CN115433871A - High-strength steel resistant to hydrogen embrittlement delayed fracture and manufacturing method thereof - Google Patents
High-strength steel resistant to hydrogen embrittlement delayed fracture and manufacturing method thereof Download PDFInfo
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- 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
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- 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
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Abstract
The invention provides a high-strength steel resisting hydrogen embrittlement and delaying fracture, which comprises the following chemical components in percentage by mass: c:0.38-0.48%, si:0.03 to 0.12%, mn:0.23-0.43%, cr:1.00-1.40%, mo:0.30-0.50%, ni:0.15-0.40%, V:0.18-0.35%, nb:0.02-0.12%, al:0.025-0.045%, N: less than or equal to 0.0050 percent, and the balance of Fe and inevitable impurities. Through the control of alloy components, structure and steel purity, the hydrogen embrittlement resistance delayed fracture performance is improved, the sensitivity to hydrogen embrittlement is reduced, and the hydrogen embrittlement resistance delayed fracture performance is excellent. The invention also provides a manufacturing method of the steel, which comprises smelting, casting, rough rolling, high-speed wire rod rolling, stelmor controlled cooling, spheroidizing or quenching and tempering heat treatment, drawing or straightening, cold heading and quenching and tempering heat treatment or turning. Can process high-strength steel of high-strength fasteners above 1200MPa and other parts, and ensures safe and long-term use.
Description
Technical Field
The invention belongs to the field of metal materials, and particularly relates to hydrogen embrittlement-resistant delayed fracture high-strength steel and a manufacturing method thereof.
Background
The fastener is a general name of a type of mechanical parts adopted when two or more parts (or components) are fastened and connected into a whole, the fastener is a mechanical basic part which has the widest application range and the largest use quantity of various departments of the national economy, is called industrial rice, has the advantages of simplicity, convenience, repeated disassembly and reassembly, high standardization degree, low cost and the like in bolt fastener connection, and is used for various and considerable fasteners on various mechanical equipment, vehicles, ships, aircraft satellites, railway bridges, building structures, tool instruments, meters, articles for daily use and the like. Currently, global fasteners are used primarily in the automotive industry, the electronics industry, and the construction and repair industry. Wherein, the automobile industry is the largest user, and the demand accounts for about 23.2% of the total sales volume of the fasteners; secondly, the maintenance industry market and the construction industry account for about 20 percent of the total sales volume of the fasteners; third, the electronics industry accounts for approximately 16.6% of the total fastener sales. The high-strength fastener for the automobile has four performance grades which are respectively 8.8 grade, 9.8 grade, 10.9 grade and 12.9 grade, and the high-strength (more than 8.8 grade) bolt is mainly made of medium-carbon or medium-carbon alloy steel because the high-strength bolt needs to bear larger load and the stress state is very complicated, and the high-strength bolt is subjected to quenching and tempering (high-temperature tempering after quenching) so as to ensure that the product has enough strength and yield ratio.
Automobile, machinery and building trade still use round pin, connecting rod, axle class spare part in a large number, adopt high strength steel processing, this type of part also requires high strength in order to reduce the part size, improve joint strength, this type of spare part is similar with fastener application environment, often needs to bear higher load, perhaps works under harsh alternating stress, easily takes place the corrosion and leads to oozing hydrogen when contacting with atmosphere, water, corrosive liquid, takes place unpredictable delay destructive fracture in the spare part use, leads to very big potential safety hazard.
The delayed fracture phenomenon is an environmental embrittlement caused by material-environment-stress interaction, and is a form of hydrogen-induced material deterioration (hydrogen damage or hydrogen embrittlement). The delayed fracture phenomenon occurs because hydrogen inside the part diffuses and accumulates to the stress concentration portion, and the stress concentration portion has many metal defects (such as dislocation of atomic lattice, holes, etc.). Hydrogen diffuses into these defects and hydrogen atoms become hydrogen molecules, creating a large pressure which, together with residual stresses inside the material and the applied stresses to which the material is subjected, constitute a resultant force which, when it exceeds the yield strength of the material, causes fracture to occur. Since hydrogen embrittlement is associated with diffusion of hydrogen atoms, diffusion is time-consuming, and the rate of diffusion is related to concentration gradients, temperature, and material species. Thus, hydrogen embrittlement is often manifested as delayed fracture. The actual steel subjected to delayed fracture in the natural environment is mainly tempered martensitic steel which generally has the following characteristics: when the tensile strength is more than 1200MPa and the hardness HRC is more than or equal to 38, the sensitivity of delayed fracture is obviously increased; delayed fracture generally occurs around room temperature, but from room temperature to around 100 ℃, the sensitivity of delayed fracture increases with increasing temperature; macroscopically, delayed fracture is not accompanied by large plastic deformation; occurs under static load (strain rate is zero); occurs at stresses much lower than the yield strength.
The automobile, bridge and machinery industries use more than 8.8-grade high-strength fasteners, high-strength connecting rods, pins, shafts and other parts in quantity, when the use strength of the parts reaches more than 1200MPa, hydrogen embrittlement delayed fracture is easy to generate, the damage of the high-strength steel parts is often sudden and unpredictable, the fracture is instantaneous and is a very unsafe point for the application of the high-strength steel, and therefore the hydrogen embrittlement resistance delayed fracture performance of the products is urgently needed to be improved so as to meet the safe use requirements of various industries.
Patent publication 202010604975.0 discloses a round steel for bolt with excellent corrosion resistance and delayed fracture resistance, which has carbon content of 0.55-0.60%, contains a large amount of Si element up to 1.80-2.00%, and contains Cu element 0.20-0.35%, and has great difficulty in decarburization control and cracking control during alloy hot rolling and heat treatment, and poor bolt formability.
The patent publication 201810357699.5 discloses that high-strength bolt steel with excellent atmospheric corrosion resistance and delayed fracture resistance needs to be added with 0.30-1.20% of Ni and 0.20-0.60% of Cu, and also needs to be added with 0.005-0.030 of Re rare earth element, so that the alloy cost is high, and the smelting control difficulty is high.
Patent publication 201911230974.8 discloses niobium-titanium-containing atmospheric corrosion-resistant 14.9-grade high-strength bolt steel, which contains 0.80-1.00% of Mo, is added with a large amount of V, nb, ti, cr and Cu elements, and has the disadvantages of high alloy production difficulty, high cost and poor stability of the performance of processed parts.
Disclosure of Invention
In order to solve the problems, the invention relates to high-strength steel with hydrogen embrittlement resistant and delayed fracture resistance, which remarkably improves the hydrogen embrittlement resistant and delayed fracture resistance through alloy components, optimized design and structure and steel purity control, so that the sensitivity of processed parts to hydrogen embrittlement is reduced in the using process, and the high-strength steel has excellent hydrogen embrittlement resistant and delayed fracture resistance. The high-strength steel can be used for processing high-strength fasteners with the pressure of over 1200MPa and other parts such as connecting rods, pins, shafts and the like, can ensure that processed parts can be safely used for a long time, can still be safely and permanently used in a hydrogen environment, and can meet the use requirements of the industries of automobiles, machinery and buildings.
The invention provides hydrogen embrittlement-resistant delayed fracture high-strength steel, which comprises the following chemical components in percentage by mass:
c:0.38-0.48%, si:0.03 to 0.12%, mn:0.23-0.43%, cr:1.00-1.40%, mo:0.30-0.50%, ni:0.15-0.40%, V:0.18-0.35%, nb:0.02-0.12%, al:0.025-0.045%, N: less than or equal to 0.0050 percent, and the balance of Fe and inevitable impurities.
According to another embodiment of the invention, the embodiment of the invention discloses a high-strength steel resisting hydrogen embrittlement delayed fracture, the size of the carbonitride precipitates of V and Nb of the high-strength steel resisting hydrogen embrittlement delayed fracture is less than 70nm, and the austenite grain size of the material is less than 60um.
According to another specific embodiment of the invention, the embodiment of the invention discloses a high-strength steel capable of resisting hydrogen embrittlement delayed fracture, which further comprises the following chemical components in percentage by mass: V/Nb is more than or equal to 2, and (V + Nb) × (C + N) is less than or equal to 0.16; al/(O + N) Tg > 5.
According to another embodiment of the present invention, there is disclosed a high strength steel resistant to hydrogen embrittlement delayed fracture, the inevitable impurities including: cu: less than or equal to 0.02 percent, P: less than or equal to 0.010 percent, S: less than or equal to 0.010%, O: less than or equal to 0.0008 percent.
According to another specific embodiment of the invention, the embodiment of the invention discloses hydrogen embrittlement resistant delayed fracture resistant high-strength steel, which further comprises the following chemical components in percentage by mass: mn/S > 35.
According to another embodiment of the invention, the embodiment of the invention discloses a high-strength steel capable of resisting hydrogen embrittlement delayed fracture, the microstructure of the high-strength steel capable of resisting hydrogen embrittlement delayed fracture has a refined tempered sorbite structure, and the strength of the high-strength steel capable of resisting hydrogen embrittlement delayed fracture is larger than or equal to 1200MPa.
The invention also provides a manufacturing method of the high-strength steel resisting hydrogen embrittlement delayed fracture, which comprises the following steps: smelting, namely smelting by using the components of the high-strength steel with hydrogen embrittlement resistance and delayed fracture resistance; casting; rough rolling; rolling the high-speed wire rod; controlling cooling by stelmor, and controlling the structural transformation of the wire rod by adjusting the fan component of a stelmor line after the wire rod is rolled; spheroidizing or quenching and tempering heat treatment; drawing or straightening; cold heading and quenching and tempering heat treatment or turning.
According to another embodiment of the invention, the embodiment of the invention discloses a method for manufacturing high-strength steel with hydrogen embrittlement resistance and delayed fracture resistance, in the alloy smelting step, the high-vacuum degassing time is more than 18 minutes after smelting in an electric furnace or a converter and then external refining is carried out.
According to another embodiment of the invention, the embodiment of the invention discloses a method for manufacturing high-strength steel resisting hydrogen embrittlement delayed fracture, in the casting step, argon gas is used for protection; adjusting parameters of drawing speed, cooling and tail end soft reduction in the casting process to control the core carbon segregation of the blank to be lower than 1.09; after eddy current inspection, magnetic powder inspection, grinding wheel die repairing, magnetic powder inspection supplementing and die repairing, the blank is placed into a heating furnace for heating, the heating is controlled to be 960-1200 ℃, and the heat preservation time is 1.0-3.0 hours.
According to another specific embodiment of the invention, the embodiment of the invention discloses a method for manufacturing high-strength steel resisting hydrogen embrittlement delayed fracture, in the high-speed wire rod rolling step, the rolling speed is controlled to be 8-120m/s, the inlet temperature of a finishing mill group is 750-980 ℃, the inlet temperature of a reducing sizing mill group is 750-980 ℃, and the spinning temperature is 700-900 ℃.
Further, in the stelmor cooling control step, the stelmor line comprises fans F1-F14, wherein the air volume of the fans F1-F5 is 0-70%, the air volume of the fans F6-F12 is 0-60%, and the air volume of the fans F13-F14 is 0-50%.
Further, in the spheroidizing or quenching and tempering heat treatment step, the heat preservation temperature of the wire rod spheroidizing heat treatment is 750-800 ℃, the heat preservation time is 4-15 hours, the wire rod spheroidizing heat treatment is slowly cooled after heat preservation, the speed is lower than 20 ℃/h, the drawing reduction rate of the wire rod is 5-30%, the heating temperature of the quenching and tempering heat treatment is 850-1000 ℃, and the tempering temperature is 425-600 ℃.
The beneficial effects of the invention are:
the invention aims to provide high-strength steel capable of processing parts such as high-strength fasteners, connecting rods, pins, shafts and the like with the pressure of more than 1200MPa, the steel obviously improves the hydrogen embrittlement resistance and delayed fracture performance through design and control of alloy components, structures and steel purity, obviously reduces the hydrogen diffusion rate in high-strength parts through V and Nb composite addition and carbide precipitation and grain structure refinement, improves the endurance time by more than 5 times in a corrosive environment with hydrogen, and can greatly improve the service life and safety of the processed parts.
Detailed Description
The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure. While the invention will be described in conjunction with the preferred embodiments, it is not intended that features of the invention be limited to these embodiments. On the contrary, the invention has been described in connection with the embodiments for the purpose of covering alternatives or modifications as may be extended based on the claims of the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The invention may be practiced without these particulars. Moreover, some of the specific details have been left out of the description in order to avoid obscuring or obscuring the focus of the present invention. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
In the description of the present invention, unless otherwise specified, terms in the present specification have the same meaning as those generally understood by those skilled in the art, but if different, the definitions in the present specification shall control; unless otherwise specified, the test methods are all conventional methods; unless otherwise specified, the raw materials and test materials used in the present specification are all available commercially in a conventional manner; unless otherwise specified, the percentages (%) in the present specification are all mass percentages (% by mass).
The high-strength steel resistant to hydrogen embrittlement delayed fracture in the embodiment comprises the following chemical components in percentage by mass:
C：0.38-0.48％、Si：0.03-0.12％、Mn：0.23-0.43％、Cr：1.00-1.40％、Mo：0.30-0.50％、Ni：0.15-0.40％、V：0.18-0.35％、Nb：0.02-0.12％、Al：0.025-0.045％、Cu：≤0.02％、P：≤0.010％、S：≤0.010％、O：≤0.0008％、N：≤0.0050％。
and 2 is less than or equal to V/Nb, (V + Nb) is less than or equal to 0.16, (C + N) is less than or equal to 0.16) the size of carbon-nitrogen precipitates of V and Nb is less than 70nm, al/(O + N) is controlled to be more than 5 and Mn/S is controlled to be more than 35 for improving the purity of steel, the number of inclusions in steel is reduced, and the austenite grain size of the material is less than 60um.
The reason why the alloy steel of the present embodiment is selected in the chemical composition range is as follows:
the C element is a necessary chemical component for ensuring the high-strength steel for parts, the content of the C element determines the quantity of precipitated carbides after quenching and tempering heat treatment of a wire rod and finished parts, and the hardness and the strength of the alloy are greatly influenced, so that the carbon content in the alloy is higher than 0.38%, but the excessive carbon content design causes the excessive precipitation quantity of the carbides in the material, the size of the carbide is large, the ductility and toughness of the material are reduced, and the delayed fracture resistance is deteriorated, and the carbon content is required to be controlled to be lower than 48%.
Si element is often added into steel as a deoxidizer in the smelting process, and meanwhile, si which is solid-dissolved in an alloy ferrite phase can obviously improve the strength of the material, but the excessively high Si content can reduce the plasticity of the material and is unfavorable for the hydrogen embrittlement resistance and delayed fracture resistance of the material. Therefore, the content of Si in the alloy is controlled to be 0.03-0.12%.
Mn is also commonly used as a deoxidizer to be added in the steel-making process, and meanwhile Mn is easy to combine with harmful elements S in steel to form MnS, so that the harm is reduced, and the Mn/S is controlled to be more than 35.Mn is also a common strengthening element in steel and mainly plays a role in solid solution strengthening, and formed alloy cementite has higher strength, so that the content of Mn in the alloy needs to be controlled to be higher than 0.23%. However, when the content of Mn is too high, the tendency of grain coarsening during heating of the material increases, and further, mn element tends to promote segregation of the residual elements, so that the amount of Mn element to be added should be controlled to be less than 0.43%.
The Cr element is added to facilitate the improvement of the hardenability of the alloy, the refinement of the structure is facilitated in the bolt quenching and tempering process, the strength of cementite is improved, the strength and the plasticity of the material are improved, the corrosion resistance of the material is improved, and the hydrogen brittleness sensitivity is reduced, so that the Cr content added to the material is higher than 1.0 percent, the control difficulty of the wire rod structure is reduced, and the Cr content is required to be lower than 1.40 percent in order to prevent the occurrence of martensite abnormal structure and reduce the wire rod structure control difficulty.
The addition of Mo element is beneficial to refining the structure, improving the tempering stability of the material, improving the strength and hardness of the material under high-temperature tempering and improving the delayed fracture resistance of the material, but the difficulty in controlling the structure of the material is increased due to the excessive addition of Mo element, and the alloy cost is increased, so that the addition range of the Mo element is 0.30-0.50%.
The Ni element is an austenite forming element, is dissolved in a ferrite phase to be beneficial to improving the strength of the material, can effectively improve the hardenability of the material, and improves the structure uniformity and refined structure in the quenching and tempering process of the bolt, but the excessively high Ni content can cause martensite abnormal structure to easily appear in the production process of the material, and can also influence the alloy cost, so the control range of the Ni element is 0.15-0.40%.
The V and Nb elements are easy to react with the C and N elements in the high-strength steel to precipitate carbonitride, the nano-scale precipitate has strong promotion effect on the material strength and plasticity, and the carbonitride of the V and Nb can be used as a hydrogen trap, particularly when the V and Nb elements are compositely added, the lattice mismatching degree of the precipitate and ferrite in the steel is increased, the lattice distortion energy is larger, the fixation effect on hydrogen atoms is stronger, the harm is reduced, the V content is controlled to be 0.18-0.35%, the Nb addition is controlled to be 0.02-0.12%, the V/Nb is more than or equal to 2 and the (V + Nb) ((C + N) < 0.16), the size of the carbonitride precipitate of the V and Nb is less than 70nm, and the promotion of the delayed fracture resistance of the material is realized.
Al element is the most effective deoxidizing element in the steel-making process, but Al2O3 particles are easy to produce in the Al deoxidizing process, have sharp edges and corners, particularly when the oxygen content in steel is too high, the fatigue life, the durability and the delayed fracture resistance of finished parts can be greatly influenced, the oxygen content in the material needs to be controlled to be below 0.0008% in order to ensure the performance of high-strength parts, and the purity of the steel is improved. The content range of Al is controlled to be 0.025-0.045%, al/(O + N) is larger than 5, the oxygen content in steel and the number of inclusions in steel are reduced, small-particle carbon-nitrogen precipitates of Al2O3 and Nb are reduced, the grain size of the material is favorable for refining grains of the material and improving the ductility and toughness, the grain size of the material is smaller than 60 mu m, and the increase of the number of grain boundaries is also favorable for capturing hydrogen elements and improving the hydrogen capacity of the material.
The N element also causes the material to be enlarged, and meanwhile, the too high content of the N and C elements causes the size of microalloy precipitates in the steel for the high-strength bolt to be enlarged and reduces the delayed fracture resistance of the material, so that the N content in the material is less than or equal to 0.0050 percent.
The Cu element is easy to cause the hot brittleness of the high-strength steel, and meanwhile, the excessive non-uniform distribution of the Cu element in the material can cause the content of the residual austenite in the material to be increased and the performance stability to be reduced, so that the Cu is required to be controlled to be less than or equal to 0.02 percent.
The brittleness of the material is increased when the contents of P and S elements are too high, particularly when segregation occurs, so that the P needs to be controlled to be less than 0.010 percent and the S needs to be controlled to be less than 0.010 percent in the design composition range of the material.
By adopting the scheme, the material has a refined tempered sorbite structure after quenching and tempering heat treatment, the size of V and Nb composite carbon and nitrogen precipitates is less than 70nm, the austenite grain size of the material is less than 60 microns, the strength of processed parts can reach more than 1200MPa, the fatigue life and the hydrogen embrittlement resistance delayed fracture performance are obviously improved compared with those of conventional high-strength part steel, and the requirements of long service life, safety and reliability in use in industries such as automobiles, machinery, buildings and the like can be met.
In the embodiment, the manufacturing method of the hydrogen embrittlement resistant delayed fracture resistant high-strength steel comprises key steps of smelting, casting, rough rolling, high-speed wire rod rolling, stelmor controlled cooling, spheroidizing or thermal refining treatment, drawing or straightening, cold heading thermal refining treatment or turning, and specifically comprises the following steps:
1) The alloy is smelted in an electric furnace or a converter and then is refined outside the furnace, the degassing treatment process of adding VD or RH into an LF furnace is adopted for the external refining, the components and the adding amount of synthetic slag are adjusted in the smelting process, the contents of P and S elements in steel are controlled to be respectively lower than 0.010 percent and 0.010 percent, the high vacuum degassing time needs to be longer than 18 minutes, the end point O content is controlled to be lower than 0.0008 percent, the N content is lower than 0.0050 percent, al/(O + N) is larger than 5, and the H content is lower than 2ppm.
2) In the casting step, argon is adopted for protection; adjusting parameters of drawing speed, cooling and tail end soft reduction in the casting process to control the core carbon segregation of the blank to be lower than 1.09; after eddy current inspection, magnetic powder inspection, grinding wheel die repair, magnetic powder inspection supplement and die repair, the blank is put into a heating furnace for heating, the heating is controlled to be 960-1200 ℃, and the heat preservation time is 1.0-3.0 hours.
Specifically, the casting may be bloom casting, billet casting, or die casting. More specifically, in the embodiment, when the bloom continuous casting method is used for casting, a bloom continuous casting machine is used for casting a bloom, argon protection is adopted in the casting process, the size of the bloom is 250-500mm, and the carbon segregation in the center of the bloom is controlled to be lower than 1.09 by adjusting the parameters of the drawing speed, cooling and terminal soft reduction in the continuous casting process. Adopting a secondary-heating material forming process to perform primary rolling and cogging on the continuous casting billet at the temperature of 1000-1350 ℃ to form a 135-240mm square billet. After eddy current inspection, magnetic powder inspection, grinding wheel die repair, magnetic powder supplement inspection and die repair, the square blank is put into a heating furnace for heating, the heating is controlled to be 960-1200 ℃, and the heat preservation time is 1.0-3.0 hours.
3) And in the process of rolling the wire rod high-speed wire rod, the rolling speed is controlled to be 8-120m/s. The online temperature control preferred scheme is as follows: the inlet temperature of the finishing mill group is 750-980 ℃, the inlet temperature of the reducing sizing mill group is 750-980 ℃, and the spinning temperature is 700-900 ℃.
4) The dimension specification of rolled wire rods is phi 5.5-28mm, and the wire rod organization is changed by adjusting the component of a Stelmor fan after the wire rods are rolled, so that the wire rod organization is optimized. In the stelmor cooling control step, the stelmor line comprises fans F1 to F14, and the adjustment range of the fan components of 14 stelmor lines is as follows: the air volume of the F1-F5 fans is 0-70%, the air volume of the F6-F12 fans is 0-60%, and the air volume of the F13-F14 fans is 0-50%. The wire rod has good plasticity and toughness after stelmor cooling.
5) The heat preservation temperature of the wire rod spheroidizing heat treatment is 750-800 ℃, the heat preservation time is 4-15 hours, and the wire rod spheroidizing heat treatment is slowly cooled at the speed of lower than 20 ℃/h after heat preservation. The wire rod drawing reduction rate is 5-30%. The heating temperature of the quenching and tempering heat treatment is 850-1000 ℃, and the tempering temperature is 425-600 ℃.
Examples
The high strength steel resistant to hydrogen embrittlement delayed fracture and the method of manufacturing the same according to the present invention will be further described below according to specific examples. However, the present invention is not limited to the following embodiments, and various modifications thereof should fall within the scope of the present invention.
Examples A1-a10 of the present invention the chemical composition of the high strength steel products resistant to hydrogen embrittlement delayed fracture is shown in table 1 below. The wire rods and parts of examples A1-A10 were prepared as follows:
1) The alloy is smelted by an electric furnace or a converter and then refined and VD treated by an LF furnace, the content of P and S elements in steel is controlled to be lower than 0.010 percent, meanwhile, the high vacuum degassing time needs to be longer than 18 minutes, the content of O in the steel is controlled to be lower than 0.0008 percent, the content of N in the steel is controlled to be lower than 0.0050 percent, and the content of H in the steel is controlled to be lower than 2ppm.
2) A large square billet caster is adopted to pour A1-A4 into 250 square billets, A5-A8 into 400 square billets and A9-A10 into 500mm square billets under the protection of argon, and the parameters of casting speed, cooling and terminal soft reduction in the continuous casting process are adjusted to control the core carbon segregation of the billets. Then the A1-A4 continuous casting billets are respectively subjected to primary rolling and cogging at 1000 ℃, A5-A8 and A9-A10 at 1200 ℃ to form 135 mm, 160 mm and 240mm square billets. After eddy current inspection, magnetic powder inspection, grinding wheel die repair, magnetic powder supplement inspection and die repair, the square blank is put into a heating furnace for heating, wherein the heating temperature of A1-A4 is 960 ℃, the heating temperature of A5-A8 is 1100 ℃, the heating temperature of A9-A10 is 1200 ℃, and the heat preservation time is 1.0-3.0h.
3) In the high-speed wire rod rolling process, the rolling speed of a 5.5mm wire rod is 110m/s, the rolling speed of a10 mm wire rod is 45m/s, the controlled rolling speed of a 15mm wire rod is 23m/s, and the controlled rolling speed of a 25mm wire rod is 15m/s. The online temperature control is as follows: the inlet temperature of the A1-A3 finishing mill group is 750 ℃, and the inlet temperature of the A4-A10 finishing mill group is 980 ℃; the inlet temperature of the A1-A5 reducing sizing mill set is 800 ℃, the inlet temperature of the A6-A8 reducing sizing mill set is 980 ℃, and the inlet temperature of the A9-A10 reducing sizing mill set is 950 ℃; the spinning temperature of the A1-A7 alloy is 700 ℃, and the spinning temperature of the A8-A10 alloy is 900 ℃.
4) The dimension specifications of rolled wire rods A1 to A3 are phi 5.5 and 10mm, and the component adjustment range of 14 typhoons on stelmor lines after the wire rods are rolled is as follows: the air volume of the F1-F5 fans is 0-40%, and the air volume of the F10-F14 fans is 0%. The dimension specification of rolled wire rods A4-A6 is phi 15mm, and the component adjustment range of 14 typhoons on stelmor lines after the rolled wire rods is as follows: the air volume of the F1-F5 fans is 5-65%, and the air volume of the F10-F14 fans is 0%. The dimension specification of the rolled wire rods A7-A10 is phi 25mm, and the component adjustment range of 14 fans of the Steyr Moire line after the wire rods are rolled is as follows: the air volume of the F1-F5 fans is 10-90%, the air volume of the F6-F10 fans is 0-25%, and the air volume of the F11-F14 fans is 0%.
5) And (3) carrying out spheroidizing heat treatment on the wire rod, wherein the heat preservation temperature of the spheroidizing heat treatment of the A1-A5 alloy is 750 ℃, the heat preservation time is 6 hours, the wire rod is slowly cooled at 40 ℃/h after heat preservation, the drawing reduction rate of the wire rod is 10%, the heating temperature of the quenching and tempering heat treatment is 850-1000 ℃, and the tempering temperature is 425-580 ℃. The heat preservation temperature of the spheroidizing heat treatment of the A6-A10 alloy is 790 ℃, the heat preservation time is 12 hours, the slowly cooling is carried out at 35 ℃/h after the heat preservation, the drawing reduction rate of the wire rod is 20 percent, the heating temperature of the quenching and tempering heat treatment is 890-950 ℃, and the tempering temperature is 550-600 ℃.
TABLE 1 inventive alloy Steel examples A1-A10 and comparative Steel grades chemistry (% by weight)
| Steel grade | C | Si | Mn | Cr | Mo | Ni | V | Nb | Al | Cu | P | S | O | N |
| A1 | 0.38 | 0.03 | 0.4 | 1.1 | 0.35 | 0.4 | 0.18 | 0.08 | 0.045 | 0.01 | 0.007 | 0.002 | 0.0008 | 0.0045 |
| A2 | 0.4 | 0.12 | 0.4 | 1 | 0.4 | 0.2 | 0.2 | 0.08 | 0.03 | 0.02 | 0.001 | 0.008 | 0.0005 | 0.0019 |
| A3 | 0.39 | 0.05 | 0.42 | 1.1 | 0.3 | 0.25 | 0.25 | 0.12 | 0.025 | 0.015 | 0.01 | 0.009 | 0.0008 | 0.0015 |
| A4 | 0.48 | 0.05 | 0.4 | 1.2 | 0.5 | 0.2 | 0.2 | 0.02 | 0.035 | 0.015 | 0.008 | 0.005 | 0.0005 | 0.005 |
| A5 | 0.4 | 0.07 | 0.23 | 1.2 | 0.4 | 0.3 | 0.3 | 0.04 | 0.025 | 0.016 | 0.008 | 0.003 | 0.0001 | 0.004 |
| A6 | 0.41 | 0.1 | 0.3 | 1 | 0.42 | 0.15 | 0.3 | 0.02 | 0.04 | 0.008 | 0.008 | 0.007 | 0.0006 | 0.003 |
| A7 | 0.4 | 0.05 | 0.3 | 1 | 0.45 | 0.15 | 0.35 | 0.03 | 0.03 | 0.007 | 0.008 | 0.005 | 0.0008 | 0.002 |
| A8 | 0.39 | 0.05 | 0.43 | 1.4 | 0.3 | 0.24 | 0.25 | 0.04 | 0.029 | 0.011 | 0.006 | 0.010 | 0.0002 | 0.005 |
| A9 | 0.44 | 0.03 | 0.39 | 1.3 | 0.44 | 0.4 | 0.3 | 0.05 | 0.03 | 0.018 | 0.006 | 0.003 | 0.0004 | 0.0035 |
| A10 | 0.45 | 0.1 | 0.4 | 1.05 | 0.4 | 0.4 | 0.25 | 0.05 | 0.04 | 0.009 | 0.005 | 0.004 | 0.0007 | 0.0043 |
| Comparative example 1 | 0.4 | 0.25 | 0.75 | 1.1 | 0.2 | 0 | 0 | 0 | 0.035 | 0.09 | 0.008 | 0.01 | 0.0025 | 0.006 |
| Comparative example 2 | 0.45 | 1.7 | 1.2 | 1.5 | 0.4 | 0 | 0.5 | 0.08 | 0.02 | 0.21 | 0.006 | 0.008 | 0.0015 | 0.005 |
| Comparative example 3 | 0.4 | 0.02 | 0.8 | 1.05 | 0.2 | 0.05 | 0.1 | 0 | 0.005 | 0.004 | 0.01 | 0.016 | 0.0008 | 0.0065 |
| Comparative example 4 | 0.35 | 0.2 | 0.78 | 1.05 | 0.65 | 0 | 0.25 | 0 | 0.04 | 0 | 0.009 | 0.006 | 0.0022 | 0.0035 |
The structure and mechanical properties of the inventive examples A1 to A10 and the comparative steel grades are shown in Table 2 below.
TABLE 2 comparison of the mechanical properties of the structures of the inventive alloy steels examples A1-A10 and the comparative steel grades
The hydrogen embrittlement resistance delay performance of parts processed by the steel grades A1-A10 and the comparative steel grade of the invention with the pressure of more than 1200MPa is shown in the following table 3, and the result shows that the hydrogen diffusion rate of the high-strength part processed by the new invention steel grade is obviously reduced, the hydrogen embrittlement resistance delay fracture performance of the new high-strength steel alloy is greatly improved in the environment with hydrogen corrosion, and the durability time is improved by more than 5 times.
TABLE 3 comparison of the hydrogen embrittlement resistance and delayed fracture properties of inventive alloy steel examples A1-A10 and comparative steel grades
| Steel grade | Hydrogen diffusion Rate (mm) 2 /s) | Durability time (hours) of sample loading in 0.1mol/L dilute hydrochloric acid |
| A1 | 1.69×10 -5 | 403 |
| A2 | 1.80×10 -5 | 390 |
| A3 | 1.92×10 -5 | 500 |
| A4 | 1.89×10 -5 | 450 |
| A5 | 1.99×10 -5 | 564 |
| A6 | 1.87×10 -5 | 498 |
| A7 | 1.50×10 -5 | 650 |
| A8 | 2.02×10 -5 | 561 |
| A9 | 1.78×10 -5 | 660 |
| A10 | 1.84×10 -5 | 532 |
| Comparative example 1 | 3.15×10 -5 | 51 |
| Comparative example 2 | 2.78×10 -5 | 60 |
| Comparative example 3 | 2.95×10 -5 | 68 |
| Comparative example 4 | 3.07×10 -5 | 46 |
The feasibility and prospect of popularization and application of the invention are predicted:
in the fields of automobiles, machinery and buildings, a large number of parts such as fasteners, pins, shafts, connecting rods and the like are processed by high-strength steel, and when the strength of the parts is higher than 1200MPa, unexpected delayed fracture is easy to occur in the using process, so that serious potential safety hazards exist. The invention provides a high-strength steel with hydrogen embrittlement resistance and delayed fracture, which realizes that the durability of the material in a hydrogen environment is greatly improved through alloy component design and structure regulation, has very wide application prospect in the fields of automobiles, machinery, buildings and the like in the future, and brings good economic benefit and social benefit.
While the invention has been described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing is a more particular description of the invention than is possible with reference to the specific embodiments, which are not to be construed as limiting the invention. Various changes in form and detail, including simple deductions or substitutions, may be made by those skilled in the art without departing from the spirit and scope of the invention.
Claims (10)
1. The high-strength steel with hydrogen embrittlement resistance and delayed fracture resistance is characterized by comprising the following chemical components in percentage by mass:
c:0.38-0.48%, si:0.03 to 0.12%, mn:0.23-0.43%, cr:1.00-1.40%, mo:0.30-0.50%, ni:0.15-0.40%, V:0.18-0.35%, nb:0.02 to 0.12%, al:0.025-0.045%, N: less than or equal to 0.0050 percent, and the balance of Fe and inevitable impurities.
2. The hydrogen embrittlement delayed fracture resistant high strength steel of claim 1, wherein the hydrogen embrittlement delayed fracture resistant high strength steel has a carbonitride precipitate size of V, nb of less than 70nm, and a material austenite grain size of less than 60um.
3. The hydrogen embrittlement delayed fracture resistant high strength steel according to claim 1, wherein the chemical composition content by mass further satisfies:
V/Nb is more than or equal to 2, and (V + Nb) × (C + N) is less than or equal to 0.16;
Al/(O+N)﹥5。
4. the hydrogen embrittlement delayed fracture resistant high strength steel as claimed in claim 2, wherein the inevitable impurities include: cu: less than or equal to 0.02%, P: less than or equal to 0.010 percent, S: less than or equal to 0.010 percent, O: less than or equal to 0.0008 percent.
5. The hydrogen embrittlement delayed fracture resistant high strength steel according to claim 3, wherein the chemical composition content by mass further satisfies: mn/S > 35.
6. The hydrogen embrittlement delayed fracture resistant high strength steel according to claim 4, wherein a microstructure of the hydrogen embrittlement delayed fracture resistant high strength steel has a refined tempered sorbite structure, and a strength of the hydrogen embrittlement delayed fracture resistant high strength steel is not less than 1200MPa.
7. A method for manufacturing a high-strength steel resistant to hydrogen embrittlement delayed fracture, comprising the steps of:
smelting using the composition of the hydrogen embrittlement delayed fracture resistant high strength steel according to any one of claims 1 to 6;
casting;
rough rolling;
rolling the high-speed wire rod;
controlling cooling by stelmor, and controlling the structural transformation of the wire rod by adjusting the fan component of a stelmor line after the wire rod is rolled;
spheroidizing or quenching and tempering heat treatment;
drawing or straightening;
cold heading and quenching and tempering heat treatment or turning.
8. The method for producing a hydrogen embrittlement delayed fracture resistant high strength steel as claimed in claim 7, wherein in the alloy smelting step, the alloy is smelted in an electric furnace or a converter and then refined outside the furnace, and the high vacuum degassing time is more than 18 minutes.
9. The method of manufacturing a hydrogen embrittlement delayed fracture resistant high strength steel as claimed in claim 7, wherein in the casting step:
argon is adopted for protection;
adjusting parameters of drawing speed, cooling and tail end soft reduction in the casting process to control the core carbon segregation of the blank to be lower than 1.09;
and after eddy current inspection, magnetic powder inspection, grinding wheel die repair, magnetic powder inspection supplement and die repair, the blank is placed into a heating furnace for heating, the heating is controlled to be 960-1200 ℃, and the heat preservation time is 1.0-3.0 hours.
10. The method for manufacturing a hydrogen embrittlement delayed fracture resistant high-strength steel according to claim 7, wherein in the high-speed wire rod rolling step, a rolling speed is controlled to be 8-120m/s, and an inlet temperature of a finishing mill group is 750-980 ℃, an inlet temperature of a reducing sizing mill group is 750-980 ℃, and a spinning temperature is 700-900 ℃;
in the stelmor cooling control step, the stelmor line comprises fans F1-F14, wherein the air volume of the fans F1-F5 is 0-70%, the air volume of the fans F6-F12 is 0-60%, and the air volume of the fans F13-F14 is 0-50%; and
in the spheroidizing or thermal refining heat treatment step, the temperature of the spheroidizing heat treatment of the wire rod is 750-800 ℃, the heat preservation time is 4-15 hours, the wire rod is slowly cooled after heat preservation, the speed is lower than 20 ℃/h, the drawing reduction ratio of the wire rod is 5-30%, the heating temperature of the thermal refining heat treatment is 850-1000 ℃, and the tempering temperature is 425-600 ℃.
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