JP2006299360A - Heat treatment method of complex roll for rolling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat treatment method of a complex roll for rolling with which in the heating to austenizing temperature at the quenching time, the heat-rising of an inner layer is restricted to the minimum at the heating of an outer layer, and the brittleness of the inner layer and the coarsening of crystal grain are prevented and also, only the outer layer can be austenized in a short time and the carbide in the outer layer is sufficiently made to solid-solution in the matrix and thus, the excellent characteristic of a high speed steel can be obtained. <P>SOLUTION: In the heat treatment method of the complex roll for rolling, the heating to austenizing temperature when the quenching is applied to the complex roll for rolling, is performed as the followings, that is; a first process for heating the complex roll for rolling in a first heating furnace at 10-30°C/Hr temperature-rising speed from the room temperature to 600-700°C, after heat-insulating the portion held into a second heating furnace in the inner layer and both end surface parts in the outer layer in the complex roll for rolling; and a second process for heating the outer layer at 300-600°C/Hr temperature-rising speed from 600-700°C to 1050-1150°C, after transporting the complex roll for rolling into the second heating furnace are contained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a heat treatment method of a composite roll for hot rolling or cold rolling using a high-speed material as an outer layer.

  Generally, composite rolls for hot rolling or cold rolling are required to have wear resistance on the outer surface side and toughness on the inner side. Therefore, an outer layer formed by centrifugal casting of high-speed cast iron material with excellent wear resistance. In addition, a roll having a composite structure in which the inner layer (or core) of cast iron, cast steel or alloy steel having excellent toughness is integrated metallurgically is used.

  The composite roll as described above is manufactured by the centrifugal casting method, and the austenite temperature is maintained by holding the roll in a heating furnace at 850 to 1000 ° C. for 2 to 10 hours in order to give the outer layer high hardness characteristics. After quenching, quenching is performed by quenching by spray water cooling, blast cooling, etc., and after tempering, holding at 500 to 650 ° C. for 2 to 10 hours is performed several times for the purpose of adjusting the hardness and reducing residual stress. Yes.

  Here, in order to obtain sufficient hardness by quenching, it is necessary to increase the austenitizing temperature. In this case, if cast iron material is used as the inner layer material, the internal segregation part melts. In addition, when steel-based materials are used as the inner layer material, there is a problem that the crystal grains become coarse and both the toughness deteriorates.

  As a method for solving such a problem, for example, Patent Document 1 discloses the following method. That is, in the method described in Patent Document 1, the entire roll is preheated uniformly to 1000 ° C. or lower, for example, 800 ° C., and then the roll is rotated by a burner provided at a plurality of locations in the axial direction of the roll while rotating the roll. Only the outer layer part is heated, and as a result, the temperature of the boundary between the outer layer and the shaft core part (inner layer) is set to a temperature of 1100 ° C. or less, so that the inner segregation part is melted when the cast iron material is used. In addition, it is intended to solve the problem that the toughness is deteriorated by suppressing the coarsening of crystal grains by the steel-based material.

JP-A-4-66619 Japanese Patent No. 3230899

  However, the method described in Patent Document 1 has the following problems and is not a practical technique. That is, it is disclosed that the entire roll is uniformly preheated at the heating temperature described in Patent Document 1 at the time of quenching, that is, 1000 ° C. or less, and in the examples at 800 ° C., but at this temperature, the inner layer is already austenitized. This is not sufficient from the viewpoint of preventing embrittlement of the inner layer and coarsening of crystal grains.

In Patent Document 1, as a heating method after uniformly preheating the entire roll, only the outer layer portion of the roll is heated by the burners provided at the plurality of locations, and the temperature at the boundary between the outer layer and the shaft core portion is set. It is disclosed that the temperature is 1100 ° C. or lower. However, if this is done in a heating furnace,
It will receive the radiant heat in the heating furnace when the burner is heated. Therefore, it receives heat transfer from the roll shaft part other than the roll body part and both cylinder ends, and it is difficult to set the boundary between the outer layer and the shaft core part to 1100 ° C. or less.
Therefore, if cast iron is used for the shaft core (inner layer), the segregated part inside will melt, and if steel-based materials are used, the grains will become coarser and the toughness will deteriorate in either case. There was also a problem.

  Therefore, in order to prevent embrittlement of the inner layer and coarsening of crystal grains by carrying out this method, it is necessary to work outside the heating furnace, so the environment is significantly polluted by the flue gas accompanying the work, A fire may occur, making the work environment extremely dangerous.

  Therefore, the present invention has been made in view of such problems, and the object thereof is to suppress the heating of the inner layer to a minimum during the heating of the outer layer in the heating up to the austenitizing temperature at the time of quenching, It is a new and capable of preventing embrittlement of the inner layer and coarsening of the crystal grains, as well as being able to austenite only the outer layer in a short time, sufficiently dissolving the carbide of the outer layer in the base, and extracting the characteristics of high speed. An object of the present invention is to provide an improved heat treatment method for a composite roll for rolling.

  In order to solve the above-mentioned problems, according to one aspect of the present invention, rolling is produced by metallurgically integrating an outer layer made of a high-speed material formed by centrifugal casting with an inner layer made of a material having toughness. A heat treatment method for a rolling composite roll is provided in which the composite roll is subjected to a quenching treatment that is cooled after heating to the austenitizing temperature and then tempered.

  In the heat treatment method, the heating to the austenitizing temperature includes a first step performed in a first heating furnace and a second step performed in a second heating furnace. Specifically, in the first step, after the part of the composite roll for rolling accommodated in the second heating furnace of the inner layer and the both end face parts of the outer layer are insulated, the composite for rolling is performed in the first heating furnace. The entire roll is heated from room temperature to 600 to 700 ° C. at a heating rate of 10 to 30 ° C./Hr, and the second step is to move the rolling composite roll to the second heating furnace and Is heated from 600 to 700 ° C. to 1050 to 1150 ° C. at a temperature rising rate of 300 to 600 ° C./Hr.

  Thus, in the heat treatment method for a composite roll for rolling according to the present invention, first, only the roll shaft portion of the composite roll for rolling housed in the second heating furnace used in the second step and both end portions of the roll body portion are used. Is heated to the maximum within a temperature range of 600 ° C. or higher and 700 ° C. or lower, that is, a range in which the inner layer does not become austenite, in the first heating furnace (first step). Next, the roll is moved to the second heating furnace. Here, in this 2nd heating furnace, the roll axial part which is not the said heat insulation process in the both ends of the said roll is contacting the furnace shell and external air. Further, both end surfaces of the roll shaft portion and the roll body portion accommodated in the second heating furnace are heat-insulated as described above. In such a state, by raising the temperature to 1050 to 1150 ° C. in the shortest time (second step), the temperature rise of the inner layer is minimized, and the embrittlement of the inner layer and the coarsening of crystal grains are prevented. Only the outer layer can be converted to austenite in a short time, and the carbides of the outer layer can be sufficiently dissolved in the matrix to bring out the characteristics of high speed steel.

  According to the present invention, in heating up to the austenitizing temperature at the time of quenching, the temperature rise of the inner layer during the heating of the outer layer is minimized, and the embrittlement of the inner layer and the coarsening of the crystal grains are prevented. Thus, it is possible to provide a method for heat treatment of a composite roll for rolling, in which only the outer layer can be austenitized, carbides in the outer layer can be sufficiently dissolved in the matrix, and high speed properties can be obtained.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

  A heat treatment method for a composite roll for rolling according to an embodiment of the present invention includes a rolling process in which an inner layer made of a material having toughness is integrated metallurgically with an outer layer made of a high-speed material formed by centrifugal casting. The composite roll is subjected to a tempering treatment after being quenched to austenitizing temperature and then cooled.

  First, a rolling composite roll that is a target of heat treatment of the heat treatment method according to the present embodiment will be described. The outer layer of the composite roll for rolling is formed of a high speed material which is a known material. As typical components of the high-speed material, for example, as disclosed in Patent Document 1 or Patent Document 2, C: 1.2 to 2.5%, Si: 0.3 to 1.5% , Mn: 0.3 to 1.5%, Cr: 4.0 to 10.0%, Mo: 3.0 to 10.0%, W: 0.5 to 10.0%, V: 2.0 It is comprised from -10.0%. In addition to the above components, other chemical components, for example, Ni: 0.1 to 3.0%, Co, depending on the size of the roll to be applied, required usage characteristics of the roll, and the like. : 0.1 to 10.0%, Nb: 0.1 to 3.0% may be appropriately selected and contained. The outer layer of the rolling composite roll according to the present embodiment can be formed by, for example, a centrifugal casting method using a molten metal composed of the high-speed chemical components as described above.

  Moreover, the inner layer of the composite roll for rolling according to the present embodiment can be formed of a material having toughness such as known ductile cast iron, high-grade cast iron, and graphite steel. Furthermore, this inner layer is integrated with the outer layer as described above by metallurgical integration, for example, by a centrifugal casting method or the like, whereby the rolling composite roll according to this embodiment is formed.

  Next, the heat treatment method for the rolling composite roll according to this embodiment will be described in detail. In the heat treatment method according to this embodiment, as described above, heating to the austenitizing temperature is performed during quenching, and this heating is performed in the first heating furnace and in the second heating furnace. And performing step 2.

  First, based on FIG. 1, the structure of the 1st heating furnace used for the process 1 of the heat processing method of the composite roll 5 for rolling which concerns on this embodiment is demonstrated. In addition, FIG. 1 is explanatory drawing which shows schematic structure of the 1st heating furnace used for the process 1 which concerns on this embodiment.

  As shown in FIG. 1, the furnace shell 1 of the first heating furnace is made of a refractory material, and one side surface thereof is configured as a furnace door 2, and the lower surface thereof is configured as a roll mounting table 3. By opening and closing the furnace door 2, the rolling composite roll 5 can be carried into and out of the first heating furnace. Further, on the lower surface side of the roll mounting table 3, for example, a plurality of rollers 4 are provided as moving means, and the first heating furnace mounted on the substantially flat floor surface FL is rolled by the rollers 4. The composite roll 5 can be moved in the axial direction. On the other hand, in the first heating furnace, a first roll support portion 6 for supporting a rolling composite roll 5 (specifically, a roll body portion 54 to be described later) is provided on the upper surface side of the roll mounting table 3. In addition, burners 7 (two locations in FIG. 1) are provided as heating means for heating the roll for rolling. The first roll support portion 6 is provided with a rolling composite roll 5 that is carried into a second heating furnace used in the next step 2. The rolling composite roll 5 includes a roll shaft portion 52 as an inner layer and a roll barrel portion 54 as an outer layer, and a portion of the roll shaft portion 52 accommodated in the second heating furnace and both ends of the roll barrel portion 54. These are heat-insulated by covering the surface part with a heat insulating material such as ceramic fiber 56, for example.

  After the rolling composite roll 5 is installed in such a first heating furnace, the burner 7 is ignited, and heating in Step 1 described later is performed.

  Next, based on FIG. 2 and FIG. 3, the structure of the 2nd heating furnace used for the process 2 of the heat processing method of the composite roll 5 for rolling which concerns on this embodiment is demonstrated. FIG. 2 is an explanatory diagram showing a schematic configuration of the second heating furnace used in step 2 according to the present embodiment, and FIG. 3 is a view taken along the line AA of FIG.

  As shown in FIGS. 2 and 3, the main body of the second heating furnace is composed of two furnace shells 10 having a substantially semi-cylindrical shape made of a refractory material. The furnace shell 10 is configured to be openable and closable. As shown in FIG. 3, the two furnace shells 10 that are in contact with each other at the closing position 10a are respectively opposite in the horizontal direction (the direction of the arrow in the figure). By moving to the open positions 10b and 10c, the rolling composite roll 5 to be heat-treated can be carried into and out of the second heating furnace. Note that the heat treatment of the rolling composite roll 5 is performed in a state where the furnace shell 10 is closed (a state where the furnace shell 10 is located at the closing position 10a).

  In the second heating furnace, at least a part of the furnace shell 10 is accommodated in a pit 20 which is a recess formed in a substantially flat floor surface FL, and a second roll provided outside the pit 20 on the floor surface FL. Both ends of the roll shaft portion 52 are supported by the support portion 30. The second roll support portion 30 is formed in a substantially cylindrical shape, and in this embodiment, both ends of the roll shaft portion 52 are supported by two second roll support portions 30 respectively. However, the shape and number of the second roll support portions are not limited to the above example, and any shape and number can be used as long as they can support the rolling composite roll 5.

  In addition, as described above, heat insulation of 50 mm or more in thickness is performed in advance on the portion inside the second heating furnace of the roll shaft portion 52 and the both end surface portions of the roll body portion 54 with the ceramic fiber 56 in step 1. ing. On the other hand, portions of the roll shaft 52 that are not insulated at both ends of the rolling composite roll 5 are in contact with the furnace shell and the outside air. Therefore, in this state, even if the inside of the second heating furnace is rapidly heated by, for example, the heater 40 as a heating means, the temperature of only the roll body portion 54 of the rolling composite roll 5, that is, the outer layer portion, increases. , The temperature rise of the inner layer can be prevented.

  When the product length of the rolling composite roll 5 to be heat-treated is short and cannot be supported by the second roll support portion 30 of the second heating furnace used in the above step 2, for example, the second roll What is necessary is just to manufacture to the length of the composite roll for rolling which can be supported by the support part 30, and cut | disconnect to the length of the predetermined composite roll for rolling after heat processing. As another method, for example, the second roll support portion 10 may be configured to be movable / installable in the axial direction of the rolling composite roll.

  Next, the process 1 and the process 2 performed in the 1st heating furnace and the 2nd heating furnace mentioned above are demonstrated in detail.

  First, after heat-insulating the part accommodated in the 2nd heating furnace of the inner layer (roll shaft part 52) and the both-ends surface part of an outer layer (roll body part 54) among the composite rolls 5 for heat processing to heat-process, In the first heating furnace, the entire composite roll for rolling 5 is heated from room temperature to 600 to 700 ° C. at a heating rate of 10 to 30 ° C./Hr.

  Here, first, as a heat insulating means for insulating the roll body portion 54 as the outer layer and the roll shaft portion 52 as the inner layer, for example, a heat insulating material such as ceramic fiber is used so that the construction thickness becomes 50 mm or more. It is preferable. If the thickness of the heat insulating material is less than 50 mm, the heat insulating effect on both end faces of the roll shaft portion 52 and the roll body portion 54 is poor, and it is not suitable as a heat insulating means.

  As described above, in step 1, the outer layer (roll body portion 54) and the inner layer (roll shaft portion 52) of the composite roll 5 for rolling are raised from room temperature to 600 to 700 ° C. at a rate of 10 to 30 ° C./Hr. Heating is performed at a temperature rate.

  This is because when the heating temperature is less than 600 ° C., the outer roll surface of the roll 5 is moved to 1050 to 1150 after the rolling composite roll 5 is moved into the second heating furnace, which is the content of step 2 following step 1. Since it takes a long time to heat during the temperature, it is not preferable. On the other hand, if the temperature exceeds 700 ° C., the temperature can be raised in a short time after the rolling composite roll 5 is moved to the second heating furnace, but the temperature rise of the inner layer is also accelerated and reaches the austenitizing temperature, which is not preferable. As described above, the appropriate heating temperature is preferably 600 ° C. or higher and 700 ° C. or lower.

  Moreover, in the said process 1, the temperature increase rate in the range of the suitable heating temperature mentioned above is 10-30 degreeC / Hr. This is not preferable if the rate of temperature increase is less than 10 ° C./Hr, because it takes a long time for heating and becomes inefficient and uneconomical. On the other hand, if the rate of temperature rise exceeds 30 ° C./Hr, the temperature difference between the outer layer surface and the center increases, and there is no plastic deformation in the low temperature range, which is not preferable because there is a risk of the roll breaking. As described above, an appropriate temperature increase rate is preferably 10 ° C./Hr or more and 30 ° C./Hr or less.

  Step 2 is a step of rapidly heating the outer layer from 600 to 700 ° C. to 1050 to 1150 ° C. at a heating rate of 300 to 600 ° C./Hr after moving the rolling composite roll 5 to the second heating furnace. It is.

  Thus, as the heating temperature of the outer layer of the composite roll 5 for rolling in the process 2, it is preferable to heat between 1050-1150 degreeC. When the heating temperature is less than 1050 ° C., the diffusion temperature is low, and the carbide cannot be sufficiently dissolved in the matrix, which is not preferable. On the other hand, if the temperature exceeds 1150 ° C., the influence of heat on the inner layer is increased, which leads to embrittlement of the inner layer and coarsening of crystal grains. As described above, the appropriate heating temperature is preferably 1050 ° C. or higher and 1150 ° C. or lower.

  Moreover, in the said process 2, the temperature increase rate in the range of the suitable heating temperature mentioned above is 300-600 degreeC / Hr. This is not preferable when the temperature rising temperature is less than 300 ° C./Hr, because heating requires a long time, so that the inner layer becomes austenite, causing embrittlement of the inner layer and coarsening of crystal grains. On the other hand, if the rate of temperature rise exceeds 600 ° C./Hr, it is difficult to ensure a uniform temperature distribution on the outer layer surface, and there is a concern that the hardness may vary in the outer layer axial direction, which is not preferable. As described above, an appropriate temperature increase rate is preferably 300 ° C./Hr or more and 600 ° C./Hr or less.

  In addition, as the tempering performed after the quenching including the steps 1 and 2 as described above, a known method can be used, but the purpose of the embodiment in this embodiment is to retain residual γ (austenite) at the time of quenching. Is to promote the transformation of martensite or bainite and to precipitate secondary carbide, stabilize the structure, and improve the hardness and toughness. Therefore, as a method of tempering in the present embodiment, for example, the rolled composite roll 5 after quenching is put in a heating furnace and tempered in the range of 500 to 550 ° C. once or twice.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

(Manufacture of the composite roll for rolling which concerns on Examples 1-6)
As an outer layer material, C: 1.9 to 2.1%, Si: 0.7 to 1.0%, Mn: 0.6 to 1.0%, Cr: 4.5 to 7.5%, Mo: 5.0 to 8.0%, V: 4.0 to 5.5%, the outer layer was formed by centrifugal casting using a molten metal composed of a high-speed chemical component consisting of Fe and inevitable elements as the balance. . Next, an inner layer material made of ductile cast iron was statically cast inside the outer layer to produce a composite roll for rolling having a body size diameter of 809 mm, a length of 2210 mm, and an outer layer thickness of 80 mm.

  Thereafter, the following heat treatment was performed. As shown in FIGS. 1 to 3 and the description thereof, a portion of the roll shaft portion of the rolling composite roll to be heat-treated and a portion accommodated in the second heating furnace and both end surface portions of the roll body portion are 55 mm thick. The composite roll for rolling is further insulated by covering with a ceramic fiber, and the heating temperature and the temperature are increased in the first heating furnace described in the column of step 1 in Table 1 (Examples 1 to 6) below. Heated at a warm rate.

  Subsequently, the rolling composite roll is moved to the second heating furnace, and then the rolling composite roll is heated at the heating temperature and rate of temperature described in Step 2 of Table 1 (Examples 1 to 6). Each was heated. Further, quenching was performed by quenching by blast cooling, followed by tempering that was held at about 550 ° C. for about 15 hours twice, to produce a heat-treated composite roll according to Examples 1 to 6.

(Manufacture of the composite roll for rolling which concerns on Comparative Examples 1-8)
As an outer layer material, after forming the outer layer by centrifugal casting using the same high-speed chemical component as in Examples 1 to 6, the inner layer material made of ductile cast iron is statically cast inside the outer layer, A composite roll for rolling with a body size diameter of 809 mm, a length of 2210 mm, and an outer layer thickness of 80 mm was produced.

  Thereafter, the following heat treatment was performed. As shown in FIGS. 1 to 3 and the description thereof, a portion of the roll shaft portion of the rolling composite roll to be heat-treated and a portion accommodated in the second heating furnace and both end surface portions of the roll body portion are 55 mm in length. Each of the heating rolls described in the column of step 1 of the following Table 1 (Comparative Examples 1 to 8) in the first heating furnace is further insulated by covering with a ceramic fiber having a thickness. It heated at the temperature increase rate.

  Subsequently, this rolling composite roll is moved to the second heating furnace, and then the rolling composite roll is heated at the heating temperature and rate of temperature described in Step 2 of Table 1 (Comparative Examples 1 to 8). Each was heated. Further, quenching was performed by quenching by blast cooling, followed by tempering that was held at about 550 ° C. for about 15 hours twice, to produce a heat-treated composite roll according to Comparative Examples 1-8.

  About the composite roll for rolling which concerns on Examples 1-6 and Comparative Examples 1-8 manufactured as mentioned above, the tension test and the measurement of hardness were performed as follows.

(Tensile test)
About the composite roll for rolling of the said Examples 1-6 and Comparative Examples 1-8, the tension test piece of JIS4 was extract | collected from the inner-layer part of each roll, and the tension test was implemented (JISZ2201). The results are also shown in Table 1 below.

(Measurement of hardness)
About the composite roll for rolling of the said Examples 1-6 and Comparative Examples 1-8, in order to remove the oxide film of the outer layer of each roll, 15 mm was shaved off from the outer peripheral surface by the single-piece | unit thickness to the radial direction. The surface after scraping is used as the initial diameter surface of the composite roll for rolling. The hardness of this initial diameter surface was measured with a Shore hardness meter. The results are also shown in Table 1 below.

(Evaluation of results)
As shown in Table 1, in the rolling composite rolls according to Examples 1 to 6, all the tensile strengths were higher than 400 MPa as compared with the rolls according to Comparative Examples 3, 5, 6 and 8, which were described above. Thus, it is judged that the deterioration of toughness due to melting of the segregated portion of the inner layer that occurred when the cast iron agent was used as the inner layer material did not occur. Furthermore, also about hardness, the composite roll for rolling which concerns on Examples 1-6 has a high value similarly to the roll which concerns on Comparative Examples 1-8, and it is clear that the sound heat processing is implemented. It can be said that there is.

  On the other hand, since the roll according to Comparative Example 1 is carried out at 9 ° C./Hr, the temperature increase rate in Step 1 is lower than 10 ° C./Hr, which is the lower limit value in the heat treatment method according to the present invention. Has a high value as in Examples 1 to 6, and it is judged that segregation does not occur in the inner layer. However, as described above, a long processing time is required. From the point of view, it is not preferable.

  Moreover, since the roll according to Comparative Example 2 is performed at 34 ° C./Hr, which is higher than the upper limit of 30 ° C./Hr, which is the upper limit value in the heat treatment method according to the present invention, in the step 1, The roll broke during the heat treatment. In addition, since the roll was broken during the process 1, the process 2 was not performed for the comparative example 2.

  Moreover, since the roll according to Comparative Example 3 is carried out at 290 ° C./Hr where the rate of temperature increase in Step 2 is lower than 300 ° C./Hr, which is the lower limit in the heat treatment method according to the present invention, the tensile strength is Compared to Examples 1 to 6, the value was extremely low. From this, in the roll which concerns on the comparative example 3, since many heating time is required as above-mentioned, it is judged that the inner layer is austenite and the inner layer becomes embrittled or the crystal grain is coarsened.

  Moreover, since the roll according to Comparative Example 4 is performed at 615 ° C./Hr, which is higher than the upper limit of 600 ° C./Hr in the heat treatment method according to the present invention, the tensile strength in Step 2 is Although test results comparable to those of Examples 1 to 6 were obtained, it was difficult to ensure a uniform temperature distribution on the outer layer surface, and the hardness varied in the surface layer axis direction. Specifically, the hardness Hs was 78, 78 at both axial end portions of the roll, and the hardness Hs was 82 at the axial central portion.

  Moreover, since the roll which concerns on the comparative example 5 is implemented at 580 degreeC in which the heating temperature in the process 1 is lower than 600 degreeC which is the minimum value in the heat processing method which concerns on this invention, tensile strength is in Examples 1-6. Compared to the lower value. Therefore, as described above, the roll according to Comparative Example 5 requires a lot of heating time, and therefore, it is determined that the inner layer is austenitic and the inner layer is brittle or the crystal grains are coarsened.

  Moreover, since the roll which concerns on the comparative example 6 is implemented at 715 degreeC whose heating temperature in the process 1 is higher than 700 degreeC which is the upper limit of the heat processing method which concerns on this invention, tensile strength is in Examples 1-6. Compared to the lower value. From this, as described above, in the roll according to Comparative Example 6, it is determined that the inner layer is austenitized during heating, so that the inner layer is embrittled or crystal grains are coarsened.

  Further, the roll according to Comparative Example 7 has a remarkably low hardness because the heating temperature in step 2 is 1000 ° C. which is lower than the lower limit of 1050 ° C. in the heat treatment method according to the present invention. From this, as mentioned above, in the roll which concerns on the comparative example 7, it is judged that a diffusion temperature is low and a carbide | carbonized_material cannot fully dissolve in a base.

  Moreover, since the roll which concerns on the comparative example 8 is implemented at 1160 degreeC whose heating temperature in process 2 is higher than 1150 degreeC which is the upper limit in the heat processing method which concerns on this invention, tensile strength is from Examples 1-6. Is also low. From this, as described above, in the roll according to Comparative Example 8, it is judged that the inner layer is austenitized during heating, so that the inner layer is embrittled or crystal grains are coarsened.

  Thus, according to the heat treatment method for a composite roll for rolling according to the present embodiment, the heating of the inner layer is minimized, the embrittlement of the inner layer and the coarsening of the crystal grains are prevented, and only the outer layer is formed in a short time. The austenite can be converted into austenite, and the carbides of the outer layer can be sufficiently dissolved in the matrix to bring out the characteristics of high speed steel.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are of course within the technical scope of the present invention. Understood.

  The present invention can be applied to a heat treatment method for a hot roll or a cold roll composite roll using a high-speed steel as an outer layer.

It is explanatory drawing which shows the outline | summary of a structure of the 1st heating furnace used for the process 1 which concerns on one Embodiment of this invention. It is explanatory drawing which shows the outline | summary of a structure of the 2nd heating furnace used for the process 2 which concerns on one Embodiment of this invention. It is an AA arrow line view of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Furnace shell 2 Furnace door 3 Roll mounting stand 4 Roll 5 Composite roll for rolling 6 First roll support member 7 Burner 10 Furnace shell 20 Pit 30 Second roll support member 40 Heater 52 Roll shaft part 54 Roll body part 56 Ceramic fiber ( Insulation)

Claims (1)

Quenching treatment that cools after heating to the austenitizing temperature for a composite roll for rolling manufactured by metallurgically integrating an inner layer made of a tough material with an outer layer made of high-speed steel formed by centrifugal casting In the heat treatment method for a composite roll for rolling that is tempered after performing:
The heating to the austenitizing temperature includes a first step performed in a first heating furnace and a second step performed in a second heating furnace,
The first step insulates the portion of the inner roll that is accommodated in the second heating furnace and both end faces of the outer layer, and then rolls the rolling in the first heating furnace. The entire composite roll is heated from room temperature to 600 to 700 ° C. at a heating rate of 10 to 30 ° C./Hr.
In the second step, after the rolling composite roll is moved to the second heating furnace, the outer layer is heated from 600 to 700 ° C. to 1050 to 1150 ° C. at a temperature rising rate of 300 to 600 ° C./Hr. A heat treatment method for a composite roll for rolling, which is a process.

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