JPH0770692A - Wear resistant composite roll for hot rolling and its production - Google Patents

Abstract

PURPOSE:To provide a wear resistant composite roll for hot rolling excellent in wear resistance and surface roughening resistance by metallically joining the external layer of a ferrous alloy having a specified compsn. constituted of C, Si, Mn, Cr, V, Mo, W, Nb and Fe to the axis of cast steel or the like by a cladding method by continuous casting. CONSTITUTION:The external layer excellent in wear resistance is metallically joined to a shaft made of cast steel or forged steel excellent in toughness to obtain a wear resistant composite roll. The componental compsn. of the same external layer is constituted of a one contg., by weight, 0.5 to 3.5% C, <=3.0% Si, <=1.5% Mn, 2.0 to 7.0% Cr, 3.0 to 15.0% V, <=12% Mo, <=20% W and 5.0 to 10.0% Nb, furthermore contg. prescribed amounts of Ni, Co, B, N, P and S, and the balance substantially Fe with inevitable impurities. This composite roll is obtd. by freely inserting a roll shaft 5 into a combined mold 10, moving it in the lower direction, cooling and solidifying the molten metal with the same compsn. heated and stirred in a fire resistant frame 1 provided with a coil 2 for induction heating by a cooling die 4 and forming the external layer 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abrasion resistant composite roll for hot rolling and a method for producing the same.

[0002]

2. Description of the Related Art As a rolling roll, a cast iron composite roll manufactured by a centrifugal casting method is widely used. This is a structure in which a cast iron-based material in which a large amount of carbide having large wear resistance is crystallized is used for the outer layer, and a gray cast iron or ductile cast iron having toughness is arranged for the inner layer. The range of materials that can be applied to is limited.

Carbides formed by elements such as W, V and Nb have a Vickers hardness Hv of 2000 or more and are hard, and if these carbides are contained in the outer layer material, it is effective in improving the wear resistance of the roll. In reality, it is impossible to manufacture a composite roll in which the outer layer and the inner layer in which the carbide is crystallized are welded together by a centrifugal casting method.

The reason for this is that the carbides formed by these elements have different specific gravities from the molten metal, so that they tend to cause segregation during casting due to the action of so-called centrifugal separation. Also, some of these elements have a strong tendency to oxidize, and it is difficult to weld them to the inner layer. Further, in the centrifugal casting method, toughness is obtained by using gray cast iron or ductile cast iron in which graphite is crystallized as the inner layer material, but the outer layer material contains a large amount of the element having a strong tendency to white pig iron as described above. Then, the components of the outer layer are slightly dissolved in the inner layer, so that the graphitization of the inner layer is deteriorated and becomes brittle. In particular, since carbide is concentrated near the boundary with the inner layer, it becomes brittle, and peeling of the outer layer from the boundary is likely to occur.

The tensile strength of gray cast iron or ductile cast iron in the inner layer is limited to about 55 kg / mm ² , and the elongation is less than 1%. To obtain a value higher than this, it is necessary to use a steel-based material for the inner layer, but this is also difficult with the centrifugal casting method. The reason is that the inner layer has a higher melting point than the outer layer, and when the inner layer is cast, the boundary portion where the outer layer melts and becomes a mixed state has a lower melting point than the inner layer and becomes the final solidified layer. This is because defects are likely to occur.

Further, in order to rationalize the rolling by performing a large amount of rolling at a time and to improve the dimensional accuracy of the rolled material, it is necessary to greatly improve the wear resistance of the rolling roll. . At the same time, in order to improve the dimensional accuracy of the rolled material, bending is applied to the shaft of the roll in the direction opposite to the bending caused by rolling of the roll, and one rolling stand is used to complete rolling with a smaller number of stands. Since a large rolling force is applied, the bending stress applied to the shaft of the roll becomes large, and it is necessary to improve the strength of the roll shaft. However, with rolls having a structure in which the outer layer material and the shaft material are shrink-fitted or assembled, there are problems that the outer layer and the shaft slip during rolling and the outer layer is easily cracked, so the outer layer and the shaft are completely metallically joined. There is a need.

In order to satisfy these requirements at the same time,
It is necessary that the outer layer is made of a material having a component that crystallizes a large amount of carbides of elements such as W, V, and Nb, the shaft is made of strong steel, and the outer layer and the shaft are completely metallically joined. However, for the above reason, it cannot be manufactured by a casting method such as a centrifugal casting method. In addition, the method of diffusion bonding between solids is not practical because the manufacturing equipment becomes extremely expensive with a relatively large one such as a rolling roll.

In the above situation, a so-called cast overlay method of producing a composite roll by drawing and solidifying a molten metal of an outer layer material around a preformed steel shaft made of cast steel or forged steel has attracted attention. Composite rolls have been proposed, which are combinations of various outer layer materials and shaft materials manufactured using the same.

For example, Japanese Unexamined Patent Publication No. 60-180608 is a composite roll in which an outer layer and a core material are metallurgically bonded, and the outer layer is C: 2.0 to 3.5% by weight and Si: 0.5 to 1.5% by weight. , Mn: 0.4 ~
Consists of high chromium cast iron consisting of 1.5%, Cr: 8-25%, Mo: 0.5-3.0%, V: 10% or less, and 1.5% or less of Ni, and the core material has a tensile strength of 55 kg / mm ² or more. , Made of cast steel or forged steel with an elongation of 1.0% or more,
The outer layer is formed by a method in which a melt of the outer layer component is poured onto the outer circumference of a core material prepared in advance and metallurgically bonded, and the bonding strength at the boundary between the outer layer and the core material is at least weak between the outer layer material and the core material. Hot rolling excellent in seizure resistance and surface roughening, characterized in that the outer layer has a hardness of 70 or more, a Shore hardness of 70 or more, and a hardness decrease of 100 mm below the surface is a Shore hardness of 3 or less. Discloses a composite roll for use.

Further, JP-A-60-180609 discloses a composite roll having an outer layer portion made of high chromium cast iron, a core material made of cast steel and forged steel and having a surface hardness of Shore hardness of 90 or more, and the outer layer having a core prepared in advance. It is formed by the method of pouring a molten metal of the outer layer component on the outer periphery of the material and metallurgically joining it, and the high chromium cast iron composition of the outer layer is C2.5-3.5% by weight%, Si0.5-1.5% by weight.
%, Mn0.4-1.5%, Ni0.5-3.0%, Cr8-25%, Mo
1.0 to 5.0%, the balance consisting essentially of Fe, the strength and elongation of the core material being 55 kg / mm ² or more and 1.0% or more, respectively, and the bonding strength at the boundary between the outer layer and the core material being at least the outer layer material and the core. Disclosed is a high-chromium cast iron roll for cold rolling, which is characterized in that the strength is higher than that of the weaker one.

However, in these composite rolls for rolling, since the outer layer is made of high chromium cast iron, it has good wear resistance, but it is not always sufficient to meet the demand level that has been increasing in recent years.

Japanese Examined Patent Publication No. 51-24969 has carbon content of 0.2 to 0.6.
At least one element selected from the group consisting of 2% by weight or less nickel, 2 to 6% by weight chromium, 1 to 6% by weight molybdenum, 1 to 6% by weight tungsten, and 10% by weight or less cobalt. Carbide formed by the combination of 5 to 12% by weight of vanadium, 3 to 10% by weight of niobium, and the amount of carbon required to bind them in an iron-based matrix containing Disclosed is a super wear resistant steel. Although it is stated that this super wear resistant steel can be used for rolling rolls and the like, there is no disclosure that it is a composite roll.

In view of the above, the present applicant has previously proposed that the weight ratio
1.5 to 3.5% C, 0.3 to 3.0% Si, 0.3 to 1.5%
Mn, 2-7% Cr, 9% or less Mo, 20% or less W, 3
What is claimed is: 1. A wear-resistant composite roll comprising an outer layer made of an iron-based alloy consisting of -15% V and the balance substantially Fe, and a steel shaft metallically bonded to the outer layer, wherein the surface hardness of the outer layer is Shore hardness of 70 or more, tensile strength and elongation of the shaft are 55 kg / mm ² or more and 1.0% or more, respectively, and the joint strength at the boundary between the outer layer and the shaft is weaker in the outer layer and the shaft. We have proposed a wear-resistant composite roll characterized by a strength of at least (PCT / JP88 / 00304).

This wear-resistant composite roll is manufactured by the so-called continuous casting overlay method, and has good wear resistance and the shaft material has good mechanical strength. However, further improvement in wear resistance has been strongly desired especially in hot rolling.

Therefore, an object of the present invention is to form an outer layer material having excellent wear resistance and a tough steel-based shaft material, and to form a hot-worked material having excellent wear resistance in which the outer layer and the shaft are metallically joined. It is to provide a composite roll for rolling and a method for producing the same.

[0016]

The wear-resistant composite roll for hot rolling of the present invention comprises, by weight, 0.5 to 3.5% of C, 3.0% or less of Si, 1.5% or less of Mn, and 2.0 to 7.0% of Cr. , 3.0 to 1
5.0% V, 12% Mo or less, 20% W or less, 5.0 to 10.0
% Nb, and the balance consisting of an outer layer consisting of an iron-based alloy consisting essentially of Fe and unavoidable impurities, and a composite roll consisting of a cast steel or forged steel shaft metallically bonded to the outer layer,
The outer layer is joined to the shaft by a continuous casting overlay method.

The method of the present invention for producing the wear-resistant composite roll for hot rolling is also a combination mold comprising a refractory frame surrounded by induction heating coils and a cooling mold coaxially installed under the frame. In the space provided inside, the steel shaft member is coaxially loosely fitted, and the molten iron-based alloy for the outer layer of the composition is injected into the void formed between the shaft and the mold, The surface of the molten metal is sealed with a flux, and the molten metal is held in a temperature range from the primary crystallization temperature to a temperature higher than 100 ° C with heating and stirring, and the shaft is moved downward coaxially with the mold to melt the molten metal. Is contacted with the cooling mold to be solidified and welded to the shaft, whereby the outer layer is continuously formed around the shaft.

[0018]

EXAMPLE AND FUNCTION The wear resistant composite roll for hot rolling of the present invention comprises an outer layer made of an iron-based alloy and a steel shaft metallically joined to the outer layer. Further, the iron-based alloy has a weight ratio of 0.5.
~ 3.5% C, 3.0% or less Si, 1.5% or less Mn, 2.0
~ 7.0% Cr, 3.0 ~ 15.0% V, 12% or less Mo, 20%
It is preferable that the following W, 5.0 to 10.0% of Nb, and the balance substantially consist of Fe and inevitable impurities.

C is necessary for the formation of carbides for improving the wear resistance, but the crack resistance decreases as the amount of C increases. Therefore, it is necessary to be within the range of 0.5 to 3.5%. If the amount is less than 0.5%, the amount of crystallized or precipitated carbide is too small, and the wear resistance is not sufficient. On the other hand, when C exceeds 3.5%, the wear resistance is good, but the crack resistance tends to decrease.

Si is an element necessary as a deoxidizing agent in cast iron materials. Also, it is effective in replacing expensive elements such as W and Mo by forming a solid solution in M ₆ C carbide to save energy. However, if it exceeds 3.0%, brittleness tends to occur, so
3.0% by weight or less. If the amount is less than 0.3%, there is no deoxidizing effect and casting defects are likely to occur in the cast iron material, which is not preferable.

[0021] Mn is a deoxidizing agent and Mn
It has the function of fixing as S. However, if it exceeds 1.5%, retained austenite is liable to be formed, and stable and sufficient hardness cannot be maintained. If the amount is less than 0.3%, deoxidation is poor, which is not preferable.

If Cr is less than 2.0%, the hardenability is poor, and
If it exceeds 7.0%, it is inconvenient because the chromium-based carbide becomes excessive. That is, Cr-based carbides such as M ₂₃ C ₆ are MC, M
Hardness is low compared to ₂ C and wear resistance is reduced.

V is an essential element for forming MC type carbide which is effective in improving wear resistance. Therefore, if it is less than 3.0%, there is no sufficient effect, and if it is more than 15.0%, the oxidation of the molten metal becomes violent and the increase in viscosity makes it difficult to obtain a sound casting.

Mo is necessary in order to obtain hardenability and high temperature hardness, but if it exceeds 12%, the balance of C, V and Mo will increase M ₆ C and M ₂ C type carbides, resulting in toughness and resistance. Since it is not preferable in terms of skin roughness, the upper limit of Mo content is 12%. The preferable addition amount of Mo is 2 to 7%.

W is necessary for maintaining high temperature hardness,
If it exceeds 20%, M ₆ C-based carbides increase and it is not preferable in terms of toughness and skin roughening resistance, so the upper limit is made 20%. The preferable upper limit of W is 12%.

Nb, like V, forms MC type carbides and has the effect of improving wear resistance, but the specific gravity of NbC is 7.8.
It is heavier than 5.5 and close to the specific gravity of iron. In the case of a VC having a small specific gravity, it floats on the riser portion above the molten metal, and the wear resistance effect cannot be sufficiently exerted. The use of Nb improves the yield of MC and improves wear resistance. Nb content is
If it is less than 5.0%, there is no sufficient effect, and if it is more than 10.0%, the oxidation of the molten metal becomes violent, and defects tend to occur due to an increase in viscosity.

The iron-based alloy for outer layer material of the present invention may contain Ni and Co in addition to the above elements, alone or in combination.

Ni has the effect of improving hardenability. Therefore, it is possible to add less than 4.0%. However, if the amount is larger than that, the amount of retained austenite increases, and problems such as cracking and roughening during rolling occur, so the maximum content is 4%.

Co is a useful element in terms of resistance to temper softening and secondary hardening, but if it exceeds 8.0%, hardenability deteriorates.

In addition, one or more of Ta, Zr, Hf, and Ti which form MC type carbides can be appropriately added for the purpose of improving wear resistance.

Further, one or more rare earth elements such as La, Ce and Nd may be appropriately added.

The iron-based alloy for the outer layer material used in the present invention also preferably has a N content of 0.020 to 0.15%. N in this range is effective in improving the tempering hardness in the material of the present invention. However, if it is excessive, the material becomes brittle, so the upper limit of the content is 0.15% or less.

Further, by adding a very small amount of B, the hardenability can be improved. However, if added excessively, the toughness deteriorates, so it is necessary to suppress it to 500 ppm or less.

In addition to the above elements, iron-based alloys consist essentially of iron except for impurities. The main impurities are P and S
However, P is preferably 0.1% or less and S is similarly 0.06% or less for preventing embrittlement.

The shaft of the composite roll of the present invention is made of steel and may be either cast steel or forged steel. Its tensile strength is 55kg / mm
^It must be ² or more and the elongation must be 1.0% or more. This is because when it is used as a rolling roll, a large reduction force is applied and it is necessary to withstand the bending force applied to both ends of the shaft in order to correct the deflection during rolling. Further, the shaft needs to be firmly bonded to the outer layer made of the iron-based alloy. For this purpose, the joint strength at the boundary between the two must be equal to or higher than the mechanical strength of the weaker one of the outer layer and the shaft.

As described above, in order to form the outer layer on the outer circumference of the steel shaft with a large bonding strength, the manufacturing method shown in the publication of PCT / JP88 / 00304 is basically used.

FIG. 1 shows an example of a device that can be used to carry out the method of the present invention. The present apparatus is a combination mold 10 comprising a funnel-shaped fire-resistant frame 1 having a tapered portion and a peripheral wall of a parallel portion, and a cooling die 4 coaxially installed thereunder.
Have.

An annular induction heating coil 2 is arranged so as to surround the outer periphery of the fireproof frame 1, and an annular hole having the same diameter as the lower part of the fireproof frame 1 is coaxially arranged at the lower part thereof. 3 is provided. Further, the cooling die 4 therebelow has an inner diameter substantially the same as that of the buffer die 3, and is coaxial. Cooling water is continuously introduced into the mold from the inlet 14 of the cooling mold 4 and discharged from the outlet 14 '.

The shaft 5 of the roll is set inside the combination mold 10 having the above construction. A closing member (not shown) having an outer diameter substantially the same as the outer diameter of the injection outer layer is fixed at the lower end of the shaft 5 or at a position appropriately separated from the lower end as necessary, and the lower part thereof is a lifting mechanism for the shaft 5. (Not shown). The molten metal 7 is poured into the space between the shaft 5 and the refractory frame 1, and the molten metal surface is sealed with the molten flux 6 so as not to come into contact with air. Then, the molten metal 7 is heated and stirred by the heating coil 2 so as not to solidify. The molten metal 7 flows in a direction indicated by an arrow A in the figure and causes a stirring motion. Next, the closing member fixed to the shaft 5 is successively lowered together with the shaft member. The molten metal 7 also descends in conjunction with the descent of the shaft member and the closing member, and the buffer mold 3 and the water-cooled mold 4
The solidification of the molten metal 7 begins on the surface. During this solidification, the shaft and outer layer are completely metallically joined. Although the surface of the molten metal in the puddle is lowered as the shaft member and the closing member are lowered, new molten metal is appropriately injected to maintain the liquid level at a certain level. Then, the lowering and the pouring are repeated in sequence to solidify the molten metal from below in order to form the outer layer 8.

The composite roll thus obtained is subjected to heat treatment such as quenching and tempering to obtain the desired outer layer hardness. The surface hardness of the outer layer of the obtained composite roll is Shore hardness of 70 or more, the tensile strength of the shaft is 55 kg / mm ² or more,
The elongation is 1.0% or more, and since the outer layer and the shaft are metallically joined, the bond strength at the boundary is greater than the strength of the weaker outer layer and the shaft.

The present invention is further described in detail by the following examples. Examples 1 to 2 The molten metal for the outer layer having the composition shown in Table 1 was prepared with a diameter of 80 mm and a height of 80 mm.
It was poured into a CO ₂ sand mold to cast a small roll material for rolling wear test. This material is hardened from 1000 to 1100 ℃ and 50
After heat treatment of tempering at 0 ~ 550 ℃, outer diameter 60mm,
A sleeve-shaped test roll having an inner diameter of 35 mm and a length of 40 mm was produced.

Table 2 shows the results of measuring the hardness of the outer layer surface of each test roll with a Shore hardness tester. Next, a rolling wear test of this test roll was performed. As shown in FIG. 2, the rolling wear tester includes a rolling mill 21, an upper roll 22 and a lower roll 23 incorporated in the rolling mill 21, a heating furnace 24 for preheating the rolled material S, and cooling the rolled material S. It comprises a cooling water tank 25, a winder 26 that applies a constant tension during rolling, and a tension controller 27 that adjusts the tension. The test conditions were as follows.

Rolled material: SUS 304, thickness 1 mm, width 15 mm Rolling distance: 800 m Rolling temperature: 900 ° C Reduction ratio: 25% Rolling speed: 150 m / min Roll cooling: Water cooling

The depth of wear on the surface of the test roll was measured using a stylus type surface roughness meter (SURFCOM). Table 2 shows the results of obtaining the average wear depth by averaging the wear depths of the rolls in the rolling width.

Comparative Examples 1 and 2 As conventional materials, high chromium cast iron (Comparative Example 1) and PCT / JP
With respect to the roll outer layer material (Comparative Example 2) described in 88/00304, a test roll was prepared in the same manner as in Example 1. However, the heat treatment was performed according to these materials. Example 1
A wear test is performed in the same manner as above, and the measured value of the wear depth is
Shown in the table. The hardness measurement results are also shown in Table 2.

Table 1 Composition (wt%) of molten iron-based alloy for outer layer Sample No. C Si Mn Ni Cr Mo V W Co Nb Example 1 1.8 0.8 0.5 0.1 5.1 6.3 1.5 3.2 − 6.3 Example 2 3.0 0.8 0.4 0.1 4.5 7.2 2.1 4.5 2.5 7.5 Comparative Example 1 2.6 0.7 1.0 1.3 15.0 1.1 − − − − Comparison Example 2 2.7 0.8 0.9 0.2 4.4 6.3 7.8 4.2 1.4 −

Table 2 Sample No. Hardness (HS) Average Wear Depth (μm) Example 1 82 0.7 Example 2 83 0.5 Comparative Example 1 75 1.5 Comparative Example 2 83 0.6

Example 3 Using a shaft material made of SCM440 forged steel having a diameter of 300 mm and the molten metal for the outer layer having the composition shown in Table 3, a composite roll was manufactured using the apparatus shown in FIG. The preheating temperature of the shaft is 900 ° C, and the temperature of the molten metal for the outer layer is 1300 ° C. The surface of the molten metal was sealed with flux in a molten state so as not to come into contact with air.
The composite roll thus obtained was examined for internal defects by ultrasonic flaw detection, and the result was normal. The dimensions of the composite roll are 450 mmφ x 700 mmL. This composite roll is further quenched from 1100 ° C and tempered at 500 to 550 ° C for 3 times.
Repeated times.

The composite roll was sound without cracks and the like due to the above heat treatment. As a result of measuring the hardness of the outer layer surface with a Shore hardness meter, it was HS85. When hot rolling of flat steel was performed using a composite roll, wear was small and a good rolled product was obtained.

Table 3 Composition (wt%) of molten iron-based alloy for outer layer Sample No. C Si Mn Ni Cr Mo V W Nb Example 3 2.8 0.8 0.4 0.1 4.3 6.2 2.0 4.0 7.0

[0051]

As described above in detail, the composite roll for hot rolling of the present invention has good mechanical strength and excellent wear resistance.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an apparatus used to carry out the present invention.

FIG. 2 is a schematic view showing a rolling wear tester used for a wear test of a roll outer layer.

[Explanation of symbols]

 1 Refractory Frame 2 Induction Heating Coil 3 Buffer Type 4 Cooling Type 5 Roll Axis 6 Melting Flux 7 Molten Metal 8 Outer Layer 10 Combination Mold 14 Cooling Water Inlet 14 'Cooling Water Outlet A Melt Movement Direction S Rolled Material 21 Rolling Mill 22 Top Roll 23 Lower Roll 24 Heating Furnace 25 Cooling Water Tank 26 Winding Machine 27 Tension Controller

Claims (7)

[Claims] 1. A weight ratio of 0.5 to 3.5% C, 3.0% or less Si, 1.5% or less Mn, 2.0 to 7.0% Cr, and 3.0 to 15.0.
% V, 12% or less Mo, 20% or less W, 5.0 to 10.0%
A wear-resistant composite roll for hot rolling consisting of Nb, and an outer layer consisting of an iron-based alloy consisting essentially of Fe and the unavoidable impurities, and a cast steel or forged steel shaft that is metallically joined to the outer layer. The wear-resistant composite roll, wherein the outer layer is bonded to the shaft by a continuous casting overlay method. 2. The wear-resistant composite roll according to claim 1, wherein the iron-based alloy further contains Ni in a weight ratio of 4.0% or less. 3. The wear-resistant composite roll according to claim 1, wherein the iron-based alloy further contains 8.0% or less by weight of Co. 4. The wear resistant composite roll according to claim 1, wherein the content of B in the iron-based alloy is
A wear resistant composite roll characterized by being 500 ppm or less. 5. The wear resistant composite roll according to claim 1, wherein the iron-based alloy has a weight ratio of 0.020.
A wear-resistant composite roll characterized by containing 0.15% of N. 6. The wear-resistant composite roll according to claim 1, wherein the content of P in the iron-based alloy is
A wear-resistant composite roll, characterized in that it is 0.1% or less and the S content is 0.06% or less. 7. A weight ratio of 0.5 to 3.5% C, 3.0% or less Si, 1.5% or less Mn, 2.0 to 7.0% Cr, and 3.0 to 15.0.
% V, 12% or less Mo, 20% or less W, 5.0 to 10.0%
Manufacture a wear-resistant composite roll for hot rolling consisting of an outer layer made of an iron-based alloy consisting of Nb and the balance substantially Fe and unavoidable impurities, and a cast steel or forged steel shaft that is metallically joined to the outer layer. In the method, the shaft is coaxially loosely fitted in a space provided inside a combination mold including a refractory frame surrounded by an induction heating coil and a cooling mold coaxially installed under the frame. Injecting the molten iron-based alloy for the outer layer of the above composition into the void formed between the shaft and the mold, sealing the molten metal surface with flux, and melting the molten metal up to the primary crystallization temperature up to 100 ° C. The shaft is heated and agitated in a high temperature range, the shaft is moved downward coaxially with the mold, the melt is brought into contact with the cooling mold to solidify, and the shaft is welded to the shaft. Around Wherein the forming a continuous outer layer.