JP2648307B2 - Composite cermet roll - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cermet roll used in cold rolling, warm rolling, hot rolling, etc., and more particularly, to a cermet having a cermet outer skin around the outer periphery of an alloy core material. It is formed.

[Background Art] Conventionally, materials such as cast steel and tool steel have been used for rolling members. However, these materials have low wear resistance and thus have short service lives. For this reason, recently, WC-Co-based cemented carbides having excellent wear resistance have been used.
However, the specific gravity of WC-Co based cemented carbide is about 15, which is almost twice that of cast steel and tool steel. As a result, chatter and vibration occur during operation.In addition, the weight of the roll increases, and thus the inertia force increases, and the peripheral speed of the roller greatly deviates from the speed at which the workpiece is passed. The amount is generated and the quality of the workpiece on the roller is impaired. For this reason, there are further improved rolls as described below.

JP-A-53-56147 discloses that a light-weight TiC-Ni-based cermet (specific gravity of 5.1) is used for the inner layer (core material) to reduce the weight of the roll.
A composite guide roll having an outer layer made of a hard and wear-resistant WC-Co-based cemented carbide (specific gravity: 14.0) on its outer periphery is shown. Although it is stated that this roll uses the thermal expansion coefficients of the inner layer and the outer layer that are close to each other, the difference is as large as 25%, and the occurrence of residual stress due to the difference in the thermal expansion rate cannot be sufficiently reduced. Further, since the inner layer is made of a cermet having a lower toughness than a cemented carbide, it lacks reliability.

JP-A-51-84711 discloses a sintered WC-Co.
A roll obtained by fitting an inner cylinder made of a press-formed WC-Co alloy around the outer periphery of an alloy cylinder and sintering the same is shown. However, no consideration is given to the difference in the coefficient of thermal expansion between the inner cylinder and the outer cylinder.

Further, JP-A-55-62103 discloses that an outer surface of a core material made of a heat-resistant alloy is coated with a corrosion-resistant alloy powder such as a Ni-based alloy, a Co-based alloy, or an Fe-based alloy having a higher Cr content than the core material by a HIP method. 2 shows a coated composite heat-resistant alloy member. This composite heat-resistant alloy member has improved high-temperature strength and high-temperature corrosion resistance, but does not consider any difference in the coefficient of thermal expansion between the core material and the exterior.

"Means for Solving the Problems" The present invention is a composite cermet roll in which a lightweight and hard cermet skin is formed on the outer periphery of a tough core material. As the core material, for example, it is formed of an ingot material such as SCM440 alloy to improve toughness, and its coefficient of thermal expansion is about 12.5 × 10
^-6 / ° C was used.

The cermet, which is the outer skin, is composed of a hard phase that is dispersed in the structure and contributes to abrasion resistance and a binder phase formed therebetween and contributes to improvement in toughness. The hard phase is composed of at least one of carbides and nitrides of group IVa, Va and VIa elements, and the binder phase is
It is composed of at least one of Fe, Ni, Co, Cr, W, and Mo and unavoidable impurities. In addition to the above components, the thermal expansion coefficient of the outer shell was kept to ± 20% or less at each temperature from room temperature to 1000 ° C., and the residual stress between the core and the outer shell was reduced. If the difference in the coefficient of thermal expansion is ± 20% or more, cracks occur at the bonding interface, resulting in poor bonding.

In the outer skin cermet, if the total weight of the hard phase is 30% or less, the abrasion resistance is poor, and if it exceeds 95%, the toughness is poor. In addition, when chromium carbide is included in the hard phase, oxidation resistance, skin roughness resistance, and abrasion resistance are improved, but a type of Cr ₃ C ₂ , Cr ₇ C ₃ , (Cr, Fe) ₇ C ₃ Alternatively, if two or more of them are 20% by weight or less, the oxidation resistance is poor, so that chromium carbide is contained in the hard phase in an amount of 20% by weight or more.

The binder phase of the cermet is composed of 5% by weight of Cr and 5% by weight of Cr and 5% by weight. And Further, by making the components of the cermet as described above, the austenite phase and the diffusion phase exist at the joint interface between the core material and the outer skin, as shown in FIG.

"Example 1" The core material of the roll was formed into a cylindrical shape having an outer diameter of 140 mm, an inner diameter of 50 mm, and a length of 85 mm by using an alloy SCM440 by a melting method.

The outer skin that coats the outer periphery of the core material is A to A shown in Table 1 below.
Cermet was formed around the outer periphery of the core material using each of C3 compositions, and the characteristics of each were compared. In addition, the carbides and nitrides of the IVa, Va, and VIa group elements, which are the hard phases of the cermet, should be in the range of 30 to 95 wt% in total so as to have sufficient wear resistance. F formed
An appropriate toughness is provided by a binder phase composed of e, Co, Ni, Cr and unavoidable impurities.

Formation of the outer skin is mixed in a ball mill for each composition, and CIP molding at a molding pressure of 500~1000kg / cm ^2, the molded body fitted to the outer circumference of the core material, to preliminary sintering at 1000 to 1300 ° C. Thus, the two were integrated to be integrated. After this sintering, in order to further generate an interfacial phase at the interface between the core material and the outer skin and strongly bond the same, the temperature is reduced from the preliminary sintering temperature to a temperature of 25 ° C or less, 1000 atm.
250mm outside diameter, 140mm inside diameter after HIP treatment to hold at 2m for 2 hours
Three types of composite cermet rolls having a length of 85 mm were prepared.
For each composite cermet roll, the difference in the coefficient of thermal expansion between the core material and the outer cermet was measured. The results are shown in Table 2.
The difference in the coefficient of thermal expansion showed the maximum value at each temperature from room temperature to 1000 ° C.

FIGS. 1 to 3 show cross-sectional photographs of the joint surface between the core material and the outer skin of each composite cermet roll using cermets A to C, respectively.

From the photograph of Fig. 1, the one using cermet A
It can be seen that a large crack has occurred on the cermet side of the bonding interface. This is probably because the difference in thermal expansion coefficient between the core material and the outer cermet is as large as 25%.

From the photograph in Fig. 2, the one using cermet B
In this case, the bonding interface between the core material and the outer cermet is good. This is presumably because the difference in thermal expansion coefficient between the core material and the outer skin was 18%, which was 20% or less.

From the photograph in Fig. 3, the one using cermet C
The diffusion layer and the austenite layer are present at the joint interface between the core material and the outer cermet, resulting in good joint. In this case, it is considered that the difference in the coefficient of thermal expansion between the core material and the outer cermet is as small as 5%, and that both Ni and Cr are in the range of 5 wt% to 30%.

From the above, the coefficient of thermal expansion of the core material is +20 than the coefficient of thermal expansion of the outer skin.
% Or less, it can be seen that the outer skin is strong and is joined without cracking. Even if the difference in the coefficient of thermal expansion is within -20%, the applied state of the force is the same, so that the preferable joined state is obtained.

Although SCM440 was used as the core material in the above embodiment,
YHD50 (C: 0.6
wt%, Si: 1.0 wt%, Mn: 13.0 wt%, Ni: 2.2 wt%, Cr: 10.0
wt%, V: 2.0 wt%, balance Fe), HRA286 (C: 0.05 wt%, Cr:
15 wt%, Ni: 26 wt%, Mo: 1.3 wt%, Ti: 2.15 wt%, Al: 0.2
5wt%, V: 0.3wt%, B: 0.004wt%, balance Fe)
Similarly, due to the nature of the alloy, the outer skin can be desirably formed around the core material.

Example 2 Next, the weight ratio of the hard phase component composed of TiCN, Cr ₃ C ₂ , Mo ₂ C, WC and VC and the binder phase component composed of Fe, Co, Cr, W and Mo in the cermet was calculated. By changing, each hardness and bending force were measured and shown in Table 3.

As can be seen from Table 3, when the hard phase is less than 30%, the hardness is low and the wear resistance is poor, and when the hard phase exceeds 95%, the transverse rupture strength is low and the toughness is poor. Therefore, the hard phase of the cermet is desirably 30 wt% or more and 95 wt% or less.

Example 3 In order to examine the oxidation resistance of the composite cermet roll,
With respect to the rolls using the cermets of the seven types of compositions shown in the table, the increase in oxidation when heated from room temperature to 1000 ° C. was measured, and the results are shown in Table 5. Cermets A to C in Table 4 are the same as those corresponding to A to C in Table 1.

Cermet A has a hard phase of Cr ₃ C ₂ of 6% by weight, an oxidation weight gain of 28 × 10 ⁻² mg / mm ² , and is inferior in oxidation resistance. Cermet B has a hard phase of Cr ₃ C ₂ of 21% by weight and 20% by weight or more, an oxidation weight gain of 15 × 10 ⁻² / mm ² , and has oxidation resistance.
Cermet C has a hard phase of Cr ₃ C ₂ of 24 wt% and a small oxidation weight increase of 11 × 10 ⁻² / mm ^2, and has good oxidation resistance.

Cermet D has a hard phase of Cr ₃ C ₂ of 24 wt%, but has an oxidation weight increase of 24 × 10 ⁻² mg / mm ² , and is inferior in oxidation resistance. It is considered that the oxidation resistance is lowered because the binder phase of cermet D is less than 5% by weight together with Ni4wt% and Cr4wt%.

Cermet E has an oxidation weight gain of 9 × 10 ^-2 mg / mm ² because Cr ₃ C ₂ of the hard phase is 24 wt% and has oxidation resistance, but the binder phase is 5 wt% of Ni by weight%, Cr31wt% and C
Since r is included by 30% or more, the transverse rupture strength is 51 kg / mm ² , and the case of cermet C is much lower than that of 190 kg / mm ^2, which is not desirable.

Further, the cermet F has a hard phase of Cr ₇ C ₃ of 24 wt%, so that the weight gain of oxidation is 10 × 10 ⁻² mg / mm ² and the oxidation resistance is good. Cermet G consists of the hard phases Cr ₃ C ₂ and Cr ₇
Since the total amount with C ₃ is 24 wt%, the oxidation increase is 11 × 10
^-2 mg / mm ² , indicating good oxidation resistance. Cermet H has a total of 24 wt% of the hard phases Cr ₇ C ₃ and (Cr, Fe) ₇ C _3.
%, The oxidation weight gain is 11 × 10 ^-2 mg / mm ² ,
Oxidation resistance is good.

From the above, in order for the outer skin cermet to have oxidation resistance, the total of the hard phases Cr ₃ C ₂ , Cr ₇ C ₃ and (Cr, Fe) ₇ C ₃ is 20 watts.
It is desirably at least t%. In addition, Ni, C
r is desirably 5 wt% or more, respectively. However, if the amount is too large, the toughness is inferior. Therefore, r is desirably 30 wt% or less.

[Effect of the Invention] The composite cermet roll of the present invention reduces residual stress at the interface between the core material and the outer skin by making the difference in thermal expansion coefficient between the core material and the outer skin cermet 20% or less. In addition, since the bonding between them can be strengthened, the problems of cracking and poor bonding can be prevented even when used in a hot rolling apparatus. In addition, since the core material is made of an alloy by a melting method, the composite cermet roll has toughness, and has excellent wear resistance as a roll by setting the hard phase component of the outer cermet to 30 wt% to 95 wt%. Further, by containing a large amount of chromium carbide in the hard phase, the outer skin cermet has corrosion resistance and oxidation resistance.

[Brief description of the drawings]

FIGS. 1, 2, and 3 are microscopic metallographic photographs showing a joint portion between a core material and a skin obtained by cutting a composite cermet roll according to different examples of the present invention.

Claims (3)

(57) [Claims] 1. An outer surface of a roll core material made of an alloy containing iron as a main component manufactured by a melting method and having a difference in thermal expansion coefficient at a temperature from room temperature to 1000 ° C. of ± 20% of the thermal expansion coefficient of the alloy. % Of the cermet skin is formed, and the cermet is composed of a hard phase of 30% by weight or more and 95% or less and a binder phase of the remainder, and the hard phase is composed of a group IVa, Va, or VIa element. It is composed of at least one of carbides and nitrides, and the binder phase is Fe, N
A composite cermet roll comprising at least one of i, Co, Cr, W, and Mo and unavoidable impurities. 2. The hard phase of the cermet contains at least 20% by weight of Cr.
_{3, C 2, Cr 7 C} 3, (Cr, Fe) 7 C 3 in one or the composite cermet roll Claims paragraph 1, characterized in that it consists of two or more. 3. The binder phase of the cermet has a content of 5 ≦ Cr ≦% by weight.
3. The composite cermet roll according to claim 1, wherein 30 and 5 ≦ Ni ≦ 30, and the balance is composed of Fe and inevitable impurities.