JP2963579B2 - High speed steel based sintered alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed steel-based sintered alloy useful as a constituent material for members requiring wear resistance, surface roughness resistance, seizure resistance, etc., such as rolls for steel rolling. About.

[0002]

2. Description of the Related Art The surface of a body of a roll for hot or cold rolling of a steel material has good abrasion resistance, hardly causes rough surface (cracks, irregularities, chipping, etc.), and seizure with a material to be rolled. It is necessary for things to hardly occur. Conventionally, cast iron rolls have been used as hot rolling rolls, and forged steel rolls have been used as cold rolling rolls. Recently, as a measure to reduce the rolling conditions and to improve the service life of the roll, a roll with a sintered alloy layer having a high-speed steel-based chemical composition formed on the body surface by hot isostatic pressing sintering, etc. It has also been tried for use (JP-A-58-21856, JP-A-63-297).
No. 510).

[0003]

The high-speed steel alloy has a metal structure in which fine carbide particles are precipitated and dispersed in a hard matrix of a martensite or bainite phase by being subjected to a quenching and tempering tempering heat treatment. . Due to its hard matrix and the effect of strengthening the dispersion of carbide particles, it has good abrasion resistance and rough surface resistance, etc., and it can be expected to improve the roll life by applying it to rolling rolls. Becomes
The present invention has been made to further improve the material properties of a high-speed steel-based sintered alloy.

[0004]

The high-speed steel-based sintered alloy of the present invention has a C content of more than 1.7%, not more than 3.5%, not more than 0.6% of Si, and not more than 0.6% of Mn. 6% or less, Cr:
3-8%, Mo: 3-9%, W: 5-14%, V, T
one or more of i and Nb: 8% or less (total amount ),
And one or more of B: 2% or less, Ni: 3% or less
The seed has a chemical composition consisting essentially of Fe . Hereinafter, the reasons for limiting the components of the sintered alloy according to the present invention will be described.
All percentages indicating elemental content are weight percent.

C: more than 1.7% and 3.5% or less C is a carbide forming element, and V, Ti, Nb, W, M
Combines with o, Cr, etc. to form carbides of MC type, M ₆ C type, M ₂ C type, etc., and increases the hardness of the alloy. In order to sufficiently enhance this effect, the content is set to more than 1.7%. However, an increase in the amount of C, on the other hand, causes deterioration of the toughness of the alloy due to excessive precipitation and coarsening of the carbide and a decrease in workability. Therefore, the upper limit is 3.5%.

Si: 0.6% or less Si is an element having a deoxidizing effect and an effect of improving hardenability. This effect can be sufficiently obtained by adding up to 0.6%, and it is not necessary to add more. Also,
An increase in the amount of Si causes excessive precipitation of carbides and the resulting embrittlement of the alloy. Therefore, the content is set to 0.6% or less. Preferably, it is 0.2 to 0.4%.

Mn: 0.6% or less Mn has a deoxidizing effect and an effect of improving hardenability. The addition amount for obtaining this effect is sufficient up to 0.6%, and a large amount of addition causes coarsening of austenite grains at a high temperature and causes embrittlement of the alloy. For this reason,
The upper limit was 0.6%. Preferably, 0.2-0.4%
It is.

[0008] Cr: 3 to 8% Cr is an element for improving the hardenability of the alloy and contributes to the improvement of corrosion resistance. This effect requires at least 3%. The effect increases as the amount of addition increases, but the effect of improving hardenability can be sufficiently obtained by adding up to about 5%. The effect of improving corrosion resistance becomes remarkable when added over 5%, and is particularly effective in enhancing pitting corrosion resistance. However, the addition of a large amount causes a decrease in impact characteristics and a decrease in softening resistance at high temperatures.
% As the upper limit.

Mo: 3 to 9% Mo is remarkably effective in improving hardenability and contributes to improvement in temper softening resistance. Further, it precipitates finely as an M ₂ C-type carbide and causes secondary hardening. These effects are ensured by adding 3% or more. However, if it exceeds 9%, the effect is almost saturated.

W: 5 to 14% W has the effect of forming a solid solution at the time of austenitization for quenching to enhance quenchability. W is a strong carbide-forming element, and is finely precipitated as M ₆ C-type carbide by tempering to bring about remarkable secondary hardening. In addition, it shows tempering softening resistance. The lower limit of the addition amount is set to 5% in order to obtain sufficient secondary hardening due to precipitation of the carbide. The effect is increased by increasing the addition, but on the other hand, the toughness and the like are reduced due to the coarsening of the precipitated carbide, so the upper limit is 14%.

V, Ti, Nb: 8% or less Each of the elements V, Ti, and Nb precipitates as fine MC-type carbides by tempering after quenching and brings about remarkable secondary hardening. The effect is increased by increasing the amount of addition, but excessive addition of carbide causes excessive precipitation of carbides, which lowers the toughness of the alloy and deteriorates the workability. Therefore, the upper limit is 8%.

[0012] The sintered alloy of the present invention, together with the above elements,
Contains one or two elements of up to 2% B and up to 3% Ni.

B: 2% or less B is an alternative element to C and forms boride to contribute to improvement of wear resistance. 2% B is equivalent to 1% C. In addition, solid solution in the base strengthens the base. However, the addition of a large amount lowers the melting point of the alloy and lowers the strength, so the upper limit is 2%. Preferably it is 0.5-1%.

Ni: 3% or less Ni is an austenite phase stabilizing element, and is effective in improving toughness by increasing the amount of retained austenite. However, the increase in the amount of austenite, on the other hand, causes difficulty in machining, so that it should not exceed 3%. Preferably, it is 0.1 to 2.5%.

The sintering method for producing the sintered alloy of the present invention is arbitrary, but preferably a hot isostatic pressing sintering method (HIP sintering method) is applied. According to the HIP sintering method, a high-density sintered alloy can be obtained under a uniform action of a high pressing force.

The sintered alloy of the present invention is used for various purposes. However, since the wear resistance and rough surface resistance are problems of the surface of the member, for example, the sintered alloy of the present invention may be provided on the body of a rolling roll. When applying a suitable metal material (for example, JIS
G 4105 Cr-Mo alloy steel, 4103 Cr
-Ni-Mo alloy steel or the like), a roll body having a laminated structure in which a hollow or solid cylindrical body is used as a base material and the outer periphery thereof is coated with the sintered alloy of the present invention.

The manufacturing process of a composite member (for example, a roll for rolling) coated on the surface of a metal substrate with the sintered alloy of the present invention will be described. First, a suitable encapsulant (for example, carbon steel) is formed around the metal substrate. And filled with an alloy powder having a predetermined chemical composition (gas atomized powder or the like, particle size of, for example, 500 μm or less) as a sintering raw material.
The powder-filled layer is degassed, sealed, and subjected to hot isostatic pressing sintering to form a sintered alloy layer. If the sintered alloy powder is accompanied by a relatively large amount of oxide film, a reducing gas such as a hydrogen-containing gas is introduced into the powder packed layer, the oxide film is reduced and removed under heating, and then degassed and sealed. Hot isostatic pressing sintering may be performed. The hot isostatic pressing sintering is performed at a temperature of 900 to 1200 ° C. and a pressure of about 500 to 1
It is preferably achieved by maintaining the pressure at 500 kgf / cm ² for an appropriate time (about ² to 4 hours). During the sintering process, a strong close bonding relationship is formed at the interface between the sintered alloy layer and the metal substrate. After the completion of sintering, the capsule material is removed by machining and the necessary shape is corrected.

After forming the sintered alloy layer on the surface of the metal substrate as described above, the sintered alloy layer is subjected to a heat treatment (quenching / tempering). The quenching / tempering treatment may be performed according to a conventional method, and the quenching temperature is about 1050 to 1250 ° C.
Preferably, the temperature is from 1100 to 1200 ° C. For cooling from the same temperature, an oil bath, a salt bath, or the like can be used, but in order to prevent cracking and cracking of the sintered alloy layer due to thermal stress. The gas (N ₂ gas or the like) may be used as a refrigerant and cooled at a controlled cooling rate (for example, 5 to 20 ° C./min) in a substantially normal pressure or a pressurized (for example, 3 to 7 kgf / cm ² ) atmosphere. .

The tempering treatment following quenching is about 500
After heating and maintaining the temperature at 徐 600 ° C., preferably 520-580 ° C., the operation is gradually cooled (for example, air-cooled) once or a plurality of times (for example, 2 to 4 times).

In the sintered alloy of the present invention, carbides are finely precipitated by quenching and tempering in a martensite or bainite phase or a matrix containing these phases as a main phase and a small amount of a retained austenite phase. A distributed metallographic structure is provided. The precipitated carbides occupy about 20 to 45% in area ratio, are abundant compared to the amount of carbides (usually about 10 to 15%) in general ingots, and are uniformly dispersed. The sintered alloy of the present invention has improved abrasion resistance, skin roughness resistance, seizure resistance, corrosion resistance, etc., which are desired as a material for the body of a rolling roll, etc., by the chemical composition and the metal composition. Have.

FIG. 1 shows, as a specific example of the use of the sintered alloy according to the present invention, a cross-sectional structure of a cylindrical body having a laminated structure in which a sintered alloy layer 12 is formed on the outer peripheral surface of a cylindrical metal base material 11. Is shown. The composite member 10 is used as a roll for rolling, for example, by fitting an arbor 20 separately prepared in the hollow hole. In the example of the figure, the sintered alloy layer 12 having a constant layer thickness is formed over the entire outer peripheral surface of the base material 11, but this is not always necessary, and for example, a round steel finish rolling roll or the like may be used. In the roll having the caliber, it is needless to say that the sintered alloy layer may be formed only on the circumferential groove surface, and the other portion may have a partial composite structure in which the surface of the substrate is exposed. The thickness of the sintered alloy layer 12 is not particularly limited, but in the case of a roll for rolling, if it is too thin,
Since the peeling of the sintered alloy layer is easily caused by the action of the shear stress caused by the rolling load, the thickness is preferably about 3 mm or more. However, if the thickness is too large, cracks easily occur due to thermal stress. Therefore, it is appropriate to set the thickness to about 25 mm.

[0022]

EXAMPLE A metal powder (average particle size: 200 μm) prepared to a predetermined chemical composition is used as a sintering material, hot isostatic pressing and sintering, and then quenched and tempered in the sintered alloy block. By performing the treatment, a test sintered alloy was obtained. However, the sintering process was performed at a temperature of 1150 ° C. and a pressure of 1000 kgf / cm.
^2. Holding time: 3 hours, quenching treatment is performed after holding at 1200 ° C. for 1 hour in a vacuum quenching chamber.
The gas pattern was cooled by introducing N ₂ gas (normal temperature and normal pressure), and the tempering treatment was repeated three times in a heat pattern of heating and holding at 540 ° C. for 5 hours and allowing to cool.

Table 1 shows the chemical compositions of the test sintered alloys. For each of the test sintered alloys, a hardness (Hs) measurement, a wear test, a corrosion resistance test, a seizure test, a thermal shock test, and a bending test were performed, and the results shown in Table 2 were obtained. Test No. Nos. 1 to 6 are invention examples. 101 to 105 are comparative examples.

(1) Abrasion test The specific wear amount Ws (mm ² / kg)
f) measuring (i) rotating ring: SUJ2: hardness (H _RC) 60, the rotation wheel width 3.0 mm (ii) the wear rate: 3.4m / sec (iii) Wear distance: 200 meters (iv) final load: 16 .8kg ・ f

(2) Corrosion test A test piece (test area 35 × 35, mm) was subjected to salt water (about 800
(cc + NaCl 69.5 g, concentration 8%) for 24 hours, and left to dry in the air for 24 hours. This process is repeated five times, and the pitting corrosion of the test specimen is visually observed. The numerical value in the column of "number of pits" in Table 2 indicates the number of micro-pits due to pitting generated on the surface of the test piece.

(3) Seizure resistance test By a Falex-type seizure test (pressing load: 150 kg), a mating material (SUS304 stainless steel) was pressed against the surface of the test piece, and the rotational torque was measured. The presence or absence of seizure between the sliding surfaces of the test piece and the mating material is determined (test time: 5 minutes). In Table 1, "Seizure resistance"
In the column, “” means no seizure (low torque stability), and “×” means seizure occurrence (abnormal torque fluctuation).

(4) Thermal Shock Test A test specimen (Φ25 × t5, mm) was heated to 900 ° C. for 1 hour, and then a heat cycle of heating and quenching was repeated. The presence or absence of cracks on the test piece surface was determined by die check. In Table 2, the numerical value in the column of "thermal shock resistance" indicates the number of heat cycle repetitions up to the occurrence of cracks, and the mark "○" indicates that no cracks occurred after the repetition of 20 times.

(5) Bending test The bending strength (Kgf / mm ² ) was measured by a three-point bending method.
Specimen size: 3 × 4 × 50, mm, span distance 30m
m.

[0029]

[Table 1]

[0030]

[Table 2]

The test results of the above examples, sintering case of Invention Example
This shows that gold has improved wear resistance, strength, corrosion resistance, surface roughening resistance, thermal shock resistance, etc., over conventional high-speed steel-based sintered alloys.

[0032]

The sintered alloy of the present invention has excellent and stable wear resistance, strength, corrosion resistance, rough surface resistance, seizure resistance, etc. due to its chemical composition and metal structure. By coating the surface of the metal cylinder with the sintered alloy of the present invention and using it as a body member of a rolling roll, effects such as improvement of roll life, reduction of roll maintenance, etc. are obtained, and the body surface When the state is stable, a great effect can be obtained in improving the quality of the material to be rolled. The sintered alloy of the present invention is also useful as a material for a structural part such as a mold, a bearing, a cylinder, or a surface modifying material thereof.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing an example in which a sintered alloy according to the present invention is applied to a surface of a metal substrate.

[Explanation of symbols]

 11 Metal substrate 12 Sintered alloy layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-171373 (JP, A) JP-A-2-310344 (JP, A) JP-A-2-175847 (JP, A) JP-A-58-1983 213856 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 38/00 304 C22C 33/02

Claims (3)

(57) [Claims] 1. C: more than 1.7%, not more than 3.5%, S
i: 0.6% or less, Mn: 0.6% or less, Cr: 3 to 8
%, Mo: 3 to 9%, W: 5 to 14%, V, Ti, Nb
High-speed steel-based sintered alloy consisting of one or more of the following: 8% or less, B: 2% or less, the balance being substantially Fe. 2. C: more than 1.7% and not more than 3.5%,
i: 0.6% or less, Mn: 0.6% or less, Cr: 3 to 8
%, Mo: 3 to 9%, W: 5 to 14%, V, Ti, Nb
High-speed steel-based sintered alloy consisting of one or more of the following: 8% or less; Ni: 3% or less; 3. C: more than 1.7%, not more than 3.5%,
i: 0.6% or less, Mn: 0.6% or less, Cr: 3 to 8
%, Mo: 3 to 9%, W: 5 to 14%, V, Ti, Nb
One or more of the following: 8% or less, Ni: 3% or less,
B: High-speed steel-based sintered alloy consisting of 2% or less, with the balance being substantially Fe.