JPH01162745A - Roll for rolling - Google Patents

Abstract

PURPOSE:To improve the wear resistance and resistance to surface rough of a composite roll by using a high-Cr cast iron in which the contents of C, Si, Mn, Ni, Cr, Mo, V, etc., and the range of Cr/C are specified, respectively, as an outer layer and also using a high grade cast iron, etc., as an inner layer. CONSTITUTION:The outer layer of a composite roll for rolling is formed of a high-Cr cast iron having a composition which consists of 2.5-3.5% C, <=2.0% Si, <=2.0% Mn, <=5.0% Ni, 9.0-16.0% Cr, 1.0-4.0% Mo or W, <=1.0% V or Nb, and the balance Fe with inevitable impurities and in which the value of Cr/C is regulated to 3-5. The inner layer material is composed of high grade cast iron, spheroidal graphite cast iron, or cast steel. By this method, the characteristics of a matrix structure are improved by means of eutectic Cr carbide without inhibiting wear resistance inherent in high-Cr cast iron, and the coefficient of friction between the rolls and a rolling stock can be reduced.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a work roll for a rolling composite roll, particularly a hot strip finishing mill, and its feature resides in a composite roll for rolling that employs an improved high Cr cast iron material as the outer layer material.

[Conventional technology]

Recently, the front stage of the hot strip mill has a compound height of C.
rThe cast iron roll is an adamite roll (1.6~1.8%G
, 0.8-1.5% Cr). Additionally, composite high Cr cast iron rolls are beginning to be used in the middle and later stages of finishing. Commonly used composite height C rolls for hot rolling are
The chemical composition of the outer layer material is in the range A of the Fc-CrC system phase diagram (liquidus diagram) shown in Figure 1 (2.3 to 3.1% C11
3 to 23% Cr, Cr/C ratio -5.5 to 7.5), and 20 to 35 volume% Cr co-synthetic carbide M t c 3
It has a finely dispersed structure, and is characterized by excellent wear resistance. However, with the recent trend toward higher surface quality of rolled products, the demand for not only wear resistance but also roughness resistance is becoming stronger. In particular, during low-temperature, high-reduction rolling or stainless steel rolling, there is less scale (black scale) that forms on the roll surface, which forms a protective film between the roll and the rolled material. In this case, roughness due to thermal fatigue and plastic flow becomes severe, and the surface condition of the rolled product may be significantly impaired. For example, Fig. 7 shows a conventional composite tooth Cr cast iron roll (2,7'5% C1I roll) during stainless steel rolling.
This is a surface photograph showing a roll set after using 8% Cr) for finishing and bending, and it can be seen that the surface roughness due to plastic flow is severe and seizure has also occurred in some parts. As a countermeasure for this, when rolling stainless steel, 1'J
+G cast iron rolls are used, -;π and graphite crystallized high Cr rolls are used. These N1-G cast iron rolls and graphite crystallized high Cr
All rolls are said to prevent rough skin due to the self-lubricating effect of graphite precipitated in the structure.
On the other hand, since the graphite grains become a starting point for shedding and flaking of the roll structure, it has the disadvantage of being significantly inferior in wear resistance compared to conventional composite tooth Cr cast iron rolls.

Problems to be Solved by the Invention The present invention aims to improve the characteristics of the matrix structure without impairing the inherent wear resistance of high Cr cast iron material due to Cr co-synthetic carbides.
By reducing the friction coefficient μ between the roll and the rolled material,
The object of the present invention is to provide a composite tooth Cr cast iron roll with excellent wear resistance and surface roughness resistance.

[Findings that form the basis of the invention]

The present inventor first investigated the relationship between the wear amount of the high Cr cast iron roll and the N1-G cast iron roll in each stand of a hot strip mill and the total frictional work W' between the roll and the rolled material, and calculated this as shown in Figure 2a. , b. The total frictional work W' is calculated using the following formula according to the rolling load conditions. Wf = μ Pm Vr Tr Here, pH 1 is the average rolling pressure Vr is the relative The average value Tr of the absolute value of the speed and the contact time μ between the roll and the rolled material were set to 0.3 as a general value.As shown in Figure 2, the wear amount of the roll is approximately equal to Wr. Since the roughness of the surface of stands with a large W' is large, the present inventors have reduced μ, which is an inherent characteristic of roll materials.
Based on this, we conducted research on setting comprehensive optimal conditions. As a result, the outer layer material of the composite roll maintains wear resistance by containing 20 to 37% by volume of Cr co-synthetic carbide, and has a Cr/C ratio in a range different from that of conventional high Cr cast iron materials. By setting the value to 3 to 5, we succeeded in reducing μ and improving both wear resistance and roughness resistance. That is, in the present invention, C2.5 to 3.5%, Si 2.0%
Below, Mn 2.0% or less, Ni 5.0% or more F1Cr
9.0-16.0%, Mo or Wl, 0-4.0
%,■ or containing 1.0% or less of Nb, with the balance being Fe
and unavoidable impurities, and the ratio of Cr and C (Cr
/C) is a high Cr cast iron material in the range of 3 to 5 as the outer layer material, and the inner layer material is high-grade cast iron, spheroidal graphite cast iron, or cast steel.Composite Cr tooth for rolling with excellent wear resistance and roughness resistance. The gist is cast iron rolls.

[Basis for setting conditions]

The reason why C and Cr in conventional high Cr cast iron roll materials have been limited to the range shown in Figure 1 is because they were set through trial and error in actual mills as improvements in wear resistance were required. This is thought to be mainly due to the following reasons. First of all, the reason why the Cr/C ratio in conventional high Cr cast iron roll materials is in the range of 5.5 to 7.5 is that, as shown in Figure 3, the highest quenching hardness is achieved when the Cr/C ratio is around 6. Therefore, when aiming at wear resistance, Cr/
This is because setting the ratio to C was effective. Also, the reason why the Cr-component carbide amount %K has been limited to the range of 20 to 35 area % is because %K is 2 as shown in Figure 4.
Wear resistance begins to decrease below 0 area%, %K
35 area% or more"2, line a-1) (γ-
This is because coarse primary carbides are crystallized beyond the M 7 G-eutectic line, resulting in significant deterioration of wear resistance and toughness. The test shown in Fig. 4 was conducted using an aluminum slurry type high-temperature wear tester, and the temperature of the mating material was 800°C and the linear pressure was 20 kg/
mm, slip rate of 2%, and wear amount were measured after lXl0' rotational contact. Such conventional high Cr cast iron roll material has a base structure of 6
Since it accounts for as much as 0 to 80%, some attempts have been made to improve the wear resistance and roughness resistance by changing the properties of the matrix structure. However, Goret et al.'s attempt was to remove retained austenite in the base structure through heat treatment. It only decreases the +1 and does not fundamentally change the base structure or the properties of the roll material. Therefore, as a result of intensive research, the present inventor discovered that the conventional high-C
It has been found that by making the Cr/C ratio smaller than that of the r-cast iron material, the matrix structure, that is, the properties of the high-Cr cast iron material, can be significantly improved. In other words, Fig. 5 shows the relationship between the amount of C in the base of high Cr cast iron and the Cr1C ratio. This indicates that the amount of small precipitated carbides increases and the friction coefficient μ may become smaller. Although Figure 6 does not show the relationship between the CrlC ratio, the amount of wear, and μ, it is clear from this figure that μ is minimum when the Cr/C ratio is in the range of 3 to 5, and the wear resistance is It can be seen that the results have also improved. In addition, the reason why the wear resistance deteriorates when the CrlC ratio is less than 3 is because the carbide becomes coarse and soft due to the mixture of Fc co-conjugated carbide (MG C type) and because graphite is used for crystallization. be. The test shown in FIG. 6 used a testing machine similar to that shown in FIG. 4.

[Reason for limited ingredients]

Next, the reason for limiting each component of the outer layer material in the present invention will be described. The basic idea is that %K is 20 due to two reasons:
The amounts of C and Cr are limited so that the Cr/C ratio is in the range of 3 to 5. C; 2.5 to 3.5% The lower limit is 2.5% (20% K) that can maintain the necessary wear resistance, and 3.5% (37% K) that does not crystallize coarse primary carbides.
%K) is the −L limit. Cr; 9.0 to 1 6.0% By setting the Cr content to 9.0% or more and setting the lower limit of the Cr/C ratio to 3, graphite that inhibits wear resistance can be used for crystallization. A structure in which fine Cr co-formed carbides are dispersed can be obtained without the use of Cr. Moreover, rll of Cr and 1 of Cr1C ratio
- By setting the limits to 16.0% and 5, respectively, [
” /7 small high Cr cast iron materials can be changed. Region B in FIG. 1 shows the range of C and Cr described below. Si: 2.0% or less Si is necessary for adjusting deoxidation and assisting in improving hardenability, but if it exceeds 2.0%, graphite crystallization occurs and wear resistance is significantly deteriorated. The second limit is 0%. Mn and Ni; 2.0% or less and 5.0% or more Mn
and Ni are effective in improving hardenability, but Mn is 2.0%
In -1-, the toughness deteriorates severely and becomes 7, so 2.0% is added to L.
limited. If Ni exceeds 5.0%, the Ms point becomes too low and cracks are likely to occur during manufacturing, and retained austenite also stabilizes and impedes roughness resistance, so the content should be 5.0% or less. Mo and W; 1.0 to 4.0% Mo improves hardenability without stabilizing retained austenite like Mn and Ni, increases tempering resistance, and hardens carbides. Since it is effective, it is actively included. FT with the addition of Mo of 1.0% or more
However, adding more than 4.0% is excessive and increases costs, so the range is set to 1.0 to 4.0%. Since W has the same effect as Mo, it can be added in place of part or all of Mo up to a total rt'L of 4.0%. Nb and V: 1.0% or less Nb and V are both effective in refining carbides and increasing hardness, so they are added individually or in combination in an amount of 1.0% or less. 1.
Even if the content exceeds 0%, the effect will not increase and the cost will increase. As the inner layer material in the composite roll of the present invention, materials commonly used for this type of inner layer material, such as high-grade cast iron, spheroidal graphite cast iron, or cast steel, are used, and the method for manufacturing the composite roll is known centrifugal casting. Law etc. are used. The surface hardness of the outer layer material in the present invention varies depending on the use, but is approximately selected as appropriate within the range of l1s 70 to 80. The composite tooth Cr cast iron roll of the present invention is useful mainly as a work roll for hot rolling, especially for hot strip mills, but is not limited thereto. It also exhibits its effect as a composite height for rolling.

[Examples and effects]

Example 1 0-le body diameter φ768, body length 1780 (2, total length 3824
Two No. 12 hot rolling finishing work rolls were manufactured as described in F. (a) A composite roll was manufactured by a normal centrifugal casting method using a high Cr cast iron molten metal having the chemical composition shown in Table 1 as an outer layer material and a spheroidal graphite cast iron molten metal as an inner layer material. (b) After being cast, predetermined heat treatment and machining were performed to obtain a final product composite roll. The surface hardness of rolls 1 and 2 was l-1s 72.3 and 75.0, respectively, and the desired hardness was obtained. When the roll manufactured in this manner was used during stainless steel rolling in the pre-hot rolling finishing stage, as shown in Figure 8, a beautiful roll surface was obtained with no roughness due to plastic flow or seizure. Ta. In addition, as shown in Table 2, even during regular rolling, the wear resistance was lower than that of conventional high Cr.
It was confirmed that the roll was superior to cast iron rolls and graphite crystallization height Cr rolls. (See margin below) Table 1 Examples! The chemical composition and Cr/C ratio of the outer layer material,
Table 2 Comparative Example 2 of abrasion resistance between rolls of the present invention and other rolls Two cold rolling rolls for pipe making with a diameter of 480 mm, a length of 260 mm, and a total length of 900 Q were used as outer layer materials in Table 3 It was manufactured in the same manner as in Example 1 using a high Cr cast iron material having the components shown in and spheroidal graphite cast iron as the inner layer material. When the obtained roll was used for printing purposes, it was found that the wear resistance was significantly improved and the seizure flaws at the contact position with the plate edge were eliminated. (The following is a blank space) Table 3 Chemical composition and Cr/C ratio of the outer layer material of Example 2,
to %

[Brief explanation of the drawing]

FIG. 1 is a graph showing the chemical composition region A of the conventional high Cr cast iron material and the chemical composition region B of the high Cr cast iron material of the present invention in the Fe-Cr-C system phase diagram (liquidus diagram). , Figure 2 a and b are graphs showing the amount of roll wear and total frictional work in each stand of a hot strip mill, Figure 3 shows the relationship between Cr/C ratio and quenching hardness in high Cr cast iron material. Figure 4 is a graph showing the relationship between Cr co-product carbide % of high Cr cast iron material and amount of friction. Figure 5 is a graph showing the relationship between the Cr/C ratio in high Cr cast iron material and C in the matrix. Figure 6 is a graph showing the relationship between Cr/C ratio and wear characteristics of high Cr cast iron materials. Figure 7 is a graph showing the rough surface of a conventional composite high Cr cast iron roll during stainless steel rolling. FIG. 8 is a surface photograph of the roll of the present invention during stainless steel rolling. Figure 1 z Figure 2 ~ Stand Figure 3 Figure 4 Figure 10K Figure 5 Figure 6 Engraving of CRLC drawings Figure 8 Procedural amendment (voluntary) IJ12γ Day 1, 1985, Indication of incident 1988 Patent Application No. 321939 2, Name of the invention: Composite height for rolling 3, Person making the amendment 4, Agent address: 2-4-1 Marunouchi, Chiyoda-ku, Tokyo, Figure 1 θ No. 02. θ 30 4.
0 5. DC′/ζ

Claims (1)

[Claims] C2.5-3.5%, Si2.0% or less, Mn2.0%
Below, Ni5.0% or less, Cr9.0-16.0%, M
o or W1.0-4.0%, V or Nb1.0
% or less, the remainder being Fe and unavoidable impurities,
The outer layer material is a high Cr cast iron material with a ratio of Cr and C content (Cr/C) in the range of 3 to 5, and the inner layer material is high-grade cast iron, spheroidal graphite cast iron, or cast steel, which has wear resistance and roughness resistance. Composite high Cr cast iron roll for rolling with excellent properties.