Three-stage anchor chain steel with high strength, high low-temperature toughness and low welding sensitivity and production method of three-stage anchor chain steel

Abstract

The invention relates to three-level anchor chain steel with high strength, high low-temperature toughness and low welding sensitivity and a production method of the three-level anchor chain steel, and different ranges of alloy elements are scientifically and reasonably designed according to different specifications of round steel for machining anchor chains. In the production method, a relatively single alloying and deoxidizing mode in the converter tapping process is changed, and during alloying, a certain amount of deoxidizing agent is mixed in an alloy to realize synchronous deoxidizing and alloying; and in different LF furnace refining stages, different types of deoxidizing agents are selected to realize slag surface deoxidization of the molten steel, so that generation of D and DS non-metallic inclusions is controlled, and the D and DS non-metallic inclusions are controlled to be relatively low in grade. The anchor chain processed through the method is good in comprehensive cost performance, the production process is easy to operate, the production cost is low, adaptability is high, and the anchor chain can be used and popularized in the industry.

Description

Technical Field

[0001] The invention relates to a third-grade anchor chain steel with high strength, high low-temperature toughness and low welding sensitivity and a production method thereof, belonging to the field of anchor chain steel manufacturing. Background Art

[0002] Generally, anchor chains are used to connect the anchor and the hull. The anchor chain and the anchor are connected as a whole. The whole is mainly used for ship mooring, which is related to the safety of the ship. Usually, the anchor chain may need to be immersed in river water or sea water for a long time. For this, the anchor chain needs to have certain corrosion resistance and low-temperature toughness; the processing of the chain link adopts flash welding, which requires the welding performance of the anchor chain to be good; at the same time, with the development of ship transportation towards large-scale and heavy-weight and its use, the anchor chain needs to have higher strength and certain wear resistance. Furthermore, since the anchor chain is composed of many chain links in series, the quality of any one of the chain links will directly affect the quality and life of the entire anchor chain. It can be seen that for the anchor chain and the chain link, the whole is as important as the individual, which also puts forward very high quality requirements for the round steel used to process the anchor chain.

[0003] At present, there are relatively few studies on anchor chain steel, and the existing studies are all for some small-sized anchor chain steel. For example, the application with application number 201410451615.6 discloses an alkali corrosion-resistant anchor chain steel and production method. The patent improves the alkali corrosion resistance of the anchor chain by adding corrosion-resistant elements Cu, Ni, etc. to the chemical composition, and improves the alkali corrosion resistance of the anchor chain steel. However, it does not solve the problems of high strength, high and low temperature toughness and low welding sensitivity, which makes the patent not surpass the traditional method in production method. At the same time, the specifications of the round steel in the embodiments given in the patent are relatively small. The application with application number 201980009724.3 discloses an anchor chain steel and anchor chain. The patent only gives the chemical composition, and the range of the given chemical composition is very wide. The anchor chain also contains special chemical elements such as Sb, W, Sn, etc. In the process of adding these special elements, some of them will cause harm to the environment and the workers' bodies, and will also bring disadvantages to the mechanical properties, especially low temperature toughness. Application No. 202311788835.3 discloses a method for manufacturing steel that can meet the performance requirements of anchor chains without heat treatment. The patent essentially provides a non-quenched and tempered anchor chain steel. According to the processing technology of the anchor chain, the anchor chain steel needs to be reheated. At the same time, flash welding is required. These two processes will cause large differences and fluctuations in the performance of the anchor chain and the anchor chain steel, especially for larger specifications (>Ø80mm) and welding parts. Therefore, the scope of application of this patent is only Ø20mm-Ø80mm.

[0004] In summary, the development of a high-strength, high-low-temperature toughness, low-welding-sensitivity tertiary anchor chain steel and its method is not only a practical requirement for the development of the shipbuilding industry, but also has very good economic benefits, and will further enhance the competitiveness and market share of related industries in my country in the international market. Summary of the invention

[0005] In view of the shortcomings between the specifications and performance of the existing third-grade anchor chain hot-rolled round steel, such as the unsatisfactory welding performance, which makes the specifications of the processed anchor chain can only be controlled to be relatively small, and the limitations of the component design also make the anchor chain insufficient in welding performance. The present invention provides a third-grade anchor chain steel with high strength, high low temperature toughness and low welding sensitivity and a production method thereof.

[0006] The technical solution adopted by the present invention to solve its technical problem is: A high-strength, high-low-temperature toughness, low-welding sensitivity three-grade anchor chain steel, wherein the round steel used for processing the anchor chain comprises the following elements in mass percentage: C: 0.24-0.27%, Si: 0.12-0.16%, Mn: 1.70-1.80%, Cr: 0.13-0.32%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.01%, Nb≤0.01%, As≤0.0070%, Al is 0.020-0.035%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.015-0.025%, N≤0.0050%, and the balance is Fe and unavoidable impurity elements; wherein Mn / Mo>170, Ti / Al is controlled at 0.40-1.25, and Ti / N≥3; Further, if the diameter of the round steel used for processing the anchor chain is Ø≤80mm, the round steel includes the following elements in mass percentage: C: 0.25-0.27%, Si: 0.13-0.16%, Mn: 1.75-1.80%, Cr: 0.13-0.18%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.008%, Nb≤0.008%, As≤0.0070%, Al: 0.020-0.035%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.015-0.020%, N≤0.0040%, and the balance is Fe and unavoidable impurity elements; wherein Mn / Mo>175, Ti / Al is controlled at 0.40-1.00, and Ti / N≥3.75; Further, if the diameter of the round steel used for processing the anchor chain is Ø>80-140mm, the round steel includes the following elements in mass percentage: C: 0.25-0.27%, Si: 0.13-0.16%, Mn: 1.73-1.78%, Cr: 0.20-0.25%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.008%, Nb≤0.008%, As≤0.0070%, Al: 0.020-0.032%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.015-0.020%, N≤0.0040%, and the balance is Fe and unavoidable impurity elements; wherein Mn / Mo>173, Ti / Al is controlled at 0.47-1.00, and Ti / N≥3.75; Further, if the diameter of the round steel used for processing the anchor chain is Ø>140-180mm, the round steel includes the following elements in mass percentage: C: 0.25-0.26%, Si: 0.13-0.16%, Mn: 1.70-1.75%, Cr: 0.27-0.32%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.008%, Nb≤0.008%, As≤0.0070%, Al: 0.025-0.035%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.018-0.025%, N≤0.0050%, and the balance is Fe and unavoidable impurity elements; wherein Mn / Mo>170, Ti / Al is controlled at 0.51-1.00, and Ti / N≥3.60; The production method of the three-grade anchor chain steel with high strength, high low temperature toughness and low welding sensitivity specifically comprises the following steps: Step S1: pre-desulfurization of molten iron KR, removing sulfur slag after pre-desulfurization of molten iron, and controlling the sulfur content in the desulfurized molten iron to ≤0.006%; Step S2: in top and bottom combined blowing rough refining, scrap steel is added during the smelting process, and the smelting end point includes the following elements in mass percentage: C ≥ 0.12%, P ≤ 0.016%, and the temperature when tapping is 1600℃-1670℃; When the steel is tapped to 1 / 5, a deoxidizer is added to the molten steel. When the steel is tapped to 2 / 5, an iron-aluminum-calcium alloy is added to the molten steel. When the steel is tapped to 3 / 5, a mechanical mixture of a manganese-containing alloy and a deoxidizer is added to the molten steel. Finally, refined slag and lime are added. Step S3: LF refining, refining electrified slag, after all the slag is melted, adding a mixture of calcium carbide and aluminum particles to the slag surface for deoxidation, continuing refining, adding carbon ferrochrome to the molten steel in the middle of refining, and adding high-purity silicon carbide to the slag surface for deoxidation in the later stage; Step S4: RH vacuum refining, set the vacuum degree ≤100Pa, and continuously treat the molten steel for 15 minutes, then detect the active oxygen content in the molten steel online. If [O]≤4ppm, add a preset proportion of CaAl alloy to the molten steel through a vacuum chamber. After adding the CaAl alloy, perform vacuum treatment again for 3 minutes. After the vacuum treatment is completed, perform soft blowing, and the soft blowing time is set to 15-20 minutes. Step S5: During continuous casting, when the superheat of the molten steel is 20-35°C, the casting speed is kept constant, and the ratio of the casting speed to the secondary cooling water ratio is set to 1.72; when the superheat of the molten steel is lower than 20°C, the ratio of the casting speed to the secondary cooling water ratio is adjusted to 1.90; when the superheat of the molten steel is higher than 35°C, the ratio of the casting speed to the secondary cooling water ratio is adjusted to 1.25; Step S6: rolling, the billet is heated before entering the heating furnace, and the billet entry temperature is set to 100℃-300℃; the heating temperature in the heating furnace is set to 1230℃-1250℃, and the heating time of the billet at this temperature is ≥1.25mm / min; after completing the heating process, the billet enters the pit for slow cooling; Furthermore, in step S2, scrap steel is added during the smelting process, and the amount of scrap steel added is ≤10%; When the steel is tapped to 1 / 5, the deoxidizer added is aluminum cake. When the steel is tapped to 2 / 5, the elements in the iron-aluminum-calcium alloy added are aluminum: calcium: iron = 2:1:4 by mass percentage. The deoxidizer added when the steel is tapped to 3 / 5 is aluminum particles. The manganese-containing alloy and aluminum particles are mechanically mixed in a ratio of 20:1. The manganese-containing alloy is a mixture of metallic manganese and ferromanganese, with 15 kg / t metallic manganese and 5.7 kg / t ferromanganese. Further, in step S3, in the early stage of refining, a mixture of calcium carbide and aluminum particles is added to the slag surface, and the mass percentage of calcium carbide: aluminum particles is 5:2; Further, in step S4, the CaAl alloy added to the molten steel has a mass percentage of each element, i.e., Ca:Al=4:3; After the vacuum treatment, it is forbidden to add any wire or alloy to the molten steel; Further, in step S5, during the continuous casting process, the straightening temperature is set to 920°C-980°C; Furthermore, in step S6, when the steel enters the pit for slow cooling, the slow cooling temperature is set to 300°C-550°C.

[0007] Through the above technical solution, compared with the prior art, the present invention has the following beneficial effects: 1. The chemical composition of the high-strength, high-low-temperature toughness, and low-welding-sensitivity grade 3 anchor chain steel provided by the present invention is designed, and the mechanical properties and the cost-effectiveness of the design are considered at the same time. According to the different specifications of the round steel used for processing the anchor chain, the different ranges of alloy elements are scientifically and reasonably designed, which can not only tighten the alloy elements, but also stabilize the process, providing a strong guarantee for the stability of product performance; 2. The chemical composition of the high-strength, high-low-temperature toughness, and low-welding-sensitivity grade-3 anchor chain steel provided by the present invention innovatively introduces the control of the elements Mn and Mo, and at the same time makes special requirements for the elements B, Nb, V, N, etc., to prevent the abnormal structure that may appear in the steel during the cooling process after rolling, thereby avoiding the adverse effects of the abnormal structure on the performance; 3. The production method of the high-strength, high-low-temperature toughness and low-welding-sensitivity third-grade anchor chain steel provided by the present invention changes the relatively single alloying and deoxidation method in the converter steel-making process. During alloying, a certain amount of deoxidizer is mixed in the alloy to achieve synchronous deoxidation and alloying. This innovative feeding method achieves the stability of the converter steel-making to the LF slag condition, so as to facilitate rapid deoxidation in the refining process, and at the same time greatly improves the alloying yield of the converter steel-making; 4. The production method of the third-grade anchor chain steel with high strength, high low-temperature toughness and low welding sensitivity provided by the present invention selects different types of deoxidizers at different stages of refining in the ladle refining furnace to achieve slag surface deoxidation of the molten steel. Through targeted deoxidation measures, the D and DS non-metallic inclusions in the molten steel are controlled at a relatively low level, so as to produce the third-grade anchor chain steel with high strength, good high and low temperature toughness and low welding sensitivity to meet specific use requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0009] Figure 1 This is a 1.0 grade electron microscope image of the non-metallic inclusions of type A fine system in the steel obtained in Example 1; Figure 2 This is an electron microscope image of the austenite grain size of the steel obtained in Example 1, which is 8.0 grade; Figure 3 The electron microscope image of the microstructure of the steel obtained in Example 1; Figure 4 This is a 1.0 level electron microscope image of the D-type fine system of non-metallic inclusions in the steel obtained in Example 2; Figure 5 This is an electron microscope image of the austenite grain size of the steel obtained in Example 2, which is 7.5 grade; Figure 6 The electron microscope image of the microstructure of the steel obtained in Example 2; Figure 7 This is the electron microscope image of the non-metallic inclusions of type A coarse system 0.5 level in the steel obtained in Example 3; Figure 8 This is an electron microscope image of the austenite grain size of the steel obtained in Example 3 at level 6.5; Fig. 9 This is an electron microscope image of the microstructure of the steel obtained in Example 3. DETAILED DESCRIPTION

[0010] The present invention is now further described in detail in conjunction with the accompanying drawings. In the description of this application, it should be understood that the specific dimensions used in this embodiment are only for illustrating the technical solution and do not limit the protection scope of the present invention.

[0011] As explained in the background technology, the quality of the anchor chain affects the safety of the ship (if the quality of the anchor chain is poor, it may break under the action of strong external force, causing the ship to lose its fixation and face the risk of collision, stranding or even sinking), navigation efficiency (high-quality anchor chains run smoothly during the process of lifting and dropping anchor, without problems such as jamming and entanglement, thereby reducing operation time and labor costs) and long-term economic benefits (long life and high reliability, in the long run, it can reduce the frequency and cost of replacing the anchor chain). However, in the prior art, the process of improving the performance of anchor chain steel has the following problems: it is impossible to take into account the alkaline corrosion resistance, high strength, high and low temperature toughness and low welding sensitivity of the anchor chain steel, and it is impossible to adapt to the production requirements of round steel of various specifications.

[0012] Therefore, the present application provides a high-strength, high-low-temperature toughness, low welding sensitivity third-grade anchor chain steel and a production method thereof, starting from the composition and process of the round steel used for processing the anchor chain, to develop an anchor chain steel that not only meets the actual requirements of the development of the shipbuilding industry, but also has better economic benefits, so as to improve the competitiveness and market share of related industries in my country in the international market.

[0013] First, regarding the design of the chemical composition of the provided high-strength, high-low-temperature toughness, and low-welding-sensitivity third-grade anchor chain steel, compared with the prior art, this application innovatively introduces the relative control requirements for the elements Mn and Mo, and also makes special requirements for the elements B, Nb, V, N, etc., and scientifically and reasonably designs the range of these elements to prevent abnormal tissues from affecting the performance. After considering the mechanical properties and cost-effectiveness, the specific elements include the following elements in mass percentage: C: 0.24-0.27%, Si: 0.12-0.16%, Mn: 1.70-1.80%, Cr: 0.13-0.32%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.01%, Nb≤0.01%, As≤0.0070%, Al is 0.020-0.035%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.015-0.025%, N≤0.0050%, and the balance is Fe and unavoidable impurity elements; among which Mn / Mo>170, Ti / Al is controlled at 0.40-1.25, and Ti / N≥3.

[0014] The determination of the mass percentage of each element mentioned above is based on the characteristics of the element itself. Combined with the performance requirements of the round steel used for processing anchor chains in this application, the main elements involved and the multiple elements introduced innovatively are described one by one here. C element: Carbon has a direct impact on the strength, hardness, plasticity and welding performance of steel. When the carbon content is below 0.8%, the strength and hardness of steel increase with the increase of carbon content; the increase of carbon content is not conducive to the improvement of welding performance. Generally, when the carbon content is above 0.3%, the welding performance will be significantly deteriorated, and the atmospheric corrosion resistance will also decrease. Therefore, the C content is designed to be 0.24-0.27%.

[0015] Si element: Silicon is generally used as an important deoxidizer in the steelmaking process. The silicon content is limited in the present invention. The main considerations are three aspects. On the one hand, high silicon content will affect the decarburization of the steel surface, which is a consensus in the industry. On the other hand, the adverse effect of silicon on welding performance is considered, and its contribution to strength is limited. The third aspect is that silicon will react with calcium, aluminum and magnesium in the steel to affect non-large particle non-metallic inclusions with relatively poor plasticity in the late smelting and casting process. Therefore, when designing the composition, the Si content is determined to be 0.12-0.16%.

[0016] Mn element: Because Mn has a relatively small effect on plasticity while improving strength, and Mn has a very high cost performance; Mn can significantly improve the hardenability of quenched and tempered steel, but a Mn content exceeding 1.8% will have an adverse effect on plasticity and welding performance. Therefore, the Mn content is determined to be 1.70-1.80%.

[0017] Mo element: Considering that molybdenum element will promote the formation of bainite structure in high manganese steel (Mn≥1.70%), which will bring extremely adverse effects on material cutting and subsequent processing in production, the present invention controls Mo as a residual element. Therefore, the Mo content is determined to be <0.01%.

[0018] Cr element: The high-strength, high-low-temperature toughness, and low-welding sensitivity grade 3 anchor chain steel provided in this application needs to be immersed in river water or sea water. Considering the adverse effect of Cr on temper brittleness, different contents of chromium are added to the steel according to different specifications of the steel. Therefore, the Cr content is determined to be 0.13-0.32%.

[0019] Ti element: The addition of Ti is mainly considered from two aspects. First, the present invention adds Ti element to fix the residual N in the steel; second, Ti interacts with Al to achieve effective control of grains. At the same time, a high Ti content will increase the content of TiN non-metallic inclusions in the steel. Improper control will easily produce large particles. Therefore, the Ti content is determined to be 0.015-0.025%.

[0020] Al element: Aluminum is widely used in iron and steel metallurgy. Generally, Al is used as a grain-refining element in composition design. In this application, Al is also used as a grain-refining element in the steel grade design, and is used in combination with Ti element. Therefore, the Al content is determined to be 0.020-0.035%.

[0021] Nb and V elements: In medium-carbon high-manganese steel, the addition of Nb and V will refine the grains. However, the round steel used for processing anchor chains in the present invention is used after quenching and tempering heat treatment, and the chemical composition design mainly adopts the composite microalloying design concept of aluminum and titanium. Therefore, the influence of other grain-refining elements on the grains is relatively limited. In order to stabilize the various properties of the steel, Nb and V that affect the grains are restricted as residual elements. Therefore, the Nb content is determined to be ≤0.01%, and the V content is determined to be ≤0.01%.

[0022] N element: Since the production method of the high-strength, high-low-temperature toughness, and low-welding sensitivity three-grade anchor chain steel provided in this application adopts the composition design concept of Al and Ti dual composite microalloying, and the Al content and Mn content are relatively high, and the N element will combine with the Al element to precipitate at the grain boundary, embrittle the bonding force of the grain boundary, in order to weaken this adverse effect, the characteristic that Ti is easier to combine with N is used, and a part of titanium is used to solidify N, but the N content is high, and large particles of titanium nitride inclusions will also be formed. In the composition design, the N content is determined to be ≤0.0050%.

[0023] P and S elements: In view of the fact that this application is for processing round steel for anchor chains, low temperature toughness and welding performance need to be considered during the use and processing of anchor chains. P and S have adverse effects on low temperature toughness and welding performance. Therefore, both must be controlled while considering cost factors. Determine that the P content is ≤0.020% and the S content is ≤0.004%.

[0024] In order to make the mechanical properties of the processed anchor chain more stable, this application continues to strictly control the relevant residual elements Ni, Cu, B, and As, and thus determines that Ni≤0.08%, Cu≤0.10%, B≤0.0006%, and As≤0.0070%.

[0025] As the first prominent innovation of this application, in terms of chemical composition design, different ranges of alloy elements are scientifically and rationally designed according to different round steel specifications to meet the balance between different specifications of steel and performance, breaking the problem that the current processed anchor chain specifications can only be controlled at a relatively small size and the composition design is limited.

[0026] The present application provides design components for three round steel specifications. If the diameter of the round steel used for processing the anchor chain is Ø≤80mm, the round steel includes the following elements in mass percentage: C: 0.25-0.27%, Si: 0.13-0.16%, Mn: 1.75-1.80%, Cr: 0.13-0.18%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.008%, Nb≤0.008%, As≤0.0070%, Al: 0.020-0.035%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.015-0.020%, N≤0.0040%, and the balance is Fe and unavoidable impurity elements; wherein Mn / Mo>175, Ti / Al is controlled at 0.40-1.00, and Ti / N≥3.75.

[0027] If the diameter of the round steel used for processing anchor chain is Ø>80-140mm, the round steel includes the following elements in mass percentage: C: 0.25-0.27%, Si: 0.13-0.16%, Mn: 1.73-1.78%, Cr: 0.20-0.25%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.008%, Nb≤0.008%, As≤0.0070%, Al: 0.020-0.032%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.015-0.020%, N≤0.0040%, and the balance is Fe and unavoidable impurity elements; among which Mn / Mo>173, Ti / Al is controlled at 0.47-1.00, and Ti / N≥3.75.

[0028] If the diameter of the round steel used for processing anchor chain is Ø>140-180mm, the round steel includes the following elements in mass percentage: C: 0.25-0.26%, Si: 0.13-0.16%, Mn: 1.70-1.75%, Cr: 0.27-0.32%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.008%, Nb≤0.008%, As≤0.0070%, Al: 0.025-0.035%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.018-0.025%, N≤0.0050%, and the balance is Fe and unavoidable impurity elements; among which Mn / Mo>170, Ti / Al is controlled at 0.51-1.00, and Ti / N≥3.60.

[0029] As another innovation of this application, the production method of the above-mentioned high-strength, high-low-temperature toughness, and low-welding-sensitivity three-grade anchor chain steel changes the relatively single alloying and deoxidation method in the converter steelmaking process in the traditional process. During alloying, a certain amount of deoxidizer is mixed in the alloy to achieve synchronous deoxidation and alloying. This innovative feeding method is mainly to achieve the stability of the converter steelmaking to the LF slag condition, so as to facilitate rapid deoxidation during the refining process, and at the same time greatly improve the alloying yield of the converter steelmaking.

[0030] The specific steps include: Step S1: Pre-desulfurization of molten iron KR, remove sulfur slag after pre-desulfurization of molten iron, and control the sulfur content in the molten iron after desulfurization to be ≤0.006%; the sulfur slag needs to be removed cleanly here, combined with the pretreatment process, to prevent resulfurization.

[0031] Step S2: in top and bottom combined blowing rough refining, scrap steel is added during the smelting process, and the amount of scrap steel added during the smelting process is ≤10%; the smelting end point includes the following elements in mass percentage: C ≥ 0.12%, P ≤ 0.016%, and the temperature when tapping is 1600°C-1670°C; When the steel is tapped to 1 / 5, a deoxidizer is added to the molten steel. When the steel is tapped to 2 / 5, an iron-aluminum-calcium alloy is added to the molten steel. The deoxidizer added when the steel is tapped to 1 / 5 is an aluminum cake. When the steel is tapped to 2 / 5, the mass percentage of each element in the iron-aluminum-calcium alloy added is aluminum: calcium: iron = 2:1:4; When the steel is tapped to 3 / 5, a mechanical mixture of manganese-containing alloy and deoxidizer is added to the molten steel, and finally refined slag and lime are added; when the steel is tapped to 3 / 5, the deoxidizer added is aluminum particles, and the ratio of mechanical mixing of manganese-containing alloy and aluminum particles is 20:1. The manganese-containing alloy is a mixture of metallic manganese and ferromanganese, with metallic manganese of 15Kg / t and ferromanganese of 5.7Kg / t.

[0032] In the steel-making process, the alloying operation is to adjust the chemical composition of the steel. In this step, iron-aluminum-calcium alloy and manganese-containing alloy are added to the molten steel. The content of aluminum, calcium, iron, manganese and other elements in the molten steel can be adjusted in combination with the limited content to meet the performance requirements of specific steel grades. This step is a more prominent innovation in the application, that is, synchronous deoxidation is performed during alloying. The deoxidation part includes aluminum cakes added to the molten steel when the steel is tapped to 1 / 5, and aluminum particles added to the molten steel when the steel is tapped to 3 / 5. Both are deoxidation operations. Aluminum can react with oxygen in the molten steel to generate oxides such as aluminum oxide, thereby removing oxygen in the molten steel and playing a deoxidation role.

[0033] Synchronous deoxidation during alloying can remove oxygen from molten steel in time, prevent oxygen from reacting with alloying elements and other impurities to form non-metallic inclusions, reduce the formation of inclusions, and significantly improve the purity of molten steel. Pure molten steel helps to form a more uniform organizational structure. Secondly, during the alloying process, synchronous deoxidation can ensure that alloying elements are better dissolved and distributed in molten steel, promote the formation of an ideal crystal structure, and thus improve the mechanical and physical properties of steel. Finally, synchronous deoxidation can effectively reduce the oxygen content in molten steel and reduce the oxidation of alloying elements, thereby increasing the recovery rate of alloying elements and reducing the consumption cost of alloys. This means that the alloy composition in steel can be controlled more accurately, which helps to produce steel with uniform composition and stable performance.

[0034] Step S3: LF refining, refining electrified slag, after the slag is completely melted, add a mixture of calcium carbide and aluminum particles to the slag surface for deoxidation, preferably, calcium carbide: aluminum particles = 5:2 according to mass percentage; a specific ratio of calcium carbide and aluminum particles to achieve the best deoxidation effect. Continue refining, in order to adjust the chromium content in the molten steel to meet the composition requirements of a specific steel grade, add carbon ferrochrome to the molten steel in the middle of refining, so that chromium can be better dissolved and evenly distributed in the molten steel, while avoiding unnecessary reactions or losses that may occur during early addition. As the refining process proceeds, the oxygen content and impurity level in the molten steel change, and different deoxidizers are needed to meet the deoxidation requirements at different stages. Therefore, adding high-purity silicon carbide to the slag surface for deoxidation in the later stage can more effectively remove the remaining oxygen. The refining in this step is conducive to removing impurities in the molten steel, controlling D and DS non-metallic inclusions at a relatively low level, and creating good conditions for the subsequent refining process.

[0035] Step S4: RH vacuum refining, set the vacuum degree ≤100Pa, and continuously treat the molten steel for 15 minutes under a relatively low vacuum pressure environment to remove the gas and impurities in the molten steel and improve the quality of the molten steel. Then the active oxygen content in the molten steel is detected online. If [O]≤4ppm, the next step is performed, and a preset proportion of CaAl alloy is added to the molten steel through a vacuum chamber. The CaAl alloy added to the molten steel is composed of each element in mass percentage, that is, Ca:Al=4:3; Ca and Al can react with impurities such as oxygen in the molten steel to further purify the molten steel. After adding the CaAl alloy, a short-term vacuum treatment of 3 minutes is performed again to promote the alloy to fully react with the impurities in the molten steel and further remove the gases that may be generated. After the vacuum treatment is completed, any wire and alloy are prohibited from being added to the molten steel to ensure that the composition of the molten steel will not be changed during the subsequent treatment process and to ensure the stability of the molten steel quality. Soft blowing is performed to make the composition of the molten steel more uniform and remove inclusions. The soft blowing time is set to 15-20 minutes. It is prohibited to allow the soft blowing time to exceed 20 minutes. Exceeding 20 minutes may have an adverse effect on the quality of the molten steel.

[0036] Step S5: Continuous casting: During the entire process of molten steel being poured from the ladle into the tundish, and then poured from the tundish into the crystallizer until the ingot is pulled out, various measures are taken to prevent the molten steel from contacting with air, and full-process protective casting is performed to prevent the molten steel from being oxidized, so as to improve the purity of the molten steel. During the full-process protective casting process, the relationship between the superheat of the molten steel and the pulling speed / secondary cooling water ratio is set to further improve the quality of the ingot.

[0037] Specifically, when the superheat of the molten steel is 20-35°C, the pulling speed is kept constant, and the ratio of the pulling speed to the secondary cooling water ratio is set to 1.72; when the superheat of the molten steel is lower than 20°C, the ratio of the pulling speed to the secondary cooling water ratio is adjusted to 1.90; when the superheat of the molten steel is higher than 35°C, the ratio of the pulling speed to the secondary cooling water ratio is adjusted to 1.25.

[0038] During the continuous casting process, the ingot needs to be straightened at a specific stage. Too high or too low temperature during straightening may cause defects such as cracks in the ingot, affecting the quality of the ingot and subsequent processing performance. Therefore, the straightening temperature is set at 920℃-980℃.

[0039] Step S6: Rolling, the billet is heated before entering the heating furnace to avoid problems such as uneven heating and thermal stress caused by too high or too low furnace temperature. The billet furnace temperature is set to 100℃-300℃ to ensure that the billet can be heated in a relatively stable state during the heating process. The heating temperature in the heating furnace is set to 1230℃-1250℃, and the heating time of the billet at this temperature is ≥1.25mm / min; this setting ensures that the billet can be fully and evenly heated, so that the internal structure of the billet reaches the required state, so as to carry out subsequent processing operations. After the billet completes the heating process, it enters the pit for slow cooling. The purpose of slow cooling is to slowly cool the steel, reduce the internal stress caused by rapid cooling, and prevent defects such as cracks in the steel; setting the slow cooling temperature to 300℃-550℃ can ensure that the steel can be cooled at a more appropriate speed during the slow cooling process, so as to obtain good structure and performance.

[0040] Finally, through the above production method, the mechanical properties of the anchor chain processed from the round steel after quenching and tempering are Rp0.2≥682Mpa, tensile strength≥780Mpa, elongation≥22.5%, cross-sectional shrinkage≥65%, 0℃ V-type impact energy≥152J, the mechanical properties of the weld of the anchor chain are Rp0.2≥690Mpa, tensile strength≥786Mpa, elongation≥18%, cross-sectional shrinkage≥51%, 0℃ V-type impact energy≥60J, non-metallic inclusions (A-type inclusions ≤1.0 grade, B-type inclusions ≤0.5 grade, C-type inclusions ≤0.5 grade, D-type inclusions ≤1.0 grade, DS-type inclusions ≤0.5 grade), and fine austenite grains (austenite grain size ≥6.5 grade).

[0041] In order to further verify the scientific rationality of the high-strength, high-low-temperature toughness, low-welding-sensitivity third-grade anchor chain steel and its production method provided by the present application, the present application provides three embodiments for verification, and at the same time, provides comparative example 1 for embodiment 1, provides comparative example 2 for embodiment 2, and provides comparative example 3 for embodiment 3, so as to further verify the advantages of the present application, which will be specifically elaborated below.

[0042] Example 1 and Comparative Example 1: The mass percentage compositions of the elements in the round steel used for processing anchor chains are shown in Tables 1, 2 and 3. Table 1 Main chemical components (wt%)

[0043] Table 2 Residual elements (wt%)

[0044] Table 3 Other requirements for chemical composition

[0045] The production method of the third-grade anchor chain steel with high strength, high low temperature toughness and low welding sensitivity specifically comprises the following steps: The first step is KR pre-desulfurization of molten iron: After pre-desulfurization of the molten iron by KR mechanical stirring method, the sulfur content of the molten iron after desulfurization is controlled to 0.005% to prevent resulfurization. The desulfurization slag must be scraped clean; The second step is converter smelting: in the top and bottom combined blowing rough refining, the amount of scrap steel added during smelting shall not exceed 10%, the main chemical composition at the end of smelting is controlled to be C 0.15%, P 0.014%, the tapping temperature is 1659℃, when the tapping reaches 1 / 5, aluminum cake is added to the molten steel, when the tapping reaches 2 / 5, iron-aluminum-calcium alloy (aluminum: calcium: iron = 2:1:4) is added to the molten steel, when the tapping reaches 3 / 5, manganese-containing alloy (the manganese-containing alloy specifically refers to a mixture of metallic manganese and ferromanganese) and aluminum granule mechanical mixture (the mixing ratio of the two is 20:1) is added to the molten steel, of which 15Kg / t of metallic manganese and 5.7Kg / t of ferromanganese are added, and finally refined slag and lime are added; The third step is LF furnace refining: refining electrified slag, after all the slag materials are melted, start to add a mixture of calcium carbide and aluminum particles to the slag surface (the ratio of calcium carbide to aluminum particles is 5:2), and use high-purity silicon carbide to deoxidize the slag surface in the later stage of refining; add medium-carbon ferrochrome to the molten steel in the middle stage of refining; Step 4, RH vacuum refining: treat the molten steel for 15 minutes under the condition of vacuum degree ≤100Pa. After the 15-minute treatment, the active [O] content in the molten steel is measured online to be 6ppm. Continue to treat for 5 minutes under high vacuum degree. The active [O] content in the molten steel is measured online to be 2ppm. Add CaAl alloy (Ca:Al=4:3) to the molten steel through the vacuum chamber. After the CaAl alloy is added, vacuum treatment is performed for another 3 minutes. After the vacuum treatment is completed, no wires or alloys are allowed to be added to the molten steel. The molten steel is soft-blown for 17 minutes. Step 5, continuous casting: full protection casting, superheat 26℃, casting section 200mm×200mm, constant drawing speed, drawing speed / secondary cooling water ratio 1.72, continuous casting straightening temperature 928℃; Step 6, rolling: The temperature of the steel billet entering the furnace must be controlled at 200℃, and the heating temperature should be 1230℃-1240℃. At this temperature, the heating time of the steel billet must be ≥1.25mm / min, the rolling specification is Φ50mm, and the steel enters the pit for slow cooling, and the slow cooling temperature is controlled at 300-400℃.

[0046] Step 7: Anchor chain processing: The round steel is heated, bent, flash welded, braided, and tempered in a vertical continuous furnace (quenching at 910°C + tempering at 650°C).

[0047] The mechanical properties of the produced anchor chain are shown in Table 4. Table 4 Mechanical properties of anchor chain

[0048] The non-metallic inclusions of round steel are shown in Table 5. As an example, the present application also provides a non-metallic inclusion diagram of Example 1, namely, Figure 1 As shown, Table 5 Non-metallic inclusions

[0049] The austenite grain size of Example 1 is 8.0 grade. Figure 2 As shown, the microstructure of round steel in hot-rolled state is as follows Figure 3 shown.

[0050] Example 2 and Comparative Example 2: The mass percentage compositions of the elements in the round steel used for processing anchor chains are shown in Tables 6, 7 and 8. Table 6 Main chemical components (wt%)

[0051] Table 7 Residual elements (wt%)

[0052] Table 8 Other requirements for chemical composition

[0053] The production method of the third-grade anchor chain steel with high strength, high low temperature toughness and low welding sensitivity specifically comprises the following steps: The first step is KR pre-desulfurization of molten iron: After pre-desulfurization of the molten iron by KR mechanical stirring method, the sulfur content of the molten iron after desulfurization is controlled to 0.006% to prevent resulfurization. The desulfurization slag must be scraped clean; The second step is converter smelting: in the top and bottom combined blowing rough refining, the amount of scrap steel added during smelting shall not exceed 10%, the main chemical composition at the end of smelting is controlled to be C 0.16%, P 0.009%, the tapping temperature is 1661℃, when the tapping reaches 1 / 5, aluminum cake is added to the molten steel, when the tapping reaches 2 / 5, iron-aluminum-calcium alloy (aluminum: calcium: iron = 2:1:4) is added to the molten steel, when the tapping reaches 3 / 5, manganese-containing alloy (the manganese-containing alloy specifically refers to a mixture of metallic manganese and ferromanganese) and aluminum granule mechanical mixture (the mixing ratio of the two is 20:1) is added to the molten steel, of which 15Kg / t of metallic manganese and 5.7Kg / t of ferromanganese are added, and finally refined slag and lime are added; The third step is LF furnace refining: refining electrified slag, after all the slag materials are melted, start to add a mixture of calcium carbide and aluminum particles to the slag surface (the ratio of calcium carbide to aluminum particles is 5:2), and use high-purity silicon carbide to deoxidize the slag surface in the later stage of refining; add medium-carbon ferrochrome to the molten steel in the middle stage of refining; Step 4, RH vacuum refining: treat the molten steel for 15 minutes under the condition of vacuum degree ≤100Pa. After the 15-minute treatment, the active [O] content in the molten steel is measured online to be 3ppm. CaAl alloy (Ca:Al=4:3) is added to the molten steel through the vacuum chamber. After the CaAl alloy is added, vacuum treatment is performed for another 3 minutes. After the vacuum treatment is completed, no wires or alloys are allowed to be added to the molten steel. The molten steel is soft-blown for 20 minutes. Step 5, continuous casting: full protection casting, superheat 30℃, casting section Φ380mm, constant drawing speed, drawing speed / secondary cooling water ratio 1.72, continuous casting straightening temperature 959℃; Step 6, rolling: The temperature of the steel billet entering the furnace must be controlled at 200℃, and the heating temperature should be 1230℃-1240℃. At this temperature, the heating time of the steel billet must be ≥1.25mm / min, the rolling specification is Φ105mm, and the steel enters the pit for slow cooling, and the slow cooling temperature is controlled at 350-500℃.

[0054] Step 7: Anchor chain processing: The round steel is heated, bent, flash welded, braided, and tempered in a vertical continuous furnace (quenching at 910°C + tempering at 650°C).

[0055] The mechanical properties of the produced anchor chain are shown in Table 9. Table 9 Mechanical properties of anchor chain

[0056] The non-metallic inclusions of round steel are shown in Table 10. As an example, the present application also provides a non-metallic inclusion diagram obtained in Example 2, namely Figure 4 , Table 10 Non-metallic inclusions

[0057] The austenite grain size of Example 2 is 7.5. Figure 5 As shown, the microstructure of round steel in hot-rolled state is as follows Figure 6 shown.

[0058] Example 3 and Comparative Example 3: The mass percentage compositions of the elements in the round steel used for processing anchor chains are shown in Tables 11, 12 and 13. Table 11 Main chemical components (wt%)

[0059] Table 12 Residual elements (wt%)

[0060] Table 13 Other requirements for chemical composition

[0061] The production method of the third-grade anchor chain steel with high strength, high low temperature toughness and low welding sensitivity specifically comprises the following steps: The first step is KR pre-desulfurization of molten iron: After pre-desulfurization of molten iron by KR mechanical stirring method, the sulfur content of the molten iron after desulfurization is controlled to 0.003% to prevent resulfurization. The desulfurization slag must be scraped clean; The second step is converter smelting: in the top and bottom combined blowing rough refining, the amount of scrap steel added during smelting shall not exceed 10%, the main chemical composition at the end of smelting is controlled to be C 0.15%, P 0.011%, the tapping temperature is 1655℃, when the tapping reaches 1 / 5, aluminum cake is added to the molten steel, when the tapping reaches 2 / 5, iron-aluminum-calcium alloy (aluminum: calcium: iron = 2:1:4) is added to the molten steel, when the tapping reaches 3 / 5, manganese-containing alloy (the manganese-containing alloy specifically refers to a mixture of metallic manganese and ferromanganese) and aluminum granule mechanical mixture (the mixing ratio of the two is 20:1) is added to the molten steel, of which 15Kg / t of metallic manganese and 5.7Kg / t of ferromanganese are added, and finally refined slag and lime are added; The third step is LF furnace refining: refining electrified slag, after all the slag materials are melted, start to add a mixture of calcium carbide and aluminum particles to the slag surface (the ratio of calcium carbide to aluminum particles is 5:2), and use high-purity silicon carbide to deoxidize the slag surface in the later stage of refining; add medium-carbon ferrochrome to the molten steel in the middle stage of refining; Step 4, RH vacuum refining: treat the molten steel for 15 minutes under the condition of vacuum degree ≤100Pa. After the 15-minute treatment, the active [O] content in the molten steel is measured online to be 4ppm. CaAl alloy (Ca:Al=4:3) is added to the molten steel through the vacuum chamber. After the CaAl alloy is added, vacuum treatment is performed for another 3 minutes. After the vacuum treatment is completed, no wires or alloys are allowed to be added to the molten steel. The molten steel is soft-blown for 15 minutes. Step 5, continuous casting: full protection casting, superheat 30℃, casting section Φ500mm, constant drawing speed, drawing speed / secondary cooling water ratio 1.72, continuous casting straightening temperature 972℃; Step 6, rolling: The temperature of the steel billet entering the furnace must be controlled at 200℃, and the heating temperature should be 1230℃-1240℃. At this temperature, the heating time of the steel billet must be ≥1.25mm / min, the rolling specification is Φ180mm, and the steel enters the pit for slow cooling, and the slow cooling temperature is controlled at 430-550℃.

[0062] Step 7: Anchor chain processing: The round steel is heated, bent, flash welded, braided, and tempered in a vertical continuous furnace (quenching at 910°C + tempering at 650°C).

[0063] The mechanical properties of the produced anchor chain are shown in Table 14. Table 14 Mechanical properties of anchor chain

[0064] The non-metallic inclusions of round steel are shown in Table 15. As an example, the present application also provides a non-metallic inclusion diagram obtained in Example 3, namely Figure 7 , Table 15 Non-metallic inclusions

[0065] The austenite grain size of Example 3 is 6.5. Figure 8 As shown, the microstructure of round steel in hot-rolled state is as follows Fig. 9 shown.

[0066] pass Figure 1 , Figure 4 as well as Figure 7 , combined with the rating of non-metallic inclusions of the respective objects, it can be seen that under the deoxidation system of the present invention, no Class B coarse inclusions were found, only Class B fine inclusions were found, and the Class B fine inclusion level was only 0.5, and the levels of Class A and Class D inclusions were also relatively small, and the levels did not exceed 1.0. It can be seen that the production method provided by the present invention performs well in controlling non-metallic inclusions, especially brittle inclusions Class B. Fewer inclusions and low-level inclusions mean fewer potential crack sources in steel, thereby improving the toughness of steel and maintaining good performance in high and low temperature environments.

[0067] Under the dual effects of microalloying and rolling processes, the austenite grain size of the steel is fully refined. Normally, the austenite grain size of this type of steel with specifications of > Ø140mm-Ø180mm is only about level 5, while this application can ensure that the austenite grain size of specifications of > Ø140mm-Ø180mm is above level 6.5. Smaller austenite grains can form finer ferrite and pearlite structures in the subsequent phase transformation process, thereby improving the strength of the steel.

[0068] pass Figure 3 , Figure 6 as well as Fig. 9 It can be seen that on the basis of scientific and reasonable composition design, the rolling process ensures that the microstructure of the steel is only ferrite and pearlite, and no other abnormal structures appear. For this type of high manganese steel, bainite structure is often very easy to appear. The uniform structure of the steel is conducive to reducing welding sensitivity.

[0069] Combined with the mechanical properties of the anchor chain in Table 4 and the non-metallic inclusions in Table 5 in Example 1 and Comparative Example 1, the mechanical properties of the anchor chain in Table 9 and the non-metallic inclusions in Table 10 in Example 2 and Comparative Example 2, and the mechanical properties of the anchor chain in Table 14 and the non-metallic inclusions in Table 15 in Example 3 and Comparative Example 3, it can be seen from the comparative examples that the interaction between specific elements can effectively control the stability of performance and the level of non-metallic inclusions, especially the impact toughness and Class B, Class D and Class DS at the serial weld.

[0070] In summary, the high-strength, high-low-temperature toughness, and low-welding-sensitivity grade-3 anchor chain steel provided in this application has high strength, high impact toughness, and low welding sensitivity. The anchor chain has a good overall cost-effectiveness, the production method is simple to operate, the production cost is low, and the adaptability is strong, and it can be promoted and used in this industry.

[0071] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0072] The meaning of "and / or" described in this application means that the situations where each exists alone or both exist at the same time are included.

[0073] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0074] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A high-strength, high-low-temperature toughness, and low-welding sensitivity grade 3 anchor chain steel, characterized by: The round steel used for processing anchor chains includes the following elements in mass percentage: C: 0.24-0.27%, Si: 0.12-0.16%, Mn: 1.70-1.80%, Cr: 0.13-0.32%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.01%, Nb≤0.01%, As≤0.0070%, Al is 0.020-0.035%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.015-0.025%, N≤0.0050%, and the balance is Fe and unavoidable impurity elements; among which Mn / Mo>170, Ti / Al is controlled at 0.40-1.25, and Ti / N≥3.

2. The high-strength, high-low-temperature toughness, and low-welding-sensitivity grade 3 anchor chain steel according to claim 1, characterized in that: If the diameter of the round steel used for processing anchor chain is Ø≤80mm, the round steel includes the following elements in mass percentage: C: 0.25-0.27%, Si: 0.13-0.16%, Mn: 1.75-1.80%, Cr: 0.13-0.18%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.008%, Nb≤0.008%, As≤0.0070%, Al: 0.020-0.035%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.015-0.020%, N≤0.0040%, and the balance is Fe and unavoidable impurity elements; among which Mn / Mo>175, Ti / Al is controlled at 0.40-1.00, and Ti / N≥3.

75.

3. The high-strength, high-low-temperature toughness, and low-welding-sensitivity grade 3 anchor chain steel according to claim 1, characterized in that: If the diameter of the round steel used for processing anchor chain is Ø>80-140mm, the round steel includes the following elements in mass percentage: C: 0.25-0.27%, Si: 0.13-0.16%, Mn: 1.73-1.78%, Cr: 0.20-0.25%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.008%, Nb≤0.008%, As≤0.0070%, Al: 0.020-0.032%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.015-0.020%, N≤0.0040%, and the balance is Fe and unavoidable impurity elements; among which Mn / Mo>173, Ti / Al is controlled at 0.47-1.00, and Ti / N≥3.

75.

4. The high-strength, high-low-temperature toughness, and low-welding-sensitivity grade 3 anchor chain steel according to claim 1, characterized in that: If the diameter of the round steel used for processing anchor chain is Ø>140-180mm, the round steel includes the following elements in mass percentage: C: 0.25-0.26%, Si: 0.13-0.16%, Mn: 1.70-1.75%, Cr: 0.27-0.32%, Cu≤0.10%, Ni≤0.08%, Mo<0.01%, V≤0.008%, Nb≤0.008%, As≤0.0070%, Al: 0.025-0.035%, P≤0.020%, S≤0.004%, B≤0.0006%, Ti: 0.018-0.025%, N≤0.0050%, and the balance is Fe and unavoidable impurity elements; among which Mn / Mo>170, Ti / Al is controlled at 0.51-1.00, and Ti / N≥3.

60.

5. The production method of the high-strength, high-low-temperature toughness and low-welding-sensitivity grade 3 anchor chain steel according to claim 2, 3 or 4, characterized in that: The specific steps include: Step S1: pre-desulfurization of molten iron KR, removing sulfur slag after pre-desulfurization of molten iron, and controlling the sulfur content in the desulfurized molten iron to be ≤0.006%; Step S2: in top and bottom combined blowing rough refining, scrap steel is added during the smelting process, and the smelting end point includes the following elements in mass percentage: C ≥ 0.12%, P ≤ 0.016%, and the temperature when tapping is 1600℃-1670℃; When the steel is tapped to 1 / 5, a deoxidizer is added to the molten steel. When the steel is tapped to 2 / 5, an iron-aluminum-calcium alloy is added to the molten steel. When the steel is tapped to 3 / 5, a mechanical mixture of a manganese-containing alloy and a deoxidizer is added to the molten steel. Finally, refined slag and lime are added. Step S3: LF refining, refining electrified slag, after all the slag is melted, adding a mixture of calcium carbide and aluminum particles to the slag surface for deoxidation, continuing refining, adding carbon ferrochrome to the molten steel in the middle of refining, and adding high-purity silicon carbide to the slag surface for deoxidation in the later stage; Step S4: RH vacuum refining, set the vacuum degree ≤100Pa, and continuously treat the molten steel for 15 minutes, then detect the active oxygen content in the molten steel online. If [O]≤4ppm, add a preset proportion of CaAl alloy to the molten steel through a vacuum chamber. After adding the CaAl alloy, perform vacuum treatment again for 3 minutes. After the vacuum treatment is completed, perform soft blowing, and the soft blowing time is set to 15-20 minutes. Step S5: During continuous casting, when the superheat of the molten steel is 20-35°C, the casting speed is kept constant, and the ratio of the casting speed to the secondary cooling water ratio is set to 1.72; when the superheat of the molten steel is lower than 20°C, the ratio of the casting speed to the secondary cooling water ratio is adjusted to 1.90; when the superheat of the molten steel is higher than 35°C, the ratio of the casting speed to the secondary cooling water ratio is adjusted to 1.25; Step S6: Rolling, the steel billet is heated before entering the heating furnace, and the temperature of the steel billet entering the furnace is set to 100℃-300℃; the heating temperature in the heating furnace is set to 1230℃-1250℃, and the heating time of the steel billet at this temperature is ≥1.25mm / min; after completing the heating process, the steel billet enters the pit for slow cooling treatment.

6. The method for producing the high-strength, high-low-temperature toughness and low-welding-sensitivity third-grade anchor chain steel according to claim 5, characterized in that: In step S2, scrap steel is added during the smelting process, and the amount of scrap steel added is ≤10%; When the steel is tapped to 1 / 5, the deoxidizer added is aluminum cake. When the steel is tapped to 2 / 5, the elements in the iron-aluminum-calcium alloy added are aluminum: calcium: iron = 2:1:4 by mass percentage. The deoxidizer added when the steel is tapped to 3 / 5 is aluminum particles. The manganese-containing alloy and the aluminum particles are mechanically mixed in a ratio of 20:

1. The manganese-containing alloy is a mixture of metallic manganese and ferromanganese, with metallic manganese being 15 kg / t and ferromanganese being 5.7 kg / t.

7. The method for producing the high-strength, high-low-temperature toughness and low-welding-sensitivity grade 3 anchor chain steel according to claim 5, characterized in that: In step S3, a mixture of calcium carbide and aluminum particles is added to the slag surface in the early stage of refining, and the mass percentage of calcium carbide: aluminum particles is 5:

2.

8. The method for producing the high-strength, high-low-temperature toughness and low-welding-sensitivity third-grade anchor chain steel according to claim 5, characterized in that: In step S4, the CaAl alloy added to the molten steel has a mass percentage of each element, i.e., Ca:Al=4:3; After the vacuum treatment, it is forbidden to add any wire or alloy to the molten steel.

9. The method for producing the high-strength, high-low-temperature toughness and low-welding-sensitivity third-grade anchor chain steel according to claim 5, characterized in that: In step S5, during the continuous casting process, the straightening temperature is set to 920°C-980°C.

10. The method for producing the third-grade anchor chain steel with high strength, high low temperature toughness and low welding sensitivity according to claim 5, characterized in that: In step S6, when the steel enters the pit for slow cooling, the slow cooling temperature is set to 300°C-550°C.

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