JPH0641676A - Wear resistant composite roll - Google Patents

Abstract

PURPOSE:To manufacture a composite work roll for rolling a metallic sheet excellent in wear resistance by welding an outer layer made of a low allot cast iron contg. hard metallic carbides to the outer circumference of a tough axial member of cast steel or the like. CONSTITUTION:A shaft member 2 for high strength structural purposes made of a steel such as cast steel and forget steel is vertically set in a casting mold 10. A high frequency induction heating coil 8 is energized, and while cooling water is allowed to flow into an inside water passage 9, the molten metal 12 of low alloy cast iron contg., by weight, 1.5 to 2.5% C, 0.3 to 2.0% Si, 0.3 to 2.0% Mn, 4 to 7% Cr, 4 to 8% Mo, 3 to 6% W, 3 to 8% V, 1 to 3% Co, less than 10% Ni (excluding 0%) and Ti so as to satisfy 0.5<Ni+Ti<=2.0%, is poured into a space formed by the casting mold 10 and the shaft member 2. The molten metal 12 is heated and stirred by the coil 8, and in a state in which the surface of the shaft member 2 is melted and they are mutually diffused, the shaft member 2 is lowered in the direction of the arrow A. The molten metal 12 is cooled and solidified by a water-cooled die 4 to form the hard outer layer 3 on the outer circumference of the shaft member 2, thereby, the composite roll for rolling excellent in wear resistance can be manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite roll for mainly hot or cold rolling of metal sheets, and more particularly to a wear resistant composite roll suitable as a work roll for hot rolling.

[0002]

2. Description of the Related Art As a work roll for hot rolling which is particularly required to have wear resistance, a cast iron composite roll manufactured by a centrifugal casting method has been widely used.
In this cast iron composite roll, the outer layer is formed of a cast iron-based material in which carbide having high wear resistance is crystallized, while the shaft member that is the inner layer is generally formed of gray cast iron or ductile cast iron having high toughness. However, when such a composite roll is manufactured by the above-mentioned centrifugal casting method, there are restrictions on the material forming the inner and outer layers. That is, although forming the outer layer with a material that crystallizes a large amount of carbide formed by elements such as W, V, Nb, Ti, Ta, Zr, and Hf is effective in improving wear resistance, It is practically impossible to produce such inner and outer layers by the centrifugal casting method for the following reason.

The first reason is that the carbides formed by the elements listed above have a specific gravity different from that of the molten metal in the outer layer, and as a result of the action of centrifugal separation during the formation of the outer layer, they are uniformly dispersed. Without segregation is likely to occur. In addition, many of the above elements have a strong oxidation tendency,
Welding with the inner layer in the atmosphere is very difficult. Furthermore, in the centrifugal casting method, as the material for forming the inner layer, it is common to secure toughness by using gray cast iron or ductile cast iron in which graphite is crystallized, but in the material for forming the outer layer If a large amount of the above-mentioned element having a strong tendency to white pig iron is contained, the components of the outer layer are slightly dissolved in the inner layer, which hinders the graphitization of the inner layer, lowers the toughness, and becomes brittle. Furthermore, since carbide is concentrated and generated near the boundary between the inner and outer layers, it is brittle, and it is easy to cause inconvenience such as separation of the outer layer from the boundary.

Secondly, the tensile strength of gray cast iron or ductile cast iron forming the inner layer is generally 55.
The limit is about kg / mm ² and the elongation value is 1%
It is the following. Therefore, if you try to get more than that,
Since it is necessary to use a steel-based material for the inner layer, it is difficult to manufacture by the centrifugal casting method. That is, when the inner layer is melted and the inner part of the outer layer is melted and joined after the outer layer molten metal is cast, the inner layer has a higher melting point than the outer layer, so the inner and outer layer components are in a molten / mixed state. Is the final solidified layer, and casting defects are likely to occur at that portion.

On the other hand, as the rolling roll, one having an integral structure by shrink-fitting or assembling the outer layer material and the shaft member is also used. However, in recent years, in order to rationalize the rolling by rolling a large amount at a time on the rolling roll and to improve the dimensional accuracy of the material to be rolled, it is necessary to significantly improve the wear resistance of the roll. Is strongly demanded. Further, in order to improve the dimensional accuracy of the material to be rolled, the means for bending the roll shaft in the direction opposite to the bending caused by rolling and the work for increasing the amount of reduction in one rolling stand are widely adopted. , The bending stress applied to the roll shaft is extremely large,
In order to meet these demands, the strength of the roll shaft has been required to be improved. In this case, when the shrink fitting or the assembly roll as described above is used, there are problems such as slippage between the outer layer and the shaft member during rolling, and the outer layer is easily cracked. And are required to be completely joined together metallically.

As an effective means for simultaneously satisfying each of the above requirements, for example, Japanese Patent Laid-Open No. 61-60256.
There has been proposed a method for overlaying cast metal as described in Japanese Patent Laid-Open Publication No. In this method, a refractory frame whose outer side is surrounded by an induction heating coil and a mold made of a cooling die coaxially installed in the lower part of the refractory frame are coaxially loosely fitted with a shaft member made of steel, In a space formed between the shaft member and the mold, a molten metal for forming an outer layer is injected and welded to the shaft member, and the molten metal is cooled and solidified,
By intermittently moving downward together with the shaft member,
The outer layer molten metal is continuously cast and built up on the outer periphery of the shaft member. Further, Japanese Patent Application Laid-Open No. 62-69666 proposes a wear-resistant composite roll using a wear-resistant alloy melt as the above-mentioned outer layer melt and a method for producing the same.

[0007]

SUMMARY OF THE INVENTION In a composite roll prepared by the method of build-up casting and a composite roll formed by using a molten alloy, the outer layer having wear resistance is made of a tough steel material. Although it can be firmly welded to the outer periphery of the shaft member, the wear resistance and the strength of the roll shaft part can be improved without causing a casting defect or the like at the boundary between the outer layer and the shaft member. , There were still problems with the following points.

That is, the first problem is the occurrence of drawing cracks in the outer layer when the roll is used. The cause of this drawing crack is that the roll surface is austenite due to friction heat and plastic deformation heat because it is used in a state where it is strongly bitten into the material to be rolled while being exposed to extremely high temperature during hot rolling. This is because the temperature becomes higher than the oxidization temperature and the structure is austenitized and then instantaneously cooled, so that martensitic transformation occurs. The second problem is that with this kind of roll,
Since many carbides are crystallized and precipitated in order to improve wear resistance, the toughness is low, and when cracks occur, the crack depth immediately increases and the service life is shortened.

The present invention has been made in view of the above circumstances, and paying attention to the fact that the refinement of the structure and the spheroidization of carbides are greatly related to the heat crack resistance, and the wear resistance under high temperature use and the wear resistance It is an object of the present invention to provide a wear resistant composite roll capable of sufficiently improving heat crack resistance.

[0010]

In order to achieve the above object, the wear-resistant composite roll according to the present invention has a C: 1.5-wt% on the outer circumference of a shaft member made of steel.
2.5%, Si: 0.3 to 2.0%, Mn: 0.3 to
2.0%, Cr: 4.0-7.0%, Mo: 4.0
8.0%, W: 3.0 to 6.0%, V: 3.0 to 8.0
%, Co: 1.0 to 3.0%, 0.5 <Ni + Ti ≦
2.0% and Ni <1.0% (excluding 0%),
The outer layer is formed by welding a melt having a composition of Fe and impurities as the balance.

The grounds for limiting the content (% by weight) of each element of the composition of the molten metal forming the outer layer in the present invention having the above-mentioned structure will be described respectively as follows. C is
By combining with chromium (Cr), vanadium (V), tungsten (W), molybdenum (Mo), etc., MC type and M ₇ C ₃ type carbides with high hardness are crystallized and precipitated to improve wear resistance. It is an element necessary to make it. Therefore,
When the content is less than 1.5%, the amount of carbides is small and it is not possible to expect sufficient improvement in wear resistance. On the other hand, if it exceeds 2.5%, the amount of carbides becomes too large, the toughness becomes low, and the thermal crack resistance deteriorates.

Si is an element required as a deoxidizing agent.
However, if its content is less than 0.3%, its effect is small, and if it exceeds 2.0%, it tends to become brittle. M
n is an element necessary for fixing S, which is an impurity, as MnS together with the deoxidizing action. However, if it is less than 0.3%, its effect is small, and if it exceeds 2.0%, retained austenite is apt to occur, and sufficient hardness cannot be obtained. Cr is an element that forms a solid solution in the matrix to strengthen the matrix, forms a Cr-based carbide by combining with C, and contributes to improvement in wear resistance. However, its content is 4.0
If it is less than 1.0%, the effect is small, and if it exceeds 7.0%, the amount of coarse Cr-based carbides increases, the toughness decreases, and the lack of coarse carbides deteriorates the surface roughening resistance.

Mo is an element that is required to form a solid solution in the matrix to improve the hardenability and high temperature characteristics, and at the same time, to combine with C to form a Mo-based carbide and contribute to the improvement of wear resistance. Is. However, if the content is less than 4.0%, improvement in hardenability cannot be expected, and the amount of produced carbide is small, resulting in poor wear resistance. On the other hand, if it exceeds 8.0%, it becomes supersaturated, and the retained austenite of the matrix cannot be stabilized to obtain sufficient hardness. V is an element that combines with C to form a fine and high-hardness VC carbide and contributes most to the improvement of wear resistance. However, its content is 3.0%
If it is less than 1.0%, the effect is small, and if it exceeds 8.0%, the amount of carbides becomes too large and the toughness deteriorates, and it is not uniformly distributed. Furthermore, the oxidation of the molten metal becomes severe.

W is an element that combines with C to form a high hardness W-based carbide and contributes to the improvement of wear resistance and the improvement of high temperature strength. However, if its content is less than 3.0%, its effect is small, and if it exceeds 6.0%, the amount of W-based carbides increases and the toughness decreases. Co is an element necessary for increasing the high temperature strength and hardness by forming a solid solution in the matrix to give temper softening resistance without forming a carbide. However, if its content is less than 1.0%, its effect is small, and if it exceeds 3.0%, the hardenability deteriorates.

Ni is an element that makes the structure fine and solid-dissolves in the matrix to strengthen the matrix and contribute to the improvement of toughness and hardenability. However, this Ni is an austenite stabilizing element, and if its content exceeds 1.0%,
The amount of retained austenite after heat treatment is increased, sufficient hardness cannot be obtained, and cracks and rough skin occur. Ti is a fine, high-hardness TiC combined with C
It is an element that contributes to the improvement of wear resistance by forming a carbide and by uniformly distributing it. Moreover, this Ti is V
It also has a function of crystallizing C carbides into fine and spherical shapes. However, if the content is 2.0% or more, the amount of carbides increases, the toughness decreases, and the oxidation of the molten metal becomes severe. By adding Ti, Ni, Al, N, etc.,
At the same time as refining the structure, the carbides are made spherical, which improves toughness. However, the combined effect is more effective than the individual addition, and among these, the addition of Ti + Ni is most effective.
In the range of Ti + Ni ≦ 2.0 (however, Ni <1.0), the structure becomes finer and the spheroidization rate of carbide is high.

As described above, by appropriately limiting the content (% by weight) of each element of the molten metal composition forming the outer layer as described above, C and Ti are combined to form a high hardness MC type carbide. One TiC carbide is generated and distributed to make the carbide fine and spheroidized, and N
By adding i, the structure can be made finer, and a composite roll having improved wear resistance and excellent heat crack resistance can be obtained.

[0017]

EXAMPLES The structure of the abrasion-resistant composite roll of the present invention and the method for producing the same will be described below. FIG. 1 is a vertical cross-sectional view showing a wear-resistant composite roll 1 of the present invention. In FIG. 1, 2 is a shaft member, and the shaft member 2 is, for example, cast steel, forged steel, carbon steel for machine structural use, or Cr. -Mo steel, Ni-Cr
-It is composed of a high-strength structural steel material such as Mo steel. 3 is an outer layer formed on the outer periphery of the shaft member 2,
The composition of the outer layer 3 will be described later.

FIG. 2 is a vertical cross-sectional view showing an example of a continuous casting overlay welding manufacturing apparatus used in the method for manufacturing the abrasion-resistant composite roll 1 having the above-described structure. Stand (not shown)
An annular water-cooling mold 4 is arranged on the outer peripheral portion of the steel shaft member 2 set perpendicularly to the outer periphery of the shaft member 2 at a predetermined interval required to obtain the thickness of the outer layer 3. A heating die 7 made of a refractory material is set above the water cooling die 4 via a buffer die 5 made of a graphite refractory material and a magnetic field blocking water-cooled copper plate 6. Within the wall thickness of the heating die 7, a high-frequency heating coil 8 and a coil cooling water passage 9 located inside thereof are arranged in an annular shape having an inner-outer double structure. ，
7, a casting mold 10 for build-up welding by continuous casting is constructed. Reference numeral 11 in FIG. 2 is an initial receiving plate for preventing molten metal outflow.

A method of manufacturing the composite roll 1 by using such a manufacturing apparatus will be described. First, the shaft member 2 is attached to the mold 10.
It is set vertically inside and an elevating mechanism (not shown) is attached to its lower end. Next, the high frequency heating coil 8
The molten metal 12 for forming the outer layer 3 is injected into the space formed by the mold 10 and the shaft member 2 in a state where the cooling water is circulated in the water passage 9 by energizing. The surface of the molten metal 12 is covered with a molten flux 13 for heat insulation and oxidation prevention, and is heated and stirred by the high frequency heating coil 8 to prevent the molten metal 12 from solidifying.

In this state, when the shaft member 2 is intermittently lowered in the direction of the arrow A through the elevating mechanism, the molten metal 12 is also interlocked and descends to the buffer mold 5 and the water cooling mold 4 to gradually solidify. Be started. On the other hand, the surface of the shaft member 2 is partially melted by the heat of the molten metal 12, and while being mixed with the molten metal 12, it is completely welded and integrated with the outer layer 3 by the gradual solidification of the molten metal 12. Then, as the surface of the molten metal 12 descends, the molten metal 12 is newly replenished to maintain the surface at a constant level, so that the abrasion-resistant composite roll 1 as shown in FIG. 1 is continuously manufactured.

Next, examples and comparative examples of the present invention will be described in detail. Using Examples 1 to 5 of the present invention and Comparative Examples 1 to 8 of the present invention shown in Table 1, the molten metal 12 forming the outer layer 3 of the composition and the shaft material 2 of the SCM material having a diameter of 300 mm were combined using the apparatus shown in FIG. A roll was manufactured. The shaft material is preheated to 800 ° C in order to improve welding with the molten metal, and the molten metal is 155
It was cast into the mold 10 at 0 ° C. The surface of the molten metal was prevented from being oxidized by the molten flux. After lathing these rolls, apply anti-oxidant to the surface of the body and
Quenching from ~ 1150 ° C and tempering heat treatment at 500-600 ° C were performed. In this way the body diameter is 400 mm
A composite roll having a body length of 1000 mm was obtained. Samples were cut from these rolls by lathe processing, and at the same time, the structure was observed and hardness was measured. The crack depth at the time of drawing crack occurrence was simulated for these samples by the test procedure as described below.

[0022]

[Table 1]

First, regarding the test method, it is considered that most of the causes of the squeezing cracks are due to the structural transformation caused by the instantaneous cooling of the roll surface from the high temperature as described above, and the sample is instantly changed. At a specific high temperature, specifically 900 ° C., hold it at that heating temperature for 3 seconds, then drop it in a water bath at 20 ° C. and cool it all at once, thereby generating cracks and increasing the depth. The index of crack resistance was measured. The results are shown in Table 2.

[0024]

[Table 2]

From the above test results, sample N of the comparative example
o. Regarding Nos. 1 and 2, the spheroidization of carbide did not proceed so much because the total addition amount of Ti and Ni was insufficient, and the crack depth became deep at 1.5 and 1.6 mm. It was found that it was not suitable as the material for the composite roll. In addition, the sample No. of the comparative example. Like 3-5,
When the amount of Ni exceeds 1.0%, the amount of retained austenite increases, and the hardness (HsD) is 72 regardless of the amount of Ti.
It was found that an appropriate hardness of about ~ 76 cannot be obtained. Furthermore, the sample No. of the comparative example. Like 6
It was found that when the amounts of i and Ni added were large, the spheroidization rate of the carbides was low and the crack depth was deep, and at the same time, the oxidation of the molten metal was severe and the dissolution became difficult.

Furthermore, the sample No. of the comparative example in which Ti and Ni were not added was used. 7 and No. In No. 8, although sufficient hardness was obtained, the spheroidization rate and crack depth were both Ti and N, regardless of the microstructure of elements such as Cr, Mo, V, and W.
It was found to be worse than the sample to which i was added. In comparison with these comparative examples, Examples 1 to 5 of the present invention have a high spheroidization rate of carbide, a shallow crack depth, and a high hardness.

Based on the above test results, a graph as shown in FIG. 3 was prepared in order to examine the correlation between the amounts of Ti and Ni. In this graph, the crack depth (mm) is plotted on the left vertical axis, the spheroidization rate (%) is plotted on the right vertical axis, and the (Ti + Ni) amount (%) is plotted on the lower horizontal axis. In the graph of FIG. 3, the black filled circles indicate the crack depth, and the black filled squares indicate the spheroidization rate.
It is obvious that when the total addition amount of Al is in the range of more than 0.5% to 2.0%, the spheroidization rate of the carbide is high and the crack depth is shallow. The composition other than Ti and Ni of the sample shown in the graph of FIG.
2.2%, Si: 0.3 to 0.5%, Mn: 0.3 to
0.5%, Cr: 5.5 to 6.5%, Mo: 5.5
6.5%, V: 5.6 to 6.5%, W: 4.0 to 5.0
%, Co: 1.5 to 2.5%, and others are Fe.

From the results of these tests and investigations, attention was paid to the spheroidization of carbides and the refinement of the structure, and the optimum amounts of Ti and Ni were determined. The following conclusions were reached. That is, 0.5 <Ti + Ni ≦ 2.0 (however, Ni <1.0). The above-mentioned spheroidization rate is obtained by measuring the area (S1) of each carbide existing in the target range and the area (S0) of a circle having the maximum length of the spheroidized carbide as a diameter, and measuring the area ratio. Calculate the average value. If the spheroidization rate by this method is S (%),

[0029]

[Equation 1]

It is represented by In addition, each area (S1, S
The measurement of 0) was performed using an image analyzer (computer) through a microscope.

[0031]

As described above, according to the present invention, a large amount of carbide is crystallized / precipitated in this type of composite roll in order to improve the wear resistance, so that the toughness is lowered and the toughness is reduced during use. However, there is a problem that the crack depth becomes large when a drawing crack occurs. Therefore, by appropriately setting the amounts of addition of Ti and Ni, it is possible to generate and distribute TiC, which is a high-hardness MC type carbide, to make the carbide fine and spheroidized, and also to make the structure fine. Not only abrasion resistance but also heat crack resistance under high temperature use can be sufficiently improved. Therefore,
It is possible to significantly extend the service life of the roll in rolling and to improve the quality of the rolled material.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an abrasion resistant composite roll of the present invention.

FIG. 2 is a vertical cross-sectional view showing an example of a continuous casting surfacing welding manufacturing apparatus used in a method for manufacturing a wear-resistant composite roll.

FIG. 3 is a graph showing the correlation between the amounts of Ti and Ni.

[Explanation of symbols]

 1 Wear-resistant composite roll 2 Shaft member 3 Outer layer

Claims (1)

[Claims] 1. A shaft member made of steel, on the outer periphery thereof, in weight%, C: 1.5-2.5%, Si: 0.3-
2.0%, Mn: 0.3 to 2.0%, Cr: 4.0 to
7.0%, Mo: 4.0-8.0%, W: 3.0-6.
0%, V: 3.0 to 8.0%, Co: 1.0 to 3.0
%, 0.5 <Ni + Ti ≦ 2.0%, and Ni <
A wear-resistant composite roll characterized in that an outer layer is formed by welding a melt having a composition of 1.0% (excluding 0%) and the balance being Fe and impurities.