JPS63242408A - Composite roll for rolling - Google Patents

Abstract

PURPOSE:To prevent generation of deformations, peelings, and cracks by plasma thermal spraying powders having wear resistance and spalling resistance on the body of a core member through a boundary layer formed by sequentially changing a linear thermal expansion coefficient of the layer. CONSTITUTION:Different type powders 8, 8' for performing plasma thermal spraying on a thermal spray build-up layer 3 and a boundary layer 4 whose linear thermal expansion coefficient is sequentially changed are prepared in powder suppliers 6, 6', respectively. An action gas 10 and a cooling water 11 are supplied to a thermal spray torch 5; a powder carrying gas is fed from a gas cylinder 9; the boundary layer 4 whose linear thermal expansion coefficient value sequentially changes from that of a core member 1 is formed on the rotating core member 1. Then, the powders 8, 8' having wear resistance and spalling resistance are thermally sprayed to form a prescribed thickness layer. Deformations of a roll are prevented because the build-up layer 3 has wear resistance and peelings and cracks of the roll are prevented because the boundary layer 4 whose linear thermal expansion coefficient changes exists on the core member.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to rolling composite rolls used for rolling metals, and is particularly suitable for mill work rolls and Sendzimya rolls that require high strength and wear resistance. Regarding A composite role.

[Conventional technology]

As for recent needs for Senjimyarol, sustainability of high brightness has become important. To deal with this,
It is necessary to make the structure of the roll material finer, more homogeneous, and higher alloyed. In rolling mills such as 6-high mills, it is necessary to roll under high pressure, so there is a trend toward reducing the diameter of the rolls.

Therefore, the characteristics required of the roll include spall resistance and abrasion resistance for the body of the roll, and high strength suction and toughness for the shaft of the roll.

It has reached its limit to make rolling rolls that have both of these characteristics using so-called ingot material by conventional melting, casting, and forging. Although giant carbides contribute to wear resistance, they have the disadvantage of significantly deteriorating heat treatability, forgeability, and spalling resistance. Furthermore, ingot material has a coarse dendrite structure, which causes severe roughening of the roll surface during rolling. These drawbacks are fatal to molten lumber.

Techniques to overcome the above drawbacks include (1) hot isostatic pressure method, which utilizes the effect of rapid solidification and starts from metal powder with a low coefficient of thermal expansion and high modulus of elasticity; (2) insert method (
(3) liquid phase sintering method, or (4) thermal spray overlay method is attracting attention.

(1) is a method of manufacturing a composite roll by cold-forming gas atomized powder arranged around a core material (shaft), and then using a hot isostatic pressure method (H, 1, P,), hot extrusion method, etc. is (``
"Composite Processing Technology" first edition published in January 1980, 1997-12
(See page 8, edited by Composite 7 JO Engineering Research Group) 0 However, in this method, since the diffusion layer at the boundary is small, stress concentration occurs during heat treatment, leading to cracking and peeling.

(2) is a method of making a composite roll by inserting a sleeve made by powder sintering into a core material by so-called shrink fit or cold fit (``Plasticity and Processing J VOI 23° Flat 261,
(October 1982, pp. 945-951) However, it is impossible to shrink fit materials with high elastic modulus and low coefficient of thermal expansion, so cold fit is inevitably adopted, but If it becomes too large, there are problems such as peeling of the joint and increased damage to the backup roll.

(3) is a method of metallurgically bonding the sintered sleeve to the core material ("Steel Handbook", edited by the Iron and Steel Institute of Japan, 1972).
(Published in October 2015, pp. 445-456), because the thickness of the transition layer at the boundary layer between the core material and the sintered body of the composite roll is less than 0.2 m, residual stress concentrates near the boundary, causing cracking. 0 (4), which had the problem of inducing delamination and peeling, is a method in which thermal spray overlay is applied to the roll surface (Japanese Patent Application Laid-open No. 55
149710, JP-A No. 52-88526), however, it was not possible to prevent the problem of cracking and splitting due to the difference in thermal expansion coefficient in the boundary layer between the core material and the thermal spray overlay.

[Problem to be Solved by the Invention 3] As mentioned above, in the rolling composite rolls made by any of the conventional methods, the coefficient of thermal expansion and elasticity at the boundary layer between the core material and the sintered powder layer are Since the difference in the ratio is large, there is a problem in that stress concentration is induced starting from the vicinity of the boundary layer, resulting in peeling or cracking.

The purpose of the present invention is to overcome the above-mentioned problems, to avoid cracking or peeling of the thermally sprayed overlay layer, to make it possible to reduce the diameter of the roll, and to ensure that the body has good wear resistance and spall resistance under high loads. Another object of the present invention is to provide a composite roll for rolling having a shaft portion having excellent strength and toughness and having a thermal spray overlay.

[Means for solving problems]

The rolling composite roll of the present invention is a rolling composite roll in which a thick thermal sprayed layer is formed by plasma spraying powder having wear resistance and spall resistance on the body of a core material having high strength and toughness. Therefore, the boundary layer between the sprayed layer and the core material is
This is achieved by forming a laminated structure in which the coefficient of linear thermal expansion is sequentially changed such that the closer the layer is to the core material, the closer the coefficient of linear thermal expansion is to that of the core material.

The difference in coefficient of thermal expansion between the core material and the innermost layer of the boundary layer, the difference in coefficient of thermal expansion between the layers of the boundary layer, and the linear heat between the outermost layer of the boundary layer and the sprayed layer. The difference in expansion rate is 3
10 (1/'C)/m or less is desirable in order to prevent cracking or peeling of the sprayed layer due to stress concentration.

In addition, in order to prevent cracking and peeling of the sprayed layer and maintain strength, the thickness Δγ (,,) of the boundary layer portion is set to 1.5≦△, where the radius of the composite roll is R (fi). γ≦0.3R
It is desirable to satisfy the following.

[Example of ability]

As shown in FIG. 1, the rolling composite roll according to the present invention has a core material 1 (for example, steel) having high strength and toughness, and a body portion 2 having high elasticity, low thermal expansion, spalling resistance, and A thick sprayed ma is formed by plasma spraying rapidly cooled powder that has abrasive properties, and consists of a core material 1 and a sprayed layer 3.
There is a boundary layer s4 between. In the present invention, the boundary layer portion 4 has a laminated structure as described above.

When joining two materials, steel and cemented carbide, which have different coefficients of linear thermal expansion, if the thickness of the boundary layer is made very thin as in the case of diffusion joining, as shown in Figure 2, heat will be released from the joining interface. It has been reported that the maximum tensile stress occurs on the superalloy side surface, which has a small expansion coefficient, and compressive stress occurs on the steel side surface (Akiomi Kono: Diffusion bonding of cemented carbide and tool steel; Proceedings of the Welding Society, Vol. 3, No. 1, February 1985). Furthermore, this report researches the relaxation of thermal stress by inserting an insert material into the boundary layer region, and as a result, as shown in Figure 3, as the thickness of the insert material increases, the thickness decreases to a certain level. It is stated that although the bonding strength improves, it decreases above a certain thickness.

Based on this research report, the present inventors believe that there is an optimal thickness of the boundary layer portion 4 even in powder sprayed composite rolls, and believe that the thickness of the boundary layer 4 can be considered as a thermal spray overlay material for actual rolling composite rolls. The coefficient of thermal expansion and thickness of the boundary layer were investigated using steel or ceramic powder, either alone or in a blend. The results are described below.

Figure 4 shows the experimental results showing the relationship between the coefficient of linear thermal expansion and the occurrence of cracks in sprayed I-, where the horizontal axis is the coefficient of linear thermal expansion of the sprayed layer;
The vertical axis indicates the coefficient of linear expansion of the core material. Referring to this figure, it was determined that the difference in linear thermal expansion coefficients is desirably less than axlo 1/'C■.

Figures 5, 6, and 7 are diagrams showing the relationship between the thickness Δr) of the boundary layer portion and the tensile stress when steel is used as the core material and the sprayed materials are as shown in the figures. FIG. 8 is a diagram showing the thickness of the boundary layer portion, the coefficient of linear expansion of the sprayed material, and the occurrence of cracking and peeling of the sprayed layer.

From these figures, the thickness of the boundary layer (Δr) is at least 1.5
If it is more than 1, it is less than the critical tensile stress value of the material of 7.
No peeling or cracking occurs. The maximum thickness of the boundary layer portion is preferably 30% or less of the radius of the composite roll.

When considering the actual diameter of the roll used, it is desirable that the material from the roll surface layer to the roll diameter of 3096 mm is made of a material that has rolling characteristics.

FIG. 9 shows an example of a manufacturing device for manufacturing a composite roll according to the present invention, which includes a thermal spraying torch 5 equipped with a thermal spraying nozzle 13, a plurality of powder feeding devices 6゜6', and a control device 7. It is considered as a component. The powder feeding devices 6, 6' include
As mentioned above, different powders 8 and 8' to be thermally sprayed to form a thermally sprayed layer including a plurality of boundary layer portions having varying coefficients of linear thermal expansion are stored, and the powders are fed from the gas cylinder 9. By introducing the feed dregs, the powders 8, 8' can be sequentially fed to the thermal spraying torch 5. Further, the thermal spraying torch 5 is supplied with a working gas 10 and cooling water 11 via a control device ff7. Note that 12 is a power source.

The sprayed layer 3 is formed on the body of the core material 1 using such a manufacturing apparatus. In this case, multilayer thermal spraying is performed by rotating the core material 1 as shown by arrow a. In the thermal spraying operation, it is preferable to perform so-called reduced pressure thermal spraying in an Ar/Hm gas atmosphere after reducing the pressure to a degree of vacuum of about 50 To, rr. Hereinafter, specific embodiments of the present invention will be described. As a core material,
A round bar made of material SCM-4 with a diameter of 60mm and a length of 1000+w+ (modulus of elasticity E=21000Kf/lJ, coefficient of linear thermal expansion α=
12X10 ・1/'C/III), and 0.1 m/Pa! 18/-f 50~
Under a reduced pressure of 80 Torr, using Ar/H gas, the surface of the core material was first coated with a thickness of 101 so that the difference in linear thermal expansion coefficient between the core material and the core material was 3x.
10 ・1/C/w (r) Spray material, next iteration, E
=50000 first/-2α=6X10 ・1/℃/WI
II super steel powder was sprayed to a thickness of 40 mm. That l&
, 1050℃.

Vacuum sintered at 10 mHg for 10 hours, then sintered at 1150 mHg.
While heating to
1! A desired composite roll was produced by hot forging until it became Ill, then rough processing, and then performing a predetermined heat treatment.

All this roll with ultrasonic waves! As a result, the sprayed layer was completely metallurgically bonded and the sealing ratio was 100%. When this sprayed layer was compared with the case where a roll core material was coated with a conventional ingot material, the carbides were finely and evenly dispersed.

Note that the chemical compositions of the core material, boundary layer portion, and sprayed light layer portion of this example exhibited changes over time as shown in Table 1.

Table 1 The life of this rolling composite roll is 23 times 8 degrees per polishing compared to a conventional metal roll, and the Hertzian contact stress during rolling is 250 Ky/-, and the roll rotation speed is N = 6X.
10', no problems such as peeling or cracking occurred in this decoupling roll. [Effects of the Invention] According to the present invention, the 4@ part (core material) has high strength and high toughness. On the other hand, the thermal sprayed layer that the material to be rolled comes into contact with has excellent spall and wear resistance, so even when rolled under high pressure and high rotation, it does not easily become flattened, and does not cause peeling or cracking. A composite roll for rolling can be provided.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view of a mating roll for rolling according to the present invention;
Figures 3 and 3 are diagrams explaining the stress distribution due to joining of materials with different coefficients of thermal expansion and residual bonding depending on the thickness of the insert material, respectively, and Figure 4 shows the experimental results showing the relationship between the coefficient of thermal expansion and the occurrence of cracks. Figures 5 to 7 are diagrams of experimental results for examining the thickness of the boundary layer, and Figure 8 is the thickness of the boundary layer.
FIG. 9 is a diagram showing the experimental results showing the relationship between the PA expansion coefficient of the thermal spray material and the occurrence of cracks, and FIG. 9 is an illustrative diagram of the apparatus used for manufacturing the composite roll of the present invention. 1... Core material 3... Thermal spray overlay 1-4...
・Part of boundary J 5...Spraying torch 6.6'...
・Powder feeding device 7... Suppressing device 8.8'... Powder for thermal spraying 9... Gas cylinder 10... Gas cylinder
11... Cooling water 12... Power supply. Agent Honta Kohira-1, J Kotabe Tani J Figure 1 Figure 2 Figure 4 × ' ＞**t/1ji (JljJ695ti! (,
1Q-61,7°. 7゜9, Figure 5, Figure 6, Figure 7, boundary, 1 thickness (rnTrL)

Claims (1)

[Scope of Claims] 1. A rolling composite roll in which a thick thermal sprayed layer is formed by plasma spraying a powder having wear resistance and spall resistance on the body of a core material having high strength and toughness, comprising: The boundary layer between the thick thermal sprayed layer and the core material has a laminated structure in which the coefficient of linear thermal expansion is sequentially changed so that the closer the layer is to the core material, the closer the coefficient of linear thermal expansion is to that of the core material. Composite roll for rolling. 2. Difference in linear thermal expansion coefficient between the core material and the innermost layer of the boundary layer,
The difference in coefficient of linear thermal expansion between the layers of the boundary layer part and the difference in coefficient of linear thermal expansion between the outermost layer of the boundary layer part and the thick thermal spraying are 3 × 10
The composite roll for rolling according to claim 1, which has a rolling rolling temperature of ^-^61/°C/mm or less. 3. The thickness Δγ (mm) of the boundary layer portion satisfies 1.5≦△γ≦0.3R, where the radius of the composite roll is R (mm). Composite roll for rolling.