Steel for high-strength mining round-link chain and manufacturing method thereof

Abstract

The invention relates to high-strength mine round-link chain steel and a manufacturing method thereof, and belongs to the technical field of round-link chain steel preparation. In order to solve the problems of insufficient alloy strengthening effect and high cost of the existing steel for the mining round-link chain, the invention provides a manufacturing method of the high-strength steel for the mining round-link chain, smelting, refining and continuous casting are performed according to target chemical components to obtain a casting blank, and quenching heat treatment and tempering heat treatment are performed after the casting blank is rolled to the size of a finished product to obtain the high-strength steel for the mining round-link chain. The high-strength steel for the mining round-link chain is obtained. Through V-N microalloying component design and an optimized heat treatment process, precipitation strengthening and secondary hardening of V (C, N) compounds are promoted through V-N microalloying at relatively high quenching and tempering temperatures, collaborative optimization of strength and toughness is realized, and the produced steel for the mining round-link chain completely meets extreme load requirements of deep mining. The material cost of the steel for the mining round-link chain is remarkably reduced, and a feasible solution is provided for large-scale industrial application of the mining round-link chain.

Description

Technical Field

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

[0002] Scraper conveyors are the core transportation equipment for underground coal mines, and their operational reliability directly affects the mining efficiency of coal mines. As a key component of scraper conveyors, mining round link chains simultaneously perform the dual functions of power transmission and load bearing. The quality of their service performance directly determines the reliability of the equipment's overall operation. Mining round link chains are constantly exposed to complex working conditions such as heavy loads, impacts, wear, and corrosion. If the material performance is insufficient, it can easily cause problems such as fatigue fracture and wear failure, and even lead to equipment shutdown and safety hazards. Therefore, the coal mining industry has put forward more stringent technical requirements for the strength, toughness, and fatigue life of the steel used in mining round link chains.

[0003] The alloying design of steel for mining round-link chains is the core guarantee of its high performance. Through element ratio and process control, the comprehensive performance of strength, toughness, etc. is improved. For example, Chinese patent application publication number CN119710455 A relates to "a high-strength steel for mining round-link chains resistant to stress corrosion and its preparation method". This invention adds V and W elements to make the material's stress intensity factor KISCC ≥ 85MPa for stress corrosion cracking, but its tensile strength only reaches 1210MPa. Chinese patent application publication number CN119710456 A relates to "an ultra-high-strength steel for mining round-link chains and its preparation method". This invention adopts a high Mo and V, W alloying design to achieve a tensile strength ≥ 1350MPa under laboratory conditions. However, the large-scale addition of expensive elements such as Mo, V, and W significantly increases the cost of steel, making it difficult to achieve large-scale industrial application.

[0004] By comparing with existing technologies, it can be found that although the combined addition of V and elements such as Mo, W, and Nb can improve some performance, the overall mechanical properties are only improved to a limited extent, and the cost is high, which limits practical applications. In addition, the large-scale addition of elements such as Si and Mn will significantly increase the carbon equivalent, which will have an adverse effect on the welding performance of steel. Summary of the Invention

[0005] In order to solve the problems of insufficient strengthening effect and high cost of existing steel alloys for mining round link chains, the present invention provides a high-strength mining round link chain steel and a manufacturing method thereof, aiming to achieve a balance between performance improvement and cost control by optimizing material composition and process design.

[0006] The technical solution of the present invention:

[0007] The application discloses a high-strength steel for mining round-link chains, and chemical components of the steel include the following by mass percentage: C: 0.21-0.28%, Si: 0.20-0.60%, Mn: 0.90-1.75%, P: <=0.018%, S: <=0.015%, Cr: 0.4-0.9%, Ni: 0.8-1.3%, Mo: 0.4-0.7%, Cu: <=0.20%, V: 0.1-0.3%, N: 0.007-0.015%, and the balance of Fe and other inevitable impurities.

[0008] The application provides the following component design principle of the high-strength steel for mining round-link chains.

[0009] The carbon (C) element can effectively improve the strength of the steel, and plays a core role in the component system of the steel for mining round-link chains, and the content of the carbon element significantly affects the strength and toughness of the steel. For the mining round-link chain serving under the long-term impact and alternating load, the mechanical properties are directly related to the service reliability of the component. However, too much carbon introduced in Fe-Mn-Ni-Mo-Cr can increase the carbide at the grain boundary, so that the steel is more prone to crack under stress, the brittle transition temperature is increased, and the ductility and toughness of the steel are reduced. And the increase of the carbon content can significantly increase the carbon equivalent of the material, which has an adverse effect on the welding operation in the round-link chain preparation process. In combination, the carbon content is controlled to be 0.21-0.28% in the application.

[0010] The silicon (Si) element can reduce the oxygen content of the molten steel, inhibit the formation of non-metallic inclusions, and effectively improve the fatigue resistance of the round-link chain under alternating load. The silicon element can inhibit the pro-eutectoid ferrite precipitation, promote the uniform transformation of the martensite, improve the hardenability to ensure the uniformity of the cross-section structure of the round-link chain after quenching. However, excessive silicon will deteriorate the toughness and welding performance of the steel. In combination, the silicon content in the application is 0.20-0.60%.

[0011] The manganese (Mn) element can improve the performance of the material through multiple mechanisms in the steel for mining round-link chains. As a deoxidizing and desulfurizing agent, manganese can improve the cleanliness of the molten steel, reduce the inclusions of oxygen and sulfur impurities in the molten steel, and then improve the fatigue resistance of the material. Meanwhile, the manganese element can improve the hardenability of the steel, ensure the uniformity of the cross-section structure of the steel, and then optimize the matching of the strength and toughness of the material. However, when the content of the manganese element is too high, the grain will be coarsened, the toughness of the material will be reduced, and segregation may occur in the material, therefore, the content of the manganese element in the steel is 0.90-1.75%.

[0012] Chromium (Cr) element improves the hardenability to promote the homogenization of quenched structure, which ensures the consistency of the cross-section performance of the round link chain. At the same time, chromium can enhance the oxidation resistance and corrosion resistance of the steel, effectively delay the erosion in the complex environment of the mine, and prolong the service life of the chain ring steel. However, chromium is a noble metal element, and excessive addition will significantly increase the cost of the steel. When the content of Cr element in the steel is too high, 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 welding performance of the chain steel. After comprehensive consideration, the content of chromium is determined to be 0.4%~0.9%.

[0013] Nickel (Ni) element can improve the hardenability and corrosion resistance of the steel, effectively refine the grain and increase the density of the inner rust layer, which can ensure that the toughness does not decrease significantly after the strength is improved, and reduce the brittle transition temperature of the steel. However, due to the high price of nickel, it is not suitable to add a large amount of nickel. Therefore, the content of Ni is controlled to be 0.8%~1.3% under the condition of ensuring a certain corrosion resistance.

[0014] Molybdenum (Mo) element can improve the hardenability of the steel, so that the chain ring with a larger cross-section can be quenched and hardened. At the same time, molybdenum can improve the tempering stability of the steel, so that it can be tempered at a higher temperature, thereby more effectively reducing or even eliminating residual stress and improving plasticity. However, excessive molybdenum is harmful to the welding performance of the steel, and its high price also limits the large amount of addition. Therefore, the content of molybdenum is controlled to be 0.4%~0.7%.

[0015] Vanadium (V) element is a commonly used micro-alloying element, which can form fine carbides, nitrides or carbonitrides to significantly delay static recrystallization kinetics, and the precipitates will be dispersedly distributed in the steel matrix to hinder dislocation movement and inhibit the initiation and propagation of fatigue cracks. However, excessive V will promote the formation of V(C, N) particles with larger size, which will adversely affect the performance of the steel. Therefore, the content of vanadium in the steel is controlled to be 0.1%~0.3%, which can obtain significant strengthening effect without significantly increasing the cost.

[0016] Nitrogen (N) element is one of the important control elements in the mine chain steel, which can be dissolved in the crystal lattice to induce lattice distortion, significantly improve the yield strength and hardness of the steel. In this study, nitrogen and other micro-alloying elements such as vanadium form nanoscale precipitates (such as VN), which can pin the austenite grain boundary to inhibit grain coarsening and refine the microstructure, thereby improving the wear resistance and fatigue resistance of the material. However, excessive nitrogen can cause grain boundary embrittlement and low-temperature toughness deterioration, so it is necessary to combine the heat treatment process and micro-alloying ratio to realize the synergistic optimization of strength and toughness. In addition, N increases the carbon equivalent of the steel, and excessive addition will significantly deteriorate the welding performance of the steel. Therefore, the content of nitrogen in the steel is controlled to be 0.007%~0.015%.

[0017] Further, the mass percentage content ratio of V and N is V / N=8~30.

[0018] V needs to be added with N in a proper ratio to fully play a micro-alloying role. If V / N is too small (i.e. N is relatively excessive), free N exceeding the binding capacity of V is easy to gather at the grain boundary, causing grain boundary embrittlement, reducing the low-temperature toughness and impact resistance of the steel, and being difficult to meet the service requirements of the mine round link chain under heavy load and impact working conditions; if V / N is too large (i.e. V is relatively excessive), V not combined with N may form coarse precipitated particles instead of fine dispersed VN, and these coarse particles will become stress concentration points, promote crack initiation, and damage the toughness of the steel, while excessive V will increase the alloy cost, which is not conducive to industrial production. Therefore, the ratio of V / N is selected in the range of 8-30 to achieve the best combination efficiency.

[0019] Further, in the inevitable impurities, the mass percentage of Al is controlled to be less than or equal to 0.03%, the mass percentage of O is controlled to be less than or equal to 0.0015%, and the mass percentage of H is controlled to be less than or equal to 0.00015%.

[0020] In the steel for mine round link chain of the present application, P, S, O and H elements are all impurity elements. In the case where the technical conditions permit, in order to obtain a mine high-strength round link chain steel with better performance and higher quality, the content of impurity elements in the material should be reduced as much as possible.

[0021] P and S elements are both inevitable harmful impurity elements in steel. Although P and S can improve the corrosion resistance and processing performance of the steel to a certain extent, their deteriorating effect is more significant in general. Therefore, in the present application, the content of P element is controlled to satisfy P≤0.018%, the content of S element is controlled to satisfy S≤0.015%, and P+S≤0.03%.

[0022] Impurity element O can form oxides and complex inclusions with deoxidizing elements such as Si in steel, which is not conducive to the performance of the steel. Therefore, in the present application, the content of O element is controlled to satisfy O≤0.0015%.

[0023] Impurity element H will gather at the defects of the steel, especially in high-strength steel with a tensile strength exceeding 1000 MPa, which is more sensitive to the content of H, and hydrogen-induced delayed fracture may occur to cause early failure of the chain. Therefore, in the present application, the content of H element is controlled to satisfy H≤0.00015%.

[0024] Cu element is a residual element in the smelting process. An appropriate amount of Cu element can improve the corrosion resistance of the steel and reduce the hydrogen-induced crack sensitivity of the steel. However, it should be noted that too high Cu content is not conducive to the welding performance of the steel, and may cause copper embrittlement and deteriorate the surface performance of the steel. Therefore, the mass percentage of Cu element is controlled to be less than or equal to 0.20% in the present application.

[0025] Al acts as a residual deoxidizer, deoxidizing and fixing nitrogen. Al combines with nitrogen to form AlN, effectively refining grains. However, excessive Al content in steel not only affects the castability but also compromises its toughness. Therefore, the present invention limits the Al content to less than 0.03% by weight.

[0026] A preparation method for high-strength steel for round-link chains for mining comprises the following steps: smelting, refining and continuous casting are performed according to the target chemical composition of the steel for round-link chains for mining to obtain a casting billet; the casting billet is rolled to a finished size and then subjected to a quenching heat treatment and a tempering heat treatment, wherein the heating temperature for the quenching heat treatment is 890-960°C, the holding time is 1-3 hours, and the steel is subsequently water-cooled to room temperature within 25 seconds; and the heating temperature for the tempering heat treatment is 400-480°C, the holding time is 1-3 hours, and the steel is subsequently water-cooled to room temperature within 25 seconds, thereby obtaining the high-strength steel for round-link chains for mining.

[0027] The present invention adopts a VN microalloying design, and through a heat treatment process of rapid cooling after high-temperature quenching at 890°C to 960°C and rapid cooling after tempering at 400°C to 480°C, a large number of dispersed nanoscale precipitates M7C3, M23C6, and M(C,N) are formed, while the dislocation density is effectively increased, thereby improving the strength and toughness of the round link chain steel. On the basis of ensuring the processing performance, a significant performance improvement is achieved with a small increase in cost.

[0028] Furthermore, the smelting adopts an electric furnace or a converter. During the smelting process, the final composition of the steel is controlled to be not less than 0.21% C and P≤0.0018%, and the steel temperature is not less than 1300°C, and the steel enters LF refining.

[0029] Furthermore, the refining includes LF refining and VD or RH vacuum treatment, argon is passed during the LF refining process, and the white slag is kept for not less than 20 minutes; sampling is performed for component analysis, and the composition is fine-tuned according to the internal control composition requirements based on the composition results; when the composition meets the requirements, the temperature is 1550~1800℃ and enters VD or RH vacuum degassing.

[0030] Furthermore, during the VD or RH vacuum degassing process, vacuum is drawn and maintained at a vacuum degree of ≤70Pa for not less than 25 minutes before breaking the vacuum, and weak argon stirring is performed for 35 minutes before entering the continuous casting.

[0031] Furthermore, during the continuous casting process, the superheat of the molten steel in the continuous casting tundish is 10-30° C., the casting speed of the continuous casting machine is 0.5-0.8 m / min, the specific water content is set to 0.53 kg / t, and the distribution ratio is 36 / 39 / 25%.

[0032] Furthermore, during the continuous casting process, the parameters of the electromagnetic stirring at the head end are 150A / 2Hz, the stirring intensity is controlled at 360Gs, and the stirring mode is continuous stirring; the parameters of the electromagnetic stirring at the end are 350A / 10Hz, and the stirring mode is continuous stirring; the parameters of the light pressure at the end are 2 / 3 / 5 / 5, and the total pressure reduction is 15mm.

[0033] Furthermore, during the rolling process, the starting rolling temperature is not lower than 1150°C, the heating time is 3-6 hours, the final rolling temperature is not lower than 850°C, and the steel is air-cooled or slowly cooled to room temperature after rolling.

[0034] Beneficial effects of the present invention:

[0035] Aiming at the high-stress service environment faced by mining round-link chains in deep coal mining, the present invention provides a high-strength mining round-link chain steel and a manufacturing method thereof. Through VN microalloying composition design and optimized heat treatment process, while achieving high strength and toughness matching, the material cost is significantly reduced, providing a feasible solution for the large-scale industrial application of mining round-link chains.

[0036] The present invention adopts a low-cost VN microalloying design, adding only a small amount of V and N elements, achieving VN microalloying at higher quenching and tempering temperatures to promote the precipitation strengthening and secondary hardening effect of V(C,N) compounds, while forming a large number of dispersed fine precipitates and effectively improving the dislocation density, thereby achieving synergistic optimization of the strength and toughness of steel for mining round link chains. Under experimental conditions, the yield strength of steel for mining round link chains is ≥1250MPa, the tensile strength is ≥1350MPa, and the elongation is ≥13%, which fully meets the extreme load requirements of deep mining and is particularly suitable for high-stress scenarios such as scraper conveyors and mine hoisting systems. At the same time, the refined microstructure and high dislocation density effectively delay fatigue crack propagation, and the V(C,N) precipitate phase significantly improves the service life of the round link chain under friction and wear conditions.

[0037] The heat treatment method for high-strength mining round link chain steel of the present invention has a simple process, is compatible with conventional equipment, can achieve stable production without additional investment, and has stable and controllable product quality, and is suitable for industrial promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The calculated curve and partial enlarged diagram of the phase diagram of the mining round link chain steel prepared in Example 1, a is the calculated curve, b is the partial enlarged diagram;

[0039] Figure 2 This is a microstructure photograph of the mining round link chain steel prepared in Example 1;

[0040] Figure 3 This is a microstructure photograph of the mining round link chain steel prepared in Comparative Example 1;

[0041] Figure 4 Micrograph of original austenite grains of the steel for mining round link chain prepared for Example 1;

[0042] Figure 5 Micrograph of original austenite grains of the steel for mining round link chain prepared for Comparative Example 1. DETAILED DESCRIPTION

[0043] The technical solutions of the present application are further described below in combination with examples, but are not limited thereto, any modification or equivalent replacement to the technical solutions of the present application without departing from the spirit and scope of the technical solutions of the present application shall be covered in the protection scope of the present application. The process equipment or device not specifically mentioned in the following examples is all the conventional equipment or device in the field, and the raw materials used in the examples of the present application are all commercially available if not specifically mentioned; and the technical means used in the examples of the present application is all the conventional means well known to the person skilled in the art if not specifically mentioned.

[0044] Example 1

[0045] The chemical composition of the high-strength steel for mining round link chain in the present example includes, in terms of mass percentage: C: 0.21%, Si: 0.20%, Mn: 0.95%, Cr: 0.59%, Ni: 0.82%, Mo: 0.49%, P: 0.008%, S: 0.006%, Al: 0.03%, Cu: 0.20%, V: 0.16%, N: 0.0096%, and the balance of Fe and other unavoidable impurities. The mass percentage of V and N in the present example is 16.7 in terms of V / N.

[0046] The preparation method of the high-strength steel for mining round link chain in the present example, and the preparation process flow includes electric furnace or converter smelting→LF refining→VD vacuum degassing→continuous casting→rolling→quenching heat treatment→tempering heat treatment.

[0047] In the electric furnace smelting process of the present example:

[0048] The steel furnace charge is composed of 5wt% return steel and 95wt% pig iron, and the carbon content is 1.5~1.8%.

[0049] The slag material is composed of lime and light-burned dolomite; the amount of lime and light-burned dolomite is adjusted according to the slag condition, and the total amount of slag material is 1550Kg / 100 tons of steel.

[0050] The temperature after full melting of the slag material is 1620℃, and the oxidation starts; the oxygen blowing pressure is controlled at 0.3~0.7 MPa; and the decarburization amount is ≥0.35%.

[0051] The composition and content at the end of oxidation are: C is 0.21%, P is 0.012%;

[0052] Mn-Fe 1600-1630 kg / 100 tons of steel, boiling with manganese;

[0053] Deoxidizing alloying with Si-Fe 250 kg / 100 tons of steel, Al ingot 350 kg / 100 tons of steel, and V-Fe 210-230 kg / 100 tons of steel; slag removal temperature 1630 °C, slag removal amount ≥95%.

[0054] The components are appropriate, and the end-point components of tapping are controlled at C: 0.21-0.25%, P: 0.012%. When the tapping temperature is not lower than 1300 °C, the tapping enters the LF refining.

[0055] In the LF refining process of the present embodiment:

[0056] The temperature of the molten steel entering the LF is 1550 °C, argon gas is passed, the argon gas pressure is controlled at 0.5-0.8 MPa, and electric heating is given for 35 min.

[0057] According to the S content in the steel, slag condition, etc., lime is appropriately added to adjust the slag, and diffusion deoxidizers SiC powder and SiFe powder are added according to the component requirements of the product to perform diffusion deoxidization, with a total amount of 58 kg / 100 tons of steel.

[0058] The white slag in the LF refining process is kept for ≥40 minutes. After the slag turns white, SiC powder is added in multiple batches, 5 kg / batch.

[0059] According to the analysis results of the ladle sample, the components are adjusted according to the internal control component requirements, the temperature is heated and raised, the components are analyzed by sampling, according to the component results, the components are fine-tuned according to the internal control component requirements; the components meet the requirements, the temperature is 1550-1800 °C, and the VD degassing is entered, the S is controlled below 0.005% before degassing, and the steam pressure is controlled at 0.85-1.2 MPa.

[0060] In the VD vacuum degassing process of the present embodiment:

[0061] During vacuum (VD) degassing, vacuum is extracted, the vacuum degree is ≤70 Pa, and after keeping for 30 min, the vacuum is broken; the argon gas flow control during degassing operation: argon gas flow 70-120 NL / min when the vacuum degree >70 Pa, and argon gas flow 230-350 NL / min when the vacuum degree ≤70 Pa.

[0062] After the vacuum is broken, weak argon stirring is performed for 35 min, and then continuous casting is entered.

[0063] In the continuous casting process of the present embodiment:

[0064] The intermediate ladle liquid steel superheat degree is 30℃, the casting speed of the continuous caster is 0.6m / min, the specific water quantity is set to be 0.53Kg / t, and the distribution ratio is 36 / 39 / 25%. The first end electromagnetic stirring parameter is 150A / 2Hz, the stirring intensity is controlled to be 360Gs, and the stirring mode is continuous stirring; the last end electromagnetic stirring parameter is 350A / 10Hz, and the stirring mode is continuous stirring; the last end light pressing parameter is 2 / 3 / 5 / 5, and the total pressing amount is 15mm.

[0065] In the rolling process of the example:

[0066] The open rolling temperature is not lower than 1150℃, the heating time is 3-6h, the finish rolling temperature is not lower than 850℃, and the rolled material is air-cooled or slowly cooled to room temperature to obtain a φ30mm rod-shaped material.

[0067] In the heat treatment process of the example:

[0068] The heating temperature of the quenching heat treatment is 917℃, the holding time is 88min, and then the material is water-cooled to room temperature for 23s; the heating temperature of the tempering heat treatment is 415℃, the holding time is 162min, and then the material is water-cooled to room temperature for 22s, to obtain the high-strength mine round-link chain steel.

[0069] Example 2

[0070] The chemical composition of the high-strength mine round-link chain steel in the example includes, by mass percentage: C: 0.23%, Si: 0.54%, Mn: 1.19%, Cr: 0.61%, Ni: 0.95%, Mo: 0.45%, P: 0.012%, S: 0.015%, Al: 0.03%, Cu: 0.16%, V: 0.20%, N: 0.0099%, and the balance is Fe and other inevitable impurities. The mass percentage of V and N in the example is 22.7.

[0071] The preparation method of the high-strength mine round-link chain steel in the example, and the preparation process flow includes electric furnace or converter smelting→LF refining→VD vacuum degassing→continuous casting→rolling→quenching heat treatment→tempering heat treatment, and the difference from the example 1 is that,

[0072] In the rolling process of the example:

[0073] The open rolling temperature is not lower than 1150℃, the heating time is 3-6h, the finish rolling temperature is not lower than 850℃, and the rolled material is air-cooled or slowly cooled to room temperature to obtain a φ30mm rod-shaped material.

[0074] In the heat treatment process of the example:

[0075] The heating temperature of quenching heat treatment is 941 DEG C, the holding time is 71 min, then water cooling to room temperature for 22 s; the heating temperature of tempering heat treatment is 422 DEG C, the holding time is 86 min, then water cooling to room temperature for 24 s, the high-strength mine round link chain steel is obtained.

[0076] Example 3

[0077] The chemical composition of the high-strength mine round link chain steel in the example includes, by mass percent: C: 0.28%, Si: 0.22%, Mn: 1.58%, Cr: 0.45%, Ni: 1.12%, Mo: 0.50%, P: 0.015%, S: 0.007%, Al: 0.02%, Cu: 0.20%, V: 0.25%, N: 0.0133%, and the balance of Fe and other inevitable impurities. The mass percent ratio of V and N in the example is V / N = 18.8.

[0078] The preparation method of the high-strength mine round link chain steel in the example, the preparation process flow includes electric furnace or converter smelting→LF refining→VD vacuum degassing→continuous casting→rolling→quenching heat treatment→tempering heat treatment, and the difference from the example 1 is that,

[0079] In the rolling process of the example,

[0080] The open rolling temperature is not less than 1150 DEG C, the heating time is 3-6 h, the finish rolling temperature is not less than 850 DEG C, and the rolled material is air-cooled or slowly cooled to room temperature to obtain a φ42 mm rod-shaped material.

[0081] In the heat treatment process of the example,

[0082] The heating temperature of quenching heat treatment is 898 DEG C, the holding time is 91 min, then water cooling to room temperature for 21 s; the heating temperature of tempering heat treatment is 437 DEG C, the holding time is 159 min, then water cooling to room temperature for 20 s, the high-strength mine round link chain steel is obtained.

[0083] Example 4

[0084] The chemical composition of the high-strength mine round link chain steel in the example includes, by mass percent: C: 0.23%, Si: 0.53%, Mn: 1.26%, Cr: 0.72%, Ni: 1.10%, Mo: 0.55%, P: 0.008%, S: 0.010%, Al: 0.03%, Cu: 0.16%, V: 0.28%, N: 0.0102%, and the balance of Fe and other inevitable impurities. The mass percent ratio of V and N in the example is V / N = 27.5.

[0085] The preparation method of the high-strength mine round-link chain steel in the embodiment, the preparation process flow comprises electric furnace or converter smelting, LF refining, VD vacuum degassing, continuous casting, rolling, quenching heat treatment, and tempering heat treatment, and the only difference from the embodiment 1 is that,

[0086] In the rolling process of the embodiment,

[0087] The opening rolling temperature is not lower than 1150 DEG C, the heating time is 3-6h, the final rolling temperature is not lower than 850 DEG C, and the rolled material is air-cooled or slowly cooled to room temperature to obtain the φ42mm rod-shaped material.

[0088] In the heat treatment process of the embodiment,

[0089] The heating temperature of the quenching heat treatment is 953 DEG C, the holding time is 105 min, and then the material is water-cooled to room temperature for 22s; the heating temperature of the tempering heat treatment is 455 DEG C, the holding time is 93 min, and then the material is water-cooled to room temperature for 23s, to obtain the high-strength mine round-link chain steel.

[0090] Embodiment 5

[0091] The chemical composition of the high-strength mine round-link chain steel in the embodiment comprises, in percentage by mass: C: 0.22%, Si: 0.46%, Mn: 1.07%, Cr: 0.49%, Ni: 0.98%, Mo: 0.44%, P: 0.010%, S: 0.004%, Al: 0.02%, Cu: 0.12%, V: 0.17%, N: 0.0148%, and the balance of Fe and other inevitable impurities. The mass percentage of V and N in the embodiment is 11.5.

[0092] The preparation method of the high-strength mine round-link chain steel in the embodiment, the preparation process flow comprises electric furnace or converter smelting, LF refining, VD vacuum degassing, continuous casting, rolling, quenching heat treatment, and tempering heat treatment, and the only difference from the embodiment 1 is that,

[0093] In the rolling process of the embodiment,

[0094] The opening rolling temperature is not lower than 1150 DEG C, the heating time is 3-6h, the final rolling temperature is not lower than 850 DEG C, and the rolled material is air-cooled or slowly cooled to room temperature to obtain the φ48mm rod-shaped material.

[0095] The heating temperature of the quenching heat treatment is 934 DEG C, the holding time is 86 min, and then the material is water-cooled to room temperature for 24s; the heating temperature of the tempering heat treatment is 478 DEG C, the holding time is 86 min, and then the material is water-cooled to room temperature for 21s, to obtain the high-strength mine round-link chain steel.

[0096] Embodiment 6

[0097] The chemical composition of the steel for high-strength mining round link chain in the embodiment includes, in terms of mass percentage: C: 0.24%, Si: 0.28%, Mn: 1.22%, Cr: 0.82%, Ni: 1.03%, Mo: 0.48%, P: 0.013%, S: 0.006%, Al: 0.03%, Cu: 0.18%, V: 0.22%, N: 0.0085%, and the balance of Fe and other unavoidable impurities. The mass percentage of V and N in the embodiment is 25.9.

[0098] The preparation method of the steel for high-strength mining round link chain in the embodiment includes the following preparation process flow: electric furnace or converter smelting→LF refining→VD vacuum degassing→continuous casting→rolling→quenching heat treatment→tempering heat treatment. The difference from the embodiment 1 is that,

[0099] In the rolling process of the embodiment,

[0100] The open rolling temperature is not less than 1150°C, the heating time is 3-6h, the final rolling temperature is not less than 850°C, and the rolled material is air-cooled or slowly cooled to room temperature to obtain a φ48mm rod-shaped material.

[0101] The heating temperature of the quenching heat treatment is 951°C, the holding time is 128min, and then the material is water-cooled to room temperature for 25s; the heating temperature of the tempering heat treatment is 452°C, the holding time is 92min, and then the material is water-cooled to room temperature for 25s, to obtain the steel for high-strength mining round link chain.

[0102] Comparative Example 1

[0103] The chemical composition of the steel for mining round link chain in the comparative example includes, in terms of mass percentage: C: 0.21%, Si: 0.54%, Mn: 0.96%, Cr: 0.64%, Ni: 1.30%, Mo: 0.41%, P: 0.008%, S: 0.003%, Al: 0.02%, Cu: 0.18%, N: 0.0046%, and the balance of Fe and other unavoidable impurities.

[0104] The preparation method of the steel for mining round link chain in the comparative example includes the following preparation process flow: electric furnace or converter smelting→LF refining→VD vacuum degassing→continuous casting→rolling→quenching heat treatment→tempering heat treatment. The difference from the embodiment 1 is that,

[0105] In the rolling process of the comparative example,

[0106] The open rolling temperature is not less than 1150°C, the heating time is 3-6h, the final rolling temperature is not less than 850°C, and the rolled material is air-cooled or slowly cooled to room temperature to obtain a φ38mm rod-shaped material.

[0107] In the heat treatment process of the comparative example,

[0108] The heating temperature of quenching heat treatment is 896 ℃, the holding time is 72 min, and then 18 s water cooling to room temperature; the heating temperature of tempering heat treatment is 425 ℃, the holding time is 153 min, and then 27 s water cooling to room temperature, to obtain the steel for mine round link chain.

[0109] Comparative Example 2

[0110] The steel for mine round link chain of the present comparative example has the chemical composition in mass percent including: C: 0.25%, Si: 0.22%, Mn: 1.75%, Cr: 0.75%, Ni: 1.13%, Mo: 0.68%, P: 0.018%, S: 0.015%, Al: 0.03%, Cu: 0.23%, N: 0.0055%, and the balance of Fe and other inevitable impurities.

[0111] The preparation method of the steel for mine round link chain of the present comparative example has a preparation process flow including electric furnace or converter smelting→LF refining→VD vacuum degassing→continuous casting→rolling→quenching heat treatment→tempering heat treatment, and the difference from Example 1 is that,

[0112] In the rolling process of the present comparative example,

[0113] The starting rolling temperature is not less than 1150 ℃, the heating time is 3-6 h, the final rolling temperature is not less than 850 ℃, and then air cooling or slow cooling to room temperature to obtain a φ48 mm rod-shaped material.

[0114] In the heat treatment process of the present comparative example,

[0115] The heating temperature of quenching heat treatment is 955 ℃, the holding time is 98 min, and then 18 s water cooling to room temperature; the heating temperature of tempering heat treatment is 460 ℃, the holding time is 96 min, and then 17 s water cooling to room temperature, to obtain the steel for mine round link chain.

[0116] The steels for mine round link chain of Examples 1-6 and Comparative Examples 1-2 are subjected to heat treatment after the rod-shaped material, and then the mechanical properties under the test conditions are detected, and the results are shown in Table 1.

[0117] Table 1

[0118]

[0119] As can be seen from the performance data comparison in Table 1, the steel for mining round link chains prepared in Examples 1-6 of the present invention all have excellent comprehensive properties. They not only have high strength, but also have excellent toughness-plasticity matching. Under experimental conditions, the yield strength is between 1250-1350 MPa, the tensile strength is between 1350-1450 MPa, the elongation is between 13.0-14.8%, and the reduction of area is between 62-68%. Compared with Comparative Examples 1-2, the strength is greatly improved. In addition, Examples 1-6 adopt a quenching + tempering heat treatment process, which has low production difficulty and easy control of product quality.

[0120] Figure 1 The calculated curve and local enlarged diagram of the phase diagram of Example 1 are shown in FIG. Figure 1 It can be found that when the temperature is around 900℃, the precipitation of V(C,N) type precipitates increases. Figures 2-5 From the comparison of the medium- and microscopic metallographic structures and the original austenite grains, it can be seen that the microstructure of the steel for mining round link chains after high-temperature quenching + tempering heat treatment of the present invention is tempered martensite, the interlamellar spacing is small, and a large number of fine and dispersed nano-scale carbides are distributed between the lamellae. In addition, the original austenite grain size of the embodiment is significantly smaller than that of the comparative example.

Claims

1. A high-strength steel for round-link mining chains, characterized in that: The chemical composition by mass percentage includes: C: 0.21%~0.28%, Si: 0.20%~0.6%, Mn: 0.90%~1.75%, P: ≤0.018%, S: ≤0.015%, Cr: 0.4%~0.9%, Ni: 0.8%~1.3%, Mo: 0.4%~0.7%, Cu: ≤0.20%, V: 0.1%~0.3%, N: 0.007%~0.015%, and the balance is Fe and other inevitable impurities.

2. The high-strength round-link chain steel for mining according to claim 1, characterized in that: The mass percentage ratio of V to N is V / N, which is 8~30.

3. A high-strength round-link chain steel for mining according to claim 1 or 2, characterized in that: Among the unavoidable impurities, the mass percentage of Al is controlled within 0.03%, the mass percentage of O is controlled within 0.0015%, and the mass percentage of H is controlled within 0.00015%.

4. A method for preparing high-strength mining round link chain steel according to any one of claims 1 to 3, characterized in that: According to the target chemical composition of the steel for mining round link chains, smelting, refining and continuous casting are carried out to obtain ingots, which are rolled to the finished size and then subjected to quenching heat treatment and tempering heat treatment. The heating temperature of the quenching heat treatment is 890~960℃, the holding time is 1~3h, and then the steel is water-cooled to room temperature within 25s; the heating temperature of the tempering heat treatment is 400~480℃, the holding time is 1~3h, and then the steel is water-cooled to room temperature within 25s to obtain high-strength steel for mining round link chains.

5. The method for preparing high-strength round-link chain steel for mining according to claim 4, characterized in that: The smelting adopts an electric furnace or a converter. During the smelting process, the final composition of the steel is controlled to be not less than 0.21% C and P ≤ 0.018%. When the steel tapping temperature is not less than 1300° C., the steel enters LF refining.

6. The method for preparing high-strength round-link chain steel for mining according to claim 4 or 5, characterized in that: The refining includes LF refining and VD or RH vacuum treatment. Argon is passed during the LF refining process, and the white slag is kept for not less than 20 minutes. Samples are taken for composition analysis, and the composition is fine-tuned according to the internal control composition requirements based on the composition results. If the composition meets the requirements, the temperature is 1550-1800° C. and the slag enters VD or RH vacuum degassing.

7. The method for preparing high-strength round-link chain steel for mining according to claim 6, characterized in that: During the VD or RH vacuum degassing process, vacuum is drawn and the vacuum degree is maintained at ≤70Pa for not less than 25 minutes before breaking the air, and weak argon stirring is carried out for 35 minutes before entering the continuous casting.

8. The method for preparing high-strength round-link chain steel for mining according to claim 7, characterized in that: During the continuous casting process, the superheat of the molten steel in the tundish is 10-30° C., the casting speed of the continuous casting machine is 0.5-0.8 m / min, the specific water volume is set to 0.53 kg / t, and the distribution ratio is 36 / 39 / 25%.

9. The method for preparing high-strength round-link chain steel for mining according to claim 8, characterized in that: During the continuous casting process, the electromagnetic stirring parameters at the head end are 150A / 2Hz, the stirring intensity is controlled at 360Gs, and the stirring mode is continuous stirring; the electromagnetic stirring parameters at the end end are 350A / 10Hz, and the stirring mode is continuous stirring; the parameters of the end light pressure are 2 / 3 / 5 / 5, and the total pressure reduction is 15mm.

10. The method for preparing high-strength round-link chain steel for mining according to claim 9, characterized in that: During the rolling process, the starting rolling temperature is not lower than 1150° C., the heating time is 3 to 6 hours, the final rolling temperature is not lower than 850° C., and the rolling is followed by air cooling or slow cooling to room temperature.

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