JPS62176657A - Production of centrifugal casting complex roll - Google Patents

Abstract

PURPOSE:To improve strength of complex roll product by forming an outer shell layer by high alloy grain cast iron having less than a specified value for S content and an inner layer by spheroidal graphite cast iron having a specified content of Mg, and also executing Si inoculation except the first layer in the inner layer at the time of divide-pouring for the inner layer. CONSTITUTION:S content in the high alloy grain cast iron for the outer shell layer 1 is regulated to <=0.02%, and further Mg content in the spheroidal graphite cast iron from the inner layer is regulated to 0.030-0.070%. At the time of divide-pouring for the inner layer, pouring thickness of the first layer 2 for the inner layer which is brought into contact with the outer shell layer 1, is regulated to 10-70% of the thickness of the outer shell layer, and the inner layer 3-5 except the first layer 2 is inoculated by 0.05-0.40% Si content to molten metal. In this way, the generation of flake graphite at the boundary is prevented and the tensile strength is improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a centrifugally cast composite roll for steel rolling, in which the outer shell layer is made of high-grade gold grain cast iron and the inner layer is made of spheroidal graphite cast iron, and the boundary and internal properties of the roll are This is related to the manufacturing method for obtaining excellent rolls.

[Conventional technology]

Among rolls for rolling steel, work rolls for hot rolling in particular are required to have various properties such as wear resistance, accident resistance, roughening resistance, and spalling resistance.

Manufacturing composite rolls using centrifugal casting has become commonplace. Furthermore, recently there has been a demand for stronger inner layers for reasons such as energy saving and compact rolling mills.

The material of the work roll for hot rolling that corresponds to these trends in rolling technology is, for example, the material of the outer shell layer is C: 3.0 to 3.0 by weight.
5%, Si: 0.6-1.0%, Mn: 0.4
~1.0%, Ni: 4-5%, Cr: 1.2-2.0%
, Mo: 0.2 to 0.8%, and the inner layer contains, for example, C: 2.5 to 3.5%, Si.
: 0.8-1.5%, Mn: 0.2-0.6%, Ni
: O,'5~1.5%, Cr: O,1~0.6
%, which used high-grade cast iron.

For the inner layer, for example, C: 2.8 to 3.5%.

Si: 1.5-2.5%, Mn: 0.2-0.
8%.

Ni: 0.5-2.0%, Cr: 0.1-0.
6%.

High-strength spheroidal graphite cast iron containing Mg: 0.02 to 0.10% has come to be used. However, regarding the manufacturing method, a centrifugal casting method is used, in which an outer shell layer similar to conventional inner layer high-grade cast iron is injected, and an inner layer is injected after solidification.
In this case, an abnormal layer of flaky graphite was formed at the boundary between the outer shell layer and the inner layer, resulting in a significant decrease in mechanical strength and poor spalling resistance. Therefore, as a method for improving the boundary properties when the inner layer is made of spheroidal graphite cast iron, methods such as providing an intermediate layer as a third layer between the outer shell layer and the inner layer, as shown in Japanese Patent No. 1068098, have been taken.

[Problem that the invention seeks to solve]

As mentioned above, work rolls for hot rolling are required to have tougher inner layers, and spheroidal graphite cast iron has come to be used.
When manufactured using the same centrifugal casting method as conventional high-grade cast iron, an abnormal layer of flaky graphite is formed at the boundary, resulting in a mechanical strength of 20%.
A phenomenon occurred in which the spalling resistance decreased significantly to ~30 Kgf/mrd, and the spalling resistance was poor. The reason for this is that compared to high-grade cast iron, spheroidal graphite cast iron has a higher content of the graphitizing elements C and Si, and at the boundary where it is easy to graphitize, the C contained in the outer shell layer segregates due to centrifugal heel action. Mg in the inner layer, which is added and has a spheroidizing effect, is added to S in the outer shell layer.
It is thought that this causes a large amount of graphite to crystallize and grow as flake graphite, causing a decline in financial resources.

In addition, since spheroidal graphite cast iron undergoes large solidification shrinkage, defects such as open channels and reverse chills are likely to occur in the center.To prevent this, it is necessary to achieve sufficient graphitization in the inner layer, but the graphitization at the boundary This is the opposite of restraint.

Further, although the method of casting an intermediate layer as the third layer can mutually solve these problems, it complicates the manufacturing process and increases costs.

The purpose of the present invention is to overcome these problems and obtain a centrifugally cast composite roll using spheroidal graphite cast iron for the inner layer, which has a strong boundary and good internal properties, without complicating the manufacturing method. It is said that

[Means for solving problems]

The present invention relates to a centrifugally cast composite roll using high-alloy grain cast iron for the outer shell layer and spheroidal graphite for the inner layer.

At the boundary, the S content in the outer shell layer is reduced to 0.020% or less, causing Mg in the inner layer to disappear as MgS, and 0.02% is added to the inner layer.
By securing 0.030% to 0.070% of Mg, even if it disappears to a certain extent, it will still have a spheroidizing effect, making it possible to suppress the growth of flaky graphite at the boundary, and by dividing the inner layer into injection. By reducing the implantation thickness of the first inner layer in contact with the outer shell layer to 10 to 70% of the outer shell layer thickness, Cr, which is a white ironing element, is diffused from the outer shell layer and graphitization of the boundary area is achieved. In order to suppress the
By applying it to the inner layers other than the first layer without applying it to the layers, it is possible to promote only internal graphitization without promoting boundary graphitization, and it is possible to improve the internal properties while improving the boundary area at the same time. have.

Furthermore, according to this method, the third layer does not need to be newly melted, and the working process does not become complicated.

[Effect]

The reasons for setting the ranges of the items regulated in this invention will be explained below. First, the S content in the outer shell layer and the Mg content in the inner layer are interrelated, so if the S content in the outer shell layer increases, the Mg content in the inner layer must also increase. Although the spheroidization effect is lost at the boundary, Mgt
If c' is increased beyond 0.070%, the tendency to become white inside increases, causing defects such as open ditches.

Therefore, the outer shell layer S was fixed at 0.020% or less, and the inner layer M
The upper limit of g was set to 0.070%. Also, the lower limit of Mg is 0.
Regarding 040%, it was limited to a range where the graphite spheroidization at the boundary part did not collapse. Next is the thickness of the first injection of the inner layer.
When the thickness is less than 10% of the outer shell layer thickness, whitening due to Cr diffusion from the outer shell layer becomes excessive, and conversely, weakening of the boundary portion occurs. In addition, since graphitization at the boundary is not significantly suppressed when the thickness exceeds 70%, the thickness is limited to 10 to 70%. Furthermore, for the second and subsequent inoculations in the inner layer, if the Si content is less than 0.05%, graphitization inside the inner layer will not be sufficient.

On the other hand, if # exceeds 0.4%, it becomes excessive and defects such as cracks in the outer shell layer may occur during cooling, so 0.05 to 0.4
It was regulated at 0%.

The present invention provides a centrifugally cast composite roll in which the outer shell layer is made of high-grade gold grain cast iron and the inner layer is made of spheroidal graphite cast iron, and the properties can be improved by suppressing graphitization at the boundary and preventing disappearance of Mg, and the spalling resistance can be improved at the same time.

The inside has the function of promoting graphitization, preventing defects, and improving breakage resistance.

〔Example〕

An example in which the present invention is applied to a hot-rolled post-stage roll will be described below in comparison with a centrifugally cast composite roll manufactured by a conventional method.

In the example of this method and the comparative example of the conventional method, as shown in FIG. A composite roll was manufactured by injecting spheroidal graphite cast iron into inner layers 2 to 5 in parts. The components of the outer shell layer and inner layer in this case are shown in Table 1, divided into the present method and the conventional method.

The chemical components of this method are characterized by lowering the S content in the outer shell layer to 0.010% or less and the M content in the inner layer compared to conventional methods.
The g content is set to 0.040 to 0.060%. Next, regarding the split injection method for the inner layer, in the conventional method, the injection thickness of the first inner layer 2 that is in contact with the outer shell layer is 80% of the injection thickness of the outer shell layer, and the remaining amount is Eye 4,
In contrast to the 4th layer and 5 injections, which were injected separately, the single injection method resulted in J!
! The injection thickness of the first layer is 35% of the injection thickness of the outer shell layer,
The remaining amount was similarly divided and injected into the second to fourth layers.

Injection flow inoculation 11 to each layer is as shown in Table 2. In the conventional method, the first inner layer was inoculated with a Si content of 0.05%, but in this method, this layer was not inoculated. Ta. Furthermore,
Regarding the inoculation for the second and subsequent layers, the amount added was 0.07% in the conventional method, whereas in this method, the amount was doubled to 0.15%.

Figures 2 and 3 show the microstructure at the boundary of the roll produced in this way.In contrast to the conventional method, in which the flake graphite aggregates into the product, in the single-roll method, almost no such particles are observed. First, it is a good quality spheroidal graphite cast iron. In addition, the tensile strength of the boundary part is as shown in Figure 4, and the conventional method has a tensile strength of 24
~25Kgf/mrt? 48~
The speed improved to 50Kgf/m. Furthermore, as for the internal properties of the roll, as seen in the macrostructure in Figure 5.6, in the conventional method there is a reverse chill in the center, but in the present method, this is hardly seen.

Table 2 (Si%) [Effects of the Invention] As explained above, the present invention uses high-alloy grain cast iron for the outer shell layer and spheroidal graphite cast iron for the inner layer when manufacturing a centrifugally cast composite roll. By dividing and injecting the first layer thinly, graphitization near the boundary is suppressed, the S content of the outer shell layer is reduced, and spheroidization is promoted by securing residual Mg. This has the effect of correcting the agglomeration of flaky graphite produced in all directions and improving the tensile strength.

In addition, by applying injection flow inoculation to the second and subsequent inner layers, it is possible to suppress graphitization at the boundary while promoting graphitization only in the center, which has the effect of preventing defects such as open ditch and reverse chill. .

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the centrifugal casting method of the present invention, and Figure 2 is a microscopic diagram of the boundary area of a roll manufactured by the conventional method using high-grade gold grain cast iron for the outer shell layer and spheroidal graphite cast iron for the inner layer. Structure photograph, Figure 3 is a boundary microstructure photograph of a roll manufactured by this method, Figure 4 is a diagram comparing the tensile strength of the boundary area between the conventional method and this method, and Figure 5 is a roll manufactured by the conventional method. Figure 6 shows a cross-sectional macro-structure sketch of the roll manufactured by this method. 1... Outer shell layer 2... Inner N1st layer 3... Inner layer 2nd layer 4... Inner layer 3rd layer 5... Inner layer 4th layer 6... Outer mold 7... Inner mold 8... Mold 9... Injection funnel 10... Ladle 11... Injection flow inoculant Patent applicant Nippon Steel Corporation Representative Patent attorney Yasushi Furushima 1st figure 1 No. 31g (

Claims (1)

[Claims] In a centrifugally cast composite roll in which the outer shell layer is made of high-alloy grain cast iron and the inner layer is made of spheroidal graphite cast iron, the S content of the high-alloy grain cast iron of the outer shell layer is set to 0.020% or less by weight, and furthermore, the S content of the high-alloy grain cast iron of the outer shell layer is made of spheroidal graphite of the inner layer. Mg content of cast iron is 0.030-0.07
At the same time, the inner layer is injected in parts, and the injection thickness of the first inner layer in contact with the outer shell layer is set to 10 to 70% of the outer shell layer thickness, and the Si content is 0 to the inner layer molten metal other than the first layer. .05-0.4
A method for manufacturing a centrifugally cast composite roll, characterized by performing 0% inoculation.