CN116904849A - Non-quenched and tempered cold-forging steel with excellent corrosion resistance and production method thereof - Google Patents

Non-quenched and tempered cold-forging steel with excellent corrosion resistance and production method thereof Download PDF

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Publication number
CN116904849A
CN116904849A CN202310792402.9A CN202310792402A CN116904849A CN 116904849 A CN116904849 A CN 116904849A CN 202310792402 A CN202310792402 A CN 202310792402A CN 116904849 A CN116904849 A CN 116904849A
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equal
percent
less
steel
quenched
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尹德福
汪开忠
张晓瑞
丁雷
谢钊远
姜婷
郭湛
余良其
唐鹏
牟祖茂
郝杰
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Maanshan Iron and Steel Co Ltd
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Maanshan Iron and Steel Co Ltd
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    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
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    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0025—Adding carbon material
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    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0075—Treating in a ladle furnace, e.g. up-/reheating of molten steel within the ladle
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    • C21—METALLURGY OF IRON
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    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/06—Deoxidising, e.g. killing
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    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • 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
    • C21D11/00—Process control or regulation for heat treatments
    • C21D11/005—Process control or regulation for heat treatments for cooling
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C22C33/06—Making ferrous alloys by melting using master alloys
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract

The application provides a non-quenched and tempered cold-heading steel with excellent corrosion resistance and a production method thereof, wherein the components comprise, by weight, 0.21% -0.30% of C, 0.02% -0.1% of Si, 1.8% -2.5% of Mn, 0.05% -0.20% of V, 0.0005% -0.0030% of B, 0.02% -0.04% of Ti, 0.1% -0.3% of Cr, 0.1% -0.3% of Ni, 0.1% -0.3% of Cu, 0.015% -0.035% of Alt, less than or equal to 0.010% of P, less than or equal to 0.010% of S, less than or equal to 0.0020% of T.O, less than or equal to 0.0065% of N, and the balance of Fe and other unavoidable impurities; compared with the prior art, the application has the advantages that through component design and process optimization, the austenite grain size of the product is more than or equal to 11.0 level, the product has good strength and plastic toughness, and simultaneously has good atmospheric corrosion resistance, and spheroidizing annealing and tempering can be omitted.

Description

Non-quenched and tempered cold-forging steel with excellent corrosion resistance and production method thereof
Technical Field
The application belongs to the technical field of non-quenched and tempered cold-forging steel, and particularly relates to non-quenched and tempered cold-forging steel with excellent corrosion resistance and a production method thereof.
Background
The fastener is the most common general basic member which is very important and has a large range, is widely applied to the industries of machinery manufacturing, engineering structures, railways, automobiles, tractors, buildings and the like, and about 70 percent of the connected members and combined devices are connected by the fastener. The fastener is mainly formed by cold heading, the material bears up to 70-80% of total deformation in the manufacturing process, and the material is required to have better plasticity and low hardness before cold heading, so that the cold-headed steel wire produced by the traditional process needs two heat treatment procedures of time-consuming and energy-consuming spheroidizing annealing and tempering before cold heading and drawing.
In recent years, under the pressure of energy conservation and cost reduction, a fastener manufacturer is urgent to develop a novel energy-saving cold heading steel wire rod capable of omitting quenching and tempering and spheroidizing annealing before drawing in place of quenched and tempered steel, so that energy can be saved, and the highest electric energy per ton of steel can be saved by 2500 kw.h according to statistics.
At present, the same quenched and tempered steel level is achieved mainly by adopting microalloying, rolling control and cooling control and cold work hardening at home and abroad. The cold work reinforced non-quenched and tempered steel is researched and developed in the 80 s of the last 20 th century internationally, and the non-quenched and tempered cold heading steel is developed successfully in China, can be used for producing fasteners with small deformation such as screws, tooth bars and the like, and is mainly oriented to the mechanical and building industries.
However, with the rapid development of construction and construction industry, the use environment of the fastener is more and more complex, so that the fastener is required to have good mechanical properties, corrosion resistance and meet the use requirement of the complex environment.
Patent publication No. CN 106480376A published in 3/8/2017 discloses a non-quenched and tempered cold heading steel wire rod for a 10.9-grade fastener and a production method thereof. The components and weight percentages thereof are as follows: c0.10-0.15%; si 0.50-0.80%; mn 1.60-2.10%; p is less than or equal to 0.015 percent; s is less than or equal to 0.010 percent; 0.30 to 0.50 percent of Cr; 0.002 to 0.005 percent of B, 0.03 to 0.05 percent of Ti, not more than 0.1 percent of unavoidable impurities and the balance of iron; the method realizes accurate control of the wire rod structure and performance through accurate design of alloy components, matching with smelting, continuous casting and rolling and wire rod controlled rolling and cooling processes, and the produced non-quenched and tempered cold heading steel wire rod for the 10.9-grade fastener has uniform components, granular bainite structure, enough strength and better cold drawing property, and meets the requirement of adopting the non-quenched and tempered process to produce the 10.9-grade high-strength fastener. But the fasteners produced by this method do not have good corrosion resistance.
The patent with publication number CN112359275A published in 2 months of 2021 discloses a non-quenched and tempered cold-heading steel wire rod for high-strength fasteners and a preparation method thereof, wherein the composition of the non-quenched and tempered cold-heading steel wire rod is C:0.16 to 0.18 percent, si: less than or equal to 0.20 percent, mn:1.40 to 1.50 percent, P: less than or equal to 0.008 percent, S: less than or equal to 0.008 percent, ti:0.05 to 0.06 percent, V:0.10 to 0.13 percent, al: less than or equal to 0.01 percent, N: 60-90 ppm, and the balance of Fe and unavoidable impurities. The preparation method comprises converter smelting, LF refining, billet continuous casting and wire rod rolling. The method has the advantages that through optimizing the component design of elements in the components and adopting an innovative smelting process and combining an advanced rolling and cooling control technology, the strength and plasticity of steel are effectively improved, the production of a 10.9-level high-strength fastener without annealing and tempering is realized, and the processing cost of downstream industries is remarkably reduced. But the fasteners produced by this method do not have good corrosion resistance.
Therefore, it is necessary to provide economical, high strength and corrosion resistant non-quenched and tempered cold-heading steel products.
Disclosure of Invention
The application aims to provide non-quenched and tempered cold-heading steel with excellent corrosion resistance and a production method thereof, and the produced non-quenched and tempered cold-heading steel has good strength and plastic toughness, good atmospheric corrosion resistance and can be used for manufacturing high-strength fasteners with the tensile strength of more than 1000MPa, spheroidizing annealing and quenching and tempering processes can be omitted, and the alloy is simple and has low cost through component design and process optimization.
The specific technical scheme of the application is as follows:
the application provides non-quenched and tempered cold heading steel with excellent corrosion resistance, which comprises the following components in percentage by mass:
0.21 to 0.30 percent of C, 0.02 to 0.1 percent of Si, 1.8 to 2.5 percent of Mn, 0.05 to 0.20 percent of V, 0.0005 to 0.0030 percent of B, 0.02 to 0.04 percent of Ti, 0.1 to 0.3 percent of Cr, 0.1 to 0.3 percent of Ni, 0.1 to 0.3 percent of Cu, 0.015 to 0.035 percent of Alt, less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.0020 percent of T.O, less than or equal to 0.0065 percent of N, and the balance of Fe and other unavoidable impurities.
The components of the non-quenched and tempered cold heading steel with excellent corrosion resistance also meet the following conditions: 4.5.ltoreq.15XCr+10× (Ni+Cu) +20XTi.ltoreq.10.0.
The non-quenched and tempered cold heading steel with excellent corrosion resistance is used for manufacturing high-strength fasteners with tensile strength of more than 1000MPa, and spheroidizing annealing and quenching and tempering can be omitted.
The non-quenched and tempered cold heading steel hot-rolled microstructure with excellent corrosion resistance is a granular bainite/ferrite dual-phase structure, wherein the area content of the granular bainite is 85% -95%, the grain size is more than or equal to 11.0 level, and the grain size is 11-14 mu m; the tensile strength is more than or equal to 800MPa and less than or equal to R m Less than or equal to 860MPa; the strength is ensured to meet the use requirement of the 10.9-grade high-strength bolt.
After the non-quenched and tempered cold heading steel with excellent corrosion resistance is subjected to drawing and stabilizing treatment, the austenite grain size is more than or equal to 11.0 grade; tensile strength R m Not less than 1020MPa, yield ratio R P0.2 /R m Not less than 0.9, elongation after break A not less than 15%, shrinkage Z not less than 52%, impact energy KV at room temperature 2 More than or equal to 52J, the steel has good strength and toughness, and also has good atmospheric corrosion resistance, and the corrosion rate (72 h) is less than or equal to 1.25g/m 2 ·h。
The application provides a production method of non-quenched and tempered cold heading steel with excellent corrosion resistance, which comprises the following process flows: proportioning according to the component proportion, smelting in an electric furnace, refining in an LF furnace and RH vacuum refining, continuous casting of bloom, rolling of bloom, finishing and peeling, heating, rolling of large coil wire rods, cooling by a Steyr cooling line, large coil finished products, packaging and warehousing.
The electric furnace smelting comprises the following steps: the end point C of the electric furnace is controlled to be 0.06-0.20%, and P is less than or equal to 0.005%; adding refining slag and lime when tapping 1/5-1/4 molten steel, and adding deoxidizer and alloy when tapping 1/4-1/3, wherein the sequence is as follows: aluminum iron, silicon manganese, medium carbon manganese, high carbon ferrochrome and carburant, and uniformly throwing a proper amount of aluminum particles to the steel slag surface according to the slag discharging amount after tapping.
Refining in the LF furnace: argon is blown to the bottom of the whole ladle, and the argon flow is based on the condition that molten steel does not splash the ladle; adding premelted refining slag and lime for slagging, wherein the alkalinity is R3-5, the white slag time is more than or equal to 20 minutes, and adding alloy to adjust the Si, mn and Cr contents before and during refining according to the analysis result of the components before entering an LF furnace.
The RH vacuum degassing: in the early stage of vacuum, if the vacuum degree is less than or equal to 100 Pa, the vacuum holding time is more than or equal to 10 minutes, and if the vacuum degree is less than or equal to 100 Pa and less than or equal to 200 Pa, the vacuum holding time is more than or equal to 15 minutes; the holding time of the vacuum later period is more than or equal to 10 minutes. According to the result of the vacuum early-stage component analysis, if component adjustment is required in the middle stage, a vacuum holding time of 5 minutes or more is required after the adjustment. And (5) carrying out calcium wire feeding treatment after vacuum breaking. And (5) carrying out soft argon blowing treatment before the station is out, wherein the soft argon blowing time is more than or equal to 15min. And adjusting the V, ti, B, ni content of the added alloy according to the analysis result of the RH end point component.
And (3) continuously casting the bloom: the application adopts continuous casting of a large square billet with 380mm multiplied by 450mm, in order to ensure the uniformity of wire rod structure, the application adopts the large square billet to effectively reduce segregation of materials, ensure the uniformity of core and edge structures, and protects casting in the whole process, a protective sleeve and an argon seal are adopted between a ladle and a tundish, the tundish is protected by molten steel covering agent and argon blowing, a submerged nozzle is adopted between the tundish and a crystallizer, and the primary cooling water flow is 100-130 m 3 And/h, the secondary cooling specific water quantity is 1.0-1.4 l/kg, the liquid level, the drawing speed and the superheat degree in the casting process are stable, the superheat degree is controlled at 15-30 ℃, and the drawing speed is 1.9-2.1mm/min.
The square billet is rolled by adopting 150 square billets, the temperature of the square billets in the soaking section of the heating furnace is controlled between 1250 and 1350 ℃, and the total heating time is controlled between 250 and 350 minutes, so that the alloy elements, especially Ti, are fully dissolved. The initial rolling temperature is controlled at 1100+/-50 ℃, the stack cooling temperature after rolling is more than or equal to 400 ℃, and the surface and end part grinding treatment is carried out at 150 sides after rolling, so that good surface quality is provided for subsequent high-line rolling, and meanwhile, the decarburization sensitivity of the surface of the wire rod is reduced.
The large coil wire rod is rolled: through the steps, a qualified rolling raw material billet can be obtained, and the rolling of large-coil wires with phi of 16-30mm can be realized. The high-line rolling adopts low-temperature large-deformation rolling, and the rolling deformation is more than or equal to 50%. In order to ensure that alloy elements are fully dissolved, the initial rolling temperature is 970-1030 ℃, the rolling is completed in an austenite recrystallization region to realize recrystallization refinement, the final rolling temperature is 760-800 ℃, then the mixture enters an LCC roller way to control cooling, in order to obtain a granular bainite+ferrite dual-phase structure, the first 4 heat preservation covers are opened in a mode of quick cooling firstly and then slow cooling secondly, a fan is opened to 100 percent for quick cooling, the cooling rate is 4-7 ℃/s to 450-500 ℃, and the generation of pearlite structure is avoided; and the rear 5 to 11 fans are completely closed, the heat-insulating cover is completely closed, the cooling rate is 0.7 to 1.0 ℃/s, the generation of martensitic structure is avoided, then the heat-insulating tunnel is discharged for collecting coils at the temperature of 400 to 440 ℃, hooked, air-cooled to room temperature for packing and weighing.
The hot-rolled microstructure of the non-quenched and tempered cold heading steel with excellent corrosion resistance, which is produced by the method, is as follows: granular bainite and ferrite dual-phase structure, and the tensile strength is 860MPa or more than or equal to R m ≥800MPa。
The non-quenched and tempered cold heading steel with excellent corrosion resistance produced by the method adopts the following steps: cold drawing, cold heading forming, thread machining, low-temperature stabilization treatment and surface treatment for machining the fastener. The low-temperature stabilization treatment process comprises the following steps: heating to 350+ -10deg.C, maintaining for 30-40min, and air cooling, and can be combined with surface treatment process such as zinc plating and Dacromet.
After the drawing and stabilizing treatment, the tensile strength R of the product m Not less than 1020MPa, yield ratio R P0.2 /R m Not less than 0.9, elongation after break A not less than 15%, shrinkage Z not less than 52%, impact energy KV at room temperature 2 More than or equal to 52J, the austenite grain size of the steel is more than or equal to 11.0 grade, and the steel has good strength and plasticity and toughness and good performanceIs resistant to atmospheric corrosion.
The design idea of the application is as follows:
c: the C element is necessary for obtaining high strength and hardness. In order to obtain a non-quenched and tempered steel mainly composed of bainite, the content of C should be 0.15% or more, but too high a content of C is advantageous for strength and the like of the steel, but is extremely disadvantageous for cold heading property, plasticity and toughness of the steel, deteriorating fatigue resistance and workability of the steel. The C content is preferably controlled to be 0.21-0.30%.
Si: si is a main deoxidizing element in steel, and as a solid solution hardening element contributes to the improvement of strength and at the same time significantly improves yield ratio, but too high a Si content will decrease plasticity and toughness of steel, and increase the activity of C, promote decarburization and graphitization tendency of steel during rolling heating, and make smelting difficult and inclusion formation easy, deteriorating fatigue resistance of steel. Therefore, the Si content is controlled to be 0.02% -0.10%.
Mn: mn is an effective element for deoxidation and desulfurization, and can promote bainite transformation. When the content is less than 2.0%, the above-mentioned effects are hardly exerted. However, the content of Mn is too high, so that the content of residual austenite after transformation is too high, the transformation temperature of bainite is too low, the yield strength and yield ratio of steel are too low, the internal stress is too high, and the fatigue performance is deteriorated. Thus controlling the Mn content to be 1.8% -2.5%.
V: v is an excellent deoxidizer for steel, and vanadium is added into the steel to refine structure grains and improve strength and toughness. V forms V (C, N) precipitated phase with N, C element in steel, has stronger precipitation strengthening effect, but because the bainite transformation temperature is lower, V diffusion is restrained in the transformation process, so that a large amount of V is solid-solved in the steel, but because V is a strong carbide forming element, the solid-solved V can obviously restrain C diffusion in the bainite transformation process, can play a role in refining bainitic ferrite, and thus ensures high yield ratio. The V content is too high and the cost is high, so the V content is controlled to be 0.05-0.20%.
B: b can obviously delay the beginning of ferrite line precipitation and increase the possibility of obtaining air-cooled bainite, but the B content is too high, so that thermal embrittlement is easy to occur, and the hot processing performance is influenced, so that the B is controlled to be 0.0005% -0.0030%.
Ti: ti and N, C elements in steel form Ti (C, N) precipitated phases, and have the effect of inhibiting the growth of crystal grains in the heating process. The excessive Ti content is easy to produce liquid large-particle TiN inclusion, reduces the fatigue performance of steel, is easy to produce forging cracks, can improve corrosion resistance and inhibit the absorption and occurrence of hydrogen in a corrosion environment, so that the Ti content is controlled to be 0.02-0.04%.
Cr: cr can effectively delay bainite transformation to obtain required high strength, and can also remarkably improve the bainite hardness through solid solution strengthening; meanwhile, cr can improve corrosion resistance by forming a passivation film on the surface of the steel, and can obviously improve weather resistance of the steel by being added in a compounding way with Cu. However, too high a content deteriorates toughness and cold workability of the steel, and thus the Cr content is controlled to be 0.10% to 0.30%.
Ni: ni can stabilize austenite, enhance the hardenability of steel, improve low-temperature toughness and reduce notch sensitivity of the fastener. The addition of Ni element can improve rust layer structure, density and cohesiveness to steel surface, corrosion resistance of steel, inhibit hydrogen adsorption, and improve delayed fracture resistance. The Ni content is controlled to be 0.10-0.30%.
Cu: the Cu element can obviously improve the corrosion resistance of the steel, and the cathode contact between the steel and Cu secondarily precipitated on the surface can promote the anodization of the steel and form a rust layer with better protection. The copper element also changes the hygroscopicity of the rust layer, thereby increasing the critical humidity. However, too high a Cu content reduces the high temperature plasticity of the steel and tends to crack during hot working. Therefore, the Cu content is controlled to be 0.10-0.30%.
Alt: alt is a stronger deoxidizing element, improves the oxidation resistance of steel, refines austenite grains and improves the delayed fracture resistance. In addition, the high Alt element is added to combine with nitrogen to form AlN, so that the pinning effect of dislocation is reduced, the blue embrittlement tendency is obviously reduced, meanwhile, the impact toughness is improved, but the Alt content is too high, coarse carbonitride is formed to cause the content of inclusions to be increased, and the delayed fracture resistance is reduced. The Alt content is controlled to be 0.015-0.035%.
S and P: impurity elements such as S, P are aggregated at grain boundaries, so that the delayed fracture resistance is greatly reduced. The P element can form micro segregation when molten steel is solidified, and then the P element is biased to a grain boundary when heated at an austenitizing temperature, so that the brittleness of the steel is obviously increased, and the delayed fracture sensitivity of the steel is increased; the S element forms Mn S inclusion and segregation in grain boundary, so that the delayed fracture sensitivity of the steel is increased, and therefore, the content of P, S is controlled to be less than or equal to 0.010 percent of P and less than or equal to 0.010 percent of S.
T.o and N: oxygen forms various oxide inclusions in the steel. Under the action of stress, stress concentration is easy to occur at the oxide inclusions, so that microcrack initiation is caused, and the mechanical properties, particularly toughness and fatigue resistance, of the steel are deteriorated. Therefore, in the metallurgical production, measures are taken to reduce the content of the T.O as much as possible to be less than or equal to 0.0020 percent; n precipitates Fe4N in steel, the diffusion speed is low, the steel generates timeliness, meanwhile, the cold processing performance of the steel is reduced, and the N is controlled to be less than or equal to 0.0065%.
Compared with the prior art, the application ensures that the wire rod has high strength, properly improves the C content, selects Cr, V and Ti as fine-tuning alloy elements, improves the toughness of steel, reduces the content of granular bainite, and leads ferrite to appear in a structure to form a dual-phase steel structure. In order to improve the atmospheric corrosion resistance, a certain amount of Ni and Cu are added, and carbide formed by Ti elements can inhibit the absorption and occurrence of hydrogen in a corrosion environment, so that the corrosion resistance is improved, and the chemical composition is required to be 4.5-15 xCr+10 x (Ni+Cu) +20 xTi-10.0. The fastener produced by the application can omit quenching and tempering treatment, and has tensile strength R after heat preservation for 30-40min at 350+/-10 DEG C m Not less than 1020MPa, yield ratio R P0.2 /R m Not less than 0.9, elongation after break A not less than 15%, shrinkage Z not less than 52%, impact energy KV at room temperature 2 More than or equal to 52J, the austenite grain size of the steel is more than or equal to 11.0 grade, and the steel has good strength and plasticity and toughness, and simultaneously has excellent atmospheric corrosion resistance which is 1.5 times of that of a conventional fastener.
Drawings
FIG. 1 shows a microstructure of a non-quenched and tempered cold-heading steel in a hot rolled state, which is granular bainite+ferrite, having excellent corrosion resistance.
Detailed Description
The present application is further illustrated by the following examples and comparative examples.
Example 1 to example 5
The non-quenched and tempered cold-heading steel with excellent corrosion resistance comprises the following components in percentage by mass: as shown in table 1, the balance not shown in table 1 is Fe and other unavoidable impurities.
Comparative example 1-comparative example 3
The non-quenched and tempered cold heading steel comprises the following components in percentage by mass: as shown in table 1, the balance not shown in table 1 is Fe and other unavoidable impurities.
TABLE 1 chemical composition (wt%) of each of examples and comparative examples of the present application
The production method of the non-quenched and tempered cold heading steel of each example and the comparative example is carried out according to the following process flow:
proportioning according to the component proportion, smelting in an electric furnace, refining in an LF furnace and RH vacuum refining, continuous casting of bloom, rolling of bloom, finishing and peeling, heating, rolling of large coil wire rods, cooling by a Steyr cooling line, large coil finished products, packaging and warehousing.
The process parameters are as follows:
the electric furnace smelting comprises the following steps: smelting by adopting an electric arc furnace, fixing oxygen before tapping, and strictly controlling slag discharging in the tapping process; the end point C of the electric furnace is controlled to be 0.06-0.20%, and P is less than or equal to 0.005%; adding refining slag and lime when tapping 1/5-1/4 molten steel, and adding deoxidizer and alloy when tapping 1/4-1/3, wherein the sequence is as follows: aluminum iron, silicon manganese, medium carbon manganese, high carbon ferrochrome and carburant, and uniformly throwing a proper amount of aluminum particles to the steel slag surface according to the slag discharging amount after tapping.
Refining in the LF furnace: argon is blown to the bottom of the whole ladle, and the argon flow is based on the condition that molten steel does not splash the ladle; adding premelted refining slag and lime for slagging, wherein the alkalinity is R3-5, the white slag time is more than or equal to 20 minutes, and adding alloy to adjust the Si, mn and Cr contents before and during refining according to the analysis result of the components before entering an LF furnace.
The RH vacuum degassing: in the early stage of vacuum, if the vacuum degree is less than or equal to 100 Pa, the vacuum holding time is more than or equal to 10 minutes, and if the vacuum degree is less than or equal to 200 Pa, the vacuum holding time is more than or equal to 15 minutes; the holding time of the vacuum later period is more than or equal to 10 minutes. According to the result of the vacuum early-stage component analysis, if component adjustment is required in the middle stage, a vacuum holding time of 5 minutes or more is required after the adjustment. And (5) carrying out calcium wire feeding treatment after vacuum breaking. And (5) carrying out soft argon blowing treatment before the station is out, wherein the soft argon blowing time is more than or equal to 15min. The pure degassing time is more than or equal to 15 minutes, and the H content after vacuum treatment is less than or equal to 1.5ppm; and adjusting the V, ti, B, ni content of the added alloy according to the analysis result of the RH end point component.
In continuous casting, the target temperature of molten steel in a tundish is controlled to be 10-40 ℃ above the liquidus temperature, large round billets with the diameter of 380mm are continuously cast in a whole-process protection way, a protection sleeve and argon seal are adopted between a ladle and a tundish, the tundish is protected by using a molten steel covering agent and argon blowing, a submerged nozzle is adopted between the tundish and a crystallizer, and the primary cooling water flow is 100-130 m 3 And/h, the secondary cooling specific water quantity is 1.0-1.4 l/kg, the liquid level, the drawing speed and the superheat degree in the casting process are stable, the superheat degree is controlled at 15-30 ℃, and the drawing speed is 1.9-2.1mm/min.
The square billet is rolled by adopting 150 square billets, the temperature of the square billets in the soaking section of the heating furnace is controlled between 1250 and 1350 ℃, and the total heating time is controlled between 250 and 350 minutes, so that the alloy elements, especially Ti, are fully dissolved. The initial rolling temperature is controlled at 1100+/-50 ℃, the stack cooling temperature after rolling is more than or equal to 400 ℃, and the surface and end part grinding treatment is carried out at 150 sides after rolling, so that good surface quality is provided for subsequent high-line rolling, and meanwhile, the decarburization sensitivity of the surface of the wire rod is reduced.
The large coil wire rod is rolled: through the steps, a qualified rolling raw material billet can be obtained, and the rolling of the large-coil wire rod with the diameter of 16-30mm can be realized. The high-line rolling adopts low-temperature large-deformation rolling, and the rolling deformation is more than or equal to 50%. In order to ensure that alloy elements are fully dissolved, the initial rolling temperature is 970-1030 ℃, the rolling is completed in an austenite recrystallization region to realize recrystallization refinement, the final rolling temperature is 760-800 ℃, then the mixture enters an LCC roller way to control cooling, in order to obtain a granular bainite+ferrite dual-phase structure, the first 4 heat preservation covers are opened in a mode of quick cooling firstly and then slow cooling secondly, a fan is opened to 100 percent for quick cooling, the cooling rate is 4-7 ℃/s to 450-500 ℃, and the generation of pearlite structure is avoided; and the rear 5 to 11 fans are completely closed, the heat-insulating cover is completely closed, the cooling rate is 0.7 to 1.0 ℃/s, the generation of martensitic structure is avoided, then the heat-insulating tunnel is discharged for collecting coils at the temperature of 400 to 440 ℃, hooked, air-cooled to room temperature for packing and weighing.
The wire rod rolling process of each of the examples and comparative examples of the present application is shown in table 2.
Table 2 inventive and comparative wire rolling process
The non-quenched and tempered cold-heading steels of each of the examples and comparative examples produced according to the above methods do not require quenching and tempering, and employ: cold drawing, cold heading forming, thread machining, low-temperature stabilization treatment and surface treatment for machining the fastener. The low-temperature stabilization treatment process comprises the following steps: heating to 350+ -10deg.C, maintaining the temperature for 30-40min, air cooling, and cooling to obtain a tensile strength R with mechanical properties shown in Table 3 m Not less than 1020MPa, yield ratio R P0.2 /R m Not less than 0.9, elongation after break A not less than 15%, shrinkage Z not less than 52%, impact energy KV at room temperature 2 The austenite grain size of the steel is more than or equal to 52J and is more than or equal to 11.0, which shows that the embodiment has better toughness and good atmospheric corrosion resistance.
Mechanical property test method GB/T228.1 first part of tensile test of metal material: room temperature test method;
the corrosion performance adopts a TB/T2375 periodic infiltration corrosion test method of weather-resistant steel for railways;
TABLE 3 mechanical Properties after quenching and tempering Heat treatment in the examples of the application
The underlined data above are not satisfactory for the present application.
In Table 3, the properties of comparative example 1 are properties after heat treatment, and the specific heat treatment process is: quenching the process at 890 ℃, preserving heat for 90min, tempering at 500 ℃ and preserving heat for 100min; comparative example 1 was a ferrite + pearlite + bainite + martensite structure obtained by the conventional slow cooling process using the chemical components of example 1, and the aim of omitting the tempering was not achieved.
In comparative example 2, cr, ni, cu, V, ti element was not added, but on the one hand, the strength was insufficient, the toughness was insufficient, and the corrosion resistance was insufficient.
Comparative example 3 is a composition which satisfies the requirements but does not satisfy the requirements of the formula in the present application, and is insufficient in corrosion resistance.

Claims (10)

1. The non-quenched and tempered cold-heading steel with excellent corrosion resistance is characterized by comprising the following components in percentage by mass:
0.21 to 0.30 percent of C, 0.02 to 0.1 percent of Si, 1.8 to 2.5 percent of Mn, 0.05 to 0.20 percent of V, 0.0005 to 0.0030 percent of B, 0.02 to 0.04 percent of Ti, 0.1 to 0.3 percent of Cr, 0.1 to 0.3 percent of Ni, 0.1 to 0.3 percent of Cu, 0.015 to 0.035 percent of Alt, less than or equal to 0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.0020 percent of T.O, less than or equal to 0.0065 percent of N, and the balance of Fe and other unavoidable impurities.
2. The non-quenched and tempered cold-heading steel having excellent corrosion resistance according to claim 1, wherein the composition of the non-quenched and tempered cold-heading steel having excellent corrosion resistance further satisfies: 4.5.ltoreq.15XCr+10× (Ni+Cu) +20XTi.ltoreq.10.0.
3. A method for producing a non-quenched and tempered cold-forging steel having excellent corrosion resistance as claimed in claim 1 or 2, characterized in that said method comprises the following steps: proportioning according to the component proportion, smelting in an electric furnace, refining in an LF furnace and RH vacuum refining, continuous casting of bloom, rolling of bloom, finishing and peeling, heating, rolling of large coil wire rods, cooling by a Steyr cooling line, large coil finished products, packaging and warehousing.
4. A production method according to claim 3, characterized in that the LF furnace refines: argon is blown to the bottom of the whole ladle, and the argon flow is based on the condition that molten steel does not splash the ladle; adding premelted refining slag and lime for slagging, wherein the alkalinity is R3-5, and the white slag time is more than or equal to 20 minutes.
5. A production method according to claim 3, characterized in that the RH vacuum degassing: in the early stage of vacuum, if the vacuum degree is less than or equal to 100 Pa, the vacuum holding time is more than or equal to 10 minutes, and if the vacuum degree is less than or equal to 100 Pa and less than or equal to 200 Pa, the vacuum holding time is more than or equal to 15 minutes; the holding time of the later vacuum period is more than or equal to 10 minutes; and (5) carrying out soft argon blowing treatment before the station is out, wherein the soft argon blowing time is more than or equal to 15min.
6. A production method according to claim 3, characterized in that the bloom is continuously cast: adopting 380mm multiplied by 450mm bloom continuous casting, protecting casting in the whole process, adopting a protective sleeve and argon sealing between a ladle and a tundish, adopting molten steel covering agent and argon blowing protection for the tundish, adopting a submerged nozzle between the tundish and a crystallizer, and controlling the primary cooling water flow to be 100-130 m 3 And/h, the secondary cooling specific water quantity is 1.0-1.4 l/kg, the superheat degree is controlled at 15-30 ℃, and the pulling speed is 1.9-2.1mm/min.
7. The production method according to claim 3, wherein the square billets are rolled by adopting 150 square billets, the temperature of the square billets in a soaking section of a heating furnace is controlled to 1250-1350 ℃, the total heating time is controlled to 250-350 min, the initial rolling temperature is controlled to 1100+/-50 ℃, and the post-rolling stack cooling temperature is more than or equal to 400 ℃.
8. The production method according to claim 3, wherein the large coil wire is rolled, the rolling deformation is more than or equal to 50%, the initial rolling temperature is 970-1030 ℃, the final rolling temperature is 760-800 ℃, then the large coil wire enters an LCC roller way to control cooling, the rapid cooling rate is 4-7 ℃/s to 450-500 ℃, then the large coil wire is slowly cooled, and the cooling rate is 0.7-1.0 ℃/s; and (3) the heat preservation tunnel is cooled to room temperature after the temperature is 400-440 ℃.
9. The production method according to any one of claims 3 to 8, wherein the non-quenched and tempered cold-heading steel having excellent corrosion resistance is produced by the method having a hot-rolled microstructure of: granular bainite and ferrite dual-phase structure, and the tensile strength is 860MPa or more than or equal to R m ≥800MPa。
10. The method according to any one of claims 3 to 8, wherein the non-quenched and tempered cold-headed steel having excellent corrosion resistance is produced, after drawing and stabilizing, to give a product having a tensile strength R m Not less than 1020MPa, yield ratio R P0.2 /R m Not less than 0.9, elongation after break A not less than 15%, shrinkage Z not less than 52%, impact energy KV at room temperature 2 More than or equal to 52J, and the austenite grain size of the steel is more than or equal to 11.0 grade.
CN202310792402.9A 2023-06-30 2023-06-30 Non-quenched and tempered cold-forging steel with excellent corrosion resistance and production method thereof Pending CN116904849A (en)

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