Y-doped high-carbon-content austenite low-density steel and preparation method thereof

Abstract

The invention relates to Y-doped high-carbon-content austenitic low-density steel and a preparation method thereof, and belongs to the technical field of metal materials, and the Y-doped high-carbon-content austenitic low-density steel comprises the following chemical components in percentage by mass: 1.5-2.0 wt% of C, less than or equal to 0.2 wt% of Si, 25-30 wt% of Mn, 7-10 wt% of Al, 0.01-0.3 wt% of Y, less than or equal to 0.015 wt% of P, less than or equal to 0.008 wt% of S and the balance of Fe. According to the method, the Y-doped high-carbon-content austenitic low-density steel is subjected to homogenization treatment, primary hot rolling, secondary hot rolling and water cooling in sequence after being smelted, and the Y-doped high-carbon-content austenitic low-density steel has high strength synergistically contributed by grain boundary strengthening, solid solution strengthening and large-proportion shearable precipitation strengthening. And by adding Y, formation of harmful grain boundary precipitated phases and inclusions is inhibited, the plastic loss of the material is reduced, and the oxidation resistance of the material is enhanced.

Description

Technical Field

[0001] The invention relates to Y-doped high-carbon-content austenitic low-density steel and a preparation method thereof, belonging to the technical field of metal materials. Background Art

[0002] Fe-Mn-Al-C austenitic low-density steel is considered to be a high-quality structural material comparable to high-entropy alloys due to its high strength, good plasticity and low density. Its low raw material cost and simple production process make it possible to prepare it on a large scale. Austenitic low-density steel is mainly strengthened by κ-carbides that are completely coherent with the matrix. Its main components are (Fe, Mn)3AlC x Increasing the content of Al and C can increase the proportion of κ-carbides, thereby improving the yield strength of the material. However, excessive Al content exceeding 10 wt.% will accelerate the formation of harmful precipitation phases such as D03. Therefore, increasing the C content is an effective way to increase the proportion of κ-carbides.

[0003] Current research shows that carbon is easy to segregate at grain boundaries. High carbon content increases the precipitation range of κ-carbides, making it easier for κ-carbides to precipitate at grain boundaries, resulting in reduced plasticity. Therefore, the precipitation kinetics of κ-carbides can be targeted by component design. As a rare earth element, Y is more likely to diffuse to the grain boundaries, thereby inhibiting the segregation of C elements at the grain boundaries. This effect of purifying grain boundaries is believed to inhibit the precipitation of carbides at grain boundaries. In addition, the addition of Y to the FeCrAl system has also been shown to refine grains and increase the proportion of Σ3 twin boundaries. These contributions all indicate that by adding an appropriate amount of Y element and increasing the C content, it is possible to obtain high-strength, high-toughness, low-density steel with further improved strength and less plasticity loss. However, there has been no report on the application of this solution to improve the performance of low-density steel. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a Y-doped high carbon content austenitic low density steel and a preparation method thereof, wherein a Y-doped high carbon content austenitic low density steel ingot is prepared by vacuum induction melting, homogenized after mold repair, and subjected to two-step hot rolling treatment, and finally water-cooled to room temperature. The obtained material has a large κ-carbide ratio and a small grain size, and no obvious carbide precipitation at the grain boundary. The yield strength of the low-density steel is significantly improved and still has good plasticity.

[0005] To achieve the above-mentioned purpose, the technical solution of a Y-doped high-carbon-content austenitic low-density steel described in the present invention is as follows: the total mass of the steel is 100%, and the mass percentages of the chemical components are: C 1.5~2.2 wt.%, Si ≤0.2wt.%, Mn 25~30 wt.%, Al 7~10 wt.%, Y 0.01~0.3 wt.%, P ≤0.015 wt.%, S ≤0.008wt.%, and the balance is Fe.

[0006] Preferably, the total mass of the steel is 100%, and the mass percentages of the chemical components are: C 1.65~1.95wt.%, Si ≤0.2 wt.%, Mn 27.5~29 wt.%, Al 8.0~9.5 wt.%, Y 0.08~0.15 wt.%, P ≤0.015wt.%, S ≤0.008 wt.%, and the balance is Fe.

[0007] The method for preparing a Y-doped high-carbon austenitic low-density steel of the present invention comprises the following steps: (1) vacuum induction melting: vacuum induction melting is performed according to the mass percentage of the chemical components of a Y-doped high-carbon austenitic low-density steel, and the melting temperature is greater than 1600°C; (2) homogenization treatment and hot rolling: the ingot obtained by the melting in step (1) is homogenized at 1200°C, and then the temperature is adjusted to 1100-1200°C to start preliminary hot rolling, the final rolling temperature is ≥950°C, water cooling is performed, and the plate is sheared and trimmed; the second hot rolling is performed, the hot-rolled plate is heated to 1100-1200°C and rolling is started, and the final rolling temperature is ≥900°C.

[0008] Preferably, the ingot in step (1) is obtained by the following method: vacuum induction melting, the Al balls loaded need to be laid layer by layer to avoid concentrated accumulation; vacuum ≤ 0.5 Pa, heating temperature to above 1600°C to melt the raw materials, passing argon gas for protection, keeping warm for 0.5~2 h, in order to prevent the volatilization of Mn vapor during the sampling process, sampling is not performed during the smelting process, the alloy is melted and stirred evenly before steel can be tapped, and the ingot is refined into a square shape after demolding. The square ingot obtained in step (2) is homogenized at 1200°C for 180 minutes; the treated sample is naturally cooled to 1150°C and then directly hot rolled, the final rolling temperature is ≥950°C, and it is cooled to room temperature after final rolling; the sample after preliminary hot rolling is heated to 1150°C and then hot rolled for the second time, the hot rolling is performed in 4~6 passes, the total reduction is 80%, the final rolling temperature is controlled to be greater than 900°C, and it is cooled to room temperature.

[0009] Preferably, vacuum induction melting of Y-doped high carbon content austenitic low density steel is carried out in a 50kg vacuum induction melting furnace, and the Al balls loaded need to be laid layer by layer to avoid concentrated accumulation. The vacuum degree is ≤0.1Pa, the raw materials are melted at a heating temperature of 1600-1700°C, argon gas is introduced for protection, and the temperature is kept for 0.5-2 hours. In order to prevent the volatilization of Mn vapor during the sampling process, sampling is not performed during the smelting process. The alloy can be tapped after being melted and stirred evenly, and the ingot is refined into a square ingot after demolding.

[0010] Preferably, the square ingot of Y-doped high carbon content austenitic low density steel is homogenized at 1200°C for 180 min. The treated sample is naturally cooled to 1150°C and then directly hot rolled, the final rolling temperature is ≥950°C, and the final rolling is cooled to room temperature, with a thickness of 25 mm. The sample after preliminary hot rolling is heated to 1150°C and then hot rolled for the second time, the hot rolling is carried out in 4 to 6 passes, the total reduction is 80%, the final rolling temperature is controlled to be greater than 900°C, and the sample is cooled to room temperature, with a thickness of 5 mm.

[0011] Beneficial effects of the present invention: The present invention provides a Y-doped high-carbon austenitic low-density steel and a preparation method thereof. First, raw materials are laid in a vacuum induction melting furnace in order, heated to above 1600°C, and cast into an ingot after being kept warm for 0.5 to 2 hours. After demoulding, the steel is refined into a square ingot and homogenized at 1200°C, and then hot-rolled in two steps. The rolling reduction and rolling rate of each pass are strictly controlled to ensure that recrystallization is just complete after each rolling pass, and the final rolling temperature is ensured to be greater than 900°C, so that the grain size is greatly reduced after each rolling pass, thereby improving grain boundary strengthening. As the carbon content increases, carbon is easily segregated on the grain boundary during high-temperature rolling to form grain boundary κ-carbides, but the enrichment of Y on the grain boundary inhibits the formation of grain boundary carbides. With the addition of high carbon content, the formation dynamics of κ-carbides are enhanced, and a large volume fraction of intracrystalline κ-carbides can be formed during high-temperature hot rolling. The steel of the present invention combines grain boundary strengthening, solid solution strengthening, and large-proportion shearable precipitation phase strengthening, greatly improves yield strength, and maintains good plasticity. The present invention can obtain high strength-plasticity and toughness matching only through smelting, homogenization treatment and two-step hot rolling, has few processing steps, simple process, and is easy to industrialize.

[0012] The composition design basis of the present invention is as follows: The main function of C is to promote the formation of κ-carbide and improve the strength of steel. C can promote solid solution strengthening, improve the stability of austenite, and further reduce the density of the material. However, too high a C content will lead to a significant decrease in the plasticity of the steel and a significant tendency to graphitization.

[0013] Mn is an austenite stabilizing element, which stabilizes the austenite structure and reduces the starting temperature of the martensite phase transformation. The austenite structure has good plasticity and good low-temperature stability. However, too high a Mn content will promote the precipitation of brittle β-Mn at the grain boundary, resulting in a greater tendency of intergranular cracking.

[0014] Al is the main element to reduce the density of steel. When adding 1 wt.%, the density decreases by 0.101 g / cm 3 For every 1wt.% of Al added, the stacking fault energy value increases by 7 mJ / cm 2 , which can promote plane slip. However, Al cannot be added in excess, otherwise it will promote the formation of ferrite and affect the casting performance.

[0015] The addition of Y can purify the grain boundaries. It easily diffuses to the grain boundaries, thereby inhibiting the segregation of C elements at the grain boundaries and inhibiting the precipitation of carbides at the grain boundaries. In addition, Y can refine the grains and increase the proportion of Σ3 twin boundaries. However, excessive addition of Y will promote the 17 Intermetallic compounds such as precipitate at the grain boundaries, causing the material to become embrittled. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is an optical microscope (OM) image of the Y-doped high carbon content austenitic low density steel prepared in Example.

[0017] Figure 2 This is an optical microscope (OM) image of a carbon-content austenitic low-density steel without high Y doping prepared in comparative example.

[0018] Figure 3 This is the selected electron diffraction (SAED) pattern of the Y-doped high carbon content austenitic low density steel prepared in this example. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below in conjunction with specific embodiments.

[0020] In the following examples and comparative examples: Tensile testing equipment: electronic universal material testing machine model INSTRON5985.

[0021] The sample processing and testing process are carried out according to the national standard ASTM E8 / E8M; the tensile strength and yield strength are measured according to ASTM E8 / E8M using the tensile stress-strain curve obtained from the tensile test, and the elongation is the elongation after fracture.

[0022] TEM test: The transmission electron microscope model is JEM-F200 from Japan Electron.

[0023] Table 1 shows the chemical composition weight percentages of Y-doped high carbon content austenitic low density steel in the embodiments of the present invention and the comparative examples. According to Table 1, 2 furnaces of 50 kg alloy ingots were prepared by vacuum induction melting.

[0024] .

[0025] Example

[0026] Use a 50kg vacuum induction furnace for smelting, and the Al balls loaded need to be laid layer by layer to avoid concentrated accumulation. The vacuum degree of the vacuum pump is ≤50 Pa, and the heating temperature is above 1600℃ to melt the raw materials. Argon gas is introduced for protection and kept warm for 0.5~2 h. In order to prevent the volatilization of Mn vapor during the sampling process, sampling is not performed during the smelting process. The alloy can be tapped after being melted and stirred evenly. After demolding, the ingot is refined into a square. The square ingot is kept warm for 180 min at 1200℃ for homogenization treatment. The treated sample is naturally cooled to 1150℃ and then directly hot rolled. The final rolling temperature is ≥950℃, and it is cooled to room temperature after final rolling. After the initial hot rolling, the sample is heated to 1150℃ and then hot rolled for the second time. The hot rolling is carried out in 4 passes with a total reduction of 80%. The final rolling temperature is controlled to be greater than 900℃ and cooled to room temperature.

[0027] Comparative Example The processing technology of the comparative example and the embodiment is completely consistent.

[0028] .

[0029] As shown in Table 2, the Y-doped high carbon content austenitic low density steel described in this method is subjected to homogenization treatment, initial hot rolling and secondary hot rolling, and water cooling in sequence after smelting, and has high strength contributed by the synergistic contribution of grain boundary strengthening, solid solution strengthening, and large proportion of shearable precipitation strengthening. Figure 1 As shown in Figure 2, the addition of Y inhibits the formation of harmful grain boundary carbides. Figure 2 The high carbon and low density steel without Y addition has less precipitation phase at the grain boundaries, which effectively reduces the loss of material plasticity. Figure 1 The addition of Y refines the grains of low-density steel and makes up for the strength loss caused by the absence of grain boundary precipitation. Figure 3 The selected electron diffraction patterns in the figure prove that the addition of Y does not affect the formation of κ-carbides. The large proportion of κ-carbides produced at high carbon content can still play a precipitation strengthening role, indicating that high carbon content and the addition of Y are not contradictory.

[0030] In summary, the invention includes but is not limited to the above embodiments. Any equivalent substitution or partial improvement made under the spirit and principle of the invention shall be deemed to be within the protection scope of the invention.

Claims

1. A Y-doped high carbon content austenitic low density steel, characterized in that: The total mass of the steel is 100%, and the mass percentages of the chemical components are: C 1.5~2.2wt.%, Si≤0.2 wt.%, Mn 25~30 wt.%, Al 7~10 wt.%, Y0.01~0.3 wt.%, P≤0.015 wt.%, S≤0.008 wt.%, and the balance is Fe.

2. A Y-doped high carbon content austenitic low density steel as claimed in claim 1, characterized in that: The total mass of the steel is 100%, and the mass percentages of the chemical components are: C 1.65~1.95 wt.%, Si ≤0.2 wt.%, Mn 27.5~29 wt.%, Al 8.0~9.5 wt.%, Y 0.08~0.15 wt.%, P ≤0.015 wt.%, S ≤0.008 wt.%, and the balance is Fe.

3. A method for preparing Y-doped high carbon content austenitic low density steel, characterized in that: The method comprises the following steps: (1) vacuum induction melting: vacuum induction melting is performed according to the mass percentage of the chemical composition of a Y-doped high-carbon austenitic low-density steel according to claim 1 or 2, and the melting temperature is greater than 1600°C; (2) homogenization treatment and hot rolling: the ingot obtained by melting in step (1) is homogenized at 1200°C, and then the temperature is adjusted to 1100-1200°C to start preliminary hot rolling, the final rolling temperature is ≥950°C, water cooling is performed, and the plate is sheared and trimmed; the second hot rolling is performed, the hot-rolled plate is heated to 1100-1200°C and rolling is started, and the final rolling temperature is ≥900°C.

4. The method for preparing a Y-doped high carbon content austenitic low density steel according to claim 1, characterized in that: The ingot in step (1) is obtained by the following method: vacuum induction melting, the Al balls are laid layer by layer to avoid concentrated accumulation; vacuum ≤ 0.5 Pa, heating the raw materials to a temperature above 1600°C to melt the raw materials, introducing argon gas for protection, and keeping the temperature for 0.5 to 2 hours. In order to prevent the volatilization of Mn vapor during the sampling process, sampling is not performed during the smelting process. The alloy can be tapped after being melted and stirred evenly. After demoulding, the ingot is refined into a square shape.

5. The method for preparing a Y-doped high carbon content austenitic low density steel as claimed in claim 3, characterized in that: The square ingot obtained in step (2) is subjected to homogenization treatment at 1200°C for 180 min. The treated sample is naturally cooled to 1150°C and then directly hot rolled, with the final rolling temperature being ≥950°C. The sample is cooled to room temperature after the final rolling. The sample after the initial hot rolling is heated to 1150°C and then subjected to secondary hot rolling, with the hot rolling being carried out in 4 to 6 passes with a total reduction of 80%. The final rolling temperature is controlled to be greater than 900°C and then cooled to room temperature.

6. The method for preparing a Y-doped high carbon content austenitic low density steel as claimed in claim 4, characterized in that: In step (1), vacuum induction melting is carried out in a 50kg-class vacuum induction melting furnace, the vacuum degree is ≤0.1Pa, and the heating temperature is 1600-1700°C to melt the raw materials.

7. The method for preparing a Y-doped high carbon content austenitic low density steel as claimed in claim 5, characterized in that: The method of cooling to room temperature after hot rolling in step (2) is water cooling.

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