JP6104445B1 - Preparation method and characteristic evaluation method of metal material characteristic evaluation sample - Google Patents

Abstract

A method for producing a metal material property evaluation sample and a property evaluation method capable of more appropriately evaluating the thermal degradation of the metal material. A method for producing a sample for evaluating characteristics of a metal material includes a step of heat-treating the metal material so that work hardening of the metal material is recovered, and a step of determining a cooling rate threshold value of the heat-treated metal material. And cooling the heat-treated metal material at a cooling rate equal to or lower than the threshold value in at least a part of the temperature range, and forming a sample for characteristic evaluation, and determining the threshold value, Heat treating a plurality of samples made of a metal of the same material as the metal material, cooling the plurality of samples after the heat treatment under a plurality of cooling rates, respectively, and cooling rate and conductivity of the sample after cooling From the correlation with the index, the cooling rate is smaller than the first range of the cooling rate, and the absolute value of the slope of the conductivity index with respect to the cooling rate is smaller than the first range. The cooling rate of the second range of serial cooling rate is determined as the threshold value. [Selection] Figure 3

Description

  The present disclosure relates to a method for producing a sample for property evaluation of a metal material and a property evaluation method.

  In general, metal materials such as alloys change in properties such as crystal structure according to the thermal history. Therefore, for metal products that are used under special conditions such as high temperature and for a long time, the material properties are evaluated in consideration of changes in the properties of the metal materials before and after the use of the metal products under those conditions.

  For example, a metal cask for transporting or storing spent fuel is transported to a reprocessing facility or the like after storing spent nuclear fuel therein for a long period (for example, 60 years). That is, the metal cask and its structural members are exposed to heat due to the decay heat of the spent nuclear fuel (heating element) over a long period of storing the spent fuel. For such a metal cask, for example, when performing safety evaluation when the cask falls during transportation, a sample simulating the property change such as thermal deterioration of the component due to long-term heat exposure during actual use is used. The soundness evaluation (material characteristic evaluation) of the cask constituent member is performed.

  For example, Non-Patent Document 1 describes a component of a metal cask (for example, an aluminum alloy basket) at a temperature at which the component is exposed to heat (for example, 200 ° C.) or slightly higher (for example, 250 ° C.). ) For a long time (for example, 10,000 hours), and then a material property evaluation (for example, a strength test) is performed on the sample.

  Further, in Patent Document 1, in order to more appropriately simulate a thermal deterioration phenomenon such as coarsening of precipitates that may occur in an actual product such as a metal cask, a state of supersaturated solid solution is avoided after heat-treating the metal material. While cooling the additive component, etc. while cooling it at a cooling rate that can accelerate the coarsening of the precipitate, that is, the slope of the conductivity index with respect to the cooling rate is below a predetermined value, for material property evaluation It is described that a sample is prepared.

Japanese Patent No. 5960335

The Japan Society of Mechanical Engineers, "Spent Fuel Storage Facility Standard, Metal Cask Structure Standard 2007 Edition", published in February 2008

With the preparation method disclosed in Patent Document 1, it is expected that a sample simulating a thermal deterioration phenomenon that can occur in an actual product can be prepared.
However, as a result of intensive studies by the present inventors, it is clear that depending on the chemical composition of the metal material, there can be multiple cooling rate ranges in which the slope of the conductivity index of the metal material cooled after the heat treatment becomes relatively small. became. Therefore, as described in Patent Document 1, if the threshold value of the cooling rate determined only under the condition that the slope of the conductivity index with respect to the cooling rate is equal to or less than a predetermined value, an appropriate material property evaluation is not necessarily performed. It may be impossible to do this.

  In view of the above circumstances, at least one embodiment of the present invention aims to provide a method for producing a metal material property evaluation sample and a property evaluation method, which can more appropriately evaluate the thermal degradation of the metal material. To do.

(1) A method for producing a sample for evaluating characteristics of a metal material according to at least one embodiment of the present invention includes:
Heat treating the metal material so that work hardening of the metal material is restored;
Determining a cooling rate threshold for the heat treated metal material;
Cooling the heat-treated metal material at a cooling rate equal to or lower than the threshold in at least a part of the temperature range, and forming a sample for characteristic evaluation,
Determining the threshold comprises:
Heat treating a plurality of samples made of the same metal as the metal material;
Cooling the plurality of samples after heat treatment under a plurality of cooling rates,
From the correlation between the cooling rate and the conductivity index of the sample after cooling, the cooling rate is smaller than the first range of the cooling rate, and the absolute value of the slope of the conductivity index with respect to the cooling rate is Determining a cooling rate in a second range of the cooling rate smaller than the first range as the threshold value.

As a result of intensive studies by the inventor, depending on the chemical composition of the metal material (for example, when the content of impurities in the alloy is low), the slope of the conductivity index of the metal material cooled after the heat treatment is relatively slow. It is clear that there is a range that shows a substantially constant value in a region where the value is large, and once the cooling rate is further reduced, it increases once, and then the slope starts to decrease and converges to a substantially constant value. It was. In this case, the inclination can be a relatively small value even in a cooling rate range larger than the cooling rate range in which the inclination converges to a substantially constant value.
Therefore, when the cooling rate threshold value determined only under the condition that the slope of the conductivity index with respect to the cooling rate is equal to or less than the predetermined value is adopted, the cooling rate is larger than the cooling rate range in which the slope converges to a substantially constant value. There is a possibility that the threshold value is erroneously determined. Then, using the cooling rate of the region where the cooling rate is relatively high as a threshold value, when the heat-treated metal material is cooled at a cooling rate less than the threshold value, supersaturated solid solution of additive components occurs in the metal material, or precipitates There is a possibility that the thermal deterioration phenomenon that may occur in the actual product cannot be simulated as intended, such as the coarsening of the product does not proceed sufficiently. If the metal material obtained in this way is used, it may not always be possible to perform an appropriate material property evaluation.

In this regard, according to the above method (1), the slope of the conductivity index with respect to the cooling rate is the first in the region where the cooling rate is smaller than the first range where the slope of the conductivity index with respect to the cooling rate is relatively large. A cooling rate in the second range smaller than the first range is determined as a threshold value. Thereby, even in the region of the cooling rate where the cooling rate is larger than the first range, even when there is a cooling rate range (third range) where the slope of the conductivity index with respect to the cooling rate is relatively small, The cooling rate in the second range in which the inclination converges substantially constant can be appropriately set as the threshold value.
Therefore, by cooling the metal material after the heat treatment at a cooling rate below the threshold, it is possible to obtain a sample for characteristic evaluation in which the metal material is cooled in a state close to an equilibrium state at each temperature during cooling. Can do. That is, in the sample for characteristic evaluation, it is possible to precipitate the added components and the like while avoiding the supersaturated solid solution state, and to sufficiently advance the coarsening of the precipitate. Therefore, according to the above method (1), it is possible to more reliably perform the evaluation of the characteristics of the metal material in consideration of the thermal degradation that may occur during the long period of use of the actual product.

(2) In some embodiments, in the method of (1) above,
In the step of determining the threshold value,
When the content of impurities contained in the metal material is equal to or less than a specified value, the cooling rate in the second range is determined as the threshold value.

As a result of intensive studies by the inventor, when the impurities contained in the metal material are relatively small, as the cooling rate is reduced, the slope of the conductivity index of the metal material cooled after the heat treatment once increases and then the slope decreases. It became clear that there was a case where it converged to an almost constant value. In this case, the inclination can be a relatively small value even in a cooling rate range larger than the cooling rate range in which the inclination converges to a substantially constant value.
This is considered to be due to the following reason. That is, compared with a metal material having a relatively large impurity element content, a metal material having a relatively small amount of impurities has a relatively small content of an impurity element serving as a nucleus for precipitation of an additive component. For this reason, the additive component contained in the metal material heat-treated in the heat treatment step is relatively difficult to precipitate when the metal material is cooled. In addition, as the cooling rate increases, it is more difficult to cool the metal material heat-treated in the heat treatment step while maintaining the equilibrium state, and the additive components contained in the metal material are less likely to precipitate.
In this regard, according to the above method (2), when the content of impurities contained in the metal material is equal to or lower than the specified value, the heat-treated metal sample is cooled at a rate equal to or lower than the cooling rate in the second range. To do. Therefore, when the content of impurities contained in the metal material is not more than the specified value, the additive components and the like are more reliably precipitated while avoiding the supersaturated solid solution state, and the precipitate is sufficiently coarsened. A sample for property evaluation in an advanced state can be obtained.

(3) In some embodiments, in the method of (2) above,
The metal material is an aluminum alloy containing at least one of magnesium or manganese as an additive component,
In the step of determining the threshold value,
When the content of the impurity, which is a component other than the magnesium and the manganese, is 0.8% by mass or less, the cooling rate in the second range is determined as the threshold value.

According to the inventor's knowledge, in the aluminum alloy containing magnesium or manganese, when the content of impurities other than magnesium and manganese is 0.8% by mass or less, as described above, the inclination is almost equal. Even in a cooling rate range larger than the cooling rate range that converges to a constant value, the slope can be a relatively small value. As a result, when the cooling rate threshold value determined only under the condition that the slope of the conductivity index with respect to the cooling rate is equal to or less than the predetermined value is adopted, the cooling rate is larger than the cooling rate range in which the slope converges to a substantially constant value. May be erroneously determined as a threshold value.
In this regard, according to the method of (3) above, the cooling rate in the second range is determined as the threshold when the content of the impurity is 0.8% by mass or less. It is possible to obtain a sample for characteristic evaluation in a state where the additive components and the like are precipitated while avoiding the state and the coarsening of the precipitate has sufficiently progressed.

(4) In some embodiments, in any of the above methods (1) to (3),
In the step of determining the threshold value, a cooling rate at which an absolute value of the slope of the conductivity index with respect to the cooling rate is equal to or less than a predetermined value among the cooling rates belonging to the second range is determined as the threshold value.

According to the above method (4), the cooling rate at which the absolute value of the gradient is equal to or less than a predetermined value among the cooling rates belonging to the second range is determined as a threshold value. Even when there are variations in absolute values, the threshold value of the cooling rate can be set appropriately.
As a result, it is possible to obtain a characteristic evaluation sample in which the metal material is cooled in a state close to an equilibrium state at each temperature during cooling. Therefore, in the characteristic evaluation sample, an additive component is avoided while avoiding a supersaturated solid solution state. Etc. can be deposited. In addition, since the metal material is cooled at a cooling rate equal to or less than the threshold value determined as described above, it is possible to obtain a sample for property evaluation in a state in which the coarsening of the precipitate has sufficiently progressed. Therefore, according to the above method (4), it is possible to perform the characteristic evaluation of the metal material sufficiently considering the thermal degradation that can occur in the long-term use period of the actual product.

(5) In some embodiments, in the above methods (1) to (4),
The conductivity index of the sample is at least one of conductivity, electrical resistance, or thermal conductivity of the sample.

  According to the method of (5) above, the threshold value of the cooling rate of the metal material is determined using at least one of general conductivity, electrical resistance, or thermal conductivity as the conductivity index indicating the conductivity of the metal material. be able to. By cooling the metal material at a cooling rate equal to or lower than the threshold value determined in this manner, a sample for characteristic evaluation capable of more appropriate evaluation can be produced.

(6) The metal material property evaluation method according to at least one embodiment of the present invention includes:
Creating the characteristic evaluation sample by the method according to any one of (1) to (5) above;
Performing the material property evaluation of the metal material using the obtained sample for property evaluation;
Is provided.

According to the method of (6) above, the slope of the conductivity index with respect to the cooling rate is smaller than that of the first range in the cooling rate region where the cooling rate is smaller than the first range where the slope of the conductivity index with respect to the cooling rate is relatively large. The cooling rate in the second range that is also smaller is determined as the threshold value. As a result, even in a cooling rate region where the cooling rate is higher than the first range, even if there is a cooling rate range in which the slope of the conductivity index with respect to the cooling rate is relatively small, the slope is substantially constant. It is possible to appropriately set the cooling rate of the second range that converges as a threshold value.
Therefore, by cooling the metal material after the heat treatment at a cooling rate below the threshold, it is possible to obtain a sample for characteristic evaluation in which the metal material is cooled in a state close to an equilibrium state at each temperature during cooling. Can do. That is, in the sample for characteristic evaluation, it is possible to precipitate the added components and the like while avoiding the supersaturated solid solution state, and to sufficiently advance the coarsening of the precipitate. Therefore, according to the method (6), it is possible to more reliably evaluate the characteristics of the metal material in consideration of the thermal degradation that may occur in the actual product over a long period of use.

  According to at least one embodiment of the present invention, there are provided a method for producing a metal material property evaluation sample and a property evaluation method, which can more appropriately evaluate the thermal degradation of the metal material.

It is a flowchart which shows the outline | summary of the preparation methods of the sample for the characteristic evaluation of the metal material which concerns on one Embodiment. It is a figure which shows the time change of the temperature of a metal material in the preparation process of the sample for the characteristic evaluation of the metal material which concerns on one Embodiment. It is a figure which shows the flow of the step (S3) which determines the threshold value of the cooling rate of the metal material after heat processing. It is a figure which shows a part of state diagram of a certain aluminum alloy in simulation. It is a figure which shows an example of the correlation of the cooling rate and the electrical conductivity of the sample after cooling about the sample formed from a certain metal material. It is a figure which shows an example of the correlation of the cooling rate and the electrical conductivity of the sample after cooling about the sample formed from a certain metal material. It is a figure which shows an example of the correlation with a cooling rate and the electrical conductivity of the sample after cooling about the sample for cooling rate examination formed from the aluminum alloy from which content of an impurity differs.

  Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. Absent.

  First, an outline of a method for producing a metal material property evaluation sample according to an embodiment will be described. FIG. 1 is a flowchart showing an outline of a method for producing a sample for evaluating characteristics of a metal material according to an embodiment. Moreover, FIG. 2 is a figure which shows the time change of the temperature of a metal material in the preparation process of the sample for the characteristic evaluation of the metal material which concerns on one Embodiment. In the graph of FIG. 2, the horizontal axis represents time t, and the vertical axis represents the temperature T of the metal material.

As shown in FIG. 1, in the method for producing a metal material property evaluation sample (hereinafter, also simply referred to as “evaluation sample”) according to an embodiment, first, the metal material to be evaluated is formed into the shape of the evaluation sample. Mold (S1). In the figure shown in FIG. 2, the molding temperature in step S1 is _TF . Further, the determined heat treatment conditions including a heat treatment temperature T _H at the heat treatment of a metallic material molded to the sample after in step S4 (S2), at the time of cooling the metal material after the heat treatment in step S5 A threshold _Cth of the cooling rate for determining the cooling condition is determined (S3). Then, the metal material molded in step S1 is heat-treated under the heat treatment conditions determined in step S2 (S4), and then the metal material is cooled at a cooling rate equal to or lower than the threshold value _Cth determined in step S3 to obtain an evaluation sample. (S5). In FIG. 2, a heat treatment of metal material in the heat treatment temperature T _H in step S4, the temperature change of the metal material when cooling the metallic material at a constant cooling rate from the annealing temperature T _H to room T _R at step S5 It is shown.

Steps S2 and S3 for determining the heat treatment conditions and the cooling rate threshold are performed before steps S4 and S5 for heat treating and cooling the metal material, respectively, and the metal material is formed into a sample shape. As long as steps S4 and S5 for heat-treating and cooling the formed metal material are performed in this order, the order in which steps S1 to S5 are performed is not limited to the above. For example, step S2 for determining the heat treatment condition of the metal material or step S3 for determining the threshold value of the cooling rate may be performed prior to step S1 of forming the metal material.
Hereinafter, each of the above-described steps S1 to S5 will be described in more detail.

In step S1 of forming the metal material, the metal material to be evaluated is formed into a sample shape (for example, the same shape as the actual product).
The method for forming the metal material into the sample shape is not particularly limited, and the actual material may be formed using the same conditions and method. For example, the metal material may be formed into a sample shape by a method such as extrusion molding, injection molding, casting or forging.
The temperature T _F (see FIG. 2) at the time of molding the metal material differs depending on the material metal and the molding method. For example, when an aluminum alloy is formed by extrusion, the metal material may be formed into a sample shape by extruding the aluminum alloy at a temperature of about 450 ° C. to 550 ° C., for example.

In step S2 for determining the heat treatment condition of the metal material, the heat treatment including the temperature (heat treatment temperature T _H ) and time (heat treatment time t _H ) when the metal material formed into the sample shape in step S1 is heat treated in the subsequent step S4. Determine the conditions.

When the actual product is used, when it is exposed to heat for a long time, the work hardening is recovered and the transition (strain) is released. At this time, the transition becomes a nucleus and a recrystallized structure is generated. In step S2, a temperature capable of generating such recrystallization texture in the metal material, is determined as the heat treatment temperature T _H.

In step S2, a plurality of heat treatment temperature examination samples (hereinafter simply referred to as “temperature examination samples”) made of the same metal material as the metal material formed in step S1 are prepared. A temperature examination sample is heat-treated under a plurality of heat treatment conditions having different heat treatment temperatures, and an appropriate heat treatment temperature _TH is determined by observing the metal structure of each temperature examination sample formed by the heat treatment. Also good.

The heat treatment temperature T _H can be temperature near (molding temperature or the actual products) molding temperature of the metal material in step S1. During actual product use, it is not normally assumed that the product will be exposed to a temperature higher than the molding temperature. However, if the actual product is actually subjected to heat treatment, the metal material will be heat-treated at a temperature that greatly exceeds the temperature in the thermal history. As a result, the structure of the metal material may be different from the structure obtained by the actual thermal history. On the other hand, the structure after heat treatment may not be stabilized at a temperature lower than the molding temperature of the actual metal material (or actual product). Metal Thus, by setting the temperature near the molding temperature of the metal material (or actual products) and heat treatment temperature T _H, it is possible to perform the heat treatment in consideration of the actual thermal history, which after heat treatment the tissue is stabilized A sample can be obtained.
For example, if the molding temperature of the metal material in step S1 is 500 ° C., a temperature in the range of 400 ° C. to 600 ° C. may be the heat treatment temperature _{T H.}

The heat treatment temperature T _H is the temperature at the time of use of the real product (for example, in the case of baskets metal cask formed of aluminum alloy 200 about ° C.) may be a temperature higher than the. Such temperature by heat treatment at a heat treatment temperature T _H, the relatively restoration work hardening that occurs during prolonged low temperature when using the actual product can give a shorter time to occur.

The heat treatment temperature T _H can be a temperature lower than the temperature at which abnormal grain growth occurs. When the metal material is heat-treated at such a high temperature that abnormal grain growth occurs, the recrystallized structure that may be obtained as a result of heat exposure in the actual product is broken in the metal material. Therefore, the heat treatment is performed at the abnormal grain growth occurring low heat treatment temperature than the temperature T _H, as described above, it is possible to obtain a metal material in a state in which recrystallization structure is not broken should give the actual product .

Step S2 determines the heat treatment conditions of the metal material, as the heat treatment conditions for the heat treatment in step S4 after the metal material, in addition to the heat treatment temperature T _H, may determine the heat treatment time t _H. In this case, by heat-treating the metal material at the heat-treatment temperature _TH , the time during which the recrystallized structure that would be generated by long-time heat exposure during the use of the actual product is sufficiently generated in the metal material is heat-treated. Determine as time t _H.
For example, a plurality of temperature studied sample, based on a result of the heat treatment each under different heat treatment conditions heat treatment time from one another, to determine the heat treatment time that is suitable for heat treatment of the metal sample in step S4 as the heat treatment time t _H May be.
Alternatively, when experienced by a known time required for the heat treatment may be determined such time as the heat treatment time t _H.

The heat treatment temperature T _H and the heat treatment time t _H determined in this way are also used as heat treatment conditions when heat-treating the cooling rate examination sample (sample) in Step S3 described later.

FIG. 3 is a diagram showing the flow of step S3 for determining the threshold value _Cth of the cooling rate of the metal material after the heat treatment. In step S3, the threshold value _Cth of the cooling rate when the metal material heat-treated in step S4 is cooled in the subsequent step S5 is determined.

In step S3 for determining the threshold _Cth of the cooling rate of the metal material after the heat treatment, first, a plurality of cooling rate examination samples (samples) made of the same metal as the metal material are heat-treated (S302).
The heat treatment conditions at this time may be heat treatment conditions including the heat treatment temperature T _H and / or the heat treatment time t _H determined in step S2. By heat-treating the metal material under such a heat treatment condition, a sample in which the recovery of work hardening progresses and a recrystallized structure is generated can be obtained.

Next, the plurality of cooling rate examination samples heat-treated in S302 are respectively cooled under the plurality of cooling rates (S304), and the cooling rate in step S304 and the conductivity index of the cooling rate examination sample after cooling are determined. A correlation is obtained (S306). In step S306, a conductivity index at a specified temperature (for example, room temperature) is acquired for each of the cooling rate examination samples after cooling, and a correlation between the cooling rate and the conductivity index is acquired based on the conductivity index. To do.
And based on this correlation, threshold value _Cth of the cooling rate at the time of cooling a metal material by step S5 is determined (S308). That is, in S308, the cooling rate is smaller than the first range of the cooling rate examination sample, and the second range of the cooling rate in which the absolute value of the slope of the conductivity index with respect to the cooling rate is smaller than the first range. _Is determined as the cooling rate threshold C _th used in step S5.

The conductivity index of the cooling rate examination sample is an index indicating the conductivity of the cooling rate examination sample.
The conductivity of the sample for examining the cooling rate has a correlation with the solid solution amount of the additive component (for example, additive component in the alloy) contained in the sample. The greater the solid solution amount of the additive component in the sample, the greater the electrical resistance. Increases the conductivity and conductivity index. That is, the conductivity index of the cooling rate examination sample is an index indicating the solid solution amount of the additive component.
Therefore, by obtaining the correlation between the cooling rate of the cooling rate examination sample and the conductivity index in step S306, the correlation between the cooling rate and the solid solution amount can be grasped.
As the conductivity index of the cooling rate examination sample, for example, at least one of the conductivity, electrical resistance, and thermal conductivity of the cooling rate examination sample can be used.

Here, FIG. 4 is a diagram schematically showing a part of a phase diagram of an aluminum alloy. In the state diagram of FIG. 4, the horizontal axis represents the chemical composition of the aluminum alloy, aluminum is 100% at the origin, the aluminum content decreases and the additive component content increases in the positive direction. . In the state diagram of FIG. 4, the vertical axis represents the temperature T. In the state diagram of FIG. 4, the curves passing through the points K, M, and N are solid lines, and the curves passing through the points M, Q, S, and T are curves L (solid solution lines) indicating the solid solubility limit. .
5 and 6 are examples of the correlation between the cooling rate and the conductivity of the sample after cooling, which are obtained by performing the above steps S302 to S306 for a sample formed from a certain metal material. FIG.

If the cooling rate of the sample for examining the cooling rate is relatively large, the sample is cooled while maintaining the state of the structure in the equilibrium state at a high temperature before cooling, so that the additive component in the sample is in a supersaturated solid solution state. Cheap. Referring to FIG. 4, for example, an aluminum alloy chemical compositions is in the state of point P X ₁ (solid solution), when quenched in a relatively large cooling rate, the point U through the point Q supersaturation It moves toward the state of solid solution.
On the other hand, if the cooling rate is relatively low, the sample is cooled while approaching the equilibrium state at each temperature during cooling, so that the supersaturated solid solution state of the additive component is relaxed in the sample, and the precipitation of the additive component is prevented. move on. Referring to FIG. 4, for example, the curve showing the aluminum alloy is a chemical component composition of the point P of X ₁ state (solid solution), when gradually cooled at a sufficiently small cooling rate, the solubility limit from the point Q The state shifts toward the point S while maintaining a state close to the equilibrium state along.
By making the cooling rate sufficiently low, the sample can be brought close to the equilibrium state at each temperature during cooling. In this case, even if the cooling rate is further reduced, solid solution and precipitation occur in the sample after cooling. Since no significant change appears in this state, the conductivity index of the sample after cooling hardly changes. That is, the absolute value of the slope of the conductivity index with respect to the cooling rate is small.

  For example, as shown in FIG. 5, in the first range of the cooling rate with a relatively high cooling rate, the conductivity increases as the cooling rate decreases, so the slope of the conductivity with respect to the cooling rate is relatively large. This is because in the first range, as the cooling rate is reduced, the sample can be cooled in a state closer to the equilibrium state, and the precipitation of the additive component can be further advanced. On the other hand, in the second range where the cooling rate is relatively small, even when the cooling rate is reduced, the conductivity hardly changes and the absolute value of the slope of the conductivity is small. Therefore, if the sample is cooled at the cooling rate in the second range, the sample can be cooled while the sample is sufficiently close to the equilibrium state at each temperature during cooling.

  Here, as a result of intensive studies by the present inventors, depending on the chemical composition of the metal material, there is a range in which the slope of the conductivity index of the metal material cooled after the heat treatment shows a substantially constant value in a region where the cooling rate is relatively high. It has been found that as the cooling rate is further decreased and the cooling rate is further decreased, the gradient is once decreased and then the gradient is decreased to converge to a substantially constant value. In this case, the slope of the conductivity index can be a relatively small value even in a cooling speed range larger than the cooling speed range (the second range described above) in which the slope of the conductivity index converges to a substantially constant value. That is, as shown in FIG. 6, the conductivity index does not change much with respect to the cooling rate not only in the second range where the cooling rate is lower than the first range, but also in the region where the cooling rate is higher than the first range. There may be a third range in which the slope of the conductivity index is smaller than the first range.

  Accordingly, when the threshold value of the cooling rate determined only under the condition that the gradient of the conductivity index with respect to the cooling rate is equal to or less than the predetermined value is adopted as the cooling rate in step S5, the cooling in which the conductivity index gradient converges to a substantially constant value. There is a possibility that a cooling rate (cooling rate in the third range) larger than the speed range (second range) is erroneously determined as a threshold value. And using the cooling rate of the region (third range) where the cooling rate is relatively high as a threshold, the heat-treated metal material is cooled at a cooling rate (for example, the cooling rate belonging to the third range or the first range) below the threshold. When cooled, there is a possibility that the thermal degradation phenomenon that may occur in the actual product cannot be simulated as intended, such as supersaturated solid solution of the additive component in the metal material, or the coarsening of the precipitate does not proceed sufficiently. If the metal material obtained in this way is used, it may not always be possible to perform an appropriate material property evaluation.

Therefore, small cooling rate than the first range and the cooling rate belonging to the second range has a small absolute value of the slope of the conductivity indication than the first range determined as a threshold C _th, following cooling the threshold C _th By cooling the metal material at step S5 at a speed, the metal material can be cooled in a state close to the equilibrium state at each temperature during cooling, and the added components and the like are precipitated while avoiding a supersaturated solid solution state. A sample for evaluation in a state of being allowed to be obtained can be obtained.

In order to specify the second range of the cooling rate, in step S304, both the cooling rate of the first range and the cooling rate of the second range are included in the “plurality of cooling rates”. Therefore, the “plural cooling rates” may be selected from a relatively wide range of cooling rates.
Such a range of cooling rates (ie, a range of cooling rates that can include both the first range of cooling rates and the second range of cooling rates) depends on the type of metal material, but for example in the case of an aluminum alloy, the step In S304, the cooling rate examination sample may be cooled under a plurality of cooling rates within a range of 0.1 ° C./h to 10 ° C./h.

In step S4, heat treating the molded metal material in S1 in the heat treatment under conditions including a heat treatment temperature T _H determined in step S2 described above.
In step S5, the metal sample heat-treated in step S4 is cooled at a cooling rate equal to or lower than the threshold value _Cth determined in step S3 in at least a part of the temperature region, and used for evaluation of the characteristics of the metal material. Form.

In step S5, in the entire temperature region, or a portion of the temperature region from the cooling start temperature (e.g. a temperature in the region of the heat treatment temperature T _H) to a cooling end temperature (e.g. room temperature), the threshold C _th following constant determined in step S3 The metal material may be cooled at a cooling rate of In this case, the temperature of the metallic material during cooling the metal material, as shown in FIG. 2, the cooling start temperature (e.g. a temperature in the vicinity of the heat treatment temperature T _H) to a cooling end temperature (eg, room temperature T _R), linear To drop.

Alternatively, in step S5, the metal material may be cooled by appropriately changing the cooling rate within the range of the threshold value _Cth or less.
Alternatively, in step S5, the metal material is cooled at a cooling rate equal to or lower than the threshold value _Cth determined in step S3 in a part of the temperature range (for example, a temperature range including the precipitation temperature of the additive component), In the temperature region, the metal material may be cooled at a cooling rate larger than the threshold value _Cth .

According to the method comprising the steps S1~S5 described above, in step S3 for determining a threshold C _th of the cooling rate of the metallic material, the slope is relatively large first range of conductivity indication of temperature studied sample against cooling rate In the region of the cooling rate where the cooling rate is lower than that, the cooling rate in the second range in which the slope of the conductivity index of the temperature examination sample with respect to the cooling rate is smaller than the first range is determined as the threshold value _Cth . As a result, even in the cooling rate region where the cooling rate is higher than the first range, there exists a cooling rate range (the above-described third range) in which the slope of the conductivity index of the temperature examination sample with respect to the cooling rate is relatively small. Even in this case, the cooling rate in the second range in which the slope of the conductivity index of the temperature examination sample with respect to the cooling rate converges substantially constant can be appropriately set as the threshold value _Cth .
In step S5, the metal material is cooled at a cooling rate equal to or lower than the threshold value _Cth determined in step S3, thereby cooling the metal material in a state close to an equilibrium state at each temperature during cooling. In addition, it is possible to precipitate added components and the like while avoiding a supersaturated solid solution state, and it is possible to obtain a sample for property evaluation in a state where the coarsening of the precipitate has sufficiently progressed. Therefore, by using the sample for property evaluation obtained by the method including the above-described steps S1 to S5, it is possible to perform the property evaluation of the metal material sufficiently considering the thermal degradation that may occur in the long-term use period of the actual product. it can.
For example, when performing a metal cask drop test using an aluminum alloy basket as a constituent member, a drop using an evaluation sample obtained by the method including steps S1 to S5 described above using the same material as the basket. By performing the test, it is possible to perform the characteristic evaluation that sufficiently considers the thermal deterioration that may occur in the long-term use period of the metal cask (actual product).

In step S3 (step of determining the cooling rate threshold _Cth ) described above, in step S308, the absolute value of the slope of the conductivity index of the temperature examination sample with respect to the cooling rate among the cooling rates belonging to the second range is predetermined. A cooling rate that is less than or equal to the value may be determined as the threshold value C _th .
In this case, among the cooling rates belonging to the second range, the cooling rate at which the absolute value of the slope of the conductivity index of the temperature examination sample is equal to or less than a predetermined value is determined as the threshold value C _th . In this case, even if there is a variation in the absolute value of the slope of the conductivity index of the temperature examination sample, the threshold value of the cooling rate can be set appropriately.

In one embodiment, the conductivity of the cooling temperature examination sample is used as the conductivity index of the cooling temperature examination sample.
In this case, among the cooling rates belonging to the second range, the cooling rate at which the absolute value of the conductivity gradient is 1.0% IACS / (° C./h) or less, or the absolute value of the conductivity gradient is 0. You may determine the cooling rate used as 5% IACS / (degreeC / h) or less as the threshold value _Cth .
Alternatively, in this case, the cooling rate at which the absolute value of the slope of conductivity is equal to or lower than a predetermined value (for example, 1.0% IACS / (° C./h) or 0.5% IACS / (° C./h)) is a metal material. For example, in the case of a magnesium-containing aluminum alloy or a manganese-containing aluminum alloy, a cooling rate of 2.0 ° C./h or less, or a cooling rate of 1.0 ° C./h or less is set as the threshold value C _th May be.

The method for producing a characteristic evaluation sample including steps S1 to S5 described above may be employed when the content of impurities contained in the metal material is not more than a specified value.
That is, in step S3 for determining the threshold value C _th of the cooling rate, the cooling rate in the second range may be determined as the threshold value C _th when the content of impurities contained in the metal material is not more than a specified value. .

  Here, FIG. 7 shows the cooling rate obtained after performing the above-described steps S302 to S306 on the cooling rate examination samples (sample 1 and sample 2) formed from aluminum alloys having different impurity contents. It is a figure which shows an example of the correlation with the electrical conductivity of this sample.

  The chemical composition of Sample 1 and Sample 2 is as shown in Table 1 below. That is, the sample 1 has almost the same chemical component composition as the actual product of a metal cask that is industrially produced, contains manganese (Mn) and magnesium (Mg) as additive components, silicon (Si), iron (as impurities) It is a sample formed from an aluminum alloy containing Fe) and copper (Cu). On the other hand, sample 2 is a sample formed of an aluminum alloy containing the same amount of additive components (manganese (Mn) and magnesium (Mg)) as sample 1, but with a reduced amount of impurities.

  As a result of intensive studies by the inventor, when the impurities contained in the metal material are relatively small, there is a range in which the slope of the conductivity index of the metal material cooled after the heat treatment shows a substantially constant value in a region where the cooling rate is relatively large. It has been found that as the cooling rate is further decreased and the cooling rate is further decreased, the slope may decrease and then converge to a substantially constant value. In this case, the inclination can be a relatively small value even in a cooling rate range larger than the cooling rate range in which the inclination converges to a substantially constant value.

  More specifically, referring to FIG. 7, in the case of the sample 1 having a relatively large impurity content, as the cooling rate is decreased, the slope of the conductivity of the metal material cooled after the heat treatment is relatively large at first. At a certain cooling rate (at about 1 ° C./h in the example of FIG. 7), the slope of the conductivity starts to decrease and converges to a substantially constant value. On the other hand, in the case of the sample 2 having a relatively small impurity content, as the cooling rate is reduced, the slope of the conductivity of the metal material cooled after the heat treatment is initially relatively small (the above-mentioned third range), and a certain cooling rate. In FIG. 7 (at about 30 ° C./h in the example of FIG. 7), the conductivity slope once increases (the above-mentioned first range), and then at a certain cooling rate (at about 1 ° C./h in the example of FIG. 7). The slope of the rate starts to decrease and converges to a substantially constant value (the second range described above).

  Thus, when the content of impurities contained in the metal material is relatively small, a cooling rate range (third range) that is larger than the cooling rate range (second range) in which the slope of conductivity with respect to the cooling rate converges to a substantially constant value. (Range), the slope of the conductivity can be a relatively small value.

This is considered to be due to the following reason. That is, in the above-described aluminum alloy containing manganese and magnesium, manganese or magnesium as an additive component is likely to be precipitated using silicon or iron as an impurity element as a precipitation nucleus.
Here, when the content of silicon or iron as an impurity element is relatively large as in Sample 1 described above, manganese or magnesium as an additive component contained in a heat-treated metal material (aluminum alloy) is a metal material. It precipitates relatively easily with the impurity elements (silicon, iron) present therein as precipitation nuclei.
On the other hand, when the content of silicon or iron as an impurity element is small as in Sample 2 described above, manganese or magnesium as an additive component contained in a heat-treated metal material (aluminum alloy) is present in the metal material. Since there are few precipitation nuclei to be formed, it is relatively difficult to precipitate when the metal material is cooled. In addition, as the cooling rate increases, it is more difficult to cool the heat-treated metal material while maintaining the equilibrium state, and the additive component (manganese or magnesium) contained in the metal material is less likely to precipitate.

  Therefore, as described above, when the content of impurities contained in the metal material is equal to or less than the specified value, the metal sample is cooled by cooling the heat-treated metal sample at a rate equal to or lower than the cooling rate in the second range. When the content of impurities contained in is less than or equal to the specified value, the additive components are more reliably precipitated while avoiding the supersaturated solid solution state, and the coarsening of the precipitate is sufficiently advanced. A sample for characteristic evaluation can be obtained.

The specified value of the content of impurities described above varies depending on the type of metal material and the type of impurity.
For example, the metal material may be an aluminum alloy containing at least one of magnesium and manganese as an additive component.
In this case, when the content of impurities other than magnesium and manganese (for example, silicon, iron, and copper) is 0.8% by mass or less, the cooling rate in the second range described above is set to The cooling rate threshold _Cth may be determined. Alternatively, in the case of the above-mentioned aluminum alloy, when the content of silicon as an impurity is 0.05% by mass or less, or when the content of iron as an impurity is 0.20% by mass or less, the second range. The cooling rate may be determined as the threshold value _Cth .

  As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment mentioned above, The form which added the deformation | transformation to embodiment mentioned above and the form which combined these forms suitably are included.

In this specification, the expression indicating that things such as “identical”, “equal”, and “homogeneous” are in an equal state not only represents an exactly equal state, but also includes a tolerance or the same function. It also represents a state in which a difference exists.
In this specification, the expression “comprising”, “including”, or “having” one constituent element is not an exclusive expression for excluding the existence of another constituent element.

Claims (6)

Heat treating the metal material so that work hardening of the metal material is restored;
Determining a cooling rate threshold for the heat treated metal material;
Cooling the heat-treated metal material at a cooling rate equal to or lower than the threshold in at least a part of the temperature range, and forming a sample for characteristic evaluation,
Determining the threshold comprises:
Heat treating a plurality of samples made of the same metal as the metal material;
Cooling the plurality of samples after heat treatment under a plurality of cooling rates,
From the correlation between the cooling rate and the conductivity index of the sample after cooling, the cooling rate is smaller than the first range of the cooling rate, and the absolute value of the slope of the conductivity index with respect to the cooling rate is A cooling rate in a second range of the cooling rate smaller than the first range, and a third rate of the cooling rate in which the cooling rate is larger than the first range and the absolute value is smaller than the first range. A method for producing a sample for evaluating characteristics of a metal material, comprising: selecting a cooling rate in the second range as the threshold among the cooling rates . Ru Der content below the specified value of an impurity in the prior SL metallic material
The method for manufacturing a characteristic evaluation sample of a metal material according to claim 1, wherein the this. The metal material is an aluminum alloy containing at least one of magnesium or manganese as an additive component,
In the step of determining the threshold value,
The cooling rate in the second range is determined as the threshold value when the content of the impurity that is a component other than the magnesium and the manganese is 0.8 mass% or less. A method for producing a sample for evaluating characteristics of a metal material.   In the step of determining the threshold value, a cooling rate at which an absolute value of an inclination of the conductivity index with respect to the cooling rate is equal to or less than a predetermined value among the cooling rates belonging to the second range is determined as the threshold value. A method for producing a sample for property evaluation of a metal material according to any one of claims 1 to 3.   The characteristic of the metal material according to any one of claims 1 to 4, wherein the conductivity index of the sample is at least one of conductivity, electrical resistance, or thermal conductivity of the sample. A method for producing a sample for evaluation. Creating the sample for property evaluation by the method according to claim 1;
Performing the material property evaluation of the metal material using the obtained sample for property evaluation;
A method for evaluating characteristics of a metal material, comprising:

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