JPH07207411A - High speed steel composite roll and its production - Google Patents

Abstract

PURPOSE:To provide a high speed steel composite roll formed by welding and integrating an inside layer consisting of a cast steel material having toughness to the inside surface of an outside layer consisting of a high speed steel material and to provide a production method therefor. CONSTITUTION:The outside layer consisting of the high speed cast steel material contg. 1.0 to l.9wt.% carbon is centrifugally cast. The melt of a cast steel material for forming the inside layer contg. 0.4 to 0.8wt.% carbon is kept at the temp. of the inside surface of the outside layer or above and is cast on the inside surface of the outside layer when the temp. of the inside surface of the cast outside layer is at the solidification temp. of the cast steel material described above after the outside surface of the outside layer solidifies.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite roll in which an inner layer made of a cast steel material having high toughness is welded to the inner surface of an outer layer formed of a high-speed cast iron material, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, high-speed composite rolls have been manufactured in which an outer layer, which is a layer used for rolling, is formed of a high-speed cast iron material having excellent wear resistance and an inner layer is formed of a steel material having excellent toughness. As the high-speed cast iron material, for example, a material having the following chemical composition (wt%) is disclosed in JP-A-4-176840.

C: 1.0-3.0%, Si: 0.1-2.0
%, Mn: 0.1 to 2.0%, Cr: 3.0 to 10.0%, M
o: 0.1 to 6.0%, W: 1.5 to 10.0%, V or Nb, a total of one or two kinds: 3.0 to 10.0%, the balance being substantially Fe. The high speed cast iron material containing Mo, W and V is It has excellent properties at high temperature, and has high hardness crystallized carbides such as VC, M ₂ C, and M ₆ C in its structure, so it has extremely good wear resistance and rough skin resistance. Suitable as an outer layer material of a composite roll.

Conventionally, as a method of manufacturing a composite roll, after an outer layer made of a high alloy wear resistant material is centrifugally cast, a molten metal for an inner layer made of a tough cast iron material is cast on the inner surface of the outer layer and the inner layer is welded to the inner surface of the outer layer. There is a way to do it. When the HSS-based composite roll is cast by such a method, if the inner layer solidifies before the inner surface of the outer layer, shrinkage cavities occur at the boundary between the outer layer and the inner layer. Therefore, in order to secure the weldability between the outer layer and the inner layer, a material having a lower melting point than the high-speed cast iron material forming the outer layer is required as the inner layer material, and normally ductile cast iron or graphite steel is used.

On the other hand, in order to form the inner layer of the composite roll with a tougher material, an inner layer member made of a low alloy steel for machine structure such as SCM material is manufactured in advance, and is disclosed in JP-A-60-
According to the continuous casting overlay method disclosed in Japanese Patent No. 180660, an outer layer is continuously cast on the outer peripheral surface of the inner layer, or HSS powder is applied to the outer peripheral surface of the inner layer by hot isostatic pressing (HIP). The outer layer is formed by sintering and integrating.

[0006]

However, in order to carry out the continuous casting surfacing method and the HIP method, a special device is required, and such a device is expensive. For this reason, there is a demand for a method of manufacturing a tough composite roll having an inner layer by conventional compounding by casting. The present invention has been made in view of the above problems, and an object thereof is to provide a high-speed composite roll in which an inner layer made of a cast steel material having toughness is integrally welded to the outer surface of a high-speed material and a suitable manufacturing method thereof. To do.

[0007]

The composite roll of the present invention comprises:
The carbon content is 0.4 to 0.9 wt% on the inner surface of the outer layer made of the high-speed cast iron material having the carbon content of 1.0 to 1.9 wt%.
The inner layer made of cast steel is welded by centrifugal casting. The method for producing a composite roll of the present invention comprises centrifugally casting an outer layer made of a high-speed cast iron material having a carbon content of 1.0 to 1.9 wt% to solidify the outer surface of the outer layer, and then to cast the outer layer. When the inner surface temperature is equal to or higher than the solidification temperature of the cast steel material for forming the inner layer, the cast steel material having a carbon content of 0.4 to 0.8 wt% is cast into the outer layer inner surface as the outer layer inner surface temperature or more,
This is a method of forming the inner layer by welding on the inner surface of the outer layer. On this occasion,
When the outer layer is thick, the chemical composition (wt%) is used as the outer layer material.
, C: 1.0 to 1.5%, Si: 0.2 to 1.5%, M
n: 1.5% or less, Cr: 2.0 to 6.0%, 2 × Mo +
It is preferable that W: 3.0 to 7.0%, V: 2.0 to 4.0%, and the balance being substantially Fe.

[0008]

When the inner surface temperature of the cast outer layer is equal to or higher than the solidification temperature of the cast steel material for forming the inner layer, that is, the solidus line (solidification end temperature), the casting temperature of the cast steel material is equal to or higher than the inner surface temperature of the outer layer. It is possible to solidify the inner layer made of a cast steel material in which the unsolidified portion of the inner surface of the outer layer is melted on the inner surface of the solidified outer layer. Therefore, shrinkage cavities do not occur at the boundary between the outer layer and the inner layer, and good welding can be obtained.

Further, since the carbon content of the cast steel material for forming the inner layer is regulated to 0.4 to 0.8 wt%, the cast steel material has a higher solidification temperature than the outer layer material. After the solidification temperature difference of 90 ° C. or less is reached and a considerable portion of the molten outer layer material is solidified, the cast steel material can be cast. Further, even if the high alloy component of the outer layer is mixed in the molten cast steel material, the formation of primary carbide is small, and the toughness is not significantly deteriorated as in the case of casting graphite steel or ductile cast iron.

Further, by using the outer layer material according to the third aspect, even when the outer layer thickness is more than 140 mm, the segregation of Mo, W and V can be suppressed and the outer layer can be effectively used. Can be used.

[0011]

EXAMPLES As the outer layer material used in the present invention, a high-speed cast iron material containing 1.0 to 1.9 wt% C,
Any one can be used. The reason for limiting C is that if it is less than 1.0%, the amount of carbides such as Cr, Mo, W, and V decreases, and the wear resistance decreases, while if it exceeds 1.9%, it is a cast steel for forming the inner layer. The difference in freezing point from the material becomes excessively large, and defective welding tends to occur. Below, an example of the composition of the outer layer material and the reasons for the limitation are described. However, the reason for limiting C is omitted because it is as described above.・ Outer layer high-speed cast iron material composition example (wt%) C: 1.0 to 1.9%, Si: 0.2 to 1.5
%, Mn: 1.5% or less, Cr: 2.0 to 8.0%, 2Mo
+ W: 3.0 to 14%, V: 2.0 to 8.0%, balance substantially F
e.・ Reason for component limitation Si: 0.2 to 1.5% If less than 0.2%, deoxidizing action and melt flowability are insufficient, while if over 1.5%, hardenability deteriorates and the material becomes brittle. Become.

Mn: 1.5% or less Mn combines with S to form MnS, prevents brittleness due to S, and improves hardenability and wear resistance. If it exceeds, the material becomes brittle. Cr: 2.0 to 8.0% Cr forms a solid solution in the matrix and improves hardenability, and at the same time, a part of the Cr combines with C to form a carbide, which improves wear resistance. If it is less than 2.0%, such action is insufficient,
On the other hand, if it exceeds 8.0%, its action is saturated and the material becomes brittle.

2Mo + W: 3.0 to 14% Mo and W combine with C to form M ₂ C type or M ₆ C type carbides, which improve wear resistance and part of them are contained in the matrix. It forms a solid solution and contributes to secondary hardening. Since Mo has twice the effect of W, the component range is defined by the sum of twice the Mo content and the W content (2Mo + W). 2Mo +
If W is less than 3.0%, such an effect is too small, and it is preferable to contain W in an amount of 6.0% or more. On the other hand, if it exceeds 14%, the amount of carbides increases, the toughness decreases, and
Retained austenite is stabilized by Mo and W dissolved in the matrix, and it is difficult to obtain high hardness.

V: 2.0 to 8.0% V combines with C to form a high hardness MC type carbide, which improves the wear resistance. If it is less than 2%, the amount of carbide is small and the wear resistance is insufficient. On the other hand, if it exceeds 8.0%, it becomes difficult to prevent segregation even if the cast wall thickness is suppressed to 140 mm or less. In addition to the above alloy components, the balance is substantially formed of Fe. However, S and P, which are impurity elements, make the material brittle, so it is preferable that the content be as small as possible, and both are preferably kept to 0.1% or less.

Within the above composition range of the outer layer, segregation can be relatively easily prevented by adjusting the casting temperature up to a thickness of the outer layer (when cast) of about 140 mm.
When a thick outer layer having a thickness of 50 mm or more is cast, the segregation cannot be prevented even by adjusting the casting temperature. In this case, C: 1.5% or less, Cr: 6.0
% Or less, 2 × Mo + W: 7.0% or less, and V: 4.0% or less, it becomes possible to cast even a thick wall of about 200 mm without causing segregation. In addition, since the content of high alloy components is suppressed,
The amount mixed into the inner layer is also reduced, and the toughness of the inner layer is improved. The reasons for limiting the upper limits of the above components are as follows.

When C exceeds 1.5%, the solidification temperature range (the temperature difference between the liquidus and solidus) is widened, and the alloy components tend to be biased during solidification. On the other hand, Cr, Mo and W
Has a low content in the primary crystal (initial solidification part), tends to be concentrated in the final solidification part, and is easily segregated. Therefore, from the viewpoint of preventing segregation, it is preferable to keep the content below the above content. Further, V crystallizes as primary austenite with MC type carbide having a low specific gravity, but when it exceeds 4.0%, the difference in specific gravity between primary crystals (austenite and MC type carbide) and the unsolidified molten metal becomes large, Segregation easily occurs due to gravity or centrifugal force.

The state of segregation is such that the high alloy component is formed in layers in the form of carbide on the inner peripheral surface side of the outer layer. However, when such a segregation layer is formed, the outer layer, which is the layer used for rolling, is formed. The effective use layer is reduced, and in the case of the cylindrical composite roll for H-section steel rolling in which the H-section steel is roll-formed on the side surface of the roll, rolling defects on the forming surface are caused. On the other hand, the cast steel material for forming the inner layer used in the present invention is a cast steel material containing 0.4 to 0.8 wt% of C,
Any one can be used. The reason for limiting C is that if it is less than 0.4%, the freezing point becomes too high, so that defective welding tends to occur. On the other hand, if it exceeds 0.8%, the C content of 0. If it is 9% or more, net-like cementite appears during casting or high temperature heat treatment, resulting in significant strength deterioration. An example of the composition of the cast steel after the inner layer welding and the reasons for limiting its components are shown below. The composition of the cast steel material before casting may be appropriately determined in consideration of the amount of penetration from the inner surface of the outer layer.・ Composition example of inner layer cast steel after welding (wt%) C: 0.4 to 0.9
%, Si: 0.2 to 1.0%, Mn: 0.2 to 1.0%, N
i: 0.2 to 2.5%, Cr: 0.4 to 2.5%, Mo: 0.1
~ 1.0%, W: 2.0% or less, V: 2.0% or less,
Remainder Substantially Fe. · Component limiting reason C: 0.4 to 0.9% The lower limit is limited by the C content of the original hot water, and the upper limit is specified to avoid the formation of net-like cementite.

Si: 0.2 to 1.0% If it is less than 0.2%, the deoxidizing action is insufficient, while if it exceeds 1.0%, the material becomes brittle. Mn: 0.2 to 1.0% Mn combines with S to form MnS and has an action of preventing embrittlement due to S, but if it is less than 0.2%, such action is insufficient, while 1.0 If it exceeds%, the material becomes brittle.

Ni: 0.2-2.5% Ni increases hardenability and improves toughness. 0.2
If it is less than 2.5%, the action is insufficient, while if it exceeds 2.5%, the action is saturated, which is not economical. Cr: 0.4 to 2.5% Cr increases hardenability and is effective in improving toughness.
If it is less than 0.4%, such action is insufficient, while if it exceeds 2.5%, chilling occurs and the material becomes brittle.

Mo: 0.1 to 1.0% Like Ni and Cr, Mo increases hardenability and contributes to improvement of toughness. If it is less than 0.1%, such action is insufficient, while if it exceeds 1.0%, it becomes too hard and brittle. W: 2.0% or less Although not positively contained, it is inevitably mixed from the outer layer. It is set to 2.0% or less as a range that does not adversely affect the material such as brittleness.

V: 2.0% or less V combines with C to form MC type carbides, which has the effect of lowering the C concentration in the matrix, but even if the content exceeds 2%, the effect is saturated. It is not economical. Since it is an expensive element, the amount mixed from the outer layer is sufficient. In addition to the above alloy components, the balance is substantially formed of Fe,
The impurity elements S and P are preferably kept at 0.1% or less as in the outer layer.

Next, specific examples of the present invention will be given. Example 1 A high-speed cast iron material shown in the following Table 1 was centrifugally cast into a vertical centrifugal casting mold having an inner diameter of 1000 mm and a length of 1100 mm. The mold rotation speed was 80 in GNo., The outer layer casting temperature was 1455 ° C., and the casting thickness was 110 mm.

When the inner surface temperature of the outer layer reached 1400 ° C., the inner layer-forming cast steel material molten metal described in the same table was cast on the inner surface of the outer layer by a casting thickness of 145 mm. The casting temperature was 1550 ° C. After the inner layer was solidified, the rotation of the mold was stopped, the mold was separated, and dimension processing and heat treatment were performed to obtain a cylindrical composite roll having an outer diameter of 950 mm, an inner diameter of 600 mm and a length of 270 mm.

[0024]

[Table 1]

When the composite roll was subjected to an ultrasonic flaw detection test, it was confirmed that the outer layer and the inner layer were completely welded. The outer layer thickness was 25 to 35 mm thinner than the casting thickness. The results of analysis of the composition of the inner layer after welding are also shown in Table 1. Next, after holding the composite roll at 1150 ° C. for 2 hours, it is quenched by forced air cooling, and then at 550 ° C. for 10 hours.
The tempering heat treatment of hr was repeated 3 times. After performing such heat treatment, a test piece was taken from the inner layer and a tensile test was performed. As a result, the tensile strength is 780 MPa and the elongation is 2.3%.
It was confirmed that the toughness was excellent.

Example 2 A high-speed cast iron material shown in the following Table 2 was centrifugally cast into a vertical centrifugal casting mold having an inner diameter of 1190 mm and a length of 1100 mm. The mold rotation number was 80 in G No., the outer layer casting temperature was 1490 ° C., and the casting thickness was 225 mm. When the inner surface temperature of the outer layer reached 1420 ° C., the inner layer-forming cast steel material molten metal described in the same table was cast on the inner surface of the outer layer by a casting thickness of 130 mm. The casting temperature was 1560 ° C. After the inner layer has solidified, the rotation of the mold is stopped, the mold is disassembled, dimension processing and heat treatment are applied, and outer diameter φ1130 × inner diameter φ580 ×
A cylindrical composite roll for rolling H-shaped steel having a length of 266 mm was obtained.

[0027]

[Table 2]

When the cross section of the composite roll was visually observed, it was confirmed that the outer layer and the inner layer were completely welded. The outer layer thickness was 25 to 30 mm thinner than the cast thickness, but segregation of alloy components was not recognized. The results of analysis of the composition of the inner layer after welding are also shown in Table 2. Next, the composite roll was held at 1050 ° C. for 2 hours, then quenched by forced air cooling, and thereafter, tempering heat treatment of holding at 550 ° C. for 10 hours was repeated three times. After performing such heat treatment, a test piece was taken from the inner layer and a tensile test was performed. As a result, it was confirmed that the tensile strength was 710 MPa and the elongation was 2.6%, and the toughness was excellent.

Example 3 Using the high speed cast iron material for outer layer and the cast steel material for inner layer shown in Table 3 below, a cylindrical composite roll for H-shaped steel rolling having the same dimensions was prepared under the same conditions as in Example 2 above. Vertical centrifugal casting.

[0030]

[Table 3]

When the cross section of the composite roll was visually observed, it was confirmed that the outer layer and the inner layer were completely welded. The outer layer thickness was 30 to 40 mm thinner than the casting thickness. Further, no segregation layer was observed up to about 70 mm from the outer layer surface, but a whitish segregation layer composed of carbide with a high alloy component was observed on the inner surface side thereof. The results of analysis of the composition of the inner layer after welding are also shown in Table 3.

Next, the composite roll was heat-treated under the same conditions as in Example 2, and the tensile strength of the inner layer material was 67.
At 0 MPa and an elongation of 1.7%, it had practical strength, but its toughness was slightly reduced compared to Example 2.

[0033]

EFFECTS OF THE INVENTION According to the present invention, regardless of the use of a low C cast steel material as the inner layer material, no shrinkage cavities are generated at the boundary between the outer layer and the inner layer, and good welding can be obtained. Further, since the carbon content of the cast steel material before the inner layer welding is regulated to 0.4 to 0.8 wt%, even if the high alloy component of the outer layer is mixed in the cast steel molten metal, the formation of primary crystal carbides is small. It is possible to secure the toughness of the inner layer without causing a significant deterioration of the toughness.

As the outer layer material, C: 1.0 to 1.5
%, 2 × Mo + W: 3.0 to 7.0%, V: 2.0 to
By using a high-speed cast iron material having a specific composition containing 4.0%, it is possible to suppress the formation of segregation even in a thick outer layer having a wall thickness of about 200 mm, and manufacture a high-quality composite roll. can do.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location B22D 13/02 E 9266-4E 19/16 F C22C 38/24 (72) Inventor Hiroaki Katayama Hyogo 64, Nishimukojima-cho, Amagasaki City Kubota Amagasaki Plant, Inc. (72) Inventor Naga Morikawa 64, Nishimukojima-cho, Amagasaki City, Hyogo Prefecture Kubota Amagasaki Plant, Inc. (72) Inventor Toyoji Tsujimoto, 64, Nishimukojima-cho, Amagasaki Kubota Amagasaki Factory

Claims (3)

[Claims] 1. The inner surface of an outer layer made of a high-speed cast iron material having a carbon content of 1.0 to 1.9 wt% has a carbon content of 0.
A high-speed composite roll in which an inner layer made of cast steel material of 4 to 0.9 wt% is welded by centrifugal casting. 2. An outer layer made of a high-speed cast iron material having a carbon content of 1.0 to 1.9 wt% is centrifugally cast to solidify the outer surface of the outer layer, and then the inner surface temperature of the cast outer layer is an inner layer. When the solidification temperature of the cast steel material is not less than, the cast steel material having a carbon content of 0.4 to 0.8 wt% is cast on the inner surface of the outer layer at a temperature of the inner surface of the outer layer or more, and the inner layer is welded to the inner surface of the outer layer. Of manufacturing a composite composite roll. 3. The chemical composition of the outer layer material is% by weight, C: 1.0 to 1.5%, Si: 0.2 to 1.5%, Mn: 1.5% or less, Cr: 2.0 to 6.0%, 2 × Mo + W: 3.0 to 7.0%. , V: 2.0 to 4.0%, and the balance substantially consisting of Fe.