JPH0211740A - Sintered material of nickel chromium cast iron powder containing graphite and composite ring roll - Google Patents

Abstract

PURPOSE:To provide superior slip resistance while securing wear resistance and seizuring resistance by subjecting a sintered material in which composition of Ni-Cr powder is specified to graphitizing heat treatment to precipitate graphite in the structure. CONSTITUTION:A cast iron stock is constituted of a sintered material of powdered Ni-Cr cast iron having a composition consisting of, by weight, 1.0-1.9% C, 4.0-15.0% Ni, 1.5-4.0% Si, 2.0-4.5% Cr, 0.5-1.5% Mn, 0.4-0.50% Mo, <=0.1% P, <=0.08% S, and the balance essentially Fe. Further, graphite is precipitated in the structure by means of graphitizing heat treatment. Then, an inner layer composed of tough and hard material is diffusion-joined to the internal surface of an outer layer composed of the above high-alloy roll stock, by which a composite ring roll is formed. By this method, slip resistance can be improved, and further, structure is refined and wear resistance can be improved.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a nickel-chromium cast iron material with excellent wear resistance, seizure resistance, and slip resistance, which is mainly used as a roll material, and a method for rolling the cast iron material. This invention relates to a composite ring roll used for the outer layer.

(Prior technology) In the past, Adamite rolls were mainly used as work rolls in the front stage of hot strip mill finishing stands and rough stand work rolls in the same mills, but in recent years, high chromium roll materials with excellent wear resistance have been used for rolling. High chrome rolls applied in layers are popular.

However, high chromium roll materials have a problem in that they have low thermal conductivity and are prone to seizure.

Therefore, as disclosed in Japanese Patent Publication Nos. 61-16415 and 61-16336, the present applicant has developed a graphite-crystallized high-chromium cast iron material with significantly improved seizure resistance by crystallizing graphite in a high-chromium structure. was developed.

When special steel such as stainless steel, which is conventionally considered to be prone to seizure, was rolled using a rolling roll having this graphite crystallized high chromium cast iron material as a rolling layer, no seizure occurred and the result was good. The results were obtained.

On the other hand, cemented carbide ring rolls made of sintered cemented carbide powder such as tags have been used as rolls for wire rod rolling mills, but they are expensive and difficult to fix to the roll shaft. This was difficult due to the large difference in thermal expansion.

For this reason, as shown in Part 1, the applicant proposed a composite ring in which an outer layer 2 made of a high alloy roll material and an inner layer 3 made of a tough material were diffusion bonded by high temperature isostatic pressing (referred to as HIP). Roll 1 was proposed in Japanese Patent Application No. 6017913. In the figure, 4 is an arc-shaped caliber for rolling wire rod.

With this roll, it can be easily fixed to the roll shaft using normal joining means such as shrink fitting, and although it has slightly lower wear resistance than carbide ring rolls, it is an inexpensive composite ring roll that does not pose any practical problems. were able to provide.

However, since the above-mentioned high chromium cast iron material is used as the high alloy roll material, as mentioned above, there is a drawback that the thermal conductivity is low and seizure is likely to occur. To solve this problem, the graphite crystallized high chromium 1 no. Iron steel may be used as the outer layer material.

(Problem to be Solved by the Invention) However, since the graphite-crystallized high-chromium cast iron material has a large amount of high-hardness eutectic chromium carbide, it tends to slip during rolling, and therefore has poor biting properties. This problem necessitated a decline in productivity. Also,
There is a problem that the resistance to plastic deformation decreases due to the softening of the base and the decrease in the amount of carbide caused by the decrease in the Cr content, and the wear resistance deteriorates due to the cracks in the base around the crystallized graphite falling off. .

The present invention has been made in view of these problems, and aims to provide a cast iron material that has improved slip resistance while ensuring wear resistance and seizure resistance, and a composite ring roll that has both of the above characteristics. (Means for solving the problem) The cast iron material of the present invention, which was made to achieve the above object,
Chemical composition in weight%: C: 1.0-19%, old: 4.0-15.0% Si:
1.5-4.0%, Cr: 2.0-4.5
%Mn: 0.5-1.5%, Mo: 0.
4-5. O% P: o, 1% or less, S: 0.08% or less, the balance is a sintered material of nickel-chromium cast iron powder consisting essentially of Fe, and graphite is precipitated in the structure by graphitization annealing heat treatment. This is the structure of the invention.

Further, the composite ring roll of the present invention is one in which an inner layer made of a tough material is diffusion bonded to the inner surface of an outer layer made of a high alloy roll material, and the outer layer is made of nickel chromium cast iron powder containing graphite. The structure of the invention is that it is formed of a binder.

(Example) First, the reason for limiting the components of the cast iron powder constituting the nickel chromium cast iron powder sintered material according to the present invention will be explained. Hereinafter, the unit is weight %.

C: 1.0 to 1.9% C is added to precipitate as graphite through heat treatment after sintering due to the graphitization effect of St and Ni.

In the component range of Si and Ni in the present invention, 1
．． If it is less than 0%, precipitation of graphite is difficult. On the other hand, 1.9
If the content exceeds %, the amount of eutectic carbides in the powder will increase and the slip resistance will deteriorate.

Si: 1.5-4.0% Si is necessary for precipitating graphite by heat-treating the nickel-chromium cast iron powder after sintering. In the case of the present invention, 2.0 to 4.5% of Cr and 0.4 to 5.0% of Mo are contained in order to increase the strength of the base, so if it is less than 1.5%, graphite precipitation becomes difficult. On the other hand, if it exceeds 4.0%, graphite precipitation will be excessive and wear resistance and mechanical properties will deteriorate.

Mn: 0.5-1.5% Mn is added to S to deoxidize the molten metal before making fine quenched powder.
It is actively added together with i. If it is less than 0.5%, the deoxidizing effect will be insufficient, while if it exceeds 1.5%, mechanical properties, particularly toughness, will deteriorate significantly.

P: 0.1% or less P makes the material brittle, so it is desirable to have less P, and 0.1%
The following shall apply.

S: 0.08% or less For the same reason as P, the lower the S content, the more desirable it is 0.08
% or less.

N: 4.0 to 15.0% Ni is actively added for the purpose of graphite precipitation and improvement of the matrix structure. If it is less than 4.0%, precipitation of graphite becomes difficult. On the other hand, if the content exceeds 15.0%, residual austenite becomes stable and it becomes difficult to decompose the austenite even by heat treatment, causing problems in terms of ensuring hardness and roughening resistance.

Cr: 2. O ~ 4.5% Cr combines with C to form Cr carbide, and also partially dissolves in the base and contributes to strengthening the base, but in the case of the present invention, it is mainly added for the latter purpose. be done.

If it is less than 2.0%, the amount of Cr dissolved in the base is small;
It becomes difficult to strengthen the base. On the other hand, if it exceeds 4.5%, excessive crystallization of carbides in the powder will inhibit the improvement of slip resistance, and the carbides will crystallize in a network shape, causing problems in terms of roughness resistance. .

Mo: 0.4 to 5.0% Mo is an element that suppresses the precipitation of graphite, but it also penetrates into carbides and increases the hardness of the carbides, and dissolves in the matrix to improve tempering softening resistance. It is valid. In the present invention, since the amount of carbide is very small, it is actively added mainly for the purpose of improving the matrix structure. If it is less than 0.4%, it is not possible to effectively improve the base organization. On the other hand, when it exceeds 1.0%, graphite precipitation is reduced, but the graphite precipitation suppressing effect is not significantly increased, and strengthening of the matrix is promoted. For this reason, the seizure resistance of the base portion is improved, and even if the amount of graphite is slightly reduced, the seizure resistance does not deteriorate, but rather, excellent wear resistance is obtained due to improved hardness. However, 5%
If it exceeds this, graphite precipitation is significantly suppressed and seizure resistance deteriorates. In addition to strengthening the base, Mo is preferably contained in an amount of 2.0% or more in order to penetrate into the carbide and improve the hardness of the carbide.

In addition to the above-mentioned components, the nickel-chromium cast iron powder constituting the sintered material containing graphite of the present invention is made of substantially Fe, but in order to improve the material properties, some of the Fe is replaced with the following Nb , V can be contained as necessary.

That is, both Nb and V are effective in refining the structure, and each can be contained alone or in combination at 1.0% or less. If it exceeds 1.0%, it will combine with carbon and form VC, N.
Forms carbides such as bC and NbzC and prevents precipitation of graphite. Moreover, it becomes a factor of high cost.

The nickel-chromium cast iron powder is usually manufactured by melting molten nickel-chromium cast iron having the desired composition, pulverizing it by gas atomization or water atomization, and rapidly solidifying it. The particle size of the powder used is usually about 100 to 250 mesh. Since the powder is cold solidified, the crystal structure is in a fine state. Such a fine structure cannot be obtained with conventional melt-molded materials.

The nickel chromium cast iron powder is compacted into a desired shape and sintered. In this case, uniaxial compression or cold isostatic pressing (hereinafter referred to as CIP) can be applied to powder compaction, or hot isostatic pressing where pressing and sintering are performed simultaneously. (hereinafter referred to as HIP) molding can be applied.

For example, when manufacturing a composite ring roll, as shown in FIG. A can body 5 is provided as shown above, the nickel chromium cast iron powder 6 is filled into the can body 5, and after degassing, HIP treatment is performed. As a result, the nickel chromium cast iron powder is sintered and integrated, and a composite ring is obtained in which the outer layer sintered material is diffusion bonded to the outer peripheral surface of the inner layer material ring 3a. At this time, the fine structure of the nickel chromium cast iron powder is HI
Since the structure of the sintered material is formed even after P, it is extremely fine and has high wear resistance compared to the melted material. In addition, the migration of high alloy components from the outer layer to the inner layer is suppressed as much as possible,
The toughness of the inner layer material also does not deteriorate.

After sintering, the sintered material of the nickel-chromium cast iron powder is subjected to graphitization annealing heat treatment to precipitate graphite in the structure. In the case of the composite ring, the heat treatment may be applied to the entire composite ring after rough processing.

This heat treatment is performed by heating the sintered material to 950 to 1000°C and holding it for several hours. This results in
The free carbide in the sintered material is decomposed, and C generated by the decomposition becomes fine graphite, which is uniformly dispersed and precipitated in the sintered material. Since the precipitated graphite is more finely and uniformly dispersed than crystallized graphite, it effectively prevents the base from falling off due to the presence of crystallized graphite, which not only ensures seizure resistance but also improves wear resistance. can contribute to

Note that in cast iron materials with a high Cr content, graphite usually does not precipitate even if the material is held at high temperatures for a long time. In the case of the outer layer material of the present invention, specific components containing a large amount of Si and Ni are selected, so that graphite can be precipitated.

The sintered material of the present invention obtained by the above-mentioned graphitization annealing heat treatment has the C content in the nickel chromium cast iron powder suppressed as much as possible, so almost no eutectic carbide is generated, and it has excellent slip resistance. can significantly improve sex.

In addition, the eutectic carbide referred to here is one in which Cr has entered M and C type cementite, and the M7C3 type chromium carbide that crystallizes in conventional high chromium materials and graphite crystallized high chromium materials is They differ in carbide structure, crystallization form, and crystallization amount.

On the other hand, the base structure is strengthened by adding a certain amount of Ni, Cr, and Mo, and the crystal structure is refined by using rapidly solidified powder, so the wear resistance is improved despite the reduction of eutectic carbides. It is possible to prevent the deterioration of the properties, the mechanical strength is improved, and the toughness of the tool 61 is improved.

Furthermore, through graphitization annealing heat treatment, fine graphite is uniformly dispersed in the structure, ensuring seizure resistance and effectively preventing flaking of the base around the graphite, resulting in wear resistance. It can contribute to improving sexual performance.

The base of the sintered material after graphite precipitation is made into martenza I by quenching and tempering, rechenite by austempering, or adjusted to pearlite or ferrite structure by an appropriate cooling rate.

In the case of manufacturing a composite ring roll, the entire composite ring may be subjected to heat treatment for adjusting the base structure of the outer layer material. after that,
Finishing to the final shape results in a product composite ring roll, one or more of which is shrink-fitted or otherwise secured to the roll shaft and subjected to rolling as an assembled roll.

The nickel-chromium cast iron sintered material containing graphite of the present invention is suitable as an outer layer material for rolling of composite rolls and composite ring rolls, but it can also be used in various applications that require both wear resistance and seizure resistance. (For example, rollers around rolled materials such as guide rollers and table rollers, and parts for hot plastic processing). In addition, when using the material of the present invention as the outer layer material of a composite roll, it is sufficient to form an outer layer using the nickel chromium cast iron powder on the outer circumferential surface of a roll shaft formed of a steel material, etc., and then perform a sintering treatment together with the roll shaft. .

Next, specific examples are listed.

Example 1 Manufacturing example of a round bar finishing rolling stand exit guide roller (1) Nickel chromium cast iron powder with the following composition (particle size 140
mesh under) to CTP (pressure 5kgf/cm)
A molded cylinder having an outer diameter of 165 mm, an inner diameter of 60 mm, and a width of 95 mm was obtained.

・Powder composition (unit weight %, remainder substantial Fe) C: 1.2
5%, Si: 3.50%, Mn: 0.75% P:
0.006%, S: 0.008%, Ni: 1
2.00%Cr: 2.90%, Mo: 0.5
0%, (2) pressurize the molded cylinder at 200 kgf/cJ,
HIP treatment was performed at a temperature of 1150°C to obtain a sintered cylinder. The cylindrical body was roughly machined so that a machining allowance of 1 mm was added to the product dimensions, and the heat treatment described in (1) to (4) below was performed.

■ Graphitization annealing heat treatment held in a 950°CX5TLR salt bath ■ Haenitization heat treatment of the base After heating to 1000°C, put into a 530°C salt bath, cool, hold for 5 hours, and let cool in air It was then cooled to room temperature.

(2) Transformation heat treatment of retained austenite After heating to 530°C and holding for 3 hours, it was cooled to room temperature. This process was repeated twice.

(3) After heat treatment, finishing processing was performed to obtain the product roller shown in FIG. The structure of the roller consisted of finely and uniformly precipitated graphite, a base structure, and a very small amount of carbide, and the base structure was tempered martensite. Hardness is l1s
It was 85-86.

(4) The above roller was installed on the exit side of a 32φ round steel finishing rolling mill and was actually used. The exit guide roller does not rotate when the rolled material does not come into contact with it, but is induced to rotate when the rolled material coming out of the rolling mill comes into contact with its peripheral surface. For this reason, rollers tend to seize during biting, and conventionally chilled cast iron rollers have been used. In this case, the wear resistance was poor and the rolling stock was revised once per approximately 3007 on, but in this example, the rolling amount per one revision was improved by 13 times. Incidentally, during use, the seizure and chipping disappeared, and no cranking occurred at all.

Example 2 Manufacturing example of a composite ring roll using flat steel rolling (product dimensions φ320 x width 1.50 mm) (1) Inner diameter 150 mm, outer diameter 230 mm, width 150 m
An inner layer material ring of m was prepared. The ring has a C: 0.
25%, St: 0.13%, Mn: 0.41%
It is a low C steel.

(2) The radially outer side of the ring was covered with a can plate as shown in FIG. 2, and the entire outer surface of the ring was filled with the following nickel chromium cast iron powder and then degassed.

The powder used was 140 mesounder.

Powder composition C: 1.60%, Si: 1.90%, Mn:
0.71%P: 0.005%, s:o, oo8%,
Ni: 6.90% Cr: 2.40%, Mo:
0.80%, balance substantial Fe(3) then 20
HIP at 0 kg/cffl pressure and 1180°C temperature
The powder was sintered to obtain an outer layer and the outer layer and the inner moon ring were diffusion bonded. After the HIP treatment was completed, the can plate was removed to obtain a composite ring.

(4) After rough machining the HIP-treated composite ring to product dimensions, heat it to 950°C for 511°C to precipitate graphite.
After being kept in a salt bath, it was heated to 1000°C, then placed in another salt bath at 530°C, cooled, and kept for 5 hours, then allowed to cool in the air and cooled to room temperature. After that, 530
Heating and cooling were repeated twice to °C to transform the retained austenite. In addition, the holding time at 530"C is 311r
And so.

(5) In the outer layer structure of the composite ring thus obtained, fine carbide and fine graphite were uniformly dispersed, and the base structure was tempered martensite. Its hardness was l1s90-91.

(Effects of the Invention) As explained above, the sintered nickel-chromium cast iron powder having graphite of the present invention is sintered with nickel-chromium cast iron powder having a predetermined component of C: 1.0 to 19%. , hardly any carbide is formed, and the slip resistance is good. In addition, the structure is refined in combination with the reinforcement of the base by NiCr and Mo, which improves wear resistance. Moreover, fine graphite is uniformly dispersed and precipitated in the sintered material through the graphitization annealing heat treatment, ensuring seizing resistance and further improving wear resistance.

By applying such a sintered nickel chromium cast iron powder material to the outer layer of a composite link roll, it is possible to have excellent wear resistance, seizure resistance, and slip resistance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a composite ring roll, a sectional view of an inner layer material ring provided with a second row can body, and FIG. 3 is a half sectional view of a roller according to an embodiment. 1... Composite ring roll, 2... Outer layer, 3... Inner layer.

Claims (2)

[Claims] (1) Chemical composition in weight%: C: 1.0-1.9%, Ni: 4.0-15.0%Si
:1.5~4.0%, Cr:2.0~4.5%Mn:0
．． 5-1.5%, Mo: 0.4-5.0% P: 0.1%
Hereinafter, S: 0.08% or less A sintered material of nickel-chromium cast iron powder with the balance substantially composed of Fe, which is characterized by graphite being precipitated in the structure by graphitization annealing heat treatment. Nickel chromium cast iron powder sintered material with. (2) In a composite ring roll in which an inner layer made of a tough material is diffusion bonded to the inner surface of an outer layer made of a high alloy roll material, the nickel chromium containing graphite described in claim (1) is used as the high alloy roll material. A composite ring roll characterized by using cast iron powder sintered material.