26 results about "Acicular ferrite" patented technology

The application provides a corrosion-resistant super-large line energy welding steel plate and a production method thereof, relates to the technical field of alloys, and the steel plate adopts a corrosion-resistant alloying component system with composite addition of Ce, Sn and Cu. The addition of Ce can improve the corrosion resistance of the steel plate, and Ce is easy to combine with oxygen to generate spherical oxides and has the ability to induce the nucleation of intracrystalline acicular ferrite, thereby improving the welding performance of the steel plate. On the basis of the comprehensive design of chemical components, the process parameters of rolling and cooling processes are accurately controlled to obtain the corrosion-resistant super-large line energy welding steel plate with good comprehensive performance.

The present application belongs to the technical field of hot stamping part preparation, and particularly relates to a tailor-welded part, a manufacturing method thereof and a welding wire applied to the tailor-welded part. The tailor-welded part comprises a welded joint, and a weld seam of the welded joint comprises acicular ferrite and martensite. The average length of the acicular ferrite is not greater than 80 microns, the average diameter is not greater than 15 microns, and the volume percentage of ferrite in the weld seam is 0.1-10%. The tailor-welded part is a part after hot stamping treatment. The joint elongation of the tailor-welded part is greater than 4%, the weld seam structure is martensite and ferrite, the fracture position is located in the base material during the quasi-static tensile test, and the weld seam has good strength and ductility.

The present application relates to a kind of 500MPa grade weathering steel welding process and application in low temperature service environment.The welding method of prior art 500MPa grade weathering steel has the defect that cannot meet the requirement of low temperature service, the present application provides a kind of based on flux-cored wire and cold metal transition welding process, the composition of flux-cored wire is optimized, the nucleation rate of weld metal acicular ferrite is increased, the low temperature impact toughness of joint is guaranteed;On the other hand, cold metal transition welding process is used, short-circuit current is controlled, welding heat input is reduced, and the burning loss of alloy element is reduced.Weathering steel welded joint prepared based on the process of the present application has good low temperature impact toughness, and can meet the use demand of low temperature service environment.

The embodiment of the invention discloses low-cost, high-yield-ratio and low-temperature-impact-resistant 700MPa-grade automotive beam steel as well as a preparation method and application thereof. The automobile beam steel comprises the following components in percentage by mass: 0.05 to 0.12 percent of C; si: less than or equal to 0.10%; mn: 1.2 to 2.0%; n: < = 0.005%; 0.015% to 0.03% of Nb; 0.03 to 0.08% of Ti; less than or equal to 0.3% of Cr; 0.001 to 0.003 percent of B and the balance of Fe; according to the automobile beam steel, the tensile strength Rm is not smaller than 750 MPa, the yield strength R0.2 or ReL is not smaller than 700 MPa, the total elongation A after fracture is not smaller than 20%, and the yield ratio is 0.90-0.95. The Charpy impact absorbing energy KV2 at-20 DEG C is not less than 140J; the Charpy impact absorbing energy KV2 at-40 DEG C is not less than 120J; the microscopic structure of the automobile beam steel is composed of acicular ferrite, pearlite and granular bainite, the effective grain size of the acicular ferrite is 3-5 microns, and the volume fraction of the pearlite is smaller than or equal to 10%.

This invention relates to the field of new energy infrastructure materials technology, and in particular to a high-strength weather-resistant steel for large-diameter monopile foundation structures and its preparation method. The invention utilizes the synergistic design and optimization of Nb and Ti microalloying elements, combined with controlled rolling and cooling processes, to effectively promote the formation of fine acicular ferrite and lower bainite structures and the dispersed precipitation of nano-reinforcing phases such as Ti(C,N) and Nb(C,N). While ensuring the alloy steel possesses high strength, high plasticity, and excellent corrosion resistance, it significantly reduces dependence on precious metal alloying elements such as Ni and Mo, resulting in outstanding cost-effectiveness. This steel can be used as a steel for wind power monopile foundations in harsh marine environments, solving the problems of low strength, poor corrosion resistance, and high cost in existing diameter monopile foundation structures.

The application provides a Ti-Ca treated hydrogen storage pressure vessel steel plate and a manufacturing method thereof. The steel plate comprises the following components in percentage by weight: C: 0.09% to 0.12%, Si: 0.25% to 0.40%, Mn: 1.10% to 1.30%, P: ≤0.015%, S: ≤0.005%, Cr: 0.30% to 0.40%, Ni: 0.20% to 0.30%, Mo: 0.15% to 0.25%, V: 0.09% to 0.15%, Nb: 0.01% to 0.02%, Ti: 0.01% to 0.02%, Al: 0.003% to 0.005%, Ca: 0.006% to 0.008%, V / C≥1, Ti / Ca: 1 to 3, and the balance of Fe and inevitable impurities. The production method of the steel plate comprises smelting, continuous casting, heating, rolling, cooling and heat treatment. The microstructure of the steel plate is tempered sorbite + acicular ferrite, and the volume percentage of the tempered sorbite structure is 92% to 96%. The yield strength ReL of the steel plate is greater than or equal to 650 MPa, the tensile strength Rm is 800 to 920 MPa, the elongation A is greater than or equal to 21%, the low-temperature impact toughness KV2 at-50 DEG C is greater than or equal to 100 J, the tensile yield strength ReL at-50 DEG C is greater than or equal to 660 MPa, the tensile strength Rm is 820 to 930 MPa, and the elongation is greater than or equal to 21%. The steel plate is welded by using large linear energy of 100 to 140 kJ / cm, the yield strength R eL of the heat-affected zone (HAZ) is greater than or equal to 690 MPa, the tensile strength R m is 830 to 950 MPa, the elongation is greater than or equal to 17%, and the impact toughness KV2 of the heat-affected zone (HAZ) at-50 DEG C is greater than or equal to 70 J.

The application discloses a low-cost large-heat-input welding method for common high-strength steel, selects common high-strength steel plates with thickness of 20mm-120mm and tensile strength of 450-650MPa as base materials, firstly melts thin-layer weld metal in a groove by small-line-energy gas shielded welding, forms fine and dispersed inclusions in the weld by Ti, Si, Al and Mn oxides and MnS complex, and induces generation of slender acicular ferrite (AF) structure, and then completes welding by vertical gas-electric vertical welding with large heat input, so that the thin-layer weld metal is used as new heat affected zone (HAZ), the inclusions inhibit austenite grain growth, and the AF structure is transformed into equiaxed ferrite. The application can realize large-heat-input efficient welding of common high-strength steel without special large-heat-input welding steel, the low-temperature impact toughness of each region of the joint is excellent, the material cost is greatly reduced, the welding efficiency is improved, and the application is suitable for thick plate welding fields such as shipbuilding and offshore platform.

The invention relates to a composite powder particle of a chromium wear-resistant alloy in submerged arc surfacing. The composite powder particle with the particle size of 12-15 meshes is prepared by the following preparation process steps: screening and weighing powder components contained in the composite powder particle, carrying out dry powder mixing, adding water glass, carrying out wet mixing, bonding and granulating wet powder, sintering at low temperature and screening the powder particle. The composite powder particles are melted and preset through an electric arc, the composite powder particles and H08A solid welding wire molten drops are fused together to form a surfacing weld pool, and the surfacing weld pool is cooled and solidified to form the wear-resistant alloy. The alloy component types and content of the composite powder particles are optimized, the matrix and wear-resistant phase structure types, number and distribution pattern of the surfacing alloy are regulated and controlled, and an organization structure comprising a (Fe, Cr) 7C3 phase distributed in a strip shape, a strip (Fe, Cr) 3C phase distributed intermittently side by side along the boundary, an intracrystalline strengthened point-shaped TiC phase and an elastic matrix composed of acicular ferrite and acicular martensite is obtained. In other words, the medium-chromium alloy with excellent wear resistance, high toughness and excellent cost performance is overlaid. The composite powder particle can be used for surfacing a wear-resistant alloy layer bearing a certain impact load for parts, such as a toothed plate of a jaw crusher.

The invention discloses a low-hardness high-toughness submerged arc welding wire which comprises the following chemical components in percentage by weight: 0.03 to 0.06 percent of C, 0.80 to 1.00 percent of Mn, less than or equal to 0.25 percent of Si, less than or equal to 0.005 percent of S, less than or equal to 0.008 percent of P, 0.30 to 0.50 percent of Mo, 0.70 to 0.90 percent of Ni, 0.03 to 0.08 percent of Ti, 0.002 to 0.008 percent of B and the balance of iron and inevitable impurities. And the chemical components meet the condition that C + Mn / 10 + Mo / 5 is less than or equal to 0.20%. The components of the welding wire are subjected to quantitative control of low-carbon and solid solution strengthening elements, a Mn-Mo-Ni-Ti-B alloy system is adopted, a welding seam with acicular ferrite as a main component is obtained, the problem that hardness and toughness of a traditional welding wire are difficult to consider at the same time is effectively solved, good matching of low hardness and high toughness is achieved, the hydrogen resistance of the welding seam is further remarkably improved, and the welding wire has good application prospects. The results of the crack sensitivity rate, the length rate and the thickness rate of the welding wire in a standard HIC test are zero, and the welding wire is particularly suitable for welding of hydrogen conveying pipeline steel pipes, low-temperature fine-grain carbon steel pipes and other severe environments.

The invention discloses a permanent magnet surface coating material and a preparation method thereof, and belongs to the technical field of corrosion prevention of permanent magnet materials. The coating material comprises a component A and a component B in a weight ratio of (10-12): 1, wherein the component A comprises 50-70 parts of epoxy resin, 3-5 parts of functionalized graphene, 3-8 parts of a modified ferrite nanofiller, 60-100 parts of an organic solvent and an auxiliary agent; and the component B comprises 15-20 parts of a polyamide curing agent and 15-20 parts of an organic solvent. The functionalized graphene is prepared by modifying triglycidyl isocyanurate through a ball milling method, so that the dispersity and the interface bonding force are effectively improved; the modified ferrite nano-filler is needle-shaped ferrite treated by a silane coupling agent, the length-diameter ratio of the modified ferrite nano-filler is 5: 1-10: 1, and the modified ferrite nano-filler can be embedded into pores of a permanent magnet matrix by virtue of magnetism, so that the adhesive force and the impermeability are enhanced. The coating has excellent binding force, acid and alkali resistance and long-acting corrosion resistance, the preparation process is simple and convenient, and the coating is suitable for industrial surface protection of the neodymium-iron-boron permanent magnet.

This invention discloses a low-cost, thick-gauge, high-strength and high-toughness X70 pipeline steel and its production method. Its chemical composition is: C: 0.05–0.07%, Si: 0.15–0.25%, Mn: 1.70–1.85%, Nb: 0.035–0.055%, Ti: 0.030–0.045%, Cr: 0.30–0.35%, Ce: 0.0015–0.0035%, Als: 0.015–0.035%, S: ≤0.003%, P: ≤0.010%, N: ≤0.0035%. The production method includes smelting and continuous casting, heating and rolling, cooling, and coiling processes. Compared with existing technologies, this invention, without adding Mo or Ni, achieves uniform and fine acicular ferrite with a small amount of Mao island (M / A) or granular bainite structure through optimized design of elements such as Nb, Ti, and Ce, combined with comprehensive control of continuous casting and controlled rolling and cooling processes. Niobium-titanium nanoprecipitates further strengthen the ferrite, enabling the pipeline steel of this invention to not only have excellent mechanical properties, weldability, and low-temperature tear resistance, but also significantly reduce production costs, achieving good service safety and economy.

The application discloses a kind of big thickness 460Mpa level high toughness marine engineering steel plate and production method thereof, alloy component mass percentage of steel plate is C=0.03%~0.06%, Si=0.10%~0.35%, Mn=1.20%~1.50%, P≤0.008%, S≤0.002%, Al=0.02%~0.05%, Nb=0.02%~0.05%, Ti=0.008%~0.02%, Ni=0.30%~0.55%, B≤0.0005%, the rest is Fe and inevitable impurity.Production procedure includes smelting casting, heating rolling and cooling, steel plate thickness ≥800mm, the microstructure of the special thick steel plate produced is acicular ferrite+mainly pearlite;The yield strength of steel plate core is ≥460MPa, tensile strength is ≥560MPa, total elongation is ≥21%, the impact energy of core-40 DEG C is >200J, CTOD value of steel plate base material-30 DEG C is ≥0.70mm, CTOD value of welding joint-30 DEG C is ≥0.38mm.

Provided are a high-strength thick hot-rolled steel sheet having excellent elongation and a method for manufacturing same. The high-strength thick hot-rolled steel sheet comprises, by weight %: 0.05-0.15% of C; 0.01-1.0% of Si; 1.0-2.0% of Mn; 0.01-0.1% of Sol. Al; 0.005-1.0% of Cr; 0.001-0.02% of P; 0.001-0.01% of S; 0.001-0.01% of N; 0.005-0.07% of Nb; 0.005-0.11% of Ti; and the remainder of Fe and unavoidable impurities, satisfies relation 1, and has a microstructure comprising, by area %: 25-50% of polygonal ferrite; 30-50% of bainitic ferrite and acicular ferrite; 20% or less of bainite; less than 5% of the sum of area fractions of carbide and pearlite structures having a diameter of 0.5 μm or more, observed within a unit area (1 cm2); and less than 5% of phase MA (martensitic-austenitic constituents).

This invention relates to the field of local heat treatment and precise control of material microstructure in high-performance tunneling machine tool steel. It discloses a laser cladding process for drill bit alloy steel based on interface toughening treatment, comprising: constructing a cladding deposition layer on the surface of the alloy steel substrate using a main laser energy field; performing heat compensation on the fusion line region from the laser energy field; adjusting the output power from the laser energy field in real time according to the cumulative total input energy to offset the background temperature rise; controlling the physical residence time above the phase transformation temperature; adjusting the physical hysteresis distance and beam spot topology of the laser according to the local three-dimensional geometric curvature of the processed surface to reduce the local heat flux intensity; and solving the problem of phase transformation path runaway caused by background heat accumulation and thermal resistance accumulation in large thermally inert components by in-situ inducing the generation of a toughened microstructure interwoven with acicular ferrite and bainite, thereby improving interfacial impact toughness and achieving global microstructure isomorphism.

The invention relates to the technical field of nodular cast iron material design and heat treatment compounding, and discloses a preparation method of a nodular cast iron profile based on horizontal continuous casting, which comprises the following steps: smelting raw materials to form molten iron, standing and cooling, spheroidizing and inoculating the cooled molten iron, and drawing and forming by adopting a horizontal continuous casting process to obtain the profile, the method comprises the following steps: cutting a sample, processing, cleaning and ultrasonically cleaning, sequentially carrying out gradient austenitizing treatment, staged salt bath quenching, two-stage salt bath heat preservation, 3-5s rapid transfer and gradient air cooling to room temperature. According to the method, a horizontal continuous casting nodular cast iron profile which is compact in structure and small and round in graphite nodule is used as a necessary base material, the problem of performance fluctuation caused by shrinkage porosity and uneven graphite form of a traditional sand casting base material is solved through coordinated regulation and control of the whole-process technology, a refined acicular ferrite and high-carbon retained austenite stable structure can be obtained, strength and toughness are synergistically improved, and the strength and toughness of the product are improved. The process is based on conventional equipment, simple and controllable in flow, easy to industrialize and suitable for preparation of high-end mechanical parts.

This invention discloses a 780MPa grade reinforced flange high fatigue hot-rolled automotive structural steel, its production method, and its application, belonging to the field of metallurgical technology. The steel's chemical composition (wt%) is: C: 0.027%–0.034%, Si: ≤0.03%, Mn: 1.21%–1.29%, P: ≤0.010%, S: ≤0.002%, Als: 0.020%–0.035%, Nb: 0.026%–0.035%, Ti: 0.101%–0.115%, N: ≤0.0028%, Ca: 0.0007%–0.0013%, and satisfies 0.087%≤Ti-3.43N-1.5S≤0.107% and C-(Ti-3.43N-1.5S) / 4-Nb / 7.75≤0.004%. The production method includes: RH forced decarburization; LF calcium treatment and low-N sponge titanium alloying; slab heating at 1250±10℃; final rolling at 865~880℃; front-stage cooling rate at 84~98℃ / s; and coiling at 555~590℃. This invention yields a quasi-polygonal ferrite + acicular ferrite + nano-precipitated phase microstructure, enabling the steel strip to possess 780MPa strength, ≥74% porosity, and ≥361MPa fatigue strength (R=-1), while maintaining low cost and suitability for manufacturing lightweight automotive structural components.

The application relates to a preparation method of axle housing steel, which comprises the following steps: providing molten steel, performing a continuous casting process on the molten steel to form a casting blank; performing heating, rough rolling and finish rolling on the casting blank to obtain a rolled steel plate, wherein the finish rolling temperature is 800-820 DEG C; cooling the rolled steel plate to 300-450 DEG C at a rate of 30-40 DEG C / s to obtain a steel plate to be coiled; coiling the steel plate to be coiled at 300-420 DEG C, and obtaining the axle housing steel after cooling, wherein the molten steel comprises 0.03%-0.06% of C, 0.05%-0.07% of Nb and 0.15-0.25% of Cr in percentage of the mass of the molten steel. By adopting a low-carbon+Cr, Mo and Nb component system and controlling the cooling rate of the rolled steel plate, superfine acicular ferrite and granular low-carbon bainite composite grain structures can be formed, the 700MPa high-strength performance of the steel plate with a thickness of more than 10 mm is ensured, and excellent cold forming performance and welding performance are achieved.

The application discloses a method for reducing mechanical property anisotropy of pipeline steel, the pipeline steel and application thereof, and belongs to the technical field of pipeline steel production. The method for reducing mechanical property anisotropy of pipeline steel is to reduce the content of {001} <110> texture in the pipeline steel, reduce the density of {001} cleavage surface, and obtain the pipeline steel with low anisotropy by controlling the production process of the pipeline steel. The pipeline steel is of X80 grade, the microstructure is acicular ferrite, the texture is mainly {112} <110>, {554} <225>, {332} <113> texture and {110} slip surface; the tensile strength is 650-710 MPa, the -20 DEG C drop weight shear area ratio is 90%-100%, the difference between the anisotropy is not higher than 30 MPa, and the difference between the anisotropy of the drop weight shear area ratio is not higher than 10%. The method can effectively solve the problem of the performance anisotropy of the existing pipeline steel.

The invention discloses a high-alkalinity sintered flux for a pressure steel pipe of a pumped storage power station and a preparation method of the high-alkalinity sintered flux, and belongs to the technical field of welding. The problems that after the pressure steel pipe of the pumped storage power station is welded through the welding flux, a weld joint cannot have high strength and low-temperature toughness at the same time, and the slag detachability is poor are solved. The flux comprises mineral dry powder and a binder, wherein the mineral dry powder comprises the following components in percentage by mass: 6-16% of wollastonite, 10-20% of fused magnesite, 25-40% of bauxite, 25-40% of fluorite, 5-10% of feldspar, 1-5% of manganese ore and 1-5% of an alloying agent. A wollastonite-bauxite-fluorite-fused magnesite quaternary system is used for deep deoxidation through oxygen potential synergistic pressing and nucleation synergistic catalysis, formation of acicular ferrite is promoted, and the low-temperature impact toughness is improved. When the welding flux is used in cooperation with a high-strength steel welding wire, the welding seam formability is good, the welding seam structure components are uniform, high strength and low-temperature toughness are achieved, the surface of a welding bead is smooth, and the deslagging performance is good.

This invention relates to a 60-100mm thick SA537CL1 steel plate with excellent die-welding performance and its manufacturing method, belonging to the field of metallurgical technology. The chemical composition of the steel plate (wt%) is: C: 0.06-0.09%, Si: 0.25-0.50%, Mn: 1.40-1.60%, P≤0.010%, S≤0.003%, Ni: ≤0.10%, Mo: 0.05-0.08%, Nb: 0.010-0.030%, Ti: 0.010-0.030%, with the balance being Fe and unavoidable impurities, and a carbon equivalent (Ceq) ≤0.36%. The surface microstructure is bainite, the microstructure at 1 / 4 thickness position is acicular ferrite + pearlite, and the core microstructure is polygonal ferrite + pearlite + acicular ferrite. The manufacturing process is as follows: oxygen converter smelting → ladle furnace refining → vacuum treatment → thick slab continuous casting → billet cooling → billet heating → controlled rolling → controlled cooling → stacking and slow cooling.

A steel for forging mechanical parts including the following elements, expressed in percentage by weight 0.2%≤C≤0.5%; 0.8%≤Mn≤1.5%; 0.4%≤Si≤1%; 0.15%≤V≤0.6%; 0.01%≤Nb≤0.15%; 0.01%≤Cr≤0.5%; 0.01%≤P≤0.05%; 0.04%≤S≤0.09%; 0.01%≤N≤0.025%; and can contain one or more of the following optional elements 0%≤Al≤0.05%; 0%≤Mo≤0.5%; 0.01%≤Ni≤0.5%; 0%≤Ti≤0.2%; 0%≤B≤0.008%; 0%≤Cu≤0.5%; the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel comprising 50% to 90% of Pearlite, 10% to 40% of Ferrite, with an optional presence of acicular ferrite between 0% and 2%, a niobium equivalent of 80% or more.

The application discloses a long rod bolt heat treatment process and relates to the technical field of metal heat treatment. The long rod bolt heat treatment process steps of the application successively comprise ultrasonic cleaning, primary salt quenching, secondary salt quenching and tempering. The molten salt solution for the primary salt quenching is magnesium borate, magnesium oxide grains are formed in the long rod bolt after the primary salt quenching, so that the grain boundaries of austenite are pinned, the growth of austenite grains is suppressed, and the formation of acicular ferrite is promoted. The molten salt solution for the secondary salt quenching is aluminum silicate. When the secondary salt quenching is performed, the aluminum silicate and the borate on the surface of the long rod bolt after the primary salt quenching are combined to form a dense ceramic layer. The long rod bolt prepared by the application has high toughness and good corrosion resistance.

This invention discloses a laser-MIG hybrid welding process for 917 steel based on laser power optimization. The core of this method lies in achieving optimal matching between the microstructure and macroscopic shape of the weld joint by controlling the laser power within a specific range (e.g., around 1400W) when the welding current is fixed (e.g., 120A). Specifically, this method optimizes the molten pool morphology, controls the weld reinforcement and backside sag, refines the grains in the weld zone and fusion zone, forming a dense structure dominated by fine lath martensite, acicular ferrite, and bainite, and reduces carbide precipitation at grain boundaries, thereby improving the overall mechanical properties of the joint. Experimental results show that using the optimized process parameters of this invention (laser power 1400W, current 120A), the weld reinforcement (approximately 1.8mm) and weld width (approximately 3.7mm) exhibit excellent control, with a reinforcement / weld width ratio of approximately 0.49. The joint formation quality is high, making it suitable for precision welding of high-strength steel.

This invention belongs to the field of metallic materials technology and provides a method for manufacturing a 460MPa grade steel plate that can be welded without preheating in a low-temperature environment. The composition employs a low-carbon, low-manganese chemical system, with the addition of microalloying elements such as V-N, Ti, and Mo to refine the grain size. Precise control of the (Ti+V) / N ratio ensures the formation of precipitates during welding. The addition of elements such as La, Ca, and Mg improves the purity of the molten steel and the quality of the continuously cast billet, forming fine, dispersed oxide particles in the steel and enhancing the overall performance in the thickness direction of the steel plate. The manufacturing method includes smelting, continuous casting, furnace heating, rolling, online cooling, and tempering. The steel plate produced using this invention has a microstructure of acicular ferrite + tempered sorbite, with precipitates of 40-60 nm in size. The steel plate exhibits excellent low-temperature toughness, enabling preheating-free welding at -10℃, and the welded joints possess excellent mechanical properties.

A tailor-welded component, and a manufacturing method therefor and a welding wire applied thereto. The tailor-welded component comprises a welded joint. A weld seam of the welded joint comprises acicular ferrite and martensite. The acicular ferrite has an average length of not greater than 80 μm and an average diameter of not greater than 15 μm, and the volume percentage of the ferrite in the weld seam is 0.1-10%. The tailor-welded component is a hot-stamped component, the welded joint has an elongation of greater than 4%, the weld seam structure comprises the martensite and the acicular ferrite, a fracture position is located at a base material during a quasi-static tensile test, and the weld seam has a good strength and ductility.

A steel for hammering and making mechanical parts containing the following elements in percentage by weight:\n0.2% ≦ C ≦ 0.5 %; 0.8% ≦ Mn ≦ 1.5 %; 0 .4% ≦ Si ≦ 1 %; 0.15% ≦ V ≦ 0.6%; 0.01% ≦ Nb ≦ 0.15%; 0.01% ≦ Cr ≦ 0.5 %; 0.01% ≦ P ≦ 0.05%; 0.04% ≦ S ≦ 0.09%; 0.01% ≦ N ≦ 0.025%\nwhich may also contain one or more of the following optional elements:\n0 % ≦ Al ≦ 0.05 %; 0% ≦ Mo ≦ 0.5%; 0.01% ≦ Ni ≦ 0.5%; 0% ≦ Ti ≦ 0.2%; 0% ≦ B ≦ 0.008%; 0% ≦ Cu ≦ 0.5%\nThe rest of the composition consists of iron and unavoidable impurities resulting from processing. The microstructure of that steel consists of 50% to 90% pearlite, 10% to 40% ferrite, with optional acicular ferrite of 0% to 2%, and a niobium equivalent of 80% or more.