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
  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
• • 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
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
  • C21D1/60—Aqueous agents
• • 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
• • 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and 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
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/005—Heat treatment of ferrous alloys containing Mn
• • 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
  • C21D6/007—Heat treatment of ferrous alloys containing Co
• • 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
  • C21D6/04—Hardening by cooling below 0 degrees Celsius
• • 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
• • 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
  • C22C38/10—Ferrous alloys, e.g. steel alloys containing cobalt
  • C22C38/105—Ferrous alloys, e.g. steel alloys containing cobalt containing Co and 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/001—Austenite

Definitions

• the present invention relates to low thermal expansion cast steel products with a low thermal expansion coefficient and a method for manufacturing the same.
• Thermal stable Invar alloys are widely used as a component material for electronics and semiconductor-related equipment, laser processing machines, and ultra-precision processing equipment.
• Patent Document 1 discloses a low thermal expansion alloy containing 29.5 to 35% Ni, 2.0 to 7.0% Co, and 0.001 to 2.0% Cr, and having a thermal expansion coefficient of 0.5 ⁇ 10 -6 /° C. to 2.0 ⁇ 10 -6 /° C. This alloy is obtained by performing homogeneous solution treatment, followed by quenching or annealing by cooling at a rate of 1° C./sec or less, and then performing cold rolling of 10% or more.
• Patent Document 2 discloses a low thermal expansion wire containing Co: 65% or less, Ni: 30% or less, and Cr: 10% or less, with the total content of Co and Ni being 25 to 65%.
• Patent Document 2 discloses a method of transforming the low thermal expansion wire into a processing-induced martensite phase, which is a part of the austenite phase, by cold working.
• Patent Document 3 discloses a low thermal expansion alloy containing Ni: 0.03-1.5%, Ni and Co combined: 53-55%, and Cr: 9-10%. Patent Document 3 discloses a method in which the alloy is annealed at 650-900°C and then cooled in a furnace at a rate of less than 20°C/min.
• Patent No. 2796966 Japanese Patent Application Publication No. 6-279945 Patent No. 5534150
• etching When plating low-thermal expansion cast steel products, they are pretreated.
• the pretreatment involves etching, which can result in etch pits on the surface of the cast steel. If etch pits occur, plating properties will decrease and pinholes may appear when plating is applied.
• the objective of the present invention is to solve the above problems and provide low-thermal expansion cast steel products with good plating properties that suppress the occurrence of etch pits during pretreatment for plating.
• the inventors of the present invention conducted extensive research into methods for suppressing etch pits in low-thermal expansion cast steel products, and developed the present invention.
• the present invention includes the following aspects.
• a low thermal expansion cast steel product having a chemical composition, by mass%, of C: 0.040% or less, Si: 0.30% or less, Mn: 0.50% or less, S: 0.010% or less, Ni: 31.00 to 34.00%, Co: 4.90 to 6.00%, O: 0.0100% or less, and Al: 0.010 to 0.100%, with the balance being Fe and unavoidable impurities, the average crystal grain size of the austenitic structure being 200 ⁇ m or less, and the average thermal expansion coefficient at 25 to 100°C being 0.4 x 10-6 /°C or less.
• a method for producing the low thermal expansion cast steel product of (1) above comprising the steps of: a cryo-treatment step of cooling a cast steel product having a chemical composition, by mass%, of C: 0.040% or less, Si: 0.30% or less, Mn: 0.50% or less, S: 0.010% or less, Ni: 31.00-34.00%, Co: 4.90-6.00%, O: 0.0100% or less, and Al: 0.010-0.100%, with the balance being Fe and unavoidable impurities, to the Ms point or below, holding the temperature at the Ms point or below for 0.5-3 hours, and then raising the temperature to room temperature; and a recrystallization step of heating the cryo-treated cast steel product to 800-1100°C, holding the temperature for 0.5-5 hours, and then quenching.
• a cryo-treatment step of cooling a cast steel product having a chemical composition, by mass%, of C: 0.040% or less, Si: 0.30% or less, Mn: 0.50% or less, S:
• the present invention makes it possible to obtain low thermal expansion cast steel products with good plating properties.
• C (C: 0.040% or less) C dissolves in austenite and contributes to increasing strength. However, C dissolves in the matrix during the recrystallization process and precipitates during cooling, increasing the thermal expansion coefficient. Average thermal expansion at 25 to 100°C In order to make the coefficient 0.4 ⁇ 10 ⁇ 6 /° C. or less, it is necessary to reduce the amount of precipitated C. Therefore, the C content is set to 0.040% or less.
• the C content may be 0.035% or less, 0.030% or less, 0.025% or less, or 0.020% or less. , 0.004% or more, or 0.005% or more.
• Si and Mn are added as deoxidizers.
• the steel castings do not need to contain Si and Mn, and the Si content and Mn content may be 0%, but the Si content and Mn content are set to 0.30% or less and 0.50% or less, respectively.
• the content of Si is within the following ranges. Since deoxidation can be performed with Al, Si and Mn do not need to be added.
• the content of Si is 0.25% or less, 0.20% or less, 0.15% or less.
• the Si content may be 0.01% or more, 0.02% or more, 0.03% or more, 0.04% or more, or 0.05% or more.
• the Mn content may be 0.40% or less, 0.30% or less, or 0.20% or less.
• the Mn content may be 0.01% or more, 0.05% or more, 0.08% or more, 0.10% or more, 0.12% or more, or 0.15% or more.
• S (S: 0.010% or less) S is contained as an impurity. S generates sulfides, which cause etch pits during pretreatment for plating. In order to suppress the generation of sulfides, the S content is set to 0. The S content may be 0.009% or less, 0.008% or less, 0.007% or less, 0.006% or less, or 0.005% or less. The lower the S content, the better, and the S content may be 0%. However, since a 0% S content increases costs, the S content is set to 0.001% or more, or 0. It may be 0.02% or more.
• Ni is an element that reduces the thermal expansion coefficient. If the Ni content is too high or too low, the thermal expansion coefficient will not be sufficiently small. Also, if the Ni content is too high, the martensitic transformation will not occur upon cooling. In order to keep the average thermal expansion coefficient at 25 to 100° C. below 0.4 ⁇ 10 ⁇ 6 /° C., it is necessary to control the Ni content within a narrow range. Generally, the Ni content is in the range of 31.00 to 34.00%. The Ni content may be 31.20% or more, 31.30% or more, or 31.50% or more. The Ni content may be 33.50% or less, 33.00% or less, or 32.50% or less.
• Co (Co: 4.90-6.00%) Co, in combination with Ni, contributes to lowering the thermal expansion coefficient.
• the Co content In order to make the average thermal expansion coefficient at 25 to 100° C. 0.4 ⁇ 10 ⁇ 6 /° C. or less, the Co content must be limited within a narrow range. Specifically, the Co content is 4.90 to 6.00%. The Co content is 5.80% or less, 5.70% or less, and 5.60% or less. The Co content may be 4.95% or more, 5.00% or more, 5.05% or more, 5.10% or more, or 5.50% or less, or 5.40% or less. .15% or more.
• O (O: 0.0100% or less) O is contained as an impurity. O generates oxides, and the generated oxides cause the generation of etch pits during pretreatment for plating. In order to suppress the generation of oxides, the O content is set to 0. The O content may be 0.0090% or less, 0.0080% or less, 0.0070% or less, 0.0060% or less, or 0.0050% or less. The lower the content of O, the better, and the content of O may be 0%. However, since a content of O of 0% increases costs, the content of O is set to 0.0001% or more and 0.0005% or less. % or more, 0.0010% or more, 0.0015% or more, or 0.0020% or more.
• Al 0.010-0.100%
• Al 0.010-0.100%
• the Al content in the steel sheet is set to 0.010 to 0.100%.
• the Al content is set to 0.015% or more, 0.020% or more, 0.025% or more, 0.030% or more, 0.040% or more, 0.050% or more, 0.060% or more, 0.070% or more, 0.080% or more, 0.090% or more, 0.100% or more.
• the Al content may be 0.090% or less, 0.085% or less, 0.080% or less, 0.075% or less, or 0.070% or less. It may be the following:
• the balance of the chemical composition is Fe and unavoidable impurities.
• Inevitable impurities are those that are not intentionally added to the steel during industrial production of steel having the chemical composition specified in the present invention, but are inevitably mixed in due to the raw materials or manufacturing environment.
• Examples of unavoidable impurities include P and Cu, which are elements that are not intentionally added in the manufacturing process.
• the content of impurities is not limited as long as it is within a range that does not affect the effects of the present invention.
• the content of impurities may be, in mass%, 0.50% or less, 0.40% or less, 0.30% or less, 0.20% or less, 0.15% or less, 0.10% or less, 0.05% or less, or 0% in total.
• the structure of the cast steel product of the present invention is an austenite structure with an average grain size of 200 ⁇ m or less.
• the structure is mainly composed of fine equiaxed crystals.
• the proportion of the equiaxed crystals is 60% or more in terms of area ratio. It is more preferable that the proportion of the equiaxed crystals is 90% or more in terms of area ratio, and even more preferable that the proportion of the equiaxed crystals is 95% or more.
• the average grain size of austenite was determined by cutting a sample for microstructural observation from near the center of the cast steel, mirror-polishing the observation surface, etching it with Marble reagent, and observing it with an optical microscope. The average grain size was calculated as the average value of the equivalent circle diameter of the grains.
• the steel cast product of the present invention has an average thermal expansion coefficient of 0.4 ⁇ 10 -6 /°C or less at 25 to 100°C.
• the thermal expansion coefficient is measured by taking a thermal expansion measurement test piece from near the center of the steel cast product and heating it from 0°C to 130°C at a temperature increase rate of 3°C/min using a thermal expansion measuring device, and measuring the average thermal expansion coefficient from 25 to 100°C.
• a thermal expansion measuring device a DIL 402C manufactured by NETZSCH can be used as the thermal expansion measuring device.
• the average thermal expansion coefficient at 25 to 100°C may be 0.40 ⁇ 10 -6 /°C or less, 0.35 ⁇ 10 -6 /°C or less, 0.30 ⁇ 10 -6 /°C or less, or 0.25 ⁇ 10 -6 /°C or less.
• molten steel is produced so that the cast steel product has the above-mentioned chemical composition.
• the method for producing the molten steel is not particularly limited, and known devices and methods may be used.
• the molten steel is poured into a mold and solidified to obtain a cast steel product.
• the mold, the device for pouring the molten steel into the mold, and the method for pouring are not particularly limited, and known devices and methods may be used.
• the structure of the cast steel product produced in the mold will be a structure mainly composed of columnar crystals.
• the obtained cast steel product is subjected to the following heat treatment.
• the cast steel product is quenched to below the Ms point, and is held at a temperature below the Ms point for 0.5 to 3 hours, and then is heated to room temperature (cryotreatment process).
• the cooling method is not particularly limited.
• the Ms point can be estimated using the composition of the steel by the following formula.
• Ms(°C) 521-353C-22Si-24.3Mn-7.7Cu-17.3Ni -17.7Cr-25.8Mo
• C, Si, Mn, Cu, Ni, Cr, and Mo are the contents (mass%) of each element. Elements that are not contained are represented as 0.
• the Ms point calculated by the above formula is approximately -10°C to -70°C, depending particularly on the Ni content, so the cooling medium can be dry ice and methyl alcohol or ethyl alcohol, or a method of immersion in liquid nitrogen, or a method of spraying liquid nitrogen.
• the cooling medium can be dry ice and methyl alcohol or ethyl alcohol, or a method of immersion in liquid nitrogen, or a method of spraying liquid nitrogen.
• the temperature can be raised by lifting the material up to room temperature in the air.
• Figure 1 shows an example of the structure after the cryo-treatment process.
• the black parts in the structure photograph are martensite.
• the generation of a large amount of martensite refines the austenite grain size in the subsequent recrystallization process.
• the cast steel product is reheated to 800 to 1100 ° C, held at 800 to 1100 ° C for 0.5 to 5 hours, and then quenched.
• the structure in which martensite is formed returns to an austenite structure.
• the crystal grain size of the structure formed by normal solidification is about 1 to 10 mm, but by going through the above-mentioned cryo-treatment process and the subsequent recrystallization process, the austenite structure becomes a fine structure with an average grain size of 200 ⁇ m or less, centered on equiaxed crystals.
• the cooling rate of the quenching is preferably 10 ° C / min or more, more preferably 30 ° C / min or more, and even more preferably 100 ° C / min or more, as the average cooling rate from the holding temperature to room temperature.
• Figure 2 shows an example of the structure after the recrystallization process. It can be confirmed that the structure after the recrystallization process has become a fine structure with an average grain size of 200 ⁇ m or less.
• a solution treatment process Before the cryo-treatment, a solution treatment process may be performed in which the cast steel product is heated to 800 to 1100°C, held for 0.5 to 5 hours, and then rapidly cooled.
• the solution treatment process is not essential and may be performed as necessary.
• the solution treatment causes the precipitates that precipitated during casting to dissolve, improving ductility and toughness.
• a diffusion treatment step may be further provided before the cryo-treatment step (or before the solution treatment step if a solution treatment step is provided) in which the cast steel product is held at 1100 to 1300°C for 5 to 50 hours.
• the diffusion treatment step is not an essential step and may be performed as necessary. This eliminates the segregation of Ni and impurities in the steel, and allows for more stable production of cast steel products having a low thermal expansion coefficient, even in the case of large-sized cast steel products.
• the cast steel product may be subjected to a martensite tempering treatment in which the product is heated to 300 to 400°C just below AC3 point and held at 300 to 400°C for 1 to 10 hours.
• the tempering treatment step is not an essential step and may be performed as necessary.
• Example 1 Using a high-frequency melting furnace, the molten metal was poured into a mold to produce a Y-type test material having the composition shown in No. 1 of Table 1.
• the produced Y-type test material was cooled to -80°C and subjected to cryo-treatment by holding for 1.5 hours, subsequently subjected to thermal refining treatment by heating to 350°C and holding for 4 hours, and further subjected to recrystallization treatment by reheating to 1100°C, holding for 2.0 hours, and quenching at 2000°C/min to obtain a low thermal expansion cast steel product.
• the above-mentioned tempering treatment step was provided between the cryo-treatment step and the recrystallization treatment step.
• the holding temperatures of the diffusion treatment step, solution treatment step, and tempering treatment step were as shown in Table 2, and the holding times were 20 hr, 2 hr, and 5 hr, respectively.
• the MS points listed in Table 2 are values obtained by the above-mentioned estimation formula.
• the plating property was evaluated by the following method: A sample of 50 mm ⁇ 50 mm ⁇ 10 mm thickness was taken from the obtained low thermal expansion cast steel product, and the surface was pickled with hydrochloric acid, and then further pickled with a mixture of hydrochloric acid and sulfuric acid, and then immersed for 8 hours so that the Ni plating thickness became about 100 ⁇ m.
• the surface of the 50 mm x 50 mm sample was observed with an optical microscope and evaluated based on the presence or absence of plating defects (pinholes) with a diameter of 200 ⁇ m or more. If no pinholes were observed, the plating was deemed to be good.
• the low thermal expansion cast steel product of the present invention has a low thermal expansion coefficient at 25 to 100°C and is confirmed to have good plating properties.
• Comparative example 1 had a low Co content and a high thermal expansion coefficient.
• Comparative Example 2 had a high content of Co, S, and O, resulting in a high thermal expansion coefficient and poor plating properties.
• Comparative Example 3 is an example in which the Ni content is high, the Al and O contents are low, and cryo-treatment and recrystallization treatment were not performed. As a result, the crystal grain size was not refined, the thermal expansion coefficient was large, and the plating properties were poor.
• Comparative Example 4 had a high Si and Mn content and a low Ni and Co content, resulting in a high thermal expansion coefficient.
• Comparative example 5 had a low Co content and a high thermal expansion coefficient.
• Comparative Example 6 had a high content of Co, S, and O, resulting in a large thermal expansion coefficient and poor plating properties.

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