High-strength and high-toughness chain steel resistant to hydrogen-induced-cracking, and manufacturing method therefor

Abstract

Disclosed in the present invention is a high-strength and high-toughness chain steel resistant to hydrogen-induced-cracking. The chain steel comprises Fe and inevitable impurities, and further contains the following chemical elements in percentages by mass: C: 0.25-0.35%, Si: 0.1-0.5%, Mn: 0.3-1.0%, Cr: 0.5-1.5%, Ni: 2.5-3.5%, Mo: 0.3-0.8%, Cu: 0.01-0.25%, Al: 0.02-0.05% and V: 0.05-0.30%. After a tempering heat treatment, the microstructure thereof has dispersedly distributed nano-scale VC particles, and the distribution density of the VC particles is greater than or equal to 1014 / m2. Further disclosed in the present invention is a manufacturing method for the high-strength and high-toughness chain steel resistant to hydrogen-induced-cracking. The method comprises the steps of: smelting and casting; heating; rolling, involving : controlling the initial rolling temperature to be greater than or equal to 1050°C and the final rolling temperature to be greater than or equal to 850°C, and after rolling, the slow cooling time in a heat preservation pit is greater than or equal to 20 h; and a tempering heat treatment, wherein the quenching heating temperature is 850-1000°C, and after a heat preservation time of 1-5 h, water quenching is performed; and the tempering temperature is 400-600°C, and after a heat preservation time of 1-5 h, air cooling is performed until room temperature.

Description

A hydrogen-induced cracking resistant high strength and toughness chain steel and a manufacturing method thereof TECHNICAL FIELD

[0001] The present application relates to a steel material and a manufacturing method thereof, and in particular to a high strength and toughness chain steel and a manufacturing method thereof. BACKGROUND

[0002] The mine round-link chain is an important component of mechanized coal mining in the coal mine, mainly used as a transmission chain on the scraper conveyor, the scraper transfer machine, the coal mining machine and the coal plough, and is required to have high strength and toughness, fatigue resistance and wear resistance in use. At the same time, since the working environment of the coal mine is mostly underground with moisture and many corrosive substances, the mine round-link chain is required to have good corrosion resistance.

[0003] At present, the mine round-link chain steel commonly used in the coal mine industry is mainly the mine chain steel grade in "GB / T 10560-2017 Steel for Mine Welded Round-Link Chain", among which the high-strength mine round-link chain steel is mainly the 23MnNiMoCr54 steel (referred to as 54 steel) grade which is most widely used. There are also some technical solutions in the prior art to prepare a chain steel with higher strength by optimizing the composition to improve the wear resistance of the mine chain and obtain a longer service life. For example:

[0004] The Chinese patent document with the publication number CN110714164A, the publication date of January 21, 2020 and the name of "A high-quality Cr54 steel for coal mine chain ring and a production method thereof" discloses a high-quality 54 steel for coal mine chain ring, which introduces carbon equivalent, cold crack sensitivity coefficient and hot crack sensitivity coefficient to ensure the welding performance of the chain steel and improve the cold and hot brittleness resistance.

[0005] The Chinese patent document with the publication number CN111101078A, the publication date of May 5, 2020 and the name of "A nickel-free high-strength mine round-link chain steel and a production method thereof" discloses a high-strength mine round-link chain steel without Ni element, which reduces the content of the noble metal element Ni alloy and increases the content of C, Si, Cr and Mo alloy elements to greatly reduce the production cost under the premise of ensuring the mechanical properties.

[0006] However, the working environment of the coal mine is mostly humid, and the high-strength mine chain will inevitably be affected by environmental corrosion in use, resulting in hydrogen adsorption in the steel matrix. In addition, the high-strength mine chain has a high stress, and the hydrogen adsorbed in the steel is also sensitive to stress concentration, which easily causes hydrogen-induced cracking (frequent low-load brittle fracture in a few months or a few days) in use, resulting in early failure of the mine chain. SUMMARY

[0007] One of the purposes of the present application is to provide a hydrogen-induced cracking resistant high strength and toughness chain steel, which has higher strength and toughness and plasticity matching and excellent hydrogen-induced cracking resistance by reasonably designing the proportioning of each alloying element and making full use of the influence of each alloying element and the interaction therebetween on the performance after quenching and tempering heat treatment.

[0008] In order to achieve the above-mentioned purpose, the present application provides a chain steel, which contains the following chemical elements in mass percentage in addition to Fe and inevitable impurities:

[0009] C: 0.25-0.35%, Si: 0.1-0.5%, Mn: 0.3-1.0%, Cr: 0.5-1.5%, Ni: 2.5-3.5%, Mo: 0.3-0.8%, Cu: 0.01-0.25%, Al: 0.02-0.05%, V: 0.05-0.30%;

[0010] The microstructure of the chain steel has dispersedly distributed nanoscale VC particles, and the distribution density of the VC particles is ≥10 14 / m 2 , preferably 10 14 / m 2 ~82*10 14 / m 2 , more preferably 50*10 14 / m 2 ~60*10 14 / m 2 .

[0011] In the present application, the inventors have studied the effect of alloying elements on the quenching and tempering heat treatment of the chain steel. By reasonably designing the proportioning of each alloying element, the influence of each alloying element and the interaction therebetween on the performance after quenching and tempering heat treatment is fully utilized, so that the high strength chain steel of the present application has higher strength and toughness and plasticity matching and excellent hydrogen-induced cracking resistance.

[0012] The inventors have further studied the influence of the microstructure of the chain steel after quenching and tempering heat treatment on the hydrogen embrittlement sensitivity. After the quenching and tempering heat treatment, the steel forms fine and dispersedly distributed nanoscale VC particles, which have face-centered cubic structure and high hydrogen solubility. The face-centered cubic structure of the VC particles has high atomic density, and it is difficult for hydrogen atoms to escape after capturing the free hydrogen atoms in the steel, so as to avoid the aggregation of free hydrogen atoms in the steel to form hydrogen-induced cracks and improve the hydrogen embrittlement resistance of the steel. The inventors have found through a large number of studies that the dispersedly distributed nanoscale VC particles in the steel have a distribution density of ≥10 14 / m 2Afterwards, the ability of capturing free hydrogen atoms is greatly improved. The hydrogen traps formed by VC particles prevent hydrogen atoms from escaping, thus improving the hydrogen embrittlement resistance of the invented steel.

[0013] In addition, in the present application, the microstructure of the hydrogen-induced cracking resistant high strength and toughness chain steel after the final quenching and tempering heat treatment is tempered martensite + dispersed carbide structure. The carbide structure is preferably VC particles. The dispersed nanoscale VC particles in the steel can effectively reduce the diffusion speed of hydrogen atoms in the steel, inhibit the long-range diffusion and aggregation of hydrogen atoms, thus avoiding the aggregation of free hydrogen atoms in the steel to form white spot defects and hydrogen-induced cracks, and can significantly improve the hydrogen embrittlement resistance of the invented steel, thus greatly improving the service life of the mining chain in harsh environments.

[0014] Preferably, in the hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application, the chain steel has the following chemical elements in terms of mass percentage:

[0015] C: 0.25-0.35%, Si: 0.1-0.5%, Mn: 0.3-1.0%, Cr: 0.5-1.5%, Ni: 2.5-3.5%, Mo: 0.3-0.8%, Cu: 0.01-0.25%, Al: 0.02-0.05%, V: 0.05-0.30%; the balance being Fe and unavoidable impurities.

[0016] In the hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application, the design principles of each chemical element are as follows:

[0017] C: In the hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application, C element is necessary to ensure the strength of the steel. Increasing the content of C element in the steel will increase the non-equilibrium structure transformation ability of the steel, thus significantly improving the strength of the steel. By controlling the cooling speed of the steel during quenching through heat treatment process, the diffusion of C element in the steel can be inhibited to form shear-type martensite phase change, thus significantly improving the strength of the steel. However, too high content of C element is not conducive to the plasticity and toughness of the steel, and will significantly increase the carbon equivalent of the material, thus deteriorating the welding performance of the steel. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application, the mass percentage of C element can be controlled between and

[0018] Si: In the hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application, Si element can be solid-solved in the steel to play a role of solid solution strengthening, which can significantly improve the yield strength, fatigue strength and hardness of the steel. The solubility of Si element in cementite is very low, and when the content of Si element is high, non-carbide bainite structure will be formed, which will increase the brittleness of the steel. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application, the mass percentage of Si element can be controlled between and

[0019] Mn: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the Mn element can improve the stability of austenite in the steel, and also can improve the hardenability of the steel. The Mn element can also improve the strength of the martensite in the steel through solid solution strengthening, thereby improving the strength of the steel. However, when the content of the Mn element is too high, the quenched austenite grains can easily grow, and the harmful elements can be promoted to segregate at the grain boundaries. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage content of the Mn element can be controlled to be between 0.5% and 2.0%.

[0020] Cr: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the Cr element can improve the hardenability of the steel and has the effect of secondary hardening, forming hardened martensite structure, which is beneficial to improve the strength of the steel. The Ni element and the Cr element are beneficial to improve the corrosion resistance of the steel. At the same time, the carbide of the Cr element has the effect of slowing down the grain growth of the heat-affected zone at the welding joint, which is very beneficial to the welding structure of the chain; but when the content of Cr is too high, a large amount of carbide will be generated, which will gather at the grain boundaries, reduce the toughness of the material and significantly increase the carbon equivalent, thereby reducing the welding performance of the chain steel. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage content of the Cr element can be controlled to be between 0.5% and 2.0%.

[0021] Ni: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the Ni element, as one of the main strengthening elements, exists in the steel in the form of solid solution, can be infinitely dissolved with iron, and is an austenite forming element. The Ni element can reduce the C content of the eutectoid point, can improve the strength of the steel without significantly affecting the plasticity of the steel. The Ni element can also improve the fatigue resistance of the steel, reduce the sensitivity of the steel to the notch, reduce the low-temperature embrittlement transition temperature of the steel, and improve the impact toughness of the steel. The Ni element can improve the strength of the steel while having less damage to the toughness, plasticity and other process performance of the steel than other alloy elements. At the same time, when the Ni element is used in combination with the Cr element, the hardenability of the steel can be significantly improved. As can be known from the carbon equivalent formula, the coefficient of Ni is smaller, and the influence on the welding performance is smaller. However, considering that Ni is a precious alloy element, based on its cost and beneficial effects, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage of the Ni element is controlled to be between 0.5% and 2.0%.

[0022] ​​​Mo: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the Mo element mainly exists in the steel in the form of solid solution, plays a solid solution strengthening effect, is beneficial to improve the hardenability of the steel, and makes the steel form martensite during quenching. However, when the Mo element is added too much, it will significantly increase the carbon equivalent of the material, thereby being detrimental to the flash welding performance of the chain steel. However, considering that Mo is a precious alloying element, based on its cost and beneficial effects, the mass percentage of Mo element in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application is controlled to be between 0.5% and 1.5%.

[0023] Cu: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the Cu element can significantly improve the corrosion resistance of the steel material and reduce the hydrogen-induced cracking sensitivity of the steel material. However, too high Cu element content is detrimental to the welding performance of the steel material, and copper embrittlement phenomenon is also prone to occur, which deteriorates the surface performance of the steel material. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage of Cu element can be controlled to be between 0.5% and 1.5%.

[0024] Al: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the main role of the Al element is deoxidation and nitrogen fixation. The A1N formed by the combination of the Al element and the N element can effectively refine the grains. However, too high Al element content will affect the pouring performance of the steel, and will also damage the toughness of the steel. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage of Al element can be controlled to be between 0.01% and 0.1%.

[0025] V: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the V element and the Fe element form a continuous solid solution, which strongly narrows the austenite phase region. V has a strong affinity with C, N and O. When the N content in the steel is controlled to be low, V mainly exists in the form of carbide in the steel. Controlling the V element to form nanoscale VC particles in the steel can capture hydrogen atoms in the steel, prevent hydrogen atoms from gathering, reduce the risk of hydrogen embrittlement and fracture of the steel material, and effectively improve the hydrogen embrittlement resistance of the chain steel. However, if the V element is added too much, the toughness and welding performance of the steel will be reduced, the hydrogen atom capturing ability will be reduced due to the formation of coarse VC particles, and the cost of the steel material will be increased. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage of V element can be controlled to be between 0.01% and 0.1%.

[0026] Preferably, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, unavoidable impurities include P, S, N, O and H, wherein the element content of the impurities satisfies at least one of the following: P≤0.015%, S≤0.01%, N≤0.006%, O≤0.0018%, H≤0.0002%. ​​​​

[0027] It should be noted that in the above technical solutions of the present application, P, S, N, O and H are all inevitable impurity elements in steel, and the content of impurity elements in steel should be controlled as low as possible under the premise of technical conditions.

[0028] P: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, P element is a harmful element. Although P element can improve the corrosion resistance of steel, it will deteriorate the performance of steel. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage of P element can be controlled as P≤0.015%.

[0029] S: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, S element is a harmful element. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage of S element can be controlled as S≤0.01%.

[0030] N: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, N element is an austenite forming element, and also an MX type precipitate forming element. In order to avoid the enrichment of N element in steel, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage of N element can be controlled as N≤0.006%.

[0031] O: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, O element can form oxides and complex inclusions with the deoxidizing element Al in steel. In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage of O element can be controlled as O≤0.0018%.

[0032] H: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, H element will gather at defects in steel, especially high strength steel with tensile strength exceeding 1000 MPa is more sensitive to H content, H element will cause hydrogen-induced delayed fracture of steel, resulting in early failure of chain. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage of H element can be controlled as H≤0.0002%.

[0033] Preferably, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the chemical elements of the chain steel also satisfy: Al / (4N+3O)≥1, wherein the numerical values of each chemical element before the mass percentage content are substituted.

[0034] In the present application, since the V element in the steel has high activity, it will react with the O and N elements in the steel, causing the V element in the steel to be consumed and unable to form a sufficient number of nanoscale VC particles. When the content of the Al element and the O and N elements in the steel satisfies Al / (4N+3O)≥1, the O and N elements in the steel fully react with the Al element, avoiding the reaction of free residual O and N elements in the steel with the V element, so that the V element in the steel can form a sufficient number of nanoscale VC particles, thereby improving the hydrogen embrittlement resistance of the steel.

[0035] Preferably, in the hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application, the microstructure is based on tempered martensite, and the nanoscale VC particles are dispersed in the tempered martensite.

[0036] Preferably, in the hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application, the hydrogen embrittlement coefficient η is ≥0.92.

[0037] In the present application, the hydrogen embrittlement coefficient η = Z1 / Z2, wherein Z1 is the reduction of area of the un-baked tensile specimen after the quenching and tempering heat treatment, and Z2 is the reduction of area of the tensile specimen after being baked at 250°C for 2 hours. Controlling the hydrogen embrittlement coefficient η ≥0.92 can ensure that the hydrogen-induced cracking resistant high strength and toughness chain steel has good hydrogen-induced cracking resistance after the quenching and tempering heat treatment.

[0038] Preferably, in the hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application, the performance satisfies at least one of the following: yield strength R p0.2 ≥1100MPa, tensile strength Rm≥1250MPa, elongation A≥14%, reduction of area Z≥50%, and Charpy impact energy Akv at -20°C≥60J.

[0039] Another object of the present application is to provide a manufacturing method of a hydrogen-induced cracking resistant high strength and toughness chain steel, which improves the hydrogen embrittlement resistance of the chain steel and greatly improves the service life of the chain steel in harsh environments.

[0040] To achieve the above object, the present application provides a manufacturing method of a hydrogen-induced cracking resistant high strength and toughness chain steel, which comprises the following steps performed in sequence:

[0041] smelting and casting;

[0042] heating;

[0043] rolling: controlling the opening rolling temperature ≥1050°C, preferably 1050-1120°C, the finish rolling temperature ≥850°C, preferably 850-990°C, and the slow cooling time in the holding pit after rolling ≥20h, preferably 20-48h;

[0044] The heat treatment includes quenching at 850–1000℃ for 1–5 hours followed by water quenching; tempering at 400–600℃ for 1–5 hours followed by air cooling to room temperature.

[0045] In this invention, the chain steel billet is held at 850–1000℃ and then subjected to quenching heat treatment, which enables the chain steel billet to become fully austenitic, with some carbide or nitride particles dissolving into the austenite. Undissolved carbides and carbide particles continue to pin the austenite grain boundaries, inhibiting austenite grain growth. During the quenching process, due to the rapid cooling rate, the Cr, Ni, and Mo elements in the steel improve the hardenability of the steel, allowing the formation of fine martensitic structures within the steel.

[0046] In this invention, the chain steel billet is tempered at 400–600°C. During the tempering process, the high-density dislocations formed during quenching are partially annihilated, and the supersaturated vanadium dissolved in the non-equilibrium structure of the steel precipitates again as carbides between the martensite lamellars. Due to the low precipitation temperature, the precipitated particles do not easily grow, resulting in finer and more dispersed particles, leading to a nanoscale vanadium particle distribution density ≥10 in the steel. 14 pcs / m 2 .

[0047] In this article, the cooling rate of air cooling is generally 0.1-1℃ / s, the cooling rate of water cooling is generally greater than 10℃ / s, and the cooling rate of quenching is generally 20-200℃ / s.

[0048] In this article, "slow cooling" refers to cooling at a rate of less than 0.1℃ / s.

[0049] Preferably, in the heating step of the manufacturing method of the present invention, the heating temperature is controlled at 1150-1250°C and the holding time is 2-10 hours.

[0050] Preferably, in the smelting and casting steps of the manufacturing method of the present invention, the superheat of the molten steel in the tundish is controlled to be 20-40°C, and the water volume in the secondary cooling section is 0.2-0.4 liters / ton of steel.

[0051] Preferably, the microstructure of the slab obtained after the rolling step is bainite.

[0052] The hydrogen-induced cracking resistant high-strength and high-toughness chain steel and its manufacturing method described in this invention have the following advantages and beneficial effects compared with the prior art:

[0053] The hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application is designed by reasonable element proportioning, the main strengthening elements C, Si, Mn, Ni, Cr and Mo in the steel are optimized, the heat treatment process in the chain steel production process is combined, the martensite structure transformation in the quenching and cooling process of the steel and the carbide precipitation in the tempering process are controlled, the fine lamellar tempered martensite structure in the chain steel is realized, a large number of nanoscale VC particles dispersedly distributed in the steel capture free hydrogen atoms, the free hydrogen atoms in the steel are avoided to gather to produce white spot induced hydrogen-induced cracks, the hydrogen embrittlement resistance of the steel is improved, and thus the service life of the mine chain in a harsh environment can be greatly improved.

[0054] In some embodiments, the hydrogen embrittlement resistance coefficient η of the hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application is greater than or equal to 0.92, the yield strength R p0.2 ≥1100MPa, the tensile strength Rm≥1250MPa, the elongation A≥14%, the reduction of area Z≥50%, and the Charpy impact energy Akv at -20℃≥60J. BRIEF DESCRIPTION OF DRAWINGS

[0055] FIG. 1 shows the scanning electron microscope image of the microstructure of the hydrogen-induced cracking resistant high strength and toughness chain steel according to Example 1 of the present application after the quenching and tempering heat treatment. DETAILED DESCRIPTION

[0056] The hydrogen-induced cracking resistant high strength and toughness chain steel and the manufacturing method thereof according to the present application will be further explained and described below in combination with the drawings and specific examples, but the explanation and description do not constitute undue limitations on the technical solutions of the present application.

[0057] Examples 1-6 and Comparative Examples 1-3

[0058] The hydrogen-induced cracking resistant high strength and toughness chain steel according to Examples 1-6 is prepared by the following steps:

[0059] (1) Smelting and casting: smelting and continuous casting are performed to obtain a cast blank, and the chemical composition proportions of each example and comparison are listed in Table 1-1 and Table 1-2. The smelting can be performed by an electric furnace or a converter, and after the composition meets the requirements, the steel is tapped after LF refining and VD or RH vacuum treatment, and then cast into an ingot blank. The superheat degree of the molten steel in the tundish is controlled to be 20-40℃, and the secondary cooling section adopts weak cooling, and the specific water consumption of the secondary cooling section is 0.2-0.4 L / t steel.

[0060] (2) Heating: the cast ingot is rolled into a finished size by one-fire material process, and the finished size specification range can be Φ26-100mm. Among them, the ingot blank heating temperature is controlled to be 1150-1250℃, and the holding time is controlled to be 2-10h.

[0061] (3) Rolling: control the opening rolling temperature or opening forging temperature ≥ 1050 ℃, control the finishing rolling temperature or finishing forging temperature ≥ 850 ℃, and the slow cooling time in the range of 400-200 ℃ after rolling into the holding pit ≥ 20 h.

[0062] (4) Quenching and tempering heat treatment: after the round steel is rolled into a chain, quenching + tempering heat treatment is carried out, wherein the quenching heating temperature is 850-1000 ℃, the holding time is 1-5 h, and then water quenching; the tempering temperature is 400-600 ℃, the holding time is 1-5 h, and after tempering, air cooling or water cooling to room temperature.

[0063] Comparative Examples 1-2 use commercially available finished steel, so they do not have the rolling process parameters in Table 2-1 and Table 2-2. Comparative Example 3 is a comparative test of Example 3 steel using a different heat treatment process.

[0064] Table 1-1 and Table 1-2 list the mass percentages of each chemical element in the hydrogen-induced cracking resistant high strength and toughness chain steels of Examples 1-6 and the comparative steels of Comparative Examples 1-3.

[0065] Table 1-1. (wt%, the balance is Fe and unavoidable impurities other than P, S, N, O and H)

[0066] Table 1-2. (wt%, the balance is Fe and unavoidable impurities other than P, S, N, O and H)

[0067] Table 2-1 and Table 2-2 list the specific process parameters of the hydrogen-induced cracking resistant high strength and toughness chain steels of Examples 1-6 and the comparative steels of Comparative Examples 1-2 in the above process steps.

[0068] Table 2-1.

[0069] Table 2-2.

[0070] Samples of the hydrogen-induced cracking resistant high strength and toughness chain steels of Examples 1-6 in the hot-rolled state were taken, and microstructure observation was carried out on each example according to "GB / T13298-2015 Metal Microstructure Inspection Method". The inventors found through microstructure observation that the microstructure of the hydrogen-induced cracking resistant high strength and toughness chain steels in the hot-rolled state prepared by the manufacturing method described in the present application is all bainite.

[0071] The hydrogen-induced cracking resistant high strength and toughness chain steel of Examples 1-6 after quenching and tempering heat treatment is sampled, and microstructure observation is carried out on each example by using a scanning electron microscope, and it is found that the microstructure of the hydrogen-induced cracking resistant high strength and toughness chain steel of Examples 1-6 after quenching and tempering heat treatment is all tempered martensite.

[0072] As shown in Figure 1, in Example 1, the microstructure of the hydrogen-induced cracking resistant high strength and toughness chain steel after quenching and tempering heat treatment is tempered martensite + dispersed carbide, and the carbide includes nanoscale VC particles.

[0073] In addition, the hydrogen-induced cracking resistant high strength and toughness chain steel of Examples 1-6 and the comparative steels of Comparative Examples 1-3 after quenching and tempering heat treatment are sampled again, and relevant microstructure and performance tests are carried out, and the test results are listed in Table 3. Among them, the relevant performance test methods are as follows:

[0074] VC particle distribution density: the chain steels of Examples 1-6 and Comparative Examples 1-3 are sampled, and after the transmission electron microscope samples are prepared, the precipitates in the field of view are observed, and more than 20 fields of view are randomly selected, and the number of VC precipitates in the field of view is divided by the total area of the field of view to obtain the particle distribution density of the sample.

[0075] Tensile test: according to the national standard GB / T 2975, the chain steels of Examples 1-6 and Comparative Examples 1-3 are sampled, and tensile samples are prepared, and according to the national standard GB / T 228.1, the tensile performance test is carried out, and the yield strength, tensile strength, elongation and reduction of area are measured.

[0076] Charpy impact test: according to the national standard GB / T 2975, the chain steels of Examples 1-6 and Comparative Examples 1-3 are sampled, and impact samples are prepared, and according to the national standard GB / T 229, the impact performance test is carried out.

[0077] Table 3 lists the relevant test results of the hydrogen-induced cracking resistant high strength and toughness chain steels of Examples 1-6 and the comparative steels of Comparative Examples 1-3 according to the present application.

[0078] Table 3.

[0079] As can be seen from the above Table 3, the hydrogen embrittlement coefficient η of the hydrogen-induced cracking resistant high strength and toughness chain steels of Examples 1-6 after quenching and tempering heat treatment is greater than 0.93, and the distribution density of VC particles is greater than 7×10 14 / m 2 In addition, the hydrogen-induced cracking resistant high strength and toughness chain steel according to the present application also has good mechanical properties, and the yield strength R p0.2 of the hydrogen-induced cracking resistant high strength and toughness chain steel is greater than 1100MPa, and the tensile strength Rm all greater than 1250 MPa, the elongation A all greater than or equal to 14%, the reduction of area Z all greater than 50%, the Charpy impact energy A at -20°C all greater than 60 J. kv The hydrogen embrittlement resistance coefficient, the elongation and the low temperature impact energy of Comparative Examples 1 to 3 cannot reach the effect of the Examples of the present application. In Comparative Example 3, since the tempering temperature does not meet the requirement of the present application, the distribution density of VC particles is reduced, and excellent hydrogen embrittlement resistance cannot be obtained.

[0080] In addition, the combination of the technical features in the present application is not limited to the combination in the claims or the combination in the embodiments, and all the technical features disclosed in the present application can be freely combined or integrated in any manner, unless contradictory.

[0081] It should also be noted that the above-mentioned embodiments are only specific embodiments of the present application, and obviously the present application is not limited to the above-mentioned embodiments, and there are many similar changes. All the variations directly derived or thought from the disclosure of the present application by those skilled in the art should belong to the protection scope of the present application.

Claims

1. A chain steel characterized in that, The chain steel contains, in mass percentage, the following chemical elements in addition to Fe and unavoidable impurities: C: 0.25-0.35%, Si: 0.1-0.5%, Mn: 0.3-1.0%, Cr: 0.5-1.5%, Ni: 2.5-3.5%, Mo: 0.3-0.8%, Cu: 0.01-0.25%, Al: 0.02-0.05%, V: 0.05-0.30%; The chain steel has nanoscale VC particles dispersed in the microstructure, and the distribution density of the VC particles is ≥10 14 / m 2 , preferably 10 14 / m 2 ~82*10 14 / m 2 .

2. The chain steel of claim 1 wherein, The chain steel contains, in mass percentage, the following chemical elements in addition to Fe and unavoidable impurities: C: 0.25-0.35%, Si: 0.1-0.5%, Mn: 0.3-1.0%, Cr: 0.5-1.5%, Ni: 2.5-3.5%, Mo: 0.3-0.8%, Cu: 0.01-0.25%, Al: 0.02-0.05%, V: 0.05-0.30%; the balance being Fe and unavoidable impurities.

3. A chain steel as claimed in claim 1 or 2, characterised in that, The unavoidable impurities include P, S, N, O and H, wherein the element content of each impurity satisfies at least one of the following: P≤0.015%, S≤0.01%, N≤0.006%, O≤0.0018%, H≤0.0002%.

4. The chain steel according to claim 1 or 2, characterized in that, The chemical elements of the chain steel also satisfy: Al / (4N+3O)≥1, wherein each chemical element is substituted by the value before the percentage sign of its mass percentage.

5. The chain steel as claimed in claim 1 or 2, characterized in that, The microstructure of the chain steel is based on tempered martensite, and the nanoscale VC particles are dispersed in the tempered martensite.

6. The chain steel as claimed in claim 1 or 2, characterized by, The hydrogen embrittlement resistance coefficient η of the chain steel is ≥0.

92.

7. The chain steel as claimed in claim 1 or 2, characterized in that, The properties of the chain steel satisfy at least one of the following: a yield strength R p0.2 ≥ 1100 MPa, a tensile strength Rm≥ 1250 MPa, an elongation A≥ 14%, a reduction of area Z≥ 50%, and a Charpy impact energy at -20°C Akv≥ 60 J.

8. A method of manufacturing a chain steel as claimed in any one of claims 1-7, characterized in that, The method comprises the following steps performed in sequence: smelting and casting; heating; rolling: the open rolling temperature is controlled to be ≥1050°C, preferably 1050-1120°C, the finish rolling temperature is ≥850°C, preferably 850-990°C, and the post-rolling entry into the holding pit for slow cooling is ≥20h, preferably 20-48h; quenching and tempering heat treatment, wherein the quenching heating temperature is 850-1000°C, the holding time is 1-5h, and then water quenching; the tempering temperature is 400-600°C, the holding time is 1-5h, and then air cooling or water cooling to room temperature.

9. The method of claim 8, wherein, In the heating step, the heating temperature is controlled to be 1150-1250°C, and the holding time is 2-10h.

10. The method of claim 8, wherein, In the smelting and casting step, the intermediate ladle molten steel superheat is controlled to be 20-40°C, and the specific water quantity of the secondary cooling section is 0.2-0.4L / t of steel.

11. The method of claim 8, wherein, The microstructure of the blank prepared after the rolling step is bainite.

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