JPH0693373A - Hardened roll steel having low hardness and prolonged rolling fatigue strength - Google Patents

Abstract

PURPOSE:To simultaneously attain the reduction of hardness and the prolongation of rolling fatigue strength by setting respective contents of Si and Ni in roll steel components to values in specific ranges. CONSTITUTION:The roll steel has a composition consisting of, by mass, 0.40-1.60% C, 0.30-3.00% Si, 0.10-2.00% Mn, 0.30-3.00% Ni, 2.5-7.5% Cr, 0.20-3.0% Mo, 0.05-2.00% V, and the balance Fe with inevitable impurities and satisfying Si+Ni>=1.0%. If necessary, 0.20-3.00% W is incorporated. By this steel composition, even if hardness is reduced and the indentation resistance of a work roll is improved, rolling fatigue life can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low hardness, long life rolling fatigue strength hardened roll steel suitable for use as an intermediate roll material for a multi-stage mill such as a Zenzimer mill and an intermediate roll material for a 6Hi mill.

[0002]

2. Description of the Related Art Conventionally, as an intermediate roll material of, for example, 6Hi mill, 5% Cr steel such as 0.8 C-5 Cr (in this specification, "%" means "mass%" unless otherwise specified).
Or as an intermediate roll material for a small-diameter multi-stage mill such as a Zenzimer mill, 0.5 C-0.5 Si-
Hot die steels such as 5Cr-1Mo-1W were used.

From the viewpoint of reducing manufacturing cost and improving quality, work roll dent measures have been conventionally promoted. As one of them, the hardness of the intermediate roll (whether for iron rolling or non-ferrous rolling) is (Currently HS 78-80)
It has been known that the depression of the work roll can be significantly suppressed by reducing the hardness of the work roll by about S5 and reducing the hardness of the work roll (currently HS 88 or more) by HS 13 to 14 or more.

FIG. 3 shows a conventional 0.5C-0.5Si-5Cr-1.
Regarding Mo-1W, the relationship between the hardness (HS) of the intermediate roll and the occurrence rate (%) of the dip flaw (dent) of the work roll is shown in a graph. From the figure, it can be seen that by reducing the hardness of the intermediate roll from HS 78-80 to HS 72-74, the incidence of work roll dive defects is drastically reduced from about 45% to about 16%. In addition, in Fig. 4, the hardness difference between the intermediate roll (IR) and the work roll (WR) is due to the work roll jump defect.
The effect of the (dent) on the occurrence rate is shown in the graph.From the figure, the hardness of the intermediate roll is higher than that of the work roll by H
It can be seen that when S 13 to 14 or more is reduced, the occurrence of dent defects on the work roll is significantly suppressed. In this way, if only the suppression of the dent defects on the work roll is considered, the hardness of the intermediate roll should be reduced by about HS 5 from the conventional level.

[0005]

However, if the hardness of the intermediate roll is simply reduced, the rolling fatigue life of the intermediate roll (fine pit-like dents appear on the surface of the intermediate roll or immediately below the surface from the start of use of the roll). However, it is necessary to interrupt the operation frequently and change the intermediate rolls at an early stage.
Therefore, it is actually impossible to lower the hardness of the intermediate roll as compared with the current one as a measure for suppressing the dent defect of the work roll.

Here, the object of the present invention is to reduce the hardness of the intermediate roll from the current HS 78 to 80 to HS 73 to 75 by about HS 5 as a measure against the dent of the work roll, thereby reducing the difference in hardness between the intermediate roll and the work roll. The rolling fatigue life is equal to or more than that of the conventional intermediate rolls even if it is expanded to HS 14 or more, and it can be used as an intermediate roll material for small diameter multi-stage mills such as Zenzimer mills or as an intermediate roll material for 6Hi mill Suitable,
It is to provide a low hardness, long life rolling fatigue strength hardened roll steel.

[0007]

In view of the above situation, the present invention provides a roll material capable of improving the dent resistance of a work roll without reducing the rolling fatigue life, for example, an intermediate roll material. It was made to do.

That is, the present invention is C: 0.40 to 1.00%,
Si: 0.30 to 3.00%, Mn: 0.10 to 2.00%, Ni: 0.30 to 3.00
%, Cr: 2.5-7.5%, Mo: 0.20-3.0%, V: 0.05-
2.00%, Si + Ni ≧ 1.0%, if necessary W: 0.20-3.00
%, The balance being Fe and an alloy being an unavoidable impurity, a low hardness, long life rolling fatigue strength hardened roll steel. The important features of the present invention are Si content and Ni
By setting the content in the optimum range, both low hardness and long life of rolling contact fatigue strength are achieved.

[0009]

The operation of the present invention will be described in detail below. First, the reasons for limiting the composition of the rolled steel according to the present invention will be described in order.

C: 0.40 to 1.00% C is one of the main elements that significantly affect various properties in steel materials and is an important element in the present invention. Since the amount of carbide required for the final product roll is determined depending on the desired wear resistance, grindability, etc., the C amount naturally has an appropriate range. That is, the amount of C is 0.
If it is less than 40%, the hardness becomes too low, while the C content is 1.00.
If it exceeds%, the amount of retained austenite becomes too large, the hardness gradually decreases, and the required hardness cannot be obtained, and the crack resistance and toughness also deteriorate. Therefore, in the present invention, the C content is limited to 0.40% or more and 1.00% or less.

Si: 0.30 to 3.00% Si usually forms a solid solution in the matrix and has the effect of increasing the tempering resistance. On the other hand, since Si is also a deoxidizer, a certain amount of Si is inevitably contained. However, the present invention has more important effects in addition to these effects. That is,
By adding a proper amount of Ni together, the rolling fatigue life of the roll can be significantly improved. In order to exert such effects, it is necessary to add 0.30% or more.
On the other hand, if it exceeds 3.00%, the roll becomes brittle. Therefore, in the present invention, the amount of Si is limited to 0.30% or more and 3.00% or less. It is preferably 0.50 to 2.00%.

Mn: 0.10 to 2.00% Mn improves the hardenability and easily forms a solid solution in the matrix.
Further, unlike the elements described so far, the transformation temperature is lowered, so that the quenching temperature can be lowered. further,
Since it is a deoxidizing element like Si, it is an element that is always contained, and is usually contained at 0.10% or more. On the other hand, if the content exceeds 2.00%, the crack resistance is deteriorated. Therefore, in the present invention, the amount of Mn is limited to 0.10% or more and 2.00% or less.

Ni: 0.30 to 3.00% Ni is an element that is effective for improving the toughness of steel materials and also significantly improves the hardenability. It stabilizes the retained austenite because it produces almost no carbides. Further, in the present invention, the rolling fatigue life is significantly improved by the composite addition with Si. To achieve this effect, 0.30
% Or more must be added. On the other hand, if it exceeds 3.00%, it becomes brittle. Therefore, in the present invention, the Si content is 0.30% or more and 3.00.
% Or less. It is preferably 0.80 to 2.00.

Si + Ni: 1.0% or more If Si + Ni is less than 1.0%, the rolling fatigue life decreases,
The desired performance cannot be obtained. Therefore, in the present invention, Si + Ni
The amount is limited to 1.0% or more.

Cr: 2.5 to 7.5% Cr is a carbide forming element and is an element which is most likely to form a solid solution in the matrix when heated to a high temperature austenite state. 1000
When quenching is performed from a temperature of ℃ or more and tempering is performed at a high temperature, the secondary hardening remarkably appears, which greatly contributes to the improvement of the dent resistance and the wear resistance. If the Cr content is less than 2.5%, such an effect is small. On the other hand, if the Cr content exceeds 7.5%, reticulated carbides become prominent, the toughness decreases and the hardness also decreases. Therefore, in the present invention, the Cr content is limited to 2.5% or more and 7.5% or less.

Mo: 0.20-3.0% Mo is a strong carbide forming element similar to Cr, and has a hardness,
It is an element that affects dent resistance and wear resistance.
Furthermore, it is an element that has a stronger action than Cr with respect to tempering resistance and precipitation hardening. If the Mo content is less than 0.20%, the above-mentioned properties are less effective, while if it exceeds 3.0%, thermal treatment becomes difficult and the microstructure also tends to increase the tendency of eutectic carbides and deteriorate the toughness. Therefore, in the present invention, the Mo content is limited to 0.20% or more and 3.0% or less.

V: 0.05 to 2.00% V is a strong carbide-forming element that combines with C to form a stable carbide. Further, V is an element that is less likely to form a solid solution in the base material than Cr or Mo, and has a strong influence on wear resistance and grindability like Mo. Since V is a strong carbide-forming element as described above, the amount of V is greatly restricted by the amount of C. If the amount of V exceeds 2.00%, the amount of C in the matrix decreases and the desired hardness cannot be obtained. On the other hand, if it is less than 0.05%, the amount of carbide having excellent wear resistance decreases, and the effect on the desired properties is significantly reduced. Therefore, in the present invention, the V amount is limited to 0.05% or more and 2.00% or less in consideration of the C amount.

W: 0.20 to 3.00% W is a carbide-forming element, and is an element which has effects similar to Mo such as being effective in improving dent resistance and wear resistance,
It is usually equivalent to twice the amount of Mo. Therefore, in the present invention, W is an optional additional element added as necessary,
It is an element used by replacing Mo. In order to exert such an effect, when W is added, it is desirable to add 0.20% or more, but if the W amount exceeds 3.00%, eutectic carbides may be greatly developed and toughness may be deteriorated. Therefore, in the present invention, when W is added, its content is 0.
It is desirable to limit it to 20% or more and 3.00% or less. Compositions other than the above are Fe and inevitable impurities.

A roll made of a low hardness, long life rolling fatigue strength hardened roll steel according to the present invention having such a composition, particularly an intermediate roll, has a conventional rolling fatigue life even if the Shore hardness is reduced by 5 degrees or more. The same as or higher than the intermediate rolls of No. 1 and suitable for use as intermediate rolls for small diameter multi-stage mills such as Zenzimer mills and 6Hi mills, low hardness, long life rolling fatigue strength hardened roll steel. is there.

The low hardness, long life rolling fatigue strength quenching roll steel according to the present invention is used as a base material to produce a low hardness, long life rolling fatigue strength quenching roll, but the manufacturing process is completely different from the conventional quenching roll. The same can be used without any limitation. For example, a normal process using an electric furnace-outside furnace smelting apparatus-vacuum degassing / casting apparatus, and an ingot manufactured using an electroslag melting furnace, followed by forging by a press or hammer, annealing, and outer diameter turning. After that, quenching and finishing processes are performed, and the product is adjusted to HS 72-74.

As described above, the low hardness, long life rolling fatigue strength quenching roll steel according to the present invention has a reduced hardness and a dent resistance of the work roll due to the selection of the novel steel composition of the composite addition of Si and Ni. Even if the property is improved, it is possible to improve the rolling fatigue life without deteriorating the most important property in the case of the intermediate roll. Further, the present invention will be described in detail with reference to examples, but this is an example of the present invention and the present invention is not limited thereto.

[0022]

[Examples] With respect to the test pieces made of steels 1 to 13 having the compositions shown in Table 1 in which the amounts of Si and Ni were variously changed, the hardness of the side surface of the test piece (the surface intersecting the rolling surface at 90 °) The hardness (HRC) is measured to detect the abnormal vibration generated when a minute spalling occurs, and the accelerometer detects the change from the vibration during normal rolling to detect the abnormal vibration and automatically detect the device. The total number of rotations when stopped was measured as the rolling fatigue number (N).

[0023]

[Table 1]

The relationship between the amount of Si + Ni (%) and the rolling fatigue number (N) is shown in FIG. 1, and the hardness is changed from HRC 52 to HRC 60 by changing the quenching conditions for sample No. 4 or sample No. 5 in Table 1. Hardness (HRC) and rolling fatigue number (N) when changed in the range of
The relationship between and is shown in the graph in FIG. Note that FIG.
Shore hardness HS is also shown on the horizontal axis.

From FIG. 1, it can be seen that the rolling fatigue number sharply increases when the amount of Si + Ni is 1.0% or more. Also, FIG.
From the above, it can be seen that the rolling fatigue number significantly increases according to the present invention.

[0026]

As described in detail above, according to the present invention,
Even if the hardness of the intermediate roll is reduced from the current HS 78-80 to HS 73-75 and the difference in hardness between the intermediate roll and the work roll is expanded to HS 14 or more as a measure against work roll dents, the rolling fatigue life is Low hardness, long life rolling fatigue strength hardened roll steel that is equivalent to or more than conventional intermediate rolls and is suitable for use as an intermediate roll material for small diameter multi-stage mills such as Zenzimer mills or as an intermediate roll material for 6Hi mills. Could be provided.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of Si + Ni and the rolling fatigue number in a low hardness, long life rolling fatigue strength quenched roll steel according to the present invention.

FIG. 2 is a graph showing the relationship between hardness and rolling fatigue number for a low hardness, long life rolling fatigue strength quenched roll steel according to the present invention and a conventional hot die steel.

FIG. 3 is a graph showing the relationship between the hardness of the intermediate roll and the occurrence rate of the dip flaw (dent) of the work roll.

FIG. 4 is a graph showing the relationship between the hardness difference between the intermediate roll and the work roll and the occurrence rate of the dip flaw (dent) of the work roll.

Claims (2)

[Claims] 1. In mass%, C: 0.40 to 1.00%, Si: 0.30 to 3.00%, Mn: 0.10 to 2.00
%, Ni: 0.30 to 3.00%, Cr: 2.5 to 7.5%, Mo: 0.20 to
3.0%, V: 0.05-2.00%, Si + Ni ≧ 1.0%, balance Fe and alloys which are inevitable impurities, low hardness, long life rolling fatigue strength hardened roll steel. 2. The low hardness, long life rolling fatigue strength hardened roll steel according to claim 1, wherein the alloy further contains W: 0.20 to 3.00% by mass%.