Ultra-low yield ratio and low yield point damping mild steel and preparation method thereof

Abstract

The present invention relates to an ultra-low yield ratio and low yield point damping mild steel and a preparation method thereof. The ultra-low yield ratio and low yield point damping mild steel comprises the following chemical components by weight: C≤0.05%, Si≤0.05%, Mn 13%-24%, Al 4%-13%, Al≥0.792%×Mn-6.5%, P 0-0.045%, S: 0-0.012%, and the balance is Fe and unavoidable impurities; the microstructure of the ultra-low yield ratio and low yield point damping mild steel is austenite and delta ferrite, wherein the delta ferrite is ≤10%. The advantages of the present invention are: a kind of material that can dissipate energy by plastic deformation during earthquakes to protect the main structure from damage, and also has the function of reducing vibration and noise within the elastic range to reduce vibration and noise; the damping mild steel has the seismic energy dissipation effect of mild steel and the function of reducing vibration and noise, and has excellent corrosion resistance. It has broad application prospects in the fields of buildings, bridges, etc. that require seismic energy dissipation and vibration and noise reduction.

Description

Technical Field

[0001] The present invention relates to the field of damping steel production, and in particular to an ultra-low yield ratio and low yield point damping mild steel and a preparation method thereof. Background Art

[0002] With the development of modern science and technology and people's ever-increasing demand for a better quality of life, the hazards of vibration and noise are attracting increasing attention from researchers. Consequently, research on vibration and noise reduction technologies has attracted widespread attention from many sectors, particularly in the fields of navigation, aerospace, aviation, and the nuclear industry. Damping alloys emerged in response to these conditions. Damping alloys are alloys that possess the strength expected of structural materials and can quickly convert vibration energy into heat through a damping process (internal friction).

[0003] Currently, the more mature metal damping materials can be classified, based on their damping mechanisms, into complex phase (cast iron), superplastic (Zn-Al alloy), dislocation (Mg and Mg alloy), twin (Mn-Cu alloy), and ferromagnetic (Fe-Cr). Fe-Mn damping steel is a new type of metal damping material developed only in the past decade. Among these metal damping materials, Fe-Mn damping steel offers the lowest cost (only one-fourth that of Mn-Cu damping alloy). Its damping performance increases with strain amplitude and is unaffected by external magnetic fields, maintaining high damping performance even at relatively high service temperatures. Fe-Mn damping steel is well-suited for use in components subject to significant vibration and impact.

[0004] In buildings, bridges, and other fields, dampers made of mild steel are often used to dissipate energy during earthquakes and protect the main structure from damage. During an earthquake, mild steel dampers first undergo plastic deformation, then undergo cyclic tensile deformation, absorbing a large amount of seismic energy. While the dampers absorb a large amount of energy, the main structure absorbs a small amount, ensuring that the building remains intact during major earthquakes and can be repaired during minor ones. Currently, commonly used mild steel only functions to dissipate energy plastically during earthquakes. Fe-Mn damping steel, a high-damping metal material with a low yield-to-strength ratio, exhibits seismic performance in its plastic range while also providing vibration and noise reduction in its elastic range. Building safety requires more than just seismic performance; vibration also poses a significant threat to buildings in daily life. Furthermore, with the public's pursuit of a better life, the noise caused by vibration in buildings is also a pressing issue. Therefore, developing a mild steel that combines both seismic energy dissipation and vibration reduction is a highly worthy research topic.

[0005] In the prior art, patent CN103898401B discloses a method for improving the damping performance of high-strength iron-manganese-based damping alloys. This method utilizes solution heat treatment, aging heat treatment, and room-temperature deformation to create segregation of solute atoms in stacking fault regions. Through room-temperature deformation, extended dislocations are separated from regions with high solute atom concentrations, enhancing their mobility and ultimately improving the damping performance of the iron-manganese-based damping alloy. However, this method, which performs deformation at room temperature, has a limited application range and can only be used in thin-gauge alloys. Furthermore, room-temperature deformation can also cause internal stress in the material, which is detrimental to the alloy's long-term life.

[0006] Patent number CN112899577B discloses a method for preparing an Fe-Mn-based high-strength, high-damping alloy. This method utilizes smelting, forging, and hot rolling to produce 2-20 mm hot-rolled plates, which are then annealed or cold-rolled to obtain the high-strength, high-damping alloy. While this method achieves a damping alloy with a tensile strength exceeding 900 MPa through complex heat treatment and cold rolling processes, it fails to consider the alloy's corrosion resistance and toughness. This significantly limits the alloy's application in today's environments, where multiple material properties are required.

[0007] Patent number CN107699668B discloses a method for improving the corrosion resistance of an iron-manganese damping alloy. This method involves performing a high-temperature heat treatment in a vacuum environment to create a layer of ferrite on the alloy's surface, thereby enhancing both the alloy's corrosion resistance and damping performance. However, this method requires high-temperature heat treatment in a vacuum environment, which creates demanding process conditions. Furthermore, the ferrite layer on the surface can significantly reduce the damping alloy's strength.

[0008] Patent number CN103966529A discloses a high-damping Mn-Fe-based vibration damping alloy and its preparation method. This method involves smelting in an induction furnace with an argon atmosphere, homogenizing heat treatment for 24 hours, forging at 900-1150°C, annealing at 1000°C, and finally solution treatment at 1000°C to obtain the high-damping vibration damping alloy. Although this method produces a damping alloy with good performance, the multiple heat treatment steps, including homogenization, annealing, and solution treatment, as well as forging, complicate the preparation process and make it suitable only for small-batch production, rather than large-scale production.

[0009] Patent CN106282786A discloses a Nb-containing iron-manganese-based damping alloy and its preparation method. This method uses vacuum arc melting, followed by homogenization heat treatment, hot rolling, shaping, and solution treatment to produce a high-damping alloy with a tanφ loss factor of 0.055. Although this method produces a high-damping damping alloy, the damping alloy prepared by arc melting is lightweight and has very limited applications. The process of placing the damping alloy in a stainless steel tube for heat treatment is even more difficult to promote. Therefore, this method is only suitable for preparing damping alloys in the laboratory or for applications requiring extremely small sizes.

[0010] Patent number CN106011636A discloses a high-strength and toughness iron-manganese-based damping alloy for marine applications. By controlling the microstructure to ensure a minimum 70% ε martensite content and a minimum 30% α martensite and austenite content, this patent achieves a well-balanced strength-toughness ratio for this marine iron-manganese-based damping alloy. While this damping alloy exhibits excellent strength and toughness, it fails to consider corrosion resistance. The main reason for the lack of widespread use of iron-manganese-based damping alloys in the marine sector is their poor corrosion resistance, which is even inferior to that of standard Q235 / Q345, making their application very challenging. Summary of the Invention

[0011] The purpose of the present invention is to provide an ultra-low yield ratio and low yield point damping mild steel and a preparation method. The present invention is not only a low yield point mild steel, but also has an ultra-low yield ratio, high plastic toughness, high damping and high corrosion resistance. At the same time, it has the seismic energy dissipation effect of mild steel and the vibration reduction and noise reduction function of damping steel. The composition and process are simple and easy to implement.

[0012] To achieve the above object, the present invention is implemented through the following technical solutions:

[0013] An ultra-low yield ratio and low yield point damping mild steel comprises the following chemical components by weight percentage: C≤0.05%, Si≤0.05%, Mn 13%-24%, Al 4%-13%, Al≥0.792%×Mn-6.5%, P 0-0.045%, S: 0-0.012%, and the balance is Fe and unavoidable impurities;

[0014] The microstructure of the ultra-low yield ratio and low yield point damping mild steel is austenite and delta ferrite, wherein the delta ferrite is ≤10%.

[0015] The ultra-low yield ratio and low yield point damping mild steel further comprises the following chemical components by weight: one or more of Nb 0.02% to 0.04%, Ti 0.013% to 0.026%, and Zr 0.02% to 0.04%.

[0016] The ultra-low yield ratio and low yield point damping mild steel further comprises the following chemical components by weight: V 0.02% to 0.04%.

[0017] The main functions of the damping mild steel component are:

[0018] C: is a key element that affects strength. It has a significant effect on improving the strength of damping steel through solid solution strengthening and precipitation strengthening. However, an increase in carbon content will affect the welding performance and low-temperature toughness of the steel, and in particular, it will significantly reduce the damping performance. In the present invention, C is a harmful element. From the performance requirements, it is best not to add C element. However, it is difficult to completely remove C element in industrial production, and the component is expensive. Considering the performance and cost comprehensively, it is preferred that the C content be controlled at ≤0.05%. This can not only ensure the damping performance of the material, but also appropriately improve the tensile properties of the material and obtain an ultra-low yield strength ratio without incurring high costs.

[0019] Si: It is the main deoxidizing component in the steelmaking process. In order to achieve a sufficient deoxidation effect, it must contain more than 0.10%. However, if the upper limit is exceeded, the toughness of the base material and the weld will be reduced. In addition, the solid-soluted Si element in the damping steel will seriously affect the mobility of partial dislocations, greatly limiting the damping performance of the material. In order to ensure high damping performance, the Si content should be as low as possible. Under the premise of ensuring low cost and meeting performance index requirements, the preferred Si content is ≤0.05%.

[0020] Mn: As the most important alloying element, Mn in damping steel can reduce the stacking fault energy. In addition to ensuring the appearance of ε martensite in the structure, it also has the effect of expanding the austenite phase region, reducing the Ar3 point temperature, and increasing the strength of the damping steel. Mn is the most important element for regulating damping steel. To ensure that the damping steel structure is mainly austenite, the Mn content and the Al content must be adjusted synchronously. Therefore, the preferred Mn content range is 13% to 24%.

[0021] Al: Aluminum is often used as a deoxidizer in steel, which can effectively reduce the oxygen content in the steel. It also has a certain grain refinement effect and can form aluminum nitride with nitrogen. However, aluminum is an extremely critical element in the damping steel of the present invention. Al will inhibit the transformation of austenite to ε martensite in the damping steel, causing the damping steel to obtain a large amount of room temperature austenite. In order to control the proportion of the austenite phase in the damping steel, the aluminum content needs to be strictly controlled, and the Mn content and Al content need to be adjusted synchronously. Therefore, the Al content is preferably 4% to 13%.

[0022] P: An element that has an adverse effect on the low-temperature impact toughness of damping steel. It can segregate in the center of the steel plate and aggregate at the grain boundaries, thereby damaging the low-temperature toughness. However, in the damping steel of the present invention, which is mainly austenitic, the effect of P on low-temperature toughness, plasticity and damping properties is relatively low. In order to achieve the purpose of low cost, the control range of P can be relatively loose. Therefore, the preferred P content is 0 to 0.045%.

[0023] S: has an adverse effect on the impact toughness of the damping steel and can form sulfide inclusions, which become crack sources. Especially in the high Mn system of the present invention, the formation of MnS will have a significant impact on the plasticity of the damping steel. To ensure that the damping steel has excellent comprehensive properties, S, as a harmful element, must be strictly controlled. Based on considerations of low cost, the S content is preferably not higher than 0.012%.

[0024] Nb: Niobium is added to promote grain refinement in the damping steel's rolled microstructure, simultaneously improving strength and toughness. Niobium inhibits austenite recrystallization during controlled rolling, effectively refining the microstructure and strengthening the matrix through precipitation. During welding, the segregation and precipitation of niobium atoms inhibits the coarsening of austenite grains during heating, ensuring a finer heat-affected zone after welding and improving weldability. The preferred Nb content is 0.02% to 0.04%.

[0025] Ti: A trace amount of Ti forms nitrides, carbides, or carbonitrides, which refine the grain size and improve the strength and toughness of the damping steel. It also enhances the toughness of the welded base metal during welding. However, if the Ti content exceeds 0.026%, the carbonitrides formed can impair the low-temperature toughness of the damping steel and reduce the toughness of the base metal and the weld heat-affected zone. Therefore, the Ti content is preferably controlled between 0.01% and 0.025%.

[0026] V: By forming fine, dispersed vanadium carbide precipitations with carbon, it effectively improves the strength of damping steel while maintaining minimal impact on its ductility and damping properties. This makes it highly effective in achieving damping steel with excellent overall performance. However, vanadium is a relatively expensive element, and excessive vanadium content can increase the size of precipitates, reducing the strength-enhancing effect and negatively impacting damping performance. Therefore, the preferred content is 0.02% to 0.04%.

[0027] Zr: Zirconium is a powerful deoxidizing and denitrifying element that can refine austenite grains and form zirconium sulfide with sulfur to prevent hot brittleness. Zirconium is also a strong carbide-forming element. In a high-carbon environment, it can also promote the spheroidization of cementite. Adding an appropriate amount of zirconium to the damping steel is beneficial to obtaining excellent comprehensive properties. Therefore, the content is preferably 0.02% to 0.04%.

[0028] The properties of damping mild steel are: yield strength ≤ 160MPa, tensile strength ≥ 400MPa, elongation after fracture ≥ 60%, -40℃ impact absorption energy ≥ 250J, damping performance (logarithmic decay rate) ≥ 0.27, and corrosion rate in cyclic immersion accelerated test ≤ 0.2g·m -2 ·h -1 .

[0029] A method for preparing ultra-low yield ratio and low yield point damping mild steel, which comprises sequentially smelting in an electric furnace or a converter, rolling in a rolling mill, and heat treatment, specifically comprising:

[0030] 1) Rolling

[0031] The steel plate is rolled in the complete recrystallization zone, with the ingot heating temperature controlled at 1150-1250°C and the holding time being T≥2.5min / mm×D / 2, where D is the ingot thickness. The steel plate is opened at 1080-1140°C and the ingot thickness is rolled to 200-250mm. The start rolling temperature of the complete recrystallization zone rolling is controlled at 1050-1100°C, with a single-pass reduction ratio of not less than 18%. The steel plate is rolled in a reciprocating manner, with the rolling process temperature always controlled at above 950°C, and the steel plate is rolled to 20-60mm. The steel plate is cooled after straightening, with the start cooling temperature being ≥900°C, the average cooling rate being 5-10°C, and the red-return temperature being 300-400°C.

[0032] 2) Heat treatment

[0033] The rolled steel plate is reheated to 850-930°C with a holding time of T≤1.5min / mm×D / 2, where D is the thickness of the steel plate. After the holding time is completed, the plate is air-cooled to room temperature.

[0034] The main functions of the damping mild steel preparation process steps are:

[0035] Rolling process: A low pre-rolling heating temperature and a relatively long holding time are used to effectively alleviate the component segregation in the damping steel ingot and prevent excessive growth of the austenite grains. Full recrystallization zone rolling is adopted, with a starting rolling temperature of 1050-1100°C, and the rolling temperature is controlled above the complete recrystallization temperature of the austenite grains (≥950°C). The reduction ratio is ≥18%. Full recrystallization zone rolling ensures that the austenite recrystallizes after each rolling pass, resulting in fully refined austenite grains. The post-rolling cooling temperature is ≥900°C. After rolling, the damping steel plate is straightened and then rapidly cooled. This prevents excessive coarsening of the austenite grains after rolling and refinement, resulting in fine and uniform austenite grains. The post-rolling red-hot temperature is controlled at 300-400°C, which allows the steel plate to achieve a self-tempering effect, reducing residual stress in the steel plate and improving its flatness.

[0036] Heat treatment process: The heating temperature is controlled low and the holding time is short. Under the premise of ensuring complete austenitization, the austenite grains will not be significantly coarsened and the structure will be fully homogenized. After the holding is completed, a slow cooling process is adopted instead of rapid cooling. The main reason is to leave a certain space for the formation of carbides and minimize the solid solution amount of carbon elements in the damping steel. At the same time, the yield strength of the damping steel under the air cooling process is low, which can meet the index requirements of low yield point.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] A kind of steel that can dissipate energy by plastic deformation in earthquakes and protect the main structure from damage is obtained, and also has the function of reducing vibration and noise within the elastic range, thereby reducing vibration and noise; by controlling the twin boundaries and stacking fault density in the Fe-Mn damping steel, the Fe-Mn damping steel can achieve high damping effect only through the fine microstructure in the austenite without the ε martensite structure. At the same time, the soft austenite structure makes the Fe-Mn damping steel have a low yield strength and excellent plastic deformation ability, thereby obtaining excellent plastic deformation performance. The ultra-low yield ratio and low yield point damping mild steel obtained has a yield strength of ≤160MPa, a tensile strength of ≥400MPa, an elongation after fracture of ≥60%, an impact absorption energy of ≥250J at -40℃, a damping performance (logarithmic attenuation rate) ≥0.27, and a corrosion rate in a cyclic immersion accelerated test of ≤0.2g·m-2·h-1; the damping mild steel has the seismic energy dissipation effect of mild steel and the function of vibration reduction and noise reduction, and has excellent corrosion resistance. It has broad application prospects in the fields of buildings, bridges, etc. that require seismic energy dissipation and vibration reduction and noise reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is an EBSD-Phase diagram of the embodiment. DETAILED DESCRIPTION

[0040] The present invention will be described in detail below with reference to the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0041] The following examples are implemented under the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the scope of protection of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0042] The chemical composition of the damping mild steel in the embodiment is shown in Table 1. The embodiment of the present invention adopts two-stage rolling, and the specific preparation process is shown in Table 2.

[0043] Table 1 Chemical composition of damping mild steel in various embodiments of the present invention (unit: wt%)

[0044] Example C Si Mn P S Al Nb Ti V Zr 1 0.05 0.02 13.5 0.013 0.003 4.2 - - - - 2 0.03 0.02 14.6 0.007 0.005 5.1 - - - - 3 0.02 0.03 15.4 0.022 0.007 5.7 - - - - 4 0.04 0.01 16.5 0.015 0.012 6.6 - - - - 5 0.03 0.04 17.5 0.005 0.003 7.4 - - - - 6 0.02 0.02 18.4 0.007 0.005 8.1 - - - - 7 0.03 0.03 19.7 0.012 0.007 9.1 - - - - 8 0.03 0.03 20.3 0.045 0.012 9.6 - - - - 9 0.02 0.02 21.4 0.007 0.005 10.5 - - - - 10 0.02 0.05 22.6 0.032 0.007 11.4 - - - - 11 0.01 0.01 23.7 0.042 0.007 12.3 - - - - 12 0.03 0.03 14.6 0.025 0.010 5.1 0.021 - 0.018 0.02 13 0.04 0.02 15.4 0.003 0.003 5.7 0.034 0.013 - - 14 0.03 0.03 16.5 0.003 0.003 6.6 0.039 0.019 0.011 - 15 0.02 0.01 17.5 0.007 0.005 7.4 - 0.026 0.023 0.02 16 0.03 0.04 18.4 0.007 0.005 8.1 0.025 - 0.039 0.03 17 0.03 0.02 19.7 0.007 0.005 9.1 - - 0.008 0.04 18 0.02 0.03 20.3 0.015 0.012 9.6 - 0.016 - 0.02 19 0.02 0.03 21.4 0.007 0.005 10.5 - 0.023 0.033 0.03

[0045] Table 2 Preparation process parameters of various embodiments of the present invention

[0046]

[0047] Table 3 Mechanical, damping and corrosion resistance test results of various embodiments and comparative examples

[0048]

[0049] As can be seen from Tables 1-3, the damping steel plate produced by the embodiment of the present invention has a yield strength of ≤160 MPa, a tensile strength of ≥400 MPa, an elongation after fracture of ≥60%, an impact energy absorption at -40°C of ≥250 J, a damping performance (logarithmic decay rate) of ≥0.27, and a cyclic immersion accelerated corrosion rate of ≤0.2 g·m -2 ·h -1 , is a low yield point steel with ultra-low yield strength ratio, high plasticity and toughness, high damping and high corrosion resistance. It is a damping mild steel with excellent comprehensive performance, and its performance fluctuation is small in the entire production process window. Figure 1 The structure of the inventive material of the embodiment of the present invention is dual phase, the red one is delta ferrite, and the blue one is austenite.

Claims

1. An ultra-low yield ratio and low yield point damping mild steel, characterized in that: The chemical composition includes the following by weight percentage: C≤0.05%, Si≤0.05%, Mn 13%~24%, Al 4%~13%, Al≥0.792%×Mn-6.5%, P0~0.045%, S: 0~0.012%, and the balance is Fe and unavoidable impurities; The microstructure of the ultra-low yield ratio and low yield point damping mild steel is austenite and delta ferrite, wherein delta ferrite is ≤10%; The method for preparing the ultra-low yield ratio and low yield point damping mild steel sequentially adopts electric furnace or converter smelting, rolling by a rolling mill, and heat treatment, specifically comprising: 1) Rolling The steel plate is rolled to a thickness of 20 to 60 mm by adopting a fully recrystallized zone rolling process, with the ingot heating temperature controlled at 1150 to 1250°C and the holding time being T≥2.5 min / mm×D / 2, where D is the ingot thickness. The steel plate is opened at 1080 to 1140°C and the ingot is rolled to a thickness of 200 to 250 mm. The start rolling temperature of the fully recrystallized zone rolling process is controlled at 1050 to 1100°C, with a single-pass reduction ratio of not less than 18%. The steel plate is rolled to a thickness of 20 to 60 mm by adopting a reciprocating rolling process, with the rolling process temperature always controlled at above 950°C. The steel plate is then cooled after straightening, with the start cooling temperature being ≥900°C, the average cooling rate being controlled at 5 to 10°C / s, and the red-return temperature being 300 to 400°C. 2) Heat treatment The rolled steel plate is reheated to 850-930°C with a holding time of T≤1.5min / mm×D / 2, where D is the thickness of the steel plate. After the holding time is completed, the plate is air-cooled to room temperature.

2. The ultra-low yield ratio and low yield point damping mild steel according to claim 1, characterized in that: The ultra-low yield ratio and low yield point damping mild steel further comprises the following chemical components by weight: one or more of Nb 0.02% to 0.04%, Ti 0.013% to 0.026%, and Zr 0.02% to 0.04%.

3. The ultra-low yield ratio and low yield point damping mild steel according to claim 2, characterized in that: The ultra-low yield ratio and low yield point damping mild steel further comprises the following chemical components by weight: V 0.02% to 0.04%.

4. The ultra-low yield ratio and low yield point damping mild steel according to claim 1, characterized in that: The properties of the damping mild steel are: yield strength ≤ 160 MPa, tensile strength ≥ 400 MPa, elongation after fracture ≥ 60%, -40°C impact absorption energy ≥ 250 J, logarithmic decay rate ≥ 0.27, corrosion rate ≤ 0.2 g·m -2 ·h -1 .

Images