JP2006159269A - Roll for scale breaker, its production method, and quenching device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roll for a scale breaker having excellent wear resistance. <P>SOLUTION: In order to obtain the roll 10 having a surface layer section of high hardness by applying a heat treatment including quenching to a roll-shaped body 11 of a high-carbon high-alloy steel composition containing a hard carbide forming element prepared through the process of sintering powder raw materials as a principal component, the roll-shaped body 11 is composed of a composition containing 1.7 to 3.5 mass% C, 10 to 20 mass% Cr, 0.5 to 5 mass% Mo, and 1 to 10 mass% V, and quenching is performed under conditions of cooling the roll shape at a temperature lowering rate of 5 to 50°C/s, after heating the roll-shaped body at a temperature rising rate of 50 to 200°C/s by induction heating in the quenching device 20 to a quenching temperature, then holding the temperature for 5 to 30 s. As a result, a wear resistant layer of Hv 700-over class, a backing region of Hv 700 to 500, a hardness rapid change section of Hv 500 to 700m and a core section of Hv ≤300 are formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention provides a work breaker for a scale breaker for increasing the descaling efficiency by causing cracks in the scale by repeatedly bending the steel plate in front of a chemical descaling line such as a pickling line for removing the scale of the hot rolled steel plate. More particularly, the present invention relates to a technique for enhancing wear resistance without increasing the sensitivity to spalling and fatigue damage.

A so-called hot coil manufactured by hot rolling has a hard oxide film called a scale. Since this scale hinders subsequent processes such as cold rolling for further reducing the plate thickness, it is removed in advance in the pickling process.
In the pickling process, prior to chemical removal with an acid solution, a steel sheet is mechanically repeatedly bent, and a scale breaking process is performed to increase the removal effect by causing cracks in the scale. As the equipment for performing the above-mentioned processing, a pinch roller group with a backup roll is generally a tension leveler type that is connected in a staggered manner in the plate direction, and a roll incorporated as a work roll in this equipment is described in this specification. It is a roll for scale breakers.

The roll for scale breaker is required to have high spalling resistance in addition to high wear resistance that can withstand rolling contact under high contact pressure and high speed and biting of scale powder. ). In addition, a certain level of corrosion resistance is required to withstand the usage environment in which descaling water is applied. As for the 1 to 3% Cr cast steel roll and the 5 to 9% Cr steel build-up roll, they have been used for a long time. However, both the wear resistance and the spalling resistance were insufficient.
Therefore, as a new roll for a scale breaker, a heat treatment hardening roll of a molten cold tool steel system (for example, see Patent Document 1), a heat treatment hardening roll of a molten high speed tool steel system (for example, see Patent Document 2), powder metallurgy. A high-speed tool steel-based heat-treatment hardening roll (see, for example, Patent Document 3) is provided, and the wear resistance is greatly improved while ensuring the spalling resistance.

  Incidentally, each of the above rolls is subjected to heat treatment (quenching and quenching) on a high carbon high alloy steel material containing hard carbide forming elements such as Cr (chromium), Mo (molybdenum), V (vanadium), and W (tungsten) as main components. Tempering), and the hardness of the surface layer portion extending from the surface to a depth of 5 to 10 mm (that is, the surface layer portion extending from the surface to a depth of at least 5 mm) is secured at a high level. However, it is Hs85-90 (Hv750-800) in the heat treatment hardening roll (Patent Document 1) of the molten cold tool steel system and the heat treatment hardening roll (Patent Document 2) of the molten high speed tool steel system, so to speak, Hv750. It is super-class, and it is Hs 90-95 (Hv 800 strong-950 weak) in the heat-treatment hardening roll (Patent Document 3) made of powder metallurgy high-speed tool steel. 00 more than class.

  In addition, there is a leveler line work roll that improves the flatness by repeatedly bending and deforming a cold-rolled steel sheet as a roll that is similar to the scale breaker roll (see, for example, Patent Document 4). This leveler work roll has an ultra-thin diameter of 20-60 mm due to the need to bend and deform a thin steel plate of 0.3-1 mm with a strain rate that causes slight plastic deformation, and the length is for a scale breaker. Equivalent to a roll. Therefore, bending deformation is more likely to occur than the scale breaker roll, and fatigue breakage resistance is particularly important. However, when the leveler work roll is quenched, the core portion is also in a cured state (Hv 500 or more) because of the ultra-small diameter. Therefore, in the invention of the above-mentioned patent document, securing of fatigue breakage resistance is achieved by providing the roll surface layer portion with compressive residual stress. In other words, although it is similar to a roll for scale breakers, there are few cases where mutual technical diversion is suitable, including ingenuity of hardness transition in the depth direction and quenching conditions.

Japanese Unexamined Patent Publication No. 64-28344 Japanese Patent Laid-Open No. 64-40112 JP-A-4-253514 JP-A-10-298716

  By the way, in addition to quenching and hardening of the steel base, the presence of hard carbides contained in a dispersed state greatly contributes to the high hardness as described above. It is considered that further hardening (and improvement in wear resistance) could be realized without sacrificing the (polling property). The powder metallurgy high-temperature tool steel heat treatment hardening roll (Patent Document 3) has a particularly high hardness of Hv800 and higher (and thus wear resistance is further improved). This is probably because the toughness was not impaired even when the hardness was higher than Hv800 due to the denseness and uniformity of the carbide derived from the material made of the product.

  However, the scale breaker roll is required to have higher wear resistance than the heat-treatment hardening roll (Patent Document 3) of the powder metallurgy high-speed tool steel system. This is because the wear life of rolls tends to be shortened due to the increase in wear load accompanying the increase in the use of high-tensile steel sheets in automobile body applications, etc. It is no longer easy.

  Therefore, it is necessary to further improve the wear resistance. First, the hardness of the roll surface layer may be further increased as compared with the above-described heat-treatment hardening roll of the powder metallurgy high-speed tool steel system (Patent Document 3). Although it is considered, the surface layer hardness of Hv800 and higher in the roll is an upper limit value obtained in view of the anti-spalling property. In addition, considering the need to further increase the sheet passing speed (and hence the roll rotation speed), the rolls are repeatedly bent and deformed easily because of the elongated shape (for example, diameter 80 to 100 mm × length 1600 to 2400 mm). It is desirable to ensure fatigue damage resistance in consideration, and from this point, it is desirable to secure a high toughness by suppressing the surface layer hardness somewhat.

On the other hand, the use of the above-mentioned tool steel-based high carbon high alloy steel is regarded as an indispensable requirement for ensuring high wear resistance. Particularly, those made of powder metallurgy are used for toughness, spalling resistance, fatigue damage resistance. This is considered to be a preferable requirement to compensate for the loss of strength characteristics such as property.
Therefore, within the category of scale breaker roll made of powder metallurgy tool steel high carbon high alloy steel material, conventional high hardness oriented roll (heat treatment hardening roll of powder metallurgy high speed tool steel system / patent document An object of the present invention is to provide a technology that realizes a product having wear resistance superior to 3) with a surface layer hardness lower than the surface layer hardness of the conventional roll (ie, higher than Hv800).

The roll for a scale breaker of the present invention (Claim 1) was created in order to solve such a problem,
A roll-shaped shaped body made of powder metallurgy made of powder metallurgy containing a hard carbide forming element as a main component is used as a raw material, and a surface layer portion at least 5 mm deep from the surface by heat treatment is a wear-resistant layer having a high hardness. In the roll for the scale breaker,
The material contains C: 1.7 to 3.5 mass%, Cr: 10 to 20 mass%, Mo: 0.5 to 5 mass%, and V: 1 to 10 mass% as main component elements, and the wear-resistant layer. The hard carbide composed of the main component element is distributed in the form of substantially spherical fine particles having a cross-sectional apparent particle size of 10 μm or less and with a high space factor of 10-30 cross-sectional apparent area%, and the wear resistance The hardness of the layer is in the range of Hv 700 to 850, and inside the wear-resistant layer, there is a backing region in an effective cured state, a hardness suddenly changing portion where the hardness suddenly drops to an uncured state, and an uncured core The hardness decreasing gradient in the depth direction of the backing region is a gentle gradient with the Hv value decrease per 10 mm depth increase being on the order of 200 points, and the hardness suddenly changing portion is , Radial direction at a distance of (1 / √2) of the roll radius from the roll center Located in the roll center side than the roll cross section bisecting position related, further, the hardness of the core region is Hv300 or less,
It is characterized by that.

The roll for scale breaker of the present invention (Claim 2)
A roll-shaped shaped body having a high carbon and high alloy steel composition prepared through a step of sintering a powder raw material is subjected to a heat treatment step including quenching, and a surface layer portion having a depth of at least 5 mm from the surface is hard. In the scale breaker roll that is the wear-resistant layer,
The roll-shaped shaped body has a composition containing C: 1.7 to 3.5 mass%, Cr: 10 to 20 mass%, Mo: 0.5 to 5 mass%, and V: 1 to 10 mass% as main component elements. The heating for quenching is based on a rapid heating condition of a temperature rising rate of 50 to 200 ° C./s and a temperature holding of 5 to 30 s at the quenching temperature,
In the wear-resistant layer, hard carbides composed of the main component elements are distributed in the form of substantially spherical fine particles having a cross-sectional apparent particle size of 10 μm or less and with a high space factor of 10-30 cross-sectional apparent area%. The wear-resistant layer has a hardness in the range of Hv 700 to 850, and on the inner side of the wear-resistant layer, there is an effective hardened backing region and a hardness suddenly changing portion where the hardness suddenly drops to an uncured state. The core region in the uncured state is connected in this order, and the hardness decreasing gradient in the depth direction in the backing region is a gentle gradient in which the Hv value decrease per 10 mm depth increase is on the order of 200 points, and The sudden hardness change portion is located on the roll center side from the roll cross-sectional area bisected position in the radial direction at a distance (1 / √2) of the roll radius from the roll center. The hardness of the core region is Hv300 or less,
It is characterized by that.

  Furthermore, the roll for scale breakers of the present invention (Claim 3) is the roll for scale breakers according to Claims 1 and 2, and the Cr content of the main component elements is 40 to 70%. Is contained in the base metal phase.

Moreover, the manufacturing method (Claim 4) of the roll for scale breakers of this invention,
A high-carbon high-alloy steel composition roll-shaped body containing a hard carbide-forming element as a main component, prepared through a step of sintering a powder raw material, is subjected to a heat treatment step including quenching, and at least a depth from the surface In a method for producing a roll for a scale breaker, obtaining a curing roll having a surface layer portion of up to 5 mm with a high hardness wear-resistant layer,
The roll-shaped shaped product has a composition containing C: 1.7 to 3.5 mass%, Cr: 10 to 20 mass%, Mo: 0.5 to 5 mass%, and V: 1 to 10 mass% as main component elements. In the above, the quenching is rapidly performed by induction heating to a quenching temperature at a heating rate of 50 to 200 ° C./s, holding the temperature for 5 to 30 s, and then cooling at a cooling rate of 5 to 50 ° C./s. By applying under short heating and slow cooling conditions,
As the hardening roll, a hard carbide composed of the main component element in the wear-resistant layer is in the form of substantially spherical fine particles having a cross-sectional apparent particle size of 10 μm or less and a high space factor of 10-30 cross-sectional apparent area%. The hardness of the wear-resistant layer is in a range of Hv 700 to 850, and the hardness of the wear-resistant layer suddenly drops to the backing region in the effective cured state and the uncured state. The suddenly changing portion and the uncured core region are connected in this order, and the hardness decreasing gradient in the depth direction in the backing region is a gentle gradient in which the Hv value decrease per 10 mm depth increase is on the order of 200 points. And the hardness suddenly changing portion is located on the roll center side from the roll cross-sectional area bisected position in the radial direction at a distance of (1 / √2) of the roll radius from the roll center, Furthermore, the hardness of the core region is Hv300 or higher. Get the roll is,
It is characterized by that.

  A quenching apparatus according to the present invention (Claim 5) is a quenching apparatus for performing the quenching in the manufacturing method according to Claim 4, and the axis of the roll-shaped shaped body is oriented in the vertical direction. Supporting and rotating device for supporting in a different posture and rotating the shaft center, induction coil for induction heating a short section in the axial direction of the roll-shaped shaped body, and at least an air cooling jacket for following the heating portion by the coil A heating / cooling unit having a cooling zone, and a workpiece-to-heating / cooling unit relative traveling mechanism configured to cause at least one of the workpiece support rotating device and the heating / cooling unit to travel in a vertical direction. Features.

  In such a roll for scale breaker of the present invention (Claim 1), first, hard carbides of substantially spherical fine particles are distributed with a high cross-sectional space factor, so that a conventional roll of Hv800 superclass (Patent Document 3). ), And the surface layer part hardness of Hv700 super class, which is lower than that of conventional rolls of Hv750 superclass (Patent Documents 1 and 2), the wear resistance is improved to a higher level than that of Hv800 superclass rolls. Confirm that with reference to the drawings. FIG. 2 shows the results of the wear test, where (a) is a comparison table and (b) is a comparison graph. FIG. 3 shows an embodiment of the abrasion test, and FIG. 4 is a drawing-substituting photograph showing a cross-section of the test material of the present invention, and has a 2000-fold microstructure by SEM (scanning electron microscope).

  In FIG. 2, the material number A1 is the powder metallurgy roll (high C-13Cr steel) of the present invention and the wear amount is 4 mg, and the material number B1 is the conventional powder metallurgy roll (powder metallurgy high speed). The wear amount of tool steel heat treatment hardening roll / Patent Document 3) is 19 mg, and the material number B2 is worn by the conventional melting roll (melting high speed tool steel heat treatment hardening roll / Patent Document 2). The amount is 75 mg, the material number B3 is a conventional smelting roll (melting cold tool steel heat treatment hardening roll / Patent Document 1), and the wear amount is 31 mg, and the material number B4 is a conventional forged steel. The wear amount was 195 mg with a roll (1 to 3% Cr).

The excellent wear resistance of the roll of the present invention, which is apparent in FIG. 2, is mainly brought about by the high cross-sectional space factor (see FIG. 4) of carbide fine particles (hard carbide) of 10-30 cross-sectional apparent area% according to claim 2. It is assumed that this is due to the micro strut function.
That is, since the carbide phase has about three times the hardness compared with the quenched base metal phase, the wear of the base metal phase starts on the roll surface first, and the carbide phase is a convex portion and the base metal phase is a concave portion. Loose undulations occur, and wear progresses in this state. In this case, since the wear speeds V1 and V2 based on the dimensions of the carbide phase and the base metal phase are equal, the weighted pressure (per unit area) applied to each phase is P1 and P2, respectively, and V1 = k1 × P1 and V2 = K2 × P2 (k1 and k2 are constants)
k1 × P1 = k2 × P2, that is, P2 = (k1 / k2) × P1 (1)
It becomes.

If the area ratio of each phase is S1: S2 = A: (1-A), the ratio of the load applied to each phase is F1: F2 = P1 × A: P2 × (1-A) = P1 × A: (K1 / k2) × P1 × (1-A) = k2 × A: k1 × (1-A) …………………………………… (2)
It becomes. Furthermore, F1 + F2 = F (total load) ……………………………… (3)
If you solve these equations,
(F1 / F) ≡θ1 = k2 × A / {k2 × A + k1 × (1-A)},
(F2 / F) ≡θ2 = k1 × (1-A) / {k2 × A + k1 × (1-A)} (4)
It becomes.

Here, if k2 = 3 × k1 (the base metal phase is likely to wear about three times as much as the carbide phase), the above equation (4) is
θ1 = 3 × A / (2 × A + 1), θ2 = (1−A) / (2 × A + 1) (5)
When A = {0.05, 0.1, 0.2, 0.3} is added to this,
θ1 = {0.136, 0.250, 0.429, 0.563}.
That is, a load exceeding the area ratio is distributed to the carbide phase having high wear resistance. In other words, this means that the loose undulation with the carbide phase as a convex portion is generated in a form that realizes load distribution biased to the carbide phase. And in this invention roll, it is that the very small carbide | carbonized_material of 10 micrometers or less functions as an infinite number of micro struts, and opposes the load which becomes a wear factor.

  In addition, the particle size of carbide fine particles of 10 μm or less is similar to the particle size of an abrasive finer than 150 mesh (see JIS R6001), and the thickness of the scale of the hot coil that is the subject of the roll of the present invention (about 50 to 100 μm). Small enough). For this reason, even if it falls off, it becomes buried in the scale powder, and there is little possibility that it will lead to wear or wrinkles due to abrasion caused by the fallen particles.

  In the scale breaker roll of the present invention (Claim 1), the hardness transition in the depth direction is a unique pattern due to quenching or the like of the minimum heating time. It has improved. Confirm that with reference to the drawings. FIG. 5 is a diagram showing a contrast of hardness transition curves from the roll surface toward the roll center. A thick line A1 with black circles is the powder metallurgy roll of the present invention (high C-13Cr steel), and a black squared middle line. B1 is a conventional powder metallurgy roll (powder metallurgy high speed tool steel heat treatment hardening roll / Patent Document 3), and short dashed line B2 is a conventional melt roll (melting high speed tool steel heat treatment hardening roll). / Patent Document 2), and the thin long broken line B3 is a conventional melting roll (melting cold tool steel heat treatment hardening roll / Patent Document 1).

The roll A1 of the present invention has a surface layer portion of at least 5 mm deep (up to a depth of 5 to 10 mm as a guide) from the surface as a wear resistant layer of Hv700 superclass, but the quench hardening layer is deeper than this. According to JIS G 0559, the high hardened steel having a C content of 0.53 mass% or more is considered to be an effective hardened layer up to a depth of Hv500.
Here, when the hardness transition curve of FIG. 5 is seen, in the powder metallurgy roll A1 (thick line) of the present invention, a depth of up to 8 mm is a wear-resistant layer of Hv700 or more, and the inner depth thereof. An area from 8 mm to 17 mm in depth is connected as a backing area of Hv 700 to 500 (that is, in an effective hardening state), and an inner area from 17 mm to 20 mm in depth is in an uncured state from Hv 500 (indication of quench hardening) In addition, there is a series of suddenly changing hardness parts where the hardness suddenly drops to a roll core part of Hv300 or less (the center of the roll and its vicinity) that can be regarded as a state where no hardness has occurred. The uncured state is secured. Therefore, the hardness decreasing gradient in the depth direction in the backing region and the hardness suddenly changing portion, respectively,
(700-500) Hv / (8-17) mm = Hv 220 points decrease / 10 mm depth increase,
(500−300) Hv / (17−20) mm = Hv670 point decrease / 10 mm depth increase.

Incidentally, in the conventional powder metallurgy roll B1, the melt roll B2, and the melt roll B3, the hardness decreasing gradient in the backing region is regarded as the backing region in the range up to Hv500, respectively (800-500). Hv / (10-18) mm = Hv 375 point decrease / 10 mm depth increase, (750-500) Hv / (8-13) mm = Hv500 point decrease / 10 mm depth increase, (750-500) Hv / (7 .5−12.5) mm = Hv 500 points decreased / 10 mm depth increased}, and this backing region is the maximum hardness decreasing gradient portion in the entire hardness transition curve. It is an area according to the sudden change part.

The above-mentioned hardness transition pattern of the powder metallurgy roll A1 of the present invention is a very preferable pattern from the viewpoint of ensuring high fatigue damage resistance for a roll for a scale breaker having a long and repeated bending fatigue load due to its elongated shape. It can be said.
That is, the rolls of A1, B1, B2, and B3 are all solid rolls of 80 mmφ (radius 40 mm), and the roll sectional area bisected position in the radial direction is (1 / √2), a distance of 1− (1 / √2) of the roll radius r from the surface of the roll ≈0.3r depth≈12 mm depth.

  Further, characteristics that are not positive for fatigue damage, such as a hardness decreasing gradient in the depth direction (it may be considered that stress concentration is more likely to occur in a portion where the hardness decreasing gradient is larger), in particular, from the above-mentioned bisecting position of the roll cross-sectional area. Also, it is desirable that the surface of the roll be as small as possible. This is because the amount of deformation (and hence deformation stress) in the repeated bending deformation is proportionally larger on the roll surface side, and the damage energy loaded on the surface side is larger (proportional to the square of the roll radius), Therefore, there is a demand for the hardness gradient to be as small as possible on the roll surface side from the above-mentioned bisected position of the cross-sectional area. In other words, the hardness is reduced on the roll center side from the bisected position of the cross-sectional area. On the contrary, the above request is established by allowing the gradient to be higher. In the powder metallurgical roll A1 of the present invention, the hardness suddenly changing portion is inside the position of 17 mm from the roll surface as described above, and is sufficiently larger than the position of the halved cross-sectional area located at a depth of 12 mm from the roll surface. Located in the back, the above requirements are met. Furthermore, the core part (namely, the area | region of 1/2 thickness of a roll) 20 mm or more deep is ensured in the unhardened state of high toughness, and comprises the robust trunk part.

  Moreover, in the scale breaker roll of the present invention (Claim 3), the necessary corrosion resistance is ensured by increasing the Cr content of the base metal phase. Confirm that with reference to the drawings. FIG. 6 shows the results of the immersion corrosion test, (a) is the test condition, (b) is a drawing substitute photograph of the roll of the present invention (high C-13Cr steel), and (c) is a drawing substitute of the comparative material (SKH51). It is a photograph. Moreover, FIG. 7 is a table | surface which shows the EDX (energy dispersive X ray spectroscopy) analysis result of the Cr content of the test material of this invention roll.

  As can be seen from the analysis results in FIG. 7, in the roll of the present invention, despite the large amount of C, the base metal phase has a Cr content with a high content of 40 to 70% of the total content. This provides a certain level of corrosion resistance required for scale breaker rolls (see FIG. 6).

  Moreover, according to the manufacturing method of the roll for scale breakers of this invention (Claim 4), the said roll product which can meet the said request | requirement regarding the roll for scale breakers is obtained, and the said subject is solved. That is, the manufacturing method according to claim 4 is made of a powder metallurgy-made tool steel material containing Cr and C at a very high level and Mo and V at a high level, and contains carbide in a very high content. It exists in the form of fine particles. Then, by applying quenching with a minimum heating time necessary for curing (see FIG. 1 (c)), the carbide surface is exposed to the roll surface with a very high cross-sectional space factor, and the surface layer hardness is increased. High wear resistance is realized while suppressing.

  The roll for scale breaker 10 of the present invention (see FIG. 1) is a hardening roll manufactured by subjecting a roll shaped body 11 integrally formed by powder metallurgy from the roll surface to the center of the roll to heat treatment including quenching, It is used as a work roll with a backup roll to mechanically repeatedly bend a steel plate. About the use aspect, it is disclosed by patent document 1 FIG. 1, patent document 2 FIG. 1, patent document 3 FIG. 1, etc., and about the powder metallurgy method which integrally forms the roll-shaped shaped object 11, it is a general technical document. In addition to being described, Patent Document 3 discloses a gas atomizing method, a pressure molding method, and a hot extrusion method. Therefore, the characteristic features of the present invention will be described below.

  About the process (powder metallurgy method) which sinters a powder raw material and forms the roll-shaped shaped body 11, the thing of the high carbon high alloy steel composition which contains a hard carbide forming element as a main component is used as a powder raw material. . The roll shaped article 11 contains C: 1.7 to 3.5 mass%, Cr: 10 to 20 mass%, Mo: 0.5 to 5 mass%, and V: 1 to 10 mass%. C forms a metal carbide to improve wear resistance and contributes to an increase in hardenability. However, under the above composition, if less than 1.7%, there is less carbide, especially less carbon in the matrix. Thus, a hardness of Hv700 (high Hs80) or higher cannot be obtained, and the wear resistance is not sufficient. On the other hand, if it exceeds 3.5%, a brittle cementite structure also appears and the amount of retained austenite increases, which is not preferable. Residual austenite invites work hardening during use and a decrease in spalling resistance, so it is desired to suppress it to 15% or less.

  Cr not only improves the wear resistance by forming Cr carbide, but also contributes to the solid solution in the matrix to improve the corrosion resistance and increase the hardenability. If it is less, the amount of carbide is small and wear resistance is reduced. On the other hand, if it exceeds 20%, it becomes brittle and the toughness is lowered, and the spalling resistance is likely to be reduced, so Cr is preferably in the range of 10 to 20%. Further, especially in a line having a severe corrosive environment, Cr is preferably 15 to 20%. Mo forms Mo carbide to increase hardenability and improve wear resistance, and also suppresses the growth of crystal grains during heating, thereby providing toughness and improving spalling resistance. However, if the Mo content is less than 0.5%, the quenching hardness decreases and the wear resistance decreases. On the other hand, if Mo exceeds 5%, the transformation point at the time of heating is lowered and the decarburized layer tends to increase, so Mo is preferably in the range of 0.5 to 5%.

  V can not only improve the wear resistance by forming V carbide, but can also be dissolved in the matrix to make the crystal grains fine and suppress the coarsening of the crystal grains during heating. If the amount of V is less than 1%, the amount of carbide is small and wear resistance is reduced. On the other hand, if the amount of V exceeds 10% under the above composition, the amount of V carbide increases and the amount of C dissolved in the matrix decreases, quenching hardness decreases and wear resistance decreases. , V is preferably in the range of 1 to 10%. In addition, V is preferably 3 to 10% particularly in a line where the use environment is severe.

  The roll-shaped shaped body 11 (see FIGS. 1 (a) and 1 (b)) is a dimension obtained by adding a slight finishing allowance to the required specifications (diameter 80 to 100 mm × length 1600 to 2400 mm) of the scale breaker roll 10. Although it is formed into a shape having a cylindrical body portion, it may be integrally formed including the small-diameter end portions 12 and 13 at both ends at the time of sintering, and auxiliary hot forming or You may make it provide a small diameter edge part by giving a cutting process. That is, since it can form without casting of a molten metal, the composition distribution of the roll 10 for scale breakers becomes uniform in the whole region, without segregation etc. The above characteristics are inherited by the scale breaker roll 10 after the heat treatment.

In the process of heat-treating the roll-shaped shaped body 11, appropriate tempering or the like is performed in addition to quenching using the high-frequency induction heating quenching apparatus 20.
The quenching apparatus 20 (see FIGS. 1A and 1B) includes an elevating means 21, an upper end support tool 22, an induction coil 23, an air cooling jacket 24, a rotating means 25, and a lower end support tool 26 as main parts. . The lower end support 26 that supports the small-diameter end 13 of the roll-shaped shaped body 11 and the upper end support 22 that sandwiches the small-diameter end 12 of the roll-shaped shaped body 11 from above are opposed to the roll-shaped shaped body 11. It is a work support mechanism that supports the roll shaped body 11 in a posture in which the axis is oriented in the vertical direction.

  The work support mechanism is provided with a rotating means 25, which is a work support rotating device for rotating the roll shaped body 11 axially. Further, the work support mechanism is also provided with lifting means 21, which is a work-to-heating / cooling unit relative travel mechanism that causes the work support rotating device to travel in the vertical direction. The workpiece-to-heating / cooling unit relative travel mechanism may move the heating / cooling unit composed of the induction coil 23 and the air cooling jacket 24 up and down, or may move both up and down at the same time. Or any other vehicle that can stably run at a variable speed.

  In the heating / cooling unit, both the induction coil 23 and the air cooling jacket 24 are formed in an annular shape so that the roll-shaped shaped body 11 can be loosely inserted. Although the relative distance between the heating zone in which the induction coil 23 is arranged and the cooling zone in which the air cooling jacket 24 is arranged may be fixed or adjustable, the induction coil 23 may be adjusted during relative running during quenching. The air cooling jacket 24 is preceded and followed. The induction coil 23 is connected to a power supply cable from a high-frequency power supply device (not shown), and the induction coil 23 induction-heats a short section in the axial direction of the roll-shaped shaped body 11 during high-frequency energization. A hose extending from an air source (not shown) is connected to the air cooling jacket 24, and the air cooling jacket 24 blows air to follow and cool the heating part by the induction coil 23 in the roll shaped body 11. . If the cooling capacity is insufficient only by forced air cooling with the air cooling jacket 24, water cooling or the like may be used in combination.

  When quenching by induction heating is performed on the roll shaped article 11 using such a quenching apparatus 20, the quenching conditions (see FIG. 1C) are first selected from the following range. That is, the induction coil 11 is heated so that the roll-shaped shaped body 11 is heated to the quenching temperature at a temperature rising rate of 50 to 200 ° C./s, maintained at a temperature of 5 to 30 s, and further cooled at a temperature decreasing rate of 5 to 50 ° C./s. Control conditions such as energization 23, air blowing of the air cooling jacket 24, and travel of the roll shaped body 11 are set. And after hardening the roll-shaped shaped object 11 on the selection conditions, and also giving appropriate tempering etc., hardness, a carbide | carbonized_material state, and Cr distribution ratio are confirmed about a cross section.

  Specifically, regarding hardness (see FIG. 5), hardness measurement is performed for a range extending from the roll surface to a depth of 20 mm or more to obtain a hardness transition curve from the roll surface toward the roll center. Check the wear-resistant layer on the roll surface side, and check the hardness gradient closer to the roll center. For the wear-resistant layer, it is confirmed that the hardness of the surface layer portion extending from the surface to a depth of at least 5 mm is in the range of Hv 700 to 850 (Hs 80 strong to 90 strong) by heat treatment. Regarding the hardness gradient, the hardness suddenly changing portion is located closer to the roll center than the bisection position of the cross-sectional area, and the gradient between Hv500 and 300 is steeper than the gradient between Hv700 and 500. Confirm. It is also confirmed that the roll core (the roll center and its vicinity) is in an uncured state of Hv300 or less.

  Regarding the carbide state in the cross section (see FIG. 4), the cross section of the wear-resistant layer is photographed with an optical microscope or an electron microscope, the image is taken into a computer, and further image analysis is performed to determine the carbide particle size, area ratio, And measure the spacing. And that the hard carbide is dispersed in the form of substantially spherical fine particles having a cross-sectional apparent particle size of 0.1 to 10 μm, and that the hard carbide is distributed with a high space factor of 10-30 cross-sectional apparent area%, It is confirmed that the interval between the hard carbides is 10 μm or less. Metal carbide (hard carbide) contributes to the improvement of wear resistance because of its high hardness, but wear resistance decreases when the particle size is less than 0.1 μm, and becomes brittle when the particle size exceeds 10 μm. Decreases. Further, if the area ratio occupied by the hard carbide is less than 10%, the wear resistance is insufficient, and if the area ratio exceeds 30%, it becomes brittle, the toughness is lowered, and the spalling resistance is reduced. Furthermore, if the distance between the hard carbides exceeds 10 μm, the wear resistance decreases. In particular, the line between the hard carbides is preferably 5 μm or less in a line having a severe wear load on the roll.

  For the ratio of the Cr distribution (see FIG. 7), for example, EDX (energy dispersive X-ray spectroscopy) analysis is performed to measure the Cr amount (A) of the base metal phase and the entire Cr amount (B). By calculating the ratio, the Cr ratio (A / B) of the base metal phase is obtained, and it is confirmed that this ratio value is 0.4 to 0.7. When the Cr ratio of the base metal phase with respect to the total amount of Cr is less than 40%, the corrosion resistance decreases, so the Cr content of the hard carbide-forming elements is not only high in total, but also only the base metal phase is seen. It is also desirable that the content is high. On the other hand, in a state where the Cr ratio of the base metal phase exceeds 70%, carbides are reduced at the same time, and the wear resistance tends to decrease, and the toughness of the base metal phase cannot be ignored.

After confirming such hardness, carbide state and Cr distribution ratio, if they are out of the proper range, modify the composition and quenching conditions and start again, Confirm and fix the quenching conditions. And the required number of scale breaker rolls 10 are manufactured under the conditions.
Since the correction guideline for the composition has been described above, when describing the correction guideline for the quenching conditions, the hardness of the wear-resistant layer is in a suitable range of Hv 700 to 850 in view of the balance between wear resistance, toughness and spalling resistance. However, if the depth is less than 5 mm, the wear life provided in proportion to “depth−α” is not secured sufficiently high, and the cost increase associated with the implementation of the present invention is not met. On the other hand, when the depth of the wear-resistant layer exceeds 10 mm, there may be a case where the toughness against bending stress or impact during scale braking is insufficient, so the depth of the wear-resistant layer, specifically the depth of the hardness Hv700 region. Is preferably in the range of 5 to 10 mm.

In addition, when the rate of temperature rise during quenching is less than 50 ° C./s, the amount of carbide solid solution increases, so the particle size of the carbide decreases and the area ratio of the carbide decreases, resulting in a decrease in wear resistance. . And, the higher the rate of temperature rise, the better the presence of the carbide and the better the wear resistance. However, when the temperature exceeds 200 ° C./s, the above effect is saturated and the equipment cost of the high frequency power supply device is prohibitive. growing.
Furthermore, if the holding time at the quenching temperature is shorter than 5 s, sufficient hardness cannot be obtained. On the other hand, when the holding time at the quenching temperature is longer than 30 s, the particle size of the carbide is reduced and the area ratio of the carbide is also reduced, so that the wear resistance is lowered.
The above-mentioned preferable temperature rise and temperature holding conditions result in the optimization of the effective heating time, that is, the temperature above the α → γ transformation point that affects the existence form of carbides. Incidentally, the effective heating time is desirably 10 to 40 seconds.

An equivalent of a roll for scale breaker having a diameter of 80 mm was produced (see FIG. 1), and the test material was subjected to a wear test (see FIGS. 2 and 3), cross-sectional image analysis (see FIG. 4), hardness distribution measurement ( 5), immersion corrosion test (see FIG. 6), Cr content measurement (see FIG. 7).
The powder raw material is manufactured by gas atomization after vacuum melting, and the material is high C-13Cr steel. This contains C: 2.3 mass%, Cr: 13 mass%, Mo: 1 mass%, and V: 4 mass% as hard carbide forming elements, with the remainder being Fe (iron) and inevitable impurities.

Quenching (see FIGS. 1A and 1B) was performed by induction heating using the quenching apparatus 20 described above. The quenching conditions at that time (see FIG. 1C) were a temperature rising rate of 100 ° C./s, a quenching temperature of 1150 ° C., a holding time of 10 s, and a temperature falling rate of 10 ° C./s.
Tempering was performed in an electric furnace, and was performed twice under the conditions of a tempering temperature of 530 ° C. and a holding time of 4 hours.

In the abrasion test (see FIGS. 2 and 3), a Nishihara type abrasion test was performed on the test material 14 cut out in a disk shape of φ30 × 8t. More specifically (see FIG. 3), it is possible to rotate the mating material 30 made of the quenching and tempering material of SUJ2 and the test material 14 at 800 rpm while sliding at a sliding degree of 30% and applying a load of 1470 N. Continued for 20 hours under.
As a result of the test (see FIG. 2), the powder metallurgy roll A1 of the present invention has an abrasion amount of only 4 mg, which is superior to the conventional product tested under the same conditions. Specifically, the amount of wear was less than 19 mg of powder metallurgy roll B1, 75 mg of melt roll B2, 31 mg of melt roll B3, and 195 mg of forged steel roll B4.

  For cross-sectional image analysis (see FIG. 4), a cross-sectional part 1 mm deep from the surface of the test material is photographed with an SEM (scanning electron microscope) to obtain a 2000-fold microstructure image, which is taken into a computer. I went there. According to this, most of the hard carbides are fine particles having a particle diameter of 1 to 4 μm, and are dispersed in a substantially uniform state in the base metal, and each shape is substantially spherical. Further, the area ratio of the hard carbide is a high space factor of 20% in terms of the apparent area% of the cross section.

  The hardness distribution measurement (see FIG. 5) was performed at 1 mm intervals from the surface to a depth of 24 mm. According to this, the surface hardness is Hv850, and the hardness Hv700 is in a portion having a depth of about 8 mm, and the depth up to this depth becomes the wear-resistant layer. The hardness Hv500 is at a site having a depth of about 17 mm, and the hardness sudden change portion is at a deeper side, specifically, a depth of about 17 to 20 mm. The hardness gradient is approximately 220 Hv / 10 mm between Hv 700 and 500, approximately 670 Hv / 10 mm between Hv 500 and 300, and apparently the gradient between Hv 500 and 300 is steeper than the gradient between Hv 700 and 500. . Furthermore, the core part region of 1/2 thickness of the roll is Hv300 or less that can be regarded as uncured. The characteristic regarding the hardness sudden change part and gradient in such a hardness transition curve exists only in the powder metallurgy roll A1 of the present invention, and does not exist in the conventional powder metallurgy roll B1 and the melt rolls B2 and B3.

  The immersion corrosion test (see FIG. 6) was performed by keeping tap water having a dissolved oxygen amount of 8 ppm at 25 ° C. and immersing it in 168 Hr (see FIG. 6A). When comparing the corrosion state (see FIG. 6 (b)) of the powder metallurgy roll (high C-13Cr steel) of the present invention and the corrosion state of the SKH51 material immersed simultaneously (see FIG. 6 (c)), the difference is Obviously, the powder metallurgy roll of the present invention shows high corrosion resistance.

  The Cr content was measured (see FIG. 7) by qualitative analysis by EDX and simple quantitative analysis. Component analysis, etc. was performed on precipitates (hard carbide) and base metal (matrix), and the amount of Cr was tabulated. The Cr amount (A) of the base metal phase was 6%, and the total Cr amount (B) was At 13%, the Cr ratio (A / B) of the base metal phase was 0.46. This is in an appropriate range of 0.4 to 0.7 for the Cr ratio.

About one Embodiment of this invention, the structure of quenching apparatus and quenching conditions are shown, (a) is the principal part schematic diagram which looked at the quenching apparatus which set the roll-shaped shaped body in front, (b) is the longitudinal cross-sectional view, (C) is a temperature schedule at the time of quenching. The result of an abrasion test is shown, (a) is a comparison table, (b) is a comparison graph. The embodiment of an abrasion test is shown, (a) is a schematic diagram, (b) is a test condition. It is a drawing substitute photograph which shows the cross section of a test material. It is the figure which contrasted and displayed the hardness transition curve. The result of an immersion corrosion test is shown, (a) is a test condition, (b) is a drawing substitute photograph of the roll of the present invention (high C-13Cr steel), and (c) is a drawing substitute photograph of the comparative material (SKH51). It is a table | surface which shows the EDX analysis result of Cr content of a test material.

Explanation of symbols

10 Scale breaker roll (curing roll)
DESCRIPTION OF SYMBOLS 11 Roll-shaped shaped object 12, 13 Small diameter edge part 14 Test material 20 Quenching apparatus 21 Lifting means (work | work vs. heating / cooling unit relative travel mechanism)
22 Upper end support (work support mechanism, work support rotation device)
23 Induction coil (short section heating unit, heating / cooling unit)
24 Air cooling jacket (cooling zone cooling unit, heating cooling unit)
25 Rotating means (work rotating mechanism, work supporting rotating device)
26 Lower end support (work support mechanism, work support rotation device)
30 Counterpart material

Claims (5)

A roll-shaped shaped body made of powder metallurgy made of powder metallurgy containing a hard carbide forming element as a main component is used as a raw material, and a surface layer portion at least 5 mm deep from the surface by heat treatment is a wear-resistant layer having a high hardness. In the roll for the scale breaker,
The material contains C: 1.7 to 3.5 mass%, Cr: 10 to 20 mass%, Mo: 0.5 to 5 mass%, and V: 1 to 10 mass% as main component elements, and the wear-resistant layer. The hard carbide composed of the main component element is distributed in the form of substantially spherical fine particles having a cross-sectional apparent particle size of 10 μm or less and with a high space factor of 10-30 cross-sectional apparent area%, and the wear resistance The hardness of the layer is in the range of Hv 700 to 850, and inside the wear-resistant layer, there is a backing region in an effective cured state, a hardness suddenly changing portion where the hardness suddenly drops to an uncured state, and an uncured core The hardness decreasing gradient in the depth direction of the backing region is a gentle gradient with the Hv value decrease per 10 mm depth increase being on the order of 200 points, and the hardness suddenly changing portion is , Radial direction at a distance of (1 / √2) of the roll radius from the roll center Located in the roll center side than the roll cross section bisecting position related, further, scale breaker rolls the hardness of the core region is Hv300 or less, and wherein the. A roll-shaped shaped body having a high carbon and high alloy steel composition prepared through a step of sintering a powder raw material is subjected to a heat treatment step including quenching, and a surface layer portion having a depth of at least 5 mm from the surface is hard. In the scale breaker roll that is the wear-resistant layer,
The roll-shaped shaped body has a composition containing C: 1.7 to 3.5 mass%, Cr: 10 to 20 mass%, Mo: 0.5 to 5 mass%, and V: 1 to 10 mass% as main component elements. The heating for quenching is based on a rapid heating condition of a temperature rising rate of 50 to 200 ° C./s and a temperature holding of 5 to 30 s at the quenching temperature,
In the wear-resistant layer, hard carbides composed of the main component elements are distributed in the form of substantially spherical fine particles having a cross-sectional apparent particle size of 10 μm or less and with a high space factor of 10-30 cross-sectional apparent area%. The wear-resistant layer has a hardness in the range of Hv 700 to 850, and on the inner side of the wear-resistant layer, there is an effective hardened backing region and a hardness suddenly changing portion where the hardness suddenly drops to an uncured state. The core region in the uncured state is connected in this order, and the hardness decreasing gradient in the depth direction in the backing region is a gentle gradient in which the Hv value decrease per 10 mm depth increase is on the order of 200 points, and The sudden hardness change portion is located on the roll center side from the roll cross-sectional area bisected position in the radial direction at a distance (1 / √2) of the roll radius from the roll center. The core region has a hardness of Hv300 or less. To scale breaker for the roll.   The scale breaker roll according to claim 1 or 2, wherein 40 to 70% of the Cr content of the main component elements is contained in the base metal phase. A high-carbon high-alloy steel composition roll-shaped body containing a hard carbide-forming element as a main component, prepared through a step of sintering a powder raw material, is subjected to a heat treatment step including quenching, and at least a depth from the surface In a method for producing a roll for a scale breaker, obtaining a curing roll having a surface layer portion of up to 5 mm with a high hardness wear-resistant layer,
The roll-shaped shaped product has a composition containing C: 1.7 to 3.5 mass%, Cr: 10 to 20 mass%, Mo: 0.5 to 5 mass%, and V: 1 to 10 mass% as main component elements. In the above, the quenching is rapidly performed by induction heating to a quenching temperature at a heating rate of 50 to 200 ° C./s, holding the temperature for 5 to 30 s, and then cooling at a cooling rate of 5 to 50 ° C./s. By applying under short heating and slow cooling conditions,
As the hardening roll, a hard carbide composed of the main component element in the wear-resistant layer is in the form of substantially spherical fine particles having a cross-sectional apparent particle size of 10 μm or less and a high space factor of 10-30 cross-sectional apparent area%. The hardness of the wear-resistant layer is in a range of Hv 700 to 850, and the hardness of the wear-resistant layer suddenly drops to the backing region in the effective cured state and the uncured state. The suddenly changing portion and the uncured core region are connected in this order, and the hardness decreasing gradient in the depth direction in the backing region is a gentle gradient in which the Hv value decrease per 10 mm depth increase is on the order of 200 points. And the hardness suddenly changing portion is located on the roll center side from the roll cross-sectional area bisected position in the radial direction at a distance of (1 / √2) of the roll radius from the roll center, Furthermore, the hardness of the core region is Hv300 or higher. Obtaining a roll is, the production method of roll scale breaker, characterized in that.   A quenching apparatus for performing the quenching in the manufacturing method according to claim 4, wherein the roll shaped shaped body is supported in a posture in which the axis is oriented in the vertical direction and the work support rotating device rotates the axis. A heating / cooling unit having an induction coil for induction heating of a short section in the axial direction of the roll shaped object, and a cooling zone provided with at least an air cooling jacket for cooling the heating portion by the coil, and the work support A quenching apparatus, comprising: a rotating device and a workpiece / heating / cooling unit relative traveling mechanism configured to cause at least one of the heating / cooling unit to travel in a vertical direction.