JP2005105296A - Roll external layer material for hot rolling and composite roll for hot rolling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roll external layer material for hot rolling having both of excellent wear resistance and roughening resistance. <P>SOLUTION: The roll external layer material for hot rolling having both of excellent wear resistance and roughening resistance has: a composition comprising 2.5 to 3.5% C, 1.0 to 2.5% Si, 0.3 to 1% Mn, 3 to 5% Ni, 1.5 to 2.5% Cr, 1.0 to 4% Mo, 1.4 to 3.0% V, 0.1 to 0.5% Nb and 0.0005 to 0.2% B, and the balance Fe with inevitable impurities; and a structure which contains secondary carbide particles with the maximum length of 0.1 to 5 μm by 50,000 to 1000,000 pieces/mm<SP>2</SP>at least in part of the matrix. Further, either Al or Ti may be contained therein. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a composite roll for hot rolling, and in particular, to a composite roll for hot rolling suitable for a post-stand of a steel sheet after hot rolling.

  In recent years, the progress of hot rolling technology for steel sheets has been remarkable, and accordingly, there has been a strong demand for improvement of the properties of hot rolling rolls used, particularly improvement of wear resistance. In response to such demands for improving wear resistance, the outer layer composition is similar to that of the high-speed tool steel composition, and hard carbides are precipitated to significantly improve the wear resistance. Is also developed and put into practical use.

  On the other hand, Ni-grain cast iron rolls with excellent seizure resistance are incorporated into rolling stands that tend to cause squeezing of the material to be rolled and seizure of the material to be rolled, for example, post-finishing rolls after hot finish rolling. It is. However, conventional Ni grain cast iron rolls have the problem of poor wear resistance and short roll life. On the other hand, high-speed rolls with excellent wear resistance do not contain graphite, so when a squeeze accident occurs, seizure and coarse thermal shock cracks are generated. There was a problem using it on the stand. For this reason, the hot-rolling post-stage stand is inferior in wear resistance, but it is necessary to use a Ni grain cast iron roll with excellent seizure resistance, and there is a demand for improved wear resistance of the Glen cast iron roll. It had been.

In response to such a demand, for example, Patent Document 1 proposes a hot rolling roll in which 1.0 to 5.0% of V is added to Ni grain cast iron to improve wear resistance. Further, in Patent Document 2, when 2.0 to 8.0% V is added to Ni grain cast iron, and 0.2 to 10% MC type carbide appears in addition to 0.5 to 5% graphite, the wear resistance is improved. A hot rolling roll has been proposed.
JP-A-1-287248 JP-A-6-335712

  Recently, in order to improve the quality and efficient production of rolled products, increasing the rolling speed and increasing the amount of continuous rolling have been aimed at, and the usage environment of hot rolling rolls has become increasingly severe. Furthermore, hot rolling work rolls with excellent wear resistance and seizure resistance as well as excellent surface roughness resistance have been demanded due to high alloying of materials to be rolled and stricter surface quality requirements for rolled products. . However, in the techniques described in Patent Document 1 and Patent Document 2, if the wear resistance is improved, the rough skin resistance tends to decrease, and both the wear resistance and the rough skin resistance cannot be improved. was there.

  An object of the present invention is to advantageously solve such problems of the prior art and to propose a hot rolling roll outer layer material and a hot rolling composite roll excellent in both wear resistance and skin roughness resistance. .

  In order to achieve the above-described problems, the present inventors diligently studied various factors that affect the wear resistance and the rough skin resistance of Ni grain cast iron rolls. As a result, when the wear resistance of the Ni-glen cast iron roll is improved, rough skin occurs, but this rough skin is caused by the scale attached to the base part starting from the MC-type carbide protruding from the base part, while eutectic. It was ascertained that the carbide was caused by unevenness due to the absence of scale. And based on this knowledge, the present inventors suppress the adhesion of scales to the base part by precipitating a large number of secondary carbides on the base part where MC carbides exist, and thereby make the base part convex. I came up with the idea that it could be prevented. Based on this idea, as a result of further investigation, the present inventors can precipitate a large number of secondary carbides in the base part by specifying the combination of the roll chemical composition and the heat treatment. It was found that scale adhesion to the skin was reduced and rough skin could be prevented.

The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.
(1) By mass%, C: 2.5-3.5%, Si: 1.0-2.5%, Mn: 0.3-1%, Ni: 3-5%, Cr: 1.5-2.5%, Mo: 1.0-4% V: 1.4-3.0%, Nb: 0.1-0.5%, B: 0.0005-0.2%, the composition consisting of the balance Fe and unavoidable impurities, and at least a part of the base, the maximum length: 0.1-5 μm A roll outer layer material for hot rolling excellent in wear resistance and surface roughness resistance, characterized by having a structure containing 5000 to 100,000 pieces / mm ^{2 of} secondary carbide.
(2) In (1), in addition to the above-mentioned composition, the roll outer layer material for hot rolling characterized by having a composition containing Al: 0.06% or less and / or Ti: 0.05% or less by mass% .
(3) A composite roll for hot rolling in which an outer layer and an inner layer are integrated by welding, wherein the outer layer is in mass%, C: 2.5 to 3.5%, Si: 1.0 to 2.5%, Mn: 0.3 to 1%, Ni: 3-5%, Cr: 1.5-2.5%, Mo: 1.0-4%, V: 1.4-3.0%, Nb: 0.1-0.5%, B: 0.0005-0.2%, with the balance Fe and A composition comprising inevitable impurities, and a structure including 5000 to 100000 pieces / mm ² of fine secondary carbide having a maximum length of 0.1 to 5 μm in at least a part of the matrix, and wear resistance, Composite roll for hot rolling with excellent resistance to rough skin.
(4) The composite roll for hot rolling according to (3), wherein in addition to the above composition, the composition further contains, by mass%, Al: 0.06% or less and / or Ti: 0.05% or less.
(5) By mass%, C: 2.5-3.5%, Si: 1.0-2.5%, Mn: 0.3-1%, Ni: 3-5%, Cr: 1.5-2.5%, Mo: 1.0-4% V: 1.4 to 3.0%, Nb: 0.1 to 0.5%, B: 0.0005 to 0.2%, or further Al: 0.06% or less and / or Ti: 0.05% or less, the balance from Fe and inevitable impurities A roll outer layer for hot rolling excellent in wear resistance and rough skin resistance, characterized in that a material for a roll outer layer material having a composition as described above is subjected to quenching treatment by heating to 800 to 950 ° C. and further tempering treatment. A method of manufacturing the material.
(6) In (5), the heating time of the said quenching process is 4-40h, The manufacturing method of the roll outer-layer material for hot rolling characterized by the above-mentioned.

  ADVANTAGE OF THE INVENTION According to this invention, the composite roll which combines the outstanding abrasion resistance and the outstanding skin-resistance property can be manufactured cheaply as a roll for post-stage stands of the hot finish rolling of a steel plate, and there exists a remarkable effect on industry.

  The reason for limiting the composition of the outer layer (outer layer material) of the composite roll for hot rolling of the present invention will be described. The mass% in the composition is simply referred to as%.

C: 2.5-3.5%
C is an element necessary for forming hard carbide to improve the wear resistance of the roll by combining with V, Nb, Cr, and Mo, and also necessary for ensuring seizure resistance by crystallization as graphite. In the present invention, the content of 2.5% or more is required. On the other hand, if the content exceeds 3.5%, a large amount of eutectic carbide appears, the MC type carbide becomes coarse, and the rough skin resistance decreases. For this reason, C was limited to the range of 2.5 to 3.5%.

Si: 1.0-2.5%
Si is an element that acts as a deoxidizing agent and increases the activity of C to promote crystallization of graphite. In the present invention, it is necessary to contain 1.0% or more. On the other hand, even if the content exceeds 2.5%, the above-described effects are saturated and the wear resistance is lowered, and an effect commensurate with the content cannot be expected, which is economically disadvantageous. For this reason, Si was limited to 1.0 to 2.5%.

Mn: 0.3-1%
Mn fixes S in the molten metal as MnS and has the effect of removing S that inhibits wear resistance, and also has the effect of improving hardenability, increasing the hardness of the material, and improving wear resistance. . Such an effect is recognized when the content is 0.3% or more. On the other hand, if the content exceeds 1%, segregation becomes remarkable and the material becomes brittle. For this reason, Mn is limited to a range of 0.3 to 1%. In addition, Preferably it is 0.3 to 0.8%.

Ni: 3-5%
Ni has the effect of improving hardenability, increasing the hardness of the material, and improving wear resistance. Moreover, it has the effect of promoting crystallization of graphite. Such an effect is recognized when the content is 3% or more. However, when the content exceeds 5%, austenite is stabilized, the amount of retained austenite is increased, the amount of precipitation of secondary carbide is reduced, and wear resistance is increased. Decreases. For this reason, in this invention, Ni was limited to 3 to 5% of range. In addition, Preferably it is 3.5 to 4.8%.

Cr: 1.5-2.5%
Cr is an element that forms a hard eutectic carbide together with Mo, improves the wear resistance and contributes to the precipitation of secondary carbide. In the present invention, it is required to contain 1.5% or more. On the other hand, if the content exceeds 2.5%, crystallization of graphite is suppressed and seizure resistance is lowered, and a large amount of eutectic carbide is formed, thereby reducing wear resistance. For this reason, Cr was limited to the range of 1.5 to 2.5%. In addition, Preferably it is 1.5 to 2.3%.

Mo: 1.0-4%
Mo is an element that generates carbides that are effective in improving wear resistance without inhibiting the crystallization of graphite. Further, when Mo is contained together with V and Nb, it has the effect of generating MC type carbides which are tougher hard carbides and improving wear resistance. In order to obtain such an effect, the content of 1.0% or more is required. However, if the content exceeds 4%, the MC type carbide becomes prominent, and it becomes difficult to suppress rough skin. For this reason, Mo was limited to the range of 1.0 to 4%. In addition, Preferably it is 1.5 to 3.2%.

V: 1.4-3.0%
V forms a hard MC type carbide and has the effect of significantly improving the wear resistance. In order to ensure wear resistance of a certain level or more, the present invention needs to contain 1.4% or more. However, if the content exceeds 3.0%, the MC type carbide is coarsened, and the rough skin resistance is remarkably lowered. For this reason, in this invention, V was limited to the range of 1.4 to 3.0%.

Nb: 0.1-0.5%
When Nb is contained together with V and Mo, Nb has the effect of forming a solid solution in the MC type carbide to strengthen the MC type carbide and significantly improving the wear resistance. Moreover, Nb has the effect | action which refines | miniaturizes MC type carbide | carbonized_material, and contributes to skin-resistance improvement. In order to obtain such an effect, the content of 0.1% or more is required. On the other hand, when the content exceeds 0.5%, segregation of MC type carbides is promoted and coarsening of MC type carbides is caused, and the rough skin resistance is lowered. For this reason, Nb was limited to the range of 0.1 to 0.5%.

B: 0.0005-0.2%
B has an action of promoting a large amount of precipitation of fine secondary carbides and is an important element in the present invention, and needs to be contained in an amount of 0.0005% or more. On the other hand, if the content exceeds 0.2%, the carbides become brittle and wear resistance decreases, and the amount of graphite decreases. For this reason, B was limited to the range of 0.0005 to 0.2%. In addition, Preferably, it is 0.01 to 0.1%.

  In the present invention, in addition to the above basic composition, Al: 0.06% or less and / or Ti: 0.05% or less can be contained.

Al: 0.06% or less and / or Ti: 0.05% or less
In both Al and Ti, oxides, nitrides, carbides, etc. become the crystallization nuclei of Nb carbide, finely disperse Nb carbide, and finely disperse MC type carbide with the Nb carbide as the core to improve skin resistance. Improve. Such an effect becomes remarkable when Al is contained in an amount of 0.006% or more and Ti is contained in an amount of 0.005% or more. On the other hand, if the content of Al exceeds 0.06% and Ti exceeds 0.05%, fine MC type carbides are densely formed, and a large skin roughness is generated at that portion. Therefore, Al is preferably 0.06% or less and Ti is 0.05% or less. .

  The balance other than the above components is Fe and inevitable impurities.

  Next, the reason for limiting the structure of the outer layer material for hot rolling of the present invention will be described.

The roll outer layer material for hot rolling according to the present invention has a composition in the above-described range, and includes a structure in which at least a portion of the base contains 5000 to 100,000 pieces / mm ^{2 of} secondary carbide having a maximum length of 0.1 to 5 μm. Have The outer roll layer material of the present invention has a structure composed of graphite, eutectic carbide, MC type carbide, and matrix in addition to the fine secondary carbide. Needless to say, a small amount of inclusions with Ti (CN) and MnS may be contained in the structure. The base structure is preferably bainite and / or martensite.

By dispersing the fine secondary carbide in a part of the base, scale adhesion to the base is prevented, and thereby rough skin is suppressed and the rough skin resistance is remarkably improved. In order to obtain such an effect, it is necessary to disperse fine secondary carbide having a maximum length of 0.1 to 5 μm in a part of the base at a density of 5000 to 100000 pieces / mm ² .

If the density of the fine secondary carbide is less than 50000 pieces / mm ² , the effect of preventing the adhesion of scale due to the secondary carbide is insufficient, and the expected rough skin prevention effect cannot be expected. On the other hand, the effect is saturated even if more than 1000000 pieces / mm ² is deposited. Further, if the size of the fine secondary carbide is less than 0.1 μm in the maximum length, the expected effect cannot be expected because the scale adhesion preventing action is small. On the other hand, when the maximum length exceeds 5 μm, the secondary carbide density in the base decreases and the rough skin resistance deteriorates. For this reason, the fine secondary carbide dispersed in a part of the matrix was limited to a maximum length of 0.1 to 5 μm and a dispersion density of 5000 to 100000 / mm ² .

The “part of the base” in the present invention is a region at least 10 μm away from the eutectic carbide. In addition, the “maximum length” of the secondary carbide referred to in the present invention means that the specimen is corroded, observed with a scanning electron microscope (5000 times), the length of each secondary carbide grain is measured, and the maximum value is determined. The maximum length of the carbide grains. The dispersion density of the secondary carbide is determined by observing and imaging the cross section of the outer layer material of the roll with a scanning electron microscope (5000 magnifications) over 2 fields of view, and by using an image analyzer, the unit area of carbide grains having a maximum length of 0.1 to 5 μm The number per unit was measured to obtain the dispersion density (pieces / mm ² ). The area of one visual field is 16 × 16 μm = 256 μm ² .

  The greatest feature of the present invention is that it is a roll outer layer material having a structure in which fine secondary carbide is dispersed in at least a part of the base. Thereby, it becomes the roll outer layer material for hot rolling which has both abrasion resistance and skin roughening resistance.

  Below, the preferable manufacturing method of the roll outer layer material for hot rolling of this invention and the composite roll for hot rolling is demonstrated.

  In the present invention, the method for producing the roll outer layer material is not particularly limited, but it is preferable from the viewpoint of production cost that the molten metal having the above composition is formed into a roll outer layer material having a predetermined size and shape by centrifugal casting.

  When the roll outer layer material is cast by the centrifugal casting method, it is preferable that after the roll outer layer material is solidified or completely solidified, the rotation of the mold is stopped and the inner layer material is statically cast to form a composite roll. Thereby, the inner surface side of the roll outer layer material is redissolved and the outer layer and the inner layer are fused 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 having excellent castability and mechanical properties. An intermediate layer made of graphite steel or high carbon steel may be provided between the outer layer and the inner layer. When a roll is manufactured by the centrifugal casting method, the intermediate layer may be centrifugally cast following the centrifugal casting of the outer layer.

  The outer layer material for hot rolling and the composite roll for hot rolling of the present invention are subjected to heat treatment after casting. The heat treatment is preferably a quenching treatment in which heating is performed at 800 to 950 ° C. and a tempering treatment is further performed. If the heating temperature for quenching is less than 800 ° C., the heating temperature is too low and the dispersion of fine secondary carbides becomes insufficient. On the other hand, when the heating temperature is higher than 950 ° C., the generated secondary carbide is coarsened, and the amount of fine secondary carbide having a desired size is insufficient. For this reason, the quenching heating temperature is preferably set to a temperature in the range of 800 to 950 ° C. The heating time is preferably about 4 to 40 hours from the viewpoint of securing the diffusion / aggregation time of C. The heating temperature is more preferably 850 to 930 ° C. After quenching and heating, air cooling or quenching at a cooling rate of 80 ° C./h or more is preferable from the viewpoint of preventing pearlite transformation.

  The tempering treatment is preferably performed at a temperature of about 400 to 550 ° C. If the tempering temperature is less than 400 ° C., the tempering effect is insufficient from the viewpoint of recovery of the toughness of the base, while if it exceeds 550 ° C., softening occurs, which is not preferable.

  After melting the molten metal having the composition shown in Table 1 in a high-frequency furnace and inoculating with Ca-Si, a ring-shaped test piece (outer diameter: 250 mmφ, wall thickness: 70 mm) corresponding to the roll outer layer material is obtained by centrifugal casting. Casted. The casting temperature was 1320 ° C., and the centrifugal force was 160 G as a multiple of gravity. After casting, quenching treatment and tempering treatment were performed under the conditions shown in Table 2. The hardness after tempering was Hs79-82. Ni-grain cast iron was used as a conventional example (ring-shaped test material No. 14).

Test pieces were collected from the obtained ring-shaped test materials, and subjected to structure observation, wear test, and seizure test. The test method was as follows.
(1) Structure test A specimen for structure observation was collected from a ring-shaped test material, and the presence or absence of graphite was first observed on the cross section of the test material. Subsequently, the cross section of the test piece was subjected to Nital corrosion, and the microstructure was observed with a scanning electron microscope (magnification: 5000 times) to investigate the size and dispersion density of the fine secondary carbide. The number of fields of view was two, and the maximum length in each field: the density of fine secondary carbide particles of 0.1 to 5 μm was determined, and the average value of each field was determined as the dispersion density of the fine secondary carbide in each test material. It was. Note that the area of one field of view is 256 μm ² . An example of the dispersion state of the fine secondary carbide in the present invention is shown in FIG. Further, the amount of graphite (area%) was observed with an optical microscope of 100 times and measured with an image analyzer. The measurement area was 16 mm ² .
(2) Abrasion test Take a test piece (outer diameter: 60mmφ, wall thickness: 10mm) from a ring-shaped test material, and the other material (material: S45C, size: 190mmφ, wall thickness: 16mm) and test piece 2 A wear test was carried out by the disc sliding wear method. While rotating the test piece at 700 rpm. The mating material was heated to 430 ° C., the test piece was water-cooled, the sliding rate between the test piece and the mating material was 10%, and rolled for 90 min while being pressed with a load of 100 kgf (980 N). After the test, the wear loss of the test piece (wear amount) is measured, and the wear resistance is evaluated by the ratio (= (wear amount of Ni grain cast iron) / (wear amount of test piece)) with the wear amount of Ni grain cast iron. did. When the ratio is larger than 1.0, it means that the wear resistance is improved. Furthermore, the surface roughness of the surface of the test piece was visually observed, and a part of large surface roughness was defined in JIS B 0601-2001 using a stylus type roughness meter over the length of 4 mm in the test piece circumferential direction. Rz (10-point average roughness) was determined according to the above.
(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 using a tester of the type shown in FIG. A disk-shaped mating material (material: SUS410, size: 190mmφ, wall thickness: 14mm) heated to 900 ° C and rotated at 150rpm by a high-frequency induction heating coil is used for 10s at a load of 100kgf (980N). Welded. When the surface of the specimen after the test has a burr on the mating material, it indicates “With seizure” (×), and when there is no burr and the surface is worn, it indicates “No seizure” (○). The adherability was evaluated.

  The obtained results are shown in Table 2.

  All of the inventive examples have superior wear resistance compared to the conventional example (Ni-grain cast iron: ring-shaped test material No. 14), and there is no occurrence of seizure or rough skin, and wear resistance and seizure resistance. In addition, it is a roll material with excellent skin resistance. On the other hand, in the comparative example that is out of the scope of the present invention, either the seizure resistance or the rough skin resistance is lowered. The comparative example (ring-shaped test piece No. 13) in which the contents of Mo and V are outside the scope of the present invention is not sufficient in abrasion resistance.

It is a microscope picture which shows an example of the dispersion state of the fine secondary carbide in the example of the present invention (ring-shaped test material No. A). It is explanatory drawing which illustrates the outline | summary of the testing machine used for the seizure test typically.

Claims (5)

% By mass
C: 2.5-3.5%, Si: 1.0-2.5%,
Mn: 0.3-1%, Ni: 3-5%,
Cr: 1.5-2.5%, Mo: 1.0-4%
V: 1.4-3.0%, Nb: 0.1-0.5%,
B: 0.0005-0.2%
And a composition comprising the balance Fe and inevitable impurities, and a structure containing 5000 to 100000 fine carbides / mm ² having a maximum length of 0.1 to 5 μm in at least a part of the base. Roll outer layer material for hot rolling with excellent wear resistance and rough skin resistance. The roll outer layer material for hot rolling according to claim 1, wherein in addition to the composition, the composition further contains, by mass%, Al: 0.06% or less and / or Ti: 0.05% or less. It is a composite roll for hot rolling formed by welding and integrating the outer layer and the inner layer, and the outer layer is in mass%,
C: 2.5-3.5%, Si: 1.0-2.5%,
Mn: 0.3-1%, Ni: 3-5%,
Cr: 1.5-2.5%, Mo: 1.0-4%
V: 1.4-3.0%, Nb: 0.1-0.5%,
B: 0.0005-0.2%
And a composition comprising the balance Fe and inevitable impurities, and a structure containing 5000 to 100000 fine carbides / mm ² having a maximum length of 0.1 to 5 μm in at least a part of the base. Composite roll for hot rolling with excellent wear resistance and rough skin resistance. The composite roll for hot rolling according to claim 3, wherein in addition to the composition, the composition further contains, by mass%, Al: 0.06% or less and / or Ti: 0.05% or less. % By mass
C: 2.5-3.5%, Si: 1.0-2.5%,
Mn: 0.3-1%, Ni: 3-5%,
Cr: 1.5-2.5%, Mo: 1.0-4%
V: 1.4-3.0%, Nb: 0.1-0.5%,
B: 0.0005-0.2%
Or further containing Al: 0.06% or less and / or Ti: 0.05% or less, and a material for a roll outer layer material composed of the balance Fe and unavoidable impurities is heated to 800 to 950 ° C. and quenched. And a method for producing an outer layer material for rolls for hot rolling excellent in wear resistance and rough skin resistance, characterized by further tempering.