A kind of ultra-high strength mine round link chain steel and its preparation method

Abstract

The application discloses a kind of super-high-strength mining round-link chain steel and a preparation method thereof, and belongs to the technical field of round-link chain steel, solve the problem that the strength and toughness of round-link chain steel in prior art cannot be effectively improved simultaneously.The components of the super-high-strength mining round-link chain steel include, by mass percentage: C: 0.22% to 0.27%, Si: 0.10% to 0.17%, Mn: 0.48% to 0.62%, P: ≤0.015%, S: ≤0.005%, Cr: 0.41% to 0.66%, Ni: 0.88% to 1.23%, Mo: 0.87% to 1.13%, Cu: 0% to 0.60%, V: 0.18% to 0.36%, W: 0.21% to 0.45%, and the balance is Fe and unavoidable impurities.The super-high-strength mining round-link chain steel has high strength and good plasticity and toughness.

Description

Technical Field

[0001] This invention relates to the field of steel for circular link chains, and in particular to an ultra-high strength steel for mining circular link chains and its preparation method. Background Technology

[0002] Mining round link chains are crucial transmission components in fully mechanized coal mining equipment, boasting advantages such as high transmission efficiency, large load-bearing capacity, and convenient assembly and disassembly. During underground operation, these chains simultaneously withstand tensile, alternating, and impact loads. This chain structure often exhibits dynamic variations during operation; therefore, breakage or failure can severely impact mining efficiency, resulting in significant economic losses. Consequently, the comprehensive mechanical properties of the steel used for round link chains are subject to extremely high requirements. With the increasing scale, power, and strength of coal mining equipment, the limitations of existing round link chain materials have become a prominent bottleneck restricting equipment production capacity, necessitating an upgrade in the specifications and strength levels of round link chains.

[0003] High-strength circular link chains for mining can be classified into three grades: B, C, and D, according to standard GB / T 12718-91. Currently, even at grade D high strength, brittle fracture of the chain occurs frequently. Although all indicators meet national standards, it is difficult to promote its application in actual industrial production.

[0004] Therefore, new types of mining round link chain steel that meet the development requirements of the mining industry need to have a combination of ultra-high strength and excellent toughness and plasticity. However, there is very little research on this topic at present. Summary of the Invention

[0005] In view of the above, the present invention aims to provide an ultra-high strength steel for mining circular link chains and its preparation method, in order to solve the problem that the strength and toughness of existing circular link chain steels cannot be effectively improved simultaneously.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] This invention provides an ultra-high strength steel for mining round link chains. The composition of the ultra-high strength mining round link chain steel, by mass percentage, includes: C: 0.22%–0.27%, Si: 0.10%–0.17%, Mn: 0.48%–0.62%, P: ≤0.015%, S: ≤0.005%, Cr: 0.41%–0.66%, Ni: 0.88%–1.23%, Mo: 0.87%–1.13%, Cu: 0%–0.60%, V: 0.18%–0.36%, W: 0.21%–0.45%, with the balance being Fe and unavoidable impurities.

[0008] Furthermore, the composition of the ultra-high strength mining round link chain steel, by mass percentage, includes: C: 0.23%–0.27%, Si: 0.10%–0.16%, Mn: 0.50%–0.62%, P: ≤0.015%, S: ≤0.005%, Cr: 0.42%–0.64%, Ni: 0.90%–1.20%, Mo: 0.89%–1.12%, Cu: 0.30%–0.60%, V: 0.18%–0.35%, W: 0.21%–0.43%, with the balance being Fe and unavoidable impurities.

[0009] Furthermore, the microstructure of ultra-high strength mining round link steel includes lath martensite and nanoscale precipitates.

[0010] Furthermore, in the microstructure of ultra-high strength mining circular link chain steel, the nanoscale precipitates mainly include (V,Mo,W)C composite nanoscale precipitates.

[0011] Furthermore, the yield strength of ultra-high strength mining round link chain steel is ≥1310MPa, and the tensile strength is ≥1350MPa.

[0012] This invention also provides a method for preparing ultra-high strength mining round link chain steel, which includes the following steps:

[0013] Step 1: Smelting and casting into billets;

[0014] Step 2: Roll the billet into a bar stock;

[0015] Step 3: Anneal and straighten the bar stock and then perform heat treatment to obtain ultra-high strength mining round link chain steel. The heat treatment includes normalizing, quenching and tempering.

[0016] Furthermore, in step 3, the holding temperature for normalizing is 885–927℃.

[0017] Furthermore, in step 3, the quenching is carried out by heating the entire furnace to 860-890℃ and holding for 40-120 minutes.

[0018] Furthermore, in step 3, the quenching is performed using electromagnetic induction heating, heating the bar stock to 895-925℃, holding it at that temperature for 3-10 seconds, and then water cooling it to room temperature.

[0019] Furthermore, in step 3, the tempering holding temperature is 560–620℃.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] The ultra-high strength mining round link chain steel of the present invention achieves excellent comprehensive performance of ultra-high strength and good toughness and plasticity by precisely controlling the content of elements such as C, Si, Ni, Mn, Cr, and Mo, and by adding vanadium and tungsten to improve the strength of the steel and refine the grain.

[0022] The preparation method of ultra-high strength mining circular link chain steel of the present invention adopts a normalizing + quenching + tempering process and precisely controls the parameters of each step, especially the use of high temperature tempering, and finally obtains a microstructure containing a large number of nano-scale precipitates, which is very beneficial to improving the comprehensive mechanical properties of the steel.

[0023] The method for preparing ultra-high strength mining round link chain steel of the present invention utilizes electromagnetic induction heating to significantly shorten the holding time, combined with high-temperature tempering, to obtain ultra-high strength mining round link chain steel with excellent comprehensive performance matching of ultra-high strength and good toughness and plasticity. The preparation method of the present invention is simple and feasible, and has the prospect of large-scale promotion and application.

[0024] The ultra-high strength mining round link chain steel of this invention exhibits excellent performance, including high strength, good ductility and toughness, yield strength ≥1310MPa (e.g., 1311-1420MPa), tensile strength ≥1350MPa (e.g., 1360-1480MPa), reduction of area ≥60% (e.g., 66%-69%), elongation after fracture ≥16% (e.g., 16%-18%), and room temperature impact toughness A. kv2 ≥80J, for example 80~110J; Vickers hardness ≥402HV, for example 402~440HV.

[0025] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of what is particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0026] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0027] Figure 1 Here are the microscopic tissue SEM images from Example 1;

[0028] Figure 2 Here are the SEM images of the microstructure from Example 6;

[0029] Figure 3 This is a TEM image of the matrix tissue in Example 1. Detailed Implementation

[0030] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0031] This invention provides an ultra-high strength steel for mining round link chains. The composition of the ultra-high strength steel for mining round link chains, by mass percentage, includes: C: 0.22%–0.27%, Si: 0.10%–0.17%, Mn: 0.48%–0.62%, P: ≤0.015%, S: ≤0.005%, Cr: 0.41%–0.66%, Ni: 0.88%–1.23%, Mo: 0.87%–1.13%, Cu: 0%–0.60%, V: 0.18%–0.36%, W: 0.21%–0.45%, with the balance being Fe and unavoidable impurities.

[0032] The following provides a detailed explanation of the function and dosage selection of the components contained in this invention.

[0033] Carbon: Carbon is the element that contributes most to solid solution strengthening in steel. By controlling the appropriate carbon content, the hardenability of the steel can be improved while ensuring its strength. Considering the toughness requirements of the circular link chain during its service life, the carbon content needs to be guaranteed not to exceed 0.27%. Taking all factors into account, this invention controls the carbon content in the range of 0.22% to 0.27%.

[0034] Silicon: One of the deoxidizing elements in steel, and also a non-carbide-forming element. It has a strong solid solution strengthening effect, inhibiting cementite precipitation, refining cementite size, and helping to homogenize carbide distribution, thus improving material strength while reducing temper brittleness. However, excessive Si will deteriorate the toughness and weldability of steel. Taking all factors into consideration, the silicon content of the steel in this invention ranges from 0.10% to 0.17%.

[0035] Manganese: While improving the hardenability of steel, manganese also plays a certain role in solid solution strengthening. Changes in manganese content have little impact on tempering stability. Furthermore, manganese can enhance deoxidation during smelting by combining with oxygen atoms, which is beneficial for subsequent desulfurization processes and improves the material's hot working properties. However, the manganese content should not be too high, otherwise it may cause coarsening of the steel grains and may also lead to segregation within the material. The manganese content of the steel in this invention ranges from 0.48% to 0.62%.

[0036] Chromium: effectively improves the hardenability, corrosion resistance, oxidation resistance and wear resistance of steel. It forms a variety of carbides with carbon atoms. Its pinning effect can inhibit grain growth at the weld joint. However, a high Cr content is detrimental to welding performance. The chromium content of the steel in this invention ranges from 0.41% to 0.66%.

[0037] Nickel: Nickel is an element that improves the hardenability and corrosion resistance of steel. Adding nickel can effectively increase the density of the internal rust layer, ensure the toughness of high-strength steel, and lower the brittle transition temperature of the steel. However, its disadvantage is its high price. To ensure that the material itself has a certain degree of corrosion resistance, its content should be controlled between 0.88% and 1.23%.

[0038] Molybdenum (Mo) is an important element for improving the hardenability of steel, enhancing its impact toughness, reducing temper brittleness, strengthening grain boundary bonding, and refining grain size. It also improves strength and toughness by improving the thermal stability and inhomogeneity of carbides. However, excessive Mo carbide content is undesirable, as its distribution at grain boundaries increases material brittleness, saturates its contribution to strength, and is expensive. Therefore, the molybdenum content in the steel of this invention is controlled between 0.87% and 1.13%.

[0039] Copper improves the hardenability and atmospheric corrosion resistance of steel, but copper-containing steel is prone to hot brittleness due to selective surface oxidation. Therefore, the copper content of the steel in this invention is controlled at 0% to 0.60%.

[0040] Vanadium: The VC particles precipitated from the martensitic or ferrite matrix are finely dispersed and have a significant secondary hardening effect on steel. The V content of the steel in this invention is controlled between 0.18% and 0.36%. If the content is too high, the precipitation strengthening effect is not significantly improved, and the cost is also high.

[0041] Tungsten is a strong ferrite-forming element, similar in function to molybdenum but at a much lower cost. It increases tempering stability, hardenability, and hardness. Tungsten typically has a significant effect on refining precipitates and strengthening through solid solution, and high-temperature tempering can alleviate carbide aggregation. This invention employs a design approach that substitutes molybdenum for tungsten, greatly improving the strength of the steel while maintaining toughness. The tungsten content in the steel of this invention is controlled within the range of 0.21% to 0.45%.

[0042] Phosphorus and sulfur: Impurity elements in steel that significantly reduce toughness, plasticity, and weldability. Their contents should be controlled to within 0.015% and 0.005%, respectively.

[0043] Specifically, in order to further improve the overall performance of the aforementioned ultra-high strength mining round link chain steel, the composition of the aforementioned ultra-high strength mining round link chain steel, by mass percentage, includes: C: 0.23%–0.27%, Si: 0.10%–0.16%, Mn: 0.50%–0.62%, P: ≤0.015%, S: ≤0.005%, Cr: 0.42%–0.64%, Ni: 0.90%–1.20%, Mo: 0.89%–1.12%, Cu: 0.30%–0.60%, V: 0.18%–0.35%, W: 0.21%–0.43%, with the balance being Fe and unavoidable impurities.

[0044] Specifically, the microstructure of the aforementioned ultra-high strength mining round link chain steel includes lath martensite and nanoscale precipitates.

[0045] Specifically, in the microstructure of the aforementioned ultra-high strength mining round link chain steel, the mass percentage of nanoscale precipitates is approximately 0.3% to 1.5%.

[0046] Specifically, in the microstructure of the aforementioned ultra-high strength mining circular link chain steel, the nanoscale precipitates mainly include (V,Mo,W)C composite nanoscale precipitates.

[0047] Specifically, in the microstructure of the aforementioned ultra-high strength mining round link chain steel, the average lath spacing of the lath martensite is approximately 130–185 nm.

[0048] Specifically, in the microstructure of the aforementioned ultra-high strength mining circular link chain steel, the size of the nanoscale precipitated phase is approximately >0 to 25 nm, for example >0 to 20 nm.

[0049] On the other hand, the present invention also provides a method for preparing the above-mentioned ultra-high strength mining round link chain steel, comprising the following steps:

[0050] Step 1: Smelting and casting into billets;

[0051] Step 2: Roll the billet into a bar stock;

[0052] Step 3: Anneal and straighten the bar stock and then perform heat treatment to obtain ultra-high strength mining round link chain steel. The heat treatment includes normalizing, quenching and tempering.

[0053] Specifically, the steps of step 1 above include: preparing smelting raw materials according to chemical composition, raw material pretreatment, converter (or electric furnace) smelting, LF refining, RH refining, continuous casting, and slag removal and slow cooling after continuous casting to obtain billets.

[0054] Specifically, in step 3 above, considering that the normalizing holding temperature is too low and the microstructure cannot be homogenized as required, the normalizing holding temperature is controlled at 885-927℃, the holding time is 1-4 hours, and the product is air-cooled to room temperature after being taken out of the furnace.

[0055] Specifically, in step 3 above, quenching can be performed using a conventional heating furnace or electromagnetic induction heating. The conventional heating furnace can be a conventional box-type high-temperature heat treatment furnace.

[0056] Specifically, in step 3 above, quenching is performed using a traditional heating furnace. The specific steps include: placing the bar stock into the heating furnace, heating it to 860-890℃ and holding it for 40-120 minutes, and then water-cooling it to room temperature after removing it from the furnace.

[0057] Preferably, in step 3 above, the quenching is performed using electromagnetic induction heating. The specific steps include: heating the bar stock to 895-925°C using electromagnetic induction heating, holding it at that temperature for 3-10 seconds, and then water cooling it to room temperature.

[0058] Specifically, in step 3 above, considering that excessively high tempering holding temperatures would lead to severe softening of the matrix, making it difficult to maintain the required strength; excessively low temperatures would cause the precipitation behavior to fail to meet thermodynamic requirements, resulting in a reduction in the amount of precipitates; excessively long holding times would cause the precipitates to grow and coarsen, while excessively short holding times would prevent the precipitates from settling. Therefore, the tempering holding temperature is controlled at 560–620℃, the holding time at 1.5–3.5 h, and the precipitates are air-cooled to room temperature after being removed from the furnace.

[0059] Specifically, the aforementioned ultra-high strength mining round link chain steel has high strength, good ductility and toughness, with a yield strength ≥1310MPa, for example 1311~1420MPa; tensile strength ≥1350MPa, for example 1360~1480MPa; reduction of area ≥60%, for example 66%~69%; elongation after fracture ≥16%, for example 16%~18%; and room temperature impact toughness A kv2 ≥80J, for example 80~110J; Vickers hardness ≥402HV, for example 402~440HV.

[0060] The ultra-high strength mining round link chain steel of the present invention achieves excellent comprehensive performance of ultra-high strength and good toughness and plasticity by precisely controlling the content of elements such as C, Si, Ni, Mn, Cr, and Mo, and by adding vanadium and tungsten to improve the strength of the steel and refine the grain.

[0061] The preparation method of ultra-high strength mining circular link chain steel of the present invention adopts a normalizing + quenching + tempering process and precisely controls the parameters of each step, especially the use of high temperature tempering, and finally obtains a microstructure containing a large number of nano-scale precipitates, which is very beneficial to improving the comprehensive mechanical properties of the steel.

[0062] The method for preparing ultra-high strength mining round link chain steel of the present invention utilizes electromagnetic induction heating to significantly shorten the holding time, combined with high-temperature tempering, to obtain ultra-high strength mining round link chain steel with excellent comprehensive performance matching of ultra-high strength and good toughness and plasticity. The preparation method of the present invention is simple and feasible, and has the prospect of large-scale promotion and application.

[0063] The ultra-high strength mining round link chain steel of this invention exhibits excellent performance, including high strength, good ductility and toughness, yield strength ≥1310MPa (e.g., 1311-1420MPa), tensile strength ≥1350MPa (e.g., 1360-1480MPa), reduction of area ≥60% (e.g., 66%-69%), elongation after fracture ≥16% (e.g., 16%-18%), and room temperature impact toughness A. kv2≥80J, for example 80~110J; Vickers hardness ≥402HV, for example 402~440HV.

[0064] The advantages of precise control of the composition and process parameters of the steel of the present invention will be demonstrated below with specific embodiments and comparative examples.

[0065] Examples 1-7 of the present invention provide an ultra-high strength steel for mining circular link chains and its preparation method. The chemical composition of the steel in Examples 1-7 is shown in Table 1.

[0066] The methods for preparing the steel in Examples 1-5 include:

[0067] According to the above chemical composition, the smelting raw materials are pretreated, smelted in a converter, refined in LF, refined in RH and continuously cast into slabs. After slag removal and slow cooling, the continuously cast slabs are heated in a heating furnace and rolled into round bars with a diameter of 48mm. Then, they are annealed and straightened.

[0068] Cut the round bar wire into suitable lengths and place the whole section into a heating furnace for heat treatment: normalizing temperature 895~910℃, hold for 1~2 hours and then air cool; quenching temperature 875~885℃, hold for 40~60 minutes and then water cool; tempering temperature 570~610℃, hold for 2~3 hours and then air cool.

[0069] The steel preparation methods in Examples 6-7 include:

[0070] According to the above chemical composition, the smelting raw materials are pretreated, smelted in a converter, refined in LF, refined in RH and continuously cast into slabs. After slag removal and slow cooling, the continuously cast slabs are heated in a heating furnace and rolled into round bars with a diameter of 48mm. Then, they are annealed and straightened.

[0071] Cut the round bar wire into suitable lengths and place the whole section into a heating furnace for normalizing treatment: normalizing temperature 895~910℃, hold for 1~2 hours and then air cool; electromagnetic induction heating quenching temperature 905~915℃, hold for 5 seconds and then cool immediately; place the whole section into a heating furnace for tempering treatment: tempering temperature 570~610℃, hold for 2~3 hours and then air cool.

[0072] The specific process parameters for the heat treatment of Examples 1-7 are shown in Table 2; the microstructure of the ultra-high strength mining round link chain steel is shown in Table 3; and the test results of the mechanical properties of the ultra-high strength mining round link chain steel are shown in Table 4.

[0073] Figure 1 Here are the microscopic tissue SEM images from Example 1; Figure 2 Here are the SEM images of the microstructure from Example 6; Figure 3 This is a TEM image of the matrix tissue in Example 1.

[0074] The inventors conducted extensive experimental research during the research process, and some poorly performing solutions are now presented as comparative examples.

[0075] Comparative Example 1

[0076] This comparative example provides a steel for mining circular link chains and its preparation method. The composition is shown in Table 1, and the specific process parameters of the preparation method are shown in Table 2.

[0077] The composition of this comparative example is not within the scope of this application, and some process parameters of the preparation method do not meet the requirements. Therefore, the microstructure of this comparative example has a large grain size and poor toughness and plasticity.

[0078] Comparative Example 2

[0079] This comparative example provides a steel for mining circular link chains and its preparation method. The composition is shown in Table 1, and the specific process parameters of the preparation method are shown in Table 2.

[0080] The composition of this comparative example is not within the scope of this application, some process parameters of the preparation method do not meet the requirements, and the precipitated phase in the microstructure of this comparative example is large in size and has poor toughness and plasticity.

[0081] Comparative Example 3

[0082] This comparative example provides a steel for mining circular link chains and its preparation method. The composition is shown in Table 1, and the specific process parameters of the preparation method are shown in Table 2.

[0083] The components in this comparative example are not within the scope of this application, some process parameters of the preparation method do not meet the requirements, and the toughness and plasticity are poor.

[0084] The steel used for the circular link chains in the embodiments and comparative examples of this invention were all prepared into samples that met the requirements of national standards after heat treatment for testing and inspection.

[0085] Table 1 Chemical composition, wt%

[0086]

[0087]

[0088] Table 2 Specific Process Parameters

[0089]

[0090] Table 3 Microstructure of Steel

[0091]

[0092] Table 4 Mechanical Properties of Steel

[0093]

[0094]

[0095] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A type of ultra-high strength mining round link chain steel, characterized in that, The composition of the ultra-high strength mining round link chain steel, by mass percentage, includes: C: 0.22%–0.27%, Si: 0.11%–0.17%, Mn: 0.53%–0.62%, P: ≤0.015%, S: ≤0.005%, Cr: 0.41%–0.66%, Ni: 0.88%–1.08%, Mo: 0.87%–1.13%, Cu: 0.3%–0.60%, V: 0.18%–0.24%, W: 0.21%–0.45%, with the balance being Fe and unavoidable impurities; The microstructure of the ultra-high strength mining circular link chain steel includes lath martensite and nanoscale precipitates; the nanoscale precipitates mainly include (V,Mo,W)C composite nanoscale precipitates; the mass percentage of the nanoscale precipitates is 0.3%~1.5%, and the average lath spacing of the lath martensite is 130~185nm; The ultra-high strength mining round link chain steel has a yield strength ≥1310MPa, tensile strength ≥1350MPa, and room temperature impact toughness A. kv2 ≥80J.

2. The ultra-high strength mining round link chain steel according to claim 1, characterized in that, The composition of the ultra-high strength mining round link chain steel, by mass percentage, includes: C: 0.23%–0.27%, Si: 0.11%–0.16%, Mn: 0.53%–0.62%, P: ≤0.015%, S: ≤0.005%, Cr: 0.42%–0.64%, Ni: 0.90%–1.08%, Mo: 0.89%–1.12%, Cu: 0.30%–0.60%, V: 0.18%–0.24%, W: 0.21%–0.43%, with the balance being Fe and unavoidable impurities.

3. The ultra-high strength mining round link chain steel according to claim 1, characterized in that, The ultra-high strength mining round link chain steel has a yield strength of 1311-1420 MPa and a tensile strength of 1360-1480 MPa.

4. A method for preparing ultra-high strength mining round link chain steel, characterized in that, The preparation method is used to prepare the ultra-high strength mining round link chain steel according to any one of claims 1 to 3, and the preparation method includes the following steps: Step 1: Smelting and casting into billets; Step 2: Roll the billet into a bar stock; Step 3: Anneal and straighten the bar stock and then perform heat treatment to obtain ultra-high strength mining round link chain steel. The heat treatment includes normalizing, quenching and tempering.

5. The preparation method according to claim 4, characterized in that, In step 3, the holding temperature for normalizing is 885–927°C.

6. The preparation method according to claim 4, characterized in that, In step 3, the quenching is carried out by heating the entire furnace, raising the temperature to 860-890℃ and holding it for 40-120 minutes.

7. The preparation method according to claim 4, characterized in that, In step 3, quenching is performed using electromagnetic induction heating, heating the bar stock to 895-925°C, holding it at that temperature for 3-10 seconds, and then water cooling it to room temperature.

8. The preparation method according to any one of claims 4 to 7, characterized in that, In step 3, the tempering holding temperature is 560–620°C.

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