ALLOY MATERIAL AND METHOD FOR PRODUCING SAME

Abstract

An alloy material is provided which contains elements including, in mass %, C: 0.010 to 0.10%, Si: more than 0.10% to 0.50% or less, Mn:0.05 to 0.50%, Ni:34.5 to 37.0%, and Nb:0.001 to 1.0%, and which satisfies [T.sub.0≤T.sub.1-2], [C—Nb/7.7-Ta/15≤0.045], [Nb-7.7C≤0.30], and [Ta-15C≤0.30]. Where, each symbol of an element in the above formulas represents a content (mass %) of the corresponding element, T.sub.0 represents a Curie temperature (° C.) of the alloy material, and T.sub.1 represents a Curie temperature (° C.) of the alloy material after the alloy material is held at 900° C. for one minute and thereafter is cooled under conditions such that an average cooling rate in a temperature range from 600 to 300° C. is 0.2° C./s.

Claims

1. An alloy material having a chemical composition consisting of, in mass %, C: 0.010 to 0.10%, Si: more than 0.10% to 0.50% or less, Mn: 0.05 to 0.50%, P: 0.015% or less, S: 0.0015% or less, Cr: 0.005 to 0.50%, Ni: 34.5 to 37.0%, Cu: 0.005 to 1.0%, Co: 0.005 to 0.50%, Mo: 0.001 to 0.50%, Al: 0.0001 to 0.050%, Nb: 0.001 to 1.0%, N: 0.010% or less, O: 0.0060% or less, Ti: 0.0200% or less, Zr: 0.0200% or less, Hf: 0.0200% or less, V: 0.500% or less, W: 1.000% or less, Sn: 0.050% or less, Zn: 0.0020% or less, Pb: 0.0010% or less, Ta: 0 to 1.0%, B: 0 to 0.010%, Ca: 0 to 0.0050%, Mg: 0 to 0.0030%, REM: 0 to 0.050%, and the balance: Fe and unavoidable impurities, and satisfying Formula (1), Formula (2), Formula (3) and Formula (4) below, wherein: a yield stress is 240 MPa or more, and a plate thickness is 3.0 mm or more;
T.sub.0≤T.sub.1−2  (1)
C—Nb/7.7−Ta/15≤0.045  (2)
Nb—7.7C≤0.30  (3)
Ta−15C≤0.30  (4) where, each symbol of an element in the above formulas represents a content (mass %) of a corresponding element, T.sub.0 represents a Curie temperature (° C.) of the alloy material, and T.sub.1 represents a Curie temperature (° C.) of the alloy material after the alloy material is held at 900° C. for one minute and thereafter is cooled under conditions such that an average cooling rate in a temperature range from 600 to 300° C. is 0.2° C./s.

2. A method for producing the alloy material according to claim 1, comprising: a heat treatment performed on the alloy material including a cooling process, wherein the cooling process ejects water at a temperature of 35° C. or less onto the alloy material in a manner so that a water amount density (m.sup.3/m.sup.2.Math.min) of the water is [0.11 In(t)+0.02] or more, where a plate thickness of the alloy material is represented by t (mm).

3. A method for producing the alloy material according to claim 1, comprising: a hot working of the alloy material including a cooling process, wherein the cooling process ejects water at a temperature of 35° C. or less onto the alloy material in a manner so that a water amount density (m.sup.3/m.sup.2.Math.min) of the water is [0.11 In(t)+0.02] or more, where a plate thickness of the alloy material is represented by t (mm).

4. The method according to claim 2, wherein: after the cooling process, leveler straightening is performed under conditions so that an increase in yield stress at ordinary temperature is a value that is 3 MPa or more and 50 MPa or less.

5. The method according to claim 3, wherein: after the cooling process, leveler straightening is performed under conditions so that an increase in yield stress at ordinary temperature is a value that is 3 MPa or more and 50 MPa or less.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0069] FIG. 1 is a view illustrating the relation between the plate thickness of a hot-rolled alloy plate and a water amount density (m.sup.3/m.sup.2.Math.min) for making a cooling rate at a central part of the plate thickness of the hot-rolled alloy plate 2.0° C./s or more.

[0070] FIG. 2 is a view illustrating a temperature change of magnetization in an alloy material of an alloy number 1.

DESCRIPTION OF EMBODIMENTS

[0071] Hereunder, the alloy material and the method for producing the alloy material of the present invention are described. In the following description, the symbol “%” with respect to the content of each element means “mass percent”.

[0072] (Chemical Composition of Alloy Material)

[0073] C: 0.010 to 0.10%

[0074] C is effective for increasing the strength. Therefore, the content of C is set to 0.010% or more. The content of C is preferably set to 0.015% or more, and more preferably 0.020% or more. However, excessively containing C will deteriorate the hot workability and will adversely affect the thermal expansion characteristics. Therefore, the content of C is set to 0.10% or less. The content of C is preferably set to 0.08% or less, and more preferably 0.06% or less.

[0075] Si: more than 0.10% and 0.50% or less

[0076] Similarly to Mn to be described later, Si is an element that is necessary as a deoxidizer during alloy melting. Therefore, the content of Si is set to more than 0.10%. The content of Si is preferably set to 0.15% or more, and more preferably 0.20% or more. However, excessively containing Si will cause an adverse effect on the expansion characteristics. Therefore, the content of Si is set to 0.50% or less. The content of Si is preferably set to 0.40% or less, and more preferably 0.30% or less.

[0077] Mn: 0.05 to 0.50%

[0078] Similarly to Si that is described later, Mn is an element that is necessary as a deoxidizer during alloy melting. Further, Mn also has an effect of fixing S that deteriorates the hot workability, as MnS. Therefore, the content of Mn is set to 0.05% or more. The content of Mn is preferably set to 0.10% or more, and more preferably 0.15% or more. However, excessively containing Mn will cause an adverse effect on the expansion characteristics. Therefore, the content of Mn is set to 0.50% or less. The content of Mn is preferably set to 0.40% or less, and more preferably 0.30% or less.

[0079] P: 0.015% or less

[0080] P is an impurity element that significantly increases solidification cracking sensitivity and weld crack sensitivity. Therefore, the content of P is set to 0.015% or less. Whilst the content of P is preferably reduced as much as possible, extremely restricting the content of P will increase the production cost. Therefore, the content of P is preferably set to 0.001% or more.

[0081] S: 0.0015% or less

[0082] S is an impurity element that deteriorates the hot workability. Therefore, the content of S is set to 0.0015% or less. Whilst the content of S is preferably reduced as much as possible, extremely restricting the content of S will increase the production cost. Therefore, the content of S is preferably set to 0.0001% or more.

[0083] Cr: 0.005 to 0.50%

[0084] Cr is an element that is mixed in from equipment used to melt stainless steel or from raw materials, and causes an adverse effect on the thermal expansion characteristics. Therefore, the content of Cr is set to 0.50% or less. The content of Cr is preferably set to 0.40% or less. On the other hand, if it is attempted to excessively reduce Cr, the melting cost will increase. Therefore, the content of Cr is set to 0.005% or more.

[0085] Ni: 34.5 to 37.0%

[0086] Ni is an effective element for increasing the spontaneous volume magnetostriction of the alloy and lowering the coefficient of thermal expansion. Therefore, the content of Ni is set to 34.5% or more. The content of Ni is preferably set to 35.0% or more. However, if Ni is excessively contained, the production cost will increase. Therefore, the content of Ni is set to 37.0% or less.

[0087] Cu: 0,005 to 1.0%

[0088] Cu is an element that is mixed in from equipment used to melt stainless steel or from raw materials, and causes an adverse effect on the thermal expansion characteristics. Therefore, the content of Cu is set to 1.0% or less. The content of Cu is preferably set to 0.7% or less, and more preferably 0.5% or less. On the other hand, if it is attempted to excessively reduce Cu, the melting cost will increase. Therefore, the content of Cu is set to 0.005% or more.

[0089] Co: 0.005 to 0.50%

[0090] Co is an element that is mixed in from equipment used to melt stainless steel or from raw materials. Further, if Co is excessively contained, the alloy cost will increase. Therefore, the content of Co is set to 0.50% or less. The content of Co is preferably set to 0.40% or less, and more preferably 0.30% or less. On the other hand, if it is attempted to excessively reduce Co, the melting cost will increase. Therefore, the content of Co is set to 0.005% or more.

[0091] Mo: 0.001 to 0.50%

[0092] Mo is an element that is mixed in from equipment used to melt stainless steel or from raw materials, and causes an adverse effect on the thermal expansion characteristics. Therefore, the content of Mo is set to 0.50% or less. The content of Mo is preferably set to 0.40% or less, and more preferably 0.30% or less. On the other hand, if it is attempted to excessively reduce Mo, the melting cost will increase. Therefore, the content of Mo is set to 0.001% or more.

[0093] Al: 0.0001 to 0.050%

[0094] Al is an effective element for deoxidation. Therefore, the content of Al is set to 0.0001% or more. The content of Al is preferably set to 0.0003% or more, and more preferably 0.0005% or more. However, if Al is excessively contained, there will be an adverse effect on the thermal expansion characteristics. Therefore, the content of Al is set to 0.050% or less, and preferably is set to 0.040% or less.

[0095] Nb: 0.001 to 1.0%

[0096] Nb is an element that enhances strength, and also prevents cracking of the weld metal during welding and thereby improves the welding workability. Therefore, the content of Nb is set to 0.001% or more. The content of Nb is preferably set to 0.010% or more, and more preferably 0.015% or more. However, if Nb is excessively contained, the hot workability will decrease and there will be an adverse effect on the thermal expansion characteristics. Therefore, the content of Nb is set to 1.0% or less. The content of Nb is preferably set to 0.7% or less, and more preferably 0.5% or less.

[0097] N: 0.010% or less

[0098] N is an impurity element that deteriorates the hot workability. Therefore, the content of N is set to 0.010% or less. Whilst the content of N is preferably reduced as much as possible, extremely restricting N will cause the melting costs to increase. Therefore, the content of N is preferably set to 0.001% or more.

[0099] O: 0.0060% or less

[0100] O is an impurity element that exerts an adverse effect on the thermal expansion characteristics. Therefore, the content of O is set to 0.0060% or less. Whilst the content of O is preferably reduced as much as possible, extremely restricting O will cause the melting costs to increase. Therefore, the content of O is preferably set to 0.0005% or more.

[0101] T.sub.1: 0.0200% or less

[0102] Zr: 0.0200% or less

[0103] Hf 0,0200% or less

[0104] V: 0.500% or less

[0105] W: 1.000% or less

[0106] Sn: 0.050% or less

[0107] Zn: 0.0020% or less

[0108] Pb: 0.0010% or less

[0109] T.sub.1, Zr, Hf, V, W, Sn, Zn and Pb are impurity elements that exert an adverse effect on the thermal expansion characteristics, and hence the contents of these elements are preferably low. Therefore, the content of T.sub.1 is set to 0.0200% or less. The content of Zr is set to 0.0200% or less. The content of Hf is set to 0.0200% or less. The content of V is set to 0.500% or less. The content of W is set to 1.000% or less. The content of Sn is set to 0.050% or less. The content of Zn is set to 0.0020% or less. The content of Pb is set to 0.0010% or less. Note that, in some cases these elements are not contained.

[0110] Ta: 0 to 1.0%

[0111] Similarly to Nb, Ta is an element that enhances the strength, and also prevents cracking of the weld metal during welding and thereby improves the welding workability. Therefore, Ta may be contained as necessary. However, if Ta is excessively contained, the hot workability will decrease and there will be an adverse effect on the thermal expansion characteristics. Therefore, the content of Ta is set to 1.0% or less. On the other hand, to obtain the aforementioned effects, the content of Ta is preferably set to 0.01% or more.

[0112] B: 0 to 0.010%

[0113] B is an element that improves the hot workability, and therefore may be contained. However, if B is excessively contained, there will be an adverse effect on the thermal expansion characteristics. Therefore, the content of B is set to 0.010% or less. In a case where the contents of C and Nb are 0.04% or less and 0.15% or less, respectively, B need not be contained. On the other hand, to obtain the aforementioned effect, the content of B is preferably set to 0.0001% or more. The content of B is preferably set within the range of 0.0003 to 0.0030%.

[0114] Ca: 0 to 0.0050%

[0115] Mg: 0 to 0.0030%

[0116] REM: 0 to 0,050%

[0117] Ca, Mg and REM are each elements that improve the hot workability of the alloy material, and therefore may be contained. However, if these elements are excessively contained, on the contrary, in some cases these elements will cause the hot workability to decrease, and reduce the cleanliness of the alloy. Therefore, the content of Ca is set to 0.0050% or less. The content of Mg is set to 0.0030% or less. The content of REM is set to 0.050% or less. On the other hand, to obtain the aforementioned effect, the content of Ca is preferably set to 0.0005% or more. The content of Mg is preferably set to 0.0003% or more. The content of REM is preferably set to 0.001% or more.

[0118] It is necessary for the chemical composition of the alloy material to contain each element described above within the respectively defined ranges, and to satisfy the following Formula (2) and Formula (3). Further, when the chemical composition of the alloy material contains Ta, the chemical composition must also satisfy Formula (4). A compositional characteristic of the alloy material of the present invention is that the alloy material contains both of C and Nb, and NbC (Nb carbides) is formed in the alloy material. Since the coefficient of linear expansion of this alloy material increases with ΔC(=C—Nb/7.7-Ta/15) or ΔNb (=Nb-7.7C), the respective values of ΔC and ΔNb are restricted to an upper limit value or less. Ta is an element that belongs to the same group as Nb in the periodic table, and in the present alloy material Ta may be added in lieu of a part of Nb, and hence for the same reason it is important that the upper limit of ΔTa (=Ta-15C) is restricted.

ΔC≤0.045  (2)

ΔNb≤0.30  (3)

ΔTa≤0.30  (4)

[0119] Where, each symbol of an element in the above formulas represents the content (mass %) of the corresponding element.

[0120] The chemical composition of the alloy material contains the respective elements described above, with the balance being Fe and unavoidable impurities. The term “unavoidable impurities” means components which, during industrial production of the alloy, are mixed in due to various causes such as the raw material or the production equipment.

[0121] (Curie Temperature of Alloy Material)

[0122] It is necessary for the alloy material to satisfy the following Formula (1).

T.sub.0≤T.sub.1−2  (1)

[0123] Where, T.sub.0 represents the Curie temperature (° C.) of the alloy material, and T.sub.1 represents the Curie temperature (° C.) of the alloy material after the alloy material is held at 900° C. for one minute and thereafter is cooled under conditions such that the average cooling rate in the temperature range from 600 to 300° C. is 0.2° C./s.

[0124] The above Formula (1) is an index which shows that, in the temperature range from 600 to 300° C., the alloy material was cooled under conditions such that the average cooling rate of the central part of the plate thickness of the alloy material was 2.0° C./s or more. That is, with the alloy material subjected to such a heat treatment, since an increase in the coefficient of expansion caused by mixing in of impurities can be offset, the coefficient of thermal expansion can be kept low while relaxing restrictions on the concentrations of impurity elements in the raw material.

[0125] Note that, with respect to measurement of T.sub.0 and T.sub.1, for example, measurement may be performed by the following procedure. Specifically, an alloy piece having dimensions of 3 mm in thickness×5 mm in width×1 mm in length is cut out from the hot-rolled alloy material by machining, and the surface is finished with wet-type emery #600 to remove the surface-processed layer to form a test specimen A.

[0126] Similarly, a test specimen having dimensions of 3 mm in thickness×8 mm in width×12 mm in length is cut out from the hot-rolled alloy material by machining, a thermocouple is welded to the surface, and a heat cycle is applied under conditions such that holding at 900° C. for 1 minute, and after cooling rate in a section from 600 to 300° C. is 0.2° C./s. A test specimen having dimensions of 3 mm in thickness×5 mm in width×1 mm in length is cut out by machining from the test specimen to which the heat cycle was applied, and the surface is polished using wet-type emery #600 to remove the surface-processed layer and thereby obtain a test specimen B.

[0127] Using the obtained test specimen A and test specimen B, the plate thickness direction of each test specimen is set to the magnetic field application direction and the longitudinal direction is set to the sample vibration direction by a vibrating sample magnetometer (VSM) that is capable of raising the specimen temperature, and temperature changes of magnetization are measured in a magnetic field of 40000 A/m (500 Ge). The rate of temperature increase is set to 3° C./min, and the temperature dependence of the magnetization of each sample is measured while increasing the temperature from room temperature to 300° C., and the temperature at which the magnetization disappears is extrapolated from a curve of the relative magnetization with respect to room temperature, and T.sub.0 and T.sub.1 are determined.

[0128] (Microstructure of Alloy Material)

[0129] The present alloy material contains C and Nb, and fine NbC precipitates in the alloy. Since coarse NbC may promote weld crack sensitivity due to eutectic melting, preferably the average diameter (equivalent circular diameter) of NbC that precipitates in the alloy material is 1 μm or less. Note that, in the present alloy material, dispersion of fine NbC has an effect of increasing the strength of the alloy plate. Therefore, the finer the NbC is, the more preferable it is. However, if the average diameter of NbC is less than 0.002 μm, an effect that increases the strength of the alloy plate will not be sufficiently obtained. Therefore, the average diameter of NbC is preferably 0.002 μm or more. The average diameter of NbC varies depending on the contents of Nb and C in the alloy, the cooling rate during casting, the heating temperature of hot rolling, the rolling temperature, the plate thickness and the subsequent cooling rate, and the rate of temperature increase, the holding temperature and the holding time in a heat treatment and the like, and in general the greater that the contents of C and Nb are, the lower that the heating temperature of hot rolling is, and the longer that the holding time in the heat treatment is, the larger that the average diameter tends to become. The average diameter of NbC can be measured by performing microstructure observation by an extraction replica method or with a transmission electron microscope using a thin film.

[0130] (Yield Stress)

[0131] In the present alloy material, the yield stress is made 240 MPa or more. If the yield strength is less than 240 MPa, sufficient strength as a welded structure will not be obtained, and it will be difficult to obtain a sufficient degree of freedom in welding. Therefore, the yield stress of the present alloy material is made 240 MPa or more. The yield stress is more preferably made 260 MPa or more. Note that, although an upper limit of the yield stress is not particularly limited, in the present alloy material, in most cases the yield stress is usually 450 MPa or less. Note that, yield stress in the present alloy material is 0.2% proof stress when a tensile test is performed in accordance with JIS Z 2241:2011.

[0132] (Plate Thickness)

[0133] In the present alloy material, the plate thickness is set to 3.0 mm or more. If the plate thickness is less than 3.0 mm, it will be difficult to obtain a sufficient degree of freedom in welding. Therefore, the plate thickness is set to 3.0 mm or more. The plate thickness is preferably set to 4.0 mm or more, and more preferably 6.0 mm or more. Note that, although an upper limit of the plate thickness is not particularly limited, in consideration of the welding workability, the upper limit is preferably set to 80 mm or less.

[0134] (Method for Producing Alloy Material)

[0135] With regard to a production method for obtaining the alloy material, preferably the alloy material is produced under the conditions described hereunder. The conditions for performing hot rolling are not particularly limited. An ingot obtained under normal melting conditions can be performed by rolling under normal hot rolling conditions. As the hot rolling conditions, for example, conditions can be mentioned in which after heating to 1050 to 1250° C. at which Nb and C dissolve, rolling is performed in a temperature range of 900 to 1100° C. which is the recrystallization temperature of the alloy material, or in a non-recrystallization temperature range from 900 to 700° C. The rolling reduction may be determined according to the target strength and other conditions.

[0136] However, the cooling conditions after hot rolling or the cooling conditions after heat treatment are important for achieving a low coefficient of thermal expansion. That is, in the temperature range from 600 to 300° C., it is necessary to perform cooling under conditions such that the average cooling rate of the central part of the plate thickness of the alloy material is 2.0° C./s or more. In the temperature range from 600 to 300° C., if the average cooling rate of the central part of the plate thickness of the alloy material is less than 2.0° C./s, unless the concentrations of impurity elements in the raw material are sufficiently restricted, it will not be possible to suppress the coefficient of thermal expansion to a low value.

[0137] In a cooling process in a heat treatment performed on the alloy material, when the plate thickness of the alloy material is represented by t (mm), it is necessary to eject cooling water onto the alloy material in a manner so that the water amount density (m.sup.3/m.sup.2.Math.min) of the cooling water at a temperature of 35° C. or less is [0.11 In(t)+0.02] or more. This is because the thickness of the alloy material that is the object of cooling is 3 to 80 mm, and unless cooling is performed with a sufficient water amount density, the aforementioned cooling rate cannot be realized.

[0138] Further, in the case of producing the alloy material by performing cooling after hot rolling and without performing a heat treatment, similarly, when the plate thickness of the alloy material is represented by t (mm), it is necessary to eject cooling water at a temperature of 35° C. or less onto the alloy material in a manner so that the water amount density (m.sup.3/m.sup.2.Math.min) of the cooling water is [0.11 In(t)+0.02] or more.

[0139] Note that, although basically the alloy material of the present invention is produced by performing water-cooling immediately after hot rolling, or is produced by, after hot rolling, performing a heat treatment of reheating and holding, there is no prohibition on adopting a method in which water-cooling is performed immediately after hot rolling, and thereafter a heat treatment of reheating and holding is performed. In the case of performing water-cooling both after hot rolling and after heat treatment, it suffices that at least the water-cooling after the heat treatment satisfies the aforementioned cooling conditions. Further, because the alloy material of the present invention is used for welded structures and the like, as mentioned above, it is necessary to increase the yield stress to 240 MPa or more. From this viewpoint, in the case or performing a heat treatment after hot rolling, preferably the holding temperature is set to 950° C. or less.

[0140] Thereafter, that is, after the cooling process after hot working, or after the cooling process in a heat treatment, leveler straightening may be performed to correct warping or the like of the alloy material. The leveler straightening is preferably performed within a range that does not significantly change the characteristics of the alloy material, and for example, the leveler straightening is preferably performed under conditions so that the increase in yield stress (0.2% proof stress) at ordinary temperature becomes a value that is 3 MPa or more and 50 MPa or less.

Example 1

[0141] Alloys having the chemical compositions shown in Tables 1 and 2 were melted using a vacuum furnace, and depending on the plate thickness of the final product (alloy material), 17-kg flat steel ingots having a wall thickness of 48 mm or 50-kg square steel ingots having a wall thickness of 110 mm were obtained.

[0142] For examples in which the plate thickness of the final product was to be 20 mm or less, the surface of the 17-kg flat steel ingot having a wall thickness of 48 mm was cut to obtain a rolling starting material having a thickness of 44 mm, and the rolling starting material was subjected to hot rolling to prepare a hot-rolled alloy plate having a thickness of 4 mm to 20 mm. On the other hand, for examples in which the plate thickness of the final product was to be 40 mm and examples in which the plate thickness was to be 80 mm, the 50-kg square steel ingot having a wall thickness of 110 mm was subjected to hot forging to obtain a rolling starting material having a plate thickness of 100 mm or a plate thickness of 160 mm, and these rolling starting materials were subjected to hot rolling to prepare hot-rolled alloy plates which had a plate thickness of 40 mm or a plate thickness of 80 mm. Some of the obtained hot-rolled alloy plates were allowed to cool temporarily to room temperature, and thereafter a heat treatment in which the hot-rolled alloy plates were held at various temperatures was performed, and the hot-rolled alloy plates were then cooled by water spraying under various conditions. Further, the remainder of the obtained hot-rolled alloy plates were cooled as they were by water spraying or the like.

[0143] For the examples for which a heat treatment was performed, a hole was formed from a side face of the hot-rolled alloy plate toward the center of the plate thickness, and the heat treatment was performed in a state in which a thermocouple was inserted into the hole, and thereafter the hot-rolled alloy plate was cooled to 300° C. or less while measuring the temperature at the central part of the plate thickness of the hot-rolled alloy plate. Note that, the water temperature of cooling water used for spray cooling was within the range of 20 to 25° C. With regard to the water amount density ejected onto the hot-rolled alloy plates, the cooling water amount was changed to various amounts by controlling the pressure of the cooling water supply device to thereby adjust the water amount density per unit time (min) and unit area.

[0144] FIG. 1 illustrates the relation between the plate thickness of a hot-rolled alloy plate and a water amount density (m.sup.3/m.sup.2.Math.min) for making the cooling rate at the central part of the plate thickness of the hot-rolled alloy plate 2.0° C./s or more. As illustrated in FIG. 1, when the plate thickness of the hot-rolled alloy plate is represented by t (mm), in order to make the cooling rate at the central part of the plate thickness of the hot-rolled alloy plate 2.0° C./s or more it is necessary to eject cooling water at a temperature of 35° C. or less in a manner so that the water amount density (m.sup.3/m.sup.2.Math.min) is [0.11 In(t)+0.02] or more. Further, straightening was performed for some of the hot-rolled alloy materials. The various production conditions are shown in Table 3. Note that, the term “Plate Thickness” in Table 3 refers to the plate thickness of the hot-rolled alloy plate. Note that, a water amount density of 0.00 indicates that water-cooling was not performed.

TABLE-US-00001 TABLE 1 Alloy Chemical Composition (in mass %; balance is Fe and unavoidable impurities) Number C Si Mn P S Cr Ni Cu Co Mo 1 0.031 0.19 0.26 0.005 0.0005 0.012 36.0 0.018 0.021 0.013 2 0.012 0.21 0.31 0.003 0.0004 0.032 36.0 0.006 0.025 0.008 3 0.028 0.18 0.30 0.006 0.0006 0.045 35.8 0.032 0.016 0.011 4 0.024 0.13 0.13 0.009 0.0008 0.12  35.7 0.28  0.15  0.17  5 0.027 0.18 0.25 0.007 0.0007 0.32  36.1 0.032 0.022 0.008 6 0.029 0.16 0.28 0.005 0.0003 0.011 35.7 0.023 0.017 0.012 7 0.023 0.26 0.08 0.006 0.0004 0.018 35.4 0.025 0.38  0.021 8 0.031 0.15 0.29 0.005 0.0003 0.024 36.2 0.022 0.21  0.23  9 0.032 0.15 0.28 0.005 0.0004 0.023 36.2 0.023 0.22  0.023 10 0.053 0.14 0.29 0.005 0.0003 0.025 36.2 0.024 0.21  0.15  11 0.065 0.16 0.12 0.006 0.0008 0.013 36.0 0.007 0.14  0.018 12 0.028 0.16 0.26 0.006 0.0007 0.14  36.0 0.024 0.13  0.009 13 0.029 0.17 0.27 0.005 0.0008 0.009 35.9 0.032 0.12  0.010 14 0.12  0.18 0.26 0.007 0.0004 0.004 36.0 0.004 0.003 <0.001   15 0.031 0.18 0.26 0.006 0.0005 0.022 36.0 0.022 0.018 0.005 16 0.021 0.12 0.27 0.005 0.0005 0.003 36.1 0.019 0.022 0.012 17 0.011 0.19 0.25 0.005 0.0007 0.019 35.9 0.003 0.019 <0.001   18 0.013 0.18 0.26 0.004 0.0005 0.020 35.8 0.002 0.020 0.013 19 0.008 0.03 0.21 0.004 0.0005 0.008 35.9 0.006 0.025 0.005 Alloy Chemical Composition (in mass %; balance is Fe and unavoidable impurities) Number Al Nb Ta B Ca Mg REM 1 0.0006 0.001 <0.001 <0.0001   <0.0001 <0.0001 <0.001 2 0.0009 0.024 <0.001 0.0002 <0.0001 <0.0001 <0.001 3 0.0008 0.122 0.52 0.0012 <0.0001 <0.0001 <0.001 4 0.035 0.31  0.015 0.0013 <0.0001 <0.0001 <0.001 5 0.0014 0.48  <0.001 0.0025 <0.0001 <0.0001 <0.001 6 0.0012 0.015 <0.001 0.0021 <0.0001 <0.0001 <0.001 7 0.0021 0.018 <0.001 <0.0001   <0.0001 <0.0001 <0.001 8 0.0016 0.015 <0.001 0.0001 0.0003 0.0003 <0.001 9 0.032 0.016 <0.001 0.0012 0.0021 <0.0001 0.021 10 0.0035 0.29  0.12 0.0024 0.0005 0.0012 <0.001 11 0.023 0.53  <0.001 0.0025 <0.0001 <0.0001 <0.001 12 0.0013 0.019 <0.001 0.0008 0.0017 <0.0001 <0.001 13 0.0014 0.022 <0.001 0.0006 <0.0001 <0.0001 0.018 14 0.0012 <0.001   <0.001 <0.0001   <0.0001 <0.0001 <0.001 15 0.023 1.20  <0.001 0.0002 <0.0001 <0.0001 <0.001 16 0.0013 <0.001   <0.001 0.013  <0.0001 <0.0001 <0.001 17 0.033 0.43  <0.001 <0.0001   <0.0001 <0.0001 <0.001 18 0.028 0.001 0.63 <0.0001   <0.0001 <0.0001 <0.001 19 0.0004 0.001 <0.001 <0.0001   <0.0001 <0.0001 <0.001 An underline indicates deviation from the range defined by the present invention, or deviation from a desired characteristic value.

TABLE-US-00002 TABLE 2 Alloy Chemical Composition (in mass %; balance is Fe and unavoidable impurities) Reduction of Number N O Ti Zr Hf V W Sn Zn Pb ΔC ΔNb Δta Area (%) 1 0.0025 0.0012 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 0.031 −0.24 — 80 2 0.0023 0.0031 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 0.009 −0.07 — 78 3 0.0025 0.0039 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 0.012 −0.09   0.10 65 4 0.0011 0.0021 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 −0.016     0.13 −0.35 68 5 0.0008 0.0023 <0.0001 0.0005 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 −0.035     0.27 — 71 6 0.0023 0.0015 0.0003 <0.0001 <0.0001 0.008 <0.001 <0.001 <0.0001 <0.0001 0.027 −0.21 — 82 7 0.0013 0.0008 <0.0001 <0.0001 0.0012 <0.001 0.013 <0.001 <0.0001 <0.0001 0.021 −0.16 — 70 8 0.0023 0.0028 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 0.029 −0.22 — 72 9 0.0025 0.0013 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 0.030 −0.23 — 76 10 0.0063 0.0023 <0.0001 <0.0001 <0.0001 0.013 <0.001 <0.001 <0.0001 <0.0001 0.015 −0.12 −0.68 75 11 0.0026 0.0024 <0.0001 0.0006 <0.0001 <0.001 <0.001 0.003 <0.0001 <0.0001 −0.004     0.03 — 64 12 0.0013 0.0013 0.0015 <0.0001 <0.0001 0.014 0.015 <0.001 0.0008 <0.0001 0.026 −0.20 — 73 13 0.0008 0.0012 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 0.0002 0.026 −0.20 — 74 14 0.0028 0.0032 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 0.120   0.00 — 54 15 0.0027 0.0013 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 −0.125     0.96 — 52 16 0.0026 0.0024 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 0.021 −0.16 — 73 17 0.0029 0.0014 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 −0.045     0.35 — 42 18 0.0024 0.0012 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 0.013 −0.10   0.44 43 19 0.0014 0.0013 <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001 <0.0001 <0.0001 0.008 −0.06 — 80 An underline indicates deviation from the range defined by the present invention, or that the desired performance is not satisfied.

TABLE-US-00003 TABLE 3 Hot Rolling Heat Treatment Straightening End Plate Water Amount Holding Water Amount Cooling Yield Stress Alloy Temperature Thickness Density Temperature Density Rate Yes/ Increase No. Number (° C.) t (mm) (m.sup.3/m.sup.2 .Math. min) (° C.) (m.sup.3/m.sup.2 .Math.min) (° C./s) No (MPa) Inventive 1 1 700 4 — 830 0.25 0.17 132 No 0 Example 2 1 800 6 — 830 0.30 0.22 98 No 0 of 3 1 850 10 — 830 0.75 0.27 52 No 0 Present 4 1 850 20 — 830 0.75 0.35 20 No 0 Invention 5 1 900 40 — 830 0.75 0.43 8 No 0 6 1 900 80 — 830 0.60 0.50 3 No 0 7 1 900 80 — 830 0.50 0.50 2 No 0 8 1 850 10 — 830 0.75 0.27 53 Yes 25 9 1 800 10 — 760 0.75 0.27 50 Yes 25 10 2 850 10 — 830 0.75 0.27 50 No 0 11 3 900 10 — 950 0.75 0.27 49 No 0 12 4 900 10 — 900 0.75 0.27 48 No 0 13 5 900 10 — 950 0.75 0.27 45 No 0 14 6 850 10 — 830 0.75 0.27 49 No 0 15 7 850 10 — 830 0.75 0.27 50 No 0 16 8 800 6 — 830 0.30 0.22 94 Yes 20 17 8 850 10 — 830 0.50 0.27 47 Yes 20 18 8 850 20 — 830 0.50 0.35 18 Yes 20 19 8 900 40 — 830 0.50 0.43 7 Yes 20 20 8 900 80 — 830 0.60 0.50 3 Yes 20 21 9 850 10 — 830 0.50 0.27 50 No 0 22 10  850 10 — 900 0.50 0.27 49 No 0 23 11  850 10 — 950 0.50 0.27 47 No 0 24 12  850 10 — 830 0.50 0.27 49 No 0 25 13  850 10 — 830 0.50 0.27 48 No 0 26 1 800 10 0.35 — 0.27 — Yes 10 27 1 850 10 0.50 — 0.27 — Yes 15 28 1 900 10 0.50 — 0.27 — Yes 20 29 2 900 10 0.35 — 0.27 — Yes 25 30 3 950 20 0.50 — 0.35 — Yes 25 31 4 950 10 0.50 — 0.27 — Yes 25 32 5 950 10 0.50 — 0.27 — Yes 25 33 6 900 10 0.35 — 0.27 — Yes 30 34 7 900 10 0.50 — 0.27 — Yes 30 35 8 800 10 0.50 — 0.27 — Yes 10 36 8 850 20 0.50 — 0.35 — Yes 15 37 8 900 40 0.75 — 0.43 — Yes 20 Comparative 38 14  850 10 — 830 0.30 0.27 40 No 0 Example 39 15  900 40 — 950 0.50 0.43 7 No 0 40 16  850 10 — 830 0.50 0.27 47 No 0 41 17  900 40 — 950 0.00 0.43 <1 No 0 42 18  850 10 — 950 0.50 0.27 46 No 0 43 1 900 40 — 830 0.00 0.43 <1 No 0 44 1 900 40 — 830 0.05 0.43 1 No 0 45 1 900 80 — 830 0.10 0.50 1 No 0 46 8 900 40 — 830 0.00 0.43 <1 No 0 47 8 900 40 — 830 0.05 0.43 1 No 0 48 8 900 80 — 830 0.10 0.50 1 No 0 49 1 850 10 0.00 — 0.27 — Yes 15 50 2 850 10 0.00 — 0.27 — Yes 15 51 19  850 20 0.50 900 0.50 0.35 — No 0 52 1 850 10 — 1000  0.50 0.27 — No 0 An underline indicates deviation from the range of the present invention, deviation from recommended production conditions, or that the desired performance is not satisfied.  denotes calculated value of [0.11 In(t) + 0.02]

[0145] Results obtained by conducting various tests described hereunder on the obtained ingots and hot-rolled alloy materials are shown in Table 4. Note that, with respect to the obtained alloy materials of 3, 10, 13 and 23 that were each an inventive example of the present invention, when the average diameter of NbC was measured, the average diameter was 1 μm or less in each of these alloy materials.

[0146] (Reduction of Area)

[0147] A smooth high-temperature tensile test specimen of 8 mmφ×110 mmL was taken from a near-surface portion of the 17-kg flat steel ingots having a wall thickness of 48 mm or the 50-kg square steel ingots having a wall thickness of 110 mm. A 14 mmL portion at the center part of the test specimen was heated at 1180° C. for 30 seconds by high-frequency heating, and after lowering the temperature to 900° C. and holding at that temperature for 10 seconds, tensile rupture was made to occur at a speed of 20 mm/s, and the contraction of area: reduction of area (%) was measured. The results are shown in Table 1. A case where the reduction of area satisfied the condition of being 60% or more was evaluated as “Good”.

[0148] (Measurement of Curie Temperature)

[0149] An alloy piece having dimensions of 3 mm in thickness×5 mm in width×1 mm in length was cut out from the obtained hot-rolled alloy materials, and the surface was finished with wet-type emery #600 to remove the surface-processed layer and form a test specimen A.

[0150] On the other hand, a test specimen having dimensions of 3 mm in thickness×8 mm in width×12 mnm in length was cut out from the obtained hot-rolled alloy materials by machining, a thermocouple was welded to the surface, and a heat cycle was applied under conditions such that holding at 900° C. for 1 minute, and after cooling rate in a section from 600 to 300° C. is 0.2° C./s. A test specimen having dimensions of 3 mm in thickness×5 mm in width×1 mm in length was cut out by machining from the test specimen to which the heat cycle was applied, and the surface was polished using wet-type emery #600 to remove the surface-processed layer and obtain a test specimen B.

[0151] Using the obtained test specimen A and test specimen B, the plate thickness direction of each test specimen was set to the magnetic field application direction and the longitudinal direction was set to the sample vibration direction by a vibrating sample magnetometer (VSM) capable of raising the specimen temperature, and a temperature change of magnetization was measured in a magnetic field of 40000 A/m (500 Oe). The rate of temperature increase was set to 3° C./min, and the temperature dependence of the magnetization of each sample was measured while increasing the temperature from room temperature to 300° C., and the Curie temperatures T.sub.0 and T.sub.1 were determined based on the temperature at which the magnetization disappeared. Note that, T.sub.0 represents the Curie temperature (° C.) of each of the various kinds of alloy materials, and T.sub.1 represents the Curie temperature (° C.) of each of the various kinds of alloy materials after the respective alloy materials were held at 900° C. for 1 minute and thereafter cooled under conditions such that the average cooling rate at the central part of the plate thickness of the alloy material in the temperature range from 600 to 300° C. was 0.2° C./s.

[0152] FIG. 2 is a view illustrating a temperature change of magnetization (relative magnetization with respect to room temperature and inverse of magnetization) in the alloy material of alloy number 1. As illustrated in FIG. 2, the Curie temperatures T.sub.0 and T.sub.1 were determined by extrapolating the temperature at which the magnetization disappears from a curve of the relative magnetization with respect to room temperature. That is, in this example, based on the point of intersection between an extension line of a portion that linearly decreases with increasing temperature and a straight line representing that the relative magnetization with respect to room temperature is zero, the Curie temperature (described as “Tc” in FIG. 2) was taken as 244° C. Table 2 shows the Curie temperatures T.sub.0 and T.sub.1 and the difference between these temperatures.

[0153] (Mechanical Strength)

[0154] A tensile test was conducted in the atmosphere at ordinary temperature (20° C.±15° C.) in accordance with JIS Z 2241: 2011, and the tensile strength TS (MPa) and yield stress YS (MPa) were determined. Test specimens in which the YS was 240 MPa or more were evaluated as “Good”. Note that, the yield stress was 0.2% proof stress.

[0155] (Coefficient of Thermal Expansion)

[0156] A test specimen having a shape of 3 mm in diameter×15 mm in length was taken from the central part of the plate thickness of the obtained hot-rolled alloy plate, and the average coefficient of linear expansion from room temperature to −170° C. was determined using a push-rod type thermal dilatometer. Test specimens having an average coefficient of linear expansion of 1.5×10.sup.−6/K or less were evaluated as “Good”.

TABLE-US-00004 TABLE 4 Performance Evaluation 0.2% Coefficient Proof T1 − of Linear Alloy Stress T0 T1 T0 Expansion No. Number (MPa) (° C.) (° C.) (° C.) (×10.sup.−5/K) Inventive 1 1 273 219 244 25 1.0 Examples 2 1 265 220 244 24 1.1 of 3 1 262 221 244 23 1.2 Present 4 1 251 226 244 18 1.2 Invention 5 1 247 230 244 14 1.2 6 1 245 235 244  9 1.2 7 1 244 240 244  4 1.3 8 1 289 220 244 24 1.2 9 1 308 221 244 23 1.2 10 2 267 220 240 20 1.2 11 3 334 212 230 18 1.4 12 4 346 216 235 19 1.3 13 5 385 214 231 17 1.4 14 6 288 220 241 21 1.2 15 7 287 220 239 19 1.2 16 8 372 213 238 25 1.2 17 8 361 214 238 24 1.2 18 8 355 219 238 19 1.2 19 8 351 225 238 13 1.3 20 8 344 230 238  8 1.4 21 9 294 216 240 24 1.2 22 10  352 212 234 22 1.3 23 11  403 211 228 17 1.5 24 12  287 218 240 22 1.2 25 13  290 219 240 21 1.2 26 1  10 225 244 19 1.2 27 1  15 224 244 20 1.2 28 1  20 223 244 21 1.2 29 2  25 223 240 17 1.2 30 3  25 213 230 17 1.4 31 4  25 218 235 17 1.3 32 5  25 217 231 14 1.4 33 6  30 223 241 18 1.2 34 7  30 222 239 17 1.2 35 8  10 218 238 20 1.2 36 8  15 217 238 21 1.2 37 8  20 216 238 22 1.2 Comparative 38 14  374 219 235 16 1.6 Example 39 15  415 233 236 10 1.8 40 16  225 222 238 16 1.7 41 17  352 237 238  1 1.6 42 18  364 218 235 17 1.6 43 1 247 243 244  1 1.6 44 1 247 243 244  1 1.6 45 1 245 243 244  1 1.6 46 8 331 237 238  1 1.7 47 8 331 237 238  1 1.7 48 8 329 237 238  1 1.7 49 1 365 243 244  1 1.6 50 2 358 239 240  1 1.6 51 19  223 223 242 19 1.2 52 1 215 225 244 19 1.3 An underline indicates deviation from the range of the present invention, deviation from recommended production conditions, or that the desired performance is not satisfied.

[0157] As shown in Table 4, Examples 1 to 37 which satisfied all the conditions of the present invention were evaluated as “Good” with respect to each of reduction of area, strength, and coefficient of linear expansion. In contrast, Examples 38 to 52 which did not satisfy conditions of the present invention were poor with respect to at least performance regarding the coefficient of linear expansion.

INDUSTRIAL APPLICABILITY

[0158] According to the present invention, an alloy material that can increase the degree of freedom with respect to welding workability when producing a welded structure using the alloy material while maintaining low thermal expansion characteristics, and a method for producing the alloy material can be provided at a low cost. The alloy material of the present invention, for example, can suppress deformation caused by a temperature change from room temperature to a cryogenic temperature in a structure in a cryogenic environment or the like, and can also improve welding workability when produced as piping or as a structure.