JP2843145B2 - High wear-resistant roll material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a roll material used for an outer layer which is a rolling use layer of a composite roll.

(Conventional technology and problems) Conventionally, high chromium cast iron and graphite crystallized high chromium cast iron with improved seizure resistance have been used as the material for the rolling layers of steel rolling rolls that require particularly high wear resistance. It had been.

As the rolling conditions have become more severe in recent years, higher wear resistance has been required, and one or two types of Nb and V are added to the cast iron in a total amount of 2% or less, and the fine carbide is added. Attempts have been made to generate crystal nuclei and thereby refine the structure and make it denser, thereby improving the wear resistance.However, it cannot be said that it does not sufficiently meet the demand for improved wear resistance. It is a fact.

On the other hand, in order to greatly improve the wear resistance in hot rolling, a large amount of W may be added to the material. However, since the outer layer of the composite roll is mainly cast by centrifugal casting, there is a problem that W separates due to a difference in specific gravity, segregation occurs in a circumferential direction, and it is difficult to obtain a uniform material.

It is an object of the present invention to provide a roll material that can easily obtain a uniform material and has excellent wear resistance.

(Means for Solving the Problems) The roll material of the present invention made to achieve the above object has a chemical composition in terms of% by weight, C: 1.0 to 2.9%, Si: 0.2 to 2.0%, and Mn: 0.1 to 2.0%. % Ni: 0.1 to 4.5% Cr: 3.0 to 10.0% Mo: 0.1 to 9.0% W: 1.5 to 10.0% Total of one or two of V and Nb: 3.5 to 10.0% This is composed of the balance Fe and impurities. is there.

At this time, 0.01 to 0.50% of Al is added instead of part of Fe.

(Operation) The chemical composition of the high wear-resistant roll material of the present invention is limited by the following reasons. The unit is% by weight.

C: 1.0-2.9% C mainly combines with Fe and Cr to form M ₇ C ₃ type high hardness composite carbide, and combines with Cr, Mo, V, Nb, W to form MC type high hardness composite carbide. Is also formed. In order to form this high-hardness composite carbide, C% of 1.0% or more is required. On the other hand, if C is contained in excess of 2.9%, the amount of carbide increases and the material becomes brittle, and crack resistance deteriorates.

Si: 0.1 to 2.0% Si is an element necessary for securing the flowability of the molten metal because the material of the present invention is a cast alloy, and at the same time, about 0.1% is inevitably contained from the raw materials used. But 2.0%
Exceeding this is not preferable because it leads to a decrease in toughness.

Mn: 0.1 to 2.0% Mn is an element that increases the hardening ability and combines with S to form MnS and prevent embrittlement due to S. At the same time, about 0.1% is inevitably contained from the raw materials used. But 2.0%
Exceeding this is not preferable because it leads to a decrease in toughness.

Ni: 0.1-4.5% Ni dissolves in the matrix, and the bainite transformation in the continuous cooling transformation diagram (CCT diagram) and the isothermal transformation diagram (TTT diagram) moves to the longer side, improving the quenchability. However, even if the cooling rate during quenching is reduced, bainite transformation does not occur on the way, and a large amount of retained austenite undergoes martensite transformation, so that high hardness can be obtained. In the case of a roll material for rolling as in the present invention, the thermal stress due to the difference in thermal expansion between the outer layer and the core material during quenching, and the heat capacity is large because it is heavy,
Since it is difficult to increase the cooling rate, it is very important to obtain a quenched structure even when the cooling rate during quenching is low. At this time, if it is less than 0.1%, such hardening cannot be obtained, while if it exceeds 4.5%, retained austenite increases and it becomes difficult to obtain high hardness. In addition,
At 0.1% or more, a quenched structure can be obtained if the cooling rate from the quenching temperature to 400 to 650 ° C is 100 ° C / Hr or more.

Cr: 3.0 to 10.0% Cr, together with Fe. Mo, V, Nb, and W, combines with C to form a high-hardness composite carbide, thereby contributing to an improvement in wear resistance at high temperatures. In addition, a part of the alloy dissolves in the matrix to improve quenchability and wear resistance. If it is less than 3.0%, these effects are small, and improvement in wear resistance cannot be expected. On the other hand, if the content exceeds 10.0%, the toughness is deteriorated, which is not preferable.

Mo: 0.1 to 9.0% Mo easily bonds to C together with Fe, Cr, V, and W, and
Form a C-type composite carbide, increase hardness at normal and high temperatures and contribute to improvement of wear resistance. Mo exerts its effect when added in a small amount compared to W. At this time, if it is less than 0.1%, the desired wear resistance cannot be obtained, while if it exceeds 9.0%, the toughness decreases, which is not preferable.

W: 1.5 to 10.0% Similarly, W easily combines with Fe, Cr, Mo, V, and Nb to form a composite carbide, and contributes to improvement in wear resistance by increasing the hardness at ordinary temperature and high temperature. If it is less than 1.5%, the desired wear resistance cannot be obtained, while if it exceeds 10.0%, the toughness decreases and the heat crack resistance deteriorates. In addition, at the time of centrifugal casting, macro segregation is easily generated. For this reason
10.0% or less.

One of V or Nb or a total of one or two of them: 3.5 to 10.0% Like V, Nb, easily combines with C together with Fe, Cr, Mo, W,
It mainly forms MC-type composite carbides and increases normal and high temperature hardness to contribute to improvement of wear resistance. In addition, since the MC-type composite carbide is formed in a branch shape in the thickness direction, it suppresses plastic deformation of the matrix and contributes to improvement of mechanical properties and crack resistance. 3.5 alone or in combination of two
If not added, the effect is unlikely to appear. But,
If the addition amount exceeds 10.0%, the toughness is reduced in the future, and macrosegregation is easily generated during centrifugal casting. Therefore, the content is set to 10.0% or less.

The roll material of the present invention contains Al: 0.01 to 50% instead of a part of Fe, in addition to the alloy elements described above. Al
Produces oxides in the molten metal, lowers the oxygen content in the molten metal, improves the soundness of the product, and wears the oxides by acting as crystal nuclei. It is effective for improving the performance. If it is less than 0.01%, this effect is not sufficient, and if it exceeds 0.50%, it remains as inclusions and is not preferable.

In the present invention, Al is mainly added for the purpose of improving the wear resistance by making the casting structure finer, and is not simply added for the purpose of degassing.

Since the roll material of the present invention contains Ni: 0.1 to 4.5% as described above, the cooling rate may be reduced during the quenching heat treatment of the roll material, and after heating to the austenitizing temperature, outside the furnace. Quenching can be performed simply by allowing the mixture to cool or cool. Conventionally, in the quenching of the outer layer of the roll, it has been necessary to perform the quenching operation at a high cooling rate by spray water cooling so as not to produce a bainite structure or a pearlite structure. This quenching operation required uniform spraying of cooling water while measuring the surface temperature in order to prevent quenching cracks, which required smelting.However, the roll material of the present invention was allowed to cool outside the furnace. Or air cooling is enough.

In addition, the roll material of the present invention has the balance of Fe in addition to the above components.
And impurities. Although P and S are inevitably mixed from the raw material, it is preferable that the P and S be less because the material becomes brittle. It is better to keep P: 0.2% or less and S: 0.1 or less.

(Examples) Composite rolls include a roll obtained by welding a shaft portion to an outer layer, which is a layer used for rolling, and a roll obtained by fixing a composite sleeve having an inner layer welded to an inner surface of an outer layer to a roll shaft by shrink fitting or the like. The roll material of any type can be used as the outer layer material, in order to prevent alloy elements from being mixed from the outer layer into the shaft core and the inner layer to prevent the toughness of the shaft core material etc. from deteriorating. In the meantime, an intermediate layer may be formed by casting. Table 1 below (melt composition) for the shaft core and inner layer material
High-strength materials such as high-grade cast iron, ductile cast iron, and graphite steel are used, and an adamite material is used as an intermediate layer material.

The outer layer of the composite roll is usually formed by centrifugal casting. In order to weld the shaft core to the outer layer, after the outer layer casting, the centrifugal force casting mold is erected. What is necessary is just to comprise, and to melt the shaft core molten material inside. Centrifugal casting may be either horizontal or vertical, but the horizontal die is supported by rotating rollers on rotating rollers, while the vertical die is concentric on a rotatably mechanically supported base. It is fixed. Therefore, compared to horizontal centrifugal casting, vertical centrifugal casting has less fluctuation of G and vibration of the centrifugal casting mold, so that the components of the molten metal cast in the mold are less likely to move, and the structure of the centrifugal casting is less likely to occur. A roll material having excellent uniformity can be easily obtained. Therefore, when the vertical centrifugal casting is used, the casting temperature can be increased as compared with the case where the horizontal centrifugal casting is used. Can also prevent casting defects due to entrainment of oxides and the like formed on the substrate. In the case of horizontal centrifugal casting, from the viewpoint of preventing segregation, the casting is preferably performed at a relatively low temperature at a solidification start temperature of + 70 ° C. or lower.

After the roll material of the present invention is cast as an outer layer of a composite roll or a composite sleeve, the temperature range from quenching and incubation (austenitizing temperature) of the entire roll to 400 to 650 ° C is 100 ° C / Hr.
By quenching at the above cooling rate, a good quenched structure can be obtained. The tempering may be performed once or several times at a temperature of 500 to 600 ° C.

The roll material referred to in the present invention means a material applicable not only to the above-described rolling roll but also to a roller in a rolling auxiliary facility, and is not limited to the outer layer material of the rolling roll, such as a hot run table roller. As an outer layer material of the hollow cylindrical roller.

Next, a specific production example of a composite roll in which the roll material of the present invention is applied to an outer layer serving as a rolling use layer will be described.

Example A (1) In Table 2, the molten metal of the outer layer was cast into a horizontal centrifugal force casting mold (inner diameter 420 mm x 700 mm) at a solidification start temperature of 50 ° C. The casting material was 65 mm thick. In the table, Comparative Example
Samples 1 and 2 have substantially the same composition as in Example 1 except for Ni, and the conventional example is a high chromium cast iron material having improved wear resistance.

(2) After casting the outer layer, the mold having the outer layer was set up vertically, the upper mold and the lower mold were connected at both ends, and the shaft core material (high-grade cast iron) was cast into the interior.

(3) At a later date, the mold was disassembled, the roll material was taken out, and after rough processing, after holding at 1000 ° C. for 2 hours, the following quenching heat treatment was performed, and then tempering heat treatment at 550 ° C. × 10 hours was repeated twice. The surface hardness of the outer layer after the heat treatment is shown in the third section below.

Example 1 and Comparative Example 1 After cooling to 450 ° C. at 200 ° C./Hr by air cooling, it was gradually cooled at 50 ° C./Hr to cool to room temperature.

・ Comparative Example 2, Conventional Example After cooling to 450 ° C by spray water cooling at 420 ° C / Hr, 50 ° C / Hr
And gradually cooled to room temperature.

According to Table 3, when the cooling rate during quenching was reduced without containing Ni as in Comparative Example 1, high hardness was not obtained, but Ni was added as in Example 1. When the cooling rate during quenching was reduced, high hardness was obtained, indicating that high hardness can be obtained by adding Ni even when the cooling rate during quenching was reduced.

(4) When the cross section of the outer layer was visually observed, no segregation of components was observed. In addition, a plate-shaped test piece was collected from the outer layer, and a rotating wheel was pressed against the fixed test piece to measure a specific wear amount. Table 4 shows the test results.

- Test conditions Rotation wheel material ...... SUJ2 carburized (H _R C60~62) intended load ...... 18.0Kgf sliding speed ...... 3.4m / sec slippage distance ...... 200m Table 4 shows that the wear resistance of Example 1 is about 4 times better than the conventional example, and about 5 times better than that of Comparative Example 1 in which the cooling rate during quenching is the same as that of Example 1. It is.

Example B (1) Inner diameter φ700 x same length 1100m by vertical centrifugal casting
After casting the outer layer material shown in Table 5 in a m mold, the outer layer was completely solidified, and subsequently the adamite melt shown in the same table was cast as a middle layer by centrifugal force to metallurgically bond the outer layer and the middle layer. Completely welded. Wait for the middle layer to solidify completely,
The rotation was stopped, and a centrifugal force casting mold was set in the lower mold and the upper mold that were grounded in advance. Then, a shaft core material melt was cast from above and welded to the intermediate layer. Casting thickness is 70mm for outer layer, 25 for middle layer
mm. The outer layer casting temperature is the solidification starting temperature + 100 ° C
And

(2) After rough processing the above-mentioned roll, hold it at 1050 ° C for 5 hours, air-cool it at 180 ° C / Hr to 540 ° C, and then 20 ° C /
Cooled slowly with Hr. Thereafter, a tempering heat treatment maintained at 520 ° C. for 20 hours was repeated twice.

The surface hardness of the outer layer after the heat treatment was as follows: Example 2 Hs81, Example 3 Hs86, Example 4 even at a slow cooling rate of 180 ° C./Hr.
Hs84 and high hardness were obtained.

(3) After finishing the torso surface, the welding condition was confirmed by an ultrasonic deep scratch test, and the welding was good.
Further, when the product shaft core materials of Examples 2 to 4 were analyzed, all were suppressed to half or less of the concentration expected when the outer layer and the shaft core material were directly welded, and the effect of the intermediate layer was reduced. Admitted.

(4) When the cross section of the outer layer was observed, no segregation of components was observed despite casting at a high temperature. A test piece was taken from the outer layer and subjected to a wear test in the same manner as in Example A. Example 2 ... 35 × 10 ^-9 mm ² / Kg Example 3 ... 30 × 10 ^-9 mm ² / Kg Example 4 ... 33 × 10 ⁻⁹ mm ² / Kg, and had good wear resistance.

(Effect of the Invention) As described above, the roll material of the present invention has a chemical composition of C: 1.0 to 2.9% by weight, Si: 0.2 to 2.0% Mn: 0.1 to 2.0% Ni: 0.1 to 4.5% Cr: 3.0 to 10.0% Mo: 0.1 to 9.0% W: 1.5 to 10.0% One or two of V and Nb: 3.5 to 10.0% Al: 0.01 to 0.50%, balance Fe and impurities, especially above Mo: 0.1 to 9.0% in chemical composition, W: 1.5 to 10.0%, V, Nb
One or two of them contained a total of 3.5 to 10.0%, and together with the special form of V and Nb carbides, the wear resistance was dramatically improved. In addition, even when centrifugal casting is performed, macrosegregation hardly occurs, and the uniformity of the structure is excellent. Particularly, in the present invention, since Al: 0.01 to 0.50% is contained, Al generates an oxide in the molten metal, lowers the oxygen content in the molten metal, improves the soundness of the product, and improves the generated oxide. Acts as a crystal nucleus, which is effective in improving wear resistance by making the solidification composition finer.

Furthermore, since 0.1 to 4.5% of Ni was contained to shift the bainite transformation to a longer time side, the cooling rate during quenching could be reduced, and the workability of heat treatment could be greatly improved.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Kimura 64 Nishimujimajima-cho, Amagasaki-shi, Hyogo Pref. Within the Kubota Amagasaki Plant (72) Inventor Takashi Shikata 64-64 Nishimujimajima-cho, Amagasaki-shi, Hyogo Pref. 56) References JP-A-60-29422 (JP, A) JP-A-57-198243 (JP, A) JP-A-59-143048 (JP, A) JP-A-4-80344 (JP, A) Hei 2-258949 (JP, A) JP 45-40777 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 37/00-38/60 B21B 27/00

Claims (1)

(57) [Claims] The chemical composition is as follows: C: 1.0 to 2.9%, Si: 0.2 to 2.0% Mn: 0.1 to 2.0% Ni: 0.1 to 4.5% Cr: 3.0 to 10.0% Mo: 0.1 to 9.0% by weight% W: 1.5 to 10.0% V, Nb: One or two of the following: 3.5 to 10.0% Al: 0.01 to 0.50%, with the balance being Fe and impurities.