 0.7 wt. % of carbon, with the surface layers thereof being subjected to carburizing and heating treatment and having a residual austenite content of 20 to 45 vol. %.

Abstract: A method of producing a hardened non-magnetizable roller bearing element made of an austenitic material comprising carburizing the near-surface material layer of a roller bearing element in an oxygen-free atmosphere at high temperatures and then cooling the roller bearing element and the element produced by the process having a load bearing capacity equal to steel roller bearing elements but still non-magnetizable.

Abstract: A rolling bearing has an inner race, an outer race and a roller, at least one of the inner race, outer race and roller being made with an alloy steel consisting of two or more of 0.2 to 1.7% by weight of Mn, 0.2 to 1.2% by weight of Si, 0.2 to 1.7% by weight of Cr, 0.1 to 0.3% by weight of Mo and 0.1 to 1.0% by weight of Ni, 0.4 to 0.7% by weight of C and the balance of Fe, and by subjecting the alloy steel to carburizing hardening to obtain(a) an additional carbon content at the surface portion of 0.35 to 0.6% by weight and(b) a dissolved carbon content at the surface portion of 0.75 to 1.1% by weight, and having:(c) a hardness at the core portion as H.sub.R C of 57 to 64 and(d) a difference in hardness between the surface portion and the core portion within .+-.5 of H.sub.R C.

Abstract: A case hardening steel which consists essentially of 0.03-0.2 wt % of C, 1.0-3.0 wt % of Si, 0.2-2.0 wt % of Mn, 0.05-0.5 wt % of V and the balance of Fe. The primary advantage of this steel is fineness of grain size after carburizing at relatively high temperatures. Even when carburizeed at or above 950.degree. C., the grain size number is not smaller than 6 in both the hardened case and the core. Optionally the steel may contain up to 2.0 wt % of Ni, up to 2.0 wt % of Cr and/or up to 0.5 wt % of Mo for the reinforcing purpose, and/or up to 0.1 wt % of Al, up to 0.3 wt % of Ti, up to 0.1 wt % of Zr, up to 0.03 wt % of N and/or up to 0.5 wt % of Nb+Ta for the purpose of depressing the grain growth.

Abstract: A method for improving the wear characteristics and corrosion resistance of a metal surface having the basic steps of:A. case hardening the metal surface by placing the metal in a fluidized bed and exposing it to a first atmosphere of nitrogen, ammonia and natural gas at a temperature between about 750.degree. F. and about 1200.degree. F. for a period between about 1 and about 5 hours, followed by exposure to a second atmosphere containing nitrogen and water at a temperature between about 750.degree. F. and about 1200.degree. F.;B. coating the metal with an aqueous coating composition consisting essentially of a polymeric additive and water; andC. allowing the coating composition retained on the metal to cure for a period between about 2 and about 48 hours.

Abstract: A ferrous, sintered, powdered metal part is steam sealed and gas ferritic nitrocarburized to provide a part useful for high hardness applications without the brittleness normally associated with conventional hardening. The steam treating of the ferrous metal part seals off the interconnected porosity of the part with a coating of Fe.sub.2 O.sub.3, but not FeO, to limit the penetration of nitrocarburizing gases so that they produce a surface hardening without contributing to internal brittleness that results from the deeper penetration of the nitrogen treatment.

Abstract: A surface hardened pin for a chain is made from a ferrous alloy containing manganese, silicon, chromium, molybdenum and about 0.1 to 0.4% carbon, with the balance essentially iron. The layer is formed of ferrous material containing chromium and 0.6 to 0.9% carbon and has a plurality of carbide particles dispersed therethrough. The hardened surface layer is formed by gas carburizing the pin.

Abstract: A component formed of interstitial free steel is heated in a gaseous atmosphere containing 15% by volume of a nitrogen doner, e.g. ammonia, at about 500.degree. C. to about 740.degree. C. for about 30 minutes to about 4 hours to form an epsilon iron nitride surface layer, and a layer of nitrides of trace alloying elements below the surface layer.

Abstract: An improved passenger car tire chain employing heat treated medium carbon steel is disclosed. The improved tire chain is approximately twice as durable as that presently furnished to meet NACM-5179(TC) for Type PL chains when AISI 1026 or 1029 carbon steel is employed at least for links of a cross chain meeting the road surface. The cross chain links are closed by welding prepared abutting link ends which have been previously beveled. After being welded closed, the cross chain links are case hardened, quenched, tempered and air cooled. The improved tire chain is then assembled in a conventional manner to include a pair of side members, fastening means to secure a end of each side member to the other end, and a plurality of cross chains extending between the sidewall members at preselected intervals.

Abstract: An improved steel for cold forging for machine structural use, particularly, case hardening steel, contents of Al, N and Nb are selected to satisfy a specific corelation therebetween, and the amounts of O and S are controlled. The steel is resistant to cracking at the cold forging, and growth of austenite crystals to coarse grains during carburizing or carbonitriding is prevented.Disclosed are preferable structure of the steel and rolling conditions to obtain the structure, and conditions for continuous casting of the steel.