Classifications

• • 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
  • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/001—Heat treatment of ferrous alloys containing Ni
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/26—Methods of annealing
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D7/00—Modifying the physical properties of iron or steel by deformation
  • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/06—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/0081—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for slabs; for billets
• • 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
  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
• • 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
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • 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
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals

Definitions

• the present invention relates to low thermal expansion alloys, and in particular to low thermal expansion alloys with excellent machinability.
• Thermal stable Invar alloys are widely used as a material for parts in electronics and semiconductor-related equipment, laser processing machines, and ultra-precision processing equipment.
• Invar alloys traditionally have had the problem of being poorly machinable, meaning that their practical use has been limited to a fairly narrow range of fields.
• Patent Document 1 discloses a low thermal expansion cast steel that uses C and S as free-cutting elements, has an austenite matrix structure with an area ratio of 0.5 to 3% graphite, an area ratio of 0.02 to 0.3% blocky MnS, and 10 to 700 plate-like MnS particles of 8 ⁇ m or more per mm2 , and has a chemical composition, by mass%, of C: 0.3 to 0.9%, Si: 1.5% or less, Mn: 1.0% or less, S: 0.01 to 0.3%, Ni: 25 to 40%, Mg: 0.005 to 0.1%, and has an S and Mn content expressed as S ⁇ (1/4)Mn or (1/4)Mn ⁇ S ⁇ (1/4)Mn+0.05.
• Patent Document 2 discloses an alloy for casting with excellent machinability and low thermal expansion, which is made of an iron-based alloy containing, by mass%, S as a free-cutting element, C: 0.1% or less, Ni: 30-34%, and Co: 4-6%, and contains Mn: 0.1-1.0% and S: 0.02-0.15%, and satisfies (Mn/54.94) > (S/32.06), or contains MnS by volume fraction of 0.007-0.2%, and is substantially free of dissolved S.
• the objective of the present invention is to provide a low thermal expansion alloy with excellent machinability.
• the inventors have thoroughly investigated methods for obtaining a low thermal expansion alloy with improved machinability. As a result, they have discovered that by appropriately controlling the contents of Mn, S, and Ni in particular, it is possible to obtain a low thermal expansion alloy with a small thermal expansion coefficient and excellent machinability.
• the present invention was made based on the above findings and includes the following aspects:
• a low thermal expansion alloy comprising, by mass%, C: 0.050% or less, Si: 0.50% or less, Mn: 2.00-4.00%, P: 0.050% or less, S: 0.100-0.300%, Ni: 35.00-40.00%, with the balance being Fe and impurities, wherein the Mn and S contents expressed by mass%, [Mn] and [S], satisfy [Mn]/[S] ⁇ 10.0, and the average thermal expansion coefficient at 18-28°C is 5.00 ⁇ 10-6 /°C or less.
• the present invention provides a low thermal expansion alloy with excellent machinability, which makes it easy to machine into components for precision equipment, for example.
• FIG. 1 is a diagram for explaining the evaluation of tool wear in the examples.
• FIG. 2 is a diagram for explaining the evaluation of chip crushability in the examples.
• C is an element that crystallizes as graphite in castings and improves machinability, but it also increases the thermal expansion coefficient.
• the content of C is adjusted to suppress the increase in the thermal expansion coefficient.
• the amount of C is 0.050% or less.
• the inclusion of C is not essential, and the C content may be 0%.
• the C content is 0.001% or more, 0.003% or more, 0
• the C content may be 0.045% or less, 0.040% or less, 0.035% or less, 0.030% or less, 0.025% or less. It may be 0.020% or less, or 0.020% or less.
• Si is an element that improves machinability by combining with S. Since the thermal expansion coefficient increases as the Si content increases, the Si content is adjusted to a level that is appropriate for the balance between machinability and the thermal expansion coefficient.
• the Si content is set to 0.50% or less. Since the machinability can be improved by adding S, Si is not essential and the Si content may be 0%.
• Si Content The Si content may be 0.47% or less, 0.45% or less, 0.40% or less, 0.35% or less, 0.30% or less, or 0.20% or less. 0.01% or more, 0.02% or more, 0.03% or more, 0.05% or more, 0.10% or more, or 0.15% or more.
• Mn is an element that forms a compound with S to improve machinability. It is also an element that suppresses cracking during casting and forging. When the Mn content increases, the thermal expansion coefficient increases, Considering the balance between machinability and thermal expansion coefficient, the Mn content is set to 2.00 to 4.00%. %, 2.40% or more, 2.50% or more, 2.75% or more, or 3.00% or more. The Mn content may be 3.90% or less, 3.80% or less, It may be 3.70% or less, 3.60% or less, 3.50% or less, or 3.40% or less.
• P is an element contained as an impurity, and does not need to be contained in the low thermal expansion alloy of the present invention, and the P content may be 0%. If a large amount of P is contained, casting cracks are likely to occur. Therefore, the P content is set to 0.050% or less. The P content is set to 0.040% or less, 0.035% or less, 0.030% or less, 0.025% or less, or 0.020% or less. % or less. Since an excessively reduced P content increases the production cost, the P content may be 0.001% or more, 0.002% or more, 0.003% or more, or 0. It may be 0.005% or more.
• S is an element that forms a compound with Mn and improves machinability. If the S content is high, S segregates at grain boundaries, embrittling the alloy and making it more susceptible to cracking during casting and forging. Therefore, taking into consideration the balance between machinability and embrittlement of the alloy, the S content is set to 0.100 to 0.300%.
• the S content is set to 0.105% or more, 0.110% or more. , 0.120% or more, 0.130% or more, 0.150% or more, 0.170% or more, or 0.200% or more. It may be 280% or less, 0.260% or less, 0.240% or less, or 0.230% or less.
• Ni is an element that reduces the thermal expansion coefficient.
• the low thermal expansion alloy of the present invention has an average thermal expansion coefficient of 5.00 ⁇ 10 ⁇ 6 /° C. or less at 18 to 28° C. This thermal expansion coefficient is This is mainly achieved by setting the Ni content within an appropriate range. If the Ni content is too high or too low, the thermal expansion coefficient will not be sufficiently small. In order to sufficiently reduce the thermal expansion coefficient, The Ni content is 35.00 to 40.00%.
• the Ni content is 35.20% or more, 35.40% or more, 35.60% or more, 35.80% or more, 36.00% or more, 36.50% or more, 37.00% or more, or 37.50% or more.
• the Ni content is 39.80% or less, 39.60% or less, 39.40% or less, 39.20% or less, 39.00% or less, 38.70% or less, or 38.40% or less. That's fine.
• the balance of the chemical composition is Fe and impurities.
• impurities used here refers to elements that are inevitably mixed in from the raw materials and manufacturing environment when industrially manufacturing castings having the chemical composition specified in the present invention, and are elements other than those mentioned above that do not impair the machinability or thermal expansion coefficient of the low thermal expansion alloy of the present invention even if mixed in.
• the total content of impurities is preferably 0.50% or less.
• the total content of impurities may be 0.40% or less, 0.30% or less, 0.20% or less, or 0.10% or less.
• the low thermal expansion alloy of the present invention further satisfies the relationship [Mn]/[S] ⁇ 10.0, where [Mn] and [S] are the contents of Mn and S expressed in mass%.
• [Mn]/[S] is set to 10.0 or more so that S sufficiently forms a compound with Mn and improves machinability.
• [Mn]/[S] may be 10.5 or more, 11.0 or more, 11.5 or more, 12.0 or more, 13.0 or more, 14.0 or more, 15.0 or more, 20.0 or more, or 25.0 or more.
• a small [Mn]/[S] ratio means that the S content is relatively large compared to the Mn content, and the amount of S segregating to the grain boundaries increases, which may make it easier for cracks to occur during casting and forging. If [Mn]/[S] is large, the amount of S segregating to the grain boundaries decreases, so no upper limit is set for [Mn]/[S].
• [Mn]/[S] may be 50.0 or less, 46.0 or less, 43.0 or less, 37.0 or less, 30.0 or less, or 27.0 or less.
• the low thermal expansion alloy of the present invention has an average thermal expansion coefficient of 5.00 ⁇ 10 ⁇ 6 /°C or less at 18 to 28°C.
• the thermal expansion coefficient is measured by taking a test piece for measuring the thermal expansion coefficient from near the center of a cast or forged product and measuring the thermal expansion coefficient in the range of 0 to 50°C at a heating rate of 3°C/min using a thermal expansion coefficient measuring device.
• a thermal expansion measuring device a TD5030S manufactured by Bruker Japan can be used.
• the average thermal expansion coefficient may be 4.90 ⁇ 10 ⁇ 6 /°C or less, 4.81 ⁇ 10 ⁇ 6 /°C or less, 4.62 ⁇ 10 ⁇ 6 /°C or less, 4.50 ⁇ 10 ⁇ 6 /°C or less, 4.00 ⁇ 10 ⁇ 6 /°C or less, 4.43 ⁇ 10 ⁇ 6 /°C or less, or 4.34 ⁇ 10 ⁇ 6 /°C or less. There is no lower limit for the average thermal expansion coefficient.
• the average thermal expansion coefficient may be a negative value.
• the average coefficient of thermal expansion may be 0.01 ⁇ 10 ⁇ 6 /° C. or more, 0.40 ⁇ 10 ⁇ 6 /° C. or more, 0.80 ⁇ 10 ⁇ 6 /° C. or more, 1.60 ⁇ 10 ⁇ 6 /° C. or more, 2.00 ⁇ 10 ⁇ 6 /° C. or more, or 2.50 ⁇ 10 ⁇ 6 /° C. or more.
• the mold used to manufacture the low thermal expansion alloy of the present invention, the device for injecting molten steel into the mold, and the method for injecting are not particularly limited, and any known device or method may be used.
• the casting produced by casting can be directly processed by cutting or the like, or processed after forging to obtain steel parts.
• solution treatment the casting is heated to 750-850°C, held at that temperature for 0.5-3 hours, and then air-cooled. Air-cooling prevents residual stress from occurring as occurs with rapid cooling, reducing warping and distortion that occurs during cutting. Solution treatment may be performed after the forging process described below instead of after casting.
• Example No. 1 The molten metal was poured into a mold, and a casting (Y-type specimen and 10 kg ingot) having the composition shown in No. 1 of Table 1 was produced. The obtained casting was subjected to a solution treatment in which the casting was heated to 800°C, held for 1.5 hours, and then air-cooled. The ingot was then heated to 1150°C and hot forged to obtain a forged product (40 mm square bar). The forging ratio was 3. Test pieces for measuring the thermal expansion coefficient and test pieces for evaluating machinability were taken from the forged product.
• Examples No. 2 to 19> A low thermal expansion alloy was obtained in the same manner as in Example 1, except that the components were as shown in Table 1, and test pieces for measuring the thermal expansion coefficient and for evaluating machinability were taken.
• Nos. 1 to 10 are inventive examples, and Nos. 11 to 19 are comparative examples in which any of the components or the [Mn]/[S] ratio is outside the range of the present invention. Note that for Nos. 2, 3, 4, 5, 7, 8, 10, 11, 13, 14, and 19, test pieces for measuring the thermal expansion coefficient and for evaluating machinability were also taken from the cast products before forging.
• the thermal expansion coefficient was measured using a thermal expansion measuring device (TD5030S manufactured by Bruker Japan) in the range of 0 to 50° C. at a temperature increase rate of 3° C./min to determine the average thermal expansion coefficient from 18° C. to 28° C.
• TD5030S manufactured by Bruker Japan
• Machinability was evaluated by the amount of tool wear and the friability of chips.
• the amount of tool wear and the friability of chips were evaluated by drilling a hole (non-step machining) to a depth of 13 mm using a water-soluble cutting oil at a cutting speed of 45 m/min and a feed rate of 0.104 mm/min, using a drill with a diameter of ⁇ 2.6 mm (cobalt high speed steel, TiN coating).
• the amount of tool wear will be explained with reference to Figure 1.
• the amount of tool wear is the distance from where the base material of the drill is visible (1) to the cutting edge (2) as shown in Figure 1 for a drill after drilling 100 holes, and when the amount of tool wear is 0.100 mm or less, it is determined that the machinability is good.
• No. 11 had a high Si content and a high thermal expansion coefficient.
• No. 12 had a low Mn content and a low [Mn]/[S] ratio, causing cracks during forging.
• No. 13 had a high Mn content and a high thermal expansion coefficient.
• No. 14 had a low S content, which reduced machinability and increased tool wear.
• No. 15 had a high S content and a low [Mn]/[S] ratio, causing cracks during forging.
• No. 16 has a low Ni content and a high thermal expansion coefficient.
• No. 17 has a high Ni content and a large thermal expansion coefficient.
• No. 18 had a small [Mn]/[S] value and cracks occurred during forging.
• No. 19 had a low Mn and S content, which reduced the friability of the chips and increased the length of the chips.

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