JP4392376B2 - Method for producing composite roll for hot rolling - Google Patents

Description

The present invention is a composite roll for hot rolling, in which the outer layer thickness is large and the outer layer / core cross-sectional area ratio is 1.0 or more, the outer layer length is 1.5 times or more of the outer diameter, and the outer layer hardness is 80 Hs or more. those related to the hot production method of a rolling composite roll.

  As a roll for hot rolling, as shown in FIG. 3 (a), heat formed by metallicly joining the outer layer 1 made of a high-speed material around the core material 2 made of cast steel or forged steel by continuous casting. A composite roll for hot rolling is known. Reference numeral 3 denotes a boundary between the outer layer and the core material. In the production of such a composite roll, after the composite roll is formed by continuous casting, the outer layer of the roll is subjected to heat treatment such as quenching and tempering mainly for the purpose of further providing wear resistance, and the hardness of the outer layer is set to 80 Hs, for example. It is given to the extent.

A method of heat treatment for such a composite roll is disclosed in Patent Document 1, for example. The outline of this technology is that after forming a composite roll by metallicly joining an outer layer made of a high-speed material around the core material by continuous casting and overlaying, quenching and cooling are performed at an austenitizing temperature of 900 to 1100 ° C. for 3 hours or more. After heating, during the cooling to 400 ° C. in 1 to 10 hours, by holding at a temperature of 300 to 450 ° C. for 3 hours or more, the temperature difference between the outer layer and the core material becomes small during the expansion transformation of the core material, The tensile stress acting on the outer layer during the expansion transformation of the core material is reduced to prevent the outer layer from being damaged.
JP-A-10-81918

  In general, the outer layer of the composite roll for hot rolling is a component containing a large amount of an alloy element that has high hardness, that is, good hardenability, in order to impart wear resistance as described above. On the other hand, since the core material needs toughness, the alloying elements are kept from entering as much as possible. Accordingly, during cooling during the quenching process, the outer layer expands due to martensitic transformation or bainite transformation in a low temperature region. On the other hand, since the core material does not undergo transformation transformation at a low temperature range, a difference in thermal expansion occurs between the outer layer and the core material at the time of outer layer expansion transformation at a low temperature range. Therefore, an excessive tensile stress acts on the boundary between the outer layer and the core material. The stress increases as the outer layer thickness increases. That is, when the cross-sectional area ratio of the outer layer / core material becomes a certain value or more, the tensile stress in the radial direction in the composite roll for hot rolling becomes larger than the boundary strength, and as shown in FIG. The peeling part 4 is generated and the product shape cannot be secured.

  In the above-mentioned composite roll for rolling, the actual roll having a large outer layer thickness is a roll having a large effective diameter (usable diameter) in the case of having a hole shape, such as a roll of a shape steel, a steel bar and a wire rod. For the above, it is necessary to increase the outer layer thickness. In that case, there is a problem that boundary peeling occurs at the boundary between the outer layer and the core material during quenching cooling.

  When applying the technique disclosed in Patent Document 1 to the heat treatment of the composite roll for hot rolling having a large outer layer thickness, 300 to 300 at the time of quenching cooling disclosed in Patent Document 1 After being held at 450 ° C. for 3 hours or more and then cooled to room temperature and then tempered, in the roll having a large outer layer thickness targeted by the present invention, the outer layer and the core during expansion transformation of the outer layer at 300 ° C. or less The expansion difference increases with the material. In particular, when the temperature is close to room temperature, excessive tensile stress exceeding the boundary strength is generated at the boundary, which is not a practical technique.

Therefore, the present invention provides an outer layer at the time of quenching treatment. The present invention provides a method for producing a composite roll for hot rolling that can prevent troubles of peeling from the boundary of the core material.

  The present invention is a method for producing a composite roll for hot rolling, in which a molten metal composed of a high-speed component as an outer layer material is welded and integrated by a continuous casting overlay method around a core material made of low alloy steel or cast steel. After forming a composite roll material having a cross-sectional area ratio of the outer layer and the core material of 1.0 or more and an outer layer length of 1.5 times or more of the outer diameter by the continuous casting method, in the heat treatment, the austenitizing temperature: 950 After heating at ˜1150 ° C. for 3 hours or more, it is cooled to 200 to 300 ° C. for 1 to 3 hours, followed by tempering several times to obtain an outer layer hardness of 80 Hs or more.

  According to the present invention, it is possible to prevent a peeling trouble from the boundary between the outer layer and the inner layer even in a roll having a large outer layer thickness, and it is possible to produce a rolled composite roll having a large working diameter or a large outer layer thickness.

  In order to solve the above-mentioned problems, the present inventors have actually produced various boundary delaminations in the past, and the outer layer thickness of a roll having the same manufacturing method, composition and size as those of the composite roll for hot rolling targeted by the present invention. The heat treatment method was investigated and examined in detail. As a result, as shown in FIG. 4, the outer layer thickness of the composite roll for hot rolling is large. Specifically, the ratio (S1 / S2) of the outer layer cross-sectional area S1 and the core cross-sectional area S2 shown in FIG. It was found that boundary peeling occurred in any roll during the heat treatment, that is, cooling to quenching at room temperature during quenching and cooling, followed by a temperature raising process of tempering performed thereafter.

Here, even if the cross-sectional area ratio (S1 / S2) between the outer layer and the core is 1.0 or more, a composite roll having a body length of 1.0 times or less of the outer diameter, for example, a roll for rolling steel pipes in the cylinder having short section steel roll or the like, therefore barrel length is short with respect to the expansion of the body length direction which occurs during the quenching cooling, since the core expands, occurs at the boundary because the stress generated is reduced No delamination of the outer layer occurs.

  That is, the stress generated at the boundary is the stress generated by the difference in expansion strain between the circumferential direction and the trunk length direction,

  Further, through various examinations thereafter, it was found that the boundary peeling occurred as a cause of the boundary peeling due to the synergistic action of (1) and (2) described below.

(1) The stress generated at the boundary is a stress generated due to a difference in expansion strain between the outer layer and the core material in the body length direction and the circumferential direction.

  Therefore, when the trunk length is shorter than the outer diameter, the stress generated at the boundary during the outer layer expansion transformation is reduced. Conversely, when the body length is long with respect to the outer diameter, the stress generated at the boundary also increases. This generated stress increases as the outer layer thickness increases.

(2) During heat treatment, that is, quenching and cooling to room temperature, the tempering performed thereafter maximizes the stress generated at the boundary when the difference in expansion between the outer layer and the core material is maximum, and further increases during tempering. Since the temperature rises from the surface of the outer layer when it is warm, thermal stress due to the temperature rise of the outer layer is also applied to the boundary portion, and the generated stress becomes maximum.

The outer layer / core cross-sectional area ratio (S1 / S2) was calculated by the following method. Cross-sectional area S1 of outer layer: (π / 4) * (D ₁ ² −D ₂ ² ), cross-sectional area S2 of core material: (π / 4) * D ₂ ²

  Heating is performed at an austenitizing temperature of 950 to 1150 ° C. for 3 hours or more. However, when the austenitizing temperature is 950 ° C. or less, the solid solution of C that increases the quenching hardness is insufficient. On the other hand, since eutectic carbide partially melts at 1150 ° C. or higher, the temperature range is 950 to 1150 ° C. When the austenite holding time is 3 hours or less, temperature unevenness appears in the outer layer.

  After cooling to 300 ° C. in 1 to 3 hours, tempering is subsequently performed several times. If it is less than 1 hour, residual γ increases. In the subsequent tempering, residual γ remains untransformed. When it exceeds 3 hours, soft pearlite is precipitated inside (inside) the outer layer, and a hardness of 80 Hs or more cannot be secured.

  Tempering promotes martensite or bainite transformation promotion & secondary carbide of residual γ during quenching, stabilizes the structure, and improves hardness and toughness.

  The outer layer material in the present invention is a high-speed component as disclosed in, for example, Patent Document 1, and the reasons for limiting the components of the representative components will be described below.

C: 1.2 to 2.5%
C improves hardenability and increases the base hardness, and combines with Cr, Mo, W and V to form hard carbides and improve wear resistance. If it is less than 1.2%, the amount of carbide is small, the hardness is low, and the improvement in wear resistance is small. On the other hand, if the content exceeds 2.5%, the carbide is coarse or the carbide becomes a mesh, and the carbide or the periphery of the carbide is lost during use, and the wear resistance is deteriorated.

Si: 0.3 to 1.5%
Si affects the castability, and if it is too small, the hot-water flow property deteriorates and causes casting defects and the like. Further, it is combined with oxygen in the molten metal to have a deoxidizing effect, and is added to prevent the occurrence of casting defects such as gas nests. If it is less than 0.3%, there is no effect, and the lower limit is set to 0.3%. Since the effect does not change when it exceeds 1.5%, the upper limit was made 1.5%.

Mn: 0.3 to 1.5%
Mn, like Si, prevents the generation of oxygen and gas defects in the melt. Moreover, MnS is produced | generated, S in molten metal is fixed, and generation | occurrence | production of a harmful defect is prevented. If it is less than 0.3%, there is no effect, and even if it exceeds 1.5%, the effect does not change, so the upper limit was made 1.5%.

Cr: 4.0-10.0%
Cr, like carbon, increases the quenching hardness of the base and increases the hardness. Also, C and carbides are made to increase the overall hardness. If Cr is not 4% or more, the effect is small, and if it exceeds 10.0%, the carbides become coarse, the thermal fatigue characteristics deteriorate, the surface becomes rough during rolling, and the wear resistance deteriorates.

Mo: 3.0 to 10.0%
Mo is an effective element that increases the quenching hardness of the base. Mo is an element excellent in tempering resistance, and forms a high-hardness composite carbide together with Cr and W to increase high-temperature hardness and improve wear resistance. If the amount of Mo is not 3.0% or more, there is no effect and the amount is set to 3.0%. Further, if it exceeds 10.0%, the effect is not changed, and the cost is increased.

W: 0.5-10.0%
W, like Mo, improves the hardenability of the base and produces a hard composite carbide together with Cr and Mo to improve wear resistance. If it is not 0.5% or more, the effect is small, and if it exceeds 10.0%, coarse carbides are produced, which causes rough skin during use.

V: 2.0 to 10.0%
V is an effective element that combines with carbon to crystallize MC-based hard fine carbides and improve wear resistance. The amount is not effective unless it is added at least 2.0% or more. However, if it exceeds 10.0%, the amount of carbide increases too much and the solid solution C amount of the base decreases, so the base hardness becomes low.

The basic components of the outer layer in the present invention are as described above, but in addition to the above-described chemical components of the present invention as other chemical components, depending on the size of the roll to be applied, required usage characteristics of the roll, and the like. Furthermore, the chemical components described below may be appropriately selected and contained.

Ni: 0.1 to 3.0%
Ni has the effect of improving the hardenability of the base and increasing the hardness. In order to improve hardenability, 0.1% or more is necessary. However, if it exceeds 3.0%, retained austenite increases and hardness decreases, so the upper limit was made 3.0%.

Co: 0.1-10.0%
Co has the effect of improving the hardness and strength at high temperatures. This is effective when used under rolling conditions that require high temperature wear resistance and thermal cracking. Addition of 0.5% or more is effective, but its upper limit is made 10.0% or less from the viewpoint of economy.

Nb: 0.1-3.0%
Nb, like V, combines with C to form hard MC carbides and improves wear resistance. Since Nb is added together with V, it is not effective unless it is 0.1% or more. If it is added over 3.0%, MC carbide increases and the base hardness is lowered.

  Next, the present invention will be described in detail with reference to examples.

Tables 1 and 2 show the conditions of the present invention and comparative examples.

  FIG. 1A shows a heat treatment pattern of the present invention, and FIG. 1B shows a heat treatment pattern of a comparative example.

Inventions 1-6
Around the core material made of SCM440, which is a low alloy steel, a molten metal composed of a high-speed chemical component shown in Table 1 is welded and integrated as an outer layer material by a continuous casting overlay method, and the outer layer diameter, boundary diameter, A composite roll having a cross-sectional area ratio between the outer layer and the core and an outer layer length of 1.5 times or more of the outer diameter was formed.

  Subsequent heat treatment is performed after the heat treatment pattern shown in FIG. 1 (a), more specifically, after heating for 5 hours at a quenching temperature of 950 to 1150 ° C. as shown in Table 1 for 3 hours or more. It cooled to -300 degreeC in 1.2 to 2.9 hours, and it inserted again in the heat processing furnace after hold | maintaining at 1-5Hr, or without hold | maintaining, and tempered twice in the range of 500-550 degreeC.

  About the composite roll for rolling manufactured by the said manufacture, the presence or absence of boundary peeling was confirmed visually and outer layer hardness was measured. In the inventive materials 1 to 6, no boundary peeling occurred, and the hardness of the outer layer achieved a value of 80 Hs or more.

Comparative Examples 1-5
Comparative Examples 1-5 are rolls in which outer layer peeling occurred in the past as described above, and Table 1 shows the production results.

  Around the core material composed of SCM440, which is a low alloy steel, a molten steel composed of a high-speed chemical component shown in Table 1 is welded and integrated as an outer layer material by a continuous casting overlay method, and the outer layer diameter, boundary diameter, The cross-sectional area ratio between the outer layer and the core material and the outer layer length are 1.5 times or more of the outer diameter, that is, the composite roll similar to the first to sixth inventions.

  Subsequent heat treatment is performed in the heat treatment pattern of FIG. 1B. Specifically, after heating at a quenching temperature of 950 to 1150 ° C. shown in Table 1 for 5 hours, the heat treatment is performed up to room temperature (50 ° C. or lower). .After cooling in 8 to 3 hours, it was planned to be inserted again into the heat treatment furnace and tempered at 500 to 550 ° C., but any roll was removed from the boundary between the outer layer and the core material in the temperature raising process of tempering. Peeling has occurred.

A heat treatment curve is shown, wherein heat treatment pattern A in (a) is the present invention, and heat treatment pattern B in (b) is a conventional method. FIG. 6 is a diagram showing the relationship between the outer layer / core cross-sectional area ratio and boundary peeling. (A) is sectional drawing of the composite roll for hot rolling, (b) is the schematic which shows the external appearance of boundary peeling. It is a figure which shows the relationship between the generated stress / material strength of a boundary part at the time of quenching cooling, and final temperature.

Explanation of symbols

1. Outer layer 2. 3. Core material 3. Boundary between outer layer and core material Peeling part

Claims (1)

In the manufacturing method of a composite roll for hot rolling, in which a molten metal composed of a high-speed component as an outer layer material is welded and integrated around a core material made of low alloy steel or cast steel by a continuous casting overlay method,
After forming a composite roll material having a cross-sectional area ratio of the outer layer and the core material of 1.0 or more and an outer layer length of 1.5 times or more of the outer diameter by the continuous casting method, in the heat treatment, the austenitizing temperature: 950 After heating at ˜1150 ° C. for 3 hours or more, cooling to 200 to 300 ° C. in 1 to 3 hours, followed by tempering several times to obtain an outer layer hardness of 80 Hs or more, a composite for hot rolling A method for manufacturing a roll.

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