JPH0215150A - Nickel-chromium cast iron sintered material containing graphite - Google Patents

Abstract

PURPOSE:To obtain the title nickel-chromium cast iron sintered material having excellent wear resistance, seizure resistance and slipping resistance by forming it with the compsn. contg. prescribed content of specific 10 kinds of each metallic element such as C, Cr and Si, and depositing graphite into its structure by graphitizing heat treatment. CONSTITUTION:The above nickel-chromium cast iron sintered material is formed with the compsn. contg., by weight, 1.0 to 1.9% C, 2.0 to 4.5% Cr, 1.5 to 4.0% Si, 0.4 to 5.0% Mo, 0.5 to 1.5% Mn, <=13% Ni, <=0.1% P, 0.5 to 4.0% Cu, <=0.08 S, 4.0 to 15.0% Ni+Cu and the balance Fe. The nickel-chromium cast iron powder is usually manufactured by refining the molten metal of nickel-chromium cast iron contg. expected components, pulverizing it by a gas atomizing method, etc., and subjecting the powder to rapid solidifying. The above cast iron powder is then subjected to compacting into the desired shape to obtain the objective nickel-chromium cast iron sintered material in which graphite is deposited out. In the sintered material, fine graphite is uniformly dispersed and deposited by graphitizing heat treatment and seizure resistance and slipping resistance are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a nickel-chromium cast iron material that is mainly used as a roll material and has excellent wear resistance, seizure resistance, and slip resistance.

(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 Publications No. 61-16415 and No. 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 thought to be susceptible 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 good results were obtained. was gotten.

(Problems 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 low productivity.

The present invention was made in view of such problems, and an object of the present invention is to provide a cast iron material that has improved slip resistance while ensuring wear resistance and surface seizure resistance.

(Means for Solving the Problems) The cast iron material of the present invention, which has been made to achieve the above object, has the following features:
Chemical composition in weight%: C: 1.0-1.9%, Cr: 2.0-4.5
%Si: 1.5-4.0%, Mo: 0.
4-5.0%Mn: 0.5-1.5%, Ni:
13% or less p:oyt% or less, Cu:
0.5-4.0% S: 0.08% or less, Ni-
1-Cu: A sintered material of nickel-chromium cast iron powder consisting of 4.0 to 15.0% and the remainder substantially Fe, which is an invention in which graphite is precipitated in the structure by graphitization annealing heat treatment. The structure is as follows.

(Function) First, the reason for limiting the components of the nickel-chromium cast iron powder constituting the nickel-chromium cast iron powder 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 by heat treatment after sintering due to the former graphitization effect of Sl.

In the component range of Si and Ni in the present invention, 1
If it is less than 0%, it is difficult to precipitate graphite. 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 will be 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 actively added together with Si to deoxidize the molten metal before forming fine grains and cold powder. 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 less S is, the more desirable it is 0.08
% or less.

Cr: 2.0 to 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, the latter is mainly used. It is added for the purpose of

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: 0.4-5.0% Mo is an element that suppresses the precipitation of graphite, but it also penetrates into the carbide and increases the hardness of the carbide, and dissolves in the matrix to improve the 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 can be obtained by increasing the hardness. but,
When it exceeds 5%, precipitation of graphite is significantly suppressed and seizure resistance deteriorates. In addition to strengthening the base, in order to penetrate into the carbide and improve the hardness of the carbide, it is necessary to add Mo to 2.0
% or more is preferable.

Ni: 13% or less Ni is added for the purpose of graphite precipitation and improvement of the matrix structure.

If the content exceeds 13%, the residual austenite tends to increase and stabilize, and it becomes difficult to decompose the residual austenite (l·) even during subsequent heat treatment.

For this reason, when used hot, the austenite on the surface of the used member decomposes and expands, resulting in poor skin roughness resistance. The lower limit of the addition amount of Ni is determined by the total amount of Cu, which will be described later.

Cu: 0.5 to 4.0% Cu promotes graphitization and contributes to pearlite reinforcement and thermal stabilization. The graphitization effect is almost the same as Ni. If it is less than 0.5%, it will not have an effective effect;
．． If it exceeds 0%, metal Cu will precipitate and the mechanical properties will deteriorate.

Cu+Ni: 4.0-15% Cu, :! -Ni has almost the same graphitization promoting effect, and if the total amount is less than 4.0%, precipitation of graphite becomes difficult. On the other hand, if it exceeds 15%, graphite precipitation will be excessive and wear resistance will deteriorate. In addition, if graphite precipitation is attempted using N1 Eidoku, the Ni content is specified to be 4.0 to 15%, but in the present invention, since the N1 content is suppressed to 13% or less, the amount of retained austenite is reduced, Furthermore, it is advantageous in that the roughening resistance can be improved. Also, expensive Ni
It is also advantageous from an economic point of view.

The nickel-chromium cast iron powder constituting the graphite-containing sintered material of the present invention is made of substantially Fe, but in order to improve the material properties, the following Nb is substituted for a part of the Fe. , 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 Nb2C and prevents crystallization of graphite. Moreover, it becomes a factor of high cost.

The nickel-chromium cast iron powder is usually produced by melting nickel-chromium cast iron powder having the desired components, pulverizing it by a gas atomization method or water atomization method, and rapidly solidifying it. The particle size of the powder used is usually about 100 to 250 mesh. Since the powder is rapidly 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 compaction, or hot isostatic pressing (hereinafter referred to as CIP) in which pressing and sintering are performed simultaneously Hereinafter referred to as HIP) molding can be applied.

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. This heat treatment heats the sintered material to 950-1200°C.
This is done by heating and holding for several hours. As a result, free carbides in the sintered material are decomposed, and C generated by the decomposition becomes fine graphite, which is uniformly dispersed and precipitated in the sintered material.

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 present invention,
Since a specific component containing a large amount of Si, Ni, and Cu is selected, fine graphite can be uniformly dispersed and precipitated in the structure by heat treatment.

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

In addition, the eutectic carbide mentioned here refers to M and C type cementite in which Cr has entered, and is different from the M'+C3 type chromium carbide that crystallizes in conventional high chromium materials and graphite crystallized high chromium materials. are different 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 a decrease in properties, improve mechanical strength, and provide toughness.

Furthermore, the graphitization annealing heat treatment produces fine graphite uniformly dispersed in the structure, ensuring seizure resistance.

The base of the sintered material after graphite precipitation is quenched and tempered to form tempered martensite or austenbur to become haenite, or adjusted to a pearlite or ferrite structure by an appropriate cooling rate.

The nickel-chromium cast iron sintered material containing graphite of the present invention is suitable as an outer layer material, which is the rolling layer of a rolling composite roll, but it is also suitable for various uses that require both wear resistance and seizure resistance (e.g. , guide rollers, table rollers, and other rollers around rolled materials, and hot plastic processing parts). When using the material of the present invention as the outer layer material of a composite roll, the outer layer may be formed on the outer circumferential surface of a roll shaft made of steel or the like using the Ninkel chrome cast iron powder, and the roll shaft may be sintered together.

(Example) Manufacturing example of a round bar finishing rolling stand exit guide roller (1) High chromium cast iron powder (particle size 140 mesh under) with the following composition was subjected to CIP (pressure 5.5 kgf/cm2)
) to obtain a molded cylinder having an outer diameter of 170 mm, an inner diameter of 60 mm, and a width of 105 mm.

・Powder composition (unit weight %, remainder substantial Fe) C: 1.6
0%, Si: 3.01%, Mn:
0.50%P: 0.004%, S:0
．． 007%, Ni/7.03%Cr:
2.98%, Mo: 1.68%, Cu
: 2.22% (2) Pressure the molded cylinder 25%
0 kgf/cm2, temperature] HIP treatment was performed at 150°C to obtain a sintered cylinder. The machining allowance for the cylindrical body is 1 for the product size.
It was processed with a forceps so that it could be cut into mm (i), and was subjected to the following heat treatments.

■ Graphitization annealing heat treatment 1,100°C did.

(2) Transformation heat treatment of retained austenite After heating to 530°C and holding for 10 hours, it was cooled to room temperature. This process was repeated twice to reduce residual austenite.

(3) After heat treatment, finishing processing was performed to obtain the product roller shown in FIG. The structure of the roller was composed of finely and uniformly precipitated graphite, a matrix structure, and a very small amount of eutectic hide.The matrix structure was tempered martensite, and almost no residual austenite was observed. Hardness is Hs87
It was ~89.

(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, and is guided to rotate when the rolled material coming out of the rolling mill comes into contact with its peripheral surface. For this reason, rollers are likely to seize when caught, and conventionally tilted cast iron rollers have been used. In this case, the wear resistance was poor and the rolling stock had to be revised once per approximately 300 tons, 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.

(Effects of the Invention) As explained above, the sintered nickel-chromium cast iron material having graphite of the present invention is sintered with nickel-chromium cast iron powder having a predetermined component of C: 1.0 to 1.9%. Because of this, almost no carbide is produced and the slip resistance is good. In addition, in conjunction with the strengthening of the base, the structure is refined, which improves wear resistance.
Moreover, the graphitization annealing heat treatment results in fine graphite being uniformly dispersed and precipitated in the sintered material, ensuring seizure resistance. Furthermore, by reducing the N+ content, it is possible to reduce retained austenite, which is also excellent in economical efficiency.

[Brief explanation of the drawing]

FIG. 1 shows a half-sectional view of a roller according to an embodiment.

Claims (1)

[Claims] (1) Chemical composition in weight%: C: 1.0 to 1.9%, Cr: 2.0 to 4.5%, Si:
1.5-4.0%, Mo: 0.4-5.0% Mn: 0.
5-1.5%, Ni: 13% or less, P: 0.1% or less, C
u: 0.5-4.0% S: 0.08% or less, Ni+Cu
: 4.0 to 15.0% A sintered material of nickel-chromium cast iron powder with the remainder essentially consisting of Fe, which is characterized by graphite precipitated in its structure by graphitization annealing heat treatment. Nickel chromium cast iron sintered material with.