JPH062081A - High speed steel series sintered alloy - Google Patents

Abstract

PURPOSE:To provide the objective alloy high in wear resistance, surface roughening resistance, pitting corrosion resistance, seizing resistance or the like and to obtain the effect of improving the service life of a roll for rolling, e.g. at the time of applying it to its surface. CONSTITUTION:The objective high speed steel series sintered allay has a chemical compsn. contg., by weight, <=1.7% C, >0.6 to 3.5% Si, <=0.6% Mn, 3 to 8% Cr, 3 to 9% Mo, 5 to 14% W and total >8 to 11% of one or, two kinds among V, Ti and Nb, and the balance substantially Fe and, at request, in which one or two kinds of elements of <=2% B and <=3% Ni are substituted for a part of Fe.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a high-speed steel-based sintered alloy useful as a constituent material for members, such as rolls for rolling steel materials, which are required to have wear resistance, surface roughening resistance, seizure resistance and the like. Regarding

[0002]

2. Description of the Related Art The surface of the body of a roll for hot or cold rolling of steel material has good wear resistance, does not easily cause rough skin (cracks, unevenness, chipping, etc.), and prevents seizure with the material to be rolled. Things that are difficult to occur are necessary. Conventionally, cast iron rolls have been used as hot rolling rolls and forged steel rolls have been used as cold rolling rolls. In recent years, as a measure against severe rolling conditions and a roll life improvement measure, rolls with a sintered alloy layer having a high-speed steel-based chemical composition formed on the surface of the body by hot isostatic pressing have been used. Attempts have also been made to use it (JP-A-58-213856, JP-A-63-297).
510, etc.).

[0003]

The high-speed steel alloy is subjected to a refining heat treatment such as quenching and tempering to form a metal structure in which fine carbide particles are precipitated and dispersed in a hard matrix of martensite or bainite phase. . Due to its hard matrix and the action of strengthening the dispersion of carbide particles, it has good wear resistance and rough skin resistance, etc. By applying this to rolling rolls, it is possible to expect an improvement in roll life. Becomes
The present invention has been made for the purpose of further improving the material properties of high-speed steel-based sintered alloys.

[0004]

[Means and Actions for Solving the Problems] The high-speed steel-based sintered alloy of the present invention contains C: 1.7% or less and Si: 0.6%.
Over 3.5%, Mn: 0.6% or less, Cr: 3
~ 8%, Mo: 3-9%, W: 5-14%, V, Ti,
1 type or 2 types or more of Nb: more than 8% and 11% or less (total amount), the balance consisting essentially of Fe, and if desired,
It has a chemical composition in which a part of Fe is substituted with one or two elements of B: 2% or less and Ni: 3% or less. The reasons for limiting the components of the sintered alloy according to the present invention will be described below. All percentages indicating elemental contents are by weight.

C: 1.7% or less C is a carbide forming element, and V, Ti, Nb, W, M
By combining with o, Cr, etc., carbides of MC type, M ₆ C type, M ₂ C type, etc. are formed to increase the hardness of the alloy. However, increasing the amount of C causes the toughness of the alloy to deteriorate and the workability to decrease due to excessive precipitation of carbides and coarsening. For this reason,
The upper limit was 1.7%.

Si: more than 0.6% and 3.5% or less Si has a deoxidizing effect and a hardenability improving effect, and also enhances corrosion resistance, particularly pitting resistance. The effect of improving hardenability is recognized even if added in an amount of 0.6% or less, but in order to secure the effect of improving corrosion resistance, addition of more than 0.6% is required. Further, a part of Si is replaced with the M element (W, etc.) of the M ₆ C type carbide to enable the M element to be saved. Although these effects are increased by increasing the addition amount, on the other hand, the alloy becomes brittle as the precipitation amount of carbide increases, so the upper limit is 3.5%.

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

Cr: 3-8% Cr is an element for improving the hardenability of the alloy and also contributes to the improvement of corrosion resistance. At least 3% is required to obtain this effect. 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 the corrosion resistance becomes remarkable when the content exceeds 5%, and is particularly effective for strengthening the pitting corrosion resistance. However, as a large amount is added, impact properties and softening resistance at high temperatures are reduced.
% Is the upper limit.

Mo: 3-9% Mo is effective in improving the hardenability and contributes to the improvement in temper softening resistance. In addition, it is finely precipitated as M ₂ C type carbide to cause secondary hardening. These effects are secured by the addition of 3% or more. However, if it exceeds 9%, the effect is almost saturated.

W: 5 to 14% W has the effect of enhancing the hardenability by forming a solid solution during austenitization for quenching. Further, W is a strong carbide forming element, and by the tempering treatment, it is finely precipitated as M ₆ C type carbide to bring about a remarkable secondary hardening. In addition, it exhibits temper softening resistance. The lower limit of the amount added is 5% in order to obtain sufficient secondary hardening due to the precipitation of the carbide. The effect is increased by increasing the amount of addition, but on the other hand, the toughness etc. decreases due to the coarsening of precipitated carbides, so the upper limit was made 14%.

V, Ti, Nb: more than 8% and 11% or less V, Ti, and Nb elements are precipitated as fine MC type carbides by the tempering treatment after quenching to cause remarkable secondary hardening. . In order to make this effect sufficient, the addition amount is set to more than 8% (in the case of two or more kinds, the total amount). However, if too much is added, excessive precipitation of carbides causes a decrease in the toughness of the alloy and also deteriorates the workability.
% Is the upper limit.

If desired, the bond gold of the present invention is added with one or two elements of 2% or less of B and 3% or less of Ni.

B: 2% or less B is a C-substituting element and forms a boride to contribute to the improvement of wear resistance. 2% B is equivalent to 1% C. It also forms a solid solution in the base to strengthen the base. However, addition of a large amount lowers the melting point of the alloy and causes a decrease in strength, so the upper limit is 2%. It is preferably 0.5 to 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, an increase in the amount of austenite, on the other hand, causes difficulty in machining, but should not exceed 3%. It is preferably 0.1 to 2.5%.

The sintering method for producing the sintered alloy of the present invention is arbitrary, but the hot isostatic pressing method (HIP sintering method) is preferably applied. This is because according to the HIP sintering method, a highly dense sintered alloy can be obtained under the uniform action of a high pressure.

The sintered alloy of the present invention is used for various purposes, but since the wear resistance and the surface roughening resistance are problems of the surface of the member, for example, the sintered alloy of the present invention is applied to the body of a rolling roll. If applicable, a suitable metal material (for example, JIS
G 4105 Cr-Mo alloy steel, 4103 Cr
It is advisable to form a roll body having a laminated structure in which a hollow or solid cylindrical body made of —Ni—Mo alloy steel or the like) 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 rolling roll) in which the surface of a metal base material is coated with the sintered alloy of the present invention will be described. First, a suitable encapsulant (for example, carbon steel It is surrounded by a cylindrical body, and is filled with an alloy powder having a predetermined chemical composition (gas atomized powder, etc., particle diameter of 500 μm or less, for example) as a sintering raw material.
The powder-filled layer is degassed, hermetically sealed, and subjected to hot isostatic pressing 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 hydrogen-containing gas is introduced into the powder packed bed to reduce and remove the oxide film under heating, and then degassing and sealing. Hot isostatic pressing sintering may be performed. The hot isostatic pressing sintering process is performed at a temperature of 900 to 1200 ° C. and a pressure of about 500 to 1.
It is preferably achieved by holding at 500 kgf / cm ² for a suitable time (about ² to 4 hours). In 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 encapsulant is removed and necessary shape correction is performed by machining.

After the sintered alloy layer is formed on the surface of the metal base material as described above, heat treatment (quenching / tempering) is performed on the sintered alloy layer. The quenching / tempering treatment may be carried out according to a conventional method, and the quenching temperature is about 1050 to 1250 ° C.
The temperature is preferably 1100 to 1200 ° C., and cooling from the same temperature can be performed using an oil bath, a salt bath, etc., but in order to prevent cracks and fractures of the sintered alloy layer due to thermal stress. In addition, a gas (N ₂ gas or the like) is used as a refrigerant, and it may be cooled at a controlled cooling rate (for example, 5 to 20 ° C./minute) in a substantially normal pressure or pressurized (for example, 3 to 7 kgf / cm ² ) atmosphere. .

The tempering process following quenching is approximately 500
It is achieved by carrying out an operation of gradually heating (for example, air cooling) once or a plurality of times (for example, 2 to 4 times) after heating and holding at ˜600 ° C., preferably 520 to 580 ° C.

In the sintered alloy of the present invention, carbides are finely precipitated in the martensite or bainite phase or a matrix containing these phases as a main phase and a small amount of retained austenite phase by quenching and tempering treatment. A dispersed metallographic structure is provided. The precipitated carbide occupies about 20 to 45% in area ratio, is abundant in comparison with the amount of carbide in a general ingot (usually about 10 to 15%), and is uniformly dispersed. Sintered alloy of the present invention, by the chemical composition and the metal composition, improved wear resistance, surface roughening resistance, seizure resistance, corrosion resistance, etc. desired as the body material of the rolling roll, etc. I have it.

FIG. 1 is a schematic sectional view 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 substrate 11 as a specific example of the use of the sintered alloy according to the present invention. It is shown in the figure. The composite member 10 is used, for example, as a rolling roll by fitting a separately prepared arbor 20 in its hollow hole. In the illustrated example, 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 necessarily the case, and for example, a round steel finish rolling roll or the like may be used. Needless to say, in the roll having the caliber, the sintered alloy layer may be formed only on the circumferential groove surface of the roll and the other portion may have a partial composite structure in which the surface of the base material remains exposed. The layer thickness of the sintered alloy layer 12 is not particularly limited, but in the case of a rolling roll, if it is too thin,
The peeling of the sintered alloy layer is likely to occur due to the action of the shearing stress due to the rolling load, so that the layer thickness is about 3 mm or more, which is preferable. However, if it is made too thick, cracks due to thermal stress are likely to occur, so it is appropriate to set the thickness to about 25 mm.

[0022]

[Example] Using a metal powder (average particle size: 200 μm) prepared to a predetermined chemical composition as a sintering raw material, hot isostatic pressing was performed, and then the sintered alloy block was quenched and tempered. Processing was performed to obtain a test sintered alloy. However, the sintering process was performed at a temperature of 1150 ° C. and a pressure of 1000 kgf / cm.
² , holding time: performed under the condition of 3 hours, the quenching treatment, after holding for 1 hour at 1200 ℃ in a vacuum quenching chamber,
The heating pattern was performed by introducing N ₂ gas (normal temperature and normal pressure) and cooling the gas, and the tempering treatment was repeated three times with a heating pattern of heating and holding at 540 ° C. for 5 hours and allowing to cool.

Table 1 shows the chemical composition of the test sintered alloys. The test sintered alloys were subjected to hardness (Hs) measurement, wear test, corrosion resistance test, seizure test, thermal shock test, and bending test, and the results shown in Table 2 were obtained. Sample Nos. 1 to 8 are invention examples, and Nos. 101 to 105 are comparative examples.

(1) Wear test A specific wear amount Ws (mm ² / kg) was measured by the Ogoshi-type rapid wear test.
f) is measured (i) Rotating wheel: SUJ2: Hardness (H _RC ) 60, Rotating wheel width 3.0 mm (ii) Wear speed: 3.4 m / sec (iii) Wear distance: 200 m (iv) Final load: 16 .8 kg · f

(2) Corrosion test A test piece (test area of 35 × 35, mm) is treated with salt water (about 800).
The treatment of immersing in cc + NaCl 69.5 g, concentration 8%) for 24 hours and leaving it to dry in the atmosphere for 24 hours is repeatedly performed 5 times, and the pitting corrosion occurrence state of the test piece is visually observed. The numerical value in the "number of pitting corrosion" column in Table 2 indicates the number of minute concave holes due to pitting corrosion generated on the surface of the test piece.

(3) Seizure resistance test By the Falex type seizure test (pressing load: 150 kg), the 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 contact surfaces of the test piece and the mating material is determined (test time: 5 minutes). "Seizure resistance" in Table 1
In the column, "○" means no seizure (stable low torque), and "x" means seizure (torque abnormal fluctuation).

(4) Thermal shock test A test piece (Φ25 × t5, mm) was heated to 900 ° C. for 1 hour and then heated / quenched in a water cycle. The presence of cracks on the surface of the test piece is judged by die check. In Table 2, the numerical value in the "thermal shock resistance" column indicates the number of times the heat cycle was repeated until cracking occurred, and the mark "○" indicates that cracking did not occur after 20 times of repetition.

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

[0029]

[Table 1]

[0030]

[Table 2]

The test results of the above examples show that the sintered alloys of the invention examples (Nos. 1 to 8) have improved wear resistance, strength, corrosion resistance and rough skin resistance over conventional high speed steel-based sintered alloys. It has been shown that the material has heat resistance and thermal shock resistance.

[0032]

The sintered alloy of the present invention has excellent and stable wear resistance, strength, corrosion resistance, surface roughening resistance, seizure resistance, etc. due to its chemical composition and metal structure. By coating the surface of the metal cylindrical body 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 and reduction of roll maintenance can be obtained, and the body surface thereof The stable state has a great effect on improving the quality of the material to be rolled. The sintered alloy of the present invention is also useful as a material for structural parts such as molds, bearings, and cylinders, or a surface-modifying material thereof.

[Brief description of drawings]

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

[Explanation of symbols]

 11 Metal substrate 12 Sintered alloy layer

Claims (4)

[Claims] 1. C: 1.7% or less, Si: more than 0.6%, 3.5% or less, Mn: 0.6% or less, Cr: 3-8.
%, Mo: 3 to 9%, W: 5 to 14%, V, Ti, Nb
1 type or 2 types or more: a high-speed steel-based sintered alloy containing more than 8% and 11% or less and the balance substantially Fe. 2. C: 1.7% or less, Si: more than 0.6%, 3.5% or less, Mn: 0.6% or less, Cr: 3-8.
%, Mo: 3 to 9%, W: 5 to 14%, V, Ti, Nb
1 to 2 or more: more than 8% and 11% or less, B:
A high-speed steel-based sintered alloy containing 2% or less and the balance substantially Fe. 3. C: 1.7% or less, Si: more than 0.6%, 3.5% or less, Mn: 0.6% or less, Cr: 3-8.
%, Mo: 3 to 9%, W: 5 to 14%, V, Ti, Nb
1 to 2 or more: over 8% and 11% or less, N
i: High-speed steel-based sintered alloy consisting of 3% or less and the balance substantially Fe. 4. C: 1.7% or less, Si: more than 0.6%, 3.5% or less, Mn: 0.6% or less, Cr: 3-8.
%, Mo: 3 to 9%, W: 5 to 14%, V, Ti, Nb
1 to 2 or more: over 8% and 11% or less, N
i: 3% or less, B: 2% or less, the balance being a high-speed steel-based sintered alloy consisting essentially of Fe.