JPH01168843A - Graphite-crystallization-type high-chromium composite roll - Google Patents

Abstract

PURPOSE:To obtain a composite roll excellent in resistance to surface roughness by constituting the outer shell layer of a composite roll for rolling iron and steel of a high Ni-Cr-type cast iron in which graphite is crystallized out. CONSTITUTION:While rotating a cylindrical mold for metal mold whose internal surface is previously faced on its axis, a molten cast iron having a composition containing, by weight, 2.5-3.5% C, 2.0-3.5% Si, 0.3-1.5% Mn, <0.1% P, <0.05% S, 3.0-4.5% Ni, 5.0-13.0% Cr, and 0.5-1.5% Mo is poured into the above to undergo centrifugal casting, by which the outer shell layer of a composite roll for rolling iron and steel is formed. After the outer shell layer is perfectly solidified, a molten cast iron for shaft core material is poured into the above and completely welded to the outer shell layer, by which a composite roll is formed. By this method, graphite is crystallized out in the whole of the outer shell layer for use in direct rolling because proper amounts of Ni as a graphitizing agent are contained and inoculation with Si is applied prior to casting, by which the composite roll having a structure reduced in the amount of retained austenite and excellent in resistance to surface roughness can be obtained.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a graphite-crystallized high-chromium composite roll that is used for steel rolling and has graphite crystallized in the outer layer material and has excellent skin roughness resistance. .

(Prior art) Regarding high chromium composite rolls that crystallize graphite, the Japanese Patent Publication No. 61-1 was developed as a material that combines the wear resistance of high chromium cast iron with the accident and crack resistance of nihard cast iron containing graphite.
It is described in Publication No. 6415.

(Problem to be solved by the invention) However, in the composition range in the above patent publication, the alloying element N
i In the high Ni range of 4.5 to 10.0%, the retained austenite during the casting stage is difficult to reduce even by subsequent heat treatment, and the retained austenite is stabilized and surface roughness occurs frequently during rolling use, resulting in poor surface roughness resistance. This is a problem. As a solution to this problem, there is a method to reduce residual austenite by reducing the amount of Ni added.
There is a statement that graphite does not crystallize if it is less than 4.5%.
It has been thought that it is difficult to improve skin roughness resistance by reducing retained austenite in a low Ni region of less than 4.5% Ni.

That is, this is due to the fact that graphite does not crystallize within the component range of the above-mentioned publication.

(Means for solving the problem) The present invention allows graphite to be easily injected into the outer high chromium material as cast by selecting appropriate inoculation conditions even if the Ni content is below 4.5%. We believed that the above purpose could be achieved by crystallizing Ni, and as a result of intensive research, we found that Ni 4.5
By appropriately selecting the amount of inoculation even in the component range of less than %, the present invention has been achieved, which is a graphite crystallized high chromium composite roll material that enables graphite crystallization and improves roughening resistance.

The graphite crystallized high chromium composite roll of the present invention is a composite roll in which an outer layer as a rolling layer and an inner layer as a shaft core are welded and integrated, and the chemical components of the outer layer are
), C2,5~3.5 Si 2.0~3.5 Mn O,3~1.5 P O 11 or less SO, 05 or less Ni 3.0~4.5 or less Cr 5.0~13. 0 Mo 0.5 to 1.5 The remainder is substantially composed of Fe, and the structure of the invention is that graphite is crystallized throughout the outer layer, which is the layer used for rolling, on the microstructure.

(Function) The graphite crystallized high chromium composite roll of the present invention has Ni3.0~
The outer layer material has a low Ni content of less than 4.5%.

By controlling graphite crystallization by selecting the inoculation conditions, it is possible to manufacture it, and within the above composition range, graphite is found in a fine and uniform distribution in the structure throughout the entire outer layer.

As for the material of the inner layer of the shaft core of this roll, various conventional cast iron and cast steel materials can be used as long as toughness can be ensured. In addition, regarding the manufacturing method of this roll, after casting the graphite crystallized high chromium material with the above components as the outer layer by die centrifugal casting, the inner layer material of the shaft core is welded and molded using a known composite technology. It can be made and cast.

The reason for setting the component range of the graphite-crystallized high-chromium outer layer material according to the present invention will be described below. Ingredients are in weight percent.

C: Regarding the limit of 2.5 to 3.5%, C is a chromium carbide-forming element, and crystallizes fine graphite with the graphitization-forming elements of Si and Ni, which will be described later. Therefore, chromium carbide and graphite exist and there is little deterioration of wear resistance.2.5 to 3.5
%.

Regarding the Si limit of 2.0 to 3.5%, Si is an essential element for graphite production, and the amount required for graphite crystallization and the range of 2.0 to 3.5% that does not deteriorate wear resistance. And so. Furthermore, in order to control the amount of graphite crystallization by adjusting the amount of inoculation as described later, the components of the final product are adjusted within the above range.

Regarding the limitation of MnO from 3 to 1.5%, Mn was set to a range of 0.3 to 1.5% that does not cause deterioration of mechanical properties, particularly toughness.

Regarding the limitation of P O to 10% or less, P is set to 0.10% or less since it makes the material brittle.

Regarding the limitation of s o and os%, S is set to be 0.05% or less since it makes the material brittle.

Regarding the limit of 5.0 to 13.0% Cr, Cr combines with C to form hard Cr carbide, but below 5%, the amount of carbide is small and wear resistance is poor, and above 13%, the above components This is because graphite cannot be crystallized even within this range.

No: Regarding the limitation of 0.5 to 1.5%, Mo was set in the range of 0.5 to 1.5%, which maintains quenching and tempering resistance and enters into the carbide to increase carbide hardness.

Ni: Regarding the limitation to less than 3.0 to 4.5%,
As is obvious in Nihard cast iron, Ni is added for the purpose of improving the base structure and crystallizing graphite. Generally, the amount of Ni in nihard cast iron is 4 to 6%, but if the Ni content is 5% or more, about 80% or more of retained austenite will be present during the casting stage, and if excessive Ni is added, residual austenite will remain even after heat treatment. The same is true for graphite crystallized high chromium materials, which cannot reduce the Ni content by 1% when the Ni content is 4.5% or more.
The presence of residual austenite causes rough skin problems during rolling use.

There is a demand for improved skin roughness resistance. Furthermore, since Ni is an element that promotes graphitization, if a large amount is added, flaky graphite is formed and wear resistance is deteriorated. Therefore, if it is in the component range where graphite can be produced, N1 should be as low as possible.

On the other hand, this roll material has a high chromium content.

Graphite crystallization can be controlled by the amount of inoculation as described below, but from the viewpoint of improving the base structure, a minimum of 3.0% is required.
A higher Ni content is required.

For the above reasons, N1 was limited to a component range of 3.0 to less than 4.5%.

In addition to the above-mentioned components, the outer layer material according to the present invention contains substantially F.
Formed by e.

Next, examples of basic data that led to the present invention will be explained.

Figure 1 shows the relationship between the amount of N1 added and the amount of inoculation to obtain the required amount of graphite.

Conventionally, it was reported that graphite crystallization could not be obtained with less than 4.5% Ni, but as a result of various studies on inoculation conditions, graphite crystallization was made possible by increasing the amount of inoculation.

When Ni was less than 4.5%, it was possible to secure a graphite amount of 1.5% with an inoculation amount of 0.13% or more in SL. By considering the amount of inoculation in this way, graphite crystallization is possible even in a low Ni component region.

Further, FIG. 2 shows the change in the amount of retained austenite when the amount of N1 added is changed. In order to achieve the amount of retained austenite of 1% or less, it is possible to keep the amount of Ni added at 4% or less.

(Example) Next, the present invention will be explained in detail.

Product trunk diameter 800szmφ, trunk length 2436mm+, total length 5
A 121 ml+ graphite crystallized high chromium composite roll was manufactured as described below and subjected to various investigations.

■A molten metal with the chemical composition shown in Table 1 is used as the outer layer material, and it is poured into a cylindrical metal mold with a coated inner surface, rotating on a centrifugal casting machine, at a casting temperature of 1330°C with a wall thickness of 105°C. ■Cast (casting weight 47,900 kg).

Table 1 shows the chemical composition of the molten metal of the graphite crystallized high chromium composite roll material produced according to the present invention.

■After the outer layer has completely solidified (22.5 minutes after the start of casting), the molten metal for the shaft core material at 1350°C is poured in the same way on a centrifugal casting machine, and the outer and inner layers are completely welded. I made it into a roll.

(2) After the inner layer was cast, the mold was erected, and after cooling completely, the roll was taken out of the mold and subjected to the required heat treatment.

The microscopic structure of the roll of the present invention produced in this way is shown in FIG. 3, and it was confirmed that the desired structure consisting of crystallized fine graphite, chromium carbide, and matrix was obtained.

Furthermore, the manufacturing quality of this roll is shown in Table 2.

The roll manufactured for the purpose of improving skin roughness resistance has a Ni content of 3.1
At 8%, residual γ could be reduced to 0.9%.

Table 2 shows the hardness and amount of retained austenite of the roll products manufactured according to the present invention.

As mentioned above, in the roll of the present invention, ■Ni content is 0 to 0.
Graphite can be crystallized in a component range of less than 4.5%, and retained austenite can be reduced to 1% or less, and is particularly effective in improving rough skin resistance.

(Effects of the Invention) As explained above, compared to conventional graphite crystallized high chromium materials, the outer layer material of the present invention has a Ni content of less than 3.0% to 4.5% and a graphite crystallized material. We were able to obtain a material with particularly low residual austenite and excellent roughness resistance, which made it possible to reduce the amount of retained austenite to 1% or less.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the amount of Ni addition h and the amount of inoculation to obtain the required amount of graphite for the graphite crystallized high chromium material according to the present invention. FIG. 2 is a diagram showing the relationship between the amount of Ni added and retained austenite. FIG. 3 is a microscopic photograph of the metal structure showing the state of graphite crystallization of the graphite crystallized high chromium roll material produced according to the present invention. Stem 3 diagram

Claims (1)

[Claims] A composite roll in which an outer shell as a layer used for rolling and an inner shell as a core part are welded and integrated, the chemical components of the outer shell being C2.5 to 3.5 Si2 in weight percent. .0 to 3.5 Mn0.3 to 1.5 P0.1 or less S0.05 or less Ni 3.0 to less than 4.5 Cr5.0 to 13.0 Mo0.5 to 1.5 The remainder essentially consists of Fe , and a graphite crystallization type high chromium composite roll characterized in that graphite is crystallized throughout the outer shell layer in terms of microstructure.