JPH06330229A - Roll material for hot rolling excellent in surface roughening resistance - Google Patents

Abstract

PURPOSE:To produce a roll material for rolling of high performance excellent in surface roughening resistance and combining good wear resistance with cracking resistance by specifying the compsn. constituted of C, V, Cr, Co, Mo, W and iron. CONSTITUTION:This roll material excellent in surface roughening resistance is the one contg., by weight, 0.8 to 1.5% C, 3 to 6% V, 3 to 7% Cr and 5 to 10% Co and furthermore contg. 1 to <3% of at least one kind of Mo and W, and the balance substantial iron, and MC type carbides are finely deposited to improve its wear resistance and furthermore to improve its surface roughening resistance and cracking resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is applied to steel strip rolling rolls such as hot strip mills, and has excellent resistance to surface roughening, especially in hot rolling, and has both abrasion resistance and crack resistance. The present invention relates to a rolled material for rolling.

[0002]

2. Description of the Related Art Conventionally, as a roll material of this type, it has appropriate wear resistance and crack resistance, and especially from the viewpoint of resistance to roughening under a use condition of a large heat load during rolling, C: 2 to
High-chromium cast iron containing 3.2%, Cr: 12 to 18%, and Ni and Mo in an amount of 2% or less each is widely used (see Iron and Steel Basic Research Group “Abrasion of Steel Materials” P16).

Further, in JP-A-58-87249, C: 2.4 to 3.5%, V: 6.1 to 14% C
A wear-resistant cast iron roll material containing alloy elements of r, Mo, W, and Co was tried, and the wear resistance was improved. Further, in Japanese Patent Application No. 2-152576 proposed by the present applicant, it was attempted to improve the crack resistance by limiting the amount of carbide by setting C to 1.5 to 2.4%.

[0004]

Abrasion resistance, crack resistance and surface roughening resistance are the most important properties required for rolling rolls. If the wear of the roll is small, the plate thickness accuracy of the rolled steel product will be improved and the frequency of roll replacement will be reduced to improve the work efficiency. On the other hand, when the crack resistance is insufficient, cracks occur due to heat and mechanical load during use, which causes a serious trouble, interrupts the rolling operation, and eventually damages the rolling equipment. In addition, in order to improve the surface quality of rolled products, it is required that the roll surface has a beautiful resistance to roughening. Therefore, it is strongly desired to combine the above-mentioned respective characteristics. In this respect, compared with high chromium cast iron, JP-A-58-87249 and Japanese Patent Application No.
In all of the roll materials disclosed in No. 152576, the carbides that crystallize out are hard and the hardness after quenching is also high, so that the wear resistance is extremely good. Furthermore, Japanese Patent Application No. 2-15257
In No. 6, by setting C to 1.5 to 2.4%, the amount of carbide was limited and the crack resistance was improved.

However, in the case of being subjected to rolling, the oxide film formed on the roll surface was partially peeled off and rough skin was generated especially under use conditions where a large heat load was applied during rolling. Along with this, the roll surface was also transferred to the rolled product, which impaired product quality and forced replacement even though the roll was less worn. Thus, the rough surface of the roll hinders the quality and productivity of rolled products.

[0006] Therefore, it is an object of the present invention to provide a high-performance rolling material for rolling which is particularly improved in surface roughening resistance in hot rolling and has good wear resistance and crack resistance. Is.

[0007]

In order to solve the above-mentioned problems, the rolling material of the present invention has a weight ratio of C: 0.8 to 1.5% V: 3 to 6% Cr: 3 to. 7% Co: 5-10% Further, a hot rolling roll having excellent resistance to surface roughening, characterized by containing at least one of Mo and W in an amount of 1% or more and less than 3%, and the balance being substantially iron. Material.

[0008]

The reason for limiting the C content to the above range of 0.8 to 1.5% is as follows. That is, C is the lower limit value 0.8
If it is less than 0.1%, hard carbide is scarcely crystallized and wear resistance is significantly deteriorated, and improvement in performance cannot be expected. On the other hand, the upper limit of 1.5
When it exceeds%, wear resistance is improved but carbides are increased, and coarse carbides are formed and aggregated at grain boundaries.
This is released from the roll surface due to thermal fatigue during rolling, resulting in partial peeling of the oxide film generated on the roll surface from this as the starting point, and especially under large use conditions of heat load during rolling. It cannot be expected to improve the rough skin resistance, which is the main purpose of.

MC containing V is extremely hard among carbides
It is selected in balance with C to crystallize the type VC carbide. In particular, in the case of the material of the present invention, it is important to utilize this granular and minute VC carbide to improve wear resistance and to directly crystallize this carbide as a primary carbide from the molten metal to control the structure. . That is, C:
In the range of 0.8 to 1.5%, if V is less than 3%, which is the lower limit value, hard VC carbides do not crystallize and are solid-dissolved in the matrix structure. On the other hand, when the upper limit value is 6% or more, carbides increase and the crack resistance and the rough skin resistance are impaired.

The reason why Cr is limited to 3 to 7% is as follows. Cr easily bonds with C and easily forms coarse M ₇ C ₃ -based eutectic carbides at the grain boundaries, but in the roll material of the present invention, it suppresses coarse carbides that result in rough skin, and with V A small amount of MC carbide was formed, and a part of it was also dissolved in the matrix to increase the hardness of the matrix and improve the wear resistance. That is, 3% or more is indispensable in order to form a hard MC carbide and also increase the hardness of the matrix, and it must be 7% or less in order to suppress the crystallization of coarse carbide.

The reason why Co is limited to 5 to 10% will be described. Most of Co dissolves in the matrix to improve its strength,
Especially, it has a remarkable effect at high temperature. By the way, in the case of having free MC type carbide, the wear resistance of the carbide itself is extremely high, but if the surrounding base does not have the wear resistance, the surrounding wears and only the carbide remains and the skin naturally becomes rough. Therefore, it is indispensable to add Co to improve the hardness and strength of the matrix to provide wear resistance. As a lower limit for practically obtaining the effect, Co is set to 5% or more. On the other hand, since Co is extremely expensive, the upper limit for practically remarkable effect by addition is limited to 10% or less in relation to the cost.

It is useful to add appropriate amounts of Mo and W as other main alloying elements to improve roll performance. Both of them are likely to bond with C like Cr, and in the roll material of the present invention, a part thereof forms MC carbides and a part of them also forms a solid solution in the matrix to improve the hardness of the matrix. The effect is remarkable in. The lower limit value at which this effect is practically recognized is 1% or more. However, since it is easy to crystallize a coarser carbide than Cr, the upper limit is set to less than 3% so as not to impair the rough skin resistance under the use condition of a large heat load, which is the greatest feature of the present invention material.

In addition, due to the deoxidation of the molten metal and the like,
Useful elements Si and Mn are 0.5% each
The impurities, such as P and S, may be contained as long as they are 0.03% or less contained in ordinary castings, and they do not impair the effects of the present invention.

[0014]

EXAMPLE As a working example of the present invention, a work roll for a hot strip finishing mill was manufactured. The melting is performed in a high frequency induction furnace, the casting is performed by the continuous casting method disclosed in Japanese Patent Publication No. 44903/44, and the core material is forged steel (SCM44).
0) was adopted as a composite roll. After the casting, the heat treatment was annealing, quenching and tempering.

Table 1 shows concrete manufacturing qualities of the conventional example and the embodiment of the present invention. A micrograph of the metal structure of the roll material is shown in FIG. 1 for the present invention material, and FIGS. 2 and 3 for the conventional example. In all the photographs, the white portion is carbide. In each of the conventional examples, the amount of carbides is large, and in the conventional example disclosed in Japanese Patent Application Laid-Open No. 58-87249 shown in FIG. 2, a large amount of network-like agglomerated carbides are present at the grain boundaries. In the conventional example disclosed in Japanese Patent Application No. 2-152576, rod-shaped carbides are recognized although the amount of carbides is relatively smaller than that in FIG. On the other hand, in the material of the present invention shown in FIG. 1, it is clearly confirmed that only extremely fine granular carbides are uniformly dispersed as described above.

The conventional example and the embodiment of the present invention shown in Table 1 were used in a finishing pre-rolling mill having a large heat load, and the results are shown in Table 2. The roll of the present invention has a shallow roll crack caused by a trouble during use, has extremely good wear resistance, and has a significantly increased rolling durability until the peeling of the oxide film on the roll surface occurs, and Improves skin roughness. It is clear that this significantly reduces the frequency of replacement with new rolls and significantly improves the productivity of the rolling operation.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

EFFECTS OF THE INVENTION By applying the present invention to a steel rolling roll, it becomes possible to stably supply a high-performance roll having significantly improved wear resistance and crack resistance, and at the same time, the surface roughening resistance is improved. It has improved the quality of rolled products and the productivity and economic efficiency of rolling operations.

[Brief description of drawings]

FIG. 1 shows a micrograph of a metal structure of a roll material disclosed in the present invention at 100 times magnification.

FIG. 2 is a micrograph of a metal structure of a roll material disclosed in JP-A-58-87249 at 100 times magnification.

FIG. 3 is a micrograph of a metal structure of a roll material disclosed in Japanese Patent Application No. 2-152576 at 100 times magnification.

Claims (1)

[Claims] 1. C: 0.8 to 1.5% V: 3 to 6% Cr: 3 to 7% Co: 5 to 10% by weight% Further, at least one of Mo and W is 1% or more, 3 %, And the balance is substantially iron, which is a roll material for hot rolling having excellent resistance to surface roughening.