High-strength and toughness chain steel having excellent hydrogen embrittlement resistance, and manufacturing method therefor

Abstract

Disclosed in the present invention is a high-strength and toughness chain steel having excellent hydrogen embrittlement resistance. In addition to Fe and inevitable impurities, the high-strength and toughness chain steel further comprises the following chemical elements in mass percentage: 0.22-0.32% of C, 0.1-0.5% of Si, 0.3-1.0% of Mn, 0.2-0.9% of Cr, 2.2-3.5% of Ni, 0.2-0.7% of Mo, 0.01-0.2% of Cu, 0.015-0.045% of Al, 0.004-0.04% of Nb, and 0.0002-0.0015% of B. The microstructure of the chain steel has nano-scale NbC particles in dispersed distribution, the distribution density of the NbC particles being ≥ 1012 / m2. Also disclosed in the present invention is a manufacturing method for the high-strength and toughness chain steel, the method comprising the steps of: smelting and casting; heating; rolling; and quenching and tempering heat treatment.

Description

High-toughness chain steel with excellent hydrogen embrittlement resistance and method for manufacturing the same TECHNICAL FIELD

[0001] The present application relates to a steel material and a method for manufacturing the same, and in particular to a chain steel and a method for manufacturing the same. BACKGROUND

[0002] Mine round-link chain is an important component of mechanized coal mining in coal mine, mainly used as transmission chain on scraper conveyor, scraper transfer machine, coal mining machine and coal plough, which requires high strength and toughness, fatigue resistance and wear resistance. At the same time, due to the underground environment of coal mine, which is mostly humid and corrosive, the mine round-link chain needs to have good corrosion resistance.

[0003] At present, the mine round-link chain steel commonly used in 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 high-strength chain steel by optimizing the composition design, to improve the wear resistance of the mine chain and obtain a longer service life. For example:

[0004] The Chinese patent document with publication number CN110714164A and publication date of January 21, 2020, entitled "High-quality Cr54 steel for coal mine chain ring and 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 publication number CN111101078A and publication date of May 5, 2020, entitled "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, which reduces the content of noble metal element Ni alloy and increases the content of C, Si, Cr and Mo alloy elements, thereby greatly reducing the production cost while ensuring the mechanical properties.

[0006] However, the working environment in 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 high stress, and the adsorbed hydrogen in the steel is also sensitive to stress concentration, which easily causes hydrogen-induced fracture (frequent low-load brittle fracture occurs in several months or even several days), resulting in early failure of the mine chain. SUMMARY

[0007] One of the purposes of the present application is to provide a high-toughness chain steel with excellent hydrogen embrittlement resistance, which has higher strength and toughness and excellent hydrogen embrittlement 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, in addition to Fe and inevitable impurities, the following chemical elements in mass percentage:

[0009] C: 0.22-0.32%, Si: 0.1-0.5%, Mn: 0.3-1.0%, Cr: 0.2-0.9%, Ni: 2.2-3.5%, Mo: 0.2-0.7%, Cu: 0.01-0.2%, Al: 0.015-0.045%, Nb: 0.004-0.04%, B: 0.0002-0.0015%;

[0010] The microstructure of the chain steel has dispersedly distributed nanoscale NbC particles, and the distribution density of the NbC particles is ≥10 12 / m 2 , preferably 10 12 / m 2 ~87*10 12 / m 2 , more preferably 30*10 14 / m 2 ~60*10 14 / m 2 .

[0011] In the present application, after quenching and tempering heat treatment, nanoscale NbC particles with fine and dispersed distribution are formed, which have face-centered cubic structure and high hydrogen solubility. The face-centered cubic structure of NbC particles has high atomic density, and it is difficult for hydrogen atoms to escape after capturing the free hydrogen atoms in the steel, thereby avoiding the aggregation of free hydrogen atoms in the steel to form white spot defects and hydrogen-induced cracks, which can significantly improve the hydrogen embrittlement resistance of the steel. In addition, the inventors found that by controlling the distribution density of the dispersedly distributed nanoscale NbC particles in the steel to be ≥10 12 / m 2 , the ability to capture free hydrogen atoms is greatly improved. The hydrogen traps formed by NbC particles prevent hydrogen atoms from escaping, thereby improving the hydrogen embrittlement resistance of the steel.

[0012] Preferably, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, it has the following chemical elements in mass percentage:

[0013] C: 0.22-0.32%, Si: 0.1-0.5%, Mn: 0.3-1.0%, Cr: 0.2-0.9%, Ni: 2.2-3.5%, Mo: 0.2-0.7%, Cu: 0.01-0.2%, Al: 0.015-0.045%, Nb: 0.004-0.04%, B: 0.0002-0.0015%; the balance being Fe and inevitable impurities.

[0014] In the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the design principles of the chemical elements are as follows:

[0015] C: In the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the C element is an essential element for ensuring the strength of the steel, and increasing the C content in the steel will increase the non-equilibrium structure transformation ability of the steel, thereby significantly improving the strength of the steel. However, when the C content is too high, it is not conducive to the plasticity and toughness of the steel, and will significantly increase the carbon equivalent of the material, thereby deteriorating the welding performance of the steel. Therefore, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the mass percentage content of the C element is controlled to be between 0.22-0.32%.

[0016] Si: In the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the Si element can be solid-solved in the steel to play a role of solid-solution strengthening, thereby significantly improving the yield strength, fatigue strength and hardness of the steel. The solubility of the Si element in cementite is very low, and when the Si content is high, it will form non-carbide bainite structure, and at the same time, will increase the brittleness of the steel. Therefore, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the mass percentage content of the Si element is controlled to be between 0.1-0.5%.

[0017] Mn: In the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the Mn element can improve the stability of the austenite in the steel, and at the same time, 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 Mn content is too high, it can make the austenite grains grow easily during quenching heating, and can promote the segregation of harmful elements at the grain boundaries. Therefore, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the mass percentage content of the Mn element is controlled to be between 0.3-1.0%.

[0018] Cr: In the high strength and toughness chain steel with excellent hydrogen embrittlement resistance 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 high strength and toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, the mass percentage of the Cr element is controlled between 0.2-0.9%.

[0019] Ni: In the high strength and toughness chain steel with excellent hydrogen embrittlement resistance 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 notches, reduce the low temperature embrittlement transition temperature of the steel, and improve the impact toughness of the steel. While improving the strength of the steel, the Ni element has less impact on 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 small, and the influence on the welding performance is small. But considering that Ni is a precious alloy element, based on its cost and beneficial effects, in the high strength and toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, the mass percentage of the Ni element is controlled between 2.2-3.5%.

[0020] Mo: In the high strength and toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, in the high strength and toughness chain steel with excellent hydrogen embrittlement resistance 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. But 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. But considering that Mo is a precious alloy element, based on its cost and beneficial effects, in the high strength and toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, the mass percentage of the Mo element is controlled between 0.2-0.7%.

[0021] Cu: In the high-toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, the Cu element can significantly improve the corrosion resistance of the steel material and reduce the hydrogen-induced crack sensitivity of the steel material. However, too high Cu element content is not conducive to the welding performance of the steel material, and copper embrittlement phenomenon is also easy to occur, which deteriorates the surface performance of the steel material. Therefore, in the high-toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, the mass percentage content of Cu element is controlled to be between 0.01-0.2%.

[0022] Al: In the high-toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, the main role of Al element is deoxidation and nitrogen fixation. AlN formed by combination of Al element and 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 high-toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, the mass percentage content of Al element is controlled to be between 0.015 0.045%.

[0023] Nb: In the high-toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, Nb element, as a strong carbonitride forming element, first combines with nitrogen element to form NbN precipitates during high-temperature cooling of the steel, and then NbC precipitates are precipitated as the temperature decreases. By controlling the formation of nanoscale NbC particles in the steel by Nb element, hydrogen atoms in the steel can be captured, hydrogen atom aggregation can be prevented, the risk of fracture of the steel due to hydrogen embrittlement 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 relatively high, coarse NbC particles will be formed under high-temperature tempering conditions, which will reduce the hydrogen atom capturing ability and will also deteriorate the low-temperature impact energy of the steel material. Therefore, in the high-toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, the mass percentage content of Nb element is controlled to be between 0.004-0.04%.

[0024] B: In the high-toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, B element has strong affinity with oxygen and nitrogen elements. B element is used to consume free nitrogen elements in the steel to avoid the combination of N element and Nb element to form NbN precipitates to reduce the hydrogen absorption effect. The solid solution state of B element can also increase the hardenability of the steel, improve the strength of the steel after quenching and tempering, and slightly improve the plasticity, thereby saving other relatively rare metals such as nickel, chromium and molybdenum. B element is also a lively and easily segregated element, which is easy to segregate at the grain boundaries and will also produce temper brittleness, which is not conducive to the toughness of the steel material. Therefore, in the high-toughness chain steel with excellent hydrogen embrittlement resistance described in the present application, the mass percentage content of B element is controlled to be between 0.0002-0.0015%.

[0025] Preferably, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, inevitable 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≤0.0015%, and H≤0.0002%.

[0026] It should be noted that in the above technical solution 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. Among them:

[0027] P: In the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, P element is a harmful element, although P element can improve the corrosion resistance of steel, but it will deteriorate the performance of steel. Therefore, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the mass percentage of P element can be controlled as P≤0.015%.

[0028] S: In the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, P element is a harmful element, although P element can improve the corrosion resistance of steel, but it will deteriorate the performance of steel. Therefore, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the mass percentage of S element can be controlled as S≤0.01%.

[0029] N: In the high-toughness chain steel with excellent hydrogen embrittlement resistance according to 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 high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the mass percentage of N element can be controlled as N≤0.007%.

[0030] O: In the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, O element can form oxides and complex inclusions with Al deoxidizing element in steel. Therefore, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the mass percentage of O element can be controlled as O≤0.0015%.

[0031] H: In the high-toughness chain steel with excellent hydrogen embrittlement resistance according to 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 high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the mass percentage of H element can be controlled as H≤0.0002%.

[0032] Preferably, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the chemical elements satisfy the following condition: (2Al+1.3B) / N≥10, wherein the chemical elements are substituted by the values before the percentage of mass.

[0033] In the present application, in order to avoid the formation of nitrides of Nb element and N at high temperature, and to reduce the distribution density of NbC particles, the Al and B elements in the steel can be used to consume the N element in the steel, and by controlling the chemical composition of the steel, the content of Al, B and N elements in the steel satisfies the condition: (2Al+1.3B) / N≥10, so as to promote the formation of dispersedly distributed nanoscale NbC particles with a distribution density≥10 12 / m 2 , thereby improving the hydrogen embrittlement resistance of the steel.

[0034] Preferably, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the microstructure is based on tempered martensite, and the nanoscale NbC particles are dispersed in the tempered martensite.

[0035] Preferably, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the hydrogen embrittlement coefficient η≥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 specimen after quenching and tempering heat treatment, and Z2 is the reduction of area of the tensile specimen after being baked at 250℃ for 2 hours, and by controlling the hydrogen embrittlement coefficient η≥0.92, the high-toughness chain steel with excellent hydrogen embrittlement resistance can be ensured to have good hydrogen-induced cracking resistance after quenching and tempering heat treatment.

[0037] Preferably, in the high-toughness chain steel with excellent hydrogen embrittlement resistance according to the present application, the performance satisfies the following conditions: 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℃≥60J.

[0038] Another object of the present application is to provide a manufacturing method of a high-toughness chain steel with excellent hydrogen embrittlement resistance, which can form a large number of dispersedly distributed nanoscale NbC particles in the steel to capture free hydrogen atoms, avoid the aggregation of free hydrogen atoms in the steel to induce hydrogen-induced cracks, and thereby improve the hydrogen embrittlement resistance of the steel.

[0039] In order to achieve the above object, the present application provides a manufacturing method of a high-toughness chain steel with excellent hydrogen embrittlement resistance, which comprises the following steps performed in sequence:

[0040] smelting and casting;

[0041] heating;

[0042] Rolling: Control the initial rolling temperature to be ≥1050℃, preferably 1050~1120℃, the final rolling temperature to be ≥850℃, preferably 850~990℃, and the slow cooling time in the heat preservation pit after rolling to be ≥20h, preferably 20~48h;

[0043] The heat treatment includes quenching at 850–1000℃, holding for 1–5 hours, followed by water quenching; tempering at 400–600℃, holding for 1–5 hours, followed by air or water cooling to room temperature.

[0044] In this invention, the chain steel billet is held at 850–1000°C and then subjected to quenching heat treatment. Heating to the target temperature causes the chain steel billet to fully austenitize, and some carbide or nitride particles in the steel dissolve 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 400–600°C. During tempering, the high-density dislocations formed during quenching are partially annihilated, and the supersaturated 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 nanoscale NbC particle distribution density ≥102 in the steel. 12 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] In this article, "slow cooling" refers to cooling at a rate of less than 0.1℃ / s.

[0048] Preferably, in the manufacturing method of the present invention, in the heating step, the heating temperature is controlled at 1150-1250°C and the holding time is 2-10 hours.

[0049] Preferably, in the manufacturing method of the present invention, during the smelting and casting steps, 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.

[0050] Preferably, the microstructure of the slab obtained after the rolling step is bainite.

[0051] The high-toughness chain steel with excellent hydrogen embrittlement resistance and the manufacturing method thereof have the following advantages and beneficial effects compared with the prior art:

[0052] The high-toughness chain steel with excellent hydrogen embrittlement resistance and the manufacturing method thereof form a large number of nanoscale NbC particles dispersedly distributed in the steel to capture free hydrogen atoms by optimizing the main strengthening elements C, Si, Mn, Ni, Cr and Mo, and by reasonably designing the element ratio of Al, B and N, and combining the heat treatment process in the chain steel production process, so that the hydrogen-induced cracks caused by the aggregation of free hydrogen atoms in the steel are avoided, the hydrogen embrittlement resistance of the steel is improved, and the service life of the mining chain in a harsh environment can be greatly improved.

[0053] In some embodiments, the high-toughness chain steel with excellent hydrogen embrittlement resistance has a hydrogen embrittlement resistance coefficient η≥0.92, 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 Akv≥60 J at -20°C. BRIEF DESCRIPTION OF DRAWINGS

[0054] FIG. 1 shows the electron microscope scanning diagram of the microstructure of the high-toughness chain steel with excellent hydrogen embrittlement resistance after the quenching and tempering heat treatment of Example 1 of the present application. DETAILED DESCRIPTION

[0055] The high-toughness chain steel with excellent hydrogen embrittlement resistance and the manufacturing method thereof will be further explained and described in conjunction with the drawings and specific examples in the specification, but the explanation and description do not constitute an improper limitation on the technical solutions of the present application.

[0056] Examples 1-6 and Comparative Examples 1-3

[0057] The high-toughness chain steel with excellent hydrogen embrittlement resistance of Examples 1-6 is prepared by the following steps:

[0058] (1) Smelting and continuous casting: smelting and continuous casting are performed to obtain a casting blank, and Table 1-1 and Table 1-2 list the chemical composition ratio of each example and comparative example. 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°C, and the secondary cooling section uses weak cooling, and the specific water consumption of the secondary cooling section is 0.2-0.4 L / t steel.

[0059] (2) Heating: The ingot is rolled into finished size using a one-fire forming process. The finished size range is Φ26~100mm. The heating temperature of the ingot is controlled at 1150~1250℃ and the holding time is controlled at 2~10h.

[0060] (3) Rolling: Control the initial rolling temperature or initial forging temperature ≥1050℃, control the final rolling temperature or final forging temperature ≥850℃, and after rolling, put it into the heat preservation pit and slow cool for ≥20h within the range of 400~200℃.

[0061] (4) Quenching and tempering heat treatment: After rolling round steel into chains, quenching and tempering heat treatment is carried out. The quenching heating temperature is 850-1000℃, the holding time is 1-5h, and then water quenching is performed. The tempering temperature is 400-600℃, the holding time is 1-5h, and after tempering, air cooling or water cooling is performed to room temperature.

[0062] It should be noted that the chemical composition design and related processes of the high-strength and high-toughness chain steels with excellent hydrogen embrittlement resistance in Examples 1-6 all meet the design specifications of this invention. The comparative steels of Comparative Examples 1-3 are commercially available finished steels, therefore, they do not have rolled process parameters in Tables 2-1 and 2-2.

[0063] Tables 1-1 and 1-2 list the mass percentages of each chemical element in the high-strength and high-toughness chain steels with excellent resistance to hydrogen embrittlement in Examples 1-6 and the comparative steels in Comparative Examples 1-3.

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

[0065] Table 1-2. (wt%, balance Fe and unavoidable impurities other than P, S, N, O and H)

[0066] Tables 2-1 and 2-2 list the specific process parameters for the high-strength and high-toughness chain steels with excellent resistance to hydrogen embrittlement in Examples 1-6 during the above-mentioned process steps.

[0067] Table 2-1.

[0068] Table 2-2.

[0069] Samples of the hot-rolled high-strength and high-toughness chain steels with excellent hydrogen embrittlement resistance from Examples 1 to 6 were taken, and the microstructure of each example was observed according to "GB / T13298-2015 Metallic Microstructure Inspection Method". The inventors found through microstructure observation that the microstructure of the hot-rolled high-strength and high-toughness chain steels with excellent hydrogen embrittlement resistance obtained by the manufacturing method described in this invention is bainite.

[0070] Samples of the high-strength and high-toughness chain steels of Examples 1-6 with excellent resistance to hydrogen embrittlement after quenching and tempering heat treatment were taken, and the microstructure of each example was observed by scanning electron microscopy. It was found that the matrix of the microstructure of the high-strength and high-toughness chain steels of Examples 1-6 with excellent resistance to hydrogen embrittlement after quenching and tempering heat treatment was tempered martensite.

[0071] As shown in Figure 1, in Example 1, the microstructure of the high-strength and high-toughness chain steel with excellent resistance to hydrogen embrittlement after quenching and tempering heat treatment consists of a tempered martensite matrix and dispersed carbide structure. The carbide structure is NbC.

[0072] In addition, samples of the high-strength and high-toughness chain steels of Examples 1-6, which exhibit excellent resistance to hydrogen embrittlement after quenching and tempering heat treatment, and the control steels of Comparative Examples 1-3 were taken again and subjected to relevant tests. The test results are listed in Table 3. The relevant performance test methods are as follows:

[0073] NbC particle distribution density: Samples of chain steel from Examples 1-6 and Comparative Examples 1-3 were taken, and after preparing transmission electron microscope (TEM) samples, the precipitates in the field of view were observed. More than 20 fields of view were randomly selected, and the particle distribution density of the sample was obtained by dividing the number of NbC precipitates in the field of view by the total area of ​​the field of view.

[0074] Tensile test: According to national standard GB / T 2975, the chain steel of Examples 1 to 6 and Comparative Examples 1 to 3 were sampled and made into tensile specimens. Tensile properties were tested according to national standard GB / T 228.1, and the yield strength, tensile strength, elongation and reduction of area were measured.

[0075] Charpy impact test: According to national standard GB / T 2975, chain steel samples from Examples 1 to 6 and Comparative Examples 1 to 3 were taken and impact test specimens were prepared. Impact performance was tested according to national standard GB / T 229.

[0076] Tables 3-1 and 3-2 list the performance test results of the high-strength and high-toughness chain steels with excellent resistance to hydrogen embrittlement in Examples 1-6 and the comparative steels in Comparative Examples 1-3.

[0077] Table 3-1.

[0078] Table 3-2.

[0079] As shown in Table 3, the NbC particle distribution density of the high-strength and high-toughness chain steels with excellent hydrogen embrittlement resistance in Examples 1-6, prepared by the manufacturing method described in this invention, is ≥5.5×10⁻⁶. 12 pcs / m 2 The hydrogen embrittlement resistance coefficient η after quenching and tempering heat treatment is greater than 0.92, indicating good resistance to hydrogen embrittlement. Furthermore, the high-strength and high-toughness chain steels with excellent hydrogen embrittlement resistance described in Examples 1-6 of this invention also possess good mechanical properties, with a yield strength R... p0.2 All are greater than 1100MPa, tensile strength R m All values ​​are greater than 1250 MPa, elongation A is greater than or equal to 14%, reduction of area Z is greater than 50%, and Charpy impact energy A at -20℃ is... kv All values ​​were greater than 60 J. In Comparative Example 3, the tempering temperature did not meet the requirements of this invention, resulting in a lower distribution density of NbC particles and an inability to obtain excellent hydrogen embrittlement resistance.

[0080] Furthermore, the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0081] It should also be noted that the above examples are merely specific embodiments of the present invention, and the present invention is obviously not limited to the above embodiments, with many similar variations. All modifications that can be directly derived or conceived by those skilled in the art from the content disclosed in this invention should fall within the protection scope of this invention.

Claims

1. A type of chain steel, characterized in that, In addition to Fe and unavoidable impurities, the chain steel also contains the following chemical elements by mass percentage: C: 0.22~0.32%, Si: 0.1~0.5%, Mn: 0.3~1.0%, Cr: 0.2~0.9%, Ni: 2.2~3.5%, Mo: 0.2 ~0.7%, Cu: 0.01~0.2%, Al: 0.015~0.045%, Nb: 0.004~0.04%, B: 0.0002~0.0015%; The microstructure of the chain steel consists of diffusely distributed nano-sized NbC particles, with a NbC particle distribution density ≥10. 12 pcs / m 2 Preferably 10 12 pcs / m 2 ~87*10 12 pcs / m 2 .

2. The chain steel as described in claim 1, characterized in that, The chain steel has the following chemical elements in percentage by mass: C: 0.22–0.32%, Si: 0.1–0.5%, Mn: 0.3–1.0%, Cr: 0.2–0.9%, Ni: 2.2–3.5%, Mo: 0.2–0.7%, Cu: 0.01–0.2%, Al: 0.015–0.045%, Nb: 0.004–0.04%, B: 0.0002–0.0015%; balance Fe and unavoidable impurities.

3. The chain steel as described in claim 1 or 2, characterized in that, Unavoidable impurities include P, S, N, O and H, wherein the elemental content of the impurities satisfies at least one of the following: P≤0.015%, S≤0.01%, N≤0.007%, O≤0.0015%, H≤0.0002%.

4. The chain steel as described in claim 3, characterized in that, The chemical elements of the chain steel also satisfy the following: (2Al+1.3B) / N≥10, where each chemical element is represented by the value before the percentage sign of its mass percentage content.

5. The chain steel as described in claim 1 or 2, characterized in that, The microstructure of the chain steel is based on tempered martensite, and the nano-sized NbC particles are dispersed in the tempered martensite.

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

92.

7. The chain steel as described in claim 1 or 2, characterized in that, The chain steel meets the following performance requirements: yield strength R p0.2 ≥1100MPa, tensile strength Rm≥1250MPa, elongation A≥14%, reduction of area Z≥50%, Charpy impact energy Akv≥60J at -20℃.

8. A method for manufacturing chain steel as described in any one of claims 1-7, characterized in that, The method includes the following steps performed sequentially: Smelting and casting; heating; Rolling: Control the initial rolling temperature to be ≥1050℃, preferably 1050~1120℃, the final rolling temperature to be ≥850℃, preferably 850~990℃, and the slow cooling time in the heat preservation pit after rolling to be ≥20h, preferably 20~48h; The heat treatment includes quenching at 850–1000℃, holding for 1–5 hours, followed by water quenching; tempering at 400–600℃, holding for 1–5 hours, followed by air or water cooling to room temperature.

9. The method as described in claim 8, characterized in that, During the heating process, the heating temperature is controlled at 1150–1250℃, and the holding time is 2–10 hours.

10. The method as described in claim 8, characterized in that, During the smelting and casting processes, the superheat of the molten steel in the tundish is controlled at 20–40°C, and the water volume in the secondary cooling section is 0.2–0.4 liters per ton of steel.

11. The method as described in claim 8, characterized in that, The microstructure of the billet obtained after the rolling process is bainite.

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