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

Abstract

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

Description

Technical Field

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

[0002] Mining round chain is an important component used in mechanized coal mining in coal mines. It is mainly used as a transmission chain on scraper conveyors, scraper transfer machines, coal mining machines and coal plows to play a transmission role. In actual use, mining round 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 coal mines is mostly humid and corrosive underground, mining round chain is usually also required to have good corrosion resistance.

[0003] In the existing technology, 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 high-strength mining round link chain steel is mainly 23MnNiMoCr54 steel (referred to as 54 steel) and other grades are the most widely used; in addition, in response to the needs of different downstream users in actual applications, major domestic steel mills have developed a series of high-strength mining chain steel.

[0004] Chinese patent CN110714164B ("A high-quality Cr54 steel for coal mine chain links and its production method", published on November 6, 2020) discloses a high-quality 54 steel for coal mine chain links, 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 number CN104532143A ("A large-size, high-strength chain steel for mining and its manufacturing method", published on April 22, 2015) discloses an improved large-size chain steel for mining, with a diameter of 40 to 100 mm, a yield strength of ≥980 MPa, a tensile strength of ≥1180 MPa, an elongation of ≥13%, a cross-sectional shrinkage of ≥50%, and a room temperature Charpy impact energy of >100 J.

[0006] In addition, there are some technologies that optimize steel based on the composition of 54 steel. For example, Chinese patent publication number CN111101078A ("A nickel-free high-strength mining round link chain steel and its production method", published on May 5, 2020) discloses a high-strength mining round link chain steel that does not contain Ni elements. By reducing the alloy content of precious metal element Ni and increasing the content of alloy elements C, Si, Cr, and Mo, the production cost is greatly reduced while ensuring mechanical properties.

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

[0008] However, it should be noted that in actual application, the working environment underground in coal mines is mostly humid, and high-strength chains are inevitably affected by environmental corrosion during use. In addition, high-strength chains have high stress and are also sensitive to stress corrosion. They are prone to corrosion fatigue fracture in the middle of use (frequent low-load brittle fractures occur within a few months or even a few days), causing the chain to fail early.

[0009] Based on this, the inventors intend to provide a new type of chain steel with excellent comprehensive performance. By optimizing the alloy composition, it not only has high strength, but also has excellent toughness-plasticity matching and low production cost. It can well solve the problem of existing chains affecting service life due to mismatch between strength and toughness-plasticity. Summary of the invention

[0010] In view of the problem that the service life of the chains in the prior art is affected by the mismatch between strength, toughness and plasticity, the purpose of the present invention is to provide a high-strength and high-toughness mining chain steel and a manufacturing method thereof. By designing the alloy composition and optimizing the preparation process, a high-strength and high-toughness mining chain steel with high strength and matching toughness and plasticity, as well as good wear resistance and fatigue resistance is prepared.

[0011] To achieve the above object, the present invention adopts the following technical solution:

[0012] The first aspect of the present invention provides a high-strength and high-toughness mining chain steel, comprising the following chemical components in 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%, and the remainder is iron and unavoidable impurities.

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

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

[0015] Preferably, the B element existing in the solid solution form in the steel accounts for the total B element content: 固 / B 总=65~85%.

[0016] Preferably, its performance meets the following requirements: yield strength Rp 0.2 ≥1150MPa, tensile strength R m ≥1250MPa, elongation A≥13%, section shrinkage Z≥50%, room temperature impact energy A kv ≥60J.

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

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

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

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

[0021] In the early stage of LF refining, lime and fluorite are added to form slag;

[0022] Use aluminum particles or silicon carbide to strengthen deoxidation and desulfurization, and feed aluminum wire according to the target composition of Al in molten steel;

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

[0024] Preferably, during the vacuum refining process, the molten steel after LF refining is subjected to slag treatment, vacuum degassing refining is carried out in a VD furnace or a RH furnace, Al is supplemented according to the chemical composition requirements of the molten steel to ensure that the free oxygen content in the molten steel is less than 5ppm, Ca and ferrotitanium are added, and ferroboron is added after 5 to 10 minutes to adjust the composition of the molten steel to the target composition.

[0025] Preferably, when vacuum degassing and refining are carried out in the VD furnace or the RH furnace, the strong stirring time is greater than 10 minutes under the condition of a vacuum degree of less than 67 Pa.

[0026] Preferably, the ferrotitanium is made of titanium wire, and the ferroboron is made of boron wire.

[0027] Preferably, during the continuous casting process, full-process protective pouring is adopted, the superheat of the molten steel in the tundish is controlled to be 15-30°C, electromagnetic stirring is used in the crystallizer and at the end of solidification, and a process of lightly pressing down 10-25 mm at the end of solidification is used to obtain the ingot.

[0028] Preferably, the continuous casting speed in the continuous casting process is 0.5-0.8 m / min, constant pulling speed control is adopted, the secondary cooling water ratio is 0.3-0.5 L / t, and the ingot is hot transported or slowly cooled in a slow cooling pit.

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

[0030] Preferably, during the rolling process, the ingot is removed from the heating furnace and descaled with high-pressure water before rolling begins, and after rolling, it is placed in a heat preservation pit for slow cooling for ≥24 hours.

[0031] In the high-strength and high-toughness mining chain steel of the present invention, 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 structural transformation ability of steel, thereby significantly improving the strength of steel. The present invention uses a quenching and tempering heat treatment process to inhibit the diffusion of C elements in steel to form a shear-type martensitic phase transformation, thereby significantly improving the strength of steel. However, the C content in steel should not be too high. Excessive C content will have an adverse effect on 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 0.20-0.30%.

[0033] Si: Adding an appropriate amount of Si to steel can improve the stability of austenite during cooling 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, it will increase the brittleness of the steel. Based on this, the Si content is controlled to 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 invention, 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, it will make the quenching and heating austenite grains easy to grow, and will also promote the segregation of harmful elements at the grain boundaries. Based on this, the content of Mn element is controlled to 1.0-1.8%.

[0035] Cr: Cr can improve the hardenability of steel, form a hardened martensitic structure, and help improve the strength of steel. In addition, Cr carbides can slow down the grain growth in the heat-affected zone at the welded joint, which is very beneficial to the welding structure of mining chains. Adding an appropriate amount of Cr and Ni to the steel is beneficial to improving the corrosion resistance of the steel. However, it should be noted that the Cr content in the steel should not be too high. When the Cr content in the steel is too high, the formation of carbides during the heat treatment process will consume a large amount of C in the steel, and a large amount of carbides will accumulate at the grain boundaries, reducing the toughness of the material and significantly increasing the carbon equivalent, thereby reducing the flash welding performance of the chain steel. Based on this, the Cr content is controlled to 0.4-0.8%.

[0036] Ni: Ni can exist in steel in the form of solid solution. Ni can be used in combination with Cr to significantly improve the hardenability of steel. Adding an appropriate amount of Ni to steel can reduce the carbon content of the eutectoid point, which is beneficial to improving the strength of steel. In addition, it can be seen from the carbon equivalent formula that the coefficient of Ni is small and has little effect on welding performance. However, Ni is a precious alloy element, and excessive addition of Ni will lead to increased production costs. Therefore, in order to obtain excellent performance while ensuring low production costs, the content of Ni is controlled to 0.5-0.9%.

[0037] Mo: Mo exists in steel mainly in the form of solid solution, which can play a solid solution strengthening effect, which is beneficial to improve the hardenability of steel and form martensite in the quenching process. However, it is not advisable to add excessive Mo to steel. When too much Mo is added to steel, the carbon equivalent of the material will be significantly increased, which is not conducive to the flash welding performance of chain steel; moreover, Mo is a precious alloy element, and excessive addition of Mo will lead to increased production costs. Based on this, the content of Mo is controlled to 0.3-0.55%.

[0038] B: The main function of B is to increase the hardenability of steel, thereby saving other rare and expensive nickel, molybdenum, etc. However, the B element is relatively active, and it has a strong affinity with elements such as oxygen and nitrogen, and is easy to form boron oxide, boron nitride, etc., which makes the B element lose its own beneficial effect, causing the fluctuation of the hardenability of steel to increase, affecting the stability of steel performance. Excessive B will form intermetallic compounds with Fe and segregate at the grain boundary, which is unfavorable to the toughness of steel and has a tendency to increase temper brittleness. Therefore, in the high-strength and high-toughness mining chain steel of the present invention, the B element content is controlled to be: 0.0015-0.005%.

[0039] Ti: Ti has a strong affinity with nitrogen, oxygen, and carbon, and has a high precipitation temperature. It is a good effective element for fixing nitrogen and oxygen, thereby preventing the B element in the steel from combining with oxygen and nitrogen elements and losing the effect of improving hardenability. Ti forms a fine precipitate phase in the steel, which can improve the strength and toughness of the steel, especially the impact toughness at low temperatures. However, when the Ti content in the steel is too high, coarse angular particles will be formed during the smelting and solidification process, reducing the impact toughness of the steel. Therefore, in the high-strength and high-toughness mining chain steel of the present invention, the Ti content is controlled to be 0.015-0.035%.

[0040] Al: The main function of Al is deoxidation. In addition, Al combined with N to form AlN can effectively refine the grains. However, it should be noted that the Al content in the steel should not be too high. When the Al content in the steel is too high, it will affect the casting performance of the steel and damage the toughness of the steel. Based on this, in the high-strength and high-toughness mining chain steel of the present invention, the mass percentage of the Al element is controlled between 0.02 and 0.05%.

[0041] N: In the high-strength and high-toughness mining chain steel of the present invention, N is an austenite-forming element and also an MX-type precipitate-forming element, which plays a role in refining grains; in B-containing steel, the N element in the steel will combine with the B element, thereby causing the B in the steel to lose its alloying effect. In order to avoid the N element consuming the B element, the N element content in the steel must be strictly controlled. In the high-strength and high-toughness mining chain steel of the present invention, the mass percentage of the N element is controlled to be between 0.002 and 0.006%.

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

[0043] Impurity elements P and S are both unavoidable harmful elements in steel, and both will deteriorate the performance of steel. Although P can improve the corrosion resistance of steel, it has greater side effects overall. Therefore, the P content is controlled to not exceed 0.012%, and the S content is controlled to not exceed 0.01%.

[0044] The impurity element O can form oxides and complex inclusions with elements such as Al, Ti, and B in the steel, which is not conducive to the performance of the steel. Therefore, the content of O is controlled to not exceed 0.0015%.

[0045] Impurity element H will accumulate at defects in steel. In particular, high-strength steel with a tensile strength of more than 1000 MPa is sensitive to H content. Hydrogen-induced delayed fracture caused by element H can lead to early failure of the chain. Therefore, the H element content is controlled to not exceed 0.00015%.

[0046] In other embodiments, other harmful elements may also exist in the steel, such as As, Pb, Sn, Sb, Bi, etc. 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 invention, by rationally designing the main alloying elements, the steel performance is improved by adding the B element, the addition amount of the expensive alloys Ni and Mo is reduced, the influence of various alloying elements and their interactions on the microstructure and mechanical properties is fully utilized, and the microstructure of the steel of the present invention is precisely controlled, so that the high-strength steel of the present invention has both high strength and toughness-plasticity matching, and has good wear resistance and fatigue resistance.

[0048] In a specific embodiment, in order to ensure that the B element in the steel can play a role in the steel in the form of solid solution, in the high-strength and high-toughness mining chain steel of the present invention, Ti is used to fix O and N in the steel, and its composition satisfies:

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

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

[0051] In the technical solution of the present invention, in addition to the C element, the strength and toughness of the alloy are adjusted mainly by Mn, Ni, Mo, Cr, B and other elements to obtain 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 easily combined 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 to the steel to fix the O and N elements in the steel. When designing the composition, when the Ti / (O+2N) value in the steel is within the range of 2 to 4, the role of Ti in fixing O and N in the steel can be fully exerted. In addition, in order to ensure the stable role of B element in improving the hardenability of steel and replacing Ni and Mo elements, the proportion of B element in the steel in the form of solid solution should reach 65-85% of the total amount of B element in the steel; when the Ti / (O+2N) in the steel is low, less than 2, the O and N elements in the steel cannot be completely fixed by Ti, and are easy to combine with the B element in the steel to form boron-containing nitrides or oxides, thereby making the B element in the steel partially or completely ineffective, resulting in a sharp fluctuation in the hardenability of the steel, affecting the performance of the steel; when the Ti / (O+2N) in the steel is high, greater than 4, there are more excess Ti elements in the steel, which will combine with the C element in the steel during the solidification and cooling process of the steel and continue to precipitate and grow with TiN as the core, thereby forming larger particles of Ti(C,N). Such particles have sharp edges and corners, which are easy to reduce the impact and fatigue properties of the chain steel, which is not conducive to the use of the chain steel.

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

[0053] 1. The high-strength and high-toughness chain steel of the present invention adopts a reasonable chemical composition design and an optimized manufacturing process, optimizes the strengthening elements such as Si, Mn, Ni, Cr, and Mo in the steel, and adds a certain amount of B element to replace the expensive alloy Ni and Mo elements to improve the hardenability of the mining chain steel. At the same time, by controlling the content and ratio of Ti, N, and O elements in the steel, in addition, the proportion of B element in the form of solid solution in the steel accounts for 65-85% of the total amount of B element in the steel, giving full play to the role of B element in effectively improving the hardenability of the steel and preventing the performance fluctuation of the steel; through a reasonable quenching + tempering heat treatment process, the steel can obtain a good match between strength and plasticity and strength and toughness;

[0054] 2. The high-strength and high-toughness chain steel of the present invention has reasonable chemical composition and process design during the smelting and rolling process, a wide process window, convenient production and manufacturing, and can achieve mass commercial production;

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

[0056] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0057] Figure 1 This is an electron microscope scanning image of the high-strength and high-toughness mining chain steel manufactured in Example 1 of the present invention; DETAILED DESCRIPTION

[0058] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with embodiments.

[0059] The present invention provides a high-strength and high-toughness mining chain steel, which, in addition to containing more than 90% of Fe and inevitable impurities, also 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%, and N: 0.002-0.006%.

[0060] It has been found through research that when the composition of the steel meets the above chemical composition and the content meets the above range, the chain steel will show excellent performance; in the present invention, unless otherwise explicitly stated, the component content is measured in mass percentage.

[0061] In the high-strength and high-toughness mining chain steel of the present invention, P, S, O and H are all impurity elements in the steel. Under the condition that technical conditions permit, in order to obtain steel with better performance and better quality, the content of impurity elements in the material should be reduced as much as possible. Therefore, among the unavoidable 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 the form of solid solution, in the high-strength and high-toughness mining chain steel of the present invention, the Ti, O, and N elements should meet the following requirements: Ti / (O+2N)=2~4; wherein Ti, O, and N are the mass percentage contents of the corresponding elements respectively.

[0063] In the technical solution of the present invention, in addition to the C element, the strength and toughness of the alloy are adjusted mainly by Mn, Ni, Mo, Cr, B and other elements to obtain 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 easily combined 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 to the steel to fix the O and N elements in the steel. When designing the composition, when the Ti / (O+2N) value in the steel is within the range of 2 to 4, the role of Ti in fixing O and N in the steel can be fully exerted. In addition, in order to ensure the stable role of B element in improving the hardenability of steel and replacing Ni and Mo elements, the proportion of B element in the steel in the form of solid solution accounts for 65-85% of the total amount of B element in the steel; when the Ti / (O+2N) in the steel is low, less than 2, the O and N elements in the steel cannot be completely fixed by Ti, and are easily combined with the B element in the steel to form boron-containing nitrides or oxides, thereby partially or completely failing the B element in the steel, causing the hardenability of the steel to fluctuate violently, affecting the performance of the steel; when the Ti / (O+2N) in the steel is high, greater than 4, there are more excess Ti elements in the steel, which will combine with the C element in the steel during the solidification and cooling process of the steel and continue to precipitate and grow with TiN as the core, thereby forming larger particles of Ti(C,N). Such particles have sharp edges and corners, which are easy to reduce the impact and fatigue properties of the chain steel, which is not conducive to the use of the chain steel.

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

[0065] The present invention also provides a method for manufacturing the above-mentioned high-strength and high-toughness mining chain steel. The production process is simple, and the prepared high-strength and high-toughness mining chain steel has good strength and toughness. The process adopts electric furnace smelting, LF furnace refining, vacuum refining, continuous casting, rolling, quenching and tempering treatment steps; the specific process is as follows:

[0066] (1) Electric furnace smelting

[0067] Molten iron and scrap steel are used as raw materials, and the percentage of molten iron in the raw materials is controlled to be 30-60%. Foamy slag is produced during the entire electric furnace smelting process to ensure good oxidation boiling, promote the floating of inclusions and gases in the steel, control the endpoint C content of the molten steel to be 0.06-0.10%, and the molten steel tapping temperature to be 1640-1680°C.

[0068] (2) LF furnace refining

[0069] The molten steel smelted in the electric furnace enters the LF furnace station for refining. In the early stage of LF refining, appropriate amounts of lime and fluorite are added to make slag to improve the fluidity of the slag.

[0070] Use aluminum particles or silicon carbide to strengthen deoxidation and desulfurization, and feed aluminum wire according to the target composition of Al in molten steel;

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

[0072] (3) Vacuum refining:

[0073] The molten steel after LF refining is subjected to slag treatment, and vacuum degassing refining is carried out in a VD furnace or RH furnace, and the strong stirring time is greater than 10 minutes under the condition of vacuum degree less than 67Pa. After vacuum refining, alloy elements are added according to the chemical composition requirements of the molten steel. Specifically, Al is added first to ensure that the free oxygen content in the molten steel is less than 5ppm, and then Ca and ferrotitanium are added. After 5 to 10 minutes, ferroboron is added to adjust the composition of the molten steel to the target composition; ferrotitanium uses titanium wire and ferroboron uses boron wire, both of which are added by a wire feeder to improve the alloy yield and composition stability. The molten steel is calmed for more than 10 minutes, and the steel is tapped after the composition and temperature are qualified.

[0074] (4) Continuous casting

[0075] The whole process of protection casting is adopted to prevent secondary oxidation and nitrogen addition of molten steel; low superheat casting is adopted to control the superheat of molten steel in the middle package to 15-30℃, electromagnetic stirring is adopted in the crystallizer and at the end of solidification, and the ingot is obtained by light pressure of 10-25mm at the end of solidification to reduce defects such as internal segregation of the ingot and improve the quality of the ingot. The continuous casting speed during the continuous casting process is 0.5-0.8m / min, and constant pulling speed control is adopted. The water volume of the secondary cooling water is 0.3-0.5L / t. The ingot is sent hot or sent to the slow cooling pit for slow cooling.

[0076] (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 and holding time is 2-6 hours; then rolling is carried out, and the starting rolling temperature is controlled to be ≥1100°C and the final rolling temperature is ≥850°C; the rolled round steel is straightened, flaw-detected, and polished to remove surface defects.

[0077] The specification of the round steel after rolling is Φ26~100mm. In addition, the ingot starts rolling after being descaled by high-pressure water after leaving the heating furnace, and enters the insulation pit for slow cooling for ≥24h after rolling.

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

[0079] After quenching, the steel forms a martensitic structure with a fine lamellar structure. The alloying elements in the steel exist in the martensite in the form of a supersaturated solid solution, which has high strength but relatively poor plasticity and impact toughness. After tempering heat treatment, the supersaturated alloying elements in the martensite are dispersed and precipitated between the martensite lamellar layers in the form of nano-scale carbides, which can greatly improve the strength of the invention steel and avoid 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 its manufacturing method of the present invention are further introduced below with reference to specific examples.

[0081] Example

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

[0083] (1) Molten steel was smelted and continuously cast according to the proportions shown in Table 1 to obtain ingots. Electric furnace smelting, control end point [C]: 0.06-0.10%, molten steel tapping temperature 1640-1680°C.

[0084] (2) LF furnace refining: The molten steel smelted in the electric furnace is sent to the LF furnace station for refining. Aluminum particles or silicon carbide are used to strengthen deoxidation and desulfurization. Aluminum wire is fed 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 alloy composition and temperature of the molten steel are adjusted to meet the target requirements before the steel is tapped.

[0085] (3) VD / RH vacuum refining treatment: The molten steel after LF furnace refining is subjected to slag treatment, and vacuum degassing refining treatment is carried out in VD or RH furnace. The strong stirring time is greater than 10 minutes under the condition of vacuum degree less than 67Pa. After vacuum refining, Al is added according to the chemical composition requirements. After ensuring that the free oxygen content in the molten steel is less than 5ppm, Ca and ferrotitanium are added. After 5 minutes, ferroboron is added to adjust the molten steel to the target composition. The molten steel is calmed for more than 10 minutes, and the steel is tapped after the composition and temperature meet the requirements.

[0086] (4) Continuous casting: Use full-process protection pouring to prevent secondary oxidation of molten steel and nitrogen addition during the process; use low superheat pouring, the superheat of molten steel in the middle package is controlled at 15-30°C, electromagnetic stirring is used for the crystallizer and the end of solidification, and light pressure is applied at the end of solidification by 10-25mm to reduce defects such as internal segregation of the ingot and improve the quality of the ingot. The continuous casting speed is 0.5-0.8m / min, constant pulling speed control, and the water volume of the secondary cooling water is 0.3-0.5l / t. The continuous casting billet is delivered hot or sent to a slow cooling pit for slow cooling.

[0087] (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 heat preservation time is 2-6h. During rolling, the continuous casting billet starting rolling temperature is controlled to be ≥1100℃, and the final rolling temperature is ≥850℃. The rolled round steel is straightened, flaw-detected, and polished to remove surface defects. After rolling, it is slowly cooled in the heat preservation pit for ≥24h.

[0088] (6) Quenching and tempering: The round steel obtained after rolling is subjected to quenching and tempering treatment, wherein the quenching heating temperature is 850-980°C and the holding time is 1-4 hours; the tempering temperature is 400-550°C and the holding time is 1-3 hours. After tempering, it is water-cooled to room temperature.

[0089] Comparative Examples 1 and 2 are prepared using electric furnace + LF + RH + continuous casting + quenching and tempering process. The difference is that the composition and content of the steel and the process parameters are different from those of the present invention, as 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 of the embodiments and comparative examples during the manufacturing process

[0095]

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

[0097] Quenching temperature(℃) Insulation time (h) Tempering temperature(℃) 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 to 6 and Comparative Examples 1 to 2 were sampled to obtain corresponding chain steel samples. The obtained chain steels were subjected to tensile tests and Charpy impact tests to obtain performance data of the chain steels of the embodiments and comparative examples. The test results are shown in Table 3.

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

[0100] Tensile test: According to the national standard GB / T 2975, the chain steels of Examples 1 to 6 and Comparative Examples 1 to 2 were sampled and prepared into tensile specimens, and the tensile properties were tested 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 to 6 and Comparative Examples 1 to 2 were sampled and prepared into impact specimens, and the impact performance test was performed according to the national standard GB / T 229.

[0102] Table 3 Properties of chain steels of embodiments and comparative examples

[0103]

[0104] As shown in Table 3, the high-strength and high-toughness mining chain steel prepared in Examples 1 to 6 of the present invention has excellent comprehensive properties, and its yield strength Rp 0.2 ≥1186MPa, tensile strength R m ≥1293MPa, elongation A≥13.5%, section shrinkage Z≥50%, room temperature impact energy A kv ≥74J, it can be seen that the high-strength and high-toughness mining chain steel of the present invention is significantly better than the chain steels in Comparative Examples 1 and 2.

[0105] It can be seen from Table 1 and Table 3 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 invention falls within the scope of protection required, and the optimized quenching + tempering heat treatment process is used to obtain higher strength while having excellent impact toughness.

[0106] Figure 1 This is an electron microscope scanning image of the microstructure of the high-strength and high-toughness mining chain steel after quenching and tempering heat treatment in Example 1. Figure 1 As shown in the figure, 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 lamella spacing is small, and fine dispersed nano-scale carbides are precipitated between the martensite lamellae. The fine nano-scale 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 summary, the present invention obtains high-strength and high-toughness mining chain steel with excellent performance through reasonable chemical composition design combined with optimized process, which can be widely used in fields requiring high-strength steel such as marine engineering and mining machinery.

[0108] It should be noted that those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A high-strength and high-toughness mining chain steel, characterized in that: It includes the following chemical components in 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%, and the balance is iron and unavoidable impurities.

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

3. The high-strength and high-toughness mining chain steel according to claim 2, characterized in that: Its composition meets the following requirements: Ti / (O+2N)=2-4; wherein Ti, O, and N are the mass percentage contents of the corresponding elements respectively.

4. The high-strength and high-toughness mining chain steel according to claim 2, characterized in that: In the high-strength and high-toughness mining chain steel, the proportion of B element existing in the form of solid solution to the total amount of B element is B 固 / B 总 =65~85%.

5. The high-strength and high-toughness mining chain steel according to claim 1, characterized in that: Its performance meets: yield strength Rp 0.2 ≥1150MPa, tensile strength R m ≥1250MPa, elongation A≥13%, section shrinkage Z≥50%, room temperature impact energy A kv ≥60J.

6. A method for manufacturing high-strength and high-toughness mining chain steel according to any one of claims 1 to 5, characterized in that: The method comprises the steps of electric furnace smelting, LF furnace refining, vacuum refining, continuous casting, rolling, quenching and tempering treatment; in the vacuum refining process, the calming time of the molten steel before tapping is greater than 10 minutes; the heating temperature of the quenching treatment is 850-980°C, and the holding time is 1-4 hours; the tempering temperature of the tempering treatment is 400-550°C, and the holding time is 1-3 hours, and the steel is cooled to room temperature by water after tempering.

7. The method for manufacturing high-strength and high-toughness mining chain steel according to claim 6, characterized in that: In the electric furnace smelting process, molten iron and scrap steel are used as raw materials, foam slag is produced in the whole process of electric furnace smelting, the C content of the molten steel end point is controlled to be 0.06-0.10%, and the tapping temperature of the molten steel is 1640-1680°C.

8. The method for manufacturing high-strength and high-toughness mining chain steel according to claim 7, characterized in that: During the electric furnace smelting process, the percentage of molten iron in the raw material is controlled to be 30-60%.

9. The method for manufacturing high-strength and high-toughness mining chain steel according to claim 6, characterized in that: The LF furnace refining process includes the following steps: In the early stage of LF refining, lime and fluorite are added to form slag; Use aluminum particles or silicon carbide to strengthen deoxidation and desulfurization, and feed aluminum wire according to the target composition of Al in molten steel; The steel is tapped after adjusting the alloy composition and temperature of the molten steel to the target requirements.

10. The method for manufacturing high-strength and high-toughness mining chain steel according to claim 6, characterized in that: During the vacuum refining process, the molten steel after LF refining is subjected to slag treatment, vacuum degassing refining is carried out in a VD furnace or a RH furnace, Al is supplemented according to the chemical composition requirements of the molten steel, and after ensuring that the free oxygen content in the molten steel is less than 5ppm, Ca and ferrotitanium are added, and ferroboron is added after 5 to 10 minutes, and the composition of the molten steel is adjusted to the target composition.

11. The method for manufacturing high-strength and high-toughness mining chain steel according to claim 10, characterized in that: When vacuum degassing and refining is carried out 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.

12. The method for manufacturing high-strength and high-toughness mining chain steel according to claim 10, characterized in that: The titanium wire is used as the ferrotitanium, and the boron wire is used as the ferroboron.

13. The method for manufacturing high-strength and high-toughness mining chain steel according to claim 6, characterized in that: During the continuous casting process, full-process protection pouring is adopted, the superheat of the molten steel in the tundish is controlled to be 15 to 30 minutes, electromagnetic stirring is adopted in the crystallizer and at the end of solidification, and a process of lightly pressing down 10 to 25 mm at the end of solidification is adopted to obtain the ingot.

14. The method for manufacturing high-strength and high-toughness mining chain steel according to claim 13, characterized in that: The continuous casting speed in the continuous casting process is 0.5-0.8 m / min, constant casting speed control is adopted, the secondary cooling water ratio is 0.3-0.5 L / t, and the ingot is hot transported or slowly cooled in a slow cooling pit.

15. The method for manufacturing high-strength and high-toughness mining chain steel according to claim 6, characterized in that: During the rolling process, the ingot obtained by continuous casting is sent to a heating furnace for heating and then rolled, the heating temperature is controlled to be 1150-1250°C, the heating and insulation time is 2-6h, the starting rolling temperature is ≥1100°C, and the final rolling temperature is ≥850°C.

16. The method for manufacturing high-strength and high-toughness mining chain steel according to claim 15, characterized in that: During the rolling process, the ingot is removed from the heating furnace and descaled by high-pressure water before rolling, and then is placed in a heat preservation pit for slow cooling for ≥24 hours.

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