Steel production method and metal tray

Abstract

To provide a method for producing a steel material, which includes a heat treatment step of performing oil quenching after holding at a high temperature and can give homogeneous quenching, and a metal tray for oil quenching heat treatment used therefor.SOLUTION: A flat plate-shaped metal tray is used in a heat treatment process in which a rod-shaped steel material is placed on the metal tray, heated and held in a heat treatment furnace, and then immersed in oil for oil quenching. A plurality of rod-shaped support members is arranged and fixed at predetermined intervals so as to be parallel to each other on an upper main surface of a plate-shaped main body part. The support member has a curved upper surface and is in line contact with the lower surface of the steel material to support the steel material such that the steel material is spaced upward from the upper main surface of the main body part. A method for producing a steel material includes heating and holding the rod-shaped steel material at 1100°C or higher in a heat treatment furnace while the rod-shaped steel material is placed on the metal tray, and then immersing the rod-shaped steel material in oil for oil quenching.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a steel material including a heat treatment step and a metal tray used therefor, and more particularly, to a method for manufacturing a steel material including a heat treatment step of oil quenching after heating and holding at a high temperature, and a metal tray for oil quenching heat treatment used therefor.

Background Art

[0002] In the heat treatment of heat-resistant steels such as SUH616 used for turbine blade materials, etc., angle bars of heat-resistant steel as objects to be heat-treated are placed on a plate-shaped metal tray, and after heating and holding at a high temperature of 1100 °C or higher, typically at a higher temperature such as 1140 °C, in a heat treatment furnace, the entire tray is placed in an oil tank for oil quenching.

[0003] For example, in Patent Document 1, in the case of carburizing treatment of small parts such as gears, gear shafts, and cam shafts, a grid-shaped C / C composite tray used for taking out these workpieces from a heat treatment furnace in a state of being placed on a tray and directly quenching them in an oil tank is disclosed. Since the C / C composite tray is oxidized at a high temperature of 500 °C or higher, it is stated that it is used in an environment that does not contain oxidizing gas. Also, it is described that in heat treatment where the quenching temperature is high (1200 to 1300 °C), such as vacuum quenching of high-speed tool steel, a heat treatment tray made of a Ni-based superalloy material or a high melting point metal material such as Mo should be used.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, when a relatively large steel material made of heat-resistant steel, particularly a long bar steel, is heated and held at a high temperature of 1100°C or higher and then oil quenched, it is preferable to use a grid-shaped metal tray in order to improve the oil circulation around the object to be heat-treated and obtain uniform quenching. At this time, if the quenching is not uniform, unevenness will occur, and in some cases, the steel material will be bent.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a steel material that includes a heat treatment step of oil quenching after holding at a high temperature of 1100°C or higher and can give uniform quenching, and a metal tray for oil quenching heat treatment used therefor.

Means for Solving the Problems

[0007] The metal tray for heat treatment according to the present invention is a flat metal tray used in a heat treatment process in which a bar-shaped steel material is placed, heated and held in a heat treatment furnace, and then immersed in oil for oil quenching. On the upper main surface of the flat main body portion, a plurality of bar-shaped support members are arranged and fixed at predetermined intervals so as to be parallel to each other. The support member has an upper surface formed of a curved surface and is in line contact with the lower surface of the steel material to support the steel material spaced upward from the upper main surface of the main body portion.

[0008] According to such a feature, it is possible to reduce the influence on the steel material from the support member and the main body portion during heating and holding of the steel material and during oil quenching, and it is possible to give uniform quenching to the steel material.

[0009] In the above-described invention, the main body portion may be characterized in that a metal angle or a metal plate is incorporated in a grid shape inside a rectangular parallelepiped outer frame made of a metal plate material. According to such a feature, it is possible to enhance the oil circulation around the steel material during oil quenching and give uniform quenching to the steel material. In addition, the durability of the metal tray can be enhanced.

[0010] In the above-described invention, the support member may be a round bar, and may be fixed while being spaced upward from the upper main surface of the main body portion. According to such a feature, the oil circulation around the steel material during oil quenching can be further enhanced, and uniform quenching can be imparted to the steel material.

[0011] In the above-described invention, it may be characterized in that unit trays each composed of the main body portion with the support member fixed thereto are detachably stacked in two stages with a vertical space therebetween. Further, column members are implanted on the upper main surface of the unit tray in the lower stage, and pocket holes are provided on the lower main surface of the main body portion of the unit tray in the upper stage, and the pocket holes may be detachably fitted to the tips of the column members. According to such a feature, many steel materials can be processed at once without impairing the uniform quenching of the steel materials, and the processing efficiency is excellent.

[0012] Further, a method for manufacturing a steel material according to the present invention is a method for manufacturing a steel material including a heat treatment step of placing a bar-shaped steel material on a flat metal tray, heating and holding it at 1100 °C or higher in a heat treatment furnace, and then immersing it in oil for oil quenching. On the upper main surface of the flat main body portion, a plurality of bar-shaped support members are arranged and fixed at predetermined intervals so as to be parallel to each other. The support member has an upper surface formed of a curved surface, and the lower surface of the single or a plurality of steel materials arranged so as to extend in a direction perpendicular to the longitudinal direction of the support member is in line contact with the support member, and the steel materials are heat treated and oil quenched while being spaced upward from the upper main surface of the main body portion and supported.

[0013] According to such a feature, even in the heat treatment of steel materials that requires heating and holding at a high temperature, uneven heating during heating and holding can be suppressed, and uniform quenching can be imparted to the steel materials.

[0014] In the above-described invention, the main body portion may be characterized in that a metal angle material or a metal plate material is incorporated in a grid shape inside a rectangular parallelepiped outer frame made of a metal plate material. According to such a feature, the oil circulation around the steel material during oil quenching can be enhanced, and uniform quenching can be imparted to the steel material.

[0015] In the above-described invention, the unit trays each consisting of the main body part to which the support member is fixed are detachably stacked in two levels with a vertical gap therebetween, and one or a plurality of the steel materials are supported on each of the unit trays. After being heated and held in the heat treatment furnace, the unit trays are separated and each is individually oil quenched. This may be a feature. According to such a feature, many steel materials can be processed at once without impairing the uniform quenching of the steel materials, and the processing efficiency is excellent.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Embodiment for Carrying Out the Invention

[0017] A metal tray as one embodiment according to the present invention and a method for manufacturing a steel material using the same will be described with reference to FIGS. 1 to 3.

[0018] As shown in FIGS. 1 and 2, the metal tray 1 is formed by stacking two unit trays 1a and 1b in two levels. The unit trays 1a and 1b each have a main body part 10 having a flat plate shape as a whole, and a plurality of support members 11 arranged on the upper main surface 10a (particularly refer to FIG. 2) of the main body part 10. The support members 11 are rod-shaped bodies, and are arranged at a predetermined interval so as to be parallel to each other and fixed to the main body part 10. Further, the support members 11 are arranged so as to be orthogonal to the longitudinal direction of the metal tray 1 (the upper left - lower right direction of the paper surface of FIG. 1) and extend horizontally.

[0019] The metal tray 1 is used in a heat treatment process in which a rod-shaped steel material is placed on the support members 11 of the respective unit trays 1a and 1b, heated and held in a heat treatment furnace, and then immersed in oil with the steel material still placed thereon for oil quenching. Further, by the support member 11, the lower surface of the steel material is supported by the support member 11 and placed on the main body portion 10.

[0020] The main body portion 10 includes a rectangular parallelepiped outer frame 2 made of a metal plate material, and vertical beams 3 and horizontal beams 4 incorporated in a grid shape inside thereof. The vertical beams 3 and the horizontal beams 4 are each made of a metal angle material or a metal plate material, and their both ends are joined to the inner side surfaces of the outer frame 2 while being combined with each other. In the figure, it is assumed that six vertical beams 3 and three horizontal beams 4 are combined. The vertical beams 3 and the horizontal beams 4 are combined in a grid shape so as to reduce the weight of the main body portion 10 and suppress its deformation even at high temperatures. For example, the vertical beam 3 is arranged with the long side of the vertical cross-section having a rectangular shape facing the vertical direction, reducing the thickness in the left-right direction while suppressing the bending in the up-down direction. On the other hand, the horizontal beam 4 is arranged with the long side of the vertical cross-section having a rectangular shape facing the horizontal direction, reducing the thickness in the up-down direction while suppressing the bending in the horizontal direction, that is, the longitudinal displacement between the vertical beams 3.

[0021] Note that the upper main surface 10a of the main body portion 10 is an extension surface of the upper surface of the vertical beam 3 having the largest area on the upper sides of the unit trays 1a and 1b. Similarly, the lower main surface 10b is an extension surface of the lower surface of the vertical beam 3.

[0022] The upper unit tray 1a of the two - layer stack is provided with a pocket - hole portion 5 having pocket - holes at six locations, namely, at the four inner corners of the outer frame 2 and at two locations on the left and right in the longitudinal center, as viewed from the lower main surface 10b. On the other hand, the lower unit tray 1b is provided with a pedestal portion 6 at a position corresponding to the pocket - hole portion 5. Further, a column member 7 extending upward from the upper main surface 10a is implanted in the pedestal portion 6. And the pocket - hole portion 5 is detachably fitted to the tip of the column member 7. As a result, the unit trays 1a and 1b can be detachably stacked in two layers with a vertical gap therebetween. By doing so, for example, the upper unit tray 1a can be lifted and separated from the lower unit tray 1b, and even when stacked in two layers, due to the vertical gap, steel materials can be placed on the lower unit tray 1b. That is, during the heat treatment process of the steel materials, each of the unit trays 1a and 1b can be used separately or stacked in two layers.

[0023] Both ends of the support member 11 are fixed to the fixing member 12. The fixing member 12 is in the shape of a substantially flat plate, is fixed to the inner surface of the outer frame 2, protrudes upward from the upper main surface 10a of the main body portion 10, and fixes the support member 11 near the protruding end portion. As a result, the support member 11 is fixed at a distance above the upper main surface 10a. Further, the support member 11 is supported from below by convex support portions 3a (see FIG. 3) protruding from the upper surface of the vertical girder 3 at all positions where it intersects the vertical girder 3 in a top - view. That is, the support member 11 is supported by the vertical girder 3 via the convex support portions 3a.

[0024] Referring also to FIG. 3(a), the upper surface of the support member 11 is a curved surface convex upward, and is in line contact with the lower surface of the supported steel material M. As the support member 11, for example, using a round bar can easily obtain a structure in line contact with the steel material, which is preferable. Also, since the support member 11 is fixed at a distance above the upper main surface 10a as described above, the supported steel material M is also separated upward from the upper main surface 10a. As a result, the steel material supported by the support member 11 is supported at a distance above the upper main surface 10a of the main body portion 10.

[0025] Incidentally, as shown in Fig. (b), in a conventional metal tray, the support member 111 is generally a plate material and its upper surface is flat. In this case, when the lower surface of the steel material M is flat, the contact between the lower surface of the steel material M and the support member 111 is a surface contact. Then, when the steel material M is heated and held and quenched, it is affected by the metal tray including the support member 111. That is, the portion closer to the metal tray has a delay in temperature change due to the heat capacity of the metal tray compared to the farther portion. Further, at the contact portion, radiant heat is blocked and air flow does not pass, etc. As a result, the heat treatment of the steel material M becomes non-uniform. Also, in the oil quenching after heating and holding, the oil circulation to the contact surface with the support member 111 is poor, resulting in non-uniform quenching. In particular, when the steel material M is a heat-resistant steel such as that heated and held at a high temperature of 1100 °C or more in a heat treatment furnace, the non-uniformity of hardness generated in the steel material M due to such non-uniform heat treatment including quenching becomes prominent. Also, unevenness occurs in the hardness of the oxide film formed on the surface due to uneven quenching. As a result, for example, in the removal of the oxide film by shot blasting, the oxide film remains only at the contact portion with the support member 111, and problems such as instability in machining such as cutting may occur.

[0026] On the other hand, according to the above-described metal tray 1, the single or plural steel materials M are supported while being spaced upward from the upper main surface 10a of the main body portion 10, and further, are supported by line contact by the curved upper surface of the support member 11. By spacing the steel material M from the main body portion 10, the influence on the steel material M from the support member 11 and the main body portion 10 can be reduced during heating and holding and during quenching, respectively. That is, the partial delay in temperature fluctuation of the steel material M due to the heat capacity of the main body portion 10 and the support member 11 can be suppressed. Also, by supporting in line contact, the oil circulation during quenching can be made good to give uniform quenching. In particular, even in the heat treatment at 1100 °C or more as described above, uneven heating during heating and holding can be suppressed and uniform quenching can be imparted. Examples of the steel material having a heat treatment temperature of 1100 °C or more are typically martensitic heat-resistant steels such as SUH616, and the heat treatment temperature is 1140 °C.

[0027] Also, as described above, the main body portion 10 incorporates vertical beams 3 and horizontal beams 4 in a grid-like pattern inside the outer frame 2. By doing so as well, a wide passage for oil in the vertical direction is provided in the main body portion 10, enhancing the circulation of oil around the steel material M during oil quenching, enabling uniform quenching of the steel material M, and moreover, it is excellent in productivity.

[0028] As described above, the metal tray 1 can be used with the unit trays 1a and 1b alone, or can also be used in a two-tier stacked manner. By stacking two tiers, it does not impair the uniform quenching of the steel material M, can process a large number of steel materials at once, and is more excellent in productivity. Also, in heat retention, it can be stacked in two tiers, and during quenching, each unit tray can be immersed in a separate oil layer to further improve the oil circulation.

[0029] Note that as the metal tray 1 as described above, since it is used for heat treatment at a high temperature of 1100°C or higher, it is preferably made of a heat-resistant steel such as a Ni-based alloy or SUH616.

[0030] As described above, representative embodiments of the present invention have been described, but the present invention is not necessarily limited thereto, and those skilled in the art will be able to find various alternative embodiments and modification examples without departing from the gist of the present invention or the scope of the appended claims.

Explanation of Reference Numerals

[0031] 1 Metal tray 2 Outer frame 3 Vertical beam 4 Horizontal beam 7 Column member 10 Main body portion 11 Support member

Claims

1. A flat metal tray used in a heat treatment process in which a rod-shaped steel material is placed, heated and held in a heat treatment furnace, and then immersed in oil for oil quenching, comprising: On the upper main surface of the flat main body portion, a plurality of rod-shaped support members are arranged and fixed at predetermined intervals so as to be parallel to each other. The support member has an upper surface formed of a curved surface and supports the steel material by line contact with the lower surface of the steel material, separating the steel material upward from the upper main surface of the main body portion. A metal tray characterized by this.

2. The metal tray according to claim 1, wherein the main body portion is formed by incorporating metal angle members or metal plates in a grid shape inside a rectangular parallelepiped outer frame made of a metal plate material.

3. The metal tray according to claim 2, wherein the support member is a round bar and is fixed while being separated upward from the upper main surface of the main body portion.

4. The metal tray according to any one of claims 1 to 3, characterized in that unit trays each consisting of the main body portion to which the support members are fixed are detachably stacked in two stages with a vertical separation therebetween.

5. A column member is implanted on the upper main surface of the unit tray in the lower stage, and a pocket hole portion is provided on the lower main surface of the main body portion of the unit tray in the upper stage, and the pocket hole portion is detachably fitted to the tip of the column member. The metal tray according to claim 4, characterized by this.

6. A method for manufacturing a steel material, including a heat treatment process in which a rod-shaped steel material is placed on a flat metal tray, heated and held at 1100 °C or higher in a heat treatment furnace, and then immersed in oil for oil quenching, comprising: On the upper main surface of the flat main body portion, a plurality of rod-shaped support members are arranged and fixed at predetermined intervals so as to be parallel to each other. The support member has an upper surface formed of a curved surface, and one or a plurality of the steel materials arranged so as to extend in a direction perpendicular to the longitudinal direction of the support member are in line contact with the upper surface of the support member on the lower surface, and are heat treated and oil quenched while being supported while being separated upward from the upper main surface of the main body portion. A heat treatment method for steel materials characterized by this.

7. The heat treatment method for steel materials according to claim 6, wherein the main body portion is formed by incorporating metal angle members or metal plates in a grid shape inside a rectangular parallelepiped outer frame made of a metal plate material.

8. The unit trays each consisting of the main body part to which the support member is fixed are detachably stacked in two levels with a vertical separation, and one or a plurality of the steel materials are supported on each of the unit trays. After heating and holding in the heat treatment furnace, the unit trays are separated and each is individually oil quenched. The heat treatment method for steel materials according to claim 6 or 7, characterized in that.

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