A low-thermal expansion coefficient dual-phase steel material and a method for manufacturing the same

Abstract

The application relates to the technical field of alloy materials, in particular to a low-thermal-expansion-coefficient dual-phase steel iron material and a preparation method thereof. The main phase of the dual-phase steel iron material is a steel iron material, and the precipitated phase is an iron-based negative thermal expansion phase. The preparation method is as follows: steel iron material and alloy elements required by the iron-based negative thermal expansion phase are heated to be molten to obtain a molten liquid; the molten liquid is fully stirred to be uniform by using an induced electromagnetic force; the molten liquid is poured into a mold to be solidified by electromagnetic stirring to obtain a steel sample; the obtained steel sample is sequentially subjected to annealing treatment and aging treatment, and the dual-phase steel iron material is obtained, the negative thermal expansion precipitated phase is uniformly distributed in the steel iron main phase, the negative thermal expansion effect of the negative expansion phase and the positive thermal expansion effect of the steel iron main phase are offset when the temperature changes, the low-thermal-expansion-coefficient of the whole material is shown, meanwhile, the steel iron main phase ensures the basic strength, plasticity and processability of the material.

Description

Technical Field

[0001] This invention relates to a dual-phase steel material with a low coefficient of thermal expansion and its preparation method, belonging to the field of alloy materials technology. Background Technology

[0002] Most materials in nature exhibit the phenomenon of "thermal expansion and contraction." This characteristic of materials causes dimensional instability in mechanical parts, structural components, and electronic components when operating at different temperatures. Material failure and shortened lifespan due to thermal expansion are common, making the control of material thermal expansion a pressing need in modern industrial technology. For example, aerospace materials experience significant temperature differences between near and far solar surfaces; mismatches in thermal expansion coefficients can cause substantial internal stress, leading to microcracks, rapidly reducing lifespan, and structural damage. Laser resonant cavities generate heat during operation, and even minor dimensional changes can drastically affect output power. Changes in the dimensions of waveguide devices can severely impact signal frequency range. In precision systems such as electronic packaging and microelectronics, mismatches in the thermal expansion coefficients of components and packaging materials can generate significant mismatch stress, shortening lifespan and causing functional failure. Low-expansion materials, while maintaining high precision, significantly extend material lifespan and have significant application value.

[0003] Currently, commonly used low thermal expansion materials are mainly Fe-Ni Invar alloys. For example, Chinese patent application CN115717213A discloses an ultra-low thermal expansion Invar alloy material and its preparation method. This ultra-low thermal expansion Invar alloy material uses one of Fe-Ni, Fe-Ni-Co, or Fe-Co-Cr Invar alloys as the matrix, and a negative thermal expansion phase as the precipitated phase. By precipitating the negative thermal expansion phase, the Invar alloy matrix is ​​modified, thereby enabling the final alloy material to maintain stable zero thermal expansion performance over a wide temperature range. Invar alloys have characteristics such as low thermal expansion and high plasticity. However, they have low strength, poor mechanical properties, and lack good machinability. Furthermore, the thermal expansion coefficient of Invar alloys is close to zero, making them suitable for applications requiring extremely high dimensional temperature stability. For most low-expansion material applications, only a matching of thermal expansion coefficients is required. Invar alloys offer excess performance in these scenarios, and their cost is not advantageous. Other more advanced low thermal expansion metallic materials often fall into the category of intermetallic compounds. These materials are numerous, but they tend to be brittle and unsuitable for bearing loads.

[0004] As one of the most widely used metallic materials, steel plays a vital role in human civilization and social development. Its mature industrial production methods and excellent mechanical properties make it an irreplaceable material. However, the coefficient of thermal expansion of steel is often greater than 10 ppm / ℃. Reducing this coefficient by about 50% could decrease its thermal expansion by nearly half, offering significant application value. However, steel contains carbon and other elements, making it more difficult to achieve low thermal expansion. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a low thermal expansion coefficient duplex steel material and its preparation method. The duplex steel material is produced by melting commercial finished steel with several negative thermal expansion phase raw materials. The negative thermal expansion phase exhibits "thermal contraction and cold expansion" behavior within a certain temperature range and is referred to as the NTE (Negative Thermal Expansion) phase. The duplex steel material has a low thermal expansion coefficient and good strength, plasticity, and machinability.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a dual-phase steel material with a low coefficient of thermal expansion, wherein the main phase of the dual-phase steel material is steel material and the precipitated phase is an iron-based negative thermal expansion phase.

[0007] Furthermore, the mass fraction of the iron-based negative thermal expansion phase in the dual-phase steel material is no more than 50%.

[0008] Furthermore, the steel material is carbon steel, low alloy steel, or industrial pure iron.

[0009] Furthermore, the iron-based negative thermal expansion phase is: La(Fe 1-x (Co 1-y Si y ) x ) 13 、(Zr x Nb 1-x Fe2, (Hf) x Nb 1-x Fe2, (Hf) x Ta 1-x Fe2, La(Fe) 1-x Si x ) 13 ,La(Fe 1-x Al x ) 13 、(Sc x Ti 1-x Fe2, (Hf) x Ti 1-x Fe2, Fe 40+z+wMn 30-z Ga 30-w , R2Fe 17 or R2Fe 14 B, where R is a rare earth element, 0 <x<1,0<y<1,0<z<30,0<w<30。

[0010] Preferably, the iron-based negative thermal expansion phase is: La(Fe,Co,Si). 13 Zr 0.7 Nb 0.3 Fe2, Hf 0.85 Nb 0.15 Fe2, Hf 0.85 Ta 0.15 Fe2, LaFe 11.5 Si 1.5 LaFe 11.5 Al 1.5 ,Sc 0.55 Ti 0.45 Fe2, Hf 0.6 Ti 0.4 Fe2, Fe 43 Mn 28 Ga 29 , R2Fe 17 or R2Fe 14 B, where R is a rare earth element.

[0011] Furthermore, the coefficient of thermal expansion of the duplex steel material is <6ppm / ℃ within a temperature range of -50℃ to 50℃.

[0012] This invention also discloses a method for preparing the low thermal expansion coefficient duplex steel material, wherein the preparation method is as follows:

[0013] S1. Using steel materials and the alloying elements required for the iron-based negative thermal expansion phase as raw materials, heat the raw materials until they melt to obtain a uniform melt.

[0014] S2. The molten liquid is poured into a mold and then electromagnetically stirred and solidified to obtain a steel sample;

[0015] S3. Anneal the obtained steel sample under an inert gas protective atmosphere;

[0016] S4. The annealed steel sample is aged under an inert gas protective atmosphere to obtain the low thermal expansion coefficient duplex steel material.

[0017] Furthermore, in step S1, the raw material is heated to melt to obtain a molten liquid, and the molten liquid is stirred thoroughly until it is homogeneous using induced electromagnetic force;

[0018] In step S2, the electromagnetic stirring method during solidification is axial rotation stirring, and the electromagnetic stirring current is 80-120A.

[0019] Furthermore, in step S3, the annealing temperature adopts a stepped design. The first annealing is carried out at the NTE phase equilibrium temperature. After the NTE phase is formed and stabilized, the second annealing is carried out at the steel phase equilibrium temperature.

[0020] The first annealing time is 24-120 hours; the second annealing time is within 12 hours.

[0021] Furthermore, after the first annealing, the steel sample undergoes a first hot rolling treatment followed by a second annealing. After the second annealing treatment, the steel sample undergoes a second hot rolling treatment followed by aging treatment. The temperature of the first and second hot rolling treatments is 600-1000℃, the total reduction should be 50%-70%, and the number of rolling passes is 3-5.

[0022] Furthermore, the aging treatment temperature is 400-600℃, and the treatment time is 6-24h.

[0023] Furthermore, steps S1-S4 are carried out under an inert gas protective atmosphere, with the vacuum applied and the absolute pressure not exceeding 2 × 10⁻⁶. -3 After Pa, inert gas is introduced at a pressure of 2 × 10⁻⁶. 4 Pa~4×10 4 Pa.

[0024] The beneficial effects of this invention are:

[0025] (1) The dual-phase steel material described in this invention is smelted from commercial finished steel and several negative thermal expansion phase raw materials. The brittle NTE phase is uniformly precipitated in the main phase of steel, which retains the strength, plasticity and machinability of the steel material itself. At the same time, within a specific temperature range, the positive thermal expansion of the main phase of steel is partially offset by the negative thermal expansion of the NTE precipitated phase, thus exhibiting a lower coefficient of thermal expansion overall. Its expansion when the temperature rises is only about half that of the steel material itself.

[0026] (2) The dual-phase steel material described in this invention is composed of a steel main phase and a negative thermal expansion precipitate phase. Due to the thermodynamic properties of the negative thermal expansion phase, the negative thermal expansion phase can precipitate in the steel main phase in different forms such as eutectic, peritectic, eutectoid and peritectic by the preparation method described in this invention. The two phases diffuse a small amount of interfacial elements without affecting their own properties, thereby producing a combination of low thermal expansion coefficient and excellent mechanical properties.

[0027] (3) The dual-phase steel material and its preparation method described in this invention, due to the in-situ precipitation of the negative thermal expansion phase in the matrix, the phase interface may have coherent, semi-coherent or other forms. Such interfaces have more stable performance in cold and hot cycles and external force loading. After subsequent heat treatment and rolling, casting defects are further eliminated, greatly reducing the factors of crack generation and propagation, and increasing the guarantee for the mechanical properties of steel.

[0028] (3) The iron-based negative thermal expansion phase is used as raw material in the dual-phase steel material of the present invention. The negative thermal expansion of the iron-based negative thermal expansion phase intermetallic compound comes from the magnetic volume effect that accompanies the transformation of its magnetic structure. It has a negative volume thermal expansion coefficient within a certain temperature range including room temperature. There are no other intermediate phases between it and Fe, and it usually has a negative formation free energy. Therefore, it can be precipitated in situ in the main phase of steel. By using the preparation method of the present invention, the effect of reducing the thermal expansion coefficient of the main phase of steel can be maximized, while retaining the excellent mechanical properties and processing properties of the main phase of steel.

[0029] (4) In the preparation method described in this invention, electromagnetic stirring is added during the solidification process, which helps to make the two phases of the obtained steel sample uniformly distributed and can effectively control the mass transfer process. It has an inhibitory effect on element segregation during the solidification process, because carbon and other alloying elements in steel materials can easily enter the negative thermal expansion phase, thereby affecting the negative thermal expansion performance. However, the preparation method described in this invention adds electromagnetic stirring during the solidification process, which can inhibit segregation and thus make the negative thermal expansion phase maintain good negative thermal expansion performance.

[0030] Furthermore, the two-phase microstructure of the electromagnetically stirred solidified steel sample differs significantly from that of the as-cast steel sample. First, the electromagnetically stirred solidified steel sample has smaller grains; second, the electromagnetic stirring process breaks down the columnar and dendritic crystals of the as-cast microstructure, forming uniform equiaxed crystals. This is beneficial for reducing subsequent annealing time, improving the mechanical properties of the steel sample, and, more importantly, significantly reducing the anisotropy of the thermal expansion coefficient of the steel sample.

[0031] (5) In the preparation method described in this invention, the annealing temperature is designed in stages. First, annealing is performed at a higher NTE phase equilibrium temperature to ensure the formation and stability of the NTE phase. Quenching and cooling maintain the high-temperature phase composition of the alloy. At this time, the steel phase forms coarse grains at a higher temperature, and alloying elements tend to agglomerate at the interface between the two phases. Therefore, a second annealing is performed at a lower steel phase equilibrium temperature. The annealing time is short, ensuring that the recrystallization of the steel phase and the uniform diffusion of elements are achieved, thus minimizing the impact of the second annealing on the NTE phase. After the first annealing is completed, i.e., after the annealing of the NTE phase is completed, the first rolling is performed. This is beneficial for refining the coarse steel phase grains that have grown during the NTE annealing stage, providing dynamic recrystallization, and also providing nucleation sites for the second stage of annealing at the steel phase equilibrium temperature.

[0032] (6) The dual-phase steel material described in this invention uses steel material as the main phase. Compared with Invar alloy material, steel material has better mechanical properties. Invar alloy material is very soft and has poor mechanical properties. Moreover, Invar alloy itself has low thermal expansion properties, so there is no problem in solving the problem of positive thermal expansion properties. In addition, steel material is more economical than Invar alloy material.

[0033] The dual-phase steel material described in this invention uses steel as the main phase. Compared with conventionally used pure iron, the final material exhibits significant differences. Pure iron has a ferrite microstructure and poor strength, while steel can form different microstructures such as pearlite, martensite, and austenite depending on the carbon and alloying element content. Each microstructure has its own advantages, and overall, steel has superior strength. The preparation method described in this invention effectively addresses the influence of carbon or alloying elements on the negative thermal expansion phase while maintaining the high mechanical properties of steel, thus obtaining a dual-phase steel material with strong mechanical properties and excellent negative thermal expansion performance.

[0034] (7) The preparation method of the present invention is simple and easy to implement, and the whole process is highly controllable, thus improving the problem of excessively high thermal expansion coefficient of existing steel materials. Attached Figure Description

[0035] Figure 1 This is a comparison chart of the thermal expansion curves of the low thermal expansion coefficient duplex steel material described in Example 1 and commercial finished steel wire.

[0036] Figure 2 The stress-strain curve of the low thermal expansion coefficient duplex steel material in Example 1 is shown in the room temperature uniaxial compression test diagram.

[0037] Figure 3 This is a scanning electron microscope image of the low thermal expansion coefficient dual-phase steel material described in Example 1;

[0038] Figure 4 The linear expansion curve of the low thermal expansion coefficient dual-phase steel material described in Example 2 is shown.

[0039] Figure 5 This is a comparison chart of the linear expansion curves of the low thermal expansion coefficient duplex steel material described in Example 3 and industrial pure iron.

[0040] Figure 6 This is a scanning electron microscope image of the low thermal expansion coefficient dual-phase steel material described in Example 3;

[0041] Figure 7 This is a scanning electron microscope image of the low thermal expansion coefficient dual-phase steel material described in Example 4;

[0042] Figure 8This is a scanning electron microscope image of the low thermal expansion coefficient dual-phase steel material described in Example 5;

[0043] Figure 9 This is a scanning electron microscope image of the low thermal expansion coefficient dual-phase steel material described in Example 6;

[0044] Figure 10 This is a scanning electron microscope image of the low thermal expansion coefficient dual-phase steel material described in Example 7;

[0045] Figure 11 This is a scanning electron microscope image of the low thermal expansion coefficient dual-phase steel material described in Example 8;

[0046] Figure 12 This is a scanning electron microscope image of the low thermal expansion coefficient dual-phase steel material described in Example 9;

[0047] Figure 13 This is a scanning electron microscope image of the low thermal expansion coefficient dual-phase steel material described in Example 10. Detailed Implementation

[0048] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0050] A dual-phase steel material with a low coefficient of thermal expansion, wherein the main phase of the dual-phase steel material is steel material and the precipitated phase is an iron-based negative thermal expansion phase.

[0051] Specifically, the mass fraction of the iron-based negative thermal expansion phase in the dual-phase steel material is no more than 50%.

[0052] Specifically, the steel material is carbon steel, low alloy steel, or industrial pure iron, such as 45# steel, Q235 steel, DP980 steel, 300M steel, C200 steel, etc.; among which, industrial pure iron is pure iron with a total impurity content of <0.2% and a carbon content of 0.02% to 0.04%.

[0053] Specifically, the iron-based negative thermal expansion phase is: La(Fe 1-x (Co 1-y Si y ) x ) 13 、(Zr x Nb 1-x Fe2, (Hf)x Nb 1-x Fe2, (Hf) x Ta 1-x Fe2, La(Fe) 1-x Si x ) 13 ,La(Fe 1-x Al x ) 13 、(Sc x Ti 1-x Fe2, (Hf) x Ti 1-x Fe2, Fe 40+z+w Mn 30- z Ga 30-w , R2Fe 17 or R2Fe 14 B, where R is a rare earth element, 0 <x<1,0<y<1,0<z<30,0<w<30。

[0054] More specifically, the iron-based negative thermal expansion phase is: La(Fe,Co,Si). 13 Zr 0.7 Nb 0.3 Fe2, Hf 0.85 Nb 0.15 Fe2, Hf 0.85 Ta 0.15 Fe2, LaFe 11.5 Si 1.5 LaFe 11.5 Al 1.5 ,Sc 0.55 Ti 0.45 Fe2, Hf 0.6 Ti 0.4 Fe2, Fe 43 Mn 28 Ga 29 , R2Fe 17 or R2Fe 14 B, where R is a rare earth element.

[0055] Specifically, the duplex steel material has a coefficient of thermal expansion of <6ppm / ℃ within a temperature range of -50℃ to 50℃, exhibiting good strength and plasticity.

[0056] A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, wherein the preparation method is as follows:

[0057] S1. Using steel materials and the alloying elements required for the iron-based negative thermal expansion phase as raw materials, the raw materials are heated to melt to obtain a uniform melt; wherein the purity of the raw materials of the alloying elements for the iron-based negative thermal expansion phase is not less than 99%;

[0058] S2. The molten liquid is poured into a mold and then electromagnetically stirred and solidified to obtain a steel sample;

[0059] S3. Anneal the obtained steel sample under an inert gas protective atmosphere;

[0060] S4. The annealed steel sample is aged under an inert gas protective atmosphere to obtain the low thermal expansion coefficient duplex steel material.

[0061] Specifically, in step S1, the raw material is heated to melt to obtain a molten liquid, and the molten liquid is stirred thoroughly until it is homogeneous using induced electromagnetic force;

[0062] In step S2, the electromagnetic stirring method during solidification is axial rotation stirring, and the electromagnetic stirring current is 80-120A. The specific operation is as follows: the molten steel is first poured into a water-cooled mold with heating function, the electromagnetic stirring method is axial rotation stirring, the stirring current is set to 80-120A, and the mold is cooled at the same time to solidify the molten steel.

[0063] Specifically, in step S3, the annealing temperature adopts a stepped design. The first annealing is carried out at the NTE phase equilibrium temperature. After the NTE phase is formed and stabilized, the second annealing is carried out at the steel phase equilibrium temperature. The first annealing time is 24-120 hours. The second annealing time is within 12 hours.

[0064] The equilibrium temperature of the NTE phase is usually much higher than that of the ferrous phase, typically ranging from 1000 to 1100°C, depending on the specific NTE phase. The equilibrium temperature of the ferrous phase varies depending on the carbon content and alloying element content, and is usually at or below 800°C.

[0065] Specifically, after the first annealing, the steel sample undergoes a first hot rolling treatment followed by a second annealing. After the second annealing treatment, the steel sample undergoes a second hot rolling treatment followed by aging treatment. The temperature of the first and second hot rolling treatments is 600-1000℃, the total reduction should be 50%-70%, and the number of rolling passes is 3-5. Rolling can be carried out in an air atmosphere.

[0066] Specifically, the aging treatment temperature is 400-600℃, and the treatment time is 6-24h.

[0067] Specifically, steps S1-S4 are carried out under an inert gas protective atmosphere, with the vacuum drawn and the absolute pressure not exceeding 2 × 10⁻⁶. -3 After Pa, inert gas is introduced at a pressure of 2 × 10⁻⁶. 4 Pa~4×10 4 Pa. The inert gas used in this embodiment of the invention is argon.

[0068] Example 1

[0069] A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, wherein the preparation method comprises:

[0070] S1. Weigh out 45# steel, elemental lanthanum, cobalt, and silicon (purity ≥ 99.9%) according to their mass fractions of 90.2%, 5.6%, 2.4%, and 1.8%, respectively.

[0071] S2, under a vacuum degree of 2×10 -3 High-purity argon gas is introduced into the induction furnace of Pa to heat the raw material to melt, and the molten steel is stirred thoroughly with induction electromagnetic force until it is homogeneous.

[0072] S3. Pour the molten liquid into a φ20mm copper mold and let it cool and solidify. During the solidification process, add electromagnetic stirring. The electromagnetic stirring method is axial rotation stirring with a stirring current of 100A. At the same time, the mold is cooled to solidify the molten steel.

[0073] S4. The obtained steel sample is annealed under an argon protective atmosphere. First, the first annealing is carried out at the NTE phase equilibrium temperature, that is, the first annealing temperature is 1050℃ and the first annealing time is 72h. Then, the first hot rolling treatment is carried out (hot rolling temperature is 800℃, in 3 passes, with a total reduction of 70%). Then, the second annealing is carried out at the steel phase equilibrium temperature, that is, the second annealing temperature is 800℃ and the second annealing time is 6h.

[0074] S5. The obtained steel sample is subjected to a second hot rolling treatment at 800℃, in 3 passes, with a total reduction of 70%.

[0075] S6. The obtained steel sample is aged at 400℃ for 6 hours under an argon protective atmosphere to obtain the low thermal expansion coefficient duplex steel material, whose main phase is 45# steel and the precipitated phase is La(Fe,Co,Si). 13 Negative thermal expansion phase.

[0076] Figure 1 The thermal expansion curves of the low thermal expansion coefficient duplex steel material obtained by the preparation method described in Example 1 are compared with those of 45# steel. It can be seen that the thermal expansion coefficient of the low thermal expansion coefficient duplex steel material is significantly lower than that of its main phase, 45# steel, with coefficients of thermal expansion of 5.76 ppm / ℃ and 11.27 ppm / ℃ at -150℃ to 50℃, respectively. Furthermore, its precipitated phase is NaZn. 13 La(Fe,Co,Si) with a cubic structure 13 Therefore, the coefficient of thermal expansion of steel is isotropic.

[0077] Figure 2The low thermal expansion coefficient duplex steel material obtained by the method described in Example 1 is shown in the engineering stress-strain curve obtained in a uniaxial compression test. Based on the experimental results, the compressive yield strength (σ) of the low thermal expansion coefficient duplex steel material is... S The compressive strength is 510 MPa, and the compressive strength (σ) is 510 MPa. US The pressure is 1120 MPa, and the deformation (strain) max The load factor is 28%, indicating that it has basic load-bearing capacity.

[0078] Figure 3 The scanning electron microscope image shows a low thermal expansion coefficient dual-phase steel material obtained by the method described in Example 1, in which the two phases are clearly distinct, with the negative thermal expansion phase being La(Fe,Co,Si). 13 It is continuously distributed in the main phase of 45# steel, with uniform distribution and tight bonding.

[0079] Example 2

[0080] A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, wherein the preparation method comprises:

[0081] S1. Weigh out Q235 steel, erbium, and boron (purity ≥ 99.9%) according to their mass fractions of 72.25%, 26.87%, and 0.88%, respectively.

[0082] S2, under a vacuum degree of 2×10 -3 High-purity argon gas is introduced into the induction furnace of Pa to heat the raw material to melt, and the molten steel is stirred thoroughly with induction electromagnetic force until it is homogeneous.

[0083] S3. Pour the molten liquid into a φ20mm copper mold and let it cool and solidify. During the solidification process, add electromagnetic stirring. The electromagnetic stirring method is axial rotation stirring with a stirring current of 120A. At the same time, the mold is cooled to solidify the molten steel.

[0084] S4. The obtained steel sample is annealed under an argon protective atmosphere. First, the first annealing is carried out at the NTE phase equilibrium temperature, that is, the first annealing temperature is 1100℃ and the first annealing time is 24h. Then, the first hot rolling treatment is carried out (hot rolling temperature is 900℃, in 3 passes, with a total reduction of 50%). Then, the second annealing is carried out at the steel phase equilibrium temperature, that is, the second annealing temperature is 800℃ and the second annealing time is 11h.

[0085] S5. The obtained steel sample is subjected to a second hot rolling treatment at 900℃, in 3 passes, with a total reduction of 50%.

[0086] S6. The obtained steel sample is aged at 400℃ for 6 hours under an argon protective atmosphere to obtain the low thermal expansion coefficient duplex steel material, whose main phase is Q235 steel and the precipitated phase is Er2Fe. 14 B is the negative thermal expansion phase.

[0087] The obtained materials were sampled and tested, and the following results were obtained:

[0088] Figure 4 The low thermal expansion coefficient duplex steel material obtained by the method described in Example 2 has a thermal expansion curve. The low thermal expansion coefficient duplex steel material has zero thermal expansion performance of 0.49ppm / ℃ in the range of -150℃ to 50℃, which means that the thermal expansion coefficient of the steel material is reduced by nearly two orders of magnitude and includes the room temperature range.

[0089] Example 3

[0090] A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, wherein the preparation method comprises:

[0091] S1. Weigh out industrial pure iron, zirconium, and niobium (purity ≥ 99.9%) according to their mass fractions of 84.55%, 9.89%, and 5.47%, respectively.

[0092] S2, under a vacuum degree of 2×10 -3 High-purity argon gas is introduced into the induction furnace of Pa to heat the raw material to melt, and the molten steel is stirred thoroughly with induction electromagnetic force until it is homogeneous.

[0093] S3. Pour the molten liquid into a φ20mm copper mold and let it cool and solidify. During the solidification process, add electromagnetic stirring. The electromagnetic stirring method is axial rotation stirring with a stirring current of 100A. At the same time, the mold is cooled to solidify the molten steel.

[0094] S4. The obtained steel sample is annealed under an argon protective atmosphere. First, the first annealing is carried out at the NTE phase equilibrium temperature, that is, the first annealing temperature is 1000℃ and the first annealing time is 120h. Then, the first hot rolling treatment is carried out (hot rolling temperature is 1000℃, in 3 passes, with a total reduction of 50%). Then, the second annealing is carried out at the steel phase equilibrium temperature, that is, the second annealing temperature is 800℃ and the second annealing time is 8h.

[0095] S5. The obtained steel sample is subjected to a second hot rolling treatment at 1000℃, in 3 passes, with a total reduction of 50%.

[0096] S6. The obtained steel sample is aged at 400℃ for 2 hours under an argon protective atmosphere to obtain the low thermal expansion coefficient duplex steel material, whose main phase is industrial pure iron and the precipitated phase is Zr. 0.7 Nb0.3 Fe2 is a negative thermal expansion phase.

[0097] The obtained materials were sampled and tested, and the following results were obtained:

[0098] Figure 5 The thermal expansion curves of the low thermal expansion coefficient duplex steel material obtained by the method described in Example 3 are compared with those of industrial pure iron. It can be seen that the thermal expansion coefficient of the low thermal expansion coefficient duplex steel material is significantly lower than that of its main phase, industrial pure iron. Its thermal expansion coefficients at -150℃ to 50℃ are 6.12 ppm / ℃ and 12.10 ppm / ℃, respectively. Furthermore, because its precipitated phase is a C15-type cubic (Zr,Nb)Fe2, the thermal expansion coefficient of the steel is isotropic, as shown in the scanning electron microscope image. Figure 6 As shown.

[0099] Example 4

[0100] A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, wherein the preparation method comprises:

[0101] S1. Weigh out industrial pure iron, hafnium, and niobium (purity ≥ 99.9%) according to their mass fractions of 79.12%, 19.74%, and 1.14%, respectively.

[0102] S2, under a vacuum degree of 2×10 -3 High-purity argon gas is introduced into the induction furnace of Pa to heat the raw material to melt, and the molten steel is stirred thoroughly with induction electromagnetic force until it is homogeneous.

[0103] S3. Pour the molten liquid into a φ20mm copper mold and let it cool and solidify. During the solidification process, add electromagnetic stirring. The electromagnetic stirring method is axial rotation stirring with a stirring current of 100A. At the same time, the mold is cooled to solidify the molten steel.

[0104] S4. The obtained steel sample is annealed under an argon protective atmosphere. First, the first annealing is carried out at the NTE phase equilibrium temperature, that is, the first annealing temperature is 1000℃ and the first annealing time is 90h. Then, the first hot rolling treatment is carried out (hot rolling temperature is 1000℃, in 3 passes, with a total reduction of 50%). Then, the second annealing is carried out at the steel phase equilibrium temperature, that is, the second annealing temperature is 800℃ and the second annealing time is 8h.

[0105] S5. The obtained steel sample is subjected to a second hot rolling treatment at 1000℃, in 3 passes, with a total reduction of 50%.

[0106] S6. The obtained steel sample is aged at 400℃ for 2 hours under an argon protective atmosphere to obtain the low thermal expansion coefficient duplex steel material, whose main phase is industrial pure iron and the precipitated phase is Hf.0.85 Nb 0.15 Fe2+ ​​is a negatively expanding phase. Its scanning electron microscope image is shown below. Figure 7 As shown, the two phases are distinct, evenly distributed, and tightly bonded.

[0107] Example 5

[0108] A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, wherein the preparation method comprises:

[0109] S1. Weigh out a certain amount of industrial pure iron, hafnium, and tantalum (purity ≥ 99.9%) according to their mass fractions of 78.25%, 18.22%, and 3.53%, respectively.

[0110] S2, under a vacuum degree of 2×10 -3 High-purity argon gas is introduced into the induction furnace of Pa to heat the raw material to melt, and the molten steel is stirred thoroughly with induction electromagnetic force until it is homogeneous.

[0111] S3. Pour the molten liquid into a φ20mm copper mold and let it cool and solidify. During the solidification process, add electromagnetic stirring. The electromagnetic stirring method is axial rotation stirring with a stirring current of 100A. At the same time, the mold is cooled to solidify the molten steel.

[0112] S4. The obtained steel sample is annealed under an argon protective atmosphere. First, the first annealing is carried out at the NTE phase equilibrium temperature, that is, the first annealing temperature is 1000℃ and the first annealing time is 110h. Then, the first hot rolling treatment is carried out (hot rolling temperature is 1000℃, in 3 passes, with a total reduction of 50%). Then, the second annealing is carried out at the steel phase equilibrium temperature, that is, the second annealing temperature is 800℃ and the second annealing time is 8h.

[0113] S5. The obtained steel sample is subjected to a second hot rolling treatment at 1000℃, in 3 passes, with a total reduction of 50%.

[0114] S6. The obtained steel sample is aged at 400℃ for 2 hours under an argon protective atmosphere to obtain the low thermal expansion coefficient duplex steel material, whose main phase is industrial pure iron and the precipitated phase is Hf. 0.85 Ta 0.15 Fe2+ ​​is a negatively expanding phase. Its scanning electron microscope image is shown below. Figure 8 As shown, the two phases are distinct, evenly distributed, and tightly bonded.

[0115] Example 6

[0116] A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, wherein the preparation method comprises:

[0117] S1. Weigh out a certain amount of industrial pure iron, hafnium, and titanium (purity ≥ 99.9%) according to a mass fraction of 80.86%, 17.93%, and 1.21%, respectively.

[0118] S2, under a vacuum degree of 2×10 -3 High-purity argon gas is introduced into the induction furnace of Pa to heat the raw material to melt, and the molten steel is stirred thoroughly with induction electromagnetic force until it is homogeneous.

[0119] S3. Pour the molten liquid into a φ20mm copper mold and let it cool and solidify. During the solidification process, add electromagnetic stirring. The electromagnetic stirring method is axial rotation stirring with a stirring current of 100A. At the same time, the mold is cooled to solidify the molten steel.

[0120] S4. The obtained steel sample is annealed under an argon protective atmosphere. First, the first annealing is carried out at the NTE phase equilibrium temperature, that is, the first annealing temperature is 1000℃ and the first annealing time is 100h. Then, the first hot rolling treatment is carried out (hot rolling temperature is 1000℃, in 3 passes, with a total reduction of 50%). Then, the second annealing is carried out at the steel phase equilibrium temperature, that is, the second annealing temperature is 800℃ and the second annealing time is 8h.

[0121] S5. The obtained steel sample is subjected to a second hot rolling treatment at 1000℃, in 3 passes, with a total reduction of 50%.

[0122] S6. The obtained steel sample is aged at 400℃ for 2 hours under an argon protective atmosphere to obtain the low thermal expansion coefficient duplex steel material, whose main phase is industrial pure iron and the precipitated phase is Hf. 0.6 Ti 0.4 Fe2+ ​​is a negatively expanding phase. Its scanning electron microscope image is shown below. Figure 9 As shown, the two phases are distinct, evenly distributed, and tightly bonded.

[0123] Example 7

[0124] A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, wherein the preparation method comprises:

[0125] S1. Weigh out a certain amount of industrial pure iron, scandium, and titanium (purity ≥ 99.9%) according to their mass fractions of 86.27%, 5.28%, and 8.45%, respectively.

[0126] S2, under a vacuum degree of 2×10 -3 High-purity argon gas is introduced into the induction furnace of Pa to heat the raw material to melt, and the molten steel is stirred thoroughly with induction electromagnetic force until it is homogeneous.

[0127] S3. Pour the molten liquid into a φ20mm copper mold and let it cool and solidify. During the solidification process, add electromagnetic stirring. The electromagnetic stirring method is axial rotation stirring with a stirring current of 100A. At the same time, the mold is cooled to solidify the molten steel.

[0128] S4. The obtained steel sample is annealed under an argon protective atmosphere. First, the first annealing is carried out at the NTE phase equilibrium temperature, that is, the first annealing temperature is 1000℃ and the first annealing time is 98h. Then, the first hot rolling treatment is carried out (hot rolling temperature is 1000℃, in 3 passes, with a total reduction of 50%). Then, the second annealing is carried out at the steel phase equilibrium temperature, that is, the second annealing temperature is 800℃ and the second annealing time is 8h.

[0129] S5. The obtained steel sample is subjected to a second hot rolling treatment at 1000℃, in 3 passes, with a total reduction of 50%.

[0130] S6. The obtained steel sample is aged at 400℃ for 2 hours under an argon protective atmosphere to obtain the low thermal expansion coefficient duplex steel material, whose main phase is industrial pure iron and the precipitated phase is Sc. 0.55 Ti 0.45 Fe2+ ​​is a negatively expanding phase. Its scanning electron microscope image is shown below. Figure 10 As shown, the two phases are distinct, evenly distributed, and tightly bonded.

[0131] Example 8

[0132] A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, wherein the preparation method comprises:

[0133] S1. Weigh out DP980 steel, elemental lanthanum, cobalt, and silicon (purity ≥ 99.9%) according to their mass fractions of 90.2%, 5.6%, 2.4%, and 1.8%, respectively.

[0134] S2, under a vacuum degree of 2×10 -3 High-purity argon gas is introduced into the induction furnace of Pa to heat the raw material to melt, and the molten steel is stirred thoroughly with induction electromagnetic force until it is homogeneous.

[0135] S3. Pour the molten liquid into a φ20mm copper mold and let it cool and solidify. During the solidification process, add electromagnetic stirring. The electromagnetic stirring method is axial rotation stirring with a stirring current of 100A. At the same time, the mold is cooled to solidify the molten steel.

[0136] S4. The obtained steel sample is annealed under an argon protective atmosphere. First, the first annealing is carried out at the NTE phase equilibrium temperature, that is, the first annealing temperature is 1100℃ and the first annealing time is 58h. Then, the first hot rolling treatment is carried out (hot rolling temperature is 600℃, in 3 passes, with a total reduction of 70%). Then, the second annealing is carried out at the steel phase equilibrium temperature, that is, the second annealing temperature is 600℃ and the second annealing time is 6h.

[0137] S5. The obtained steel sample is subjected to a second hot rolling treatment at 600℃, in 3 passes, with a total reduction of 70%.

[0138] S6. The obtained steel sample is aged at 600℃ under an argon protective atmosphere for 6 hours to obtain the low thermal expansion coefficient duplex steel material, whose main phase is DP980 steel and the precipitated phase is La(Fe,Co,Si). 13 Negative thermal expansion phase. Its scanning electron microscope image is as follows: Figure 11 As shown, the two phases are distinct, evenly distributed, and tightly bonded.

[0139] Example 9

[0140] A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, wherein the preparation method comprises:

[0141] S1. Weigh out 300M steel, elemental lanthanum, cobalt, and silicon (purity ≥ 99.9%) according to their mass fractions of 90.2%, 5.6%, 2.4%, and 1.8%, respectively.

[0142] S2, under a vacuum degree of 2×10 -3 High-purity argon gas is introduced into the induction furnace of Pa to heat the raw material to melt, and the molten steel is stirred thoroughly with induction electromagnetic force until it is homogeneous.

[0143] S3. Pour the molten liquid into a φ20mm copper mold and let it cool and solidify. During the solidification process, add electromagnetic stirring. The electromagnetic stirring method is axial rotation stirring with a stirring current of 100A. At the same time, the mold is cooled to solidify the molten steel.

[0144] S4. The obtained steel sample is annealed under an argon protective atmosphere. First, the first annealing is carried out at the NTE phase equilibrium temperature, that is, the first annealing temperature is 1100℃ and the first annealing time is 60h. Then, the first hot rolling treatment is carried out (hot rolling temperature is 900℃, in 3 passes, with a total reduction of 50%). Then, the second annealing is carried out at the steel phase equilibrium temperature, that is, the second annealing temperature is 800℃ and the second annealing time is 3h.

[0145] S5. The obtained steel sample is subjected to a second hot rolling treatment at 900℃, in 3 passes, with a total reduction of 50%.

[0146] S6. The obtained steel sample is aged at 600℃ under an argon protective atmosphere for 6 hours to obtain the low thermal expansion coefficient duplex steel material, whose main phase is 300M steel and the precipitated phase is La(Fe,Co,Si). 13 Negative thermal expansion phase. Its scanning electron microscope image is as follows: Figure 12 As shown, the two phases are distinct, evenly distributed, and tightly bonded.

[0147] Example 10

[0148] A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, wherein the preparation method comprises:

[0149] S1. Weigh out C200 steel, elemental lanthanum, cobalt, and silicon (purity ≥ 99.9%) according to their mass fractions of 90.2%, 5.6%, 2.4%, and 1.8%, respectively.

[0150] S2, under a vacuum degree of 2×10 -3 High-purity argon gas is introduced into the induction furnace of Pa to heat the raw material to melt, and the molten steel is stirred thoroughly with induction electromagnetic force until it is homogeneous.

[0151] S3. Pour the molten liquid into a φ20mm copper mold and let it cool and solidify. During the solidification process, add electromagnetic stirring. The electromagnetic stirring method is axial rotation stirring with a stirring current of 100A. At the same time, the mold is cooled to solidify the molten steel.

[0152] S4. The obtained steel sample is annealed under an argon protective atmosphere. First, the first annealing is carried out at the NTE phase equilibrium temperature, that is, the first annealing temperature is 1100℃ and the first annealing time is 100h. Then, the first hot rolling treatment is carried out (hot rolling temperature is 900℃, in 3 passes, with a total reduction of 50%). Then, the second annealing is carried out at the steel phase equilibrium temperature, that is, the second annealing temperature is 800℃ and the second annealing time is 3h.

[0153] S5. The obtained steel sample is subjected to a second hot rolling treatment at 800℃, in 3 passes, with a total reduction of 50%.

[0154] S6. The obtained steel sample is aged at 600℃ under an argon protective atmosphere for 6 hours to obtain the low thermal expansion coefficient duplex steel material, whose main phase is C200 steel and the precipitated phase is La(Fe,Co,Si). 13 Negative thermal expansion phase. Its scanning electron microscope image is as follows: Figure 13 As shown, the two phases are distinct, evenly distributed, and tightly bonded.

[0155] Comparative Example 1

[0156] Low thermal expansion coefficient duplex steel material was prepared using the same method as in Example 1, except that electromagnetic stirring was not used during the solidification process in step S3.

[0157] Comparative Example 2

[0158] The low thermal expansion coefficient duplex steel material was prepared using the same method as in Example 1, except that the stirring current was 60A during the solidification process in step S3 (the stirring current is lower than the range defined in this invention).

[0159] Comparative Example 3

[0160] The low thermal expansion coefficient duplex steel material was prepared using the same method as in Example 1. The difference was that the annealing temperature in step S4 was not designed in a stepped manner. The specific annealing conditions were: after annealing at 1000°C for 78 hours, the material was then subjected to hot rolling in step S5.

[0161] Comparative Example 4

[0162] The same method as in Example 1 was used to prepare a dual-phase steel material with a low coefficient of thermal expansion. The difference was that the first hot rolling treatment was not performed in step S4, and the second annealing treatment was performed directly after the first annealing.

[0163] The thermal expansion coefficients and related mechanical properties of the low thermal expansion coefficient duplex steel materials prepared in Examples 1-10 and Comparative Examples 1-4 at -50℃ to 50℃ are shown in Table 1 below.

[0164] Table 1. Performance data of low thermal expansion coefficient duplex steel materials in Examples 1-10 and Comparative Examples 1-4

[0165]

[0166]

[0167] A comparison of the experimental data from Example 1 and Comparative Example 1 shows that if electromagnetic stirring is not added during solidification, the negative thermal expansion properties and mechanical properties of the final dual-phase steel material will decrease. This is because electromagnetic stirring solidification helps to achieve a uniform two-phase distribution in the resulting steel sample, effectively controls the mass transfer process, and inhibits element segregation during solidification. The two-phase distribution structure of the electromagnetically stirred solidified steel sample is significantly different from that of the as-cast steel sample. First, the electromagnetically stirred solidified steel sample has smaller grains; second, the electromagnetic stirring process breaks down the columnar and dendritic crystals of the as-cast structure, forming uniform equiaxed crystals. This is beneficial for reducing subsequent annealing time, improving the mechanical properties of the steel sample, and, more importantly, significantly reducing the anisotropy of the thermal expansion coefficient of the steel sample.

[0168] A comparison of the experimental data from Example 1 and Comparative Example 2 shows that if the electromagnetic stirring current during solidification is reduced, the negative thermal expansion properties and mechanical properties of the duplex steel material will also decrease. In addition, it was found in actual experiments that if the electromagnetic stirring current is too large, it will cause splashing, resulting in compositional deviation, and the energy consumption will be high. Therefore, the electromagnetic stirring current specified in this invention is more conducive to obtaining high-quality duplex steel materials.

[0169] A comparison of the experimental data from Example 1 and Comparative Example 3 shows that using the stepped annealing temperature specified in this invention is more conducive to obtaining duplex steel materials with good negative thermal expansion properties and excellent mechanical properties. This is because during stepped annealing, annealing is first performed at a higher NTE phase equilibrium temperature to ensure the formation and stability of the NTE phase. Quenching and cooling maintain the high-temperature phase composition of the alloy. At this time, the steel phase forms coarse grains at a higher temperature, and alloying elements tend to agglomerate at the two-phase interface. A second annealing is then performed at a lower steel phase equilibrium temperature with a shorter annealing time, ensuring recrystallization of the steel phase and uniform element diffusion, thus minimizing the impact of the second annealing on the NTE phase.

[0170] A comparison of the experimental data from Example 1 and Comparative Example 4 shows that if a first hot rolling process is performed during stepped annealing, it is more conducive to obtaining duplex steel materials with good negative thermal expansion properties and excellent mechanical properties. This is because a hot rolling process after the NTE phase annealing (first annealing) helps to refine the coarse-grained steel phase grains that grew during the NTE annealing stage, providing dynamic recrystallization. It also provides nucleation sites for the second stage annealing at the steel phase equilibrium temperature, thus making it more conducive to obtaining duplex steel materials with good negative thermal expansion properties and excellent mechanical properties.

[0171] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0172] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for preparing a dual-phase steel material with a low coefficient of thermal expansion, characterized in that, The preparation method is as follows: S1. Using steel materials and alloying elements required for iron-based negative thermal expansion phases as raw materials, heat the raw materials until they melt to obtain a uniform melt. S2. The molten liquid is poured into a mold and then electromagnetically stirred and solidified to obtain a steel sample; S3. Anneal the obtained steel sample under an inert gas protective atmosphere; S4. The annealed steel sample is aged under an inert gas protective atmosphere to obtain the low thermal expansion coefficient duplex steel material. The steel material is carbon steel, low alloy steel, or industrial pure iron, and the iron-based negative thermal expansion phase is La(Fe). 1-x (Co 1-y Si y ) x ) 13 、(Zr x Nb 1-x Fe2, (Hf) x Nb 1-x Fe2, (Hf) x Ta 1-x Fe2, La(Fe) 1-x Si x ) 13 ,La(Fe 1-x Al x ) 13 、(Sc x Ti 1-x Fe2, (Hf) x Ti 1-x Fe2, Fe 40+z+w Mn 30-z Ga 30-w , R2Fe 17 or R2Fe 14 B, where R is a rare earth element, 0 <x<1,0<y<1,0<z<30,0<w<30; In step S1, the raw material is heated to melt to obtain a molten liquid, and the molten liquid is stirred thoroughly until it is homogeneous using induced electromagnetic force; In step S2, the electromagnetic stirring method during solidification is axial rotation stirring, and the electromagnetic stirring current is 80-120A. In step S3, the annealing temperature adopts a stepped design. The first annealing is carried out at the NTE phase equilibrium temperature. After the NTE phase is formed and stabilized, the second annealing is carried out at the steel phase equilibrium temperature. The first annealing time is 24-120 hours; the second annealing time is within 12 hours. After the first annealing, the first hot rolling process is performed, followed by a second annealing. After the second annealing treatment, the steel sample is subjected to a second hot rolling treatment and then aging treatment. The temperature of the first and second hot rolling treatments is 600-1000℃, the total reduction is 50%-70%, and the number of rolling passes is 3-5.

2. The method for preparing a low thermal expansion coefficient duplex steel material according to claim 1, characterized in that, The aging treatment temperature is 400-600℃, and the treatment time is 6-24h.

3. The method for preparing a low thermal expansion coefficient duplex steel material according to claim 1, characterized in that, Steps S1-S4 are carried out under an inert gas protective atmosphere, with the vacuum drawn and the absolute pressure not exceeding 2 × 10⁻⁶. -3 After Pa, inert gas is introduced at a pressure of 2 × 10⁻⁶. 4 Pa ~ 4 × 10 4 Pa.

4. A dual-phase steel material with a low coefficient of thermal expansion, characterized in that, The duplex steel material is prepared by any one of the preparation methods described in claims 1-3, wherein the main phase of the duplex steel material is steel material and the precipitated phase is an iron-based negative thermal expansion phase.

5. The low thermal expansion coefficient duplex steel material according to claim 4, characterized in that, The mass fraction of the iron-based negative thermal expansion phase in the dual-phase steel material is no more than 50%.

6. The low thermal expansion coefficient duplex steel material according to claim 4, characterized in that, The coefficient of thermal expansion of the duplex steel material is <6ppm / ℃ in the temperature range of -50℃ to 50℃.

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