WO2023014331A2 - Next-generation micro-alloyed steel - Google Patents
Next-generation micro-alloyed steel Download PDFInfo
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- WO2023014331A2 WO2023014331A2 PCT/TR2022/050804 TR2022050804W WO2023014331A2 WO 2023014331 A2 WO2023014331 A2 WO 2023014331A2 TR 2022050804 W TR2022050804 W TR 2022050804W WO 2023014331 A2 WO2023014331 A2 WO 2023014331A2
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- 229910000742 Microalloyed steel Inorganic materials 0.000 title claims abstract description 30
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 46
- 239000010959 steel Substances 0.000 claims abstract description 46
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 25
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 25
- 239000000203 mixture Substances 0.000 claims abstract description 25
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims abstract description 24
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 20
- 239000010949 copper Substances 0.000 claims abstract description 17
- 239000011572 manganese Substances 0.000 claims abstract description 17
- 239000011651 chromium Substances 0.000 claims abstract description 16
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 claims abstract description 14
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 13
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 13
- 239000010451 perlite Substances 0.000 claims abstract description 11
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 10
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 10
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 10
- 235000019362 perlite Nutrition 0.000 claims abstract description 10
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims abstract description 8
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims abstract description 8
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims abstract description 8
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims abstract description 8
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 8
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 8
- 229910052802 copper Inorganic materials 0.000 claims abstract description 8
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 8
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 8
- 239000011733 molybdenum Substances 0.000 claims abstract description 8
- 229910052759 nickel Inorganic materials 0.000 claims abstract description 8
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 8
- 239000010703 silicon Substances 0.000 claims abstract description 8
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 7
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims abstract description 7
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 7
- 239000011574 phosphorus Substances 0.000 claims abstract description 7
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 7
- 239000011593 sulfur Substances 0.000 claims abstract description 7
- 238000001816 cooling Methods 0.000 claims description 29
- 229910045601 alloy Inorganic materials 0.000 claims description 26
- 239000000956 alloy Substances 0.000 claims description 26
- 238000005242 forging Methods 0.000 claims description 22
- 238000000034 method Methods 0.000 claims description 20
- 238000004519 manufacturing process Methods 0.000 claims description 14
- 230000008569 process Effects 0.000 claims description 13
- 239000000047 product Substances 0.000 claims description 8
- 239000011265 semifinished product Substances 0.000 claims description 6
- 239000002244 precipitate Substances 0.000 claims description 5
- 239000002994 raw material Substances 0.000 claims description 5
- 238000005275 alloying Methods 0.000 claims description 3
- 238000009749 continuous casting Methods 0.000 claims description 3
- 238000005098 hot rolling Methods 0.000 claims description 3
- 230000015572 biosynthetic process Effects 0.000 claims description 2
- 238000006243 chemical reaction Methods 0.000 description 13
- 238000010586 diagram Methods 0.000 description 13
- 239000000463 material Substances 0.000 description 13
- 239000012530 fluid Substances 0.000 description 9
- 230000007246 mechanism Effects 0.000 description 8
- 239000010936 titanium Substances 0.000 description 8
- 238000012546 transfer Methods 0.000 description 8
- 230000005540 biological transmission Effects 0.000 description 7
- 239000010955 niobium Substances 0.000 description 6
- 229910000851 Alloy steel Inorganic materials 0.000 description 5
- 239000007787 solid Substances 0.000 description 5
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 4
- 238000011161 development Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 230000033001 locomotion Effects 0.000 description 4
- 229910052719 titanium Inorganic materials 0.000 description 4
- 229910052720 vanadium Inorganic materials 0.000 description 4
- 229910000975 Carbon steel Inorganic materials 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 3
- 229910001566 austenite Inorganic materials 0.000 description 3
- 229910052758 niobium Inorganic materials 0.000 description 3
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 3
- 229910000677 High-carbon steel Inorganic materials 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 239000010962 carbon steel Substances 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000009413 insulation Methods 0.000 description 2
- 239000012774 insulation material Substances 0.000 description 2
- 238000005272 metallurgy Methods 0.000 description 2
- QMQXDJATSGGYDR-UHFFFAOYSA-N methylidyneiron Chemical compound [C].[Fe] QMQXDJATSGGYDR-UHFFFAOYSA-N 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 238000010587 phase diagram Methods 0.000 description 2
- 238000005549 size reduction Methods 0.000 description 2
- 238000011282 treatment Methods 0.000 description 2
- 229910000967 As alloy Inorganic materials 0.000 description 1
- 229910001339 C alloy Inorganic materials 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000010891 electric arc Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000009472 formulation Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 230000000670 limiting effect Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- CKFGINPQOCXMAZ-UHFFFAOYSA-N methanediol Chemical compound OCO CKFGINPQOCXMAZ-UHFFFAOYSA-N 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000002277 temperature effect Effects 0.000 description 1
- 230000001550 time effect Effects 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D7/00—Modifying the physical properties of iron or steel by deformation
- C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
Definitions
- the invention relates to high-strength, low-alloy steel developed to be used in all areas that can be used in hot forging processes as a long product raw material.
- the invention particularly relates to a micro-alloyed steel composition
- a micro-alloyed steel composition comprising; carbon (C) in a ratio of 0.42-0.480% by weight, nitrogen (N) in a ratio of 0.007% maximum by weight, silicon (Si) in a ratio of 0.250-0.300% by weight, manganese (Mn) in a ratio of 1.550-1.700% by weight, chromium (Cr) in a ratio of 0-0.120% by weight, molybdenum (Mo) in a ratio of 0- 0.020% by weight, nickel (Ni) 0-0.050% by weight, aluminum (Al) in a ratio of 0-0.005% by weight, vanadium (V) 0-0.050% by weight, phosphorus (P) in a ratio of 0-0.005% by weight, sulfur (S) by weight in the ratio of 0-0.010% and copper (Cu) steel composition in a ratio of 0-0.100% by weight and 3-5% ferrite phase, 50-55% perlite phase,
- micro-alloyed steels The most important group of engineering materials is made up of steel. There are continuous improvements in the process and physical metallurgy of steel to meet all kinds of demands and changes. In recent years, the development of micro-alloyed steels has been seen as one of the most important metallurgical successes. It can be said that this development is the result of a clear understanding of the structure-feature relations in low-carbon steels. The final product is the result of a successful combination of physical, mechanical, and process metallurgy. Micro-alloyed steels successfully replace mild steels as basic building materials.
- the total amount of alloy usually does not exceed 2%. While most of these alloy elements are formed by niobium (Nb), titanium (Ti), and vanadium (V), the nanometer-sized precipitates formed by these alloy elements with carbon (C) and nitrogen (N) atoms provide high yield strength to steel. In addition, its mechanical properties such as high corrosion resistance, ductility, and toughness also increase the use of micro-alloyed steels.
- micro-alloyed steels consist of low-perlite and nonperlite steels.
- features such as formability, toughness, and weldability are significantly increased by significantly lowering the carbon ratio.
- These features are generally desired in the production of high-strength and lightweight parts by shaping.
- these steels can only reach the yield limit of 500 N/mm 2 with controlled rolling with the thinning and hardening effects of aluminum (Al), niobium (Nb), and titanium (Ti), vanadium (V), which are micro-alloy elements.
- Carbide, nitride, and carbonitrides formed by micro-alloy elements remain undissolved in the austenite phase if the dissolution temperatures are not exceeded during hot forming processes. These insoluble hard structures prevent austenite grain growth and provide both a small-grained steel structure and increase the toughness of the material.
- Patent application EP3505652A1 has been encountered in the literature.
- the invention relates to medium carbon, low alloy round steel with high hardness for fasteners.
- the chemical composition of the steel subject to the invention contains 0.36-0.44% carbon (C), 0.15-0.40% silicon (Si), 0.80-1.0 manganese (Mn), 1.0-1.15% chromium (Cr), 0.5-0.25% nickel (Ni), 0.05-0.25% molybdenum (Mo), 0.05-0.25% copper (Cu), 0.015-0.050% aluminum (Al), 0.0010-0.0050% titanium Ti) by weight, with the remaining consisting of iron (Fe) and impurities in balance with other elements.
- the yield strength of the steel according to the invention is >940 Mpa, the tensile strength is 1040-1140 Mpa, the hardness is 320-380 HV.
- Patent application CN104911486A relates to non-quenched and tempered steel for car retaining screws.
- the carbon content is the main element affecting the strength of non-quenched and tempered steel.
- the carbon content of non-quenched and tempered steel is designed to be 0.35-0.45%, which ensures that the perlite percentage is 70-80%.
- Patent application EP1070153B1 relates to a steel composition containing 0.6-0.65% carbon (C) by weight, maximum 0.4% silicon (Si), 0.6-0.9% manganese (Mn), 0.03-0.07% phosphorus (P), 0.07-0.11% sulfur (S), maximum 0.5% chromium (Cr), maximum 0.1% molybdenum (Mo), maximum 0.5% nickel (Ni), 0.5% copper (Cu), maximum 0.5% aluminum (Al), maximum 0.03% nitrogen (N), vanadium and iron.
- the present invention relates to next-generation micro-alloyed steel that meets the aforementioned needs and eliminates all the disadvantages and provides advantages thereof.
- the object of the invention is to provide high-strength, low-alloy steel developed to be used in all areas that can be used in hot forging processes as a long product raw material.
- the object of the invention is to obtain steel with a yield strength of 690-700 MPa, a tensile strength of 940-950 MPa, and a hardness of 290-298 HV after controlled forging.
- the object of the invention is to activate the strength enhancement mechanism by thinning the grain and to increase the strength together with the toughness thanks to the use of vanadium only as a carbide builder.
- the object of the invention is to provide the effect of the grain thinning elements because in the primary cooling the heat transfer coefficient is 80-120 W/m 2 K for 100-130 seconds, in secondary cooling, the heat transfer coefficient is 40-60 W/m 2 K for 1200-1500 seconds, which are required for the forging temperature and post-forging cooling environment.
- the object of the invention is to apply the strength enhancement mechanism together with solid melt hardening and grain size reduction.
- the object of the invention is to improve the mechanical properties of steel by utilizing the nitride-, carbide-, and carbonitride-making properties of vanadium with interstitial atoms such as carbon and nitrogen.
- the object of the invention is to provide an alloy composition that does not adversely affect weldability.
- the object of the invention is to achieve an increase in strength with ferrite and bainite phase structure.
- the invention is a high-strength, low-alloy microalloyed steel developed to be used in all areas that can be used in hot forging processes as long product raw material, characterized in that; it comprises a steel composition containing carbon (C) in a ratio of 0.42-0.480% by weight, nitrogen (N) in a ratio of 0.007% maximum by weight, silicon (Si) in a ratio of 0.250-0.300% by weight, manganese (Mn) in a ratio of 1.550- 1.700% by weight, chromium (Cr) in a ratio of 0-0.120% by weight, molybdenum (Mo) in a ratio of 0-0.020% by weight, nickel (Ni) 0-0.050% by weight, aluminum (Al) in a ratio of 0- 0.005% by weight, vanadium (V) 0-0.050% by weight, phosphorus (P) in a ratio of 0-0.005% by weight, sulfur (S) in the ratio of 0-0.01
- Micro-alloyed steel has a yield strength of 690-700 MPa, a tensile strength of 940-950 MPa, a hardness of 290-298 HV, and an equivalent carbon value of 0.600-0.700 Ceq to achieve the objects of the invention.
- the invention is a micro-alloyed steel production method, comprising the following process steps:
- the said forging temperature is 1200°C
- the primary cooling after forging is for 100- 130 seconds with a heat convection coefficient of 80-120 W/m 2 K
- the secondary cooling is for 1200-1500 seconds with a heat convection coefficient of 40-60 W/m 2 K under atmospheric conditions.
- next-generation micro-alloyed steel is merely described for a better understanding of the subject matter and without any limiting effect in this detailed description.
- the invention is a high-strength, low-alloy micro-alloyed steel developed to be used in all areas that can be used in hot forging processes as long product raw material, characterized in that; it comprises a steel composition containing carbon (C) in a ratio of 0.42-0.480% by weight, nitrogen (N) in a ratio of 0.007% maximum by weight, silicon (Si) in a ratio of 0.250- 0.300% by weight, manganese (Mn) in a ratio of 1.550-1.700% by weight, chromium (Cr) in a ratio of 0-0.120% by weight, molybdenum (Mo) in a ratio of 0-0.020% by weight, nickel (Ni) 0- 0.050% by weight, aluminum (Al) in a ratio of 0-0.005% by weight, vanadium (V) 0-0.050% by weight, phosphorus (P) in a ratio of 0-0.005% by weight, sulfur (S) by weight in the ratio of 0-0.010% and copper (Cu
- the alloy elements are first determined.
- the amount and variety of alloy elements in the steel composition are important parameters in the development of mechanical properties.
- the nitride-, carbide-, and carbonitride-making properties of vanadium (V) with interstitial atoms such as carbon (C), and nitrogen (N) are used.
- V vanadium
- C carbon
- N nitrogen
- TTT isothermal conversion diagram
- OCT continuous cooling conversion diagram
- a hot forging methodology is created.
- the temperature and deformation rates in the hot forging process are rearranged according to the original alloy.
- the cooling process is applied.
- the cooling regime for the target microstructure ferrite and bainite
- TTT- and CCT-based controlled dualstage functional cooling methods cooling is provided in a way that ferrite and bainite phase ratios can be changed.
- CCT diagrams can be used for all thermal processes involving continuous cooling.
- the main purpose of CCT diagrams is to know in advance which structural elements can be obtained and which hardness can be obtained by using the cooling curve. These diagrams allow the determination of the phase or phases contained in the final microstructures to be obtained after the conversion in both isothermal heat treatments where the temperature is kept constant and continuous cooling.
- Vanadium is used as a single carbide builder in the micro-alloyed steel composition of the invention. With this use, the strength enhancement mechanism is activated by thinning the grain, and strength increase is provided with toughness. It is necessary to provide the effect of the grain thinning elements and for the forging temperature and post-forging cooling environment.
- micro-alloyed steel production method according to the invention.
- the steel composition produced by micro-alloying is obtained in the form of billet by continuous casting method using electric arc furnace, crucible furnace, vacuum furnace, and tundish immersion closed ceramic tube, respectively,
- the produced billets are made into cylindrical, long semi-finished products in the round long group by hot rolling,
- the hot forging temperature used in the inventive production method is 1200°C
- the primary cooling after forging is carried out under atmospheric conditions with a heat convection coefficient of 80-120 W/m 2 K for 100-130 seconds
- the secondary cooling is carried out with a heat convection coefficient of 40-60 W/m 2 K for 1200-1500 seconds.
- Convection is a type of heat transfer between a solid surface and the fluid (liquid or gas) in motion adjacent to it. The faster the fluid movement, the greater the heat transfer through convection. If the mass or mass fluid movement disappears, the heat transfer between the solid surface and the adjacent fluid occurs only by random movement of the molecules, i.e. by conduction.
- Heat convection coefficient (K) is defined as the amount of heat carried from the unit surface area in the unit temperature difference and in the unit time. This coefficient differs depending on various elements. Some of these elements are the material and roughness of the surface with which the fluid contacts, flow pattern, flow rate, hydraulic diameter, viscosity, and density of the fluid.
- the heat convection coefficient is different according to the type of heat convection.
- thermal insulation materials The most determining feature in the selection of thermal insulation materials is the heat transmission coefficient. Because the lower the heat transmission coefficient, the higher the thermal insulation resistance of the systems. Knowing the thermal properties of the materials is very important in terms of achieving optimum performance where the material is used. Many measurement techniques have been used for this purpose for many years. Thermal properties of the materials (thermal conductivity coefficient, specific heat, thermal permeability) can be measured with the current techniques. Especially recently, there are complexities in the micro and macro level internal structure of the materials developed, and it is difficult to make accurate measurements under this condition.
- thermal insulation material or the production of new material is very important in this regard. It is necessary to know the heat transmission coefficient of that material to make the calculations after the production of new material or material selection.
- V-C precipitates are formed with a 3-5% ferrite phase, 50-55% perlite phase, and 40-45% bainite phase.
- the mechanical properties of the micro-alloyed steel of the invention are as follows:
- the long product mentioned in the preferred embodiment of the invention covers all hot- rolled, square, round, and flat steel products.
- the equivalent carbon value of the micro-alloyed steel of the invention is 0.600-0.700 Ceq. Carbon equivalent is a measure that defines weldability, and calculation is made with the amounts of alloy elements in steel. The values of the specified alloys are equivalent to the steel to be substituted and provide an advantage in terms of creating higher strength. The formula used to calculate the Ceq within the scope of the invention is given below.
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
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- Crystallography & Structural Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
The invention particularly relates to a micro-alloyed steel composition comprising; carbon (C) in a ratio of 0.42-0.480%, nitrogen (N) in a ratio of 0.007% maximum by weight, silicon (Si) in a ratio of 0.250-0.300% by weight, manganese (Mn) in a ratio of 1.550-1.700% by weight, chromium (Cr) in a ratio of 0-0.120% by weight, molybdenum (Mo) in a ratio of 0-0.020% by weight, nickel (Ni) 0-0.050% by weight, aluminum (Al) in a ratio of 0-0.005% by weight, vanadium (V) 0-0.050% by weight, phosphorus (P) in a ratio of 0-0.005% by weight, sulfur (S) by weight in the ratio of 0-0.010% and copper (Cu) steel composition by weight in a ratio of 0-0.100% and 3-5% ferrite phase, 50-55% perlite phase, 40-45% bainite phase with yield strength of 690-700 MPa, tensile strength of 940-950 MPa.
Description
NEXT-GENERATION MICRO-ALLOYED STEEL
Technical Field
The invention relates to high-strength, low-alloy steel developed to be used in all areas that can be used in hot forging processes as a long product raw material.
The invention particularly relates to a micro-alloyed steel composition comprising; carbon (C) in a ratio of 0.42-0.480% by weight, nitrogen (N) in a ratio of 0.007% maximum by weight, silicon (Si) in a ratio of 0.250-0.300% by weight, manganese (Mn) in a ratio of 1.550-1.700% by weight, chromium (Cr) in a ratio of 0-0.120% by weight, molybdenum (Mo) in a ratio of 0- 0.020% by weight, nickel (Ni) 0-0.050% by weight, aluminum (Al) in a ratio of 0-0.005% by weight, vanadium (V) 0-0.050% by weight, phosphorus (P) in a ratio of 0-0.005% by weight, sulfur (S) by weight in the ratio of 0-0.010% and copper (Cu) steel composition in a ratio of 0-0.100% by weight and 3-5% ferrite phase, 50-55% perlite phase, 40-45% bainite phase with yield strength of 690-700 MPa, tensile strength of 940-950 MPa.
Prior Art
The most important group of engineering materials is made up of steel. There are continuous improvements in the process and physical metallurgy of steel to meet all kinds of demands and changes. In recent years, the development of micro-alloyed steels has been seen as one of the most important metallurgical successes. It can be said that this development is the result of a clear understanding of the structure-feature relations in low-carbon steels. The final product is the result of a successful combination of physical, mechanical, and process metallurgy. Micro-alloyed steels successfully replace mild steels as basic building materials.
In high-strength, low-alloy, micro-alloyed steels, the total amount of alloy usually does not exceed 2%. While most of these alloy elements are formed by niobium (Nb), titanium (Ti), and vanadium (V), the nanometer-sized precipitates formed by these alloy elements with carbon (C) and nitrogen (N) atoms provide high yield strength to steel. In addition, its mechanical properties such as high corrosion resistance, ductility, and toughness also increase the use of micro-alloyed steels.
The specific development aspects of micro-alloyed steels consist of low-perlite and nonperlite steels. Features such as formability, toughness, and weldability are significantly increased by significantly lowering the carbon ratio. These features are generally desired in
the production of high-strength and lightweight parts by shaping. Despite the low carbon ratio, these steels can only reach the yield limit of 500 N/mm2 with controlled rolling with the thinning and hardening effects of aluminum (Al), niobium (Nb), and titanium (Ti), vanadium (V), which are micro-alloy elements.
Niobium (Nb), titanium (Ti), vanadium (V), and aluminum (Al), which are used as alloy elements in micro-alloyed steels, have significant direct effects on the mechanical properties of the material and form carbide, nitride, or carbonite. Carbide, nitride, and carbonitrides formed by micro-alloy elements remain undissolved in the austenite phase if the dissolution temperatures are not exceeded during hot forming processes. These insoluble hard structures prevent austenite grain growth and provide both a small-grained steel structure and increase the toughness of the material.
In the present art, to obtain high strength, increasing the amount of carbon in the alloy or grain thinning feature of micro-alloy elements is exploited. The high carbon steel alloy is heat-treated after hot forging and secondary treatment is required to increase strength. On the other hand, micro-alloyed steels are not able to increase the strength of the forged material as much as heat-treated high carbon alloy. While the yield strength of the steel alloy in the high carbon C45E standard is 500 MPa, the tensile strength is 750-850 MPa, the yield strength is 560 MPa and the tensile strength is between 580-790 MPa in micro-alloyed steel. As mentioned, increasing the strength of high carbon steel (C45E) as a result of a costly application with secondary treatment and low yield strength in micro-alloyed steel reveals the need to develop a new steel alloy.
Patent application EP3505652A1 has been encountered in the literature. The invention relates to medium carbon, low alloy round steel with high hardness for fasteners. The chemical composition of the steel subject to the invention contains 0.36-0.44% carbon (C), 0.15-0.40% silicon (Si), 0.80-1.0 manganese (Mn), 1.0-1.15% chromium (Cr), 0.5-0.25% nickel (Ni), 0.05-0.25% molybdenum (Mo), 0.05-0.25% copper (Cu), 0.015-0.050% aluminum (Al), 0.0010-0.0050% titanium Ti) by weight, with the remaining consisting of iron (Fe) and impurities in balance with other elements. The yield strength of the steel according to the invention is >940 Mpa, the tensile strength is 1040-1140 Mpa, the hardness is 320-380 HV.
Patent application CN104911486A relates to non-quenched and tempered steel for car retaining screws. In the invention, it is stated that the carbon content is the main element affecting the strength of non-quenched and tempered steel. As the carbon content increases,
the ferrite and perlite in the steel become thinner and the increase in the amount of perlite increases the strength of the steel. Therefore, the carbon content of non-quenched and tempered steel is designed to be 0.35-0.45%, which ensures that the perlite percentage is 70-80%.
Patent application EP1070153B1 relates to a steel composition containing 0.6-0.65% carbon (C) by weight, maximum 0.4% silicon (Si), 0.6-0.9% manganese (Mn), 0.03-0.07% phosphorus (P), 0.07-0.11% sulfur (S), maximum 0.5% chromium (Cr), maximum 0.1% molybdenum (Mo), maximum 0.5% nickel (Ni), 0.5% copper (Cu), maximum 0.5% aluminum (Al), maximum 0.03% nitrogen (N), vanadium and iron.
As can be seen in the aforementioned applications, there are many steel compositions in the prior art. However, the need for micro-alloyed steel alloys with high strength and high yield strength is increasing day by day.
Consequently, due to the aforementioned problems and deficiencies, there has been a need to make an innovation in the related technical field.
Object of the Invention
The present invention relates to next-generation micro-alloyed steel that meets the aforementioned needs and eliminates all the disadvantages and provides advantages thereof.
The object of the invention is to provide high-strength, low-alloy steel developed to be used in all areas that can be used in hot forging processes as a long product raw material.
The object of the invention is to obtain steel with a yield strength of 690-700 MPa, a tensile strength of 940-950 MPa, and a hardness of 290-298 HV after controlled forging.
The object of the invention is to activate the strength enhancement mechanism by thinning the grain and to increase the strength together with the toughness thanks to the use of vanadium only as a carbide builder.
The object of the invention is to provide the effect of the grain thinning elements because in the primary cooling the heat transfer coefficient is 80-120 W/m2K for 100-130 seconds, in secondary cooling, the heat transfer coefficient is 40-60 W/m2K for 1200-1500 seconds, which are required for the forging temperature and post-forging cooling environment.
The object of the invention is to apply the strength enhancement mechanism together with solid melt hardening and grain size reduction.
The object of the invention is to improve the mechanical properties of steel by utilizing the nitride-, carbide-, and carbonitride-making properties of vanadium with interstitial atoms such as carbon and nitrogen.
The object of the invention is to provide an alloy composition that does not adversely affect weldability.
The object of the invention is to achieve an increase in strength with ferrite and bainite phase structure.
To fulfill the above-described purposes, the invention is a high-strength, low-alloy microalloyed steel developed to be used in all areas that can be used in hot forging processes as long product raw material, characterized in that; it comprises a steel composition containing carbon (C) in a ratio of 0.42-0.480% by weight, nitrogen (N) in a ratio of 0.007% maximum by weight, silicon (Si) in a ratio of 0.250-0.300% by weight, manganese (Mn) in a ratio of 1.550- 1.700% by weight, chromium (Cr) in a ratio of 0-0.120% by weight, molybdenum (Mo) in a ratio of 0-0.020% by weight, nickel (Ni) 0-0.050% by weight, aluminum (Al) in a ratio of 0- 0.005% by weight, vanadium (V) 0-0.050% by weight, phosphorus (P) in a ratio of 0-0.005% by weight, sulfur (S) in the ratio of 0-0.010% by weight and copper (Cu) steel composition in a ratio of 0-0.100% by weight and 3-5% ferrite phase, 50-55% perlite phase, 40-45% bainite phase.
Micro-alloyed steel has a yield strength of 690-700 MPa, a tensile strength of 940-950 MPa, a hardness of 290-298 HV, and an equivalent carbon value of 0.600-0.700 Ceq to achieve the objects of the invention.
To fulfill the above-described objects, the invention is a micro-alloyed steel production method, comprising the following process steps:
• obtaining the steel produced by micro-alloying in the form of billets by continuous casting method,
• making the produced billets into cylindrical semi-finished products in the round long group by hot rolling,
• formation of precipitates by passing long semi-finished products through controlled hot forging and cooling stages, characterized in that;
• the said forging temperature is 1200°C, the primary cooling after forging is for 100- 130 seconds with a heat convection coefficient of 80-120 W/m2K, and the secondary cooling is for 1200-1500 seconds with a heat convection coefficient of 40-60 W/m2K under atmospheric conditions.
The structural and characteristic features of the present invention will be understood clearly by the following detailed description and therefore the evaluation shall be made by considering the detailed description.
Detailed Description of the Invention
The next-generation micro-alloyed steel is merely described for a better understanding of the subject matter and without any limiting effect in this detailed description.
The invention is a high-strength, low-alloy micro-alloyed steel developed to be used in all areas that can be used in hot forging processes as long product raw material, characterized in that; it comprises a steel composition containing carbon (C) in a ratio of 0.42-0.480% by weight, nitrogen (N) in a ratio of 0.007% maximum by weight, silicon (Si) in a ratio of 0.250- 0.300% by weight, manganese (Mn) in a ratio of 1.550-1.700% by weight, chromium (Cr) in a ratio of 0-0.120% by weight, molybdenum (Mo) in a ratio of 0-0.020% by weight, nickel (Ni) 0- 0.050% by weight, aluminum (Al) in a ratio of 0-0.005% by weight, vanadium (V) 0-0.050% by weight, phosphorus (P) in a ratio of 0-0.005% by weight, sulfur (S) by weight in the ratio of 0-0.010% and copper (Cu) steel composition in a ratio of 0-0.100% by weight and 3-5% ferrite phase, 50-55% perlite phase, 40-45% bainite phase.
Formulation of the micro-alloyed steel composition according to the invention;
To obtain the micro-alloyed steel according to the invention, the alloy elements are first determined. The amount and variety of alloy elements in the steel composition are important parameters in the development of mechanical properties.
To ensure the coexistence of different strength enhancement mechanisms, the nitride-, carbide-, and carbonitride-making properties of vanadium (V) with interstitial atoms such as carbon (C), and nitrogen (N) are used. On the other hand, by utilizing the fact that TTT (isothermal conversion diagram) and OCT (continuous cooling conversion diagram) diagrams vary according to the alloy element, a fine-grained structure is obtained with the solid melt hardening mechanism. In the developed alloy structure, it is ensured to reveal the bainite phase together with the ferrite phase.
Secondly, a hot forging methodology is created. The temperature and deformation rates in the hot forging process are rearranged according to the original alloy. Finally, the cooling process is applied. According to the TTT (isothermal conversion diagram) and CCT (continuous cooling conversion diagram) diagrams, the cooling regime for the target microstructure (ferrite and bainite) is determined. With TTT- and CCT-based controlled dualstage functional cooling methods, cooling is provided in a way that ferrite and bainite phase ratios can be changed.
In the iron-carbon phase diagram, martensite and bainite conversion have an important place in the hardening mechanism of the alloy. However, due to the process conditions in industrial steel production, the cooling rates are considerably higher than the equilibrium conditions. With the increase in the cooling rate, the iron-carbon phase diagram used in the determination of phase conversions is not used. The most important reason for this is that the diagram in question is formed under very slow cooling conditions. For this reason, diagrams called TTT, which show the change of phase conversion depending on
temperature and time, are used at high cooling rates. With isothermal conversion diagrams, subjects are determined such as when austenite will start to be converted in fast-cooled steels, how long the conversion will take, and which products will eventually form. Therefore, TTT diagrams are preferred in determining the phase conversions that will occur in the alloy under extreme cooling conditions as a function of temperature and time.
In the conversion reaction, it is necessary to change the conversion curve to see the time and temperature effects separately. Curves showing this situation are called continuous cooling conversion curves (CCT). CCT diagrams can be used for all thermal processes involving continuous cooling. The main purpose of CCT diagrams is to know in advance which structural elements can be obtained and which hardness can be obtained by using the cooling curve. These diagrams allow the determination of the phase or phases contained in the final microstructures to be obtained after the conversion in both isothermal heat treatments where the temperature is kept constant and continuous cooling.
Vanadium is used as a single carbide builder in the micro-alloyed steel composition of the invention. With this use, the strength enhancement mechanism is activated by thinning the grain, and strength increase is provided with toughness. It is necessary to provide the effect of the grain thinning elements and for the forging temperature and post-forging cooling environment.
The micro-alloyed steel production method according to the invention;
• The steel composition produced by micro-alloying is obtained in the form of billet by continuous casting method using electric arc furnace, crucible furnace, vacuum furnace, and tundish immersion closed ceramic tube, respectively,
• The produced billets are made into cylindrical, long semi-finished products in the round long group by hot rolling,
• The said semi-finished product is subjected to controlled hot forging and cooling stages,
• With the resulting precipitate hardening mechanism, steel alloy is obtained at the desired mechanical values.
The hot forging temperature used in the inventive production method is 1200°C, the primary cooling after forging is carried out under atmospheric conditions with a heat convection coefficient of 80-120 W/m2K for 100-130 seconds, and the secondary cooling is carried out with a heat convection coefficient of 40-60 W/m2K for 1200-1500 seconds.
Convection is a type of heat transfer between a solid surface and the fluid (liquid or gas) in motion adjacent to it. The faster the fluid movement, the greater the heat transfer through convection. If the mass or mass fluid movement disappears, the heat transfer between the solid surface and the adjacent fluid occurs only by random movement of the molecules, i.e. by conduction.
Heat convection coefficient (K) is defined as the amount of heat carried from the unit surface area in the unit temperature difference and in the unit time. This coefficient differs depending on various elements. Some of these elements are the material and roughness of the surface with which the fluid contacts, flow pattern, flow rate, hydraulic diameter, viscosity, and density of the fluid.
In addition, the heat convection coefficient is different according to the type of heat convection. There are two types of heat convection. The first is the forced heat convection where the fluid moves due to the pressure applied to the system. The second is the natural heat convection where the fluid moves in the system due to the density difference.
The most determining feature in the selection of thermal insulation materials is the heat transmission coefficient. Because the lower the heat transmission coefficient, the higher the thermal insulation resistance of the systems. Knowing the thermal properties of the materials is very important in terms of achieving optimum performance where the material is used. Many measurement techniques have been used for this purpose for many years. Thermal properties of the materials (thermal conductivity coefficient, specific heat, thermal permeability) can be measured with the current techniques. Especially recently, there are complexities in the micro and macro level internal structure of the materials developed, and it is difficult to make accurate measurements under this condition.
The smaller the coefficient of thermal conductivity, the less heat loss occurs. Effective use of this energy is possible with thermal insulation. The choice of thermal insulation material or the production of new material is very important in this regard. It is necessary to know the heat transmission coefficient of that material to make the calculations after the production of new material or material selection.
Correct calculation of the heat transmission coefficient is of great importance in engineering problems. In addition to the occurrence of experimental and theoretical errors in the calculation of the heat transmission coefficient, inevitably, the time and cost loss spent will also occur. The heat transmission coefficient is towards the side where the temperature
decreases. In the calculation of the heat convection coefficient, the following unitless characteristic identification values are used:
Reynolds number;
Prandtl number;
Nusselt number;
These are; v: Speed of fluid,
I: It is the characteristic length related to flow and heat transfer; it is the wall height in the walls and the pipe diameter in the pipes. v: Kinematic viscosity, v=g/p, p: Density, cp: Specific heat at constant pressure,
A: Heat transmission coefficient g: Gravitational acceleration, y: Volumetric expansion coefficient, t: Temperature difference a: Temperature dissipation coefficient, (a=A/.cp)
Newton’s Law of Cooling (Q) is used to calculate the amount of heat transferred in unit time by convection and the formula used in its calculation is given below. The typical values of the convection heat transfer coefficient are given in Table- 1.
Q = hA, Ts - r. )
Table- 1: Typical values of convection heat transfer coefficient
With the alloy composition according to the invention and the controlled cooling process applied to this composition;
• Solid melt hardening and grain size reduction and strength enhancement mechanisms are applied together.
• Strength increase is obtained with ferrite and bainite phase structure.
• The alloy composition used has no negative impact on weldability.
With the steel composition and production method of the invention, V-C precipitates are formed with a 3-5% ferrite phase, 50-55% perlite phase, and 40-45% bainite phase.
The mechanical properties of the micro-alloyed steel of the invention are as follows:
• Yield strength of 690-700 MPa,
• Tensile strength of 940-950 MPa,
• Hardness of 290-298 HV,
• The equivalent carbon value of 0.600-0.700 Ceq.
The long product mentioned in the preferred embodiment of the invention covers all hot- rolled, square, round, and flat steel products.
The equivalent carbon value of the micro-alloyed steel of the invention is 0.600-0.700 Ceq. Carbon equivalent is a measure that defines weldability, and calculation is made with the amounts of alloy elements in steel. The values of the specified alloys are equivalent to the steel to be substituted and provide an advantage in terms of creating higher strength. The formula used to calculate the Ceq within the scope of the invention is given below.
International Institute of Welding (IIW):
Ce (I I W)=C+Mn/6+(Cr+Mo+ V)/5+(Ni+Cu)/15
Claims
CLAIMS The invention is a high-strength, low-alloy micro-alloyed steel developed to be used in all areas that can be used in hot forging processes as long product raw material, characterized in that; it comprises a steel composition containing carbon (C) in a ratio of 0.42-0.480% by weight, nitrogen (N) in a ratio of 0.007% maximum by weight, silicon (Si) in a ratio of 0.250-0.300% by weight, manganese (Mn) in a ratio of 1.550- 1.700% by weight, chromium (Cr) in a ratio of 0-0.120% by weight, molybdenum (Mo) in a ratio of 0-0.020% by weight, nickel (Ni) 0-0.050% by weight, aluminum (Al) in a ratio of 0-0.005% by weight, vanadium (V) 0-0.050% by weight, phosphorus (P) in a ratio of 0-0.005% by weight, sulfur (S) by weight in the ratio of 0-0.010% and copper (Cu) steel composition by weight in a ratio of 0-0.100% and 3-5% ferrite phase, 50- 55% perlite phase, 40-45% bainite phase. A micro-alloyed steel according to claim 1 , characterized in that; it has a yield strength of 690-700 MPa. A micro-alloyed steel according to claim 1, characterized in that; it has a tensile strength of 940-950 MPa. A micro-alloyed steel according to claim 1 , characterized in that; it has a hardness of 290-298 HV. A micro-alloyed steel according to claim 1, characterized in that; it has a carbon value equivalent to 0.600-0.700 Ceq. The invention is a micro-alloyed steel production method, comprising the following process steps:
• obtaining the steel produced by micro-alloying in the form of billets by continuous casting method,
• making the produced billets into cylindrical semi-finished products in the round long group by hot rolling,
• formation of precipitates by passing long semi-finished products through controlled hot forging and cooling stages, characterized in that;
• the said forging temperature is 1200°C, the primary cooling after forging is for 100-130 seconds with a heat convection coefficient of 80-120 W/m2K, and the secondary cooling is for 1200-1500 seconds with a heat convection coefficient of 40-60 W/m2K under atmospheric conditions. A micro-alloyed steel production method according to claim 6, characterized in that; it comprises a steel composition containing carbon (C) in a ratio of 0.42-0.480% by weight, nitrogen (N) in a ratio of 0.007% maximum by weight, 0.250-0.300% silicon (Si) by weight in the ratio of 0.250-0.300%, manganese (Mn) by weight in the ratio of 1.550-1.700%, 0-0.120% chromium (Cr) by weight in the ratio of 0-0.120%, molybdenum (Mo) by weight in the ratio of 0-0.020%, 0-0.050% nickel (Ni) by weight, aluminum (Al) by weight in the ratio of 0-0.005%, 0-0.050% vanadium (V) by weight, phosphorus (P) by weight in the ratio of 0-0.005%, sulfur (S) by weight in the ratio of 0-0.010% and copper (Cu) steel composition by weight in the ratio of 0-0.100% and 3-5% ferrite phase, 50-55% perlite phase, 40-45% bainite phase. A micro-alloyed steel production method according to any of claims 6-7, characterized in that; it has a yield strength of 690-700 MPa. A micro-alloyed steel production method according to any of claims 6-7, characterized in that; it has a tensile strength of 940-950 MPa. A micro-alloyed steel production method according to any of claims 6-7, characterized in that; it has a hardness of 290-298 HV. A micro-alloyed steel production method according to any of claims 6-7, characterized in that; it has an equivalent carbon value of 0.600-0.700 Ceq.
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