103 results about "Cementite" patented technology

Provided is a hot rolled steel sheet having a predetermined chemical composition and a microstructure comprising, by area ratio, pearlite: 90 to 100% and pro-eutectoid ferrite: 0 to 10%, wherein the pearlite has an average lamellar spacing of 0.08 to 0.30 μm, and the percentage of cementite in the pearlite having a major axis length of more than 0.3 μm and an aspect ratio of less than 3.0 is less than 15%.

A steel wire for machine structural parts, may include Fe, inevitable impurities, and, by mass: 0.05 to 0.60% C; 0.005 to 0.50% Si; 0.30 to 1.20% Mn; more than 0 to 0.050% P; more than 0 to 0.050% S; 0.001 to 0.10% Al; more than 0 to 1.5% Cr; and more than 0 to 0.02% N. An area of cementite present at ferrite grain boundaries in an area of all cementite of the steel wire may be 32% or more. When a C content (% by mass) of a steel is expressed as [C], an average circular-equivalent diameter of all the cementite is (1.668-2.13 [C]) μm or more and (1.863-2.13 [C]) μm or less.

A steel wire according to one embodiment of the present invention can be a high-strength and high-corrosion-resistant steel wire comprising, by wt%, 0.50-0.75% of carbon (C), 0.5-0.9% of manganese (Mn), 0.2-0.5% of silicon (Si), 0.03-0.18% of molybdenum (Mo), and the balance of iron (Fe) and inevitable impurities, wherein an average diameter of a pearlite block of the steel wire is 25 μm or less, and a carbon content of cementite in pearlite is 18 at% or higher.

The invention discloses an online spheroidizing annealing process and system for a hot-rolled wire rod, and belongs to the technical field of wire heat treatment in the metallurgical industry. The process combines controlled rolling, controlled cooling and on-line spheroidizing annealing, and specifically comprises the following steps: after a steel billet is heated, rolling is completed in an austenite and ferrite two-phase region, and the steel billet is immediately cooled to 20-30 DEG C higher than the Ar3 temperature through water; the whole coil of the hot-rolled wire rod enters a tunnel type annealing furnace by utilizing waste heat of the hot-rolled wire rod, heat preservation is conducted for 0.4-0.6 h at the temperature 60-80 DEG C below the A1 temperature, the form and number of separated cementite in austenite are controlled, and nucleation points are formed; the temperature is increased to 20-50 DEG C below the temperature A1, heat preservation is conducted for 8-12 h, and cementite is gathered and grows up through spheroidization; and finally, slowly cooling to below 550 DEG C at the speed of 10-20 DEG C / h, and discharging. The rolling waste heat is fully utilized, the long heating process of traditional annealing is omitted, energy consumption is remarkably reduced, the annealing time is shortened, and the production efficiency is improved.

The invention provides high-spheroidization-rate medium-carbon steel based on medium-low annealing temperature and a production method thereof.The method comprises the steps of a hot rolling process, specifically, a medium-carbon steel blank is subjected to hot continuous rolling, the hot rolling coiling temperature is controlled to be 650 + / -20 DEG C, and a lamellar pearlite structure is obtained; a cold rolling process: carrying out cold rolling on the hot rolled coil, controlling the total cold rolling reduction rate to be not less than 35%, and introducing high-density dislocation and distortion defects into a pearlite structure; the cold-rolled steel plate is placed in a cover annealing furnace, under the full hydrogen protection atmosphere, the cold point temperature in the furnace is controlled to be 700 + / -10 DEG C, the hot point temperature is 710 + / -10 DEG C, the heat preservation time is 4-8 hours, and the flaky cementite is fully spheroidized; according to the method, the spheroidization rate of the medium carbon steel reaches 90% or above successfully under the upper limit condition of the annealing temperature of 720 DEG C, the contradiction between insufficient equipment capacity and high-end product requirements is solved, and remarkable economic benefits are achieved.

To provide a steel pipe for an airbag and a method for producing the steel pipe that ensure strength and low-temperature toughness without performing quenching and tempering.SOLUTION: A steel pipe for an airbag has a chemical composition comprising C: 0.10 to 0.25%, Si: 0.01 to 0.50%, Mn: 1.00 to 3.00%, P: 0.030% or less, S: 0.020% or less, Cr: 0.01 to 1.00%, Al: 0.010 to 0.060%, N: 0.0020 to 0.0200%, and V: 0.05 to 0.30%, optionally containing Mo: 0.30% or less as an optional element, with the balance being Fe and unavoidable impurities, having a metal structure mainly composed of a ferrite structure and cementite, in which an average crystal grain size of the ferrite structure is 1.5 μm or less, satisfying, with respect to tensile strength TS and elongation at break EL, Formula A: TS≥850 MPa and Formula B: TS×EL≥10000 MPa%, and having a fracture appearance transition temperature vTrs of -50°C or less.SELECTED DRAWING: None

The invention discloses a method for accurately measuring the phase content in stainless steel. The method is suitable for stainless steel containing at least one phase of ferrite, austenite, cementite and martensite. The method comprises the following steps: S1, cutting, grinding and polishing a stainless steel sample to obtain a bright surface; s2, pre-judging the type and the number of contained phases through metallographic structure observation in combination with component analysis and a heat treatment process; and S3, directional detection is conducted according to the pre-judgment result, ferrite is measured through metallographic software after being subjected to electrolytic corrosion through a KOH electrolyte, austenite is measured through an X-ray diffraction technology, cementite is measured through a laser confocal microscope after being subjected to acid etching, and martensite is obtained by subtracting the sum of the measured phase content by 100%. The method integrates various technical advantages, is simple and convenient to operate, wide in detection range and high in precision, and can provide accurate data support for stainless steel process optimization and material development.

The invention discloses a high-toughness corrosion-resistant pearlite steel wire with an adjustable honeycomb structure characteristic as well as a preparation method and application of the high-toughness corrosion-resistant pearlite steel wire, and belongs to the technical field of pearlite steel wire processing. The surface of the steel wire is provided with an aluminum alloy coating which is metallurgically bonded with a base body and has the thickness of 8-10 microns; the steel wire is subjected to ultrasonic treatment to generate a structure with a honeycomb characteristic, and the obtained cementite lamella serves as a hard phase to form a regular'honeycomb wall ', so that a core supporting effect is achieved; the ferrite serving as a plastic phase is coordinated and deformed under the action of external force by forming a honeycomb unit with uniform size, so that more energy is absorbed and crack propagation is hindered; and an Al2O3 protective film is instantaneously formed on the surface of the aluminum alloy coating, so that the aluminum alloy coating has excellent corrosion resistance and better mechanical properties. The Vickers hardness of the aluminum alloy reaches up to 830-850 HV < 0.1 >, the tensile strength of the aluminum alloy reaches 3100-3200 MPa, and the ductility of the aluminum alloy reaches 16-20%.

A manufacturing method of an alloy steel for cold-forging according to an embodiment of the present disclosure comprises homogenizing a steel material, furnace-cooling the steel material, and segmentation-annealing the steel material, in which the segmentation-annealing may be performed at least once and is optionally repeated one or more times.An alloy steel for cold-forging according to an embodiment of the present disclosure may comprise segmented cementite.A gear for cold-forging according to an embodiment of the present disclosure may have a gear surface grain boundary oxide layer of 19 μm or less.

The invention relates to the technical field of full mold casting, and provides a casting method of a large-scale automobile covering part GGG70L nodular cast iron stamping die, which comprises the following steps: firstly, manufacturing a model, and then manufacturing conformal chillers according to the molded surface of the model, and arranging the conformal chillers in a large area; smelting molten iron, adding alloy raw materials, and regulating and controlling the proportion of the alloy raw materials; then molten iron is subjected to spheroidizing inoculation and then is poured, after pouring, cooling in the eutectic stage is accelerated through external forced blowing heat dissipation, and through large-area use of shape-following chilling blocks, the profile cooling speed in the eutectic cooling stage is increased, the graphitization reaction is remarkably inhibited, growth of carburizing body nucleation and pearlite is promoted, and the pearlite nucleation rate is remarkably increased; ferrite precipitation is inhibited, and finally the pearlite content in a molded surface area is stabilized to be 90% or above; and finally, cooling to 200 DEG C, opening the sand box, taking down the test bar on the casting, and carrying out stretching detection and metallographic inspection. And multi-dimensional cooperative regulation and control are realized, so that the pearlite content is greatly increased, and the balance of mechanical properties is realized.

To provide a machine structure wire rod applicable to automobiles, construction components, and the like, and a manufacturing method therefor, and to provide a wire rod having excellent drawability, and a method for manufacturing the same.SOLUTION: The present invention is a wire rod which, in weight%, consists of C: 0.8-1.2%, Si: 0.01-0.6%, Mn: 0.1-0.6%, Cr: 0.8-2.0%, Al: 0.01-0.06%, N: 0.02% or less (excluding 0), with the remainder being Fe and inevitable impurities, wherein a microstructure includes proeutectoid cementite in a pearlite main structure, includes 20 or more AlN having an average particle size of 30 nm or less per unit area (μm2), and includes a microstructure satisfying the following relational expression 1, wherein [Relational Expression 1] is [(average size of block crystal grains(μm))2 / (length of proeutectoid cementite(μm / 1200 μm2))≤0.5].SELECTED DRAWING: Figure 1

A hot-pressed member having a specified chemical composition in which Ti / Sb 2.0≤Ti / Sb≤20.0 is satisfied and a method for producing the hot-pressed member. The hot-pressed member has a microstructure in which a volume fraction of martensite is 95% or more, an average grain size of prior austenite is 7 μm or less, the number of cementite grains with a grain size of 0.10 μm or more is 2 grains / μm2 or more, and the number of Ti-based carbide grains with a grain size of 0.10 μm or less is 0.20 grains / μm2 or more, and a tensile strength of 2100 MPa or higher.

Provided is a steel sheet having a composition which contains, in terms of mass, 0.70-1.30% C, 0.01-0.50% Si, 0.05-1.30% Mn, up to 0.100% P, up to 0.100% S, up to 0.100% Al, up to 0.0150% N, 0-1.20% Cr, 0-2.800% Ni, 0-0.500% Mo, 0-0.500% V, 0-0.500% Nb, 0-0.150% Ti, and 0-0.0100% B, the remainder comprising Fe and impurities, and having a metallographic structure which includes ferrite having an average crystal-grain diameter of 15.0 μm or larger and cementite having an average grain diameter of 0.70-1.20 μm. In the cementite, the areal proportion of spheroidized cementite having aspect ratios of 3.0 or less is 85% or higher with respect to the whole cementite and the ratio of the number of intragranular cementite grains to the total number of cementite grains is 0.70 or higher.

This invention belongs to the field of metal welding technology and relates to a heat treatment method for hypereutectoid rail steel after flash welding, comprising the following steps: post-weld cooling: the welded joint is allowed to cool naturally in air after flash welding; normalizing treatment: the welded joint is heated to a normalizing temperature above the austenitizing temperature and held at that temperature; controlled cooling: the temperature of the weld heat-affected zone of the welded joint is cooled from the normalizing temperature to the isothermal transformation temperature within the pearlite phase transformation temperature range at a first cooling rate, held at that temperature until the austenite undergoes pearlite transformation, and then the welded joint is cooled from the isothermal transformation temperature to below 200°C at a second cooling rate lower than the first cooling rate. The method of this invention can effectively eliminate the network cementite structure in the flash welding heat-affected zone, while avoiding the introduction of harmful structures such as martensite or bainite, ensuring that the microstructure of the weld heat-affected zone is pearlite with fine lamellar spacing.

The invention provides a production method of a hot-rolled wire rod. The method mainly comprises a high-speed wire rolling process and a controlled rolling and controlled cooling process, and a hot-rolled wire rod with good performance is finally obtained by combining casting blank heating temperature, heating time, after-rolling spinning temperature control and a segmented controlled cooling technology. The diameter of the produced wire rod is 6.5 mm, the tensile strength is larger than or equal to 1200 MPa, the percentage elongation after fracture is larger than or equal to 15%, the percentage reduction of area is larger than or equal to 40%, the structure is pearlite, the sorbite rate is larger than or equal to 90%, centreless martensite and grain boundary cementite are adopted, and the wire rod has the advantages of being high in strength and plasticity. And the cable has the characteristics of high strength, high torsion and high bending performance after being bent for 12 times or more.

Disclosed is a technique in which the cementite conversion rate in iron carbide is greater than or equal to a target value when reduced iron is first obtained through a direct reduction process using a shaft furnace, and then the iron carbide is obtained by carburizing the reduced iron. The iron carbide manufacturing method according to the present disclosure has a reduction step in which an iron oxide raw material is reduced with a reducing gas to obtain reduced iron, and a carburization step in which the reduced iron is carburized with a carburizing gas while being cooled to obtain iron carbide. The reduction step is performed in a shaft furnace. In the carburization step, the carburizing gas includes 70 vol% or more of methane gas, the reduced iron is carburized until reaching the target cementite conversion rate or higher, and the relationship in which Y≥0.24X-0.31 and X≥3 (where "Y" is the elapsed time (minutes) for the reduced iron to reach 700°C from 800°C, and "X" is the target cementite conversion rate (%)) is satisfied.

Provided are a wire rod and an application of the wire rod, the wire rod having a prescribed chemical composition and being such that, when the diameter of the wire rod is represented by D and the C content of the wire rod is represented by [C]: at a position at which the depth from the surface is 1 / 4D, bainite accounts for 70% or more and martensite accounts for 10% or less; at a position at which the depth is 50 μm and at the position at which the depth is 1 / 4D, the aspect ratio F(AS) and the average equivalent circle diameter F(r) [μm] of cementite satisfy relationships (1) and (2); the tensile strength F(TS) [MPa] satisfies relationship (3); and the value obtained by dividing the standard deviation of the Vickers hardness by the average value in cross-sections perpendicular to and parallel to the length direction of the wire rod is 0.15 or less.　Relationship 1: F(AS) ≤ 5.2 × [C] + 0.4; Relationship 2: F(r) ≤ 0.62 × [C] + 0.1; Relationship 3: F(TS) ≥ −150 × [C] + 900

The wire according to the present disclosure contains, by weight %, 1.00 to 1.20% of C, 1.00 to 1.50% of Si, 0.10 to 0.50% of Mn, 0.30 to 0.80% of Cr, and 0.50 to 1.50% of Al, the balance of Fe and other unavoidable impurities, wherein the microstructure observed at a cross section of 1 / 2D to 3 / 2D (D: diameter) contains 95% or more of pearlite and 5% or less of blocky pro-eutectoid cementite having an average thickness of 1 μm or more in a region of 100 μm 2 2.

This steel sheet has a composition on a mass basis containing C: 0.70-1.30%, Si: 0.01-0.50%, Mn: 0.05-1.30%, P: 0.100% or less, S: 0.1000% or less, Al: 0.100% or less, N: 0.0150% or less, Cr: 0-1.20%, Ni: 0-2.800%, Mo: 0-0.500%, V: 0-0.500%, Nb: 0-0.500%, Ti: 0-0.150%, and B: 0-0.0100%, with the remainder being Fe and impurities. It has a metallic structure containing ferrite with an average grain size of 15.0 μm or more, and cementite with an average particle size of more than 0.40 μm and less than or equal to 0.75 μm. The cementite in question has a surface area ratio of 85% or more of spheroidized cementite with an aspect ratio of 3.0 or less relative to all cementite.

The present invention achieves both excellent machinability and punching workability for a cold-rolled steel sheet containing carbon at a high content of 0.80-1.25 mass%. A cold-rolled steel sheet having a prescribed component composition, the average particle diameter of cementite particles having an area of 0.06 [mu] m2 or more being 0.65 [mu] m or less, the A value being 2.0 mass% or more, the number density of pores having an area of 0.01 [mu] m2 or more being 50,000 / mm2 or more, and the Vickers hardness being 200-400 HV (inclusive).

The invention discloses a method for measuring combined carbon of an iron-based sintered product, and relates to the technical field of powder metallurgy material detection. The method comprises the following steps: preparing a metallographic specimen, and observing and analyzing by using a microscope after erosion. The method comprises the following steps: (A) determining view field proportions, namely respective volume ratios, of pores, non-iron-based structures and iron-based structures (pearlite, cementite and ferrite) in a sample through metallographic observation; (B) calculating the total mass of an iron phase on the basis of the volume ratio of pearlite, cementite and ferrite and the density of each of the pearlite, cementite and ferrite; (C) calculating the mass ratio of pearlite and cementite in the iron phase based on the total mass of the iron phase; and (D) according to the mass ratio and the carbon content of the pearlite and the mass ratio and the carbon content of the cementite, calculating to obtain the combined carbon content of the iron phase in the iron-based sintered product. The invention aims to provide a method for accurately and repeatedly measuring the content of iron-phase combined carbon in an iron-based sintered product.

The invention discloses induction heat treatment high-carbon gear steel, and belongs to the technical field of machine manufacturing. The gear steel comprises the following chemical components in percentage by mass: 0.705%-0.995% of C, 0.5%-2.5% of Si, 0.1%-0.5% of Cr, 0.010%-0.3% of Mo, 0%-0.3% of Cu, 0%-0.2% of V, 0%-0.02% of Ti and O < lt >. 30 ppm, S < lt >; 0.025%, P < lt >; 0.025%, and the balance being Fe. The material is subjected to vacuum melting to obtain a cast ingot, then the cast ingot is heated to 1050-1100 DEG C for complete austenitizing and heat preservation to achieve alloy component homogenization, then the cast ingot is continuously forged into the needed size in the cooling process, and the final forging temperature is controlled to be 850-900 DEG C. The forge piece is heated at 780-820 DEG C, subjected to heat preservation for 1-8 hours, cooled to 600 DEG C at the cooling speed of 20 DEG C / min and then discharged out of a furnace, and a structure with spherical cementite distributed on a ferrite matrix can be obtained; or heating and normalizing at 850 DEG C to obtain a pearlite structure. After induction quenching, the surface hardness of the steel plate can reach 62-64 HRC, and the depth of a hardening layer is 0.5-5 mm. The surface structure is characterized by comprising carbide with the average size of 0.3-0.6 mu m, martensite with the length of 0.5-2 mu m and a fine grain structure with the length of 7-15 mu m.

Cold rolled and heat treated steel sheet, having a composition including (in weight percent): 0.10%≤C≤0.25%, 3.5%≤Mn≤6.0%, 0.5%≤Si≤2.0%, 0.3%≤Al≤1.2%, with Si+Al≥0.8%, 0.10%≤Mo≤0.50%, S≤0.010%, P≤0.020%, N≤0.008%, said cold rolled steel sheet having a microstructure (in surface fraction) including: Between 10% and 45% ferrite, with an average grain size of maximum 1.3 m, the product of the surface fraction of ferrite and the average grain size of ferrite is maximum 35 m%, between 8% and 30% retained austenite, said retained austenite has a Mn content greater than 1.1*Mn%, Mn% indicates the Mn content of the steel, maximum 8% fresh martensite, maximum 2.5% cementite and partitioned martensite.

Provided is a railway wheel in which the generation of proeutectoid cementite can be suppressed even if the C content is high. The railway wheel according to the present embodiment has a chemical composition containing, in mass%, 0.80-1.15% of C, 0.45% or less of Si, 0.10-0.85% of Mn, 0.050% or less of P, 0.030% or less of S, 0.120-0.650% of Al, 0.0030-0.0200% of N, 0-0.25% of Cr, and 0-0.12% of V, with the remainder being Fe and impurities, and the amount of proeutectoid cementite in the microstructure of the railway wheel defined by formula (1) being 1.50 pieces / 100 [mu] m or less. The amount of pro-eutectoid cementite (root / 100 [mu] m) = the sum of the number of pro-eutectoid cementite which intersects two diagonals of a square field of view of 200 [mu] m * 200 [mu] m / (5.66 * 100 [mu] m) (1).

The invention provides a production process and application of a cold-rolled tool steel strip for a saw blade. Comprising the following steps that A1, a tool steel plate blank is heated and then continuously rolled, the coiling temperature is controlled to be 560-600 DEG C, and a hot-rolled wide plate coil is obtained; the method comprises the following steps: A1, carrying out hot rolling on a wide-width plate coil, A2, annealing the hot-rolled wide-width plate coil in a protective atmosphere, A3, carrying out acid pickling, rinsing and drying on the annealed steel coil, and then carrying out cold continuous rolling by adopting a multi-rack continuous rolling mill, A4, annealing the cold-rolled steel coil again in the protective atmosphere, and A5, cooling the annealed steel coil. The invention mainly aims to provide a production process and application of a 75Cr1 cold-rolled tool steel strip for a saw blade, and aims to solve the problems that in the prior art, in the whole-process production process of hot rolling, annealing and cold rolling, the size of cementite particles is difficult to effectively control, so that the structure of the steel strip is thick and large, and the service life of the steel strip is prolonged. And therefore, the technical problems of insufficient dissolution of carbides and low fatigue life during subsequent quenching heat treatment are solved.

This invention discloses a high-modulus ductile iron, composed of the following raw material components by mass percentage: C: 3.2%~3.9%, Si: 2.1%~2.7%, Cu: 0.5%~2.0%, Mn: 0.2%~2.0%, Cr: 0%~0.5%, Mg: 0.01%~0.05%, RE: 0.01%~0.03%, with the balance being Fe. The total mass percentage of all the above components is 100%, and the total addition of Mn and Cr is not higher than 2.0%. This invention also discloses a method for preparing the high-modulus ductile iron and its applications. The ductile iron of this invention promotes the formation of pearlite and significantly refines the pearlite lamellae due to the Cu element. After the lamellae spacing is reduced, the interface area between ferrite and cementite increases, which can effectively hinder dislocation slip and improve strength. At the same time, the deformation of ferrite lamellae is restricted to a short distance, the stress distribution is uniform, and local excessive deformation and fracture are avoided, so that the cast iron can maintain high elongation under high strength.

The invention relates to the technical field of metal materials, in particular to a novel method for simultaneously improving strength and torsion performance of a hot-dip galvanized steel wire, which is technically characterized by comprising the following steps of: S1, performing multi-pass cold drawing deformation on a pearlite wire rod with the total dependent variable of 1.4-2.0 (namely, drawing the wire rod with the specification of 14 mm into a steel wire with the specification of 7 mm or 5 mm, and drawing the steel wire with the specification of 14 mm into a steel wire with the specification of 7 mm or 5 mm; or a steel wire with the specification of 5 mm is drawn from a steel wire rod with the specification of 13 mm), and in order to restrain temperature rise in the drawing process, the steel wire is subjected to water cooling in the drawing process; s2, the cold-drawn steel wire is subjected to aging treatment for 0.1-2 h at the temperature of 200-350 DEG C; and S3, the cold-drawn steel wire subjected to pre-aging treatment is subjected to heat treatment for 1 min in molten zinc at the temperature of 400-470 DEG C, and then the steel wire is air-cooled to the room temperature. According to the scheme, before high-temperature hot galvanizing, the cold-drawn steel wire is aged for 0.1-2 h within the range of 200-350 DEG C, then hot galvanizing is conducted, abnormal growth of cementite is restrained, and under the condition that the strength and the ductility are not sacrificed, synchronous improvement of the strength and the torsion performance is achieved.

A hot-dip galvanized steel sheet is provided comprising a base steel sheet having a predetermined chemical composition and containing ferrite: 50% or less, retained austenite: 30% or less, quenched martensite: 5% or more, fresh martensite: 10% or less, and pearlite and cementite in total: 5% or less, the remaining structures consisting of bainite and a numerical ratio of quenched martensite with a Mn concentration profile that satisfies [Mn]b / [Mn]a>1.2 and [Mn]a / [Mn]<2.0 ([Mn] is the Mn content in the base steel sheet, [Mn]a is the average Mn concentration in the quenched martensite and [Mn]b is the Mn concentration at the interfaces of different phases of the quenched martensite and ferrite phase and the bainite phase) is 0.2 or more with respect to the total number of quenched martensite, and a method for producing the same.

The method comprises:-s1) determining a bainite ferrite growth rate, the bainite ferrite growth rate being proportional to the activation energy of the transformation of austenite to bainite ferrite, and the bainite ferrite growth rate being proportional to an adjustment coefficient, the free enthalpy of the bainite ferrite phase being close to the free enthalpy of the austenite phase, and the free enthalpy of the austenite phase being close to the free enthalpy of the austenite phase; the adjustment coefficient is close to zero, and the free enthalpy of the austenite phase depends on the carbon content in the austenite phase; the method comprises the following steps: (1) determining a bainitic ferrite growth rate, (2) determining a cementite growth rate at least as a function of the carbon content in the austenite phase, (3) determining values of bainitic ferrite, austenite and cementite phase fractions at the next time step based on the bainitic ferrite growth rate and the cementite growth rate, and updating the carbon content in the austenite phase based on the values of the phase fractions.

Provided is a profile for crankshafts, which has excellent wear resistance and excellent machinability even when used without high-frequency hardening. The crankshaft profile has a prescribed chemical composition, Fn1 defined by formula (1) is 3.80-5.00, the structure contains 12-40 vol% of proeutectoid ferrite, the balance being pearlite, and the thickness of the crankshaft profile at a position 50 [mu] m deep from the surface of a portion corresponding to the pin portion of the crankshaft is 10-30 [mu] m. The ratio (Mn [theta] / C [theta]) of the Mn content (Mn [theta]) to the C content (C [theta]) obtained by analyzing cementite in the pearlite by energy dispersive X-ray analysis is 0.360 or more. Fn1 = 7C + 0.5 Si + Mn + 3Cr-10Ti (1) In formula (1), the contents of the corresponding elements are substituted in mass% at C, Si, Mn, Cr, and Ti.