JP2003073767A - Outer layer material of roll for hot rolling and composite roll for hot rolling - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite roll for hot rolling, which is suitable for a post-stand in a hot finishing rolling, and is superior in abrasion resistance and seizure resistance. SOLUTION: This outer layer material has a composition consisting of 2.5-4.0% C, 0.8-2.5% Si, 0.2-1.5% Mn, 1.0-3.5% Cr, 0.5-4.0% Mo, 3.0-7.0% Ni, 1.0-3.5% V, 0.2-1.0% Nb, 0.02-0.2% Al, and 0.020-0.10% B, satisfying Cr/C of 1 or less, and including the balance Fe with unavoidable impurities. The material can further includes one or two selected from, by mass%, 0.10% or less REM (rare-earth metals), and 0.01% or less Ca, in addition to the above composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling composite roll, and more particularly to a hot rolling composite roll suitable for a post stand of hot rolling finish of steel sheet.

[0002]

2. Description of the Related Art In recent years, the progress of hot rolling technology for steel sheets and steel pipes has been remarkable, and along with this, there has been a strong demand for improvement in the properties of the hot rolling rolls used, especially in wear resistance.
In response to such demands for improved wear resistance, the outer layer composition has a composition similar to that of high-speed tool steel, and hard carbides are precipitated to significantly improve wear resistance (high-speed rolls). ) Has been developed and put into practical use.

On the other hand, a grain-cast iron roll containing graphite has been incorporated into a rolling stand or a mill in which seizure of a material to be rolled easily occurs, and hot rolling has been performed. The inclusion of graphite in the hot rolling roll is effective in preventing seizure because graphite is rich in lubricity, however, since graphite tends to promote wear and rough skin of the roll, The conventional grain cast iron roll is not sufficient for the required level of wear resistance and surface roughening resistance, and has a problem.

To solve such a problem, for example, Japanese Patent Laid-Open No.
-287248 discloses that 1.0% to 5.0% V is added to Ni grain cast iron.
Then, a hot rolling roll is proposed in which 2.0 to 10.0% of Mo is added to improve wear resistance. Further, in Japanese Unexamined Patent Publication (Kokai) No. 6-335712, 2.0 to 8.0% is added to Ni grain cast iron.
V of 0.5 to 5% of graphite and 0.2 to 10% of
Rolls for hot rolling have been proposed in which MC type carbides are introduced to improve wear resistance.

However, in recent years, from the viewpoint of improving the quality of rolled products and efficient production, the working environment of hot rolling rolls has become more and more severe due to an increase in rolling speed, an increase in the amount of continuous rolling, and the like. Along with the diversification of types of rolled products to be produced such as high alloying of rolled materials, the demand for hot rolling work rolls has been further increased and diversified. Even with the techniques described in JP-A-1-287248 and JP-A-6-335712, it is difficult to achieve both seizure resistance and wear resistance.

Furthermore, in the hot rolling of steel sheets,
As a rolling work roll, the introduction of high speed steel rolls that have different roll crowns from the grain cast iron rolls has increased the frequency of large drawing and rolling accidents. Although it is inferior, there is no choice but to use a grain cast iron roll with excellent seizure resistance. Furthermore, the demands on the surface quality of steel sheets have become stricter, and Japanese Patent Application Laid-Open No. 1-287248 and Japanese Patent Application Laid-Open No. 6-3357.
V as used in the technology described in Japanese Patent No. 12
Carbide segregation due to addition is becoming a problem. In addition, when only V is added, coarse MC carbides in the form of colonies are crystallized in the form of eutectic with austenite (dendrites), and coarsening of crystal grains promotes roughening and wear of the roll. there were.
On the other hand, also in steel pipe rolling, the alloying of rolled steel types is progressing, and there is an increasing need for preventing seizure on rolling rolls and improving wear resistance.

[0007]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above-mentioned problems of the prior art, and has excellent seizure resistance and wear resistance, and an outer layer material for hot rolling and a composite roll for hot rolling. The purpose is to propose.

[0008]

[Means for Solving the Problems] In order to achieve the above-mentioned problems, the present inventors diligently studied the outer layer composition of a hot rolling roll in order to simultaneously improve seizure resistance and wear resistance. . As a result, when 1 to 3.5% of V is added and a specific amount of Nb is added, MC type carbides become fine particles and coarsening of crystal grains is suppressed, carbide segregation is prevented, wear resistance and rough surface resistance. Have been found to improve. Further, it has been newly found that both the wear resistance and the seizure resistance are remarkably improved by containing Nb and V and further containing B and Al together. Furthermore, it was found that by adjusting the Cr content and the C content so that Cr / C is 1 or less, the amount of low Cr carbide which is less likely to cause seizure and the seizure resistance is further improved. It was

First, the experimental results concerning the composite addition of Al and B, which is the basis of the present invention, conducted by the present inventors will be described.
In mass%, 3.3% C-1.2% Si-0.5% Mn-4.7% Ni-
Using 2.0% Cr-0.9% Mo-1.5% V-0.3% Nb as a base component, a molten metal with Al: 0 to 0.07% and B: 0 to 0.14% was melted, and the outer layer of the roll was formed by centrifugal casting. A ring-shaped test material corresponding to the material was used. Test pieces were taken from these ring-shaped test materials, and a seizure test and an abrasion test were carried out.

In the seizure test, as shown in FIG.
Disc-shaped mating material (material: STBA23, size: 190 mm) that is heated to 850 ° C by a high-frequency heating coil and rotates at 50 rpm
φ) is pressed against a 25 mm thick plate-shaped test piece at 100 kg for 10 s,
As shown in FIG. 3, the seizure time was measured from the torque fluctuation of the mating material during pressure welding, and this seizure time was used as an index of seizure resistance. When the seizure time was zero or as short as 2 s or less, the seizure resistance was evaluated as excellent. The wear test was carried out by the two-disc sliding wear method of the mating material (material: S45C, size: 190 mmφ) and the test piece (size: 60 mmφ). While rotating the test piece at a rotation speed of 700 rpm, heat the mating material to 720 ° C, cool the test piece with water, and set the slip ratio of the test piece and the mating material to 10%.
Rolled in. After the test, the wear loss of the test piece was measured. As for wear resistance, the wear amount of Al, B-free material (reference piece) is used as a reference value, and the ratio of the wear amount of each test piece to the reference value, wear ratio (= (wear amount of each test piece) / (reference value) Amount of wear on one piece))
It was evaluated by.

The obtained results are shown in FIG. From Figure 1, Al
It can be seen that when 0.02 to 0.10% of B is made to coexist with B, seizure resistance and wear resistance are significantly improved at the same time. The present invention was constructed by further studies based on the above findings. That is, the present invention is an outer layer material used as an outer layer of a hot rolling composite roll, the mass%
C: 2.5-4.0%, Si: 0.8-2.5%, Mn: 0.2-
1.5%, Cr: 1.0 to 3.5%, Mo: 0.5 to 4.0%, Ni: 3.
0 to 7.0%, V: 1.0 to 3.5%, Nb: 0.2 to 1.0%, A
l: 0.02 to 0.2%, B: 0.020 to 0.10%, and Cr
/ C is less than 1 and has a composition consisting of balance Fe and unavoidable impurities and a structure containing graphite in an area ratio of 0.6 to 4%, which is excellent in seizure resistance and wear resistance. It is a roll outer layer material for hot rolling, and in the present invention,
In addition to the above composition, it is preferable to further contain, in mass%, one or two selected from REM: 0.10% or less and Ca: 0.01% or less.

The present invention is also a composite roll for hot rolling in which an outer layer and an inner layer are welded and integrated, wherein the outer layer comprises
% By mass, C: 2.5 to 4.0%, Si: 0.8 to 2.5%, Mn:
0.2 to 1.5%, Cr: 1.0 to 3.5%, Mo: 0.5 to 4.0%, N
i: 3.0-7.0%, V: 1.0-3.5%, Nb: 0.2-1.0
%, Al: 0.02 to 0.2%, B: 0.020 to 0.10%, Cr / C of 1 or less, the balance Fe and unavoidable impurities, and a graphite area ratio of 0.6 to 4%. It is a composite roll for hot rolling excellent in seizure resistance and wear resistance characterized by having a structure, and in the present invention, in addition to the composition of the outer layer, further in mass%, REM:
It is preferable to contain one or two selected from 0.10% or less and Ca: 0.01% or less. Further, in the present invention, it is preferable that the inner layer is made of a tough and good castability material such as spheroidal graphite cast iron, worm-like graphite cast iron, or graphite steel.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION First, the reasons for limiting the composition of the outer layer (outer layer material) of the composite roll for hot rolling of the present invention will be explained. In addition,% in the composition is mass%. C: 2.5-4.0% C is an element that is essential for forming hard carbide for improving the wear resistance of the roll by combining with V, Nb, Cr, Mo, and graphite for improving seizure resistance. It is an essential element to be crystallized, and in the present invention, the content of 2.5% or more is required.
On the other hand, if the content exceeds 4.0%, a large amount of brittle carbides will appear and the wear resistance will decrease. Therefore, C is 2.5-
It was limited to the range of 4.0%. In addition, preferably 2.8 to 3.7
%.

Si: 0.8 to 2.5% Si is an element which acts as a deoxidizing agent and reduces the activity of C to facilitate crystallization of graphite.
It is necessary to contain 8% or more. On the other hand, when the content exceeds 2.5%, the above-mentioned effects are saturated, the wear resistance is rather deteriorated, and the effect commensurate with the content cannot be expected, which is economically disadvantageous. From this, Si is 0.8-2.5
Limited to%. In addition, it is preferably 1 to 1.8%.

Mn: 0.2 to 1.5% Mn is useful for fixing S in molten steel as MnS and removing S which impairs wear resistance. It also has the effect of improving hardenability and increasing hardness. In order to obtain such effects, the content of 0.2% or more is required.
However, if the content exceeds 1.5%, it segregates at the solidification interface and embrittles the material. Therefore, Mn is limited to the range of 0.2 to 1.5%. The content is preferably 0.2 to 1.0%.

Cr: 1 to 3.5% Cr is an element which forms a hard eutectic carbide and is contained together with Mo to improve the wear resistance. In the present invention, the content of 1% or more is required. On the other hand, if the content exceeds 3.5%, crystallization of graphite is suppressed and seizure resistance is reduced. Therefore, Cr is limited to 1 to 3.5%.

Mo: 0.5 to 4.0% Mo is an element that forms carbides effective for improving wear resistance without inhibiting crystallization of graphite. When it is contained in combination with V and Nb, MC carbide, which is a tougher and harder carbide, is generated, and it has the effect of significantly improving wear resistance. In order to obtain such effects, the content of 0.5% or more is required. On the other hand, when the content exceeds 4.0%, a large amount of fragile carbide mainly composed of Mo is formed and wear resistance is significantly reduced.
Therefore, Mo is limited to 0.5 to 4.0%. Incidentally, it is preferably 0.6 to 3%.

Ni: 3.0 to 7.0% Ni has the effects of improving the hardenability and increasing the hardness of the material to improve the wear resistance. It also has the effect of promoting crystallization of graphite. Although such an effect is recognized at a content of 3.0% or more, if it exceeds 7.0%, austenite is remarkably stabilized, the amount of retained austenite is increased, and seizure resistance is lowered. Therefore, Ni is 3.0-
The range was limited to 7.0%. In addition, preferably 4.0 to 6.0
%.

V: 1.0 to 3.5% V has the effect of forming hard MC type carbides and improving wear resistance. In order to obtain a wear resistance of a certain level or higher, the present invention requires the content of 1.0% or higher. On the other hand, if the content exceeds 3.5%, seizure resistance is deteriorated, solidification segregation of carbide is promoted, and roll surface quality is deteriorated. Therefore, V is limited to the range of 1.0 to 3.5%.

Nb: 0.2 to 1.0% Nb is a hard MC because it contains V and Mo in combination.
It has an extremely important effect of strengthening the type carbide and further dispersing it in a granular form, suppressing carbide segregation and significantly improving wear resistance. To obtain the above effect, 0.
The content is required to be 2% or more, but if it exceeds 1.0%, the MC type carbides become coarse and solidification segregation occurs, and the roll surface quality deteriorates. Therefore, Nb
It was limited to the range of 0.2 to 1.0%.

Al: 0.02 to 0.20% Al is an element having a function of strongly promoting graphitization and improving the shape of graphite to improve seizure resistance, and in the present invention, seizure resistance of a certain level or more. To ensure 0.
Need to contain more than 02%. On the other hand, if the content exceeds 0.2%, coarse flaky graphite, which is unfavorable to wear resistance, is excessively crystallized and wear resistance is lowered. Therefore, Al is 0.02 to 0.20%
Limited to the range. The content is preferably 0.03 to 0.15%.

B: 0.020 to 0.10% B has an effect of refining and agglomerating graphite, and an effect of suppressing excessive crystallization of graphite by Al,
Also, it has the effect of improving seizure resistance without lowering wear resistance. This effect is 0.02 in the presence of Al.
Although it is recognized that the content is 0% or more, if it exceeds 0.10%, the carbide becomes brittle, the wear resistance is reduced, and the graphite amount is also reduced. Therefore, B is 0.020 to 0.10%
Limited to the range.

Cr / C: 1 or less When the Cr content exceeds the C content, that is, when Cr / C exceeds 1, the Cr concentration in the matrix and the carbide increases, and seizure easily occurs. In addition, the amount of graphite also decreases. Cr
When / C is 1 or less, a carbide having a relatively low Cr concentration is generated, the amount of graphite can be maintained, and a decrease in seizure resistance can be suppressed. Therefore, Cr / C is limited to 1 or less. The Cr / C ratio is preferably 0.85 or less.

Further, in the present invention, one or two of REM and B may be contained within the following range. REM: 0.1% or less REM has the effect of making graphite spherical and finely dispersing it, reducing the notch effect of graphite and further improving wear resistance, and may be contained as necessary. preferable.
Such an effect is recognized when the content is 0.005% or more, but the content exceeding 0.1% reduces the amount of graphite and deteriorates seizure resistance. Therefore, REM should be limited to 0.1% or less. From the viewpoint of graphite spheroidization, RE
More preferably, 30% by mass or more of M is Ce.

Ca: 0.01% or less Ca also has the effect of making graphite spherical and reducing the notch effect of graphite to further improve wear resistance. Such an effect is recognized when the content is 0.0005% or more, but the content exceeding 0.01% reduces the amount of graphite and deteriorates seizure resistance. Therefore, Ca is preferably limited to 0.01% or less.

The balance other than the above components is Fe and inevitable impurities. As inevitable impurities, P: 0.1%
Hereinafter, it is preferable that S: 0.05% or less. In addition, in the outer layer material of the present invention, in addition to the above composition, the area ratio
It has a structure containing 0.6 to 4% graphite. Graphite amount is 0.
If it is less than 6%, the lubricating effect is lowered and the seizure resistance is lowered. On the other hand, if it exceeds 4%, the wear resistance and the rough skin resistance are deteriorated. Therefore, the graphite content is limited to the above range.

In the present invention, the method for producing the outer layer material is not particularly limited, but it is preferable to use the molten metal having the above composition as the outer layer material having a predetermined size and shape by centrifugal casting. Then, it is preferable that the rotation of the mold is stopped and the inner layer material is statically cast during solidification of the outer layer material or after complete solidification to form a composite roll. As a result, the inner surface side of the outer layer material is redissolved and the outer layer and the inner layer are welded and integrated to form a composite roll.

As the inner layer to be statically cast, it is preferable to use spheroidal graphite cast iron, worm-like graphite cast iron, graphite steel or the like which are excellent in castability and mechanical properties. Further, an intermediate layer made of graphite steel or high carbon steel may be provided between the outer layer and the inner layer.
When the roll is manufactured by the centrifugal casting method, the intermediate layer may be centrifugally cast after the centrifugal casting of the outer layer. In addition,
Although the above description has been mainly described for the hot rolling roll of the steel sheet, the present invention is not limited to the hot rolling composite roll of the steel sheet, and to the caliber steel pipe rolling composite roll. It goes without saying that there is no problem even if it is applied. When manufacturing a sleeve-type roll for rolling a steel pipe, centrifugal casting of the outer layer may be followed by centrifugal casting using spheroidal graphite cast iron, black steel, or high carbon steel as the inner layer material.

[0029]

Example 1 A molten metal having the composition shown in Table 1 was melted, and a ring-shaped test material (outer diameter: 250 mm φ, wall thickness: 60 mm) corresponding to a roll outer layer material was produced by centrifugal casting. . The casting temperature is 1320 ° C, and the centrifugal force is a gravity multiple.
It was 160G. After casting, the test material was tempered at a temperature of 420 to 500 ° C. The hardness after tempering was Hs78-83. The ring material E is a ring material made of Ni-grain cast iron which is a conventional material.

Test pieces were sampled from these test materials, and a structure observation, a wear test, and a seizure test were conducted. (1) Structure observation A specimen for structure observation was taken from the ring-shaped test material, the ring-shaped test material section was corroded with an aqueous nitric acid solution, the macrostructure was observed on the test material section, and the segregation of carbides was investigated. did. Segregation was observed when a segregation pattern was observed, and no segregation was observed in other cases. Further, the cross section of the test piece was observed with an optical microscope after polishing, and the area ratio of graphite was measured with an image analyzer. (2) Abrasion test A test piece (size: 60 mmφ) was sampled from a ring-shaped test material, and a wear test was carried out using the two-disc sliding wear method of the mating material (material: S45C, size: 190 mmφ) and the test piece. . While rotating the test piece at a rotation speed of 700 rpm, heat the mating material to 720 ° C, cool the test piece with water, and measure the slip ratio
As 10%, rolling was performed for 120 min while being pressed with a load of 100 kg. After the test, the wear loss of the test piece was measured. As for wear resistance, the wear amount of Al, B additive-free material (ring material No. A;) is used as a reference value, and the wear ratio of each test piece to the reference value, wear ratio (= (wear amount of each test piece ) / (Amount of wear of reference piece)). (3) Seizure test A test piece (25 mm thick plate) was taken from the ring-shaped test material and a seizure test was carried out. As shown in Fig. 2, a disk-shaped mating material (material: STBA23, size: 190mmφ) heated to 850 ° C by a high-frequency heating coil and rotating at 50rpm was pressed onto the plate-shaped test piece for 100 seconds at 100kg. Then, as shown in FIG. 3, the seizure time was measured from the torque fluctuation of the mating material during pressure welding, and this seizure time was used as an index of seizure resistance. When the seizure time was zero or as short as 2 s or less, the seizure resistance was evaluated as excellent.

The results obtained are shown in Table 2.

[0032]

[Table 1]

[0033]

[Table 2]

Each of the examples of the present invention is a roll outer layer material excellent in both abrasion resistance and seizure resistance. On the other hand, in Comparative Examples outside the scope of the present invention, seizure resistance, wear resistance, or both are reduced. Al,
In the comparative example (ring material No. A) containing no B, the wear resistance is excellent, but the seizure resistance is lowered. Also, Cr
/ C exceeds 1, does not contain Nb and B, and is outside the scope of the present invention.
In the comparative example containing Al (ring material No. B), in addition to deterioration of wear resistance, a significant decrease in seizure resistance was observed, and segregation of carbides was also observed. In the comparative example (ring material No. C) which does not contain Nb, Al and B and further contains V which is out of the range of the present invention, seizure resistance is significantly reduced, wear resistance is deteriorated, and segregation of carbides is caused. Admitted. Cr / C is 1
In the comparative example (ring material No. D) containing Nb exceeding the range of the present invention and exceeding the range of the present invention, significant segregation of carbides was recognized in addition to a significant decrease in seizure resistance. The ring material No. E, which is a conventional material, has excellent seizure resistance, but has significantly deteriorated wear resistance. (Example 2) A composite roll having a product barrel diameter of 685 mm and a barrel length of 2380 mm was manufactured by the following procedure.

The molten metal for the outer layer material was cast into a mold rotating with a centrifugal force of 140 G so that the thickness of the outer layer was 120 mm.
After the outer layer solidified, the mold rotation was stopped, the mold was stood and the inner layer material (spheroidal graphite cast iron) was cast to integrally weld the outer layer and the inner layer, and the outer layer was cooled until the surface temperature became 80 ° C or less. After that, the mold was disassembled into a composite roll composed of an outer layer and an inner layer.

The obtained composite roll was subjected to heat treatment (tempering treatment) of heating at 420 to 500 ° C. and then gradually cooling, and the hardness of the outer layer was set to 79 to 83 Hs. After the heat treatment, a test material for chemical composition analysis of the outer layer and a test piece for structure observation were collected from the end of the roll body. For the inner layer, a sample for chemical composition analysis was taken from the center of the roll shaft end. Outer layer of each composite roll,
Table 3 shows the chemical composition of the inner layer.

[0037]

[Table 3]

The obtained composite roll was introduced as a working roll of an F7 stand of a hot finish rolling mill, and 10 medium carbon steels were subjected to test rolling. Note that one of them was subjected to reduction rolling to compare the seizure conditions. Inventive Example (Roll N
It was confirmed that o.1) has extremely good wear resistance that is 1.5 times or more that of the conventional Glen cast iron roll, and has excellent resistance to surface roughening, and that seizure does not occur even in draw rolling. It was

[0039]

According to the present invention, a composite roll having both seizure resistance and abrasion resistance can be manufactured at low cost as a roll for a post-rolling stand of hot rolling of a steel sheet, and the industrially remarkable effect is exhibited. Further, the composite roll of the present invention can be applied as a roll for rolling a steel pipe, which is required to have excellent seizure resistance and wear resistance.

[Brief description of drawings]

FIG. 1 is a graph showing the effects of Al and B on wear resistance and seizure resistance.

FIG. 2 is a schematic explanatory view showing an outline of a seizure test.

FIG. 3 is an explanatory diagram showing the definition of image sticking time.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Satoshi Ozeki             1-1 Kawasaki-cho, Handa-shi, Aichi Made in Kawasaki             Chita Works of Iron Co., Ltd. F-term (reference) 4E016 AA03 CA08 DA03 EA03 EA23                       FA02 FA03

Claims (4)

[Claims] 1. An outer layer material used as an outer layer of a composite roll for hot rolling, wherein C: 2.5 to 4.0%, Si: 0.8 to 2.5%, Mn: 0.2 to 1.5%, Cr: 1.0 in mass%. ~ 3.5%, Mo: 0.5 ~ 4.0%, Ni: 3.0 ~ 7.0%, V: 1.0 ~ 3.5%, Nb: 0.2 ~ 1.0%, Al: 0.02 ~ 0.2%, B: 0.020 ~ 0.10%, and Cr / C is less than 1 and the composition of the balance Fe and unavoidable impurities and graphite are 0.6 to 4% in area ratio.
A roll outer layer material for hot rolling which is excellent in seizure resistance and wear resistance and has a structure that contains it. 2. In addition to the composition, further, in% by mass, RE
M: 0.10% or less, Ca: 0.01% or less selected 1
The outer layer material for hot rolling according to claim 1, wherein the outer layer material for hot rolling contains two or more kinds. 3. A composite roll for hot rolling in which an outer layer and an inner layer are welded and integrated, wherein the outer layer is, in mass%, C: 2.5 to 4.0%, Si: 0.8 to 2.5%, Mn: 0.2 to. 1.5%, Cr: 1.0 to 3.5%, Mo: 0.5 to 4.0%, Ni: 3.0 to 7.0%, V: 1.0 to 3.5%, Nb: 0.2 to 1.0%, Al: 0.02 to 0.2%, B: 0.020 to 0.10 %, And Cr / C satisfies 1 or less, the composition consisting of the balance Fe and unavoidable impurities, and graphite in an area ratio of 0.6 to 4
%, A composite roll for hot rolling which is excellent in seizure resistance and wear resistance and has a structure containing 100%. 4. In addition to the composition of the outer layer, further, mass%
The composite roll for hot rolling according to claim 3, characterized in that it contains one or two selected from REM: 0.10% or less and Ca: 0.01% or less.