High-strength and high-toughness mine chain steel and manufacturing method thereof

Abstract

The application discloses a high-strength and high-toughness mine chain steel and a manufacturing method thereof. The high-strength and high-toughness mine chain steel comprises the following chemical components in percentage by mass: C: 0.20-0.30%, Si: 0.05-0.6%, Mn: 1.0-1.8%, Cr: 0.4-0.8%, Ni: 0.5-0.9%, Mo: 0.3-0.55%, Ti: 0.015-0.035%, Al: 0.02-0.05%, B: 0.0015-0.005%, N: 0.002-0.006%, and the balance of iron and inevitable impurities. The high-strength and high-toughness mine chain steel has high strength and excellent impact toughness, and can be widely applied to the fields requiring high-strength steel materials, such as ocean engineering and mine machinery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chain steel, in particular to a high-strength and high-toughness mining chain steel and a manufacturing method thereof. BACKGROUND

[0002] The mining round-link chain is an important component applied to the mechanized coal mining in the underground coal mine, which mainly serves as the transmission chain on the scraper conveyor, the scraper transfer machine, the coal mining machine and the coal plough to play a transmission role. In the actual use process, the mining round-link chain is required to have high strength and toughness, fatigue resistance, wear resistance and other properties to ensure normal use. Since the working environment of the coal mine is mostly underground with high humidity and many corrosive substances, the mining round-link chain is also required to have good corrosion resistance.

[0003] In the prior art, the mining round-link chain steel commonly used in the coal mining industry is usually the chain steel grade in “GB / T 10560-2017 Mining Welded Round-Link Chain Steel”, among which the high-strength mining round-link chain steel is mainly applied most widely in the form of 23MnNiMoCr54 steel (referred to as 54 steel) and other grades. In addition, in view of the requirements of different downstream users in actual application, a series of high-strength mining chain steels have been developed by domestic steel plants.

[0004] Chinese patent CN110714164B (“High-quality Cr54 steel for coal mine chain ring and production method thereof”, published on November 6, 2020) discloses a high-quality 54 steel for coal mine chain ring, which introduces carbon equivalent, cold crack sensitivity coefficient and hot crack sensitivity coefficient to ensure the welding performance of the chain steel and improve the cold brittleness resistance and hot brittleness resistance of the chain steel.

[0005] Chinese patent publication CN104532143A (“Mining large-specification and high-strength chain steel and manufacturing method thereof”, published on April 22, 2015) discloses an improved mining large-specification chain steel, which has a diameter of 40 to 100 mm, a yield strength of ≥980 MPa, a tensile strength of ≥1180 MPa, an elongation of ≥13%, a reduction of area of ≥50%, and a room temperature Charpy impact energy of >100 J.

[0006] In addition, some technologies have optimized the steel material on the basis of the composition of 54 steel. For example, Chinese patent publication CN111101078A (“Nickel-free high-strength mining round-link chain steel and production method thereof”, published on May 5, 2020) discloses a high-strength mining round-link chain steel without Ni element, which reduces the content of the noble metal element Ni alloy while increasing the content of C, Si, Cr and Mo alloy elements, thereby greatly reducing the production cost on the premise of ensuring the mechanical properties.

[0007] The above technology mainly prepares mine chain steel with high strength by optimizing the components, improves the wear resistance of the chain and obtains higher service life, and reduces the use cost of the chain.

[0008] However, it should be noted that in actual application, the working environment in the coal mine is usually humid, and the high-strength chain is inevitably affected by environmental corrosion during use. In addition, the high-strength chain has high stress and is sensitive to stress corrosion, and is prone to corrosion fatigue fracture during use (frequent brittle fracture occurs within a few months or even a few days under low load), which causes early failure of the chain.

[0009] Therefore, the inventors intend to provide a new type of chain steel with excellent comprehensive performance, which has high strength, excellent toughness and plasticity matching, and low production cost by optimizing the alloy components, and can well solve the problem of affecting the service life due to the mismatch of strength and toughness of the existing chain. SUMMARY

[0010] In view of the problem of affecting the service life due to the mismatch of strength and toughness of the existing chain, the purpose of the present application is to provide a high-strength and high-toughness mine chain steel and a manufacturing method thereof, which has high strength and toughness and plasticity matching, and good wear resistance and fatigue resistance by designing the alloy components and optimizing the preparation process.

[0011] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0012] The first aspect of the present application provides a high-strength and high-toughness mine chain steel, which comprises the following chemical components in percentage by mass: C: 0.20-0.30%, Si: 0.05-0.6%, Mn: 1.0-1.8%, Cr: 0.4-0.8%, Ni: 0.5-0.9%, Mo: 0.3-0.55%, Ti: 0.015-0.035%, Al: 0.02-0.05%, B: 0.0015-0.005%, N: 0.002-0.006%, and the balance is iron and inevitable impurities.

[0013] Preferably, in the inevitable impurities, P≤0.012%, S≤0.01%, O≤0.0015%, and H≤0.00015%.

[0014] Preferably, the components satisfy the following requirements: Ti / (O+2N)=2-4; wherein Ti, O and N are the mass percentage contents of the corresponding elements.

[0015] Preferably, the content ratio of B elements in the steel in solid solution form to the total B element content is: B 固 / B 总= 65-85%.

[0016] Preferably, the performance satisfies: yield strength Rp 0.2 ≥ 1150 MPa, tensile strength R m ≥ 1250 MPa, elongation A ≥ 13%, reduction of area Z ≥ 50%, room temperature impact energy A kv ≥ 60 J.

[0017] The second aspect of the present application provides a manufacturing method of the high-strength and high-toughness mining chain steel according to the first aspect of the present application, comprising the processes of electric furnace smelting, LF furnace refining, vacuum refining, continuous casting, rolling, quenching and tempering treatment; in the vacuum refining process, the steel is deslagged before tapping, and the settling time of the molten steel is greater than 10 minutes; the heating temperature of the quenching treatment is 850-980 ℃, and the holding time is 1-4 h; the tempering temperature of the tempering treatment is 400-550 ℃, the holding time is 1-3 h, and the steel is water-cooled to room temperature after tempering.

[0018] Preferably, in the electric furnace smelting process, molten iron and scrap steel are used as raw materials, foamed slag is generated throughout the electric furnace smelting process, the end-point C content of the molten steel is controlled to be 0.06-0.10%, and the molten steel tapping temperature is 1640-1680 ℃.

[0019] Preferably, in the electric furnace smelting process, the percentage of molten iron in the raw materials is controlled to be 30-60%.

[0020] Preferably, the LF furnace refining process comprises the following steps:

[0021] Lime and fluorite are added for slagging before LF refining;

[0022] Aluminum particles or silicon carbide are used for strengthening deoxidation and desulfurization, and aluminum wire is supplemented according to the target composition of Al in the molten steel;

[0023] The molten steel is tapped after adjusting the alloy composition and temperature of the molten steel to the target requirements.

[0024] Preferably, in the vacuum refining process, the molten steel after LF refining is deslagged, vacuum degassing refining is performed in a VD furnace or an RH furnace, Al is supplemented according to the chemical composition requirements of the molten steel, the free oxygen content in the molten steel is ensured to be lower than 5 ppm, Ca and ferrotitanium are added, boron iron is added after 5-10 minutes, and the composition of the molten steel is adjusted to the target composition.

[0025] Preferably, in the vacuum degassing refining in the VD furnace or the RH furnace, the strong stirring time is greater than 10 minutes under the condition that the vacuum degree is less than 67 Pa.

[0026] Preferably, the ferrotitanium is selected from titanium wire, and the boron iron is selected from boron wire.

[0027] Preferably, in the continuous casting process, full-range protection casting is adopted, the tundish liquid steel superheat is controlled to be 15-30 ℃, electromagnetic stirring is adopted at the crystallizer and the solidification end, and the process of light press-down 10-25 mm is adopted at the solidification end to obtain the ingot.

[0028] Preferably, in the continuous casting process, the continuous casting speed is 0.5-0.8 m / min, constant speed control is adopted, the specific water quantity of the secondary cooling water is 0.3-0.5 L / t, and the ingot is sent to a slow cooling pit for slow cooling.

[0029] Preferably, in the rolling process, the ingot obtained by continuous casting is sent into a heating furnace for heating and then rolling, the heating temperature is controlled to be 1150-1250 ℃, the heating holding time is 2-6 h, the starting rolling temperature is ≥1100 ℃, and the final rolling temperature is ≥850 ℃.

[0030] Preferably, in the rolling process, the ingot is sent into a slow cooling pit for slow cooling ≥24 h after being out of the heating furnace and being descaled by high-pressure water.

[0031] In the high-strength and high-toughness mine chain steel of the present application, the design principles of each chemical element are as follows:

[0032] C: C is an element necessary to ensure the strength of steel, increasing the C content in steel will increase the non-equilibrium structure transformation ability of steel, thereby significantly improving the strength of steel; the present application inhibits the diffusion of C element in steel to form shear type martensite phase change through quenching and tempering heat treatment process, thereby significantly improving the strength of steel. However, the C content in steel should not be too high, and too high C content will adversely affect the plasticity and toughness of steel, and will significantly increase the carbon equivalent of the material and deteriorate the welding performance of the steel. Based on this, the content of C element is controlled to be 0.20-0.30%.

[0033] Si: adding an appropriate amount of Si element in steel can improve the stability of austenite during cooling process and avoid the formation of coarse carbides. However, it should be noted that the Si content in steel should not be too high. When the Si content in steel is too high, the brittleness of the steel will increase. Based on this, the content of Si element is controlled to be 0.05-0.6%.

[0034] Mn: adding an appropriate amount of Mn can not only improve the stability of austenite in steel, but also improve the hardenability of steel. In addition, in the present application, Mn can also improve the strength of martensite in steel through solid solution strengthening, thereby improving the strength of steel. However, it should be noted that the Mn content in steel should not be too high. When the Mn content in steel is too high, the austenite grains after quenching heating will easily grow, and the harmful elements will also be promoted to segregate at the grain boundary. Based on this, the content of Mn element is controlled to be 1.0-1.8%.

[0035] Cr: Cr can improve the hardenability of the steel, form hardened martensite structure, and is beneficial to improve the strength of the steel. In addition, the carbide of Cr can slow down the grain growth of the heat affected zone at the welding joint, which is very beneficial to the welding structure of the mine chain. The addition of appropriate amount of Cr and Ni in the steel is beneficial to improve the corrosion resistance of the steel. However, it should be noted that the content of Cr element in the steel should not be too high. When the content of Cr element in the steel is too high, the carbide generated in the heat treatment process will consume a large amount of C element in the steel, and a large amount of carbide will gather at the grain boundary, which will reduce the toughness of the material and significantly increase the carbon equivalent, thereby reducing the flash welding performance of the chain steel. Therefore, the content of Cr element is controlled to be 0.4-0.8%.

[0036] Ni: Ni can exist in the steel in the form of solid solution. Ni element can be used with Cr element to significantly improve the hardenability of the steel. The addition of appropriate amount of Ni in the steel can reduce the carbon content of the eutectoid point, which is beneficial to improve the strength of the steel. In addition, according to the carbon equivalent formula, the coefficient of Ni is small, and the influence on the welding performance is small. However, Ni is a valuable alloying element, and excessive addition of Ni element will lead to the increase of production cost. Therefore, in order to obtain excellent performance while ensuring low production cost, the content of Ni element is controlled to be 0.5-0.9%.

[0037] Mo: Mo mainly exists in the steel in the form of solid solution, which can have a solid solution strengthening effect and is beneficial to improve the hardenability of the steel to form martensite during quenching. However, excessive Mo should not be added to the steel. When excessive Mo is added to the steel, it will significantly increase the carbon equivalent of the material, which is not beneficial to the flash welding performance of the chain steel; and Mo is a valuable alloying element, and excessive addition of Mo element will lead to the increase of production cost. Therefore, the content of Mo element is controlled to be 0.3-0.55%.

[0038] B: The main role of B is to increase the hardenability of the steel, thereby saving other relatively rare nickel, molybdenum and the like. However, B element is relatively active, and it has strong affinity with oxygen, nitrogen and the like, and can easily form boron oxide, boron nitride and the like, so that B element loses its own beneficial effect, causing the hardenability of the steel to fluctuate greatly and affecting the performance stability of the steel. Excessive B will form intermetallic compounds with Fe and segregate at the grain boundary, which is not beneficial to the toughness of the steel, and also has the tendency to increase the temper brittleness. Therefore, in the high-strength and high-toughness mine chain steel of the present application, the content of B element is controlled to be 0.0015-0.005%.

[0039] Ti: Ti element has strong affinity with nitrogen, oxygen and carbon, and the precipitation temperature is high, which is an effective element for fixing nitrogen and oxygen, thereby avoiding the combination of B element in steel with oxygen and nitrogen elements to lose the effect of improving hardenability. Ti forms fine precipitates in steel, which can improve the strength and toughness of the steel, especially the impact toughness at low temperature. However, when the content of Ti element in the steel is too high, coarse and angular particles will be formed during smelting and solidification, which reduces the impact toughness of the steel. Therefore, in the high-strength and high-toughness mining chain steel of the present application, the content of Ti element is controlled to be 0.015-0.035%.

[0040] Al: The main role of Al is deoxidation, in addition, A1N formed by the combination of Al and N can effectively refine the grain. However, it should be noted that the content of Al element in the steel should not be too high, because when the content of Al element in the steel is too high, it will affect the pouring performance of the steel, and will also damage the toughness of the steel. Therefore, in the high-strength and high-toughness mining chain steel of the present application, the mass percentage content of Al element is controlled to be 0.02-0.05%.

[0041] N: In the high-strength and high-toughness mining chain steel of the present application, N is an austenite forming element and also an MX type precipitate forming element, which plays a role in refining the grain; in the B-containing steel, the N element in the steel will combine with the B element, so that the B in the steel loses the alloying effect. In order to avoid the consumption of B element by N element, the content of N element in the steel must be strictly controlled, and in the high-strength and high-toughness mining chain steel of the present application, the mass percentage content of N element is controlled to be 0.002-0.006%.

[0042] In the high-strength and high-toughness mining chain steel of the present application, the content of impurity elements in mass percentage satisfies: P≤0.012%, S≤0.01%, O≤0.0015%, H≤0.00015%. P, S, O and H are all impurity elements in steel, and in the case of technical conditions, in order to obtain better performance and better quality of steel, the content of impurity elements in the material should be as low as possible.

[0043] Impurity elements P and S are both harmful elements in steel, which can deteriorate the performance of the steel. Although P can improve the corrosion resistance of the steel, but overall the side effects are greater. Therefore, the content of P element is controlled to be not more than 0.012%, and the content of S element is controlled to be not more than 0.01%.

[0044] Impurity element O can form oxides and complex inclusions with Al, Ti, B and other elements in steel, which is not conducive to the performance of the steel. Therefore, the content of O element is controlled to be not more than 0.0015%.

[0045] Impurity element H will gather at defects in the steel. Especially high-strength steel with tensile strength exceeding 1000 MPa is sensitive to H content. Hydrogen-induced delayed fracture caused by element H will lead to early failure of the chain. Therefore, the content of H element is controlled to be no more than 0.00015%.

[0046] In other embodiments, other harmful elements such as elements As, Pb, Sn, Sb, Bi, etc. can also exist in the steel. Under the requirements of national laws, regulations and standards, the content of these harmful elements should be reduced as much as possible.

[0047] For the present application, by reasonable design of main alloying elements, the performance of the steel is improved by adding element B, the addition amount of expensive alloying elements Ni and Mo is reduced, the influence of various alloying elements and their interaction on microstructure and mechanical properties is fully utilized, and the microstructure of the steel is precisely controlled, so that the high-strength steel of the present application has high strength and toughness plasticity matching, and has good wear resistance and fatigue resistance.

[0048] In specific embodiments, in order to ensure that the B element in the steel can play a role in the steel in solid solution form, the high-strength high-toughness mine chain steel of the present application uses Ti to fix O and N in the steel, and the composition satisfies:

[0049] Ti / (O+2N)=2~4;

[0050] In the formula, Ti, O and N are respectively substituted into the mass percentage content of the corresponding element.

[0051] In the technical scheme of the present application, the strength and toughness of the alloy are mainly adjusted by Mn, Ni, Mo, Cr, B and other elements except C element, so that the high-strength and high-toughness chain steel is obtained, wherein the B element is used to replace part of the Ni and Mo elements to reduce the production cost of the chain steel. Since the B element is easy to combine with N, O and other elements in the steel, thereby losing the effect of improving the hardenability, a certain amount of Ti element is added in the steel to fix the O and N elements in the steel. When the Ti / (O+2N) value in the steel is in the range of 2-4 during the component design, the effect of the Ti in fixing the O and N in the steel can be fully played, and in order to ensure the stable effect of the B element in improving the hardenability of the steel and replacing the Ni and Mo elements, the proportion of the B element in the steel in the form of solid solution to the total amount of the B element in the steel should reach 65-85%; when the Ti / (O+2N) in the steel is relatively low and less than 2, the O and N elements in the steel cannot be completely fixed by the Ti, and are easy to combine with the B element in the steel to form boron-containing nitrides or oxides, thereby partially or completely invalidating the B element in the steel, causing the hardenability of the steel to fluctuate sharply, and affecting the use performance of the steel; when the Ti / (O+2N) in the steel is relatively high and greater than 4, there are more surplus Ti elements in the steel, which will combine with the C element in the steel and continue to precipitate and grow in the form of TiN during the solidification and cooling process of the steel, thereby forming larger Ti(C, N) particles with sharp edges and corners, which are easy to reduce the impact and fatigue performance of the chain steel, and are not conducive to the use of the chain steel.

[0052] Compared with the existing production technology, the present application has the following beneficial effects:

[0053] 1. In the high-strength and high-toughness chain steel of the present application, reasonable chemical component design is adopted and the manufacturing process is optimized, the strengthening elements such as Si, Mn, Ni, Cr, Mo in the steel are optimized, a certain amount of B element is added to replace the expensive alloy Ni and Mo elements, the hardenability of the mining chain steel is improved, and at the same time, the content and matching relationship of Ti, N and O elements in the steel are controlled, in addition, the proportion of the B element in the steel in the form of solid solution to the total amount of the B element in the steel reaches 65-85%, the effect of the B element in effectively improving the hardenability of the steel is fully played, and the performance fluctuation of the steel is prevented; through reasonable quenching + tempering heat treatment process, the steel can obtain good strength and plasticity and strength and toughness matching;

[0054] 2. The high-strength and high-toughness chain steel of the present application has reasonable chemical composition and process design, wide process window and convenient production and manufacturing, and can realize batch commercial production;

[0055] 3. The high-strength and high-toughness chain steel obtained by the method of the present application has good strength and toughness, and can be widely used in mining, ocean engineering and other occasions requiring high-strength steel. BRIEF DESCRIPTION OF DRAWINGS

[0056] Other features, objects, and advantages of the application will become more apparent from the following detailed description of non-limiting embodiments thereof, when read in conjunction with the accompanying drawings:

[0057] Figure 1 Scanning electron microscope image of high-strength and high-toughness mine chain steel manufactured for Example 1 of the application; DETAILED DESCRIPTION

[0058] In order to better understand the above technical solutions of the application, the technical solutions of the application are further described below in conjunction with examples.

[0059] The application provides a high-strength and high-toughness mine chain steel, which comprises more than 90% of Fe and inevitable impurities, and further comprises the following chemical components in percentage by mass: C: 0.20-0.30%, Si: 0.05-0.6%, Mn: 1.0-1.8%, Cr: 0.4-0.8%, Ni: 0.5-0.9%, Mo: 0.3-0.55%, Ti: 0.015-0.035%, Al: 0.02-0.05%, B: 0.0015-0.005%, and N: 0.002-0.006%.

[0060] It is found through research that when the composition of the steel meets the above chemical components and the content meets the above range, the chain steel will show excellent performance; in the application, the content of the components is in percentage by mass, unless otherwise explicitly stated.

[0061] In the high-strength and high-toughness mine chain steel of the application, P, S, O and H are all impurity elements in the steel. In the case where the technical conditions permit, in order to obtain steel materials with better performance and quality, the content of the impurity elements in the material should be reduced as much as possible. Therefore, among the inevitable impurities, P≤0.012%, S≤0.01%, O≤0.0015%, and H≤0.00015%.

[0062] In order to ensure that the B element in the steel can play a role in the steel in a solid solution form, in the high-strength and high-toughness mine chain steel of the application, the Ti, O and N elements should meet the following requirements: Ti / (O+2N)=2-4; in the formula, Ti, O and N are the mass percentage contents of the corresponding elements.

[0063] In the technical scheme of the present application, the strength and toughness of the alloy are mainly adjusted by Mn, Ni, Mo, Cr, B and other elements except C element, so as to obtain the high-strength and high-toughness chain steel, wherein the B element is used to replace part of the Ni and Mo elements to reduce the production cost of the chain steel. Since the B element is easy to combine with N, O and other elements in the steel, thereby losing the effect of improving the hardenability, a certain amount of Ti element is added in the steel to fix the O and N elements in the steel. When the Ti / (O+2N) value in the steel is in the range of 2-4 during the component design, the effect of the Ti in fixing the O and N in the steel can be fully played. In addition, in order to ensure the stable effect of the B element in improving the hardenability of the steel and replacing the Ni and Mo elements, the proportion of the B element in the steel in the form of solid solution to the total amount of the B element in the steel reaches 65-85%. When the Ti / (O+2N) in the steel is relatively low and less than 2, the O and N elements in the steel cannot be completely fixed by the Ti, and are easy to combine with the B element in the steel to form boron-containing nitrides or oxides, thereby partially or completely invalidating the B element in the steel, causing the hardenability of the steel to fluctuate sharply, and affecting the use performance of the steel. When the Ti / (O+2N) in the steel is relatively high and greater than 4, there are more surplus Ti elements in the steel, which will combine with the C element in the steel and continue to precipitate and grow in the form of TiN during the solidification and cooling process of the steel, thereby forming larger Ti(C, N) particles. Such particles have sharp edges and corners, and are easy to reduce the impact and fatigue performance of the chain steel, which is not conducive to the use of the chain steel.

[0064] The high-strength and high-toughness mining chain steel has the following performances: yield strength Rp 0.2 ≥ 1150 MPa, tensile strength R m ≥ 1250 MPa, elongation A ≥ 13%, reduction of area Z ≥ 50%, and room temperature impact energy A kv ≥ 60 J.

[0065] The present application further provides a manufacturing method of the high-strength and high-toughness mining chain steel, which has simple production process and good strength and toughness. The manufacturing method comprises the following steps of electric furnace smelting, LF furnace refining, vacuum refining, continuous casting, rolling, quenching and tempering treatment.

[0066] (1) Electric furnace smelting

[0067] The molten iron and scrap steel are used as raw materials, and the percentage of the molten iron in the raw materials is controlled to be 30-60%. The whole process of the electric furnace smelting is controlled to generate foamed slag, so as to ensure good oxidation boiling, promote the floating of the inclusions and gas in the steel, control the final C content of the molten steel to be 0.06-0.10%, and control the molten steel tapping temperature to be 1640-1680℃.

[0068] (2) LF furnace refining

[0069] The molten steel smelted by the electric furnace is refined in the LF furnace station, and appropriate lime and fluorite are added in the early stage of LF refining to improve the fluidity of the slag.

[0070] Aluminum particles or silicon carbide are used for strengthening deoxidation and desulfurization, and aluminum wire is fed according to the target composition of Al in the molten steel;

[0071] After adjusting the alloy composition and temperature of the molten steel to meet the target requirements, the molten steel is tapped to ensure the stability of the steel performance and the temperature requirements of the continuous casting process.

[0072] (3) Vacuum refining:

[0073] The molten steel after LF refining is subjected to slagging treatment, and vacuum degassing refining is carried out in the VD furnace or RH furnace. The vacuum degree is less than 67 Pa, and the strong stirring time is greater than 10 minutes. After vacuum refining, alloying elements are supplemented according to the chemical composition requirements of the molten steel. Specifically, Al is supplemented first to ensure that the free oxygen content in the molten steel is less than 5 ppm, then Ca and ferrotitanium are added, and 5-10 minutes later, boron iron is added to adjust the composition of the molten steel to the target composition; among them, ferrotitanium is selected as titanium wire, and boron iron is selected as boron wire, both of which are added by wire feeder to improve the alloy yield and composition stability. The molten steel is settled for more than 10 minutes, and the composition and temperature are qualified before tapping.

[0074] (4) Continuous casting

[0075] Full protection pouring is adopted to prevent secondary oxidation and nitrogen increase of the molten steel; low superheat pouring is adopted to control the superheat of the molten steel in the tundish to be 15-30℃, electromagnetic stirring is adopted in the crystallizer and solidification end, and light press-down of 10-25mm is adopted in the solidification end to reduce internal segregation and other defects of the ingot and improve the quality of the ingot. The continuous casting speed during continuous casting is 0.5-0.8m / min, constant speed control is adopted, and the specific water consumption of the secondary cooling water is 0.3-0.5L / t. The ingot is hot sent or slow cooled in the slow cooling pit.

[0076] (5) Rolling, the ingot obtained by continuous casting is sent to the heating furnace for heating, and the heating temperature of the ingot is controlled to be 1150-1250℃, and the heating and holding time is 2-6h; then rolling is carried out, and the opening rolling temperature is controlled to be ≥1100℃, and the final rolling temperature is controlled to be ≥850℃; the round steel after rolling is straightened, inspected and polished to remove surface defects.

[0077] The specification of the round steel after the above rolling is Φ26-100mm. In addition, the ingot is rolled after high-pressure water descaling, and the rolled ingot is slow-cooled in the holding pit for ≥24h.

[0078] (6) Quenching and tempering: the round steel after rolling is subjected to quenching and tempering treatment, wherein the heating temperature of quenching treatment is 850-980°C, and the holding time is 1-4h; the tempering temperature of tempering treatment is 400-550°C, and the holding time is 1-3h, and the quenched steel is water-cooled to room temperature after tempering.

[0079] After quenching treatment, the steel forms a martensite structure with fine lamellar structure, and the alloying elements in the steel exist in the form of supersaturated solid solution in the martensite, so that the strength is high but the plasticity and impact toughness are relatively poor. After tempering heat treatment, the supersaturated alloying elements in the martensite are dispersedly precipitated in the form of nanoscale carbides between the martensite lamellae, which can greatly improve the strength of the steel, and also can avoid the generation of temper brittleness, so that the high-strength and high-toughness mining chain steel has high strength and excellent impact performance.

[0080] The high-strength and high-toughness mining chain steel and the manufacturing method thereof will be further described below with specific examples.

[0081] Examples

[0082] The high-strength and high-toughness mining chain steels of Examples 1-6 are prepared by the following steps:

[0083] (1) The molten steel is smelted and continuously cast according to the proportions shown in Table 1 to obtain a casting blank. The end point [C] is controlled to 0.06-0.10% during electric furnace smelting, and the molten steel temperature is controlled to 1640-1680°C.

[0084] (2) LF furnace refining: the molten steel after electric furnace smelting is refined in the LF furnace station, and aluminum particles or silicon carbide are used for strengthening deoxidation and desulfurization, and aluminum wire is added according to the target value of the Al content in the molten steel to ensure that the free oxygen content in the molten steel is less than 5ppm; the molten steel is tapped after adjusting the alloy composition and temperature to meet the target requirements.

[0085] (3) VD / RH vacuum refining treatment: the molten steel after LF furnace refining is subjected to slagging treatment, and vacuum degassing refining treatment is carried out in the VD or RH furnace, and the vacuum degree is less than 67Pa, the strong stirring time is greater than 10 minutes, and after vacuum refining, Al is added to ensure that the free oxygen content in the molten steel is less than 5ppm, and then Ca and ferrotitanium are added, and boron iron is added after 5 minutes, and the molten steel is adjusted to the target composition. The molten steel is held for more than 10 minutes, and the composition and temperature are qualified, and the molten steel is tapped.

[0086] (4) Continuous casting: full-range protection casting is adopted to prevent secondary oxidation of molten steel and nitrogen increase in the process; low superheat casting is adopted, the molten steel superheat in the tundish is controlled to be 15-30°C, electromagnetic stirring is adopted at the crystallizer and the solidification end, 10-25 mm light press-down is adopted at the solidification end to reduce internal segregation and other defects of the ingot and improve the ingot quality. The continuous casting speed is 0.5-0.8 m / min, constant speed control is adopted, and the specific water consumption of the secondary cooling water is 0.3-0.5 l / t. The continuous casting billet is hot sent or sent to the slow cooling pit for slow cooling.

[0087] (5) Rolling: the ingot obtained by continuous casting is sent to a heating furnace for heating, and the heating temperature of the ingot is controlled to be 1150-1250°C, and the heating holding time is 2-6 h. The continuous casting billet opening rolling temperature is controlled to be ≥1100°C, and the finish rolling temperature is ≥850°C. The round steel after rolling is straightened, inspected, and polished to remove the surface defects. The round steel after rolling is sent to the holding pit for slow cooling ≥24 h.

[0088] (6) Quenching and tempering: the round steel after rolling is quenched and tempered, wherein the quenching heating temperature is 850-980°C, the holding time is 1-4 h; the tempering temperature is 400-550°C, the holding time is 1-3 h, and the round steel after tempering is water cooled to room temperature.

[0089] Comparative Example 1 and Comparative Example 2 are prepared by adopting the electric furnace+LF+RH+continuous casting+quenching and tempering process, and the difference lies in that the composition and content of the steel and the process parameters are different from those of the present application, and the specific contents are shown in Table 1-1, Table 1-2, Table 2-1 and Table 2-2.

[0090] Table 1-1 Chemical composition of chain steel (wt%, the balance is Fe and other impurities except P, S, N, O and H)

[0091]

[0092] Table 1-1

[0093]

[0094] Table 2-1 Process parameters in the manufacturing process of examples and comparative examples

[0095]

[0096] Table 2-2 Process parameters in the manufacturing process of examples and comparative examples

[0097] Quenching temperature (°C) Soaking time (h) Tempering temperature (°C) Tempering time (h) Example 1 980 1 390 2 Example 2 880 1 400 1 Example 3 930 2 410 1 Example 4 910 2 450 2 Example 5 850 4 430 3 Example 6 950 3 440 3 Comparative Example 1 880 1 410 1 Comparative Example 2 880 1 430 1

[0098] The chain steels obtained in Examples 1-6 and Comparative Examples 1-2 were sampled respectively to obtain corresponding chain steel samples. The obtained chain steels were subjected to tensile test and charpy impact test to obtain the performance data of the chain steels of the examples and comparative examples, and the test results are shown in Table 3.

[0099] The test methods of the relevant performance parameters are as follows:

[0100] Tensile test: According to the national standard GB / T 2975, the chain steels of Examples 1-6 and Comparative Examples 1-2 were sampled and tensile samples were prepared, and the tensile performance test was carried out according to the national standard GB / T 228.1.

[0101] Charpy impact test: According to the national standard GB / T 2975, the chain steels of Examples 1-6 and Comparative Examples 1-2 were sampled and impact samples were prepared, and the impact performance test was carried out according to the national standard GB / T 229.

[0102] Table 3 Performance of chain steels of examples and comparative examples

[0103]

[0104] In combination with Table 3, the high-strength and high-toughness mining chain steels prepared in Examples 1-6 of the present application have excellent comprehensive performance, with yield strength Rp 0.2 ≥ 1186 MPa, tensile strength R m ≥ 1293 MPa, elongation A ≥ 13.5%, reduction of area Z ≥ 50%, and room temperature impact energy A kv ≥ 74 J. It can be seen that the high-strength and high-toughness mining chain steels of the present application are significantly better than the chain steels in Comparative Examples 1 and 2.

[0105] In combination with Table 1 and Table 3, it can be seen that compared with the chain steels of Comparative Examples 1 and 2, the chemical composition of the high-strength and high-toughness mining chain steels of Examples 1-6 of the present application falls within the scope claimed, and the optimized quenching + tempering heat treatment process is adopted to obtain higher strength while having excellent impact toughness.

[0106] Figure 1 The scanning electron microscope image of the microstructure of the high-strength and high-toughness mining chain steel after quenching + tempering heat treatment in Example 1 is shown. In combination with Figure 1 it can be seen that in Example 1, the microstructure of the high-strength and high-toughness mining chain steel after quenching + tempering heat treatment is tempered martensite, the martensite lamellar spacing is small, and fine dispersed nanoscale carbides are precipitated between the martensite lamellar. The fine nanoscale carbides can greatly improve the strength and toughness of the steel, thereby obtaining a high-strength and high-toughness mining chain steel with excellent performance.

[0107] In conclusion, the high-strength and high-toughness mine chain steel with excellent performance is obtained by reasonable chemical component design and optimized process, and can be widely applied to the fields of ocean engineering, mine machinery and other fields requiring high-strength steel.

[0108] It should be noted that the above embodiments are only used to illustrate the present application, and are not used as a limitation to the present application, and as long as the changes and modifications of the above described embodiments are within the scope of the spirit of the present application, they will fall within the scope of the claims of the present application.

Claims

1. A high-strength, high-toughness mining chain steel, characterized in that, The composition includes the following chemical components by mass percentage: C: 0.20–0.30%, Si: 0.05–0.6%, Mn: 1.0–1.8%, Cr: 0.4–0.8%, Ni: 0.5–0.9%, Mo: 0.3–0.55%, Ti: 0.015–0.035%, Al: 0.02–0.05%, B: 0.0015–0.005%, N: 0.002–0.006%, with the balance being iron and unavoidable impurities. Its composition meets the following requirements: Ti / (O+2N) = 2~4; where Ti, O, and N are the mass percentage contents of the corresponding elements, respectively. In the high-strength, high-toughness mining chain steel, the proportion of element B existing in solid solution to the total amount of element B is B. 固 / B 总 =65~85%, Its properties satisfy: yield strength Rp 0.2 ≥1150MPa, tensile strength R m ≥1250 MPa, elongation A≥13%, reduction of area Z≥50%, room temperature impact energy A kv ≥60J.

2. The high-strength, high-toughness mining chain steel according to claim 1, characterized in that, Of the unavoidable impurities, P ≤ 0.012%, S ≤ 0.01%, O ≤ 0.0015%, and H ≤ 0.00015%.

3. A method for manufacturing high-strength, high-toughness mining chain steel as described in any one of claims 1-2, characterized in that, The process includes electric furnace smelting, LF furnace refining, vacuum refining, continuous casting, rolling, quenching, and tempering. During the vacuum refining process, the molten steel is calmed for more than 10 minutes before tapping. The quenching process is heated to 850–980℃ and held for 1–4 hours. The tempering process is held to 400–550℃ and held for 1–3 hours, followed by water cooling to room temperature.

4. The method for manufacturing high-strength, high-toughness mining chain steel according to claim 3, characterized in that, In the electric arc furnace smelting process, molten iron and scrap steel are used as raw materials. Foam slag is generated throughout the electric arc furnace smelting process. The final carbon content of the molten steel is controlled at 0.06-0.10%, and the tapping temperature of the molten steel is 1640-1680℃.

5. The method for manufacturing high-strength, high-toughness mining chain steel according to claim 4, characterized in that, During the electric furnace smelting process, the percentage of molten iron in the raw materials is controlled to be 30-60%.

6. The method for manufacturing high-strength, high-toughness mining chain steel according to claim 3, characterized in that, The LF furnace refining process includes the following steps: Lime and fluorite are added to form slag in the early stage of LF refining; Aluminum granules or silicon carbide are used to enhance deoxidation and desulfurization, and aluminum wire is fed in accordance with the target Al composition of the molten steel. After adjusting the alloy composition and temperature of the molten steel to the target requirements, the steel is tapped.

7. The method for manufacturing high-strength, high-toughness mining chain steel according to claim 3, characterized in that, In the vacuum refining process, the molten steel after LF refining is slag-removed and then vacuum degassing and refining is carried out in a VD furnace or RH furnace. Al is added according to the chemical composition requirements of the molten steel to ensure that the free oxygen content in the molten steel is below 5ppm. Then, Ca and ferrotitanium are added, and ferroboron is added after 5 to 10 minutes. The composition of the molten steel is then adjusted to the target composition.

8. The method for manufacturing high-strength, high-toughness mining chain steel according to claim 7, characterized in that, When performing vacuum degassing refining in the VD furnace or RH furnace, the strong stirring time is greater than 10 minutes under a vacuum degree of less than 67 Pa.

9. The method for manufacturing high-strength, high-toughness mining chain steel according to claim 7, characterized in that, The ferrotitanium is made of titanium wire, and the ferroboronium is made of boron wire.

10. The method for manufacturing high-strength, high-toughness mining chain steel according to claim 3, characterized in that, During the continuous casting process, full-process protective pouring is adopted, the superheat of molten steel in the tundish is controlled at 15-30 minutes, electromagnetic stirring is used in the crystallizer and at the end of solidification, and the ingot is obtained by lightly pressing down 10-25mm at the end of solidification.

11. The method for manufacturing high-strength, high-toughness mining chain steel according to claim 10, characterized in that, The continuous casting speed during the continuous casting process is 0.5 to 0.8 m / min, and constant casting speed control is adopted. The secondary cooling water ratio is 0.3 to 0.5 L / t, and the ingot is hot-sent or slowly cooled in a slow cooling pit.

12. The method for manufacturing high-strength, high-toughness mining chain steel according to claim 4, characterized in that, During the rolling process, the ingot obtained from continuous casting is fed into a heating furnace for heating and then rolled. The heating temperature is controlled at 1150-1250℃, the heating and holding time is 2-6 hours, the initial rolling temperature is ≥1100℃, and the final rolling temperature is ≥850℃.

13. The method for manufacturing high-strength, high-toughness mining chain steel according to claim 12, characterized in that, During the rolling process, the ingot is descaled by high-pressure water after exiting the heating furnace and then rolled. After rolling, it is placed in a heat preservation pit for slow cooling for ≥24 hours.

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