Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
  • B22F10/20—Direct sintering or melting
  • B22F10/28—Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y10/00—Processes of additive manufacturing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y70/00—Materials specially adapted for additive manufacturing
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/25—Process efficiency

Definitions

• the present invention relates to a high-strength, high-ductility iron-based alloy and a method for producing the same.
• Patent Document 1 discloses a high-strength, high-ductility cast alloy with a tensile strength of 110.1 to 129.3 kgf/mm 2 (1079 to 1267 MPa) and an elongation of 11.8 to 18.5%, as well as a method for producing the same.
• Non-Patent Document 1 discloses a high-strength steel material for additive manufacturing, obtained by additive manufacturing of powder with a maraging steel composition, which has a tensile strength of 1000 to 2150 MPa and an elongation of 2 to 16%.
• the iron-based alloy in Patent Document 1 requires the addition of alloying elements such as Ni, Mo, and V to achieve high strength while maintaining high ductility, and undergoes complex heat treatment. Furthermore, the iron-based alloy in Non-Patent Document 1 contains, in addition to alloying elements such as Ni and Mo to ensure high strength and ductility, 9% Co, which is designated as a specific chemical substance and is subject to legal restrictions. Furthermore, aging treatment is essential to achieve high strength, but aging significantly reduces ductility such as elongation and reduction of area. Furthermore, both Patent Document 1 and Non-Patent Document 1 add relatively large amounts of expensive alloying elements, making the alloy relatively expensive.
• the present invention aims to provide a high-strength, high-ductility iron-based alloy that has a high degree of freedom in shape and can achieve both high strength and high ductility without the addition of expensive alloying elements or special heat treatment, and a method for producing the same.
• the present invention provides the following (1) to (8):
• a high-strength, high-ductility iron-based alloy according to (1) further containing, by mass%, at least one of Ni: 0.1-3%, Cr: 0.1-1.0%, and Mo: 0.01-0.5%.
• a method for producing a high-strength, high-ductility iron-based alloy in which an alloy material having the composition described in (1) or (2) above is melted and solidified using a laser or electron beam to form an additive manufacturing process.
• the present invention provides a high-strength, high-ductility iron-based alloy that has a high degree of freedom in shape and can achieve both high strength and high ductility without the addition of expensive alloying elements or special heat treatment, and a method for producing the alloy.
• FIG. 1 is a conceptual diagram showing the relationship between the carbon content of steel and hardness, tensile strength, and elongation.
• FIG. 1 is a diagram showing the relationship between tensile strength and hardness of steel.
• FIG. 1 is a diagram showing the relationship between tensile strength and total elongation of various steels and the heat treatment of Q&P steel.
• FIG. 1 is a diagram showing the relationship between the grain size and dislocation density of steel.
• FIG. 1 is a diagram showing the relationship between dislocation density and yield strength of steel.
• FIG. 1 is a diagram showing the relationship between the tensile strength and the yield point (0.2% proof stress) of steel.
• the upper part of Figure 3 shows the relationship between tensile strength and total elongation of steel materials, and the properties of alloys Nos. 1 to 4 and 6 of the present invention are plotted in this figure.
• the inventors conducted extensive research with the goal of obtaining an iron-based alloy that offers a high degree of freedom in shape and can achieve both high strength and high ductility without the addition of expensive alloying elements or special heat treatment.
• Non-Patent Document 1 also uses additive manufacturing, which may have refined the microstructure.
• [Chemical composition] C 0.35-0.65% C is an element effective in improving strength. However, if its content is less than 0.35%, a high strength of 1300 MPa cannot be obtained, and if its content exceeds 0.65%, the strength saturates and ductility decreases. Therefore, the C content is set in the range of 0.35 to 0.65%.
• Si 0.1-1.0%
• Silicon is an element added for the purpose of deoxidation. However, if the silicon content is less than 0.1%, deoxidation is insufficient, and if it exceeds 1.0%, ductility decreases. Therefore, the silicon content is set to 0.1 to 1.0%.
• Mn 0.2-2.0% Mn is an element effective in improving strength and also has a deoxidizing effect. However, if its content is less than 0.2%, this effect is small, and if its content exceeds 2.0%, ductility decreases. Therefore, the Mn content is set to the range of 0.2 to 2.0%.
• P and S are elements that have a significant effect on toughness. If the content of each exceeds 0.030%, toughness will decrease significantly. Therefore, the P and S contents are set to 0.030% or less.
• Ni, Cr, and Mo are elements that reduce ductility, but they can improve predetermined properties as described below, so they may be added in amounts sufficient to maintain the desired ductility.
• Ni is an element that has a significant austenite stabilizing effect and contributes to increased strength, so it may be added as needed. Furthermore, Ni has a smaller adverse effect on ductility than other elements, so it can be added in relatively large amounts. However, if Ni is less than 0.1%, the effect of increasing strength is small, and if it is 3% or more, the adverse effect on ductility becomes significant. Therefore, if Ni is added, its content should be in the range of 0.1 to 3%.
• Cr is an effective element for increasing strength, so it may be added as needed. However, if it is less than 0.1%, the effect is minimal, and if it exceeds 1.0%, it has a significant negative impact on ductility. Therefore, if Cr is added, its content should be in the range of 0.1 to 1.0%.
• Mo is an element that improves hardenability and suppresses temper embrittlement, and may be added as needed during heat treatment. However, at less than 0.01%, the effect is minimal, and at more than 0.5%, the adverse effect on ductility increases. Therefore, if Mo is added, its content should be in the range of 0.01 to 0.5%.
• the remainder of the alloy components having the above composition is Fe and unavoidable impurities.
• the solidification structure of an alloy having the above composition is refined so that the arithmetic mean grain size of the crystals is 10 ⁇ m or less.
• a high-strength, high-ductility iron-based alloy can be obtained, which has a high tensile strength of 1100 MPa or more, a high elongation of 13% or more, and satisfies the formula [tensile strength (MPa)] ⁇ [elongation (%)] ⁇ 16,000.
• MPa tensile strength
• elongation (%) ⁇ 16,000.
• ductility not only can the elongation be 13% or more, but also the reduction of area can be 45% or more.
• S20C steel which is carbon steel with a C content of approximately 0.2%, has a tensile strength of approximately 450 MPa and an elongation of approximately 30%
• S50C steel which is carbon steel with a C content of approximately 0.5%, has a tensile strength of approximately 700 MPa and an elongation of approximately 15%.
• the alloy with the above composition is rapidly solidified during additive manufacturing, resulting in a fine structure with an arithmetic mean grain size of 10 ⁇ m or less.
• a tensile strength of 1100 MPa or more can be achieved with a C content of 0.35%, for example, equivalent to S35C.
• advanced heat treatment such as that of Q&P steel, as shown in Figure 3 (Source: Journal of the Japan Society of Mechanical Engineers, Vol. 125, February 2022, https://www.jsme.or.jp/kaisi/1239-20/).
• the upper part of Figure 3 shows the relationship between tensile strength and total elongation for each steel type.
• Q&P steel as shown in the lower part of Figure 3, is first quenched, and cooling is stopped at a temperature where some untransformed austenite remains. The material is then held at the appropriate temperature through partitioning.
• Q&P steel stabilizes the solute carbon in the partially transformed martensite by this heat treatment by distributing it to the untransformed austenite, increasing the amount of retained austenite and achieving both high tensile strength and elongation, including a range that satisfies a tensile strength of 1100 MPa or more and an elongation of 13% or more.
• the present invention achieves both high strength of 1100 MPa or more and elongation of 13% or more without advanced heat treatment by refining the structure and limiting the alloying elements that form precipitates that hinder elongation. Furthermore, it can satisfy the condition [tensile strength (MPa)] ⁇ [elongation (%)] ⁇ 16,000 or even 20,000 or more, thereby contributing to weight reduction of structural components.
• FIG. 4 shows experimental values showing the relationship between steel grain size and dislocation density. According to this figure, when the grain size is 10 ⁇ m, the dislocation density is on the order of 2–3 ⁇ 10 14 /m 2 . As shown in Figure 5 , the yield point (0.2% proof stress) in this case is 0.35 GPa (350 MPa), which corresponds to a tensile strength of approximately 390 MPa (Source: Tomoki Tanaka et al., Iron and Steel: Vol. 104 (2016) No. 5: "Effect of Grain Size on the Yield Stress of Cold-Worked Iron").
• the alloy material having the above composition is melted and solidified by a laser or electron beam to form an additive manufacturing process. After the alloy material is melted, it is rapidly cooled, resulting in a fine structure with an arithmetic mean grain size of 10 ⁇ m or less.
• an alloy powder having a composition within the above range is prepared as an alloy material, and then melted and solidified using a laser or electron beam for additive manufacturing.
• a laser or electron beam allows the cooling rate during solidification of the alloy to be 3000°C/sec or higher, resulting in an alloy with a fine solidification structure with an arithmetic mean crystal grain size of 10 ⁇ m or less.
• additive manufacturing achieves a strength higher than the relationship between crystal grain size refinement and strength as previously known. Therefore, it is presumed that additive manufacturing not only refines the structure through rapid solidification, but also increases dislocation density or changes other physical properties. Since heat treatment after additive manufacturing may increase the crystal grain size and reduce strength, it is preferable to leave the additive manufacturing process as is.
• heat treatments that do not affect the crystal grain size such as stress relief at temperatures of approximately 150 to 250°C or strength adjustment treatments at temperatures below 500°C, are permissible.
• a dislocation density of 5 x 10 14 /m 2 or more can be maintained, and the tensile strength can be 1100 MPa or more, the elongation can be 13% or more, and the relationship [tensile strength (MPa)] x [elongation (%)] ⁇ 16000 can be satisfied.
• a raw material powder of carbon steel having the composition shown in Table 1 was prepared, granulated by gas atomization, and sieved to obtain -63 ⁇ m spherical powder, which was used as the raw material for modeling.
• the raw material for modeling was then subjected to additive manufacturing using a laser-based additive manufacturing device under the following conditions: output: 300 W, energy density: 90 J/mm 3 , and thickness per layer: 40 ⁇ m, to produce a 3D-modeled object ( ⁇ 15 ⁇ 100 mm).
• the tensile strength, elongation, reduction of area, and arithmetic mean grain size of the crystals (referred to simply as average grain size in Table 1) were measured for this 3D-modeled object.
• the measurement results are also shown in Table 1.
• Nos. 1 to 6 are invention examples that meet the scope of the present invention, while Nos. 11 to 13 are comparative examples that fall outside the scope of the present invention. Additionally, Nos. 21 and 22 are reference examples with a maraging steel composition. Note that invention examples Nos. 1 to 4 and 6, comparative examples Nos. 11 and 13, and reference example No. 21 were all formed as-cast, while invention example No. 5, comparative example No. 12, and reference example No. 22 were heat-treated after forming. Regarding heat treatment, invention example No. 5 was heat-treated at 500°C after forming, and comparative example No. 12 was heat-treated at 580°C after forming. Reference example No. 22 was heated at 820°C for 0.5 hours, air-cooled, and then aged at 490°C for 6 hours.
• Invention Examples Nos. 1 to 6 which are within the scope of the present invention, have an arithmetic mean grain size of 10 ⁇ m or less, a tensile strength of 1100 MPa or more, and an elongation of 13% or more, resulting in high-strength, high-ductility iron-based alloys that satisfy the relationship [tensile strength (MPa)] ⁇ [elongation (%)] ⁇ 16,000. Furthermore, the reduction of area is 45% or more.
• Figure 7 is a plot of the properties of Invention Examples Nos. 1 to 4 and 6 on the graph showing the relationship between tensile strength and elongation for various steels at the top of Figure 3. As shown in Figure 7, Invention Examples Nos.
• Sample 5 an inventive example with the same composition as Sample 4 but subjected to heat treatment at 500°C, has a lower tensile strength than Sample 4, but still satisfies the requirements of a tensile strength of 1,100 MPa or more, an elongation of 13% or more, and [tensile strength (MPa)] ⁇ [elongation (%)] ⁇ 16,000. Although the dislocation density is also lower than that of Sample 4, it maintains high values of 8.7 ⁇ 10 14 /m 2 and 5 ⁇ 10 14 /m 2 or more.
• Comparative Examples No. 11 to 13 which are outside the scope of the present invention, have at least one of the tensile strength, elongation, and [tensile strength (MPa)] x [elongation (%)] outside the above range.
• Comparative Example No. 12 had an arithmetic mean grain size of crystals of 15 ⁇ m or more and a dislocation density of less than 5 ⁇ 10 14 m -2 . Furthermore, Comparative Example No. 12 had an reduction of area of less than 45%.

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