JPS5887249A - Wear resistant cast iron for material of roll - Google Patents

Abstract

PURPOSE:To enhance the wear resistance of cast iron for the material of a roll for hot rolling by providing a specified composition consisting of C, Si, Mn, Ni, Cr, Mo, W, V, Co and the balance Fe. CONSTITUTION:This wear resistant cast iron for the material of a roll for hot rolling consists of 2.4-3.5% C, 0.5-1.3% Si, 0.3-0.8% Mn, 0-3% Ni, 2-7% Cr, 2-9% Mo, 0-10% W, 6-14% V, 0-4% Co and the balance Fe with ordinary impurities. This roll material can be manufactured only by casting, treatment under heating and cutting without requiring hot working such as hot compression shaping, and the hardening temp. is relatively low, so it is obtd. at a relatively low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot rolling roll with extremely high wear resistance.

The surface layer of a roll material for hot rolling is required to have wear resistance and heat crack resistance at high temperatures.

Conventionally, as rolls for this purpose, composite cast rolls of chilled alloy or chilled alloy indifinisoto type have been used. The material is, for example, C3.3%, S+0
．． 75%, 10.6%, NiS, 5%, C, 1.6%,
gate. It is an alloy consisting of 0.4% and the rest is hydrogen and ordinary impurities, and its hardness is at most -85. However, in order to improve productivity in the current rolling process, rolls with even higher hardness and wear resistance are being required. Mainly due to residual stress, it is difficult to manufacture conventional rolls by composite casting, in which the used layer and shaft are integrated, so the roll used layer and shaft are made separately, shrink-fitted, and bonded. It is necessary to adopt an assembly roll structure in which both are assembled using methods such as the following. In the case of such an assembly structure, for example, in the case of shrink fitting, a shrink fit stress that tends to stretch the roll ring in the circumferential direction acts on the layer to be used (hereinafter referred to as a roll ring). Furthermore, stress in the same direction as the shrink fit stress is generated on the inner surface of the roll ring due to the rolling load.

This stress is not seen in conventional integral rolls, and due to the occurrence of this stress, assembled rolls have not only high wear resistance but also high tensile strength and toughness in order to withstand these stresses. required.

For example, in order to increase the hardness of cast iron, a method used in chilled castings is to replace C in the composition with carbide, mainly 63C. This carbide is extremely hard compared to the base material, so increasing the amount of this carbide increases the hardness and therefore improves the wear resistance. In contrast, in low-carbon cases, it exists so as to surround primary austenite, which significantly reduces the strength and toughness of the material.

Therefore, the present inventor has completed the present invention as a result of intensive research to eliminate these drawbacks.

The present invention contains C2, 4-3.5%, SiO, 5-1.3%
, 90.3~0.8%, N+O~3%, Cr2~'
t%, bolt. 2-9%, WO-10%, 76-14%, C
This is a wear-resistant cast iron roll material for hot rolling consisting of 0.00 to 4%, the balance 1 and ordinary impurities.

Since the present invention has the above composition, during casting solidification,
(2) Carbide (VC or V2O3 hereinafter referred to as VC) crystallizes directly from the molten metal, and then austenite crystallizes surrounding it. Since this primary VC has a block-like shape, the extent to which it impairs the strength of the material is significantly less than that of other carbides, so it can be used in a cast state to produce VC, which has strengths ranging from A to A, without the need for hot working such as forging. It can be present in large amounts. On the other hand, the hardness of this VC is about Hv 2800, and other carbides in steel (M, :5 C, Ms C, M7 C3, M23
CEi, etc.), which has a hardness of HVI 300 to 1800, and therefore contributes greatly to wear resistance. Furthermore, it is possible to enhance the effect of VC by changing the composition of the austenite surrounding this VC to a structure that can ensure hot strength through heat treatment.

To obtain the cast iron roll material of the present invention, C2.4 to 3.5%
, Si0.5-1.3%, 10.3-0.8%, N+
0-3%, c2-7%, bolt. 2-9%, WO-10%,
The molten metal containing 76 to 14%, C00 to 4%, the balance 5, and impurities is cast into a mold. After solidification and cooling, annealing 1. (perform diffusion annealing if necessary) and perform rough machining, leaving a slight finishing allowance. In this case, since the hardness of this alloy in the annealed state is about 150, processing can be performed satisfactorily. Subsequently, quenching and tempering are performed to obtain a predetermined hardness of about 80 to 95 Hs. This quenching process is usually 1000 to 1
Air quenching is mainly performed at about 100°C, but other cooling means may be used.

In this way, there is no need for hot processing such as forging or hot compression shaping,
It can be manufactured only by casting, heat treatment, and cutting, and furthermore, since the quenching temperature is relatively low at 1000-1100°C, there is no need for a special furnace such as a salt bath quenching furnace. It can be manufactured at low cost.

In order to make the cast iron roll material of the present invention obtained in this way into a hot rolling roll, it is further subjected to finishing processing and fixed to a separately prepared shaft by an appropriate method to form a rolling roll.

Each component of the cast iron roll material of the present invention and its blending ratio will be explained.

As mentioned above, (2) is an element that ensures high hardness of VC.

In order to crystallize primary crystals ■C, approximately 5% V is required in the component range other than ■ of the cast iron roll material of the present invention.
Safe primary vC considering some variation or segregation
At least 6% is necessary to ensure that. ■
Increasing the amount of VC increases the wear resistance, but on the other hand, the workability deteriorates. After the rolls have been used to a certain extent, the worn parts caused by rolling are modified and reused repeatedly, so if the amount of ■ exceeds 14%, the area ratio accounted for by c will exceed approximately 40%. , modification by general-purpose machining by turning becomes extremely time-consuming, and special machining by electric discharge machining or electrolysis is required.

Further, (2) is an element with an extremely high melting point, and as the amount of V increases, it is necessary to raise the melting temperature significantly. In a general melting furnace,
And the temperature that can be melted with general furnace materials (1700℃ or less)
Considering that it is desirable for the work to be able to produce sound castings, the upper limit of the amount of (1) is around 14%.

C combines with the V to form VC, and also combines with other components such as C2, W, 1, h, etc. to form a double carbide,
Furthermore, it is an element that dissolves in solid solution in the base and gives strength to the base. If the C content is low, a large amount of V will need to be added to crystallize VC in the initial product, and the amount of C that becomes VC will increase, so the amount of C dissolved in the matrix will decrease. Insufficient base strength.

descend. In order to ensure the amount of C in the base, the cast iron roll material and component range of the present invention should be as high as C20.7 + 0.1.
The formula 8 x V% holds true, and from these, the lower limit of C is set to 2.4%, and as the content of C increases, the amount of composite carbides increases. This composite carbide is softer than VC but harder than the matrix, so it is effective for wear resistance, but it tends to precipitate as a eutectic at the primary austenite grain boundaries, and if it is in too much, it reduces the strength of the alloy.

Therefore, the upper limit of the C content is approximately 3.57%.

W is an element that imparts softening resistance to the matrix, and imparts temper hardening and high-temperature hardness to the matrix. In order to fully exhibit the effect of W, it is necessary to increase the quenching temperature. However, since the roll material of the present invention is made of high carbon cast iron, it is possible to avoid the appearance of low-melting point double carbides at the initial austenite grain boundaries or the segregation of impurity compounds such as S and P that have even lower melting points. do not have. For this reason, it is not preferable to raise the quenching temperature to 1100°C or higher, as this will cause some of these low-melting compounds to melt and form cavity-like defects.At a low quenching temperature, the amount of W Even if 7% or more of W is added, the effect of increasing the hardness of the base is saturated, but W has the effect of displacing a part of the V in the initial VC and increasing the specific gravity of the VC. It has the effect of preventing floating segregation of
It is preferable that long castings contain some amount of carbon. However, in excess, W increases the amount of eutectic carbides that crystallize at the austenite grain boundaries and decreases the strength, so the above 10%
shall be. - Also, the effect of W on hardness and wear resistance can be replaced by an appropriate amount of W, and (in small-sized castings, there is no fear of VC floating, so the lower limit + 10% may be sufficient.

Bolt. is an element having the same effect as W, and increases the hardenability of the matrix more than W, especially when the hardening temperature is low. The roll material of the present invention is used as a rolling roll, but even the smallest roll used for wire rolling is large compared to high-speed tool steel. Since the roll material is a cast product, the presence of local brittle phases cannot be avoided compared to a forged product. Therefore, performing strong quenching such as oil quenching or water quenching has a high risk of causing cooling cracks. From this point of view, when cooling from the quenching temperature, it is necessary to take a cooling rate of about 10 to 45 minutes during what is called a half-cooling period to reach an intermediate temperature between the quenching temperature and room temperature. In order to obtain the quenched hardness of the base even under such conditions and to obtain softening resistance.

The content of is preferably at least 2% or more. If the content of -〇 is increased, the same bamboo leaf-like eutectic carbides as mentioned in the section of C tend to increase at the primary austenite grain boundaries even in the same C1■ state, so the upper limit is about 9%.

N+ is considered to be an undesirable element in hot work tool steels, especially high-speed tool steels, as it makes the hardenability unstable, but this element significantly improves the hardenability of the matrix. When dealing with large objects that have a slow quenching speed, such as the roll material of the present invention, it actually helps to ensure the quenching hardness, and adding up to about 3% of N+ is sufficient without substantially reducing the tempering softening resistance. Demonstrate its effectiveness. Moreover, excessive addition will result in unstable quenching hardness. Therefore, 3% or less of the N number is added depending on the need for hardness adjustment.

% increases the transformation point of the base, increases the resistance to temper softening, and increases the solid solubility of carbides in the quenched base, increasing secondary hardening, so it is effective to add up to about 4%. However, if added in excess, hardenability deteriorates, making it impossible to obtain sufficient hardness for the roll used in the present invention. Therefore, it is added up to a maximum of 4% especially for applications requiring softening resistance, that is, particularly high-temperature wear resistance.

C7 is W, M. It is an element that has the role of imparting hardenability to the base matrix and increasing tempering hardness and high-temperature hardness. If the amount added is less than 2%, the effect will not be sufficient, and if it exceeds 7%, it will be saturated and addition of more than that will not be effective.

Sl is V, M in solution. It has the effect of preventing oxidation and improving swirl flow during casting. Addition amount is 0.5%
The above is enough to show the effect. When the amount of Si added is increased, the strength of the base is lowered, and it is preferable to add Si in an amount that does not exceed 1.3%, which has the effect of locally forming eutectic VC.

1 has a structure that prevents oxidation in the molten metal and fixes harmful S mixed in from raw materials and furnace materials into harmless iS. It is added in an amount of 0.3 to 0.8%, which is a range suitable for use in ordinary cast iron.

A photograph of the microscopic structure of this roll material at a magnification of 200 times is shown in the attached figure. In the figure, the white lump-like material is VC, the white bamboo leaf-like material is composite carbide, and the black part is the base.

Next, examples of the present invention will be shown.

Example I C3.1%, Si0.9%, r? 0.45%, c, 3.
9%, N06.5%, W6%, ■9.3%, Gol, 4
% and remainder ``.

A molten metal containing ordinary impurities was cast and quenched at 1050°C. The hardness of the roll material alloy of the present invention is 8
7-88F-1SC.

The thus obtained roll material of the present invention is fixed to a shaft to produce a wear-resistant cast iron roll for hot rolling.

Example 2 C2, 7%, Si 1.0%, M, 0.43%, c, 4.
0%, gate.

A molten metal consisting of 7.0% W, 4% W, 860% Co, 2.6% Co, and the balance 1 and ordinary impurities was treated in the same manner as in Example 1 to obtain a roll material alloy of the present invention. This hardness is 84
~85)-1sC.

A test example showing the effect of the wear-resistant cast iron roll using the roll material of the present invention shown in Example 1.2 above and its results will be shown below.

Test Example Test No. 1 is the result of measuring the rolling tonnage per caliber and the wear amount of the caliber when finishing the wire with a roll using the roll material of the present invention obtained in Example 1, as shown in the table below. show. Test No. 2 is the results of measuring the rolling tonnage per caliber and the wear amount of the caliber when the roll material of the present invention obtained in Actual I & Example 2 was used before wire finishing, and the results are shown in the table below. Indicated by

lead, as a control, C3.3%, Si0.75%, 10
．． 6%, N1.5%, ci, 6%, bar. A roll using a conventional roll material consisting of 0.4% and the remainder 5 and ordinary impurities was used for the same purpose, and the same test was conducted.The values obtained by conducting the same test are also shown for test number 1.2.

As is clear from the above test examples, the roll material of the present invention exhibits superior wear resistance compared to conventional roll materials.

[Brief explanation of the drawing]

The drawing is a photograph of the microscopic structure of the abrasion-resistant roll material of the present invention at a magnification of 200 times. Patent applicant Hitachi Metals, Ltd.

Claims (1)

[Claims] 1, c 2.4-3.5%, S; 0.5-4.3%, I
-LO, 3-0.8%, N10-3%, c, 2-7
%,gate. 2-9%, wO-IO%, 76-14%, C0
A wear-resistant cast iron roll material for hot rolling, characterized in that it consists of 0 to 4%, the balance 6 and ordinary impurities.