Method for preparing steel for construction machinery and steel for construction machinery

Abstract

The present application discloses a method for preparing steel for construction machinery and the steel for construction machinery. The method includes: a) performing deoxidation treatment on blast furnace hot metal at the end point of the converter by adding a silicon-manganese composition; b) performing alloying treatment on the product of step a) by adding easily oxidizable alloys and controlling the slag entrainment during the processes of step a) and step b); d) adding a titanium-calcium composition to the LF-refined molten steel under the conditions that the oxygen content of the LF-refined molten steel is 30-60 ppm and the temperature is 1520-1570 °C, so that titanium oxides in inclusions are dispersedly distributed in the steel for construction machinery in subsequent processes. When the oxygen content of the LF-refined molten steel is 30-60 ppm and the titanium-calcium composition is added to the LF-refined molten steel, a large amount of fine and dispersedly distributed titanium oxides can be produced, and the formation of intragranular acicular ferrite can also be promoted. In subsequent processes, the titanium oxides play a role of nailing in the steel for construction machinery, thereby improving the material toughness and welding performance.

Description

Technical Field

[0001] This application belongs to the technical field of steel for construction machinery, and specifically relates to a method for preparing steel for construction machinery and the steel for construction machinery. Background Art

[0002] Under the background of the large-scale development of construction machinery, the complexity of part structures, and the harsh use environment, the steel for construction machinery is developing towards high strength, high toughness, high strain machining properties, excellent anti-fatigue impact load characteristics, and weldability.

[0003] With the increase in the strength of steel materials, the plasticity, toughness, weldability, etc. of steel plates generally decrease significantly, severely restricting the design, processing, and use of simple part structures of large construction machinery, resulting in a large increase in the amount of steel plates used in the whole vehicle, difficult vehicle assembly, and high vehicle manufacturing costs.

[0004] Under the dual constraints of environment and resources, it is urgent to improve the processing characteristics of high-strength steel plates for construction machinery, meet the requirements of the above vehicles for the mechanical properties of steel plates, and develop high-strength steel plates with weldability and toughness at low cost. Summary of the Invention

[0005] In view of this, this application provides a steel for construction machinery, its preparation method, and a magnesium battery, aiming to provide a steel for construction machinery with high strength, high plasticity and toughness, and weldability.

[0006] In the first aspect, an embodiment of this application provides a method for preparing steel for construction machinery, including:

[0007] a) Deoxidizing the blast furnace hot metal at the end of the converter by adding a silicon-manganese composition;

[0008] b) Alloying the product of step a) by adding easily oxidizable alloys, and controlling the slag volume in the processes of step a) and step b) to be 2 Kg / t - 4 Kg / t to avoid sulfur in the surface slag from returning to the blast furnace hot metal;

[0009] c) Deoxidizing and desulfurizing the surface of the slag of the product of step b) by adding deoxidizing and desulfurizing agents in batches to provide LF refined molten steel;

[0010] d) Adding a titanium-calcium composition to the LF refined molten steel under the conditions that the oxygen content of the LF refined molten steel is 30 - 60 ppm and the temperature is 1520°C - 1570°C, so that titanium oxides of inclusions are dispersed in the steel for construction machinery in subsequent processes;

[0011] e) Adding a chromium-boron composition to the LF refined molten steel 2 - 6 minutes after the alloying with the titanium-calcium alloy is completed to alloy the LF refined molten steel;

[0012] f) Continuously cast the product of step e) to prepare steel for construction machinery.

[0013] According to an embodiment of one aspect of the present application, before step a), KR desulfurization treatment is performed on the blast furnace hot metal to make the sulfur content in the blast furnace hot metal < 0.002%.

[0014] According to an embodiment of one aspect of the present application, in step a), the silicomanganese composition is the silicomanganese composition.

[0015] According to an embodiment of one aspect of the present application, in step b), the easily oxidized alloy is a nickel-containing alloy.

[0016] According to an embodiment of one aspect of the present application, in steps c), d) and e), it further includes: soft blowing the LF-refined molten steel.

[0017] According to an embodiment of one aspect of the present application, in step d), before adding 2 Kg / t - 4 Kg / t of the LF-refined molten steel, adjust the temperature of the LF-refined molten steel to make the temperature of the LF-refined molten steel 1520°C - 1570°C and avoid heating up after adding the titanium-calcium alloy.

[0018] According to an embodiment of one aspect of the present application, step e) further includes:

[0019] After the alloying of the LF-refined molten steel is completed, continue to soft blow the LF-refined molten steel, and the soft blowing time t satisfies: 6 min ≤ t < 10 min.

[0020] According to an embodiment of one aspect of the present application, the blast furnace hot metal includes the following components by mass percentage: 3.50% ≤ C ≤ 4.50%, 0.35% ≤ Si ≤ 0.55%, 0.10% ≤ Mn ≤ 0.50%, P ≤ 0.18%, S ≤ 0.035%, Cu ≤ 0.07%, As ≤ 0.050%, Sn ≤ 0.030%, and the balance is iron and unavoidable impurities.

[0021] According to an embodiment of one aspect of the present application, the steel for construction machinery includes the following components by mass percentage: 0.18% ≤ C ≤ 0.23%, 0.20% ≤ Si ≤ 0.40%, 1.10% ≤ Mn ≤ 1.30%, P ≤ 0.020%, S ≤ 0.002%, 0.15% ≤ Cr ≤ 0.25%, 0.010% ≤ Ti ≤ 0.025%, 0.0012% ≤ B ≤ 0.0020%, 0.015% ≤ Als ≤ 0.050%, 0.015% ≤ Nb ≤ 0.025%, N ≤ 0.0070%, and the balance is iron and unavoidable impurities.

[0022] In a second aspect, an embodiment of the present application provides a steel for construction machinery, which is obtained by the preparation method of the first aspect.

[0023] According to an embodiment of one aspect of the present application, the steel for construction machinery satisfies at least one of the following conditions:

[0024] According to the detection method of GB / T 2975, the mechanical properties of the steel for construction machinery include: yield strength of 1200 - 1300 MPa, tensile strength of 1400 - 1500 MPa, elongation of 12% - 18%, hardness of 400 - 450 HBW, longitudinal impact energy of 100 - 150 AKV, and weldability of 2 - 2.4 KJ / mm;

[0025] According to the non-metallic inclusion rating of the product by GB / T10561, the inclusions in the steel for construction machinery satisfy: class B inclusions ≤ 1.5 grade, class D inclusions in the range of 0 - 1.0 grade, and class Ds inclusions in the range of 0 - 1.0 grade;

[0026] The average grain size of the inclusion titanium oxide is 0.2 μm - 3.0 μm;

[0027] The metallographic structure of the steel for construction machinery includes: by volume percentage, 98% - 100% tempered martensite, ≤ 1% retained austenite, and ≤ 1% bainite.

[0028] Compared with the prior art, the present application has at least the following beneficial effects:

[0029] In the method provided by the present application, under the conditions that the oxygen content of the LF-refined molten steel is 30 - 60 ppm and the temperature is 1520 °C - 1570 °C, the product of step b) is subjected to slag surface deoxidation and desulfurization by adding deoxidizing and desulfurizing agents in batches to provide LF-refined molten steel; d) under the conditions that the oxygen content of the LF-refined molten steel is 30 - 60 ppm and the temperature is 1520 °C - 1570 °C, a titanium-calcium composition is added to the LF-refined molten steel to make the inclusion titanium oxide disperse in the steel for construction machinery in the subsequent process; e) 2 - 6 minutes after the alloying by adding titanium-calcium alloy is completed, a chromium-boron composition is added to the LF-refined molten steel to alloy the LF-refined molten steel, which can produce a large number of fine and dispersed titanium oxides in the medium, thereby preventing the growth of grains, refining the product grains, and also promoting the formation of intragranular acicular ferrite. In the subsequent process, the titanium oxide plays a pinning effect in the steel for construction machinery, thereby improving the material toughness and welding performance; and at this temperature, the adverse effects caused by subsequent heating are avoided; first, the non-oxidizable silicon-manganese composition is heated and added after the converter tapping, then the oxidizable alloy is added, and the chromium-boron composition is added 2 - 6 minutes after the Ti-Ca alloying treatment in the LF-refined molten steel, which can stabilize the recovery rate of metal elements or non-metal elements and reduce the cost. Description of the Drawings

[0030] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on the accompanying drawings.

[0031] Figure 1 Shows the optical microscope photos of the steel plates in Embodiment 1 and Comparative Example 1 of the present application;

[0032] Figure 2 Shows the scanning electron microscope image of the steel plate in Embodiment 1 of the present application;

[0033] Figure 3 Shows the morphology and energy spectrum analysis of microscopic inclusions in Experiments 11 - 13# in the embodiments of the present application; Figure 4 Shows the morphology and energy spectrum analysis of microscopic inclusions in Experiments 14 - 16# in the embodiments of the present application. Detailed implementation manners

[0034] In order to make the application purpose, technical solutions and beneficial technical effects of the present application clearer, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application and not for limiting the present application.

[0035] For simplicity, the present application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recorded; and any lower limit can be combined with other lower limits to form a range not explicitly recorded. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, although not explicitly recorded, each point or single value between the range endpoints is included in this range. Thus, each point or single value can be used as its own lower limit or upper limit and combined with any other point or single value or combined with other lower limits or upper limits to form a range not explicitly recorded.

[0036] In the description of the present application, it should be noted that unless otherwise specified, "above" and "below" include this number, and the meaning of "multiple" in "one or more" is two or more.

[0037] The above application content of the present application does not intend to describe each disclosed embodiment or each implementation manner of the present application. The following description more specifically gives examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, and these embodiments can be used in various combinations. In each instance, the enumeration is only a representative group and should not be construed as exhaustive.

[0038] Steel for construction machinery

[0039] In a first aspect, an embodiment of the present application provides a method for preparing steel for engineering machinery, comprising:

[0040] a) deoxidizing blast furnace iron at the end of the converter by adding a silicon-manganese composition;

[0041] b) alloying the product of step a) by adding an easily oxidizable alloy, and controlling the slag amount during step a) and step b) to be 2 kg / t to 4 kg / t to prevent sulfur in the surface slag from returning to the molten iron in the blast furnace;

[0042] c) deoxidizing and desulfurizing the product of step b) by adding deoxidizing and desulfurizing agents in batches to provide LF refined molten steel;

[0043] d) adding a titanium-calcium composition to the LF refined steel liquid under the conditions that the oxygen content of the LF refined steel liquid is 30-60 ppm and the temperature is 1520° C. to 1570° C., so that the inclusion titanium oxide in the subsequent process is dispersed in the engineering machinery steel;

[0044] e) 2-6 minutes after the addition of the titanium calcium alloy for alloying, adding the chromium-boron composition to the LF refined steel liquid to alloy the LF refined steel liquid;

[0045] f) continuously casting the product of step e) to prepare steel for construction machinery.

[0046] According to the embodiments of the present application, the silicon-manganese composition belongs to the elements that are not easily oxidized, the metals that are not easily oxidized and the non-metallic elements that are not easily oxidized. The silicon-manganese composition contains, by mass percentage: 20% to 23% silicon, 65% to 72% manganese, and the silicon-manganese alloy composition also contains ≤1.2% C, ≤0.25% P, ≤0.04% S, and the remainder is unavoidable impurity elements.

[0047] In some embodiments, adding the titanium-calcium composition to the LF refined steel comprises: adding ferrotitanium and calcium wire to the LF refined steel. In some embodiments, adding the titanium-calcium composition to the LF refined steel comprises: adding ferrotitanium and calcium wire to the LF refined steel, respectively.

[0048] In some embodiments, the slag amount during step a) and step b) is controlled to be 2Kg / t to 4Kg / t. It can be understood that during step a) and step b), the slag amount per ton of molten steel is 2kg-4kg.

[0049] In some embodiments, the aluminum content in the silicon-manganese composition is less than 0.05%, and the introduction of Al needs to be avoided as much as possible to avoid the adverse effects caused by Al.

[0050] In some embodiments, by using a ferrosilicon manganese composition to weakly deoxidize hot metal after the converter end point, the effect of controlling the nitrogen content in molten steel can be achieved.

[0051] According to an embodiment of the present application, under the conditions that the oxygen content of the molten steel refined by LF is 30 - 60 ppm and the temperature is 1520 °C to 1570 °C, adding a titanium-calcium composition wire to the molten steel refined by LF can simultaneously reduce the oxygen content and sulfur content in the molten steel, facilitate the processing of the orderly process, and enable the finally produced steel for construction machinery to meet the performance requirements.

[0052] In some embodiments, before step a), KR desulfurization treatment is performed on blast furnace hot metal to make the sulfur content in the blast furnace hot metal < 0.002%. Clean scrap steel can be used for KR desulfurization treatment.

[0053] In some embodiments, in step b), the easily oxidizable alloy is a nickel-containing alloy.

[0054] According to an embodiment of the present application, the easily oxidizable alloy may include easily oxidizable metal and / or non-metal elements. The easily oxidizable alloy may be a nickel-containing alloy. Adding a nickel-containing alloy has the positive effect of improving the toughness of the steel plate.

[0055] In some embodiments, in step c), by adding a deoxidizing and desulfurizing agent to the product of step b) in batches for slag surface deoxidation to provide molten steel refined by LF. When the refining ends, the refined molten steel satisfies: (FeO + MnO) ≤ 1.5%; according to an embodiment of the present application, controlling the refined molten steel to satisfy: (FeO + MnO) ≤ 1.5% has the positive effect of controlling the oxygen content in the molten steel.

[0056] In some embodiments, the deoxidizing and desulfurizing agent includes lime and high-quality composite slag. The main components of the high-quality composite slag are 35% - 45% CaO, ≤ 5.5% SiO2, 42% - 50% Al2O3, ≤ 7% MgO, ≤ 0.5% H2O, ≤ 0.1% S, ≤ 0.05% P, etc. According to an embodiment of the present application, about 400 Kg of lime and about 450 Kg of high-quality composite slag are added during the tapping process of the converter, and the deoxidizing and desulfurizing agent is used to control the oxygen content in the molten steel.

[0057] In some embodiments, in steps c), d) and e), it further includes: soft blowing the molten steel refined by LF.

[0058] According to an embodiment of the present application, bottom blowing control of the molten steel in the ladle can be achieved by blowing gas through a porous plug, and top blowing of the molten steel can be controlled by the flow rate of the oxygen lance. The gas for bottom blowing can be an inert gas, preferably argon. The gas for top blowing can be oxygen or air. Stirring of the molten steel can be achieved by bottom blowing and the added substances can be quickly melted in the mixture.

[0059] In some embodiments, in step d), before adding the titanium-calcium composition to the LF-refined molten steel, the temperature of the LF-refined molten steel is adjusted so that the temperature of the LF-refined molten steel is 1520 °C to 1570 °C and heating treatment is avoided after adding the titanium-calcium alloy.

[0060] In some embodiments, under the conditions that the oxygen content of the LF-refined molten steel is 30 - 60 ppm and the temperature is 1520 °C to 1570 °C, ferrotitanium and calcium wire are added to the LF-refined molten steel so that titanium oxides of inclusions are diffusely distributed in the steel for construction machinery in subsequent processes.

[0061] According to the embodiments of the present application, in step d), due to the limited deoxidation ability of Ti, when the initial [O] content in the steel is above 30 ppm, after treatment with 0.02% Ti, the average [O] content in the steel is still about 18 ppm. And Ca is an active metal with better deoxidation and desulfurization abilities than Al. Therefore, treatment with a titanium-calcium alloy can make the oxygen content of the molten steel after adding the titanium-calcium alloy reach 30 PPM to 50 PPM.

[0062] In some embodiments, titanium and calcium are added to the LF-refined molten steel simultaneously. The titanium can be ferrotitanium, and the calcium can be calcium powder or calcium wire.

[0063] In some embodiments, ferrotitanium is added to the LF-refined molten steel first and then calcium wire is added. The time interval between adding ferrotitanium and calcium wire can be 3 - 5 min.

[0064] In order to verify the effect of adding ferrotitanium and calcium wire on the LF-refined molten steel, through experiments by the inventor, it is found that the titanium-calcium alloy has a unique effect of controlling the oxygen content in the steel:

[0065] Using converter end-point molten steel for simulation: T[O]: 200 - 800 ppm, T[C]: 0.05 - 0.15%. The experiment uses pure iron as the raw material, and the [C] and [O] contents in the steel are adjusted by adding Fe2O3 powder and pure carbon powder. The amount of pure iron is about 500 g. The experiment is carried out in a high-temperature carbon tube furnace at a temperature of 1600 °C. The raw materials are put into a MgO crucible, heated with the furnace, and after the temperature reaches the required value, it is kept warm for 10 min to completely melt the raw materials. The whole process is protected by passing N2 gas. After the raw materials are completely melted, steel samples are sucked by a quartz glass tube, and electrolytic manganese and ferrosilicon are added for deoxidation alloying, and it is ensured that the [O] content in the steel is greater than 30 ppm. After 5 min of adding the alloy, pure Ti-Ca powder is added in the amounts shown in Table 1 and added to 11# - 16# in sequence in the manner described in Table 1. And 15 min after all the alloy is added, the crucible is quickly taken out and cooled to obtain steel blocks numbered 11# - 16#. The cooled steel samples are tested for T[O] and microscopic inclusions to analyze the change of T[O] in the steel with time and the change of the type and particle size distribution of inclusions in the steel.

[0066] Table 1 Actual addition amount of experimental alloys

[0067]

[0068]

[0069] After all the alloy was added, the crucible was quickly taken out and cooled after 15 min. After wire cutting, embedding, and polishing, a Leica microscope and a scanning electron microscope were used to statistically analyze the morphology, composition, quantity, and particle size distribution of inclusions. Among them, the detection of the composition of typical inclusions is as Figure 3 shown and Figure 4 .

[0070] The inclusions obtained by Ti-Ca composite deoxidation Figure 3 as described above. It can be seen from Figure 3 that the morphology and energy spectrum analysis results of the inclusions obtained from the 3 groups of experiments are relatively similar. Needle-shaped titanium oxide inclusions were observed in all of them, and the inclusions wrapped outside were Al-Si-Mn-Ca-Ti-O composite inclusions. There were obvious S-containing inclusions wrapping outside the inclusions of No. 11 and No. 12. In addition to the above composite inclusions, its main components also included a certain content of MnS.

[0071] Energy spectrum analysis was carried out on the inclusions of No. 11-No. 13 using a German Zeiss field emission scanning electron microscope energy spectrometer. From the results, the MnS content was about 20%. When observing the inclusions in No. 13, no MnS was found attached to the outside of the composite inclusions.

[0072] When Ti-Ca composite deoxidation was used, the inclusions Figure 4 as shown were obtained. Needle-shaped titanium oxide inclusions could also be observed in some of the inclusions of No. 14-No. 16, and they were wrapped outside by Al-Si-Mn-Ca-Ti-O composite inclusions, but the ratio of such inclusions was relatively small.

[0073] Comprehensively Figure 3 and Figure 4It is shown that compared with using Ti-Ca complex deoxidation alone, more Al-Si-Mn-Ca-Ti-O complex inclusions are obtained by using Ti-Ca complex deoxidation, which encapsulate acicular titanium oxide inclusions. The above simulation experiment shows that in the preparation of steel for construction machinery, a large number of fine titanium oxide inclusions can be controlled to form in the steel, which plays a pinning effect at the grain boundaries, refines the grains, and can promote the formation of intragranular acicular ferrite, thereby improving the toughness and welding performance of the material. Since the oxides of Ti (TiO, TiO2, Ti2O3, Ti3O5) are effective intragranular nucleation cores, among which Ti2O3 has the strongest ability to promote intragranular nucleation. After treatment by this method, the addition of Ti mainly combines with the primary inclusions. At this time, the influence of the Ti addition time on the morphology, composition and size of the inclusions has a direct relevance to the oxide metallurgy effect. The inclusions are basically Al2O3 inclusions, and at the same time, there are some composite inclusions containing Mn, Si, and Ca. The generated MnS inclusions can promote the formation of intragranular ferrite. The precipitation of MnS has a great relationship with the surface composition of the inclusions. The Ti2O3 inclusions play a great role in promoting the precipitation of MnS. Since the surface of the Al-Si-Mn-Ca-Ti-O composite inclusion has a high Ti content, it can better promote the nucleation of MnS on the inclusion, which is beneficial to the formation of intragranular ferrite, playing a role in refining the grains, reducing the inclusion level, and improving the strength, toughness and welding performance of the steel.

[0074] In some embodiments, adding an appropriate weight of a chromium-boron composition can make the chromium and boron elements in the molten steel meet the requirements, reaching 0.15% - 0.25% Cr and 0.0012% - 0.0020% B. By adding the chromium-boron composition, a positive effect of improving the toughness of the steel plate can be achieved.

[0075] In some embodiments, 2 - 6 minutes after the alloying with titanium-calcium alloy is completed, a chromium-boron composition is added to the LF-refined molten steel to alloy the LF-refined molten steel. After 2, 3, 4, 5, or 6 minutes after the alloying is completed, the alloy yield can be stabilized.

[0076] In some embodiments, step e) further includes:

[0077] After the alloying of the LF-refined molten steel is completed, the LF-refined molten steel is continuously soft-blowed, and the soft-blowing time t satisfies: 6min ≤ t < 10min. Maintaining the soft-blowing treatment after the alloying treatment of the molten steel can promote the floating of large-sized inclusions.

[0078] In some embodiments, the hot metal of the blast furnace comprises the following components by mass percentage: 3.50% ≤ C ≤ 4.50%, 0.35% ≤ Si ≤ 0.55%, 0.10% ≤ Mn ≤ 0.50%, P ≤ 0.18%, S ≤ 0.035%, Cu ≤ 0.07%, As ≤ 0.050%, Sn ≤ 0.030%, and the balance is iron and inevitable impurities.

[0079] In some embodiments, the steel for construction machinery comprises the following components by mass percentage: 0.18% ≤ C ≤ 0.23%, 0.20% ≤ Si ≤ 0.40%, 1.10% ≤ Mn ≤ 1.30%, P ≤ 0.020%, S ≤ 0.002%, 0.15% ≤ Cr ≤ 0.25%, 0.010% ≤ Ti ≤ 0.025%, 0.0012% ≤ B ≤ 0.0020%, 0.015% ≤ Als ≤ 0.050%, 0.015% ≤ Nb ≤ 0.025%, N ≤ 0.0070%, and the balance is iron and inevitable impurities.

[0080] In a second aspect, an embodiment of the present application provides a steel for construction machinery, which is obtained by the preparation method of the first aspect.

[0081] In some embodiments, the steel for construction machinery satisfies at least one of the following conditions:

[0082] According to the detection method of GB / T 2975, the mechanical properties of the steel for construction machinery include: yield strength of 1200 - 1300 MPa, tensile strength of 1400 - 1500 MPa, elongation of 12% - 18%, hardness of 400 - 450 HBW, longitudinal impact work of 100 - 150 AKV, and weldability of 2 - 2.4 KJ / mm;

[0083] According to the non-metallic inclusion rating of GB / T10561 for the product, the inclusions of the steel for construction machinery satisfy: class B inclusions ≤ 1.5 grade, class D inclusions in the range of 0 - 1.0 grade, and class Ds inclusions in the range of 0 - 1.0 grade;

[0084] The average grain size of the inclusion titanium oxide is 0.2 μm - 3.0 μm;

[0085] The metallographic structure of the steel for construction machinery includes: 100% martensite by volume percentage.

[0086] According to the embodiments of the present application, since the oxides of Ti (TiO, TiO2, Ti2O3, Ti3O5) are effective intragranular nucleation cores, among which Ti2O3 has the strongest ability to promote intragranular nucleation. After treatment by this method, the addition of Ti mainly combines with the primary inclusions in the steel plate. At this time, the influence of the Ti addition treatment time on the morphology, composition, and size of the inclusions has a direct correlation with the oxide metallurgy effect. The inclusions are basically Al2O3 inclusions, and there are also some composite inclusions containing Mn, Si, and Ca. The generated MnS inclusions can promote the formation of intragranular ferrite. The precipitation of MnS has a great relationship with the surface composition of the inclusions. The Ti2O3 inclusions play a great role in promoting the precipitation of MnS. Since the surface Ti content of the Al-Si-Mn-Ca-Ti-O composite inclusions is relatively high, it can better promote the nucleation of MnS on the inclusions, thus being beneficial to the formation of intragranular ferrite, playing a role in refining grains, reducing the inclusion grade, and improving the strength, toughness, and welding performance of the steel.

[0087] Example

[0088] The following examples more specifically describe the content disclosed in the present application. These examples are only for illustrative purposes, because various modifications and changes within the scope of the present application disclosure are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and all instruments used in the examples are commercially available.

[0089] Example 1

[0090] This example provides a preparation method for steel for construction machinery. The specific implementation process includes: S1. 185 t of blast furnace hot metal, and the blast furnace hot metal includes the following components in mass percentages: C = 4.0%; Si = 0.45%; Mn = 0.32%; P ≤ 0.14%; S ≤ 0.026%; Cu = 0.023%; As = 0.022%; Sn = 0.018%, and the balance is iron and inevitable impurities. The blast furnace hot metal is subjected to KR desulfurization treatment to control the [S] content in the hot metal < 0.002%. In addition, 40 t of clean scrap steel is taken. The hot metal and the clean scrap steel are charged into a 210 t top-bottom combined blowing converter for oxygen blowing melting to obtain crude steel liquid.

[0091] S2. During the tapping process of the converter, first add 400 kg of lime to the ladle, then add 960 kg of ferrosilicon (75% - 80% Si) and 2700 kg of low-carbon ferromanganese (85% - 92% Mn) alloys respectively, without adding Al, for weak deoxidation treatment. After all the Mn alloys are added, then add 310 kg of non-oxidizable Ni alloy.

[0092] In the LF refining process, first add 860 kg of lime, 200 kg of deoxidizer (the main components are ≤8% SiO2, 30% - 35% Al2O3, ≥22% Al, 3% - 10% MgO), and 540 kg of premelted slag (the main components are 45% - 52% CaO, 41% - 46% Al2O3, ≤5% MgO, ≤5% SiO2,

[0093] ≤1.5% Fe2O3, ≤1.0% H2O) to reduce the oxygen and sulfur content in the molten steel to appropriate levels. At the same time, lower the electrodes to heat up by power supply. After the heating is completed, the dissolved oxygen is determined to be 46 ppm. Then, add 190 kg of Ti-Ca alloy. 3 minutes after all the Ti-Ca alloy is added, add 320 kg of easily oxidized alloy Cr and 25 kg of B for fine adjustment of the composition. Soft blow for 8 minutes, and then carry out continuous casting to obtain steel for construction machinery.

[0094] Example 2

[0095] This example provides a method for preparing steel for construction machinery. The specific implementation process includes:

[0096] S1. 175 t of hot metal from the blast furnace. The hot metal from the blast furnace includes the following components by mass percentage: C = 3.5%;

[0097] Si = 0.55%; Mn = 0.25%; P ≤ 0.11%; S ≤ 0.023%; Cu = 0.021%; As = 0.018%; Sn = 0.016%, and the balance is iron and inevitable impurities. The hot metal from the blast furnace undergoes KR desulfurization treatment to control the [S] content in the hot metal <0.002%. In addition, take 50 t of clean scrap steel. Charge the hot metal and clean scrap steel into a 210 t top-bottom combined blowing converter for oxygen blowing melting to obtain molten crude steel.

[0098] S2. During the tapping process of the converter, first add 400 kg of lime to the ladle, then add 960 kg of Si and 2700 kg of Mn alloy respectively, without adding Al for weak deoxidation treatment. After all the Mn alloy is added, add 310 kg of non-easily oxidized Ni alloy.

[0099] S3. In the LF refining process, first add 920 kg of lime, 260 kg of deoxidizer, and 600 kg of premelted slag. At the same time, lower the electrodes to heat up by power supply. After the heating is completed, the dissolved oxygen is determined to be 35 ppm. Then, add 190 kg of Ti-Ca alloy. 3 minutes after all the Ti-Ca alloy is added, add 320 kg of easily oxidized alloy Cr and 25 kg of B for fine adjustment of the composition. Soft blow for 5 minutes, and then carry out continuous casting to obtain steel for construction machinery.

[0100] Example 3

[0101] This embodiment provides a method for preparing steel for construction machinery, and the specific implementation process includes:

[0102] S1. 195 t of hot metal from the blast furnace, and the hot metal from the blast furnace includes the following components by mass percentage: C = 3.8%;

[0103] Si = 0.42%; Mn = 0.36%; P ≤ 0.12%; S ≤ 0.022%; Cu = 0.027%; As = 0.026%; Sn = 0.020%, and the balance is iron and inevitable impurities. The hot metal from the blast furnace is subjected to KR desulfurization treatment to control the [S] content in the hot metal < 0.002%. In addition, 30 t of clean scrap steel is taken. The hot metal and the clean scrap steel are charged into a 210 t top and bottom combined blowing converter for oxygen blowing melting to obtain molten crude steel.

[0104] S2. During the tapping process of the converter, first add 420 kg of lime into the ladle, then add 1020 kg of ferrosilicon and 2845 kg of low-carbon ferromanganese alloy respectively, without adding Al, for weak deoxidation treatment. After all the Mn alloy is added, then add 310 kg of Ni alloy that is not easily oxidized.

[0105] S3. During the LF refining process, first add 600 kg of lime, 200 kg of deoxidizer and 550 kg of pre-melted slag. At the same time, lower the electrode for heating. After the heating is completed, the oxygen content is determined to be 59 ppm. Then, add 190 kg of Ti-Ca alloy. 3 minutes after all the Ti-Ca alloy is added, add 320 kg of easily oxidized alloy Cr and 25 kg of B for composition fine-tuning. Soft blow for 8 minutes, and then continuous casting is carried out to obtain steel for construction machinery.

[0106] Comparative Example 1 (Adding Al for deoxidation during tapping)

[0107] This comparative example provides a method for preparing steel for construction machinery, and the specific implementation process includes:

[0108] S1. 180 t of hot metal from the blast furnace, which is subjected to KR desulfurization treatment to control the [S] content in the hot metal < 0.002%. In addition, 45 t of clean scrap steel is taken. The hot metal and the clean scrap steel are charged into a 210 t top and bottom combined blowing converter for oxygen blowing melting to obtain molten crude steel.

[0109] S2. During the tapping process of the converter, first add 400 kg of lime into the ladle, and then add 900 kg of Al, 960 kg of Si, and 2700 kg of Mn alloy in sequence for deoxidation treatment. After the deoxidation is completed, add 310 kg of Ni alloy, 320 kg of Cr and 25 kg of B.

[0110] During the LF refining process, first add 900 kg of lime, 120 kg of top slag deoxidizer, and 800 kg of pre-melted slag. At the same time, lower the electrodes for heating by power supply. After the heating is completed, the dissolved oxygen is determined to be 15 ppm. Then, add 190 kg of Ti-Ca alloy. After all the Ti-Ca alloy is added, soft blow for 8 minutes, and then continuous casting is carried out to obtain steel for construction machinery.

[0111] Comparative Example 2 (no top slag deoxidizer was added during LF refining)

[0112] This embodiment provides a method for preparing steel for construction machinery based on oxide metallurgy technology. The specific implementation process includes:

[0113] S1. 178 t of hot metal from the blast furnace is subjected to KR desulfurization treatment to control the [S] content in the hot metal < 0.002%. In addition, 48 t of clean scrap steel is taken. The hot metal and clean scrap steel are charged into a 210 t top and bottom combined blown converter for oxygen blowing smelting to obtain crude steel.

[0114] S2. During the tapping process of the converter, first add 390 kg of lime to the ladle, and then add 900 kg of Al, 960 kg of ferrosilicon, and 2700 kg of low-carbon ferromanganese alloy in sequence for deoxidation treatment. After the deoxidation is completed, add 310 kg of Ni alloy, 320 kg of Cr, and 25 kg of B. After the tapping is completed, add 200 kg of top slag deoxidizer.

[0115] During the LF refining process, first add 900 kg of lime and 800 kg of pre-melted slag. At the same time, lower the electrodes for heating by power supply. After the heating is completed, the dissolved oxygen is determined to be 79 ppm. Then, add 190 kg of Ti-Ca alloy. After all the Ti-Ca alloy is added, soft blow for 8 minutes, and then continuous casting is carried out to obtain steel for construction machinery.

[0116] Testing part

[0117] 1. Detect the metallographic structure in the steel for construction machinery

[0118] Use a Leica LEICA DMI5000M optical metallographic microscope from Germany to detect the steel for construction machinery in Example 1 and Comparative Example 1. Figure 1 The left-middle figure shows the steel plate prepared in Comparative Example 1 and Figure 1 The right-middle figure shows the optical microscope photos of the steel plate prepared in Example 1. From Figure 1 the left figure and the right figure, it can be seen that the grains in the left figure are fine, indicating that the steel plate in the example has good plasticity and toughness and strong resistance to fracture and tearing. Use a Leica LEICA DMI5000M optical metallographic microscope from Germany to detect the metallographic structure of the steel for construction machinery in Example 1. The detection results are as Figure 2 shown. From Figure 2It can be seen that a large number of overlapping and intertwined acicular ferrite structures are formed within the crystal grains, effectively inhibiting the growth and expansion of grain boundary ferrite, effectively refining the grains, and preventing the diffusion of cracks within the crystal grains.

[0119] 2. Detect the mechanical properties of the steel for construction machinery

[0120] According to the detection method of GB / T 2975, detect the yield strength, tensile strength, elongation, longitudinal impact energy, and weldability of the steel for construction machinery; according to the detection method of GB / T 231, detect the hardness of the steel for construction machinery; the results are shown in Table 2.

[0121] Table 2

[0122]

[0123] As can be seen from Table 1, using the method of this application, the mechanical properties of the steel for construction machinery with a thickness of 6 mm include: the yield strength is 1200 - 1300 MPa, the tensile strength is 1400 - 1500 MPa, the elongation is 12% - 18%, the hardness is 400 - 450 HBW, the longitudinal impact energy is 100 - 150 AKV, and the weldability is 2 - 2.4 KJ / mm, all of which are superior to the steel for construction machinery prepared by the comparative example.

[0124] 3. Detect the particle size and quantity of titanium oxides in the steel for construction machinery

[0125] For the steel for construction machinery prepared in Example 1, take 162 coils of steel, and take one finished product sample from each coil to detect the mechanical properties and inclusions, with a total of 162 test samples. Detect and grade the inclusions in the finished steel plate (material sample) according to GB / T10561 - 2005, and count the proportion of each type of inclusion grade. The test results are shown in Table 1.

[0126] Table 1: Proportion of each type of inclusion grade in the inclusion detection of the finished plate in Example 1

[0127]

[0128] Table 2 Table 1: Proportion of each type of inclusion grade in the inclusion detection of the finished plate in Comparative Example 1

[0129]

[0130] As can be seen from the inclusion detection results in the above table, the grades of Class B and Class D inclusions in the examples of this application have been reduced. In the process of tapping molten steel from the converter in the method of the present invention, silicomanganese alloy is used for weak deoxidation, and alloys that are not easily oxidized are added for alloying. During the LF refining process, power is supplied first to increase the temperature, and aluminum pellets or calcium carbide are added to deoxidize the top slag. When the free oxygen content in the molten steel is controlled at 30-60 ppm, Ti-Ca alloy wire is added for alloying, while reducing the oxygen content and sulfur content in the molten steel. After 3 minutes of Ti-Ca alloying treatment, easily oxidized alloys are added to complete the alloying operation of the molten steel. After the alloying treatment of the molten steel is completed, soft blowing treatment is maintained for 4-8 minutes to promote the floating of large-sized inclusions. Using this method to prepare steel for construction machinery can control the formation of a large number of fine titanium oxide inclusions in the steel, which play a pinning effect at the grain boundaries, refine the grains, and can promote the formation of intragranular acicular ferrite, thereby improving the toughness and welding performance of the material. Since the oxides of Ti (TiO, TiO2, Ti2O3, Ti3O5) are effective intragranular nucleation cores, among which Ti2O3 has the strongest ability to promote intragranular nucleation. After treatment with this method, the addition of Ti is mainly to compound with the primary inclusions. At this time, the influence of the Ti addition time on the morphology, composition, and size of the inclusions has a direct correlation with the oxide metallurgy effect. The inclusions are basically Al2O3 inclusions, and at the same time, there are some composite inclusions containing Mn, Si, and Ca. The formed MnS inclusions can promote the formation of intragranular ferrite. The precipitation of MnS has a great relationship with the surface composition of the inclusions. The Ti2O3 inclusions play a greater role in promoting the precipitation of MnS. Since the surface Ti content of the Al-Si-Mn-Ca-Ti-O composite inclusions is relatively high, it can better promote the nucleation of MnS on the inclusions, which is beneficial to the formation of intragranular ferrite, playing a role in refining the grains, reducing the inclusion grade, and improving the strength, toughness, and welding performance of the steel.

[0131] The above is only the specific implementation manner of this application, but the protection scope of this application is not limited thereto. Any person skilled in the art within the technical scope disclosed in this application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

Claims

1. A method for preparing steel for construction machinery, comprising: a) Deoxidizing the blast furnace hot metal at the end of the converter by adding a silicon-manganese composition, wherein the blast furnace hot metal comprises the following components by mass percentage: 3.50% ≤ C ≤ 4.50%, 0.35% ≤ Si ≤ 0.55%, 0.10% ≤ Mn ≤ 0.50%, P ≤ 0.18%, S ≤ 0.035%, Cu ≤ 0.07%, Als ≤ 0.050%, Sn ≤ 0.030%, and the balance is iron and inevitable impurities; b) Alloying the product of step a) by adding a nickel-containing alloy, and controlling the slag carry-over amount during the processes of step a) and step b) to be 2 kg / t to 4 kg / t to prevent sulfur in the surface slag from returning to the blast furnace hot metal; c) Deoxidizing and desulfurizing the surface of the slag of the product of step b) by adding a deoxidizing and desulfurizing agent in batches to provide LF-refined molten steel; d) Under the conditions that the oxygen content of the LF-refined molten steel is 30 - 60 ppm and the temperature is 1520°C to 1570°C, adding a titanium-calcium alloy to the LF-refined molten steel so that titanium oxides of inclusions in subsequent processes are dispersed in the steel for construction machinery, and avoiding heating up after adding the titanium-calcium alloy; e) 2 - 6 minutes after the alloying by adding the titanium-calcium alloy is completed, adding a chromium-boron composition to the LF-refined molten steel to alloy the LF-refined molten steel; after the alloying of the LF-refined molten steel is completed, continuously soft-blowing the LF-refined molten steel, and the soft-blowing time t satisfies: 6 min ≤ t < 10 min; f) Continuously casting the product of step e) to prepare the steel for construction machinery.

2. The method according to claim 1, wherein Before step a), it includes subjecting the blast furnace hot metal to KR desulfurization treatment so that the sulfur content in the blast furnace hot metal < 0.002%.

3. The method according to claim 1, wherein Steps c) and d) also include: soft-blowing the LF-refined molten steel.

4. The method according to claim 1, characterized in that, The steel for construction machinery comprises the following components by mass percentage: 0.18% ≤ C ≤ 0.23%, 0.20% ≤ Si ≤ 0.40%, 1.10% ≤ Mn ≤ 1.30%, P ≤ 0.020%, S ≤ 0.002%, 0.15% ≤ Cr ≤ 0.25%, 0.010% ≤ Ti ≤ 0.025%, 0.0012% ≤ B ≤ 0.0020%, 0.015% ≤ Als ≤ 0.050%, 0.015% ≤ Nb ≤ 0.025%, N ≤ 0.0070%, and the balance is iron and inevitable impurities.

5. A steel for construction machinery, prepared by the method for preparing steel for construction machinery according to any one of claims 1 to 4.

6. The steel for construction machinery according to claim 5, characterized in that, The steel for construction machinery satisfies at least one of the following conditions: According to the detection method of GB / T 2975, the mechanical properties of the steel for construction machinery include: yield strength of 1200 - 1300 MPa, tensile strength of 1400 - 1500 MPa, elongation of 12% - 18%, hardness of 400 - 450 HBW, longitudinal impact energy of 100 - 150 AKV, and weldability of 2 - 2.4 kJ / mm; The non-metallic inclusions of the product are rated according to GB / T 10561, and the inclusions in the steel for construction machinery meet the following requirements: class B inclusions ≤ grade 1.5, class D inclusions in the range of 0 to 1.0, and class Ds inclusions in the range of 0 to 1.0; The average grain size of the titanium oxide inclusions is 0.2 μm to 3.0 μm; The metallographic structure of the steel for construction machinery includes: by volume percentage, 98% - 100% tempered martensite, ≤ 1% retained austenite, and ≤ 1% bainite.

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