JP3277638B2 - Wear-resistant composite rolls for rolling section steel - Google Patents

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 section steel rolling, and more particularly to an abrasion-resistant composite roll for a section steel roll having high strength, excellent abrasion resistance and skin roughening resistance and free from breakage. About roles.

[0002]

2. Description of the Related Art Rolling rolls are required to have abrasion resistance, skin roughening resistance, accident resistance and the like. This is because there is a strong demand for prevention of deterioration of the shape of the material to be rolled due to roll wear and reduction in the number of man-hours for changing rolls. In particular, in the case of a roll for shaped steel rolling, breakage from the bottom of the caliber is apt to occur, so that the breakage resistance must be good.

In a conventional centrifugal casting roll, the chemical composition of the outer layer material is limited in order to suppress the segregation of gravity of the outer layer material and to graphitize the cast iron material as a shaft and maintain the toughness. Could not be fully satisfied. Although a sintered powder alloy roll made of HIP or the like has good abrasion resistance, when rolling an angle steel or the like having a small curvature (R) of irregularities, the roll is divided by the bottom of the caliber of the roll for shape steel rolling. In addition, there is a problem that a loss or the like is apt to occur, and a slip is likely to occur between the sleeve and the shaft.

Accordingly, the present inventors have proposed a method for producing a roll having less restrictions on the chemical composition of the outer layer material, by continuously forming the outer layer while heating and stirring the molten metal using a high-frequency coil around a steel shaft. (Japanese Patent Application No. 61-60256, Japanese Patent Application No. 63-502702). With the development of such a manufacturing method, elements such as V, W, and Mo, which form hard carbides, can be added to the outer layer material in a large amount, and the useful rolling amount is several times that of the conventional centrifugal casting roll. The production of the roll which has this became possible.

[0005] However, in the case of manufacturing a roll for shape steel rolling having a somewhat deep caliber, it is necessary to form the outer layer thickly. However, in the above-mentioned conventional method, shrinkage cavities occur near the boundary between the outer layer and the inner layer. Alternatively, there is a problem that the hardness of the deep portion of the outer layer is insufficient, and that the inner layer is apt to be broken.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a wear-resistant composite roll for rolling a shaped steel, which has high strength, excellent wear resistance and rough skin resistance, and has no breakage.

[0007]

Means for Solving the Problems As a result of intensive studies in view of the above object, the present inventors have found that the outer layer is made of a specific Fe having excellent hardenability.
The present inventors have found that even if the ratio of the outer layer to the inner layer is increased, the formation of the base alloy can prevent the shrinkage cavities and the breakage of the caliber bottom portion, and have reached the present invention.

[0008] That is, the wear-resistant composite roll for section steel rolling of the present invention has a C content of 1.5 to 3.0% by weight, a Si content of 0.3 to 3.0% by weight,
n0.3-1.5 wt%, Cr2-7 wt%, Mo5-9 wt%, V3-15 wt%, W20 wt% or less, B500 ppm or less,
A wear-resistant composite roll for section steel rolling in which the outer layer having a composition substantially composed of Fe and an impurity element and a steel inner layer having a tensile strength of 55 kg / mm ² or more and an elongation of 1.0% or more are metal-bonded. The outer layer is formed by a continuous overlay casting method, and the cross-sectional area of the outer layer / the cross-sectional area of the inner layer at the position of the maximum diameter of the roll is 1.0 to 3.0.

Hereinafter, the present invention will be described in detail. [1] Chemical Components of Outer Layer The reasons for limiting the chemical components of the outer layer are as follows. (a) C: 1.5 to 3.0% by weight C is necessary for forming carbides for improving wear resistance.
When the amount is less than 1.5% by weight, the amount of carbides to be crystallized is small and is not sufficient in terms of wear resistance. On the other hand, C is 3.0% by weight
If it exceeds 300, the amount of carbides will be excessive, and a problem will occur in terms of resistance to rough skin, and the material will become brittle. The preferred C content is 1.6-2.5% by weight.

(B) Si: 0.3 to 3.0% by weight Si is an element required as a deoxidizing agent. It is also necessary to maintain the fluidity of the molten metal. If the amount is less than 0.3% by weight, the above effects cannot be sufficiently obtained. On the other hand, if the content of Si exceeds 3.0% by weight, the amount of carbides becomes excessive and the crystallization of cementite decreases, which is liable to cause embrittlement. The preferred Si content is 0.3-1.5% by weight.

(C) Mn: 0.3 to 1.5% by weight Mn has a deoxidizing action and an action of fixing S as an impurity as MnS. If the amount is less than 0.3% by weight, the above effects cannot be sufficiently obtained. On the other hand, if Mn exceeds 1.5% by weight, retained austenite is likely to be generated, and sufficient hardness cannot be stably maintained. The preferred Mn content is 0.3-1.
0% by weight.

(D) Cr: 2 to 7% by weight When Cr is less than 2% by weight, the hardenability is poor, and when it exceeds 7% by weight, chromium carbides are excessive, which is inconvenient. That is, Cr-based carbide such as M ₂₃ C ₆ is MC, M ₄ C
_3, M ₂ C and lower hardness in comparison to lower the wear resistance. The preferred Cr content is 3.5-6.5% by weight.

(E) Mo: 5 to 9% by weight Mo crystallizes carbides of M ₂ C (Mo ₂ C) to raise the solidification completion temperature of the alloy, to prevent shrinkage cavities, and to improve hardenability and high temperature. Necessary for obtaining hardness. If the amount is less than 5% by weight, the above effects cannot be sufficiently obtained. On the other hand, when the content exceeds 9% by weight, in the balance of C, V and Mo, the amount of M ₆ C-based carbide increases as compared with the MC-based carbide, and the toughness and the surface roughening resistance decrease. The preferred Mo content is 5.5 to 7
% By weight.

(F) V: 3 to 15% by weight V is an essential element for forming an MC-based carbide effective in improving abrasion resistance. Therefore, if the content is less than 3% by weight, the effect is not sufficient. If the content is more than 15% by weight, the oxidization of the molten metal becomes severe, and the melting in the atmosphere becomes difficult. The preferred V content is 4 to 10% by weight.

(G) W: not more than 20% by weight W is necessary for maintaining high-temperature hardness, but if it exceeds 20% by weight, M ₆ C-based carbides increase, and the toughness and the resistance to rough skin are increased. Therefore, the upper limit is set to 20% by weight. The preferred W content is 10% by weight or less.

(H) Inevitable impurities A small amount of B is included as inevitable impurities. B promotes the formation of non-granular carbides in the matrix and embrittles the matrix. Microcracks are formed along the non-granular carbides, and the cracks are used as starting points to promote abrasion wear in units of crystal grains and to cause rough skin. Therefore, the amount of B as an impurity must be limited. When the concentration is 500 ppm or less, the formation of non-granular carbide in the matrix is not promoted, and cracks generated along the eutectic carbide are hardly observed. Preferably B
To 300 ppm or less.

The other main impurities are P and S.
Where P is 0.08% by weight or less to prevent embrittlement,
S must likewise be less than 0.06% by weight.

(I) Additional elements In addition to the above components, one or more of Ni, Co, Nb, N and Ti are added to the outer layer of the wear-resistant composite roll of the present invention, if necessary. be able to.

Ni has an effect of improving hardenability.
For this reason, it is preferable to add the quenching speed to a material that cannot increase the quenching speed such as a large roll. However, if the content exceeds 5% by weight, the austenite is too stabilized, the residual austenite after the heat treatment becomes excessive, and sufficient hardness cannot be obtained.

Co has the effect of improving the toughness of the material and improving the hot hardness. Therefore, the addition of Co can improve the rough skin resistance and the abrasion resistance. Since the above-mentioned improvement effect is almost saturated when the content is 8% by weight, the upper limit is 8% by weight.

Nb forms granular carbides similarly to V. Further, it has an effect of making MC carbide, which is granular carbide, fine. Thereby, abrasion resistance and skin roughening resistance are improved. However, when the content exceeds 5% by weight, the molten metal is oxidized violently, and it is difficult to melt and cast in the atmosphere.

N is effective in improving the tempering hardness. However, since the material becomes brittle when excessive, the upper limit of the content is
0.15% or less.

Ti forms an MC-based carbide, which has a Vickers hardness Hv as high as 2,000 or more. If these carbides are contained in the outer layer material, it is effective for improving the wear resistance of the roll. If the content exceeds 1% by weight, the molten metal is oxidized violently, and it is difficult to melt and cast in the atmosphere.

[2] Inner Layer (Shaft Material) The inner layer (shaft) of the wear-resistant composite roll for section steel rolling of the present invention is made of a steel material such as cast steel or forged steel.
It is preferable to use a material such as M439 which undergoes bainite transformation during quenching (a material having little pearlite transformation). By using a material that undergoes bainite transformation during quenching, it is possible to prevent residual stress during roll quenching from becoming excessive.

The tensile strength of the shaft is 55 kg / mm ² or more.
The elongation is greater than 1.0%. This is because when used as a shaped steel rolling roll, a large rolling force is applied, and it is necessary to be able to withstand the bending force applied to both ends of the shaft in order to correct deflection during rolling.

The cross-sectional area ratio of the outer layer to the shaft at the position of the maximum diameter of the roll (cross-sectional area of outer layer / cross-sectional area of inner layer) is 1.0 to 3.0, preferably 1.0 to 2.6. If the cross-sectional area ratio is less than 1.0,
Inability to form the required depth of caliber. If the upper limit of the cross-sectional area ratio exceeds 3.0, the tensile residual stress in the radial direction near the boundary between the outer layer and the shaft becomes excessively large, which is not preferable. In addition, when the above value is large, voids and sinks tend to occur, but in the present invention, the problems such as voids and sinks are solved by forming the outer layer of the above-mentioned Fe-based alloy.

The outer layer and the shaft (inner layer) need to be firmly metal-joined as described above. For this purpose, the joint strength at the boundary between the two must be equal to or greater than the mechanical strength of the weaker of the outer layer and the shaft. In order to form an outer layer with a large bonding strength on the outer periphery of a steel shaft in this way, basically, a molten metal is heated using a high-frequency coil around the steel as shown in JP-A-61-60256. It is preferable to use a so-called continuous overlay casting method in which an outer layer is continuously formed while stirring.

FIG. 1 shows an example of an apparatus that can be used to perform a continuous overlay casting method. This apparatus is a combination mold 10 comprising a funnel-shaped refractory frame 1 having a peripheral wall of a tapered portion and a parallel portion, and a cooling mold 4 coaxially installed thereunder.
Having.

An annular induction heating coil 2 is arranged in the refractory frame 1 so as to surround the outer periphery of the refractory frame 1. Is provided. The lower cooling mold 4 has substantially the same inner diameter as the buffer mold 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 roll shaft 5 is set inside the combination mold 10 having the above configuration. A closing member (not shown) having an outer diameter substantially the same as the outer diameter of the injection outer layer is fixed to the lower end of the shaft 5 or a position appropriately separated from the lower end as necessary. (Not shown). The molten metal 7 is poured into the space between the shaft 5 and the refractory frame 1, and the surface of the molten metal is sealed with a molten flux 6 so as not to come into contact with air. Then, the mixture is heated and stirred by the heating coil 2 so that the molten metal 7 does not 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 sequentially lowered together with the shaft member. In conjunction with the lowering of the shaft member and the closing member, the molten metal 7 also descends, and the buffer mold 3 and the water-cooling mold 4
Solidification of the molten metal 7 starts on the surface. During this solidification, the shaft and the outer layer are completely metallically joined. Although the surface of the molten metal in the basin also decreases as the shaft member and the closing member descend, the liquid level is maintained at a certain level by appropriately injecting a new molten metal. Then, the descending and the pouring are repeated in order to solidify the molten metal sequentially from below to form the outer layer 8.

After forming the outer layer around the shaft material by the continuous overlay casting method as described above, it may be processed into a desired shape. However, as in the present invention, the B content of the outer layer is set to 500 ppm or less. To do so, the flux used for coating the surface of the shaft before cladding and for coating the surface of the molten metal for the outer layer is B or B
It is preferable to use one that does not contain a compound.

The surface hardness of the outer layer of the wear-resistant composite roll for section steel rolling of the present invention obtained as described above is Shore hardness.
75 or more, axial tensile strength of 55 kg / mm ² or more, elongation of 1.0% or more. Since the outer layer and the inner layer are metallically bonded, the bonding strength at the boundary is weak in the outer layer or the inner layer. It is more than one strength.

[0033]

The wear-resistant composite roll for section steel rolling of the present invention has no shrinkage cavities in the outer layer and has a compressive residual stress,
Even if the caliber is deepened, no breakage occurs from the bottom of the caliber. Further, since the inner layer has good mechanical properties, there is no breakage from the inner layer.

[0034]

【Example】

The present invention is described in more detail by the following examples. Examples 1 to 5 and Comparative Example 1 Using a forged steel shaft material of 350 mmφ and a melt for the outer layer material having the composition shown in Table 1, rolls having a trunk diameter of 550 mmφ and a trunk length of 1000 mm were formed by continuous overlay casting. This roll was cast and processed to form six calipers having a body diameter of 530 mmφ and an angle shape and a depth of 36 mm.

The obtained roll was subjected to heat treatment of quenching from 900 to 1000 ° C. and tempering at 500 to 550 ° C. three times to produce a wear-resistant composite roll for section steel rolling. In addition,
The value of (cross-sectional area of outer layer / cross-sectional area of shaft) of the roll was 1.25.

Table 2 shows the results of measuring the hardness of the outer layer surface of each test roll with a Shore hardness meter, and the results of measuring the metal carbide content and the M ₂ C compound content in the roll outer layer. Next, a rolling wear test of this test roll was performed. The rolling wear test was performed on each of the above rolls using a hot rolling wear tester under the following rolling conditions.

Rolled material: ordinary steel, thickness 1 mm, width 15 mm Rolling distance: 800 m Rolling temperature: 900 ° C. Reduction rate: 25% Rolling speed: 150 m / min The results of the wear amount are shown in Table 2.

Further, the wear-resistant composite rolls for section steel rolling of each of Examples and Comparative Example 1 were subjected to ultrasonic inspection for defects such as shrinkage cavities and breakage near the boundary between the outer layer and the shaft. Was not found.

[0039] Table 1 set formed (wt%) C Si Mn Ni Cr Mo V W Example 1 2.5 0.7 0.5 0.01 5.1 7.3 5.5 2.7 Example 2 2.4 0.8 0.4 1.4 4.5 6.2 6.5 4.2 Example 3 2.3 0.5 0.4 0.01 4.8 5.1 4.0 7.5 Example 4 2.8 0.6 0.5 0.01 4.3 7.1 3.3 10.5 Example 5 1.9 0.4 0.5 0.8 4.0 5.8 8.7 6.1 Comparative Example 1 2.1 0.6 0.4 0.01 5.9 2.7 5.5 2.3

[0040] Table 1 (continued) sets formed (wt%) Co Nb Ti P S B * N * Fe Example 1 - - - 0.03 0.01 60 320 balance Example 2 - - - 0.03 0.01 150 500 balance Example 3 3.8 − − 0.02 0.01 70 400 Remaining Example 4 − 2.5 − 0.03 0.02 80 620 Remaining Example 5 − − 0.1 0.03 0.01 200 680 Remaining Comparative Example 1 − − − 0.03 0.01 90 430 Remaining Note) *: The unit is ppm.

[0041] Table 2 metal carbides M ₂ C compound surface hardness wear amount content (wt%) content _{(wt%) (H S)} (mm) Example 1 13.5 5.7 81 0.55 Example 2 13.3 5.5 84 0.5 Embodiment Example 3 12.7 7.3 83 0.6 Example 4 15.6 10.1 82 0.6 Example 5 12.9 4.7 82 0.45 Comparative example 1 12.6-80 0.6

The relationship between the depth from the roll surface and the hardness of the wear-resistant composite rolls for rolling section steels of Examples 1 to 5 and Comparative Example 1 was measured. The results are shown in FIG.

As apparent from Table 2 and FIG. 2, the wear-resistant composite roll for shaped steel rolling according to the present invention has a molybdenum content of 5.0% by weight or less. Compared to the roll, it had the same or higher wear resistance, and hardly any decrease in hardness was observed even at a position 90 mm from the surface. On the other hand, the wear-resistant composite roll for section steel rolling of Comparative Example 1 has a large decrease in hardness, particularly in a deeper portion than 50 mm.

[0044]

According to the present invention, the outer layer is formed of a specific Fe-based alloy having excellent hardenability, so that the outer layer has a certain thickness with respect to the inner layer. In addition, the shrinkage cavities of the wear-resistant composite roll for section steel rolling and the breakage of the caliber bottom are prevented.

As a result, the shape of the rolled product becomes good,
Further improvement in yield can be expected. Further, since the durable rolling amount until the reshaping increases, the number of times of roll change can be reduced, and the labor of the rolling operation can be saved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus that can be used to perform a continuous overlay casting method.

FIG. 2 is a graph showing the relationship between the depth from the roll surface and the hardness of the wear-resistant composite roll for section steel rolling of the present invention and the wear-resistant composite roll for section steel rolling of the comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Refractory frame 2 ... Induction heating coil 3 ... Buffer type 4 ... Cooling type 4 5 ... Shaft 6 ... Flux 7 ... Molten metal 8 ... Outer layer 10 ...・ Combination mold 10 14 ・ ・ ・ Inlet 14 ′ ・ ・ ・ Outlet

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI C22C 38/00 302 C22C 38/00 302X 38/24 38/24 (56) References JP-A-61-60256 (JP, A) 2-25205 (JP, A) JP-A-7-70692 (JP, A) JP-A-6-41676 (JP, A) JP-A-4-182013 (JP, A) JP-A-4-182011 (JP, A A) JP-A-4-180548 (JP, A) JP-A-3-285703 (JP, A) JP-A-3-126838 (JP, A) JP-A-1-91901 (JP, A) JP-A-62 -127108 (JP, A) JP-A-58-38655 (JP, A) WO 88/7594 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 27/00 B21B 27 / 02 B22D 11/00 B22D 19/16 C22C 38/00 302 C22C 38/24

Claims (6)

(57) [Claims] 1. C 1.5 to 3.0% by weight, Si 0.3 to 3.0% by weight, Mn 0.3 to 1.5% by weight, Cr 2 to 7% by weight, Mo 5 to 9% by weight, V 3 to 15% by weight, W 20% by weight or less, B Wear resistance for rolled section steel formed by metal bonding of an outer layer having a composition of 500 ppm or less and the balance substantially consisting of Fe and impurity elements and a steel inner layer having a tensile strength of 55 kg / mm ² or more and an elongation of 1.0% or more. A composite roll, wherein the outer layer is formed by a continuous overlay casting method, and the cross-sectional area of the outer layer / the cross-sectional area of the inner layer at the position of the maximum diameter of the roll is 1.0 to 3.0. Wear-resistant composite roll for rolling section steel. 2. The wear-resistant composite roll for section steel rolling according to claim 1, wherein the outer layer contains 5% by weight or less of Ni. 3. The wear-resistant composite roll for section steel rolling according to claim 1, wherein the outer layer contains 8% by weight or less of Co. 4. The wear-resistant composite roll for rolling a shaped steel according to claim 1, wherein the outer layer is 5% by weight.
A wear-resistant composite roll for section steel rolling, comprising the following Nb. 5. The wear-resistant composite roll for section steel rolling according to claim 1, wherein the outer layer contains 0.15% by weight or less of N. roll. 6. The wear-resistant composite roll for section steel rolling according to claim 1, wherein the outer layer is 1% by weight.
A wear-resistant composite roll for section steel rolling, characterized by containing the following Ti.