Stainless steel rectangular container for heat treatment

Abstract

Provided is a stainless steel rectangular container for heat treatment including: a container body comprising a rectangular bottom plate part having a bottom surface on which an object that must undergo heat treatment is placed, and four side wall parts respectively connected to four edges of the bottom plate part; and a reinforcement member joined to each of four corner parts formed by the bottom plate part and each side wall part of the container body. The container body is made of two-phase stainless steel in which an austenite phase and a ferrite phase are mixed.

Description

Stainless steel rectangular container for heat treatment

[0001] This invention relates to a stainless steel rectangular container used in heat treatment. This application claims priority based on Japanese Patent Application No. 2025-030351, filed in Japan on February 27, 2025, the contents of which are incorporated herein by reference.

[0002] Conventionally, lightweight aluminum containers with high thermal conductivity have been widely used as shallow metal containers for cooking and other heat treatments. In addition, various heat treatment containers made of materials other than aluminum are known (see, for example, Patent Documents 1 and 2).

[0003] Japanese Unexamined Patent Publication No. 9-117374 Japanese Unexamined Patent Publication No. 7-307195

[0004] However, because aluminum containers have relatively low high-temperature strength, repeated use can lead to significant distortion due to the accumulation of plastic deformation caused by thermal expansion and contraction.

[0005] Patent Document 1 discloses an induction cooker container made of a clad plate containing aluminum and stainless steel. Patent Document 2 describes an induction cooker container made of at least a portion of duplex stainless steel. In induction cooking, the temperature difference that occurs inside the container during heating is relatively small.

[0006] On the other hand, when performing non-electromagnetic heat treatment, the temperature difference generated inside the container during the heat treatment is relatively large. Containers made of materials other than aluminum have relatively low thermal conductivity, which can cause significant thermal deformation during non-electromagnetic heat treatment. The technology described in Patent Document 2 does not take into consideration the thermal deformation caused by the relatively large temperature difference generated inside the container during non-electromagnetic heat treatment. If the container undergoes significant thermal deformation during the heat treatment, uneven heating is likely to occur in the object being treated. In addition, for example, heat treatment may be performed while transporting the container using a heating device. The heating line in a heating device (especially the inlet and outlet of the heating line) may not have sufficient space in the height direction from the viewpoint of heating efficiency, and if the container undergoes significant thermal deformation during transport, problems may occur in transporting the container in the heating line.

[0007] This invention has been made in view of the circumstances described above, and aims to provide a stainless steel rectangular container for heat treatment that exhibits minimal thermal deformation during heating.

[0008] To solve the above problems, a stainless steel rectangular container for heat treatment according to one aspect of the present invention comprises a container body having a rectangular bottom plate portion on which an object to be heat-treated is placed, and four side wall portions connected to each of the four sides of the bottom plate portion, and reinforcing members joined to each of the four corners formed by the bottom plate portion and each of the side wall portions of the container body, wherein the container body is made of duplex stainless steel having a mixture of austenite and ferrite phases.

[0009] According to one aspect of the present invention, a stainless steel rectangular container for heat treatment that exhibits minimal thermal deformation during heating can be provided.

[0010] This is a schematic perspective view showing the configuration of a stainless steel rectangular container for heat treatment in Embodiment 1 of the present invention. This is a schematic perspective view illustrating an example of how the rectangular container deforms when heated in the reference example. This is a schematic perspective view illustrating another example of how the rectangular container deforms when heated in the reference example. This is a schematic diagram showing how the rectangular container in the reference example deforms when heated in a heating device that performs continuous heat treatment. This is a schematic diagram illustrating one example of the configuration of a reinforcing member. This is a schematic diagram illustrating another example of the configuration of a reinforcing member. This is a schematic diagram illustrating one example of the configuration of the container body. This is a partial cross-sectional view of the container body of a stainless steel rectangular container for heat treatment in one embodiment of the present invention. This is a schematic perspective view showing the configuration of a stainless steel rectangular container for heat treatment in Embodiment 2 of the present invention.

[0011] [Embodiment 1] An embodiment of the present invention will be described below. The following description is intended to help you better understand the spirit of the invention and does not limit the present invention unless otherwise specified. The present invention is not limited to the following embodiments or examples, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included in the technical scope of the present invention. In this specification, "A to B" indicates that it is between A and B.

[0012] Figure 1 is a schematic perspective view showing the configuration of a stainless steel rectangular container for heat treatment in Embodiment 1 of the present invention. In Figure 1, a partially enlarged perspective view of the stainless steel rectangular container for heat treatment is also shown, showing the corners from a different angle (diagonally downward from the rectangular container). Hereinafter, the stainless steel rectangular container for heat treatment in one embodiment of the present invention will be referred to as the stainless steel rectangular container 1. The object to be heat-treated, which is placed in the stainless steel rectangular container 1 and heated, will be referred to as the object to be treated.

[0013] The stainless steel rectangular container 1 in one embodiment of the present invention may typically be used for non-electromagnetic heat treatment. In this specification, a treatment in which an object to be treated or a container is dielectrically heated by electromagnetic waves is referred to as "electromagnetic heat treatment." On the other hand, heat treatments other than electromagnetic heat treatment are referred to as "non-electromagnetic heat treatment" or "indirect heat treatment." In indirect heat treatment, the object to be treated is heated by conduction heating and / or convection heating.

[0014] Generally, aluminum containers are used in temperature ranges lower than, for example, 300°C. The upper limit temperature for the heat treatment in which the stainless steel rectangular container 1 in one embodiment of the present invention is used is, for example, 300°C. Normally, stainless steel undergoes almost no change in strength and structure in the temperature range of 0°C to 300°C.

[0015] As shown in Figure 1, the stainless steel rectangular container 1 comprises a container body 2 having four corners 2C and reinforcing members 3 joined to each of the four corners 2C. The container body 2 comprises a rectangular bottom plate portion 21 having a bottom surface 21A on which the object to be heat-treated is placed, and four side wall portions 22 connected to each of the four sides of the bottom plate portion 21. The four corners 2C of the container body 2 are formed by the bottom plate portion 21 and each side wall portion 22. The container body 2 is made of duplex stainless steel in which austenite and ferrite phases are mixed. In the example shown in Figure 1, the stainless steel rectangular container 1 is equipped with four reinforcing members 3 joined so as to cover the outside of each corner 2C. In the example shown in Figure 1, the bottom surface 21A of the container body 2 is rectangular. The short side of the bottom surface 21A is called the first side S1, and the long side is called the second side S2. However, it is not limited to this, and the bottom surface 21A of the container body 2 may be square. The side of the bottom plate portion 21 opposite to the bottom surface 21A is referred to as the back surface 21B.

[0016] For the sake of explanation, the height direction of the container body 2 will be defined as the Z-axis direction, and the XY-axis directions will be defined perpendicular to the Z-axis direction. The X-axis direction will be the direction along the first side S1 of the bottom surface 21A, and the Y-axis direction will be the direction along the second side S2 of the bottom surface 21A. Two of the four side walls 22 of the container body 2 extend along the X-axis direction, and the remaining two extend along the Y-axis direction. The XYZ-axis directions will be defined similarly in the following explanation. For reference, the XYZ-axis coordinate system is shown in each figure as appropriate.

[0017] When a container body 2 made of duplex stainless steel is subjected to heat treatment with an object to be processed placed on its bottom surface 21A, bending deformation may occur. This is because a temperature difference is generated on the bottom surface 21A between the area where the object to be processed is placed and the area where it is not, and this temperature difference causes thermal deformation (thermal stress) in the bottom plate portion 21. In particular, when the object to be processed is placed on only a part of the bottom surface 21A (a relatively narrow area), large thermal deformation may occur during the heat treatment. This is thought to be due to the following reasons, for example. The bending deformation that occurs in the container body 2 will be explained in more detail later. - Because the above temperature difference becomes large. - The area where the object to be processed is placed becomes a low-temperature area, and the area where the object to be processed is not placed becomes a high-temperature area. Since the boundary between these low-temperature and high-temperature areas is far from the side wall portion 22, the function of restraining deformation in the side wall portion 22 does not easily act on the thermal stress generated within the bottom surface 21A.

[0018] In one embodiment of the stainless steel rectangular container 1, all four corners 2C of the container body 2 are reinforced by reinforcing members 3, making it easier to reduce the amount of deformation of the corners 2C. Therefore, it is possible to provide a stainless steel rectangular container 1 that exhibits minimal thermal deformation during heating. The strength of the stainless steel rectangular container 1 can be increased by making the container body 2 from duplex stainless steel. Duplex stainless steel has a specific strength equivalent to that of aluminum. Therefore, if the stainless steel rectangular container 1 is to have the same strength as, for example, an aluminum rectangular container, it can have the same weight as the aluminum rectangular container.

[0019] Furthermore, since duplex stainless steel is magnetic, magnetic inspection can be performed on the object being treated after heat treatment using the stainless steel rectangular container 1. If wear occurs to the container body 2, the wear can be easily identified by performing a magnetic inspection on the object being treated. Therefore, it becomes easier to perform heat treatment on the object being treated stably. By using the stainless steel rectangular container 1, the industrial line production efficiency for heat treatment of objects can be improved compared to when using aluminum containers.

[0020] Here, for example, instead of providing the reinforcing member 3, it is possible to increase the rigidity by increasing the thickness of the container body 2, thereby reducing thermal deformation during heating. However, in this case, the weight of the container body 2 increases. This increase in the weight of the container body 2 causes various disadvantages. In contrast, with the stainless steel rectangular container 1, the total weight of the container body 2 and the reinforcing member 3 (the entire stainless steel rectangular container 1) can be reduced compared to when the thickness of the container body 2 is increased.

[0021] Furthermore, in the stainless steel rectangular container 1 of one embodiment, corrosion resistance can be easily improved compared to the case where the container body 2 is made of ferritic stainless steel. Therefore, by using the stainless steel rectangular container 1, the possibility of rust forming on the container body 2 when heating the object to be processed, which contains salt, etc., can be effectively reduced.

[0022] As described above, the stainless steel rectangular container 1 has high strength because the container body 2 is made of duplex stainless steel, it is less prone to distortion even with continuous use, and it has relatively high corrosion resistance. Therefore, the service life of the stainless steel rectangular container 1 used for heat treatment can be extended, in other words, the lifespan of the stainless steel rectangular container 1 can be increased. Thus, by using the stainless steel rectangular container 1, the life cycle cost can be reduced compared to using a rectangular container in which the container body 2 is made of ferritic stainless steel.

[0023] In one embodiment, the stainless steel rectangular container 1 may be used, for example, for heating and cooking food, relatively low-temperature heat treatment in the manufacturing process of products (such as pharmaceuticals), sterilization, etc. The stainless steel rectangular container 1 may be used, for example, for heat treatment that heats a wide area uniformly. The stainless steel rectangular container 1 may be used, for example, for heat treatment under pressure (such as in an autoclave) or heat treatment under reduced pressure (such as drying). Examples of objects to be treated include raw materials, food, pharmaceuticals, various industrial products, various parts, etc. In the heat treatment (indirect heat treatment) in which the stainless steel rectangular container 1 is used, the heating method is not particularly limited. The heat treatment may be carried out by methods such as direct flame, electric heater, steam, hot air convection, etc.

[0024] For example, when heating an object that is heated at the same rate as the container body 2 (such as a metal product), or an object with a three-dimensional shape that has an extremely small contact area with the container body 2, the temperature difference generated within the container body 2 can be relatively small. In this case, thermal deformation of the container body 2 is relatively unlikely to occur. In contrast, the stainless steel rectangular container 1 can be suitably used for (a) objects to be processed whose temperature rise due to heating is slower than that of the container body 2, and / or (b) objects to be processed that have a large contact area with the container body 2.

[0025] Slower temperature rise due to heating than container body 2 means that the maximum temperature difference between the area on the bottom surface 21A where an object is placed and the area where no object is placed after heating has started is 40°C or more. The object to be processed may be one in which the above maximum temperature difference is 40°C or more and 350°C or less. The object to be processed may be in a frozen state before heating has started (it may be below 0°C). The object to be processed may be one in which the above maximum temperature difference is 50°C or more and 300°C or less, or 100°C or more and 250°C or less. Larger contact area with container body 2 means that the area on the bottom surface 21A in contact with the object is 30% or more of the total area of ​​the bottom surface 21A. The area on the bottom surface 21A in contact with the object may be 30% or more and 80% or less of the total area of ​​the bottom surface 21A.

[0026] In one embodiment of the stainless steel rectangular container 1, the reinforcing member 3 may be joined to the outside of the container body 2. In this case, the possibility of the object to be processed coming into contact with the reinforcing member 3 can be reduced. Therefore, the possibility of impurities originating from the reinforcing member 3 being contained in the object to be processed after heat treatment using the stainless steel rectangular container 1 can be effectively reduced.

[0027] Furthermore, since the reinforcing member 3 is attached to the outside of the corner 2C, unlike when it is attached to the inside, no step or gap is created between the reinforcing member 3 and the bottom surface 21A. Therefore, these do not become obstacles when cleaning the stainless steel rectangular container 1. Also, for example, if the object to be processed is food, contact between the food or the gap or welded area between the reinforcing member 3 and the container body 2 can become the starting point for corrosion. In contrast, if the reinforcing member 3 is attached to the outside of the corner 2C, the possibility of a starting point for corrosion can be reduced. Not limited to the above example, in the stainless steel rectangular container 1, the reinforcing member 3 may also be attached to the inside of the corner 2C (see Embodiment 2). In addition, in this application, the ratio of the length of the first side S1, which is the short side of the bottom surface 21A, to the length of the second side S2, which is the long side of the bottom surface 21A, may be 1:1 to 3:14, or 4:5 to 2:9.

[0028] The stainless steel rectangular container 1 according to one embodiment of the present invention will be further described below with reference to the drawings. First, the modes of thermal deformation (bending modes) that may occur in the rectangular container during heating will be explained with reference to Figures 2 and 3. Next, for ease of understanding, the conventional problems will be explained with reference to Figure 4. After that, the findings of the present inventors and the stainless steel rectangular container 1 based thereon will be described in detail.

[0029] In the following, for the sake of explanation, a container body 2 (a stainless steel rectangular container 1 with the reinforcing members 3 removed) in which the reinforcing members 3 are not attached to each corner 2C will be referred to as the rectangular container 100 of the reference example. Figure 2 is a schematic perspective view illustrating one example of how the rectangular container in the reference example deforms when heated. Figure 3 is a schematic perspective view illustrating another example of how the rectangular container in the reference example deforms when heated. The object to be processed is not shown in Figures 2 and 3.

[0030] As shown in Figures 2 and 3, when a workpiece is placed on the bottom surface 21A of the rectangular container 100 and subjected to heat treatment, two main types of bending deformation may occur. More specifically, the temperature gradient is greatest at the boundary between the area in contact with the workpiece and the area not in contact with the workpiece, and a large thermal stress is generated at this boundary due to the difference in thermal expansion. In particular, compressive stress is generated on the high-temperature side (the side not in contact with the workpiece) due to the constraint of thermal expansion. Due to such stress, two types of deformation can occur in the rectangular container 100.

[0031] In this specification, the bending deformation in which the bottom plate portion 21 bends around the diagonal DL of the bottom surface 21A as shown in Figure 2 is referred to as the first mode of bending deformation. In the first mode of bending deformation, the bottom plate portion 21 bends so that the bottom surface 21A bends rather than the short and long sides of the bottom surface 21A bending. In the first mode of bending deformation, the bottom surface 21A buckles and bends around the diagonal DL as an axis, and one or two corner portions 2C deform so that they lift significantly upward. The first mode of bending deformation can also be referred to as bottom surface bending. Based on the maximum height position of the rectangular container 100 before deformation (upper end of the side wall portion 22), the maximum height of the rectangular container 100 in the Z-axis direction when the first mode of bending deformation occurs is defined as H1. In the example shown in Figure 2, the point at the maximum height H1 is the endpoint P1 on the opposite side of the bottom surface 21A of the ridge (the edge where the two side walls 22 meet) where the two side walls 22 connect, at the highest point corner 2C. The first mode of bending deformation can occur relatively instantaneously and abruptly. Therefore, when the first mode of bending deformation occurs, for example, the material to be processed may scatter, or the corner container 100 may come into contact with the heating device that performs the heat treatment.

[0032] Also, in the present specification, the bending deformation in which the bottom plate portion 21 is curved about a first imaginary line VL1 passing through the midpoints of two opposing second sides S2 on the bottom surface 21A before deformation as shown in FIG. 3 is referred to as bending deformation in the second mode. Here, the first side S1 is a short side of the bottom surface 21A, and the bottom plate portion 21 is bent and deformed so that the second side S2, which is the long side of the bottom surface 21A, is curved. Bending deformation in the second mode can also be referred to as long-side bending. Let H2 be the maximum height in the Z-axis direction of the rectangular container 100 when bending deformation in the second mode occurs, with reference to the maximum height position (the upper end of the side wall portion 22) of the rectangular container 100 before deformation. In the example shown in FIG. 3, the uppermost portion among the upper ends of the side wall portions 22 along the second side S2 is located at the maximum height H2. Bending deformation in the second mode has a relatively small deformation amount and a relatively gentle deformation speed. Therefore, the possibility that a problem occurs due to the occurrence of bending deformation in the second mode is relatively low.

[0033] FIG. 4 is a schematic diagram showing a state when the rectangular container of FIG. 2 is thermally deformed in a heating apparatus that performs continuous heat treatment. As shown in FIG. 4, for example, in factories or the like (industrial production), heat treatment may be continuously performed on a processing target while the rectangular container 100 is conveyed by a transfer device B such as a belt conveyor using a heating device M such as an oven. In the heat treatment space HS of the heating device M, a margin height HA with respect to the height H10 of the rectangular container 100 (the height of the side wall portion 22) is secured. It is preferable that the margin height HA is as small as possible. This is to make it easy to maintain the temperature of the heat treatment space HS constant and to easily improve thermal efficiency.

[0034] Here, if bending deformation of the first mode occurs in the rectangular container 100, the following problems arise. That is, when the maximum height H1 reaches the margin height HA, for example, the end point P1 contacts the ceiling of the heat treatment space HS, and in this case, a problem may occur in the conveyance of the rectangular container 100. In particular, the entrance / exit (opening) of the heat treatment space HS is relatively narrow, and when the maximum height H1 increases, a problem that the rectangular container 100 cannot pass through the entrance / exit may occur. Further, since a part of the processing object placed on the bottom surface 21A relatively approaches the heater, uneven heating may occur in the processing object placed on the bottom surface 21A of the rectangular container 100.

[0035] On the other hand, although not shown in the figure, even if bending deformation of the second mode occurs in the rectangular container 100 in the heat treatment space HS, the maximum height H2 is relatively small. Therefore, problems are less likely to occur in the conveyance of the rectangular container 100. Further, since the entire bottom surface 21A approaches the heater, uneven heating is less likely to occur in the processing object.

[0036] As can be understood from the above examples, regarding bending deformation occurring in a container during heat treatment, it is preferable that the bending deformation of the second mode is dominant over the bending deformation of the first mode, and it is further preferable that bending deformation of the first mode does not occur. However, in general, the mode of bending deformation that occurs in a container during heat treatment is determined by various factors, so it is not easy to control the mode of bending deformation.

[0037] As a result of intensive studies on the control (factors and their influences) of bending deformation modes, the present inventors found that joining the reinforcing member 3 to the corner 2C of the container body 2 can make the bending deformation of the second mode dominant, and found the condition (relational expression) that the reinforcing member 3 should satisfy to prevent the bending deformation of the first mode from occurring during heating, and conceived the present invention. The relational expression regarding the condition that the reinforcing member 3 should satisfy will be described later.

[0038] Figure 5 is a schematic diagram illustrating one example of the configuration of a reinforcing member. As shown in Figure 5, the reinforcing member 3 includes two reinforcing side plates 32 that are joined to each side wall portion 22 at the corner portion 2C, and a reinforcing bottom plate 31 that is joined to the bottom plate portion 21 (back surface 21B) at the corner portion 2C. In the reinforcing member 3, the two reinforcing side plates 32 are connected to each other, and each of the two reinforcing side plates 32 is connected to the reinforcing bottom plate 31.

[0039] With the above configuration, the reinforcing bottom plate 31 and reinforcing side plate 32 of the reinforcing member 3 are connected, thereby ensuring the strength of the reinforcing member 3 itself. Furthermore, by joining the reinforcing member 3 and the corner portion 2C to each other, the corner portion 2C can be reinforced more firmly. As a result, deformation of the corner portion 2C can be made even less likely, and thermal deformation of the stainless steel rectangular container 1 when heated can be reduced. In addition, although further investigation is needed regarding the details of the effect of thermal stress, as a result, in the stainless steel rectangular container 1, the reinforcing member 3 being joined to the corner portion 2C allows for preferential induction of the second mode of bending deformation over the first mode of bending deformation.

[0040] Figure 5 shows an example of a reinforcing plate 30 that forms the basis of the reinforcing member 3. The reinforcing plate 30 may have a shape that can be brought into contact with, for example, the side wall portion 22 and the bottom plate portion 21 of the corner portion 2C. In the example shown in Figure 5(a), a single reinforcing plate 30 formed to have a predetermined shape is used, bent along the dotted line portion shown in Figure 5(a), positioned to contact the outside of the corner portion 2C shown in Figure 5(b), and fixed to the corner portion 2C as shown in Figure 5(c). This allows the reinforcing member 3 to be joined to the corner portion 2C. Using a single reinforcing plate 30 prevents separation of the contact portions between the reinforcing bottom plate 31 and the reinforcing side plate 32, or between adjacent reinforcing side plates 32, further suppressing deformation of the corner portion 2C and suppressing the bending deformation of the first mode. However, it is not limited to this, and three plates corresponding to two reinforcing side plates 32 and one reinforcing bottom plate 31 may be used as the reinforcing plate 30 that forms the basis of the reinforcing member 3. In this case, it is not necessary for the entire contact area between the reinforcing bottom plate 31 and the reinforcing side plate 32, or between adjacent reinforcing side plates 32, to be connected without any gaps; it is sufficient for a portion to be connected to the extent that the corner 2C can be reinforced.

[0041] Joining the reinforcing member 3 to the corner 2C means that the reinforcing plate 30 is integrally attached to the side wall portion 22 and the bottom plate portion 21 of the corner 2C, which means that the reinforcing member 3 is fixed so as not to displace relative to the corner 2C. For example, the reinforcing plate 30 may be joined to the corner 2C by welding, or it may be attached using joining members (bolts and nuts, or rivets, etc.). It is permissible for the reinforcing member 3 to shift slightly due to thermal deformation of the corner 2C. Here, being fixed so as not to displace means, for example, when joining with bolts and nuts, that the reinforcing member 3 is fixed so that there is no room for it to displace (shift) relative to the corner 2C due to a slight difference between the diameter of the bolt and the diameter of the hole drilled in the reinforcing member 3 or the side wall portion 22, or because the bolt is not tightened sufficiently.

[0042] The manufacturing method of the reinforcing member 3 is not particularly limited. The shape of the reinforcing member 3 may be formed when the reinforcing plate 30 is attached to the corner 2C, or the shape of the reinforcing member 3 may be formed in advance and then attached to the corner 2C. For example, the reinforcing member 3 may be formed by sheet metal processing (bending, pressing, welding, etc.). In the reinforcing member 3, the reinforcing side plate 32 and the reinforcing bottom plate 31 must be in a continuous, integral state. Being in a continuous, integral state means that the reinforcing side plate 32 and the reinforcing bottom plate 31 may be welded together, be bent, or in any other specific state, that the connection part has the same strength characteristics as the base material or is less prone to breakage (tougher) than the base material. The reinforcing side plate 32 and the reinforcing bottom plate 31 are connected without any gaps.

[0043] The means for joining the reinforcing member 3 to the corner portion 2C are not particularly limited. Various welding methods and various joining members (joining means) may be used. In the stainless steel square container 1, the side wall portion 22 and the reinforcing side plate 32, and the bottom plate portion 21 and the reinforcing bottom plate 31 may all be welded together. Note that the parts joined by welding will have a different color from the container body 2 and the reinforcing member 3. Also, the parts joined by welding may become a single phase of ferrite or a single phase of austenite upon heating. Therefore, the parts joined by welding can be distinguished from the other parts of the container body 2 and the reinforcing member 3.

[0044] By using welding, the reinforcing member 3 can be joined to the corner 2C relatively easily and firmly. The welding method between the side wall portion 22 and the reinforcing side plate 32, and between the bottom plate portion 21 and the reinforcing bottom plate 31 may be continuous welding, spot welding, or a combination of continuous welding and spot welding depending on the location. When the reinforcing member 3 is continuously welded to the corner 2C, the welding may be carried out along the outer circumference of the reinforcing side plate 32 and the reinforcing bottom plate 31. When the reinforcing member 3 is spot welded to the corner 2C, the spot welds may be provided with as many weld points as possible near the outer circumference of the reinforcing side plate 32 and near the outer circumference of the reinforcing bottom plate 31, as shown in Figure 1.

[0045] The spot welds between the reinforcing bottom plate 31 and the bottom plate portion 21 may be positioned so as to coincide with the diagonal of the bottom plate portion 21, and may be positioned so as to coincide with a range of 10 mm from the vertex EP1 of the reinforcing member 3 shown in Figure 5. Also, the spot welds between the reinforcing side plate 32 and the side wall portion 22 may be positioned near the joint of the two reinforcing side plates 32, for example, they may be positioned so as to coincide with a range of 10 mm from the joint of the two reinforcing side plates 32. More specifically, the spot welds between the reinforcing side plate 32 and the side wall portion 22 may be positioned so as to coincide with a range of 10 mm from the vertex EP1 of the reinforcing member 3 shown in Figure 5, and may be positioned so as to coincide with a range of 10 mm from the other vertex EP2 of the reinforcing member 3. By including one or more of the above configurations, the curvature of the bottom plate portion 21 along the diagonal can be restrained more effectively.

[0046] In the stainless steel rectangular container 1, the side wall portion 22 and the reinforcing side plate 32, and the bottom plate portion 21 and the reinforcing bottom plate 31 may be joined by connecting members. The connecting members are, for example, bolts and nuts, or rivets. If no practical problems such as liquid leakage from the joints between the side wall portion 22 and the reinforcing side plate 32, and the bottom plate portion 21 and the reinforcing bottom plate 31 occur due to the object being processed or the heating method, etc., then the container may be joined by connecting members.

[0047] Figure 6 is a schematic diagram illustrating another example of the reinforcing member configuration. As shown in Figure 6, the reinforcing bottom plate 31 is not limited to a triangular shape, but may be, for example, rectangular. The reinforcing bottom plate 31 has a shape that includes at least a triangular region A3 formed by two sides S3 connected to each of the two reinforcing side plates 32, and a virtual side VS3 connecting the endpoints P3 opposite to the intersection point PV of the two sides S3.

[0048] According to the above configuration, the corner portion 2C can be easily reinforced with the reinforcing member 3 to reduce thermal deformation of the stainless steel rectangular container 1 during heating.

[0049] Referring again to Figure 1, in the stainless steel rectangular container 1, the container body 2 has an unreinforced portion 2N on at least a part of the side wall portion 22 where the reinforcing member 3 is not joined, and the unreinforced portion 2N has less rigidity than the corner portion 2C.

[0050] The unreinforced portion 2N is the part of the side wall portion 22 to which the reinforcing side plate 32 of the reinforcing member 3 is not joined. Typically, this is the part where the reinforcing side plate 32 is absent, but it may also be covered by the reinforcing side plate 32 in a state where it is not joined to the side wall portion 22. This is because the region of the reinforcing side plate 32 that is joined to the side wall portion 22 functions as the reinforcing member 3, so the part of the reinforcing side plate 32 that is not joined to the side wall portion 22 becomes the unreinforced portion 2N.

[0051] According to the above configuration, the stainless steel rectangular container 1 has its corners 2C restrained by the reinforcing member 3, while the unreinforced portion 2N is not restrained by the reinforcing member 3. Therefore, when heated, the stainless steel rectangular container 1 is more likely to undergo the second mode of bending deformation. If the reinforcing member 3 is joined not only to the corners 2C but also around the entire circumference of the side wall portion 22, and there is no unreinforced portion 2N, the side wall portion 22 is less likely to bend, and therefore the second mode of bending deformation is less likely to occur. In other words, the first mode of bending deformation will occur preferentially over the second mode of bending deformation. For this reason, a configuration with an unreinforced portion 2N is preferable.

[0052] In the stainless steel rectangular container 1, the reinforcing member 3 may have a shape that satisfies both (i) and (ii) below. Hereinafter, in this specification, the dimension of the reinforcing side plate 32 in the Z-axis direction in Figure 1 will also be referred to as the "height of the reinforcing side plate 32", and the dimension of the reinforcing side plate 32 in the X-axis direction and / or Y-axis direction in Figure 1 will also be referred to as the "length (width) of the reinforcing member 32". (i) The height of the reinforcing side plate 32 is 1 / 2 or more of the height of the side wall portion 22 and less than or equal to the height of the side wall portion 22. (ii) The length of the reinforcing side plate 32 along the direction in which the side wall portion 22 extends is 1 / 20 or more of the length of the second side S2 which is the long side of the bottom surface 21A, and 1 / 4 or less of the length of each side to which each reinforcing side plate 32 is joined. In other words, the length of the reinforcing side plate 32 joined to the first side S1, which is the short side of the base surface 21A, is 1 / 20 or more of the length of the second side S2, which is the long side of the base surface 21A, and 1 / 4 or less of the length of the first side S1, which is the short side of the base surface 21A. Also, the length of the reinforcing side plate 32 joined to the second side S2, which is the long side of the base surface 21A, is 1 / 20 or more of the length of the second side S2, which is the long side of the base surface 21A, and 1 / 4 or less of the length of the second side S2, which is the long side of the base surface 21A. Here, the height of the reinforcing side plate 32 may or may not be uniform. Regarding (i), if the height of the reinforcing side plate 32 is uniform, the height of the reinforcing side plate 32 is 1 / 2 or more of the height of the side wall portion 22. If the height of the reinforcing side plate 32 is not uniform, the height of the lowest part of the reinforcing side plate 32 is 1 / 2 or more of the height of the side wall portion 22.

[0053] According to the above configuration, by satisfying (i) above, the corner portion 2C can be reinforced more firmly. As a result, deformation is less likely to occur at the corner portion 2C, and the second mode of bending deformation can be preferentially generated over the first mode of bending deformation. Furthermore, reinforcing only less than half the height of the side wall portion 22 cannot suppress the first mode of bending deformation. For this reason, it is necessary to reinforce at least half the height of the side wall portion 22. From the viewpoint of more firmly reinforcing the corner portion 2C and preferentially generating the second mode of bending deformation over the first mode of bending deformation, a configuration in which the height of the reinforcing side plate 32 is the same as the height of the side wall portion 22 is even more preferable.

[0054] Furthermore, by satisfying condition (i) above and ensuring that the length (width) of the reinforcing side plate 32 is 1 / 20 or more of the length of the second side S2, the corner 2C can be effectively reinforced. Also, by ensuring that the length (width) of the reinforcing side plate 32 is 1 / 4 or less of the length of the first side S1, it is easier to secure an unreinforced portion 2N. This allows for bending along the edge.

[0055] Furthermore, if the base surface 21A is square-shaped (i.e., the lengths of the first side S1 and the second side S2 are equal), the length of the reinforcing side plate 32 may be 1 / 20 or more and 1 / 4 or less of the length of one side of the base surface 21A.

[0056] The length (width) of the reinforcing side plate 32 may be 1 / 4 or less of the length of the first side S1 and 50 mm or less. In this case, the length of the first side S1 may be 2 cm or more, and the length of the second side S2 may be 10 cm or more.

[0057] Figure 7 is a schematic diagram illustrating one example of the configuration of the container body 2. Figure 7 shows an example of the container base plate 20 that forms the basis of the container body 2, and the bending line BL of the container base plate 20 is shown as a dashed line. In the example shown in Figure 7, a single container base plate 20 formed to have a predetermined shape is used, and it is bent at the bending line BL to form four side wall portions 22, and the ends of two side wall portions 22 that abut each other are welded together. This allows the container body 2 to be formed. In other words, at the corner portion 2C of the container body 2, two side wall portions 22 are connected to each other, and the ridge 22E, which is the part where the two side wall portions 22 are connected, may be, for example, a welded part. Also, the bottom plate portion 21 and the side wall portions 22 may be welded to each other.

[0058] In a stainless steel rectangular container 1, the container body 2 may have a rectangular tube shape in which the side walls 22 are perpendicular or substantially perpendicular to the bottom plate 21. The container body 2 may be a shallow container with a wide bottom area. A shallow bottom means that the height of the side walls 22 is lower than the first side S1, which is the short side of the bottom surface 21A.

[0059] Figure 8 is a partial cross-sectional view of the container body of a stainless steel rectangular container for heat treatment according to one embodiment of the present invention. As shown in Figures 7 and 8, the container body 2 has a side wall portion 22 whose height is less than the length of the first side S1, which is the short side of the bottom surface 21A, and has a bent portion 2B at the boundary between the bottom plate portion 21 and the side wall portion 22, the angle between the bottom surface 21A of the bottom plate portion 21 and the inner surface 22I of the side wall portion 22 is approximately 90 degrees, and the curvature of the bent portion 2B may be less than or equal to twice the plate thickness of the container body 2.

[0060] According to the above configuration, the angle between the bottom surface 21A and the inner surface 22I is approximately 90 degrees at corner 2C, and the ridge 22E located at corner 2C is also approximately 90 degrees. Therefore, the reinforcing member 3 can be easily joined to corner 2C. Approximately 90 degrees means that an error of about ±5 degrees from 90 degrees is allowed. The angle between the bottom surface 21A and the inner surface 22I may be 90 degrees.

[0061] The duplex stainless steel constituting the container body 2 has a chemical composition such as having a Ni content of 4% or less and a Mo content of 1% or less. The duplex stainless steel may be, for example, so-called lean duplex steel. Examples of lean duplex steel include SUS821L1 and SUS323L as specified in Japanese Industrial Standards (JIS G4304:2021, JIS G4305:2021). Ni and Mo are relatively expensive and their prices fluctuate considerably. When the container body 2 is made of lean duplex stainless steel, the Ni and Mo content is relatively low, which helps to stabilize the manufacturing cost of the stainless steel rectangular container 1.

[0062] Furthermore, the duplex stainless steel that constitutes the container body 2 is, for example, a so-called general-purpose duplex steel. Examples of general-purpose duplex steels include SUS329J1, SUS329J3L, SUS329J4L, etc., as specified in the Japanese Industrial Standards (JIS G4304:2021, JIS G4305:2021). The duplex stainless steel included in the container body 2 may also be, for example, a so-called super duplex steel. Examples of super duplex steels include SUS327L1, etc., as specified in the Japanese Industrial Standards (JIS G4304:2021, JIS G4305:2021).

[0063] In duplex stainless steel, the general-purpose duplex steel and super duplex steel have relatively higher Ni and Mo content and relatively higher strength than the lean duplex steel. The type of duplex stainless steel (chemical composition) may be selected according to the properties required for the stainless steel rectangular container 1.

[0064] The statement that the container body 2 is made of duplex stainless steel means that the metal structure of the container body 2 is duplex stainless steel consisting of a ferrite phase and an austenite phase. The statement that the metal structure of the container body 2 is duplex stainless steel consisting of a ferrite phase and an austenite phase means that in the metal structure of the container body 2, the total proportion of the ferrite phase and the austenite phase is not necessarily 100%, but is 95% or more, more preferably 98% or more, and the remainder consists of the σ phase and unavoidably formed phases. The σ phase is an intermetallic compound containing Fe, Cr, Mo, etc., and is, for example, 0% to less than 1.0%. Examples of unavoidably formed phases include precipitates and inclusions. In duplex stainless steel, the ferrite phase ratio is 30% or more and 70% or less, and the austenite phase ratio is 30% or more and 70% or less. Here, the phase ratio is the proportion of each phase when the total of the ferrite phase and the austenite phase is taken as 100%, and can be determined, for example, using EBSD (backscattered electron diffraction) measurement. For EBSD (backscattered electron diffraction) measurements, an EBSD analyzer consisting of a thermal field emission scanning electron microscope and an EBSD detector is used. For example, an EBSD analyzer consisting of a thermal field emission scanning electron microscope (JEOL JSM-7200F) and an EBSD detector (AMETEK Velocity detector) is used. In this case, the vacuum level inside the EBSD analyzer is 9.6 × 10⁻⁶. －５ The acceleration voltage is set to 15 kV below Pa. The phase ratio may also be determined as a volume fraction.

[0065] In one embodiment, during heat treatment, the stainless steel rectangular container 1 undergoes a second mode of bending deformation in the container body 2, with the second mode of bending deformation being preferentially more likely than the first mode of bending deformation, and the degree of the first mode of bending deformation may be smaller than the degree of the second mode of bending deformation. As described above, in the stainless steel rectangular container 1, by incorporating a reinforcing member 3 based on the inventors' knowledge, the second mode of bending deformation can be preferentially more likely than the first mode of bending deformation in the container body 2 during heat treatment. As a result, the degree of the first mode of bending deformation can be made smaller than the degree of the second mode of bending deformation. Therefore, the possibility of the aforementioned problems related to the first mode of bending deformation occurring can be effectively reduced.

[0066] In the example shown in Figure 1, the container body 2 has a rectangular bottom surface 21A, but is not limited to this, and for example the bottom surface 21A may be square. In this case, the first side S1 and the second side S2 are of equal length, and the bending deformation in which the bottom plate portion 21 curves around either or both of the first imaginary line along the direction in which the first side S1 extends and the second imaginary line along the direction in which the second side S2 extends is referred to as the second mode of bending deformation.

[0067] The inventors investigated the reinforcement conditions by the reinforcing member 3 to suppress the bending deformation of the first mode, under the most severe conditions from the viewpoint of suppressing the bending deformation of the first mode.

[0068] First, thermal stress occurs near the boundary line (outer edge in plan view) of the object to be processed placed on the bottom surface 21A. Therefore, if the object to be processed is positioned near the side wall 22, the rigidity of the side wall 22 makes it difficult for the first mode of bending deformation to occur. When the amount of the object to be processed is fixed, the state in which the object to be processed is positioned near the center of the bottom surface 21A is most likely to cause the first mode of bending deformation. Therefore, the inventors considered the situation in which the object to be processed is positioned in the center of the bottom surface 21A as the subject of their investigation.

[0069] Furthermore, if a folded portion or flange is provided on the side wall portion 22 of the container body 2, the rigidity of the container body 2 is improved, making it less susceptible to thermal deformation. For this reason, a container body 2 with a shape in which the upper end of the side wall portion 22 is simply an end face was considered as a target for consideration, as it creates conditions that make it prone to thermal deformation.

[0070] According to the inventors' studies, when each reinforcing member 3 satisfies the relationship in the following formula (1) during heat treatment, a stainless steel rectangular container 1 can be made in which the container body 2 does not undergo first-mode bending deformation; (10 / S) + 0.15 × ΔT - 10 × M - 30 × t ｉ <10 × t ｈ(1) Where: S: ratio of the area of the region on the bottom surface 21A where the object to be processed is placed to the area of the bottom surface 21A ΔT: difference (°C) between the heating temperature during the heat treatment and the temperature of the object to be processed at the start of the heat treatment M: weight (kg) of the object to be processed placed on the bottom plate portion 21 t ｉ : plate thickness (mm) of the container body 2 t ｈ : plate thickness (mm) of the reinforcing member 3.

[0071] For example, when heat treatment is performed on an object to be processed in an industrial production scene, conditions are predetermined for the weight M of the object to be processed, the placement area S of the object to be processed, and the temperature difference ΔT described above. When there are ranges for the weight M, the placement area S, and the temperature difference ΔT, the respective severe conditions may be adopted based on the sign of the above formula (1). Specifically, the lightest value within the range for the weight M, the smallest value within the range for the placement area S, and the smallest value within the range for the temperature difference ΔT may be substituted into the above formula (1). Then, the plate thickness t of the container body 2 is set so as to satisfy the relationship specified based on the above formula (1) ｉ and the plate thickness t of the reinforcing member 3 ｈ may be determined. At this time, the plate thickness t can be set such that the weight of the stainless steel square container 1 becomes relatively light ｉ and the plate thickness t ｈ can be determined.

[0072] Here, for the container body 2, when the plate thicknesses of the bottom plate portion 21 and the side wall portion 22 are different, basically, the plate thickness of the bottom plate portion 21 is taken as the above t ｉ to be used. This is because the bottom plate portion 21 is the main part that undergoes deformation. However, when the thicker plate thickness of the bottom plate portion 21 and the side wall portion 22 is at least twice the thinner plate thickness, the average value of the plate thicknesses of the bottom plate portion 21 and the side wall portion 22 is taken as the above t ｉ to be used. This is because it is assumed that both the bottom plate portion 21 and the side wall portion 22 affect deformation. For the reinforcing member 3, when the plate thicknesses of the reinforcing bottom plate 31 and the reinforcing side plate 32 are different, the thinner plate thickness is uniformly taken as the above t ｈ to be used.

[0073] The left-hand side of equation (1) above can be less than 0 depending on the specific conditions of the heat treatment. In this case, the container body 2 is prone to second-mode bending deformation during heat treatment, but by joining the reinforcing member 3 to the container body 2, second-mode bending deformation can be made more reliably induced. Furthermore, under heat treatment conditions in which the left-hand side of equation (1) above is greater than 0, the reinforcing member 3 that satisfies the relationship in equation (1) above is joined to the container body 2, thereby preventing first-mode bending deformation in the container body 2 and resulting in a stainless steel rectangular container 1 with minimal thermal deformation during heating. The heat treatment conditions in which the left-hand side of equation (1) above is greater than 0 are "0.15 × ΔT - 30 × t ｉ This condition can be described as "10 × M - (10 / S)" being smaller than the value of "".

[0074] [Other configurations] In the stainless steel rectangular container 1, the reinforcing member 3 may be a duplex stainless steel having a mixture of austenite and ferrite phases. The reinforcing member 3 may be made of the same material as the container body 2, or it may be made of a different material. Even if the thermal conductivity and thermal expansion coefficient of the reinforcing member 3 are different from those of the container body 2, this does not cause any major problems because the contact area between the reinforcing member 3 and the container body 2 is not large. The reinforcing member 3 may be magnetic. The reinforcing member 3 may have corrosion resistance equal to or better than that of the container body 2.

[0075] In this specification, the above-mentioned description of the duplex stainless steel included in the container body 2 also applies to the duplex stainless steel included in the reinforcing member 3. Since the duplex stainless steel included in the reinforcing member 3 can be understood by referring to the above-mentioned description, a repeated explanation will be omitted. The reinforcing member 3 may be made of ferritic stainless steel. The reinforcing member 3 may be duplex stainless steel of a grade equal to or higher than that of the container body 2, which makes it easier to improve corrosion resistance. In terms of the types of duplex stainless steel, the Ni and Mo content increases in the order of lean duplex steel, general-purpose duplex steel, and super duplex steel, and it can be said that the grade of the duplex stainless steel increases in this order.

[0076] In the stainless steel rectangular container 1, the side wall portion 22 may be inclined with respect to the bottom plate portion 21. The upper end of the side wall portion 22 may have a folded portion or a flange. Since the relationship in formula (1) above assumes the most severe conditions, it can be naturally understood that the effects of the present invention will be achieved even if the container body 2 has a structure that improves strength.

[0077] Depending on the conditions during the heat treatment, the stainless steel rectangular container 1 may undergo a first mode of bending deformation that is convex downwards, influenced by the weight of the object being treated and the heating position.

[0078] If the bottom surface 21A of the container body 2 is an extremely rectangular shape, it is considered unlikely that the first mode of bending deformation will occur, and even if the first mode of bending deformation does occur, it is considered unlikely that the amount of deformation will be large. In the stainless steel rectangular container 1, the container body 2 may have a second side S2 (long side) of the bottom surface 21A that is three times or less the length of the first side S1 (short side). Also, the container body 2 may have a side wall portion 22 that is less than or equal to the length of the first side S1 (short side), and may be 1 / 4 or less the length of the first side S1 (short side).

[0079] Thickness t of the container body 2 ｉ For example, it may be 0.1 mm or more, or 0.2 mm or more. ｉ The thickness of the reinforcing member 3 is, for example, 5.0 mm or less, 3.0 mm or less, or 2.0 mm or less. ｈ For example, it may be greater than 0 mm, may be 0.1 mm or more, may be 0.2 mm or more, and may be 0.4 mm or more. Plate thickness t ｈ For example, the thickness t may be 5.0 mm or less, 3.0 mm or less, or 2.0 mm or less. ｈ is the plate thickness t ｉ It can be larger than that.

[0080] The weight M of the object to be processed placed on the bottom plate 21 is not particularly limited, as it is related to the size of the container body 2, etc. The weight M may be, for example, 0.5 kg or more, or 2.5 kg or less.

[0081] [Embodiment 2] Another embodiment of the present invention will be described below with reference to the drawings. Note that the configuration other than that described in this embodiment is the same as that of Embodiment 1.

[0082] Figure 9 is a schematic perspective view showing the configuration of a stainless steel rectangular container for heat treatment in Embodiment 2 of the present invention. As shown in Figure 9, in the stainless steel rectangular container 1 of Embodiment 2, the reinforcing member 3 may be joined to the inside of the container body 2. If the end of the reinforcing member 3 does not protrude to the outside of the container body 2, snagging with other members can be made less likely. In addition, for example, the possibility of damage to the stand on which the stainless steel rectangular container 1 is placed can be reduced.

[0083] [Summary] The stainless steel rectangular container for heat treatment according to embodiment 1 of the present invention comprises a container body having a rectangular bottom plate portion on which the object to be heat-treated is placed, and four side wall portions connected to each of the four sides of the bottom plate portion, and reinforcing members joined to each of the four corners formed by the bottom plate portion and each of the side wall portions of the container body, wherein the container body is made of duplex stainless steel having a mixture of austenite and ferrite phases.

[0084] In the stainless steel rectangular container for heat treatment according to embodiment 2 of the present invention, in embodiment 1, the two side walls are connected to each other at the corner, and the reinforcing member includes two reinforcing side plates that are joined to each side wall at the corner, and a reinforcing bottom plate that is joined to the bottom plate at the corner, the two reinforcing side plates are connected to each other, and each of the two reinforcing side plates is connected to the reinforcing bottom plate.

[0085] In the stainless steel rectangular container for heat treatment according to embodiment 3 of the present invention, in embodiment 2, the joint between the side wall portion and the reinforcing side plate and the joint between the bottom plate portion and the reinforcing bottom plate are both welded joints.

[0086] The stainless steel rectangular container for heat treatment in embodiment 4 of the present invention further comprises, in embodiment 2, a first joining member that joins the side wall portion and the reinforcing side plate to each other, and a second joining member that joins the bottom plate portion and the reinforcing bottom plate to each other.

[0087] In embodiment 5 of the present invention, the stainless steel rectangular container for heat treatment is such that, in any one embodiment of embodiments 1 to 4, the container body has an unreinforced portion on at least a part of each side wall where the reinforcing member is not joined, and the unreinforced portion has less rigidity than the corner portion.

[0088] In embodiment 6 of the present invention, the stainless steel rectangular container for heat treatment is, in any one embodiment of embodiments 2 to 5, wherein the height of the reinforcing side plate is 1 / 2 or more of the height of the side wall and less than or equal to the height of the side wall, and the length along the direction in which the side wall extends is 1 / 20 or more of the length of the long side of the bottom surface and 1 / 4 or less of the length of the short side of the bottom surface.

[0089] In embodiment 7 of the present invention, the stainless steel rectangular container for heat treatment, in any one embodiment of embodiments 2 to 6, has a shape in which the reinforcing bottom plate has a shape that includes at least a triangular region formed by two sides connected to each of the two reinforcing side plates and a virtual side connecting the endpoints opposite to the intersection of the two sides.

[0090] In embodiment 8 of the present invention, the stainless steel rectangular container for heat treatment is, in any one embodiment of embodiments 1 to 7, wherein the height of the side wall portion is less than the length of the short side of the bottom surface of the container body, the container body has a bent portion at the boundary between the bottom plate portion and the side wall portion, the angle between the bottom surface of the bottom plate portion and the inner surface of the side wall portion is approximately 90 degrees, and the curvature of the bent portion is 2 times or less the plate thickness of the container body.

[0091] In embodiment 9 of the present invention, the stainless steel rectangular container for heat treatment, in any one embodiment of embodiments 1 to 8, has a bottom plate portion having a first side and a second side intersecting the first side, and during heat treatment, a second mode of bending deformation occurs in the container body, in which the bottom plate portion curves along either or both of a first imaginary line along the direction in which the first side extends and a second imaginary line along the direction in which the second side extends, and this second mode of bending deformation occurs preferentially over a first mode of bending deformation, in which the bottom plate portion curves along the diagonal of the bottom surface, and the degree of the first mode of bending deformation is smaller than the degree of the second mode of bending deformation.

[0092] In embodiment 10 of the present invention, when the reinforcing member satisfies the following relationship (1) during heat treatment, the stainless steel rectangular container for heat treatment does not undergo a first mode of bending deformation in the container body, in which the bottom plate portion curves with respect to the diagonal of the bottom surface as the axis; (10 / S) + 0.15 × ΔT - 10 × M - 30 × t ｉ <10 × t ｈ (1) Here, S: ratio of the area of ​​the bottom surface to the area of ​​the bottom surface on which the object to be processed is placed ΔT: difference (°C) between the heating temperature during the heat treatment and the temperature of the object to be processed at the start of the heat treatment M: weight (kg) of the object to be processed placed on the bottom plate t ｉ : Thickness of the container body (mm) t ｈ : This is the plate thickness (mm) of the reinforcing member.

[0093] In embodiment 11 of the present invention, the stainless steel rectangular container for heat treatment is made of duplex stainless steel having a mixture of austenite and ferrite phases, as is the case in any one embodiment of embodiments 1 to 10.

[0094] In embodiment 12 of the present invention, the stainless steel rectangular container for heat treatment is, in any one embodiment of embodiments 1 to 11, wherein the duplex stainless steel has a chemical composition in which the Ni content is 4% or less and the Mo content is 1% or less.

[0095] [Additional Notes] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0096] An embodiment of the present invention will be described below. The following embodiment is an example for confirming the effects of the present invention.

[0097] First, a container body made of duplex stainless steel was prepared. The container body had dimensions of 500 mm (length) x 330 mm (width) x 20 mm (height), and the material of the container body was NSSC 2120 (registered trademark). NSSC 2120 (registered trademark) is a material of the 21%Cr-2%Ni-3%Mn-1%Cu-0.17%N system. The plate thickness of the container body was 0.5 mm or 0.8 mm.

[0098] Next, a stainless steel rectangular container for heat treatment was obtained with reinforced corners by welding reinforcing members to the outside of the corners of the container body. The thickness of the reinforcing members was 1 mm, 2 mm, or 3 mm. The material of the reinforcing members was the same as that of the container body. In addition, a comparative example of a stainless steel rectangular container without corner reinforcement was also prepared.

[0099] The material to be treated was placed in the prepared rectangular container. Wet gravel was used as the material to be treated. The temperature of the material to be treated was set to -10°C or 20°C, and the weight of the material to be treated was set to 1.0 kg, 2.0 kg, or 2.5 kg. The ratio S of the area of ​​the material to be treated relative to the bottom surface of the rectangular container was set to 0.50 (50%), 0.66 (66%), or 0.80 (80%).

[0100] The object to be processed was placed on a container body that satisfies the relationship in equation (1) above, or does not satisfy the relationship in equation (1) above, or whose corners are not reinforced with reinforcing members, and then subjected to heat treatment. For the heat treatment, the stainless steel square container on which the object to be processed was placed was inserted into a heating container and heated by hot air convection. The heating temperature was set to 170°C.

[0101] The conditions and results for each test are shown in Table 1. In Table 1, the modes of bending deformation are abbreviated as follows: the first mode of bending deformation is denoted by the number 1, and the second mode of bending deformation is denoted by the number 2. In addition, in Table 1, for test examples where no reinforcing members were attached (only the container body), the reinforcing plate thickness is indicated as 0.0 mm.

[0102]

[0103] As shown in Table 1, when the relationship in equation (1) is satisfied, bending deformation of the second mode occurs instead of bending deformation of the first mode. Test examples No. 7 and 13, in which the value on the left side of equation (1) is less than 0, are provided as reference examples.

[0104] Comparing Test Example No. 1 and Test Example No. 3, although the conditions were the same except for the presence or absence of reinforcing members, heat treatment caused bending deformation of the first mode in Test Example No. 1, while in Test Example No. 3, reinforcing members were joined to the corners, satisfying the relationship in equation (1), resulting in bending deformation of the second mode. On the other hand, comparing Test Example No. 2 and Test Example No. 3, although the conditions were the same except for the plate thickness of the reinforcing members, in Test Example No. 2, the relationship in equation (1) was not satisfied, resulting in bending deformation of the first mode.

[0105] In Test Examples No. 4 and No. 5, the proportion S of the mounting area was relatively large, and from the viewpoint of suppressing the bending deformation of the first mode, the heat treatment conditions were relatively mild. However, the reinforcing members were not joined, and the relationship in equation (1) was not satisfied, resulting in the bending deformation of the first mode.

[0106] Comparing Test Example No. 5 and Test Example No. 6, although the conditions were the same except for the presence or absence of reinforcing members, the heat treatment resulted in a first-mode bending deformation in Test Example No. 5, while in Test Example No. 6, reinforcing members were joined to the corners, satisfying the relationship in equation (1), which resulted in a second-mode bending deformation.

[0107] As shown in Test Example No. 7, even without reinforcing members being joined, by significantly increasing the proportion of the mounting area S and the mounted weight M to satisfy the relationship in equation (1), a second mode of bending deformation occurred due to the heat treatment. In Test Example No. 8, the reinforcing members were not joined, the proportion of the mounting area S and the mounted weight M were relatively small, and the temperature difference ΔT was relatively large. As a result, the relationship in equation (1) was not satisfied, and a first mode of bending deformation occurred due to the heat treatment. In Test Example No. 9, the reinforcing members were joined, but the relationship in equation (1) was not satisfied, and a first mode of bending deformation occurred due to the heat treatment. In Test Example No. 10, the reinforcing members were joined and the relationship in equation (1) was satisfied, and a second mode of bending deformation occurred due to the heat treatment. Thus, it can be seen that the mode of bending deformation can be controlled based on the relationship in equation (1).

[0108] Comparing Test Example No. 11 and Test Example No. 12, although the conditions were the same except for the presence or absence of reinforcing members, the heat treatment resulted in a first-mode bending deformation in Test Example No. 11, while in Test Example No. 12, the reinforcing members were joined to the corners, satisfying the relationship in equation (1), which resulted in a second-mode bending deformation.

[0109] In Test Example No. 11, the container plate thickness t ｉ By keeping the thickness at 0.8 mm, changing the proportion S of the mounting area under the heat treatment conditions to 0.66, and increasing the mounting weight M to 2.0 kg, the relationship in equation (1) was satisfied even without reinforcing members being joined to the corners, as in Test Example No. 13, and second-mode bending deformation occurred.

[0110] According to the present invention, it is possible to provide a stainless steel rectangular container for heat treatment that exhibits minimal thermal deformation during heating. Therefore, it has high potential for industrial application.

[0111] 1 Stainless steel rectangular container 2 Container body 2C Corner section 2N Unreinforced section 3 Reinforcement members 21 Bottom plate section 21A Bottom surface 21B Back surface 22 Side wall section 31 Reinforced bottom plate 32 Reinforced side plate

Claims

1. A rectangular stainless steel container for heat treatment, comprising: a container body having a rectangular bottom plate on which an object to be heat-treated is placed, and four side walls connected to each of the four sides of the bottom plate; and reinforcing members joined to each of the four corners formed by the bottom plate and each of the side walls of the container body, wherein the container body is made of duplex stainless steel in which austenite and ferrite phases are mixed.

2. At the corner, the two side wall portions are connected to each other, and the reinforcing member includes two reinforcing side plates that are joined to each side wall portion at the corner, and a reinforcing bottom plate that is joined to the bottom plate portion at the corner, the two reinforcing side plates are connected to each other, and each of the two reinforcing side plates is connected to the reinforcing bottom plate, as described in claim 1.

3. The stainless steel rectangular container for heat treatment according to claim 2, wherein the side wall portion and the reinforcing side plate, and the bottom plate portion and the reinforcing bottom plate are all joined by welding.

4. The stainless steel rectangular container for heat treatment according to claim 2, wherein the side wall portion and the reinforcing side plate, and the bottom plate portion and the reinforcing bottom plate are all joined by a joining member.

5. The container body has an unreinforced portion on at least a part of the side wall where the reinforcing member is not joined, and the unreinforced portion has less rigidity than the corner portion, as described in claim 1.

6. The stainless steel rectangular container for heat treatment according to claim 2, wherein the height of the reinforcing side plate is at least half the height of the side wall and less than or equal to the height of the side wall, and the length along the direction in which the side wall extends is at least 1 / 20 of the length of the long side of the bottom surface and at least 1 / 4 of the length of each side to which the reinforcing side plates are joined.

7. The stainless steel rectangular container for heat treatment according to claim 2, wherein the reinforcing bottom plate has a shape that includes at least a triangular region formed by two sides connected to each of the two reinforcing side plates and a virtual side connecting the endpoints opposite to the intersection of the two sides.

8. The stainless steel rectangular container for heat treatment according to claim 1, wherein the height of the side wall portion is less than the length of the shorter side of the bottom portion, the container body has a bent portion at the boundary between the bottom plate portion and the side wall portion, the angle between the bottom surface of the bottom plate portion and the inner surface of the side wall portion is approximately 90 degrees, and the curvature of the bent portion is 2 times or less the thickness of the container body.

9. The stainless steel rectangular container for heat treatment according to claim 1, wherein the bottom plate portion has a first side and a second side intersecting the first side, and during heat treatment, a second mode of bending deformation occurs in the container body, in which the bottom plate portion curves along either or both of a first imaginary line along the direction in which the first side extends and a second imaginary line along the direction in which the second side extends, and this second mode of bending deformation occurs preferentially over a first mode of bending deformation, in which the bottom plate portion curves along the diagonal of the bottom surface, and the degree of the first mode of bending deformation is smaller than the degree of the second mode of bending deformation.

10. When heat treatment is performed, if each reinforcing member satisfies the relationship of the following formula (1), the container body does not undergo a first mode of bending deformation in which the bottom plate portion curves with the diagonal of the bottom surface as the axis, as described in claim 1; (10 / S) + 0.15 × ΔT - 10 × M - 30 × t ｉ <10 × t ｈ (1) Here, S: ratio of the area of ​​the bottom surface to the area of ​​the bottom surface on which the object to be processed is placed ΔT: difference (°C) between the heating temperature during the heat treatment and the temperature of the object to be processed at the start of the heat treatment M: weight (kg) of the object to be processed placed on the bottom plate t ｉ : Thickness of the container body (mm) t ｈ : This is the plate thickness (mm) of the reinforcing member.

11. The stainless steel rectangular container for heat treatment according to claim 1, wherein the reinforcing member is made of duplex stainless steel having a mixture of austenite and ferrite phases.

12. The stainless steel rectangular container for heat treatment according to claim 1, wherein the duplex stainless steel has a chemical composition in which the Ni content is 4% or less and the Mo content is 1% or less.

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