WO2020038019A1

WO2020038019A1 - Fe-mn-cr-ni series medium entropy stainless steel and preparation method therefor

Info

Publication number: WO2020038019A1
Application number: PCT/CN2019/085145
Authority: WO
Inventors: 乔珺威; 边斌斌; 石晓辉; 张敏; 杨慧君; 郭瑞鹏; 王重; 吴玉程
Original assignee: 太原理工大学
Priority date: 2018-08-20
Filing date: 2019-04-30
Publication date: 2020-02-27

Abstract

An Fe-Mn-Cr-Ni series medium entropy stainless steel, the chemical components thereof being: Fe40Mn20Cr20Ni20; having good strength and plastic deformation capability at room temperature, and having excellent mechanical properties and corrosion resistance at low temperatures. The preparation method comprises pre-treatment of the raw material, weighing, smelting, heat treatment, and cold machining.

Description

Fe-Mn-Cr-Ni series mid-entropy stainless steel and preparation method thereof

Technical field

The invention relates to the composition, preparation and properties of an entropy stainless steel in the Fe-Mn-Cr-Ni series, and belongs to the technical field of steel.

Background technique

For thousands of years, the history of human development and the history of metal materials have been closely linked. Metal materials have always been one of the most important materials for human beings, and have important significance in national economy and social life. In the context of the country's vigorous promotion of sustainable development strategies, we are extremely eager to develop materials that have high strength, high plasticity, high corrosion resistance and low cost, while meeting the needs of social production and life, and increasing the service life of materials. The purpose of saving resources and protecting the environment. The design principle of traditional steel is generally to select one or two elements as the main element, or to add several small amounts of steel elements to improve the comprehensive performance of the steel, such as: iron-based steel, cobalt-based steel, aluminum-based steel, etc. It is generally accepted that when a large amount of steel elements are added to steel, it is easy to form more intermetallic compounds or complex phases, and more complex phases and intermetallic compounds will cause the performance of steel to drop sharply. The emergence of high entropy steel has broken through the traditional steel design concept and provided people with a new steel design idea. Because high-entropy steel has excellent comprehensive properties such as high strength, high hardness, excellent corrosion resistance and thermal stability, outstanding fatigue strength and fracture strength, and strong radiation resistance, these are all incomparable with traditional steels. . At present, high entropy steel has attracted widespread attention.

Although multi-component high-entropy steel has many excellent properties, due to its use of a large amount of precious metal elements, its economic cost is very high compared to traditional steel materials, and it is actually difficult to realize industrial production. With the development of high-entropy steel to the second generation of non-isoatomic ratio high-entropy steel, people's horizons and research scope have been further expanded. The steel composition of the present invention uses this latest concept to design a medium-entropy stainless steel that does not contain precious elements. It can not only form a simple and stable phase structure, but also significantly reduce the economic cost. At the same time, it has better low-temperature tensile properties than high-entropy steel. In addition, this material has better corrosion resistance than stainless steel. At present, research on medium-entropy stainless steel is still in its infancy. Corrosion is one of the main failure modes of structural materials. In the process of developing new steel materials, corrosion resistance is an important factor that must be considered. Studies have shown that the addition of easily passivating elements (such as Cr, Ni) can make steel have satisfactory corrosion resistance. Therefore, this material is expected to be used as a potential low-temperature material in practical conditions.

Summary of the Invention

The invention provides a composition of a Fe-Mn-Cr-Ni series medium-entropy stainless steel and a preparation method thereof. The purpose is to develop a non-isoatomic ratio Fe-Mn-Cr-Ni series medium-entropy stainless steel by using several inexpensive elements. , While improving performance while significantly reducing its production costs, laying a solid foundation for industrial production and applications.

The steel component of the entropy stainless steel in the present invention does not contain precious elements, which significantly reduces the production cost. The medium-entropy stainless steel not only satisfies the formation of a simple and stable high-entropy phase structure, but also exhibits higher low-temperature performance than high-entropy steel, and also has better corrosion resistance than stainless steel.

The invention considers that pure Mn is easy to volatilize during the smelting process, resulting in too large a component deviation, and Fe-Mn steel having an Fe and Mn atomic ratio of 1: 1 is selected instead of pure Mn, and an additional 5% is added based on the chemical composition of the steel Of manganese was added as compensation. The preparation process includes heat treatment and cold deformation. First, the plate-shaped sample of the suction casting is homogenized, and then cold-rolled, followed by stress relief annealing. The wire-like sample was cut into a tensile specimen using wire-cut EDM, and subjected to quasi-static stretching at room temperature and low temperature.

The invention provides a Fe-Mn-Cr-Ni series medium-entropy stainless steel, wherein the proportion of each element is: the atomic percentage of the elements Fe, Mn, Cr, and Ni is 40%: 20%: 20%: 20% .

The invention provides a method for preparing Fe-Mn-Cr-Ni series medium-entropy stainless steel, which includes the following steps:

Step 1. Raw material pre-treatment: The raw materials with high purity (≥99.99%) of Fe, Ni, and Cr and Fe-Mn binary alloy with an atomic ratio of 1: 1 are respectively polished with a grinder and then placed on the surface. In a beaker filled with absolute ethanol, perform ultrasonic treatment for 10 minutes to remove impurities and dirt on the surface of the raw material, and then dry the raw material in a drying box;

Step 2: Weighing: According to the atomic percentage of Fe, Mn, Cr, and Ni in order of 40%: 20%: 20%: 20%, use the electronic balance with an accuracy of 0.001g to weigh the pre-treatment in step 1. Subsequent raw materials

Step 3: Smelting:

① The raw materials are placed in a copper crucible of a vacuum arc furnace in order from the lowest to the highest melting point, and the sponge titanium block is placed in another copper crucible of the vacuum arc furnace, and then the furnace door is closed tightly;

② Use the first-stage mechanical pump to close the vacuum to 5Pa and turn it off. Turn on the second-stage mechanical pump to ensure that the vacuum level is lower than 5Pa, then start the molecular pump, continue to evacuate to 1.5 × 10 ^-3 Pa and close all valves and molecular pumps. Fill with high-purity argon (≥99.999%) so that the pressure in the furnace is 0.4-0.5atm;

③ First, start the arc to make the titanium block smelt by the flame to check whether there is oxygen residue in the furnace cavity. After the titanium block is cooled, the surface still shows a silver-white metallic color, then you can start smelting the steel. After each smelting, The steel ingot is turned 180 ° once, and then the melting process is repeated 4-5 times to make the composition as uniform as possible;

④ After smelting multiple times, after heating the ingot to the molten state, vacuum infusion is used to suck the steel ingot into the plate-shaped cavity for water cooling. After the system is completely cooled, open the mold and take out the plate-like sample;

Step 4: Post-processing: The sample obtained in Step 3 is subjected to 1200 ± 5 ° C homogenization heat treatment for 2 hours, followed by water cooling, followed by cold rolling with 0%, 30%, 50%, and 70% reduction ratios, and finally Destress annealing at 650 ± 5 ℃ for 10 minutes.

The product of the invention can be implemented in industrial production and has practicality.

The beneficial effects of the present invention:

The steel composition of the present invention does not contain precious and rare elements, has a simple and stable high-entropy phase structure while having a low cost, and exhibits higher low-temperature performance than high-entropy steel, and at the same time, it is more excellent than stainless steel. Resistance to seawater corrosion.

The medium-entropy stainless steel according to the present invention can greatly reduce the use cost of materials at low temperatures, and also improve the service life of materials. This medium-entropy stainless steel has great potential as a structural material for use in low-temperature, high-salt environments.

In the present invention, the entropy stainless steel has a yield strength of 1182 MPa, a tensile strength of 1,320 MPa, and an elongation at break of about 24.74% at a liquid nitrogen temperature (77K). In a 3.5% sodium chloride solution, the corrosion current density I _{corr of} 304L stainless steel It is 9.2 (μA / cm ² ); the corrosion current density I _corr of the entropy stainless steel in FeMnCrNi is 1.04 (μA / cm ² ). It can be seen that the corrosion resistance of the entropy stainless steel in FeMnCrNi is significantly better than that of 304L stainless steel.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of the purchased WK-II vacuum arc furnace;

2 is an X-ray diffraction spectrum of the as-cast stainless steel and different deformation amounts of the prepared Fe ₄₀ Mn ₂₀ Cr ₂₀ Ni ₂₀ mid-entropy stainless steel;

3 is a quasi-static uniaxial tensile stress-strain curve diagram of the post-processed sample at room temperature and liquid nitrogen temperature;

4 is an electrochemical corrosion polarization curve of a sample and 304 stainless steel in a 3.5% sodium chloride solution after step 4 in Example 1;

FIG. 5 is an electrochemical corrosion resistance curve of the sample and 304 stainless steel in a 3.5% sodium chloride solution after the process of step 4 in Example 1. FIG.

In the figure, 1, handle, 2, furnace cover, 3, inlet valve, 4, exhaust valve, 5, electrode, 6, copper mold, 7, cooling water outlet pipe, 8, cooling water inlet pipe.

detailed description

The present invention is further described below through examples, but is not limited to the following examples.

Example 1:

This embodiment is a Fe-Mn-Cr-Ni series medium-entropy stainless steel composed of four elements: Fe, Mn, Cr, and Ni, and the atomic percentages of the elements of Fe, Mn, Cr, and Ni are 40%: 20%: 20%: 20%. The raw materials are selected from pure Fe, pure Ni, pure Cr and FeMn binary alloy with an atomic ratio of 1: 1.

A method for preparing Fe-Mn-Cr-Ni series medium-entropy stainless steel includes the following steps:

Step 1: Pre-treatment: The raw materials with high purity (≥99.99%) of Fe, Ni, and Cr and Fe-Mn binary alloy with an atomic ratio of 1: 1 are polished with a grinding machine, and then placed in the equipment. In a beaker with absolute ethanol, perform ultrasonic treatment for 10 minutes to remove impurities and dirt on the surface of the raw materials, and then dry the above raw materials in a drying box;

Step 3: Smelting:

Step 4: Post-processing: The sample obtained in Step 3 is subjected to 1200 ± 5 ° C homogenization heat treatment for 2 hours, followed by water cooling, followed by cold rolling with 0%, 30%, 50%, and 70% reduction ratios, and finally Annealed at 650 ± 5 ° C for 10 minutes to obtain a cold-rolled plate-like sample. Structure and performance tests were performed on the obtained samples.

As shown in Figure 1, the WK-II non-consumable vacuum arc furnace is an off-the-shelf product. WK-II non-consumable vacuum electric arc furnace includes furnace body, water-cooled crucible, vacuum device, cooling device and power supply device; the vacuum device part adopts mechanical pump and molecular pump to evacuate in stages, and the vacuum degree can be lowered to 10 ^-4 Pa The furnace body adopts a double-layer water-cooled arrangement. The inner and outer layers are made of stainless steel and steel, respectively, and are precision welded. The copper mold is connected directly below the copper crucible, and the molten steel can be sucked into a plate shape. To facilitate subsequent processing; an observation window is set on the front of the furnace, and a polarized glass plate is installed on the observation window. This part is used to protect the operator's eyes from being injured when the arc is operated; the control handle can move the electrode flexibly, and After the arc, move the arc to the designated position and smelt the steel;

FIG. 2 is an XRD pattern of the Fe ₄₀ Mn ₂₀ Cr ₂₀ Ni ₂₀ medium-entropy stainless steel after step 4. From the figure, it can be obtained that the material has a single-phase FCC structure after homogenization and deformation after casting;

Figure 3 is the room temperature and low temperature tensile curves of the entropy stainless steel of Fe ₄₀ Mn ₂₀ Cr ₂₀ Ni ₂₀ after step 4; the figure shows that the performance of the steel at each deformation is lower than that at room temperature, and As the amount of deformation increases, the properties of the material increase. The medium-entropy stainless steel has a yield strength of 1182 MPa, a tensile strength of 1,320 MPa, and an elongation at break of about 24.74% at a liquid nitrogen temperature (77 K), which can be a good candidate material at low temperatures.

FIG. 4 is a polarization curve diagram of the entropy stainless steel in the 3.5% sodium chloride solution of the Fe ₄₀ Mn ₂₀ Cr ₂₀ Ni ₂₀ treated in step 4. It is shown that the corrosion current density I _corr of 304L stainless steel in 3.5% sodium chloride solution is 9.2 (μA / cm ² ); and the corrosion current density I _corr of entropy stainless steel in FeMnCrNi is 1.04 (μA / cm ² ), indicating that the medium entropy stainless steel The corrosion resistance is better than 304L stainless steel.

FIG. 5 is an impedance curve diagram of the entropy stainless steel in the 3.5% sodium chloride solution of the Fe ₄₀ Mn ₂₀ Cr ₂₀ Ni ₂₀ treated in step 4. Figure 5 shows that the radius of the resistance curve of the entropy stainless steel in FeMnCrNi is significantly larger than that of 304L stainless steel. Further proves that its corrosion resistance is better than 304L stainless steel.

The medium-entropy stainless steel prepared in step 4 in this embodiment has a single-phase FCC structure, in which 70% of the cold-rolled material has the highest tensile properties at liquid nitrogen temperature, yield strength of 1182 MPa, tensile strength of 1320 MPa, and elongation at break. The rate is 24.74%. At the same time, it has better seawater corrosion resistance than 304L stainless steel.

As shown in Figure 4 from the impedance curves of the two, the radius of the impedance curve of the entropy stainless steel in FeMnCrNi is significantly larger than that of 304L stainless steel.

Corrosion current density I _corr of 304 stainless steel in 3.5% sodium chloride solution is 9.2 (μA / cm ² ); Corrosion current density I _corr of stainless steel in FeMnCrNi is 1.04 (μA / cm ² ). Corrosion performance is significantly better than 304L stainless steel. The corrosion rate of FeMnCrNi medium entropy stainless steel is significantly lower than that of 304L stainless steel.

Example 2: The sample processed in step 4 of Example 1 was cut by wire cutting to obtain three standard tensile patterns. The gauge length was about 10 mm and the width was 3 mm. Then use 240 #, 600 #, 800 #, 1000 #, 1200 #, 1500 #, and 2000 # to perform mechanical polishing to ensure that the gauge section is flat, the direction of the scratch is consistent, and there are no macro defects. Use an INSTRON type mechanical testing machine to perform room temperature. Static and low temperature tensile experiments. The strain rate during the experiment is 1 × 10 _-3 / s. In order to ensure the accuracy and repeatability of the experimental results, at least 3 samples of each material are tested. Finally, data with similar results are selected using Origin8. 0 software makes tensile engineering stress-strain curve diagram. It can be clearly seen from the tensile engineering stress-strain curve that the yield strength of the sample after the treatment in step 4 is significantly improved compared with the as-cast state, which is 3 times the as-yield strength of the as-cast state, reaching 1182 MPa, and the elongation at break. About 24.74%.

Claims

A Fe-Mn-Cr-Ni series mid-entropy stainless steel, the Fe-Mn-Cr-Ni series mid-entropy stainless steel has a yield strength of 1182 MPa, a tensile strength of 1,320 MPa at a liquid nitrogen temperature, and an elongation at break of 24.74% ; In a 3.5% sodium chloride solution, the corrosion current density I corr is 1.04 μA / cm 2 ; the chemical composition is: the atomic percentages of Fe, Mn, Cr, and Ni are 40%, 20%, 20%, and 20%, respectively; It is characterized in that the preparation method comprises the following steps:

(1) Pre-treatment of raw materials: Fe, Mn, Cr and Fe-Mn binary alloys with an atomic ratio of 1: 1 and purity of ≥99.99% are respectively polished with a grinder, and then placed in an anhydrous In the beaker of ethanol, ultrasonic treatment is performed for 10 minutes to remove impurities and dirt on the surface of the raw material into clean raw material, and then the clean raw material is dried in a drying box;

(2) Weighing: Prepared according to the atomic percentage of Fe, Mn, Cr, Ni elements in order of 40%: 20%: 20%: 20%. Weigh the dried raw materials using an electronic balance with an accuracy of 0.001g;

(3) Smelting:

Ⅰ Place the raw materials from bottom to top in a copper crucible of a vacuum arc furnace in accordance with the melting point from low to high, place the sponge titanium block in another copper crucible of the vacuum arc furnace, and then close the furnace door tightly;

使用 Use a first-level mechanical pump to close the vacuum to 5Pa and close it. Turn on the second-level mechanical pump to ensure that the vacuum level is lower than 5Pa and start the molecular pump. Continue to evacuate to 1.5 × 10 -3 Pa and close all valves and molecular pumps. The introduction of high-purity argon makes the pressure in the furnace 0.4-0.5atm;

Ⅲ First, start the arc to make the titanium block smelt by the flame to check whether there is oxygen residue in the furnace cavity. After the titanium block cools down, the surface still shows a silver-white metallic color, then you can start smelting steel. Turn the steel ingot once by 180 °, and then continue the smelting. The smelting process is repeated 4-5 times to make the composition as uniform as possible;

Ⅳ After several times of smelting, after heating the ingot to the molten state, use vacuum suction casting to suck the steel ingot into the plate-shaped cavity for water cooling. After the system is completely cooled, open the mold and take out the plate-like sample;

(4) Post-processing treatment: The samples obtained in step 3 are sequentially subjected to 1200 ± 5 ° C homogenization heat treatment for 2 hours, and then water-cooled, followed by cold rolling with 0%, 30%, 50%, and 70% reduction rates, and finally De-stress annealing at 650 ± 5 ° C for 10 minutes to obtain a cold-rolled plate specimen.
The medium-entropy stainless steel of Fe-Mn-Cr-Ni system according to claim 1, characterized in that the cold-rolled plate-like sample in step (4) is subjected to recovery treatment at 650 ± 5 ° C to recover a part Plasticity while retaining the effect of work hardening.