Hydrogen-induced cracking-resistant, high-strength and high-toughness chain steel and manufacturing method therefor

Abstract

Disclosed in the present invention is hydrogen-induced cracking-resistant, high-strength and high-toughness chain steel. In addition to Fe and inevitable impurities, said chain steel further comprises the following chemical elements in percentage by mass: C: 0.20-0.26%, Si: 0.1-0.5%, Mn: 1.1-1.8%, Cr: 0.4-0.8%, Ni: 0.8-1.5%, Mo: 0.3-0.8%, Cu: 0.01-0.25%, Al: 0.01-0.05%, V: 0.01-0.20%, and Nb: 0.002-0.03%. The microstructure of the chain steel comprises nano-scale NbC and VC particles which are dispersively distributed, and the distribution density of the NbC and VC particles is greater than or equal to 1013 particles / m2. Further disclosed in the present invention is a method for manufacturing the hydrogen-induced cracking-resistant, high-strength and high-toughness chain steel, comprising the steps of: smelting and casting; heating; rolling; and quenching and tempering heat treatment.

Description

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

[0001] The present invention relates to a steel material and a method of manufacturing the same, and more particularly, to a chain steel and a method of manufacturing the same. BACKGROUND

[0002] The mine round-link chain is an important component of mechanized coal mining in the coal mine, and is mainly used as a transmission chain on a scraper conveyor, a scraper transfer machine, a coal mining machine, and a coal plough. The mine round-link chain is required to have high strength and toughness, fatigue resistance, and wear resistance. In addition, since the working environment of the coal mine is mostly underground and humid, and there are 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 a mine chain steel grade in "GB / T 10560-2017 Steel for Mine Welded Round-Link Chain", and the high-strength mine round-link chain steel is mainly the 23MnNiMoCr54 steel (referred to as 54 steel) grade which is most widely used. In the prior art, there are some technical solutions for preparing a chain steel with high strength by optimizing the composition to improve the wear resistance of the mine chain and obtain a long service life. For example:

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

[0005] A Chinese patent document with the publication number CN111101078A, the publication date of May 5, 2020, and the title of "Nickel-free high-strength mine round-link chain steel and production method thereof" discloses a high-strength mine round-link chain steel without Ni element. The high-strength mine round-link chain steel is prepared by reducing the content of the noble metal element Ni alloy and increasing the contents of C, Si, Cr, and Mo alloy elements to greatly reduce the production cost while ensuring the mechanical properties.

[0006] However, the working environment of the coal mine is mostly humid, and the high-strength mine chain is inevitably affected by environmental corrosion during use, which causes hydrogen to be adsorbed 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) during 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 chain steel, which has higher strength and toughness plasticity matching and excellent hydrogen-induced cracking resistance by reasonable design of the proportion of each alloying element.

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

[0009] C: 0.20-0.26%, Si: 0.1-0.5%, Mn: 1.1-1.8%, Cr: 0.4-0.8%, Ni: 0.8-1.5%, Mo: 0.3-0.8%, Cu: 0.01-0.25%, Al: 0.01-0.05%, V: 0.01-0.20%, Nb: 0.002-0.03%;

[0010] The microstructure of the chain steel has dispersedly distributed nanoscale NbC and VC particles, and the distribution density of the NbC and VC particles is ≥10 13 / m 2 , preferably 10 13 / m 2 ~51*10 13 / m 2 , more preferably 30*10 13 / m 2 ~40*10 13 / m 2 .

[0011] In the present application, the dispersedly distributed nanoscale NbC and 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, thereby avoiding the formation of hydrogen-induced cracks due to the local aggregation of free hydrogen atoms to form white spot defects, and can significantly improve the hydrogen embrittlement resistance of the steel, thereby greatly improving the service life of the mining chain in harsh environments.

[0012] In addition, the inventors further studied the influence of the microstructure of the chain steel after quenching and tempering heat treatment on the hydrogen embrittlement sensitivity. After quenching and tempering heat treatment, the steel forms fine and dispersedly distributed nanoscale NbC and VC particles, which have a face-centered cubic structure and a high hydrogen solubility. The face-centered cubic structure of the NbC and VC particles has a high atomic density, and it is difficult for hydrogen atoms to escape after capturing free hydrogen atoms in the steel, thereby avoiding the formation of hydrogen-induced cracks due to the local aggregation of free hydrogen atoms to form white spot defects, and can significantly improve the hydrogen embrittlement resistance of the steel. The inventors found through a large number of studies that controlling the distribution density of the dispersedly distributed nanoscale NbC and VC particles in the steel to be ≥10 13 / m 2Subsequently, the ability to capture free hydrogen atoms was greatly improved. NbC and VC particles form hydrogen traps that prevent hydrogen atoms from escaping, thereby improving the hydrogen embrittlement resistance of the invented steel.

[0013] Preferably, in the hydrogen-induced cracking resistant high-strength and high-toughness chain steel of the present invention, the chain steel has the following chemical elements in weight percentage:

[0014] C: 0.20–0.26%, Si: 0.1–0.5%, Mn: 1.1–1.8%, Cr: 0.4–0.8%, Ni: 0.8–1.5%, Mo: 0.3–0.8%, Cu: 0.01–0.25%, Al: 0.01–0.05%, V: 0.01–0.20%, Nb: 0.002–0.03%; balance Fe and unavoidable impurities.

[0015] The design principles of each chemical element in the hydrogen-induced cracking resistant high-strength and high-toughness chain steel of this invention are as follows:

[0016] C: In the hydrogen-induced cracking resistant high-strength and high-toughness chain steel described in this invention, carbon (C) is an essential element for ensuring the strength of the steel. Increasing the C content in the steel will increase the steel's ability to undergo non-equilibrium structural transformation, thereby significantly improving the steel's strength. However, when the C content is too high, it is detrimental to the steel's plasticity and toughness, and will significantly increase the carbon equivalent of the material, deteriorating the weldability of the steel. Based on this, in the hydrogen-induced cracking resistant high-strength and high-toughness chain steel described in this invention, the mass percentage of C can be controlled within a certain range. between.

[0017] Si: In the hydrogen-induced cracking resistant high-strength and high-toughness chain steel described in this invention, Si can be dissolved in the steel, playing a role in solid solution strengthening, and can significantly improve the yield strength, fatigue strength, and hardness of the steel. Si has very low solubility in cementite; when the Si content is high, a carbide-free bainite structure will be formed, which will also increase the brittleness of the steel. Therefore, in the hydrogen-induced cracking resistant high-strength and high-toughness chain steel described in this invention, the mass percentage of Si can be controlled within a certain range. between.

[0018] Mn: In the hydrogen-induced cracking resistant high-strength and high-toughness chain steel described in this invention, Mn can improve the stability of austenite in the steel and also improve the hardenability of the steel. Mn can also improve the strength of martensite in the steel through solid solution strengthening, thereby increasing the strength of the steel. However, when the Mn content is too high, it can make the austenite grains grow easily during quenching and promote the segregation of harmful elements at the grain boundaries. Therefore, in the hydrogen-induced cracking resistant high-strength and high-toughness chain steel described in this invention, the mass percentage of Mn can be controlled within a certain range. between.

[0019] 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 mine chain; but when the content of Cr is too high, a large amount of carbide will be generated, which will gather at the grain boundary, 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 of the Cr element can be controlled between .

[0020] 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 notch sensitivity of the steel, reduce the low temperature embrittlement transition temperature of the steel, and improve the impact toughness of the steel. The Ni element, while improving the strength of the steel, has 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 seen 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 between .

[0021] 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, has the effect of solid solution strengthening, and is beneficial to improve the hardenability of the steel, so that the steel forms martensite during quenching. However, when the Mo element is added too much, it will significantly increase the carbon equivalent of the material, which is not conducive to the flash welding performance of the chain steel. However, considering that Mo 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 Mo element is controlled between .

[0022] 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 and reduce the hydrogen-induced cracking sensitivity of the steel. However, too high Cu element content is not conducive to the welding performance of the steel, and copper embrittlement phenomenon is also easy to occur, which deteriorates the surface performance 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 the Cu element can be controlled between .

[0023] Al: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the main role of Al element is deoxidation and nitrogen fixation. AIN formed by the combination of Al element and N element can effectively refine the grain. However, if the content of Al element is too high, it 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 content of Al element can be controlled in the range of

[0024] V: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, V element and 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, and effectively improve the hydrogen embrittlement fracture resistance of the chain steel. However, if the addition amount of V element is too high, the toughness and welding performance of the steel will be reduced, and the formation of coarse VC particles will reduce the hydrogen atom capturing ability and increase the cost of the steel. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage content of V element can be controlled in the range of

[0025] Nb: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, Nb element is a strong carbonitride forming element. During the high temperature cooling process of the steel, NbN precipitates are first formed by the combination of Nb element and nitrogen element, and then NbC precipitates are precipitated as the temperature decreases. By controlling the Nb element to form nanoscale NbC particles in the steel, hydrogen atoms in the steel can be captured, hydrogen atoms can be prevented from gathering, the risk of hydrogen embrittlement and fracture of the steel can be reduced, and the hydrogen embrittlement fracture resistance of the chain steel can be effectively improved. In addition, when the content of Nb element is high, coarse NbC particles will be formed under high temperature tempering conditions, which will reduce the hydrogen atom capturing ability and worsen the low temperature impact energy of the steel. Therefore, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage content of Nb element can be controlled in the range of

[0026] Preferably, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage contents of V and Nb also satisfy: 0.1%≤V+9Nb≤0.3%, wherein each chemical element is substituted by the mass percentage content of the corresponding element.

[0027] ​​​In the present application, in order to ensure that a sufficient number of nanoscale NbC and VC particles are formed in the steel, the V and Nb element content in the steel can be controlled to satisfy: 0.1%≤V+9Nb≤0.3%. When the V and Nb element content V+9Nb in the steel is too low, the number of nanoscale NbC and VC particles formed in the steel will decrease, resulting in fewer hydrogen atoms being captured, weakening the effect of avoiding the local aggregation of free hydrogen atoms in the steel; when the V and Nb element content V+9Nb in the steel is too high, the microalloy element content in the steel is too high, resulting in some of the precipitated NbC and VC particles aggregating and growing, reducing the ability to capture free hydrogen atoms in the steel. 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≤0.007%, O≤0.0018%, and H≤0.0002%.

[0028] It should be noted that in the above technical solutions of the present application, P, S, N, O, and H are all unavoidable impurity elements in steel, and under the premise of technical conditions, the impurity element content in the steel should be controlled as low as possible. Among them:

[0029] P: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, P is a harmful element. Although P can improve the corrosion resistance of the steel, it will deteriorate the performance 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 P can be controlled to P≤0.015%.

[0030] S: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, S 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 can be controlled to S≤0.01%.

[0031] N: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, N is an austenite-forming element and also an MX-type precipitate-forming element. In order to avoid the enrichment of N in the steel, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage of N can be controlled to N≤0.007%.

[0032] O: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, O can form oxides and complex inclusions with the deoxidizing element Al in the steel. In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the mass percentage of O can be controlled to O≤0.0018%.

[0033] H: In the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the H element will gather at defects in the steel, especially the high strength steel with tensile strength exceeding 1000 MPa is more sensitive to the content of H element, which will cause the steel to have hydrogen-induced delayed fracture, resulting in early failure of the 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 to H≤0.0002%.

[0034] Preferably, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the microstructure thereof is based on tempered martensite, and the nanoscale NbC and VC particles are dispersed in the tempered martensite.

[0035] Preferably, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the hydrogen embrittlement coefficient η thereof is ≥0.92.

[0036] In the present application, the hydrogen embrittlement coefficient η = Z1 / Z2, wherein Z1 is the reduction of area of the un-baked tensile sample after the quenching and tempering heat treatment, and Z2 is the reduction of area of the tensile sample after being baked at 250℃ for 2 hours, and the control of 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.

[0037] Preferably, in the hydrogen-induced cracking resistant high strength and toughness chain steel described in the present application, the performance thereof satisfies: yield strength R p0.2 ≥1000 MPa, tensile strength R m ≥1150 MPa, elongation A ≥14%, reduction of area Z ≥50%, and Charpy impact energy Akv at room temperature ≥50 J.

[0038] 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 can greatly improve the service life of the mining chain in harsh environments.

[0039] In order to achieve the above-mentioned objects, 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:

[0040] smelting and casting;

[0041] heating;

[0042] rolling: the opening rolling temperature is controlled to be ≥1050℃, preferably 1050-1120℃, and the finish rolling temperature is controlled to be ≥850℃, preferably 850-990℃;

[0043] quenching and tempering heat treatment, wherein the quenching heating temperature is 840-980℃, the holding time is 1-4h, and then water quenching; the tempering temperature is 380-550℃, the holding time is 1-4h, and then air cooling or water cooling to room temperature.

[0044] In this invention, the chain steel billet is held at 840–980°C 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.

[0045] In this invention, the chain steel is tempered at 380–550°C. During tempering, the high-density dislocations formed during quenching are partially annihilated, and the supersaturated V and Nb elements dissolved in the non-equilibrium structure of the steel precipitate 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 distribution density of nano-sized NbC and VC particles in the steel ≥10-1. 13 pcs / m 2 .

[0046] 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.

[0047] 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 2-8 hours.

[0048] 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 0.3-0.5 liters / ton of steel.

[0049] Preferably, the microstructure of the billet obtained after the rolling step is bainite.

[0050] 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:

[0051] The hydrogen-induced cracking resistant high-strength and high-toughness chain steel and its manufacturing method described in this invention optimize the main strengthening elements C, Si, Mn, Ni, Cr, and Mo through a reasonable Nb and V element ratio design and combined with the heat treatment process in the chain steel production process. This controls the martensitic transformation of the steel during quenching and cooling, as well as the carbide precipitation during tempering, so that a large number of dispersed nanoscale face-centered cubic NbC and VC particles are formed in the steel to capture free hydrogen atoms. This avoids the aggregation of free hydrogen atoms in the steel, which can cause white spots and induce hydrogen-induced cracks, thereby improving the hydrogen embrittlement resistance of the steel and significantly increasing the service life of mining chains in harsh environments.

[0052] In some embodiments, the hydrogen-induced cracking resistant high strength and toughness chain steel has a hydrogen embrittlement coefficient η≥0.92, a yield strength R p0.2 ≥1000MPa, a tensile strength R m ≥1150MPa, an elongation A≥14%, a reduction of area Z≥50%, and a Charpy impact energy at room temperature Akv≥50J. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 shows a scanning electron microscope image of the microstructure of the hydrogen-induced cracking resistant high strength and toughness chain steel of Example 1 after quenching + tempering heat treatment. DETAILED DESCRIPTION

[0054] The hydrogen-induced cracking resistant high strength and toughness chain steel and the method for manufacturing the same will be further explained and described below in conjunction with the accompanying drawings and specific examples, however, the explanation and description shall not constitute undue limitation on the technical solutions of the present application.

[0055] Examples 1-6 and Comparative Examples 1-3

[0056] The hydrogen-induced cracking resistant high strength and toughness chain steel of Examples 1-6 is prepared by the following steps:

[0057] (1) Smelting and continuous casting: smelting and continuous casting are performed to obtain a casting blank, and the chemical composition ratio of each example and comparative example is 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 molten steel is tapped after LF refining and VD or RH vacuum treatment, and then cast into an ingot blank. The molten steel overheat degree in the tundish is controlled to be 20-40℃, and the secondary cooling section uses weak cooling, and the secondary cooling section water consumption is 0.3-0.5 liters per ton of steel.

[0058] (2) Heating and rolling: the cast ingot is rolled into a finished size by one-fire material process, and the finished size specification range can be Φ26-70mm. Among them, the ingot blank heating temperature is controlled to be 1150-1250℃, and the holding time is controlled to be 2-8h;

[0059] (3) Rolling: the rolling temperature or forging temperature is controlled to be≥1050℃, and the finish rolling temperature or finish forging temperature is controlled to be≥850℃.

[0060] (4) Quenching + tempering heat treatment: after the round steel is rolled into a chain, quenching + tempering heat treatment is performed, wherein the quenching heating temperature is 840-980℃, the holding time is 1-4h, and then water quenching; the tempering temperature is 380-550℃, the holding time is 1-4h, and after tempering, air cooling or water cooling to room temperature.

[0061] It should be noted that the chemical composition design of the hydrogen-induced cracking resistant high strength and toughness chain steel of embodiments 1-6 and the related process meet the design specification requirements of the present application. The comparative steels of comparative examples 1-3 belong to purchased commercial finished steels, so they do not have the manufacturing process of the as-rolled state in table 2-1 and table 2-2.

[0062] Table 1-1 and table 1-2 list the mass percentage of each chemical element in the hydrogen-induced cracking resistant high strength and toughness chain steel of embodiments 1-6 and the comparative steels of comparative examples 1-3.

[0063] Table 1-1. (wt%, the balance is Fe and inevitable impurities other than P, S, N, O and H)

[0064] Table 1-2. (wt%, the balance is Fe and inevitable impurities other than P, S, N, O and H)

[0065] Table 2-1 and table 2-2 list the specific process parameters of the hydrogen-induced cracking resistant high strength and toughness chain steel of embodiments 1-6 and the comparative steels of comparative examples 1-3 in the above process steps.

[0066] Table 2-1.

[0067] Table 2-2.

[0068] The hydrogen-induced cracking resistant high strength and toughness chain steel of embodiments 1-6 in the as-rolled state was sampled, and the microstructure of each embodiment was observed according to "GB / T13298-2015 Metal Microstructure Test Method". The inventors found through microstructure observation that the microstructure of the hydrogen-induced cracking resistant high strength and toughness chain steel in the as-rolled state prepared by the manufacturing method described in the present application was bainite.

[0069] The hydrogen-induced cracking resistant high strength and toughness chain steel of embodiments 1-6 after quenching and tempering heat treatment was sampled, and the microstructure of each embodiment was observed by scanning electron microscopy, and it was found that the hydrogen-induced cracking resistant high strength and toughness chain steel of embodiments 1-6 prepared by the manufacturing method described in the present application had a microstructure of tempered martensite after quenching and tempering heat treatment.

[0070] As shown in FIG. 1, in embodiment 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 organization, which includes nanoscale VC and NbC particles.

[0071] In addition, the hydrogen-induced cracking resistant high strength and toughness chain steels of Examples 1-6 and the comparative steels of Comparative Examples 1-3 after the quenching and tempering heat treatment were sampled again, and relevant tests were performed, and the test results are listed in Table 3. Among them, the relevant test methods are as follows:

[0072] NbC and VC particle distribution density: the chain steels of Examples 1-6 and Comparative Examples 1-3 were sampled, and the precipitates in the field of view were observed after the transmission electron microscope sample was prepared, more than 20 fields of view were randomly selected, and the number of NbC and VC precipitates in the field of view was calculated by dividing the total area of the field of view to obtain the particle distribution density of the sample.

[0073] Tensile test: according to the national standard GB / T 2975, the chain steels of Examples 1-6 and Comparative Examples 1-3 were sampled, and tensile samples were prepared, and the tensile properties were tested according to the national standard GB / T 228.1, and the yield strength, tensile strength, elongation and reduction of area were measured.

[0074] Charpy impact test: according to the national standard GB / T 2975, the chain steels of Examples 1-6 and Comparative Examples 1-3 were sampled, and impact samples were prepared, and the impact performance was tested according to the national standard GB / T 229.

[0075] Table 3 lists the 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.

[0076] Table 3.

[0077] As can be seen from Table 3, the NbC and VC particle distribution densities of the hydrogen-induced cracking resistant high strength and toughness chain steels of Examples 1-6 prepared by the manufacturing method of the present application are all greater than 6×10 13 / m 2 , the hydrogen embrittlement coefficients η are all greater than 0.92, and the hydrogen embrittlement resistance is good. At the same time, the hydrogen-induced cracking resistant high strength and toughness chain steels of Examples 1-6 of the present application also have good mechanical properties, the yield strengths R p0.2 are all greater than 1000 MPa, the tensile strengths R m are all greater than 1150 MPa, the elongations A are all greater than or equal to 14%, the reductions of area Z are all greater than 50%, and the room temperature Charpy impact energy Akv are all greater than 50 J. In Comparative Example 3, the tempering temperature does not meet the requirements of the present application, so the NbC and VC particle distribution densities are reduced, and excellent hydrogen embrittlement performance cannot be obtained.

[0078] In addition, the combination mode of each technical feature in the present case is not limited to the combination mode described in the claims of the present case or the combination mode described in the specific embodiments, and all the technical features described in the present case can be freely combined or combined in any mode, unless contradictory to each other.

[0079] It should also be noted that the above-mentioned embodiments illustrate rather than limit the application, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the application. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. It is appreciated that features of the application that are, individually, known in the art can be ascribed to this application when, in connection with the present specification, new insight is obtained concerning the cooperation of such features. The application is not restricted to details given in the foregoing description.

Claims

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: 0.20-0.26%, Si: 0.1-0.5%, Mn: 1.1-1.8%, Cr: 0.4-0.8%, Ni: 0.8-1.5%, Mo: 0.3-0.8%, Cu: 0.01-0.25%, Al: 0.01-0.05%, V: 0.01-0.20%, Nb: 0.002-0.03%; The microstructure of the chain steel has dispersedly distributed nanoscale NbC and VC particles, the distribution density of the NbC and VC particles is ≥10 13 / m 2 , preferably 10 13 / m 2 ~51*10 13 / m 2 . The chain steel as set forth in claim 1, wherein The chain steel contains, in mass percentage, the following chemical elements in addition to Fe and unavoidable impurities: C: 0.20-0.26%, Si: 0.1-0.5%, Mn: 1.1-1.8%, Cr: 0.4-0.8%, Ni: 0.8-1.5%, Mo: 0.3-0.8%, Cu: 0.01-0.25%, Al: 0.01-0.05%, V: 0.01-0.20%, Nb: 0.002-0.03%; the balance being Fe and unavoidable impurities. The chain steel as claimed in claim 1 or 2, characterized in that, The mass percentage of V and Nb also satisfies: 0.1%≤V+9Nb≤0.3%, wherein each chemical element is substituted by the mass percentage of the corresponding element. The chain steel as claimed in claim 1 or 2, characterized in that, The 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≤0.007%, O≤0.0018%, H≤0.0002%. 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 NbC and VC particles are dispersed in the tempered martensite. The chain steel as claimed in claim 1 or 2, characterized in that, The hydrogen embrittlement resistance coefficient η of the chain steel is ≥0.

92. The chain steel as claimed in claim 1 or 2, characterized in that, The chain steel has the following properties: yield strength R p0.2 ≥ 1000 MPa, tensile strength R m ≥ 1150 MPa, elongation A ≥ 14%, reduction of area Z ≥ 50%, Charpy impact energy at room temperature Akv ≥ 50 J. 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, and the finish rolling temperature is ≥850°C, preferably 850-990°C; quenching and tempering heat treatment, wherein the quenching heating temperature is 840-980°C, the holding time is 1-4h, and then water quenching; the tempering temperature is 380-550°C, the holding time is 1-4h, and then air cooling or water cooling to room temperature. 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 2-8h. The method of claim 8, wherein In the smelting and casting step, the intermediate ladle steel overheat degree is controlled to be 20-40°C, and the specific water quantity of the secondary cooling section is 0.3-0.5L / t steel. The method of claim 8, wherein The microstructure of the blank prepared after the rolling step is bainite.

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