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
  • C22C38/10—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
  • 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
  • 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
  • C21D6/007—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
  • C21D6/02—Hardening by precipitation
• • 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
  • 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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • 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
• the austenite grains tend to coarsen, making them less susceptible to ultrasonic inspection compared to forged products.
• ultrasonic waves are scattered and attenuated at the grain boundaries, making it difficult to detect defects using ultrasonic inspection, a non-destructive test.
• the objective of the present invention is to solve the above problems and provide low thermal expansion cast steel products with excellent ultrasonic flaw detection properties.
• the inventors have conducted extensive research into methods for improving ultrasonic flaw detection and have developed the present invention.
• the present invention includes the following aspects:
• a low thermal expansion cast steel product characterized by its component composition, in mass percent, containing C: 0.040% or less, Si: 0.30% or less, Mn: 0.05-0.50%, S: 0.005% or less, Ni: 31.00-34.00%, Co: 2.00-6.00%, Al: 0.035-0.100%, with the balance being Fe and unavoidable impurities, the average crystal grain size of the austenitic structure being 200 ⁇ m or less, and the attenuation coefficient of the ultrasonic bottom echo being 2.0 dB/cm or less.
• a method for producing a low thermal expansion cast steel product according to (1) or (2) comprising the steps of: a cryo-treatment step of cooling a cast steel product having a composition, in mass %, of C: 0.040% or less, Si: 0.30% or less, Mn: 0.05-0.50%, S: 0.005% or less, Ni: 31.00-34.00%, Co: 2.00-6.00%, and Al: 0.035-0.100%, with the balance being Fe and unavoidable impurities, to the Ms point or below, holding the product at a temperature below the Ms point 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 and holding the product there for 0.5-5 hours.
• the present invention makes it possible to obtain low thermal expansion cast steel products with excellent ultrasonic inspection properties.
• composition of the steel cast product of the present invention will be described.
• “%” regarding the composition of the steel cast product will represent “mass %” unless otherwise specified.
• 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 1.0 ⁇ 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. C may be 0.035% or less, 0.030% or less, 0.025% or less, or 0.020% or less. C is not an essential element, and the C content may be 0%. The content may be 0.001% or more, 0.002% or more, 0.004% or more, 0.008% or more, 0.010% or more, or 0.015% or more.
• Silicon is added as a deoxidizer.
• the product does not need to contain Si, and the lower limit of the Si content is 0%.
• Si may be contained in the range of 0.30% or less. Since deoxidation can also be performed with Al, Si is not added.
• the Si content may be 0.25% or less, 0.20% or less, 0.15% or less, or 0.10% or less.
• the Si content is 0.01% or more. , 0.02% or more, 0.03% or more, 0.04% or more, 0.05% or more, or 0.07% or more.
• Mn 0.05-0.50%
• Mn is added as a deoxidizer. It is also added to react with S to form MnS, thereby fixing S.
• the Mn content is The Mn content is set to 0.05% or more. If the Mn content is too high, the effect will saturate, so the Mn content is set to 0.50% or less.
• the Mn content is set to 0.10% or more, 0.
• the Mn content may be 0.48% or less, 0.45% or less, 0.40% or less, or 0.50% or more. Or it may be 0.35% or less.
• S (S: 0.005% or less) S is contained as an impurity. When S segregates at grain boundaries, it inhibits recrystallization and reduces ultrasonic inspection properties, so the S content is preferably small.
• the S content is set to 0.005% or less.
• the S content may be set to 0.004% or less, or 0.003% or less. The lower the S content, the better.
• the lower limit is 0%. However, since a 0% S content increases costs, the S content may be 0.001% or more, or 0.002% or more.
• Ni 31.00-34.00%
• 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 1.0 x 10-6 /°C, the amount of Ni It is necessary to control the Ni content within a narrow range. Specifically, the Ni content is in the range of 31.00 to 34.00%.
• the Ni content is 31.10% or more, 31.20% or less, and The Ni content may be 33.80% or less, 33.00% or more, 31.30% or more, 31.40% or more, 31.50% or more, 31.60% or more, or 31.70% or more. .50% or less, 33.00% or less, or 32.50% or less.
• Co (Co: 2.00-6.00%) 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. 1.0 ⁇ 10 ⁇ 6 /° C. or less, the Co content must be 2.
• the Co content is in the range of 2.30% or more, 2.50% or more, 2.70% or more, 3.00% or more, 3.50% or more, or 4.00% or more.
• the Co content may be 5.80% or less, 5.60% or less, 5.40% or less, 5.20% or less, or 5.00% or less.
• Ni content (mass%) [Ni] and the Co content (mass%) [Co] satisfy 34.00 ⁇ [Ni]+0.8 ⁇ [Co] ⁇ 38.00.
• [Ni]+0.8 ⁇ [Co] may be 34.20% or more, 34.50% or more, 34.70% or more, 35.00% or more, or 35.50% or more.
• [Ni]+0.8 ⁇ [Co] may be 37.80% or less, 37.60% or less, 37.20% or less, 36.80% or less, or 36.50% or less.
• Al 0.035-0.100%
• Al is added as a deoxidizer. If the Al content is low, deoxidization is insufficient and Mn oxides are formed, preventing the formation of MnS and making it easier for S to segregate at grain boundaries. Therefore, recrystallization is inhibited. As a result, ultrasonic flaw detection performance is reduced. Therefore, the Al content is set to 0.035% or more. If the Al content is too high, the effect is saturated, so The Al content is 0.100% or less.
• the Al content may be 0.040% or more, or 0.045% or more.
• the Al content is 0.090% or less, 0.080% or less. It may be 0.070% or less, or 0.060% or less.
• the remainder of the 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 composition specified in the present invention, but are inevitably mixed in due to the raw materials or manufacturing environment.
• unavoidable impurities include P and Cu, which are elements that are not intentionally added in the manufacturing process.
• the amount of impurities is not limited as long as it does not affect the effects of the present invention.
• the amount 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. If the proportion of equiaxed crystals is low, the average grain size of the austenite becomes large.
• the proportion of equiaxed crystals is 60% or more in terms of area ratio.
• the proportion of equiaxed crystals may be 70% or more, 80% or more, 85% or more, 90% or more, or 95% or more in terms of area ratio.
• the average grain size of austenite was calculated by cutting a sample for structural observation from near the center of the cast steel, mirror-polishing the observation surface, and then etching with Marble reagent, and taking the average value of the equivalent circular diameter of the grains observed under an optical microscope.
• those with a ratio of the long side to the short side of the grain of 3 or more were judged to be columnar grains, and those with a ratio of less than 3 were judged to be equiaxed grains.
• the attenuation coefficient of the ultrasonic bottom echo of the steel casting of the present invention is 2.0 dB/cm or less.
• the attenuation coefficient is defined as a value (dB/cm) calculated by (B1-B2)/L when the height of the first bottom echo is B1 (dB), the height of the second bottom echo B2 is B2 (dB), and the distance from the sample surface to the bottom surface of the steel casting is L (cm) when the output is adjusted so that the height of the first bottom echo is 75-85% of the output of 100% of the ultrasonic wave in the bottom echo detection by the vertical method.
• the attenuation coefficient is preferably 1.8 dB/cm or less, 1.5 dB/cm or less, 1.2 dB/cm or less, or 1.0 dB/cm or less. Since the attenuation coefficient is small, it is advantageous for detecting defects by ultrasonic flaw detection, which is a non-destructive test. Such an attenuation coefficient can be obtained by setting the component composition in the above-mentioned range and manufacturing a low thermal expansion cast steel by the manufacturing method described below.
• the steel cast product of the present invention preferably has an average thermal expansion coefficient of 1.0 ⁇ 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 1.00 ⁇ 10 -6 /°C or less, 0.90 ⁇ 10 -6 /°C or less, 0.80 ⁇ 10 -6 /°C or less, 0.70 ⁇ 10 -6 /°C or less, 0.60 ⁇ 10 -6 /°C or less, or 0.50 ⁇ 10 -6 /°C or less.
• the low thermal expansion cast steel product of the present invention can be obtained by the casting and heat treatment described below. Note that in the method for producing a low thermal expansion cast steel product of the present invention, no forging is performed.
• molten steel is produced so that the cast steel product has the above-mentioned 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 about -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, immersion in liquid nitrogen, or spraying with liquid nitrogen.
• the cooling medium can be dry ice and methyl alcohol or ethyl alcohol, immersion in liquid nitrogen, or spraying with liquid nitrogen.
• This forms a structure containing fine martensite.
• 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.
• a solution treatment process After 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, in which the steel castings are 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 steel castings having a low thermal expansion coefficient, even for large sized steel castings.
• 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 adjusted to have the composition shown in No. 1 of Table 1. The produced Y-type test material was cooled to -196°C and subjected to cryo-treatment by holding for 1.5 hours, and then reheated to 900°C, held for 2.0 hours, and allowed to cool in the air for recrystallization, to obtain a low-thermal expansion cast steel product.
• Comparative Examples 1 to 6> A low thermal expansion cast steel product was obtained in the same manner as in Example 1, except that the component composition, cryo-treatment, and recrystallization treatment temperatures were set as shown in Tables 1 and 2. For each treatment temperature in Table 2, "-" means that the corresponding step was not performed. Comparative Example 6 is a forged product that was forged after casting.
• a 25 x 25 x 100L sample was taken from the Y-shaped specimen, and the bottom echo height was measured in a direction perpendicular to the longitudinal direction by the vertical method.
• the ultrasonic frequency was 2MHz, and the first bottom echo height of the sample was adjusted to 80%, and the second bottom echo height B2 (dB) was obtained. From the first height B1 (dB) and the height (L) of the sample, (B1-B2)/L was calculated as the attenuation coefficient.
• the low thermal expansion cast steel product of the present invention has a low thermal expansion coefficient at 25 to 100°C, and has a low attenuation coefficient in the as-cast state that is comparable to that of a forged product, meaning that it has excellent ultrasonic inspection properties.
• Comparative Example 1 is an example in which cryo-treatment and recrystallization treatment were not performed, resulting in coarse austenite grains in the as-cast state. As a result, the damping coefficient was large.
• Comparative Example 2 is an example in which the Al content was low, and it is believed that the formation of Mn oxides prevented the formation of MnS, which made it easier for S to segregate at the grain boundaries and inhibited recrystallization. As a result, the average grain size of austenite became larger, and the damping coefficient became larger.
• Comparative Example 3 is an example in which the S content was high and the Al content was low.
• the formation of Mn oxides prevented the formation of MnS, and the high S content also led to the segregation of S at grain boundaries, which is thought to have hindered recrystallization. As a result, the average grain size of austenite became larger, and the damping coefficient became larger.
• Comparative Example 4 is an example with a high Ni content, a high Co content, and a low Al content.
• the inappropriate Ni and Co contents resulted in a high thermal expansion coefficient, and the formation of Mn oxides prevented the formation of MnS, making it easier for S to segregate at grain boundaries and inhibiting recrystallization.
• the high Ni content stabilized austenite, reducing the amount of martensite transformation due to cryo-treatment and reducing the number of equiaxed crystals after recrystallization. As a result, the average grain size of austenite increased, and the damping coefficient increased.
• Comparative Example 5 is an example in which the Ni content, Co content, and Al content were low.
• the inappropriate Ni and Co contents resulted in a large thermal expansion coefficient, and the formation of Mn oxides prevented the formation of MnS, making it easier for S to segregate at the grain boundaries and inhibiting recrystallization.
• the average grain size of austenite became large, and the damping coefficient became large.
• Comparative Example 6 is an example of a forged product that was forged without undergoing cryo-treatment or recrystallization treatment. As it is a forged product, it has a processed structure and is different from the low thermal expansion cast steel product of the present invention, which is cast steel.

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