Hydrogen-embrittlement-resistant high-strength chain steel and manufacturing method therefor

Abstract

Provided is hydrogen-embrittlement-resistant high-strength chain steel, comprising Fe and inevitable impurities, and further comprising the following chemical elements in percentage by mass: 0.22-0.32% of C, 0.1-0.5% of Si, 0.3-0.8% of Mn, 0.4-1.2% of Cr, 2.2-3.5% of Ni, 0.2-0.7% of Mo, 0.02-0.05% of Al, and 0.02-0.20% of V. The microstructure of the chain steel is tempered martensite, and lath spacing of the tempered martensite is less than or equal to 1.5 μm. Preparation steps include: smelting and casting; heating; rolling; and quenching and tempering heat treatment, wherein quenching is conducted by heating to 850-1000°C, holding for 1-5 h, and then performing water quenching; and tempering is performed at 400-600°C for 1-5 h, followed by air cooling or water cooling to room temperature.

Description

A hydrogen embrittlement resistant high strength chain steel and method of making same TECHNICAL FIELD

[0001] The present invention relates to a steel material and a method of manufacturing the same, and more particularly, to a high strength 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, 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, which is humid and has 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. In addition, there are some schemes 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 the publication number CN110714164A, published on January 21, 2020, and 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, aiming to realize 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, published on May 5, 2020, and 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 the 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 the coal mine is mostly humid, and the high-strength mine chain will inevitably be affected by environmental corrosion during 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 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 hydrogen embrittlement resistant high strength chain steel, which has higher strength and toughness plasticity matching and excellent hydrogen embrittlement 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 containing the following chemical elements in mass percentage in addition to Fe and inevitable impurities:

[0009] C: 0.22-0.32%, Si: 0.1-0.5%, Mn: 0.3-0.8%, Cr: 0.4-1.2%, Ni: 2.2-3.5%, Mo: 0.2-0.7%, Al: 0.02-0.05%, V: 0.02-0.20%;

[0010] The microstructure of the chain steel is tempered martensite, and the interlamellar spacing of the tempered martensite is ≤1.5 μm, preferably 0.5-1.5 μm.

[0011] In the composition system described 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 plasticity matching and excellent hydrogen embrittlement resistance.

[0012] The inventors have further studied the influence of the microstructure after quenching and tempering heat treatment of the chain steel on the hydrogen embrittlement sensitivity, and found that the fine martensite phase boundary formed after quenching and tempering heat treatment of the steel can divide the hydrogen atoms in the steel to form local cages, the phase boundary between the martensites can effectively reduce the diffusion speed of the hydrogen atoms in the steel, inhibit the long-range diffusion and aggregation of the hydrogen atoms, thereby avoiding the aggregation of free hydrogen atoms in the steel to form white spot defects and hydrogen-induced cracks, and the hydrogen embrittlement resistance of the steel can be obviously improved.

[0013] In the present application, when the interlamellar spacing of the tempered martensite is less than 1.5 μm, the diffusion and aggregation speed of the hydrogen atoms in the steel can be significantly reduced, the hydrogen atoms cannot be aggregated, and white spot defects and hydrogen-induced cracks can be avoided, thereby improving the hydrogen embrittlement resistance of the steel. When the interlamellar spacing of the tempered martensite exceeds 1.5 μm, the phase boundary of the martensite gradually loses the effect of inhibiting the diffusion and aggregation of the hydrogen atoms in the steel, and the hydrogen atoms are easily aggregated in the steel to form white spot defects, so that the steel is prone to hydrogen-induced cracks and early failure. Therefore, in the hydrogen embrittlement resistant high strength chain steel described in the present application, the interlamellar spacing of the tempered martensite needs to be controlled to be ≤1.5 μm.

[0014] Preferably, in the hydrogen embrittlement resistant high-strength chain steel according to the present application, the chain steel has the following chemical elements in mass percentage:

[0015] C: 0.22-0.32%, Si: 0.1-0.5%, Mn: 0.3-0.8%, Cr: 0.4-1.2%, Ni: 2.2-3.5%, Mo: 0.2-0.7%, Al: 0.02-0.05%, V: 0.02-0.20%; the balance being Fe and inevitable impurities.

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

[0017] C: In the hydrogen embrittlement resistant high-strength chain steel according to the present application, the C element is an essential element to ensure the strength of the steel, and increasing the C element content in the steel will increase the non-equilibrium structure transformation ability of the steel, thereby significantly increasing the strength of the steel. By controlling the cooling speed of the steel during quenching through a heat treatment process, the diffusion of the C element in the steel to form shear-type martensite phase change can be inhibited, thereby significantly increasing the strength of the steel. However, when the C element content is too high, it is not good for the plasticity and toughness of the steel, and it will significantly increase the carbon equivalent of the material, thereby deteriorating the welding performance of the steel. Based on this, in the hydrogen embrittlement resistant high-strength chain steel according to the present application, the mass percentage of the C element is controlled to be between .

[0018] Si: In the hydrogen embrittlement resistant high-strength chain steel according to the present application, the Si element can be solid-solved in the steel to play a role of solid solution strengthening, which can significantly increase the yield strength, fatigue strength and hardness of the steel. The solubility of Si element in cementite is very low, but when the Si element content is too high, it will form non-carbide bainite structure, and at the same time, it will increase the brittleness of the steel. Based on this, in the hydrogen embrittlement resistant high-strength chain steel according to the present application, the mass percentage of the S element is controlled to be between .

[0019] Mn: In the hydrogen embrittlement resistant high-strength chain steel according to the present application, the Mn element can improve the stability of austenite in the steel, and at the same time, it can also improve the hardenability of the steel. The Mn element 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 element content is too high, it can make the austenite grains grow easily during quenching heating, and it can also promote the segregation of harmful elements at the grain boundaries. Therefore, in the hydrogen embrittlement resistant high-strength chain steel according to the present application, the mass percentage of the Mn element is controlled to be between .

[0020] Cr: In the hydrogen embrittlement resistant high-strength 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. In addition, both 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 the Cr element is too high, a large amount of carbide is easy to be generated, which will gather at the grain boundary and reduce the toughness of the material, and significantly increase the carbon equivalent to reduce the welding performance of the chain steel. Therefore, in the hydrogen embrittlement resistant high-strength chain steel described in the present application, the mass percentage of the Cr element is controlled to be between .

[0021] Ni: In the hydrogen embrittlement resistant high-strength 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 also reduce the C content of the eutectoid point, can improve the strength of the steel without significantly affecting the plasticity of the steel. At the same time, the Ni element can 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. In addition, while improving the strength of the steel, the Ni element has less damage to the toughness, plasticity and other process performance of the steel than other alloy elements. When the Ni element is used in combination with the Cr element, the hardenability of the steel can also be significantly improved. As can be seen from the carbon equivalent formula, the coefficient of the Ni element 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 embrittlement resistant high-strength chain steel described in the present application, the mass percentage of the Ni element is controlled to be between .

[0022] Mo: In the hydrogen embrittlement resistant high-strength 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, and Mo is a precious alloy element, and adding a higher Mo will lead to an increase in cost. Therefore, in the hydrogen embrittlement resistant high-strength chain steel described in the present application, the mass percentage of the Mo element is controlled to be between .

[0023] Al: In the hydrogen embrittlement resistant high-strength chain steel described in the present application, the main role of the Al element is deoxidation and nitrogen fixation, and the A1N formed by the combination of the Al element and the N element can effectively refine the grains. However, when the content of the 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 embrittlement resistant high-strength chain steel described in the present application, the mass percentage of the Al element is controlled to be between .

[0024] V: In the hydrogen embrittlement resistant high-strength 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. The V element has a very strong affinity with C, N, and O elements, and mainly exists in the form of carbides or nitrides, oxides in the steel, and can significantly improve the strength of the steel in the form of dispersed precipitation. However, if the V element is added in too high an amount, the toughness and welding performance of the steel will be reduced. Therefore, in the hydrogen embrittlement resistant high-strength chain steel described in the present application, the mass percentage of the V element is controlled to be between 0.5% and 1.5%.

[0025] Preferably, in the hydrogen embrittlement resistant high-strength chain steel described in the present application, the mass percentage of each chemical element also satisfies: (0.5Mn+2Ni) / (1.3Cr+1.2Mo+1.5V)≥3, wherein each chemical element is substituted into the value before the mass percentage.

[0026] In the present application, the inventors found through a large number of studies that the Mn, Cr, Ni, Mo, and V alloying elements in the steel have a direct impact on the austenite phase region and the stability of the austenite of the steel. Controlling the content of the Mn, Cr, Ni, Mo, and V alloying elements in the steel to satisfy: (0.5Mn+2Ni) / (1.3Cr+1.2Mo+1.5V)≥3 can further promote the steel to form a martensite interlamellar spacing of less than 1.5 μm when the martensite phase change occurs during subsequent quenching and tempering heat treatment.

[0027] Preferably, in the hydrogen embrittlement resistant high-strength chain steel described in the present application, 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%, and H≤0.0002%.

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

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

[0030] S: In the hydrogen embrittlement resistant high-strength chain steel described in the present application, the S element is a harmful element. Therefore, in the hydrogen embrittlement resistant high-strength chain steel described in the present application, the mass percentage of the S element can be controlled to be S≤0.01%. ​

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

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

[0033] H: In the hydrogen embrittlement resistant high strength chain steel described in the present application, the H element will gather at defects in the steel, especially high strength steel with tensile strength exceeding 1000 MPa is more sensitive to H content, the H element will cause hydrogen-induced delayed fracture of the steel, resulting in early failure of the chain. Therefore, in the hydrogen embrittlement resistant high strength chain steel described in the present application, the mass percentage of the H element can be controlled as H≤0.0002%.

[0034] Preferably, in the hydrogen embrittlement resistant high strength chain steel described in the present application, the average size of the original austenite grains is ≤22 μm.

[0035] Preferably, in the hydrogen embrittlement resistant high strength chain steel described in the present application, the hydrogen embrittlement resistant coefficient η of the chain steel is ≥0.92.

[0036] In the present application, the hydrogen embrittlement resistant 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°C for 2 hours after quenching and tempering heat treatment. Controlling the hydrogen embrittlement resistant coefficient η ≥0.92 can ensure that the hydrogen embrittlement resistant high strength chain steel has good resistance to hydrogen-induced cracking after quenching and tempering heat treatment.

[0037] Preferably, in the hydrogen embrittlement resistant high strength chain steel described in the present application, the properties after quenching and tempering heat treatment satisfy: yield strength R p0.2 ≥1100 MPa, tensile strength Rm≥1250 MPa, elongation A≥14%, reduction of area Z≥50%, room temperature impact energy AKV≥80 J, and -20°C Charpy impact energy Akv≥70 J.

[0038] Another object of the present application is to provide a manufacturing method of a hydrogen embrittlement resistant high strength chain steel, which can significantly improve the hydrogen embrittlement resistant performance of the high strength chain steel.

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

[0040] smelting and casting;

[0041] heating;

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

[0043] quenching and tempering heat treatment, wherein the quenching heat treatment temperature is 850-1000℃, the holding time is 1-5h, and then water quenching; the tempering temperature is 400-600℃, the holding time is 1-5h, and then air cooling or water cooling to room temperature.

[0044] In the quenching and tempering heat treatment of the present application, the chain steel blank of the present application is quenched after holding at 850-1000℃, and heating to the target temperature can make the chain steel blank fully austenitized, wherein the carbide or nitride particles are partially dissolved into the austenite. The undissolved carbide and carbide particles continue to pin the austenite grain boundaries, inhibit the growth of austenite grains, and make the average size of the original austenite grains of the steel≤22μm. At the same time, during quenching, the Cr, Ni, Mo elements in the steel improve the hardenability of the steel, and finer martensite structure can be formed in the steel of the present application, and the martensite interlamellar spacing in the steel is less than 1.5μm.

[0045] In addition, the chain steel of the present application can be tempered at 400-600℃, and during tempering, the high-density dislocations formed in the chain steel during quenching are partially annihilated, and the supersaturated elements in the non-equilibrium structure of the steel are precipitated in the form of carbides in the interlamellar martensite to form tempered martensite structure.

[0046] Herein, the cooling speed of air cooling is generally 0.1-1℃ / s, the cooling speed of water cooling is generally greater than 10℃ / s, and the cooling speed of quenching is generally 20-200℃ / s.

[0047] Preferably, in the manufacturing method of the hydrogen embrittlement resistant high strength chain steel of the present application, in the heating step, the heating temperature is controlled to be 1150-1250℃, and the holding time is 2-10h.

[0048] Preferably, in the manufacturing method of the hydrogen embrittlement resistant high strength chain steel of the present application, in the rolling step, the slow cooling after rolling is in the range of 200-350℃ for 20-50h.

[0049] Herein, "slow cooling" refers to cooling at a speed lower than 0.1℃ / s.

[0050] Preferably, in the manufacturing method of the hydrogen embrittlement resistant high strength chain steel according to the present application, in the smelting and casting step, the intermediate ladle baking temperature is controlled to be ≥1100℃, preferably 1100℃-1250℃, the baking time is controlled to be ≥4h, preferably 4h-6h, and the intermediate ladle molten steel superheat is controlled to be 15-40℃.

[0051] Preferably, the microstructure of the blank prepared after the rolling step is bainite.

[0052] The hydrogen embrittlement resistant high strength chain steel and the manufacturing method thereof according to the present application have the following advantages and beneficial effects compared to the prior art:

[0053] In the hydrogen embrittlement resistant high strength chain steel according to the present application, the main strengthening elements C, Si, Mn, Ni, Cr and Mo in the steel are optimized by reasonable element ratio design, and the austenite grain size of the steel and the martensite structure transformation during quenching and cooling are controlled by the heat treatment process in the chain steel production process, so that fine lamellar tempered martensite structure is realized in the chain steel. The fine martensite phase interface can effectively reduce the diffusion speed of hydrogen atoms in the steel, inhibit the short-range diffusion and aggregation of hydrogen atoms, thereby avoiding the aggregation of free hydrogen atoms in the steel to form white spot defects and hydrogen-induced cracks, and the hydrogen embrittlement resistance of the steel can be significantly improved, thereby the service life of the mining chain in harsh environments can be greatly improved.

[0054] In the hydrogen embrittlement resistant high strength chain steel according to the present application, the reasonable design of the ratio of each alloying element makes full use of the influence of various alloying elements and their interaction on the performance after quenching and tempering heat treatment, so that the high strength chain steel according to the present application has high strength and toughness and plasticity matching.

[0055] In some embodiments, the hydrogen embrittlement resistant high strength chain steel according to the present application has a hydrogen embrittlement coefficient η≥0.92, a yield strength R p0.2 ≥1100MPa, a tensile strength Rm≥1250MPa, an elongation A≥14%, a reduction of area Z≥50%, a room temperature impact energy AKV≥80J, and a-20℃ Charpy impact energy Akv≥70J. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 shows the electron microscope scanning image of the microstructure of the hydrogen embrittlement resistant high strength chain steel according to Example 1 of the present application after quenching and tempering heat treatment. DETAILED DESCRIPTION

[0057] The hydrogen embrittlement resistant high strength chain steel and the manufacturing method thereof will be further explained and described below in combination with the drawings and specific examples in the specification, but the explanation and description do not constitute undue limitations on the technical solutions of the present application.

[0058] Examples 1-6 and Comparative Examples 1-3

[0059] The hydrogen embrittlement resistant high strength chain steels of Examples 1-6 were produced using the following steps:

[0060] (1) Melting and continuous casting: The melting and continuous casting were performed to obtain a cast slab, and the chemical composition ratios of each example are listed in Table 1-1 and Table 1-2. The melting can be performed using 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. The tundish baking temperature is controlled to be greater than or equal to 1100°C, the baking time is controlled to be greater than or equal to 4h, and the tundish molten steel superheat is controlled to be 15-40°C.

[0061] (2) Heating and rolling: The cast ingot was rolled into a finished size using a one-fire material process, and the finished size can range from Φ26 to 100mm. The ingot heating temperature was controlled to be 1150-1250°C, and the holding time was controlled to be 2-10h. The rolling temperature or forging temperature was controlled to be greater than or equal to 1050°C, and the final rolling temperature or final forging temperature was controlled to be greater than or equal to 850°C. After rolling, the temperature was cooled in the holding pit at 200-350°C for 20-50h.

[0062] (3) Quenching and tempering heat treatment, wherein the quenching heating temperature was 850-1000°C, the holding time was 1-5h, and then water quenching. The tempering temperature was 400-600°C, the holding time was 1-5h, and then air or water cooling to room temperature.

[0063] Comparative Examples 1-2 were purchased finished materials without quenching and tempering heat treatment, and then quenching and tempering heat treatment was performed thereon, so they do not have the rolling state process parameters in Table 2-1 and 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 embrittlement resistant high strength chain steels of Examples 1-6 and the comparative steels of Comparative Examples 1-3.

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

[0066] Table 1-2. (wt%, the balance being 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 embrittlement resistant high strength chain steels of Examples 1-6 and the comparative steels of Comparative Examples 1-3 in the above process steps.

[0068] Table 2-1.

[0069] Table 2-2.

[0070] The hydrogen embrittlement resistant high-strength chain steels in hot-rolled state of Examples 1-6 were sampled, and microstructure observation was performed according to the "GB / T13298-2015 Metal Microstructure Test Method". The inventors found through microstructure observation that the microstructure of the hydrogen embrittlement resistant high-strength chain steels in hot-rolled state prepared by the manufacturing method described in the application was all bainite.

[0071] The hydrogen embrittlement resistant high-strength chain steels of Examples 1-6 after quenching and tempering heat treatment were sampled, and microstructure observation was performed using a scanning electron microscope, and it was found that the microstructure of the hydrogen embrittlement resistant high-strength chain steels of Examples 1-6 after quenching and tempering heat treatment was all tempered martensite.

[0072] As shown in Figure 1, in Example 1, the microstructure of the hydrogen embrittlement resistant high-strength chain steel after quenching and tempering heat treatment was tempered martensite.

[0073] In addition, the hydrogen embrittlement resistant high-strength chain steels of Examples 1-6 and the comparative steels of Comparative Examples 1-3 after quenching and tempering heat treatment were again sampled, and relevant microstructure detection and performance testing were performed, and the obtained detection results are listed in Table 3. Among them, the relevant performance testing methods are as follows:

[0074] Original austenite grain size: according to the "GB / T6394-2017 Metal Average Grain Size Determination Method" standard, the original austenite grain size of the steel was determined by the intercept method.

[0075] Tempered martensite interlamellar spacing (μm): after quenching, the chain steel was selected to make a metallographic sample, and the martensite interlamellar spacing was observed and measured under a 1000X scanning electron microscope.

[0076] Tensile test: according to the national standard GB / T 2975, the chain steels of Examples 1-6 and Comparative Examples 1-2 were sampled and made into tensile samples, and the tensile performance test was performed according to the national standard GB / T 228.1 to measure the yield strength, tensile strength, elongation and reduction of area.

[0077] Charpy impact test: according to the national standard GB / T 2975, the chain steels of Examples 1-6 and Comparative Examples 1-2 were sampled and made into impact samples, and the impact performance test was performed according to the national standard GB / T 229.

[0078] Table 3 lists the relevant performance test results of the hydrogen embrittlement resistant high-strength chain steels of Examples 1-6 and the comparative steels of Comparative Examples 1-3 described in the application.

[0079] Table 3.

[0080] As shown in Table 3, the hydrogen embrittlement resistant high strength chain steel of Examples 1-6 prepared by the manufacturing method of the present application has excellent performance, the austenite grain size of each example is less than or equal to 21 μm, the martensite interlamellar spacing is less than or equal to 1.41 μm, and the hydrogen embrittlement coefficient η is greater than or equal to 0.92. At the same time, the hydrogen embrittlement resistant high strength chain steel of Examples 1-6 has good mechanical properties, the yield strength R p0.2 is greater than 1100 MPa, the tensile strength Rm is greater than 1250 MPa, the elongation A is greater than or equal to 14%, the reduction of area Z is greater than 50%, the room temperature impact energy AKV is greater than 80 J, and the -20℃ Charpy impact energy Akv is greater than 70 J. In Comparative Example 3, the quenching and tempering temperature does not meet the requirements of the present application, so the martensite interlamellar spacing is high, and excellent hydrogen embrittlement performance cannot be obtained.

[0081] In addition, the combination of the technical features in the present application is not limited to the combination in the claims of the present application or the combination in the specific embodiments, and all the technical features disclosed in the present application can be freely combined or combined in any manner, unless contradictory.

[0082] It should also be noted that the above-mentioned is only a specific embodiment 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 of by those skilled in the art from the disclosure of the present application should belong to the protection scope of the present application.

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: 0.3~0.8%, Cr: 0.4~1.2%, Ni: 2.2~3.5%, Mo: 0.2~0.7%, Al: 0.02~0.05%, V: 0.02~0.20%; The microstructure of the chain steel is tempered martensite, and the interlamellar spacing of the tempered martensite is ≤1.5μm, preferably 0.5~1.5μm.

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: 0.3–0.8%, Cr: 0.4–1.2%, Ni: 2.2–3.5%, Mo: 0.2–0.7%, Al: 0.02–0.05%, V: 0.02–0.20%; balance Fe and unavoidable impurities.

3. The chain steel as described in claim 1 or 2, characterized in that, The chemical elements of the chain steel also satisfy the following: (0.5Mn+2Ni) / (1.3Cr+1.2Mo+1.5V)≥3, where each chemical element is represented by the value before the percentage sign of its mass percentage content.

4. The chain steel as described in claim 1 or 2, characterized in that, Unavoidable impurities include P, S, N, O, and H, wherein the content of the impurity element satisfies at least one of the following: P ≤ 0.015%, S≤0.01%, N≤0.007%, O≤0.0018%, H≤0.0002%.

5. The chain steel as described in claim 1 or 2, characterized in that, The average size of the original austenite grains in the chain steel is ≤22μm, preferably 17~22μm.

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%, room temperature impact energy AKV≥80J, -20℃ Charpy impact energy Akv≥70J.

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 ≥1050℃, preferably 1050~1120℃, and the final rolling temperature to ≥850℃, preferably 850~990℃; 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 rolling process, after rolling, the product is placed in a heat preservation pit and slowly cooled for 20 to 50 hours within the range of 200 to 350°C.

11. The method as described in claim 8, characterized in that, In the smelting and casting steps, the tundish baking temperature is controlled at ≥1100℃, preferably 1100℃~1250℃, the baking time is controlled at ≥4h, preferably 4h~6h, and the tundish steel superheat is controlled at 15~40℃.

12. The manufacturing 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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