JP2785139B2 - Composite roll for rolling and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a work roll for rolling and a method for manufacturing the same, and in particular, dendrites are used for foil rolls and materials to be rolled which require high strength and abrasion resistance. The present invention relates to a composite roll for rolling suitable for a non-transferred roll and a method for producing the same.

[Conventional technology]

Recent needs for work rolls for rolling have emphasized that the material to be rolled has high light luminance persistence and that dendrites are not transferred. In order to cope with this, it is necessary to refine the structure, homogenize it, and make it highly alloyed. Also, 6
In a rolling mill such as a step mill, since it is necessary to perform rolling under high pressure, the roll diameter has been reduced.
Therefore, as the characteristics required for the roll, spall resistance and abrasion resistance are required for the body portion of the roll, and high strength and toughness are required for the shaft portion.

In order to obtain a roll for rolling having both of these characteristics, in the case of a so-called smelting material by conventional melting-casting-forging, the improvement of the characteristics of the roll body is particularly limited.
In other words, in the work roll for rolling made of ingot, the carbide size in the matrix is widely distributed, and in particular, there is a huge carbide having a disadvantage that heat treatment property, forging property and spall resistance are significantly deteriorated. is there. In addition, the smelting method has a disadvantage that the carbide content is limited. Further, in the ingot material, there is a problem that the appearance of a coarse dendrite structure cannot be prevented, and the material is transferred to a material to be rolled or the roll surface is severely roughened.
These drawbacks are fatal to smelting,
It is a factor that limits itself to the manufacturing method and components.

As a technique for solving the above-mentioned drawbacks, the following method is known, which utilizes a rapid solidification effect to start from a metal powder, a cermet, and a ceramic powder having wear resistance and spall resistance.

(1) Hot isostatic method.

(2) Insert method (sleeve type).

(3) Liquid phase sintering method.

(1) mainly after cold-forming gas atomized powder,
Manufacturing method by hot isostatic method (HIP) or hot extrusion method (Composite Machining Study Group: “Composite Machining Technology”: P97
~ 128, (S57.10 first edition)). This method has the drawbacks that the particle shape of the raw material powder is restricted and the diffusion layer at the boundary is small, so that stress concentration occurs during heat treatment, which causes cracking and peeling.

(2) is a method of fitting the core material by so-called shrink fit or cold fit ("Plastic working" Vol23, NO261, (1982), 1
Published in May P945-951). In this method, it is impossible to shrink-fit high elasticity and low expansion materials, and inevitably employs a cold-fitting method. There is a disadvantage that the damage is increased.

(3) is a method of metallurgical bonding (edited by the Iron and Steel Institute of Japan: “Handbook of Steel”, p. 445-456, S57.10). In this method, since the thickness of the boundary layer at the boundary between the core material of the composite roll and the sintered body is 0.2 mm or less, the residual stress is concentrated near the boundary,
It has the disadvantage of inducing cracking and peeling.

2. Description of the Related Art Recently, a method of manufacturing a composite roll by a spray coating method, which is manufactured in a process as shown in FIG. 2, has attracted attention (Japanese Patent Application Laid-Open Nos. 55-14971 and 52-88526).

This method has an advantage that the properties of the powder are hardly lost compared to the above-mentioned methods.
Alternatively, it is necessary to perform sufficient swaging. now,
If the bonding temperature between the core material and the sprayed layer is to be enhanced by HIP processing, the processing temperature and pressure will increase, and the structure of the sprayed layer will become coarse, and carbides will grow, and the characteristics of the powder will increase. Will be halved. Further, in order to enhance the bonding property by swaging, it is necessary to increase the forging ratio.

However, since the body of the composite roll for rolling is made of a material that is hard and brittle compared to the core, the method of the core is inevitably forged and uneconomical. However, there has been a problem that a sufficient bonding strength cannot be obtained, and sometimes a crack is generated in the sprayed layer portion. Furthermore, during the thermal spraying operation, a crack is generated at the end face of the thermal sprayed layer, and the operation is often interrupted.

As the composition of the powder, there are JP-A-60-158906 and JP-A-55-122801, etc., but in addition to corrosion resistance, it is inferior in quenching hardness and strength and toughness of the matrix, and is sufficiently satisfactory. Nothing was satisfactory.

[Problems to be solved by the invention]

The above-mentioned prior art is to improve the hardenability and strengthen the base as the powder composition for the trunk part where the spall resistance and the wear resistance are required, and regarding the thermal spraying, regarding the thermal management before and after the thermal spraying. No consideration was given, and there was a problem in making a composite roll for high-speed rolling under high pressure and a method for producing the same.

The object of the present invention is to use a powder for the body that can impart abrasion resistance and spall resistance, perform good heat management including before and after during the spraying operation, and under high pressure, a high-speed composite roll. And a method for producing the same.

[Means for solving the problem]

In order to achieve the above object, in the present invention, a metal roll having high strength and toughness, in a composite roll having a body that is more wear-resistant than the shaft, the body comprises a plurality of sprayed layers. Each of the sprayed layers has a sprayed layer portion having a smaller particle size on the inner side than that on the outer side.

Further, in the present invention, in a method for producing a composite roll having a body portion having higher wear resistance than a metal shaft portion having high strength and toughness, the metal shaft portion is preheated, and each sprayed layer is formed on the shaft portion. Is to form the body sprayed layer portion so that the inner particle size is smaller than that of the outside, further, in the method of manufacturing a composite roll, the body sprayed layer portion, the metal shaft portion Is vertically rotated, and each layer from the first layer to the last layer is formed by moving the plasma torch in one direction from the lower part to the upper part and spraying it to have a predetermined thickness.

A composite roll obtained by spraying a powder having abrasion resistance, spall resistance and oxidation resistance on a body of a shaft part having excellent strength and toughness according to the present invention, and a composition of a powder used in a method for producing the composite roll. As: C: 1.5-4.5%, Si: 1-3%,
Cr: 12 to 35%, Mo: 1 to 6%, W: 1 to 6%, V: 1 to 6%, remaining F
It is preferable to use e or the above composition containing 3 to 10% of Ni or Co.

Furthermore, in the present invention, the insufficient bonding at the boundary between the shaft portion and the sprayed layer and the occurrence of cracks at the end of the sprayed layer are not sufficient simply by coating the canning material under reduced pressure after the spraying. The focus is on the preheating of the shaft portion, the post-heating after thermal spraying, and the thermal spraying method.

That is, the preheating temperature of the shaft portion is defined as f, where f is the weight ratio of the sprayed layer portion to the shaft portion, and when f is 0.01 ≦ f ≦ 3.5, the preheating temperature T (C) is T = 1000-170f or more, and f Is 4 when f> 3.5
The treatment is performed at a temperature of 00 ° C. or more and 1200 ° C. or less. The post-heating after the thermal spraying is performed at a cooling rate of 250 ° C./hour or less.

Thermal management is performed so as to satisfy the upper condition, and the thermal spraying is performed such that the thermal spraying range is gradually narrowed as shown in FIG. 3, and the thermal spray initial layer 23, thermal spray intermediate layer 24, and final thermal spray layer 25 are sequentially reduced. It is.

By employing the above thermal spraying method, the composite roll of the present invention has a cross section as shown in FIG. In FIG. 1, plasma-sprayed rapidly solidified powder of a high-carbon high-chromium steel system having wear resistance of a material having the composition of the present invention is applied to the surface of the body 22 of the shaft 9 having high strength and high toughness. By doing so, the thick sprayed layer 10 is formed, and in particular, the angle (θ) of the end of the sprayed layer is set to θ ≦ 70, and the boundary layer portion 21 is formed.

Further, as the thermal spray material used for the thermal spraying, powder having a particle size of 150 mesh or less and a carbide particle size of 2.0 μm or less is used. The thermal sprayed layer obtained by thermal spraying has a grain shape of 2 to 10 μm and is made of carbide having an area ratio of 15 to 55%.

In the above thermal spraying, it is important that the movement of the gun during thermal spraying be performed only in one direction from the lower portion to the upper portion of the shaft portion.
As shown in FIG. 7, the powder in the frame is distributed in coarse grains 7, medium grains 6, and fine grains 5, so if spraying is performed only from the lower part, the uniformity is obtained as shown in FIG. Since a fine spray layer portion is formed and fine particles are always sprayed first, the bondability is enhanced.

In FIG. 7, the coarse grains 8 and the fine grains 4 are scattered outside the frame, and do not contribute to the formation of the thermal spray portion.

As described above, the composite roll for rolling according to the present invention rotates the shaft 9 having high strength and high toughness in the direction of arrow a and preheats the shaft to the target temperature as shown in FIG. To achieve a predetermined thickness.

The thermal spraying at this time has a boundary layer 21 which is sequentially changed from a material close to the core material of the shaft portion to the material of the present invention, and the thermal spraying distance is gradually narrowed as shown in FIG. The joint between the shaft portion and the sprayed layer portion is strengthened, and the occurrence of cracks at the end face of the sprayed layer during spraying can be prevented. Further, by performing the thermal spraying only in one direction from the lower portion to the upper portion, it is possible to homogenize the thermal sprayed layer portion and to prevent the generation of a crack at the end surface portion of the thermal sprayed layer portion.

By cooling at 250 ° C./hr or less after thermal spraying, peeling of the boundary portion and generation of cracks in the thermal sprayed layer during the cooling process are eliminated.

(Operation)

The results of studies on C, Cr, Ni, Si, W and V in the composition of the powder are summarized as follows.

C is an element that combines with Cr, W, V, Fe, etc. to form a double carbide and further forms a solid solution in the matrix to give strength. However, if it is less than 1.5%, its wear resistance is inferior, and it exceeds 4.5%. Even if added, the hardness may not be increased but rather may be lowered.

Si is an element that improves oxidation resistance and fluidity.
If it is less than 3%, the fluidity is poor, and if it exceeds 3%, the toughness is reduced.

Cr is an element that forms carbides with C to increase hardness, thereby improving wear resistance and oxidation resistance.
If it is less than 35%, the improvement is not sufficient.

Ni is an element for stabilizing austenite, and most of it is dissolved in the matrix to improve corrosion resistance, toughness, and wear resistance. Normally, a content of 2% or less is sufficient, but 3% or more is required to convert the matrix into tempered martensite and improve abrasion resistance, and even if it exceeds 10%, the effect is small.

Co is expensive but has an austenitic matrix strengthening element and is effective in improving wear resistance, but 1%
If it is less than 6%, the effect is small, and if it exceeds 6%, it is not as effective as an increase in the added amount.

W is an element that forms a special carbide in coexistence with Cr and increases the hardness and abrasion resistance very much. However, if it is less than 1%, it is not so effective. Since this element is very heavy, it is 6%.
When the amount is more than the above, segregation occurs, and the workability of dissolving and refining is deteriorated, so that it is difficult to obtain a powder having a uniform composition.

V is an element having the same properties as W, but is a light element contrary to W, so that segregation occurs at 6% or more and the workability of dissolving and scouring is deteriorated. Is small.

Next, the preheating temperature will be described. In order to be subjected to rolling as a composite roll, it is necessary to sufficiently bond the shaft portion and the sprayed layer portion. This is because the joining boundary between the shaft portion and the sprayed layer portion receives alternately tensile and compressive stresses during rolling, and if the joining is not sufficient, the interface peels off. The inventors conducted a number of experiments to clarify the influence of the shaft preheating on the quality of the joint.

The result is shown in FIG. Here, f is the ratio of the weight of the sprayed layer portion to the weight of the shaft portion. For 0.01 ≦ f ≦ 3.5, the preheating temperature T (° C.) of the shaft portion needs to be equal to or higher than the temperature shown by the following equation. (Equation) T = 1000−170f For f> 3.5, 400 C. or higher is required, and below this temperature, good bonding cannot be obtained. Further, it is not always necessary to be above these temperatures. This is because if the preheating temperature is too high, the shaft portion is softened and deformed, and on the contrary, the bonding interface is peeled off in the process of plastic working or heat treatment after thermal spraying. From the above, the upper limit of the preheating temperature should be 1200 ° C or higher.

Next, the cooling rate after thermal spraying will be described. If the cooling rate is too high, the transformation of the sprayed layer portion proceeds rapidly, and an excessive stress is applied to the joint interface, leading to delamination. Even when the thermal sprayed layer is cooled, the center temperature of the shaft may increase, and in such a state, stress is generated at the joint interface, which leads to peeling. In order to alleviate the occurrence of such stress, it is necessary not to make the cooling rate after thermal spraying so high, and the magnitude should be 250 ° C./hr or less.

As shown in FIG. 3 above, cracks in the sprayed layer portion are formed by successively narrowing the spraying distance during spraying from the vicinity of the shaft portion at the beginning of spraying, so that the shape after spraying, particularly the shape at both ends, is reduced. Fifth
As shown in the figure, the angle (θ) at both ends is smaller than when the spray distance is constant as in the conventional case (FIG. 6), and the (Δx) portion is thicker than the spray thickness (x) at the center. Can be prevented by doing so.

The angle will be described below. The inventors formed a sprayed layer portion in which the angle was changed variously. As a result, those having an angle of 75 ° or more had cracks in the end face immediately after thermal spraying. No cracks occurred immediately after thermal spraying, but cracks occurred during the subsequent heat treatment.
On the other hand, cracks did not occur after spraying and after heat treatment for the specimens of 70 ° or less. The powder forming the sprayed layer is extremely excellent in abrasion resistance, but if the temperature is non-uniform, excessive thermal stress and transformation stress are applied to the end face to cause cracks. From the above, the angle at both ends should be 70 ° or less.

〔Example〕

Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.

Shot shot on the surface, washed 80mm in diameter, 900m long
The shaft portion of the material SUJ-2 round bar of m, was set in a thermal spraying apparatus as shown in FIG. 9, after evacuating the system to below 0.2 Torr, the 40~50Torr injecting Ar + H ₂ gas While maintaining the atmosphere, the core material is rotated at 20 rpm in the direction of the arrow in FIG. 9 and preheated by a plasma arc until the surface temperature of the shaft becomes 820 ° C., and then the spraying is started by rotating the shaft at 70 rpm. .

The thermal spraying was carried out as shown in Table 2 using powders of commercially available materials SKD-11 and SF45 in addition to the materials of the present invention as shown in Table 1.

The material SKD-11 in Table 2 was used to strengthen the joining material between the shaft portion and the material of the present invention, and the material sprayed with SF45 equivalent material was applied by coating the material portion of the present invention. This is because the same effect as that obtained by applying the canning 26 in FIG. 1 is obtained.

After the spraying is completed, the rotation speed of the shaft is reduced to 30 rpm or less, the plasma frame is moved up and down, and the coating material of the final sprayed layer is sprayed.
Slowly cooling at a cooling rate of 200 ° C./hr, rotation of the shaft and gas injection are stopped, and the inside of the device is returned to the atmosphere and taken out.

While heating this roll material to 1150 ° C, swaging was performed at a pitch of 2.0 mm from φ 125 mm, 1.0 mm, 125 to 120 mm, and then the surface of the sprayed layer was cut off by about 1.5 mm with a lathe to remove the canning material. Thereafter, a predetermined heat treatment was applied to produce a composite roll having a shaft diameter of 105 mm and a total length of 1030 mm having a sprayed layer portion of 18.0 mm and a body hardness of HS = 92 as shown in FIG.

The roll was inspected with an ultrasonic flaw detector and found to be defect-free. The area ratio and the particle size of the carbide in the sprayed layer portion were 31% and 3.0 to 4.5 μm, respectively (the aspect ratio was 0.3%).
7-0.9).

The life of the composite roll for this roll is about 2.4 times per grinding compared to the conventional composite roll. Furthermore, the Hertz contact stress during rolling is 250 kg / mm ² and the roll rotation speed is N = 6 × 10 ^6. No problem of peeling or cracking occurred in the composite roll. In addition to the rolls of sprayed material of the same material, the brightness of the material to be rolled and the thickness accuracy of the material to be rolled are improved by 10% or more and the rolling load can be reduced. It has been found to be advantageous.

[Effects of the Invention] According to the present invention, the shaft portion (core material) has high strength and high toughness, while the sprayed layer in contact with the material to be rolled is excellent in spall resistance and abrasion resistance, so that the high pressure The present invention can provide a composite roll for rolling that does not have flat deformation even when rolling at a high rotation speed and does not cause peeling and cracking.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a composite roll for rolling according to the present invention, FIG. 2 is a view showing main production steps of a composite roll by powder spraying, FIG. 3 is a schematic diagram illustrating a thermal spraying method, FIG. Is a graph showing the optimum preheating temperature range of the core material, FIG. 5 is a sectional view showing a shape after thermal spraying, FIG. 6 is a sectional view showing a shape after thermal spraying by a conventional thermal spraying method, and FIG. Fig. 8 is a schematic diagram illustrating the distribution of particles in the sprayed layer, Fig. 9 is a schematic diagram illustrating the reduced pressure spraying method, and Fig. 10 is the product shape of the composite roll. FIG. 1 ... supply port of powder conveyed by inert gas, 2 ... frame, 3 ... gun, 4 ... fine particles, 5 ... fine particles, 6 ...
... Intermediate grain, 7 ... Coarse grain, 8 ... Coarse grain, 9 ... Shaft part, 10
…… spray layer, 11… spray torch, 12,15 …… powder supply device, 13,14 …… powder, 16 …… working gas, 17,18 …… power supply,
19,20 …… Inert gas, 21 …… Boundary layer

──────────────────────────────────────────────────続 き Continuing on the front page (72) Shogo Morimoto 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Osamu Shimoyumura 832 Horiguchi Katsuta City, Ibaraki Prefecture Inside Hitachi Katsuta Plant (72) Inventor Masaki Shimizu 832 Horiguchi, Katsuta City, Ibaraki Prefecture Inside Hitachi Ltd. Katsuta Plant (56) References JP-A-1-162745 (JP, A) JP-A-61- 41747 (JP, A) JP-A-59-23846 (JP, A) JP-A-58-86974 (JP, A) JP-A-57-131348 (JP, A) JP-A-59-143048 (JP, A) JP-A-1-127646 (JP, A) JP-A-53-28057 (JP, A) JP-A-1-294853 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 4/00-6/00 B21B 27/00 C22C 38/00-38/60 C22C 37/00-37/10

Claims (10)

(57) [Claims] 1. A composite roll having a metal shaft portion having high strength and toughness and a body portion more wear-resistant than the shaft portion,
A roll for rolls, characterized in that the body comprises a plurality of sprayed layers, and each sprayed layer has a sprayed layer having an inner particle size smaller than that of the outer layer. 2. The body sprayed layer has a grain size of 2.0 to 10 μm,
The composite roll for rolling according to claim 1, wherein the composite roll is made of a carbide having an area ratio of 15 to 55%. 3. The rolling composite roll according to claim 1, wherein an angle formed at an end face of the body sprayed layer portion with respect to the shaft portion is 70 ° or less. 4. A method of manufacturing a composite roll having a metal shaft portion having high strength and toughness and a body portion more wear-resistant than the shaft portion, wherein the metal shaft portion is preheated, and each sprayed layer is formed on the shaft portion. Wherein the body sprayed layer is formed such that the inner particle size is smaller than the outer particle size. 5. A method for producing a composite roll having a metal shaft portion having high strength and toughness and a body portion more wear-resistant than the shaft portion, wherein the body sprayed layer portion makes the metal shaft portion vertical, A method for manufacturing a composite roll for rolling, comprising forming each layer from an initial layer to a final layer by rotating a plasma torch in one direction from a lower part to an upper part and spraying it to a predetermined thickness. 6. The method according to claim 4, wherein the body sprayed material has a particle size of 150 mesh or less and a carbide of 2.0 μm or less. 7. The method for manufacturing a composite roll for rolling according to claim 5, wherein the range of thermal spraying from lower to upper is reduced sequentially. 8. The preheating temperature of the metal shaft portion is defined as follows: where f is the ratio of the weight of the sprayed layer formed around the shaft portion to the weight of the shaft portion, f is in the range of 0.01 to 3.5. 5. The method for producing a composite roll for rolling according to claim 4, wherein the temperature is not lower than a temperature given by T (° C.) in the following formula and not higher than 1200 ° C. (Formula) T = 1000-170f 9. The preheating temperature of the metal shaft portion is set so that the ratio of the weight of the thermal spray layer formed around the shaft portion to the weight of the shaft portion is 3.5.
The method for producing a composite roll for rolling according to claim 4, wherein the temperature is in the range of 400 to 1200C in the range of to 10. 10. The method for producing a composite roll for rolling according to claim 4, wherein the thermal spray layer formed by thermal spraying has an average cooling rate of 250 ° C./hour or less for the thermal spray layer after thermal spraying. .