JPH0234750A - Reinforcing roll material for rolling - Google Patents

Abstract

PURPOSE:To obtain the title reinforcing roll having excellent wear resistance and long service life without impairing its spalling resistance and machinability by using a high-carbon alloy steel contg. specific amounts of Cr, etc., as a reinforcing roll material for rolling. CONSTITUTION:As a reinforcing roll material in a rolling machine, a high-carbon Cr-Mo alloy steel material contg., by weight, 0.50 to 0.90% C, 0.15 to 1.60% Si, 0.15 to 1.60% Mn, 8.10 to 10.00% Cr, 0.35 to 1.20% Mo and <0.50% V is used. A rolling mill having excellent wear resistance in the wide range of hardness without impairing its spalling resistance and machinability, having long service life in the integration of a reinforcing roll and having excellent dimensional accuracy can be constituted.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a reinforcing roll material for rolling that exhibits extremely excellent wear resistance without impairing spalling resistance and machinability. [Conventional technology]

Conventionally, as reinforcing roll material for rolling, for example, C0,4
0-0.70%, Si 0.15-1.60%,
Mn 0.1 5-1.6 0%, Cr3.0-5
．． 0%, Mo0.2-0.6%, V 0.20% or less is generally used in the range of Hs50-70, and as an example with more Cr and Mo than these,
As in Special Publication No. 55-19305<Cr4.60~8.0
A roll material made of an alloy containing Mo 0.45 to 1.10% has also been proposed. On the other hand, as rolling conditions have recently become more severe, the wear of reinforcing rolls has tended to progress rapidly, and at the same time, demands for improved dimensional accuracy of rolled products have become even stronger.
The reality is that the frequency of replacement of reinforcing rolls has increased significantly. This has become a major factor hindering productivity in rolling operations, which have become extremely continuous in recent years, and as a countermeasure to this problem, improvements in the wear resistance of reinforcing rolls are increasingly desired. By the way, in order to meet this demand with the conventional steel types mentioned above, it is necessary to increase the surface hardness of the roll to, for example, about l-1s75. Since thermal shock cracks and the like tend to develop rapidly, there is a risk of major spalling accidents occurring in reinforcing rolls that are used for a long period of time.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention and Summary of the Means The present invention has been made in view of the current situation and to provide a roll material that satisfies the demands for reinforcing rolls, the most important feature of which is Cr. The content is increasing. That is, in the present invention, C0.50 to 0.90%, Si 0
．． 15-1.60%, Mn 0.15-1.60%, C
r8.10~10.00%, Mo0.35~1.20
%, Vo, 50% or less, and the balance is Fe and unavoidable impurities as a roll material, thereby successfully achieving this objective.

[Reason for limiting the composition] C・0.50-0.90% C is an element that has a large effect on the transfer fatigue life, which is a basic characteristic that a reinforcing roll should have, and is shown in Figure 1 (
As shown in the graph showing the relationship between Cf''tl and rolling fatigue life, if it is less than 0.50%, sufficient rolling fatigue strength cannot be obtained, and if it exceeds 0.90%, the toughness decreases and some materials If so, cracks will occur early, so C
The range of Nt was defined as 0.50 to 0.90%. Si; 0.15-1.60% Si is generally contained as a deoxidizing agent and is effective in improving hardenability, but excessive addition not only impairs the cleanliness of steel due to deoxidation products, but also reduces toughness. 0.15.
~1.60%. Mn: 0.15-1.60% Like Si, Mn is a deoxidizing agent and has a remarkable effect on improving hardenability, but excessive addition will cause a significant decrease in the Ms point and increase susceptibility to quench cracking. 0.15 to 1.6 because it increases
The range was 0%. Cr; 8.10 to I 0.00% Cr is the most important element in the present invention, and a feature of the present invention is that its content is set high for the following reason. In Fig. 2 (a), (b), and (c), the hardness level is
This is a graph showing the relationship between Cr content and wear loss in Hs75.1 (s70, l-1s62).The solid line indicates contact stress of I50 kg/111m', and the dotted line indicates contact stress of I200 kg.
r7' + 11111''. These values correspond to typical values of the contact stress applied to the roll under recent rolling conditions, in standard cases and in severe cases, respectively. As is clear from comparing Fig. 2 (a), (b), and (c), the steel described in Japanese Patent Publication No. 55-19305 and the steels 3 to 3 corresponding to the conventional general w4 type 8%
Focusing on the Or content, a remarkable improvement in wear resistance is seen as the hardness increases from Hs62 to 70 to 75, and the wear resistance at the Hs75 level shown in Figure (a) shows that the wear resistance is higher due to the higher Cr content. (It is comparable to fi. Also, there is no big difference depending on the magnitude of contact stress. Therefore, if the hardness is increased to this level, even conventional steel types will not have sufficient wear resistance. However, in this case, the side effect of reducing toughness, which is an important property required for reinforcing rolls, cannot be avoided.In recent years, fracture toughness values are often used as an appropriate measure to judge the crack propagation characteristics in rolls. .3rd
The figure shows the relationship between Shore hardness and fracture toughness of conventional steel reinforced roll materials. However, from the same figure,
It can be clearly seen that the toughness decreases as the hardness increases. It is also known from experience that so-called high-hardness reinforcing rolls with a hardness exceeding 11570 develop cracks quickly and are prone to major spalling accidents. Therefore, trying to improve wear resistance by adjusting conventional steel types to around Hs75 is a measure that involves extremely great practical risks.
It is desired to provide excellent wear resistance with lower hardness. As seen in the graph in Fig. 2(b), the wear loss at the s70 level decreases as the Cr content increases, especially when the Cr content exceeds 8% for a high contact stress of 200 kgr/ttrta. Compared to the case where the amount is less than that, the wear loss is drastically reduced.This tendency is due to (C
) The same is true for Hs62 in the figure, and based on this knowledge, the roll material of the present invention, in which the lower limit of Cr content is set to 8.10%, exhibits outstanding performance under severe conditions of high contact stress compared to conventional steel. It has the property of exhibiting excellent wear resistance. In addition, if the Cr content exceeds 8%, the
As stated in No. 9305, a certain degree of increase in quenching temperature is unavoidable, but due to advances in heat treatment technology, including the adoption of induction heating, it is now possible to achieve the above-mentioned results without being subject to the same manufacturing constraints. It is a material that provides excellent properties. On the other hand, rolling rolls must be ground to remove fatigue layers and damaged areas depending on the degree of use, so no matter how good the wear resistance is, if the machinability is poor, it is not practical. I can't offer it. FIG. 4 is a graph showing how the load applied to the grindstone shaft changes with the Cr content when grinding is performed under the same conditions as an evaluation of machinability. According to the figure, when the Cr content exceeded 10%, the load on the grinding wheel shaft increased rapidly, and machinability significantly deteriorated. In addition, within this range, not only the grinding efficiency decreases, but also chattering and feed marks occur, making it difficult to achieve a proper finish. For the above reasons, the Cr content was reduced to 8. lO~to, oo%
limited to the range of Mo; 0.35 to 1.20% Mo is a useful element that not only improves wear resistance and tempering resistance but also improves toughness. In this steel type, as shown in Figure 5, a significant improvement in fracture toughness was observed with addition amounts exceeding 0.30%, and 1.2%.
Although it gradually increases up to 0%, it is set in the range of 0.35 to 20% since no great effect can be expected beyond that. V, 0.5% or less ■ is extremely effective in improving wear resistance, but 0.50%
Since machinability deteriorates if the addition exceeds 0.50%, it is specified as 0.50% or less. In addition to the above, if necessary, it is also possible to add 1% or less of Ni to improve hardenability. As shown in Figure 1-L, the reinforcing roll material according to the present invention exhibits excellent wear resistance over a wide hardness range without impairing spalling resistance and machinability through the selection of new chemical components, and as a result, This has brought about the industrial effects of extending the usage period of reinforcing rolls and improving the dimensional accuracy of rolled products.The experiments shown in each figure used in the above explanation are shown in Tables 1 to 3 below. Based on the sample material with the chemical composition (weight %) shown. The correspondence is as follows: Figure 1 is the sample material in Table 1, Figure 2 is the sample material in Table 2, Figure 3 is the sample material ll-2 in Table 2, and Figure 4 is the sample material in Table 2. The sample materials in the table and FIG. 5 are those using the sample materials in Table 3. In Tables 1 to 3, the double line range is the composition of the present invention. Table 1 Weight tn% Table 2 Table 3 Weight % Weight %

【Example】

Using alloy steel having the same composition as in Table 2 11-4,
We manufactured a reinforcing roll for the 1-stand stand of a 6-tandem mill, which has a greater amount of wear than conventional ones, and put it into practical use. The diameter of the trunk is 1430 mm. The results are shown in FIGS. 6 and 7 in comparison with a conventional roll (5% Cr). FIG. 6 is a diagram showing the relative wear amount of the rolls with respect to the rolling distance. Here, the relative wear amount refers to the difference in diameter of the roll body after use, δ, which is the decrease in diameter due to wear;
(see FIG. 6(a)), this value has a great influence on control of the plate shape during rolling. In Figure 6, the solid line range is 8%C
The dotted line range represents the relative wear amount of the roll of the present invention r and the conventional roll of 5% Cr. From this result, it can be seen that as the rolling distance increases, the roll of the present invention, compared to the conventional roll,
It can be seen that the effect of wear resistance is remarkable. Figure 7 is a graph showing the diameter at each position of the roll body before and after a series of uses, as a difference from the diameter at the center of the used piece, and can be said to be a comparison of the absolute amount of wear. According to the figure, the roll of the present invention with 8% Cr not only has a smaller absolute amount of wear at the center of the body than the conventional roll with 5% Cr, but also has a difference in the amount of wear between the center of the body and the ends of the body. It has been revealed that there are few As described above, the roll of the present invention has the excellent performance required of a reinforcing roll in actual use as shown in FIGS. 6 and 7.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between C41 and transfer fatigue life. Figure 2 is a graph showing the relationship between Cr content 77λ and wear loss at each hardness level.
b) is Hs70, (c) is Hs62, the solid line in each figure is the contact stress of 150 kgf/a+m", the dotted line is the contact stress of 20 kgf/a+m"
0 kgf/mm''. Figure 3 is a graph showing the relationship between shore hardness and fracture toughness of reinforcing roll materials of conventional steel types. , is a graph showing the relationship between the load applied to the grinding wheel shaft during grinding, and is used to evaluate machinability. Figure 5 is a graph showing the relationship between Mo addition and fracture toughness value. Figure 6 is a graph showing the relationship between the addition of Mo and the fracture toughness value. , is a graph showing the relative wear amount of the roll against the rolling distance, where the solid line range shows the relative wear amount of the present invention, and the dotted line range shows the relative wear amount of the conventional roll. This is a schematic diagram for explaining the meaning. Fig. 7 is a graph showing the difference in diameter of each part of the body before and after using the roll, as a difference from the diameter of the central part before use.
△ indicates the roll before use, the solid line indicates the roll of the present invention, and the chain line indicates the conventional roll. Patent applicant Kanto Special Steel Co., Ltd. Kawasaki Steel Co., Ltd.

Claims (1)

[Claims] C0.50-0.90% Si0.15-1.60% Mn0.15-1.60% Cr8.10-10.00% Mo0.35-1.20% V0.50% A reinforced roll material with excellent wear resistance, spalling resistance, and machinability, which is made of an alloy containing the following, with the balance being Fe and unavoidable impurities.