High-strength and high-toughness mining chain steel and manufacturing method therefor

Abstract

Disclosed are a high-strength and high-toughness mining chain steel and a manufacturing method therefor. The chain steel comprises the following chemical components in percentage by mass: C: 0.19-0.30%, Si: 0.05-0.6%, Mn: 1.0-1.8%, Cr: 0.4-0.8%, Ni: 0.5-0.9%, Mo: 0.3-0.55%, Ti: 0.015-0.035%, Al: 0.011-0.05%, B: 0.0015-0.005%, and N: 0.002-0.006%, the remainder being iron and unavoidable impurities. The high-strength and high-toughness mining chain steel of the present invention has excellent impact toughness while also having high strength, and can be widely used in fields requiring high-strength steel such as marine engineering and mining machinery.

Description

A high-strength and high-toughness mining chain steel and its manufacturing method Technical Field

[0001] The present invention relates to the technical field of chain steel, and in particular to a high-strength and high-toughness mining chain steel and a manufacturing method thereof. Background Art

[0002] Mining chain links are essential components used in mechanized coal mining underground. They primarily serve as transmission chains in scraper conveyors, scraper transfer machines, shearers, and plows. In actual use, mining chain links require high strength, toughness, fatigue resistance, and wear resistance to ensure proper operation. Because coal mines often operate in humid, corrosive environments, mining chain links are often also required to exhibit excellent corrosion resistance.

[0003] In the existing technology, the mining round link chain steel commonly used in the coal mining industry is usually the chain steel grade in "GB / T 10560-2017 Steel for Welded Round Link Chains for Mining". Among them, high-strength mining round link chain steel is mainly 23MnNiMoCr54 steel (abbreviated as 54 steel) and other grades are the most widely used; in addition, in response to the needs of different downstream users in actual applications, major domestic steel mills have developed a series of high-strength mining chain steel.

[0004] The Chinese patent with publication number CN110714164A ("A high-quality Cr54 steel for coal mine chain links and its production method", published on November 6, 2020) discloses a high-quality 54 steel for coal mine chain links, 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 brittleness and hot brittleness resistance of the chain steel.

[0005] Chinese patent publication number CN104532143A (“A large-size, high-strength chain steel for mining and its manufacturing method”, published on April 22, 2015) discloses an improved large-size chain steel for mining with a diameter of 40 to 100 mm, a yield strength of 980 MPa or higher, a tensile strength of 1180 MPa or higher, an elongation of 13%, a cross-sectional reduction of 50%, and a room temperature Charpy impact energy of >100 J.

[0006] In addition, some technologies have optimized the steel based on the composition of 54 steel. For example, Chinese patent publication number CN111101078A ("A Nickel-Free High-Strength Mining Round Link Chain Steel and Its Production Method," published on May 5, 2020) discloses a high-strength mining round link chain steel that does not contain nickel. By reducing the alloy content of the precious metal element Ni while increasing the alloy content of C, Si, Cr, and Mo, it significantly reduces production costs while ensuring mechanical properties.

[0007] The above technology mainly prepares mining chain steel with higher strength by optimizing the design of components, improves the wear resistance of the chain, obtains a longer service life, and reduces the cost of chain use.

[0008] However, it should be noted that in actual use, coal mines often operate in a humid working environment, and high-strength chains are inevitably subject to environmental corrosion during use. Furthermore, high-strength chains are subject to high stress and are more sensitive to stress corrosion. This can lead to corrosion fatigue fractures (frequent low-load brittle fractures within a few months or even days) in mid-life, causing premature failure of the chain.

[0009] Based on this, the inventors aim to provide a new chain steel with excellent overall performance. By optimizing the alloy composition, the present invention not only achieves high strength, but also achieves an excellent toughness-ductility balance and low production costs. This effectively addresses the problem of existing chains suffering from a mismatch between strength and toughness, which limits their service life.

[0010] Summary of the Invention

[0011] To address the problem of existing chains suffering from a mismatch between strength and toughness, which limits their service life, the present invention provides chain steel and a method for manufacturing the same. Specifically, by designing the alloy composition and optimizing the manufacturing process, the present invention produces high-strength and high-toughness mining chain steel that combines high strength with a good balance of toughness and ductility, while also exhibiting excellent wear resistance and fatigue resistance.

[0012] To achieve the above object, the present invention adopts the following technical solutions:

[0013] A first aspect of the present invention provides a chain steel, which contains the following chemical components in mass percentage: C: 0.19-0.30%, preferably 0.20-0.30%, Si: 0.05-0.6%, preferably 0.21-0.47%, Mn: 1.0-1.8%, Cr: 0.4-0.8%, Ni: 0.5-0.9%, Mo: 0.3-0.55%, Ti: 0.015-0.035%, Al: 0.011-0.05%, preferably 0.02-0.05%, B: 0.0015-0.005%, N: 0.002-0.006%, and the balance is iron and unavoidable impurities.

[0014] A second aspect of the present invention provides a chain steel, which, in addition to containing more than 90% of Fe and unavoidable impurities, also contains the following chemical components by mass percentage: C: 0.19-0.30%, preferably 0.20-0.30%, Si: 0.05-0.6%, preferably 0.21-0.47%, Mn: 1.0-1.8%, Cr: 0.4-0.8%, Ni: 0.5-0.9%, Mo: 0.3-0.55%, Ti: 0.015-0.035%, Al: 0.011-0.05%, preferably 0.02-0.05%, B: 0.0015-0.005%, N: 0.002-0.006%.

[0015] Preferably, among the unavoidable impurities, P≤0.012%, S≤0.01%, O≤0.0015%, and H≤0.00015%.

[0016] Preferably, the chemical composition of the chain steel satisfies the following formula: Ti / (O+2N)=2-4; wherein Ti, O, and N are the mass percentage contents of the corresponding elements, respectively.

[0017] Preferably, a portion of the B element in the chain steel exists in the form of solid solution, wherein the proportion of the B element in the form of solid solution to the total content of the B element is 固 / B 总 =65~85%.

[0018] Preferably, the microstructure of the chain steel is tempered martensite and carbides dispersed between lamellae.

[0019] Preferably, the chain steel has the following properties: yield strength Rp 0.2 ≥1150MPa, tensile strength R m ≥1250MPa, preferably ≥1293MPa, elongation A≥13%, section shrinkage Z≥50%, room temperature impact energy A kv ≥60J.

[0020] A third aspect of the present invention provides a method for manufacturing the chain steel, comprising:

[0021] (1) smelting and continuously casting molten steel to obtain ingots; the smelting steps are sequentially electric furnace smelting, LF furnace refining and vacuum refining; during the vacuum refining process, the molten steel is cooled for more than 10 minutes before tapping;

[0022] (2) subjecting the ingot to rolling, quenching and tempering treatment processes to obtain the chain steel; the heating temperature of the quenching treatment is 850-980°C, and the holding time is 1-4 hours; the tempering temperature of the tempering treatment is 390-550°C, preferably 400-550°C, more preferably 400-450°C, and the tempering time is 1-3 hours, and the steel is water-cooled to room temperature after the tempering treatment.

[0023] Preferably, during the electric furnace smelting process, molten iron and scrap steel are used as raw materials, foamed slag is produced throughout the electric furnace smelting process, the endpoint C content of the molten steel is controlled to be 0.06-0.10%, and the molten steel tapping temperature is 1640-1680°C.

[0024] Preferably, during the electric furnace smelting process, the percentage of molten iron in the raw material is controlled to be 30-60%.

[0025] Preferably, the LF furnace refining process includes the following steps performed in sequence:

[0026] 1) Add lime and fluorite to slag in the early stage of LF refining;

[0027] 2) Use aluminum particles or silicon carbide to enhance deoxidation and desulfurization, and feed aluminum wire according to the target Al composition in the molten steel;

[0028] 3) Adjust the alloy composition and temperature of the molten steel to the target requirements before tapping.

[0029] Preferably, during the vacuum refining process, the molten steel after LF refining is subjected to slag treatment, and vacuum degassing refining is carried out in a VD furnace or an RH furnace. Al is supplemented according to the chemical composition requirements of the molten steel to ensure that the free oxygen content in the molten steel is less than 5 ppm, Ca and ferrotitanium are added, and ferroboron is added after 5 to 10 minutes to adjust the composition of the molten steel to the target composition.

[0030] Preferably, when vacuum degassing and refining are carried out in the VD furnace or RH furnace, the strong stirring time is greater than 10 minutes under the condition of a vacuum degree of less than 67 Pa.

[0031] Preferably, the titanium wire is used for the titanium iron; and the boron wire is used for the boron iron.

[0032] Preferably, during the continuous casting process, full-process protective pouring is adopted, the superheat of the molten steel in the tundish is controlled to be 15-30°C, electromagnetic stirring is used in the crystallizer and at the end of solidification, and a light pressure reduction of 10-25 mm is adopted at the end of solidification to obtain the ingot.

[0033] Preferably, the continuous casting speed in the continuous casting process is 0.42-0.8 m / min, preferably 0.5-0.8 m / min, and constant casting speed control is adopted. The secondary cooling water ratio is 0.3-0.5 L / t, and the billet is hot transported or slowly cooled in a slow cooling pit.

[0034] Preferably, during the rolling process, the ingot is sent to a heating furnace for heating and then rolled, the heating temperature is controlled to be 1150-1250°C, the heating and holding time is 2-6h, the starting rolling temperature is ≥1100°C, and the finishing rolling temperature is ≥850°C.

[0035] Preferably, during the rolling process, the ingot is taken out of the heating furnace, descaled by high-pressure water and then rolled, and then sent to a holding pit for slow cooling for ≥24 hours.

[0036] In the chain steel of the present invention, the design principle of each chemical element is as follows: In this document, unless otherwise explicitly stated, the element content is expressed in mass percentage.

[0037] C: C is an essential element for ensuring steel strength. Increasing the C content in steel increases the steel's ability to undergo non-equilibrium structural transformations, significantly improving its strength. The present invention utilizes a quenching and tempering process to inhibit the diffusion of C in the steel, leading to a shear-type martensitic transformation, thereby significantly improving its strength. However, excessive C content in steel should not be excessive. Excessive C content can negatively impact the steel's plasticity and toughness, significantly increase the material's carbon equivalent, and degrade its weldability. Therefore, the C content is controlled to 0.19-0.30%, preferably 0.20-0.30%.

[0038] Si: Adding an appropriate amount of Si to steel can improve the stability of austenite during cooling and prevent the formation of coarse carbides. However, it is important to note that the Si content in steel should not be too high. Excessive Si content in steel can increase its brittleness. For this reason, the Si content is controlled to 0.05-0.6%, preferably 0.21-0.47%.

[0039] Mn: Adding an appropriate amount of Mn can not only improve the stability of austenite in steel, but also improve the hardenability of steel. In addition, in the present invention, Mn can also improve the strength of martensite in steel through solid solution strengthening, thereby improving the strength of steel. However, it should be noted that the Mn content in steel should not be too high. When the Mn content in steel is too high, it will make the quenching and heating austenite grains easy to grow, and will also promote the segregation of harmful elements at the grain boundaries. Based on this, the content of Mn element is controlled to 1.0~1.8%.

[0040] Cr: Cr can improve the hardenability of steel, form a hardened martensitic structure, and help improve the strength of steel. In addition, Cr carbides can slow down the grain growth in the heat-affected zone at the weld joint, which is very beneficial to the welding structure of mining chains. Adding an appropriate amount of Cr and Ni to the steel is beneficial to improving the corrosion resistance of the steel. However, it should be noted that the Cr content in the steel should not be too high. When the Cr content in the steel is too high, the formation of carbides during the quenching and tempering heat treatment will consume a large amount of C in the steel, and a large amount of carbides will accumulate at the grain boundaries, reducing the toughness of the material and significantly increasing the carbon equivalent, thereby reducing the flash welding performance of the chain steel. Based on this, the Cr content is controlled to 0.4-0.8%.

[0041] Ni: Ni can exist in steel in the form of a solid solution. Ni can be used in combination with Cr to significantly improve the hardenability of steel. Adding an appropriate amount of Ni to steel can reduce the carbon content of the eutectic point, which is beneficial to improving the strength of the steel. In addition, it can be seen from the carbon equivalent formula that the coefficient of Ni is small and has little effect on welding performance. However, Ni is a precious alloy element, and excessive addition of Ni will lead to increased production costs. Therefore, in order to obtain excellent performance while ensuring low production costs, the content of Ni is controlled to 0.5-0.9%.

[0042] Mo: Mo exists primarily in steel as a solid solution, providing a solid solution strengthening effect, improving the steel's hardenability and enabling the formation of martensite during quenching. However, excessive Mo addition to steel is not recommended. Excessive Mo addition significantly increases the material's carbon equivalent, impairing the flash welding performance of chain steel. Furthermore, Mo is a precious alloying element, and excessive Mo addition can lead to increased production costs. For this reason, the Mo content is controlled to 0.3-0.55%.

[0043] B: The main function of B is to increase the hardenability of steel, thereby saving other more scarce and expensive elements such as nickel and molybdenum. However, B is relatively active and has a strong affinity with elements such as oxygen and nitrogen, easily forming boron oxide and boron nitride. This causes B to lose its beneficial effects, causing the hardenability of the steel to fluctuate and affect the stability of the steel's performance. Excessive B will form intermetallic compounds with Fe and segregate at grain boundaries, which is detrimental to the toughness of the steel and tends to increase temper brittleness. Therefore, in the high-strength and high-toughness mining chain steel of the present invention, the B content is controlled to be: 0.0015-0.005%.

[0044] Ti: Ti has a strong affinity for nitrogen, oxygen, and carbon, and has a high precipitation temperature. It is an effective element for fixing nitrogen and oxygen, thus preventing the B element in the steel from combining with oxygen and nitrogen and losing its effect on improving hardenability. Ti forms fine precipitates in steel, which can improve the strength and toughness of the steel, especially its impact toughness at low temperatures. However, if the Ti content in the steel is too high, coarse, angular particles will form during the smelting and solidification process, reducing the impact toughness of the steel. Therefore, in the high-strength and high-toughness mining chain steel of the present invention, the Ti content is controlled to 0.015-0.035%.

[0045] Al: Al's primary function is deoxidation. Furthermore, Al combined with N to form AlN effectively refines grains. However, it's important to note that the Al content in steel should not be too high. Excessive Al content can affect the steel's castability and toughness. Therefore, in the high-strength, high-toughness mining chain steel of the present invention, the mass percentage of Al is controlled between 0.011% and 0.05%, preferably between 0.02% and 0.05%.

[0046] N: N is an austenite-forming element and also forms MX-type precipitates, contributing to grain refinement. In B-containing steels, N combines with B, depleting the B's alloying properties. To prevent N from consuming B, the N content in the steel must be strictly controlled. In the high-strength, high-toughness mining chain steel of the present invention, the N content is controlled to between 0.002% and 0.006% by weight.

[0047] In the chain steel of the present invention, the impurity element contents, expressed in mass percentage, satisfy the following: P ≤ 0.012%, S ≤ 0.01%, O ≤ 0.0015%, and H ≤ 0.00015%. P, S, O, and H are all impurity elements in steel. To obtain steel with improved performance and higher quality, the content of these impurity elements should be minimized, if technical conditions permit.

[0048] Impurity elements P and S are both unavoidable and harmful elements in steel, both of which deteriorate its properties. While P can improve steel's corrosion resistance, its overall negative effects are greater. Therefore, the P content is controlled to no more than 0.012%, and the S content is controlled to no more than 0.01%.

[0049] The impurity element O can form oxides and complex inclusions with elements such as Al, Ti, and B in steel, which are detrimental to the performance of the steel. Therefore, the O content is controlled to no more than 0.0015%.

[0050] The impurity element hydrogen accumulates at defects in steel. High-strength steels with tensile strengths exceeding 1000 MPa are particularly sensitive to hydrogen content. Hydrogen-induced delayed fracture caused by elemental hydrogen can lead to premature chain failure. Therefore, the hydrogen content is controlled to no more than 0.00015%.

[0051] In other embodiments, other harmful elements may be present in the steel, such as As, Pb, Sn, Sb, Bi, etc. Under the requirements of national laws, regulations and standards, the content of these harmful elements should be reduced as much as possible.

[0052] The present invention improves steel performance by rationally designing the main alloying elements and adding the element B, reduces the amount of expensive alloys Ni and Mo added, fully utilizes the effects of various alloying elements and their interactions on the microstructure and mechanical properties, and precisely controls the microstructure of the steel of the present invention, so that the high-strength steel of the present invention has both high strength and toughness-plasticity matching, as well as good wear resistance and fatigue resistance.

[0053] In a specific embodiment, in order to ensure that the B element in the steel can function in the steel in a solid solution form, Ti is used to fix O and N in the chain steel of the present invention, and its chemical composition satisfies the following formula: Ti / (O+2N)=2~4; wherein Ti, O, and N are respectively substituted into the mass percentage of the corresponding elements.

[0054] In the technical solution of the present invention, in addition to the C element, the strength and toughness of the alloy are mainly adjusted by using elements such as Mn, Ni, Mo, Cr, and B to obtain a high-strength and high-toughness chain steel. The B element is used to replace part of the Ni and Mo elements, thereby reducing the production cost of the chain steel. Since the B element easily combines with elements such as N and O in the steel, thereby losing the effect of improving the hardenability, a certain amount of Ti element is added to the steel to fix the O and N elements in the steel. When designing the composition, when the Ti / (O+2N) value in the steel is within the range of 2 to 4, the effect of Ti in fixing O and N in the steel can be fully exerted. In addition, to ensure that the B element can stably play its role in improving the hardenability of the steel and replacing the Ni and Mo elements, the proportion of B element in the steel in the form of solid solution should reach 65 to 85% of the total amount of B element in the steel. When the Ti / (O+2N) ratio in steel is low, less than 2, the O and N elements in the steel cannot be completely fixed by Ti, and are easily combined with the B element in the steel to form boron nitrides or oxides, thereby partially or completely rendering the B element in the steel ineffective, causing drastic fluctuations in the hardenability of the steel and affecting the performance of the steel. When the Ti / (O+2N) ratio in steel is high, greater than 4, there is a large amount of excess Ti in the steel. During the solidification and cooling process of the steel, it will combine with the C element in the steel and continue to precipitate and grow with TiN as the core, thereby forming larger particles of Ti(C,N). These particles have sharp edges and corners, which easily reduce the impact and fatigue properties of the chain steel, making it unfavorable for the use of the chain steel.

[0055] Compared with the existing production technology, the present invention has the following beneficial effects:

[0056] 1. The high-strength and high-toughness chain steel of the present invention adopts a reasonable chemical composition design and cooperates with optimized manufacturing processes to optimize the strengthening elements such as Si, Mn, Ni, Cr, and Mo in the steel, and add a certain amount of B element to replace the expensive alloy elements Ni and Mo to improve the hardenability of mining chain steel. At the same time, the content and ratio of Ti, N, and O elements in the steel are controlled. In addition, the proportion of B element in the steel in the form of solid solution accounts for 65-85% of the total amount of B element in the steel, giving full play to the role of B element in effectively improving the hardenability of steel and preventing fluctuations in steel performance. The present invention uses a reasonable quenching + tempering treatment process to enable the steel to obtain a good match between strength, plasticity, and toughness;

[0057] 2. The high-strength and high-toughness chain steel of the present invention has reasonable chemical composition and process design during the smelting and rolling process, a wide process window, and is easy to produce and manufacture, thus enabling mass commercial production.

[0058] 3. The high-strength and high-toughness chain steel obtained by the method of the present invention has good strength and toughness and can be widely used in mines, marine engineering and other occasions requiring high-strength steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0060] FIG1 is a scanning electron microscope image of the high-strength and high-toughness mining chain steel manufactured in Example 1 of the present invention; DETAILED DESCRIPTION

[0061] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below with reference to embodiments.

[0062] The present invention provides a chain steel, which, in addition to containing more than 90% of Fe and inevitable impurities, also includes the following chemical components by mass percentage: C: 0.19-0.30%, preferably 0.20-0.30%, Si: 0.05-0.6%, preferably 0.21-0.47%, Mn: 1.0-1.8%, Cr: 0.4-0.8%, Ni: 0.5-0.9%, Mo: 0.3-0.55%, Ti: 0.015-0.035%, Al: 0.011-0.05%, preferably 0.02-0.05%, B: 0.0015-0.005%, and N: 0.002-0.006%.

[0063] The present invention also provides a chain steel, which comprises the following chemical components by mass percentage: C: 0.19-0.30%, preferably 0.20-0.30%, Si: 0.05-0.6%, preferably 0.21-0.47%, Mn: 1.0-1.8%, Cr: 0.4-0.8%, Ni: 0.5-0.9%, Mo: 0.3-0.55%, Ti: 0.015-0.035%, Al: 0.011-0.05%, preferably 0.02-0.05%, B: 0.0015-0.005%, N: 0.002-0.006%, and the balance is iron and unavoidable impurities.

[0064] It has been found that when the steel composition meets the above chemical composition and the content meets the above range, the chain steel will show excellent performance. In the present invention, unless otherwise specified, the content of the components is expressed in mass percentage.

[0065] In the chain steel of the present invention, P, S, O, and H are all impurity elements in the steel. To obtain steel with improved performance and higher quality, the content of these impurity elements should be minimized, as far as technical conditions permit. Therefore, among the unavoidable impurities, P ≤ 0.012%, S ≤ 0.01%, O ≤ 0.0015%, and H ≤ 0.00015%.

[0066] In order to ensure that the B element in the steel can play a role in the steel in the form of solid solution, the Ti, O, and N elements in the high-strength and high-toughness mining chain steel of the present invention should meet the following requirements: Ti / (O+2N)=2~4; where Ti, O, and N are the mass percentage contents of the corresponding elements respectively.

[0067] In the technical solution of the present invention, in addition to the C element, the strength and toughness of the alloy are mainly adjusted by using elements such as Mn, Ni, Mo, Cr, and B to obtain a chain steel with high strength and high toughness. The B element is used to replace part of the Ni and Mo elements, thereby reducing the production cost of the chain steel. Since the B element easily combines with elements such as N and O in the steel, thereby losing its effect of improving hardenability, a certain amount of Ti element is added to the steel to fix the O and N elements in the steel. When designing the composition, when the Ti / (O+2N) value in the steel is within the range of 2 to 4, the effect of Ti in fixing O and N in the steel can be fully exerted. In addition, to ensure that the B element can stably play its role in improving the hardenability of the steel and replacing the Ni and Mo elements, the proportion of the B element in the steel in the form of solid solution accounts for 65 to 85% of the total amount of B elements in the steel. When the Ti / (O+2N) ratio in steel is low, less than 2, the O and N elements in the steel cannot be completely fixed by Ti, and are easily combined with the B element in the steel to form boron nitrides or oxides, thereby partially or completely rendering the B element in the steel ineffective, causing drastic fluctuations in the hardenability of the steel and affecting the performance of the steel. When the Ti / (O+2N) ratio in steel is high, greater than 4, there is a large amount of excess Ti in the steel. During the solidification and cooling process of the steel, it will combine with the C element in the steel and continue to precipitate and grow with TiN as the core, thereby forming larger particles of Ti(C,N). These particles have sharp edges and corners, which easily reduce the impact and fatigue properties of the chain steel, making it unfavorable for the use of the chain steel.

[0068] The properties of the chain steel mentioned above meet the following requirements: Yield strength Rp 0.2 ≥1150MPa, tensile strength R m ≥1250MPa, elongation A≥13%, section shrinkage Z≥50%, room temperature impact energy A kv ≥60J.

[0069] The present invention also provides a method for manufacturing the aforementioned chain steel. This simple production process produces high-strength, high-toughness mining chain steel with excellent strength and toughness. The following is an exemplary description of the aforementioned chain steel manufacturing method. Specifically, the process involves electric furnace smelting, LF furnace refining, vacuum refining, continuous casting, rolling, quenching, and tempering. The detailed process is as follows:

[0070] (1) Electric furnace smelting. Using molten iron and scrap steel as raw materials, the percentage of molten iron in the raw materials is controlled to be 30-60%. Foamy slag is produced throughout the electric furnace smelting process to ensure good oxidation boiling and promote the floating of inclusions and gases in the steel. The final carbon content of the molten steel is controlled to be 0.06-0.10%, and the tapping temperature of the molten steel is 1640-1680℃.

[0071] (2) LF furnace refining. Molten steel smelted in an electric furnace enters the LF furnace station for refining. An appropriate amount of lime and fluorite is added to the slag in the early stages of LF refining to improve slag fluidity. Aluminum granules or silicon carbide are used to enhance deoxidation and desulfurization. Aluminum wire is fed based on the target Al content in the molten steel. The molten steel alloy composition and temperature are adjusted to meet the target requirements before tapping to ensure stable steel properties and the temperature requirements of the continuous casting process.

[0072] (3) Vacuum refining. The molten steel after LF refining is subjected to slag treatment and vacuum degassing refining in a VD furnace or RH furnace. The strong stirring time is greater than 10 minutes under the condition of vacuum degree less than 67Pa. After vacuum refining, alloy elements are added according to the chemical composition requirements of the molten steel. Specifically, Al is added first to ensure that the free oxygen content in the molten steel is less than 5ppm. Then Ca and ferrotitanium are added. After 5 to 10 minutes, ferroboron is added to adjust the molten steel composition to the target composition. Titanium wire is used for ferrotitanium and boron wire is used for ferroboron. Both are added by a wire feeder to improve the alloy yield and composition stability. The molten steel is cooled for more than 10 minutes, and the steel is tapped after the composition and temperature meet the requirements.

[0073] (4) Continuous casting. Use full-process protection casting to prevent secondary oxidation and nitrogen addition of molten steel. Use low superheat casting, control the superheat of molten steel in the middle package to 15-30℃, use electromagnetic stirring in the crystallizer and at the end of solidification, and use a light pressure of 10-25mm at the end of solidification to obtain the ingot, so as to reduce defects such as internal segregation of the ingot and improve the quality of the ingot. The continuous casting speed during the continuous casting process is 0.42-0.8m / min, preferably 0.5-0.8m / min, and constant casting speed control is adopted. The water ratio of the secondary cooling water is 0.3-0.5L / t. The ingot obtained by continuous casting is hot sent or sent to a slow cooling pit for slow cooling.

[0074] (5) Rolling: The ingot is sent to a heating furnace for heating, and the heating temperature of the ingot is controlled to be 1150-1250°C, and the heating and holding time is 2-6 hours; then rolling is carried out, and the starting rolling temperature is controlled to be ≥1100°C and the final rolling temperature is ≥850°C; the rolled round steel is straightened, inspected, and polished to remove surface defects. The specifications of the rolled round steel are Φ26-100mm. In addition, preferably, after the ingot is sent out of the heating furnace, it is first descaled with high-pressure water before rolling begins, and after rolling, it is slowly cooled in a holding pit for ≥24 hours.

[0075] (6) Quenching and tempering: The round steel after rolling is subjected to quenching and tempering treatment, wherein the heating temperature for quenching treatment is 850-980°C and the holding time is 1-4 hours; the tempering temperature for tempering treatment is 390-550°C, preferably 400-550°C, more preferably 400-450°C, and the tempering time is 1-3 hours. After tempering treatment, the steel is water-cooled to room temperature. After quenching treatment, the steel forms a martensitic structure with a fine lamellar structure. The alloying elements in the steel exist in the martensite in the form of supersaturated solid solution, which has high strength but relatively poor plasticity and impact toughness. After tempering treatment, the supersaturated alloying elements in the martensite are dispersed and precipitated between the martensite lamellae in the form of nano-scale carbides, which can greatly improve the strength of the steel and avoid the occurrence of temper brittleness. The chain steel obtained by the present invention has high strength and excellent impact properties.

[0076] The following is a further introduction to the high-strength and high-toughness mining chain steel and its manufacturing method of the present invention with reference to specific examples. It should be understood that the following examples are only used to describe the specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention.

[0077] Example

[0078] Examples 1 to 6

[0079] The high-strength and high-toughness mining chain steels of Examples 1 to 6 are prepared by the following steps:

[0080] (1) Molten steel is smelted and continuously cast according to the proportions shown in Table 1 to produce a cast billet. The preparation steps include the following:

[0081] 1) Electric furnace smelting, control endpoint [C]: 0.06~0.10%, molten steel tapping temperature 1640~1680℃.

[0082] 2) LF furnace refining: The molten steel smelted in the electric furnace is fed into the LF furnace station for refining. Aluminum particles or silicon carbide are used to enhance deoxidation and desulfurization. Aluminum wire is fed according to the target Al content of the molten steel to ensure that the free oxygen content in the molten steel is less than 5ppm. The alloy composition and temperature of the molten steel are adjusted to meet the target requirements before tapping.

[0083] 3) VD / RH Vacuum Refining: The molten steel refined in the LF furnace is skimmed and vacuum degassed in a VD or RH furnace. Strong stirring is performed for more than 10 minutes at a vacuum of less than 67 Pa. After vacuum refining, Al is added according to chemical composition requirements to ensure that the free oxygen content in the molten steel is less than 5 ppm. Ca and ferrotitanium are then added. After 5 minutes, ferroboron is added to adjust the molten steel to the target composition. The molten steel is cooled for more than 10 minutes, and the steel is tapped after the composition and temperature meet the requirements.

[0084] 4) Continuous Casting: Fully protected pouring is employed to prevent secondary oxidation of the molten steel and nitrogen addition during the process. Low superheat pouring is employed, with the tundish molten steel superheat controlled at 15-30°C. Electromagnetic stirring is employed in the mold and at the end of solidification, and a light reduction of 10-25mm is applied at the end of solidification to reduce defects such as internal segregation in the ingot and improve ingot quality. The continuous casting casting speed is 0.42-0.8 m / min, with constant casting speed control. The secondary cooling water ratio is 0.3-0.5 l / t. The ingot is either delivered hot or cooled in a slow cooling pit.

[0085] (2) Rolling: The resulting ingot is sent to a heating furnace for heating. The heating temperature of the ingot is controlled to be 1150-1250°C, and the heating and holding time is 2-6 hours. During rolling, the starting rolling temperature of the continuous casting ingot is controlled to be ≥1100°C, and the final rolling temperature is controlled to be ≥850°C. The rolled round steel is straightened, inspected for flaws, and polished to remove surface defects. After rolling, it is placed in a holding pit for slow cooling for ≥24 hours.

[0086] (3) Quenching and tempering treatment: The round steel obtained after rolling is quenched and tempered, wherein the quenching heating temperature is 850-980°C and the holding time is 1-4 hours; the tempering temperature is 390-550°C and the tempering time is 1-3 hours. After tempering treatment, it is water-cooled to room temperature to obtain chain steel.

[0087] Comparative Examples 1-2

[0088] In Comparative Examples 1 and 2, chain steel was prepared using an electric furnace + LF + RH + continuous casting + quenching and tempering process. The difference is that the composition, content and / or process parameters of the chain steel do not conform to the present invention. For details, see Table 1-1, Table 1-2, Table 2-1 and Table 2-2.

[0089] Table 1-1 shows the chemical compositions of the chain steels of Examples 1-6 and Comparative Examples 1-2.

[0090] Table 1-1 (wt%, the balance is Fe and other impurities except P, S, N, O and H)

[0091] Table 1-2 shows the ratio of Ti / (O+2N) in the chemical composition of the chain steel and the ratio of the B element existing in the form of solid solution to the total amount of B elements.

[0092] Table 1-2

[0093] Table 2-1 and Table 2-2 show the process parameters of Examples 1-6 and Comparative Examples 1-2 during the manufacture of chain steel.

[0094] Table 2-1

[0095] Table 2-2

[0096] The chain steels obtained in Examples 1-6 and Comparative Examples 1-2 were sampled to obtain corresponding chain steel samples. The obtained chain steels were subjected to tensile tests and Charpy impact tests to obtain performance data of the chain steels of the Examples and Comparative Examples. The test results are shown in Table 3.

[0097] The test methods for relevant performance parameters are as follows:

[0098] Tensile test: According to the national standard GB / T 2975, the chain steels of Examples 1 to 6 and Comparative Examples 1 to 2 were sampled and tensile specimens were prepared. The tensile properties were tested according to the national standard GB / T 228.1.

[0099] Charpy impact test: According to the national standard GB / T 2975, the chain steels of Examples 1 to 6 and Comparative Examples 1 to 2 were sampled and impact specimens were prepared. The impact performance test was performed according to the national standard GB / T 229.

[0100] Table 3 shows the performance parameters of the chain steels of Examples 1-6 and Comparative Examples 1-2.

[0101] Table 3

[0102] As shown in Table 3, the high-strength and high-toughness mining chain steel prepared in Examples 1 to 6 of the present invention has excellent comprehensive performance, and its yield strength Rp 0.2 ≥1186MPa, tensile strength R m ≥1293MPa, elongation A≥13.5%, section shrinkage Z≥50%, room temperature impact energy A kv ≥74 J. This shows that the high-strength and high-toughness mining chain steels of Examples 1-6 of the present invention are significantly superior to the chain steels of Comparative Examples 1-2.

[0103] From Table 1 and Table 3, it can be seen that compared with the chain steels of Comparative Examples 1 and 2, the chemical composition of the high-strength and high-toughness mining chain steels of Examples 1-6 of the present invention falls within the scope of protection required, and the optimized quenching + tempering treatment process is adopted to obtain higher strength while having excellent impact toughness.

[0104] Figure 1 is a scanning electron microscope image of the microstructure of the chain steel after quenching and tempering in Example 1. As shown in Figure 1, the microstructure of the chain steel after quenching and tempering in Example 1 is tempered martensite with a small spacing between the martensite lamellae and fine, dispersed nanocarbides precipitated between the martensite lamellae. These fine nanocarbides significantly improve the strength and toughness of the steel, resulting in a high-strength, high-toughness mining chain steel with excellent performance.

[0105] In summary, the present invention obtains high-strength and high-toughness mining chain steel with excellent performance through reasonable chemical composition design combined with optimized process, which can be widely used in fields requiring high-strength steel such as marine engineering and mining machinery.

[0106] It should be noted that all technical features described in this application can be freely combined or combined in any way unless there is a contradiction between them. Various modifications and variations can be made to the present invention without departing from the scope of the present invention, which will be apparent to those skilled in the art. For example, a feature shown or described as part of one embodiment can be used together with another embodiment to produce another embodiment. Therefore, the present invention is intended to encompass these modifications and variations that fall within the scope of the appended claims and their equivalents.

Claims

1. A chain steel, characterized in that: The chain steel contains the following chemical components in mass percentage: C: 0.19-0.30%, preferably 0.20-0.30%, Si: 0.05-0.6%, preferably 0.21-0.47%, Mn: 1.0-1.8%, Cr: 0.4-0.8%, Ni: 0.5-0.9%, Mo: 0.3-0.55%, Ti: 0.015-0.035%, Al: 0.011-0.05%, preferably 0.02-0.05%, B: 0.0015-0.005%, N: 0.002-0.006%, and the balance is iron and unavoidable impurities.

2. A chain steel, characterized in that: In addition to more than 90% of Fe and inevitable impurities, the chain steel also contains the following chemical components by mass percentage: C: 0.19-0.30%, preferably 0.20-0.30%, Si: 0.05-0.6%, preferably 0.21-0.47%, Mn: 1.0-1.8%, Cr: 0.4-0.8%, Ni: 0.5-0.9%, Mo: 0.3-0.55%, Ti: 0.015-0.035%, Al: 0.011-0.05%, preferably 0.02-0.05%, B: 0.0015-0.005%, N: 0.002-0.006%.

3. The chain steel according to claim 1 or 2, characterized in that: Among the unavoidable impurities, P≤0.012%, S≤0.01%, O≤0.0015%, and H≤0.00015%.

4. The chain steel according to claim 3, characterized in that: The chemical composition of the chain steel satisfies the following formula: Ti / (O+2N)=2-4; wherein Ti, O, and N are the mass percentage contents of the corresponding elements respectively.

5. The chain steel according to claim 1 or 2, characterized in that: A portion of the B element in the chain steel exists in the form of solid solution, wherein the proportion of the B element existing in the form of solid solution to the total amount of the B element is 固 / B 总 =65~85%.

6. The chain steel according to claim 1 or 2, characterized in that: The microstructure of the chain steel is tempered martensite and carbides dispersedly distributed between lamellar layers.

7. The chain steel according to claim 1 or 2, characterized in that: The properties of the chain steel meet the following requirements: yield strength Rp 0.2 ≥1150MPa, tensile strength R m ≥1250MPa, preferably ≥1293MPa, elongation A≥13%, section shrinkage Z≥50%, room temperature impact energy A kv ≥60J.

8. A method for manufacturing a chain steel according to any one of claims 1 to 7, characterized in that: The manufacturing method comprises the following steps performed in sequence: (1) smelting and continuously casting molten steel to obtain ingots; the smelting steps are electric furnace smelting, LF furnace refining and vacuum refining in sequence; during the vacuum refining process, the calming time of the molten steel before tapping is greater than 10 minutes; (2) subjecting the ingot to rolling, quenching and tempering treatment steps to obtain the chain steel; the heating temperature of the quenching treatment is 850-980°C, and the holding time is 1-4h; the tempering temperature of the tempering treatment is 390-550°C, preferably 400-550°C, more preferably 400-450°C, the tempering time is 1-3h, and the steel is cooled to room temperature after the tempering treatment.

9. The manufacturing method according to claim 8, characterized in that: In the electric furnace smelting process, molten iron and scrap steel are used as raw materials, foam slag is produced in the whole process of electric furnace smelting, the C content of the molten steel end point is controlled to be 0.06-0.10%, and the tapping temperature of the molten steel is 1640-1680°C.

10. The manufacturing method according to claim 9, characterized in that: During the electric furnace smelting process, the percentage of molten iron in the raw material is controlled to be 30-60%.

11. The manufacturing method according to claim 8, characterized in that: The LF furnace refining process includes the following steps performed in sequence: 1) Add lime and fluorite to make slag in the early stage of LF refining; 2) Use aluminum particles or silicon carbide to strengthen deoxidation and desulfurization, and feed aluminum wire according to the target composition of Al in molten steel; 3) Adjust the alloy composition and temperature of the molten steel to the target requirements before tapping.

12. The manufacturing method according to claim 8, characterized in that: During the vacuum refining process, the molten steel after LF refining is subjected to slag treatment, vacuum degassing refining is carried out in a VD furnace or a RH furnace, Al is supplemented according to the chemical composition requirements of the molten steel, and after ensuring that the free oxygen content in the molten steel is less than 5ppm, Ca and ferrotitanium are added, and ferroboron is added after 5 to 10 minutes, and the composition of the molten steel is adjusted to the target composition.

13. The manufacturing method according to claim 12, characterized in that: When vacuum degassing and refining is carried out in the VD furnace or the RH furnace, the strong stirring time is greater than 10 minutes under the condition that the vacuum degree is less than 67 Pa.

14. The manufacturing method according to claim 12, characterized in that: The titanium wire is used as the titanium ferrocene; and the boron wire is used as the boron ferroboron.

15. The manufacturing method according to claim 8, characterized in that: During the continuous casting process, full-process protection pouring is adopted, the superheat of the molten steel in the tundish is controlled to be 15-30°C, electromagnetic stirring is adopted in the crystallizer and at the end of solidification, and a light pressure reduction of 10-25mm is adopted at the end of solidification to obtain the ingot.

16. The manufacturing method according to claim 15, characterized in that: The continuous casting speed in the continuous casting process is 0.42-0.8 m / min, preferably 0.5-0.8 m / min, and constant pulling speed control is adopted. The water volume of secondary cooling water is 0.3-0.5 L / t, and the ingot is hot transported or slowly cooled in a slow cooling pit.

17. The manufacturing method according to claim 8, characterized in that: In the rolling process, the ingot is sent to a heating furnace for heating and then rolled, the heating temperature is controlled to be 1150-1250°C, the heating and holding time is 2-6h, the starting rolling temperature is ≥1100°C, and the final rolling temperature is ≥850°C.

18. The manufacturing method according to claim 17, characterized in that: During the rolling process, the ingot is taken out of the heating furnace, descaled by high-pressure water and then rolled. After rolling, the ingot is sent to a heat preservation pit for slow cooling for ≥24 hours.

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