JPH04221044A - High speed steel type sintered alloy - Google Patents

Abstract

PURPOSE:To improve strength, wear resistance, surface roughing resistance, pitting corrosion resistance, and seizure resistance by specifying respective contents of C, Si, Mn, Cr, Mo, W, Co, etc., in a sintered alloy. CONSTITUTION:The sintered alloy has a composition consisting of, by weight, <=1.7% C, <=0.6% Si, <=0.6% Mn, 3-8% Cr, 3-9% Mo, 5-14% W, 7-14% Co, >8-11% of one or >=2 elements among V, Ti, and Nb, and the balance essentially Fe. Further, if necessary, either or both of <=2% B and <=3% Ni are substituted for a part of Fe. If HIP sintering, etc., are applied to this alloy, the high-density high speed steel type sintered alloy can be formed. By using this sintered alloy as a rolling roll barrel member, roll life can be prolonged.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a high-speed steel-based sintered alloy useful as a constituent material of members that require wear resistance, roughness resistance, seizure resistance, etc., such as steel rolling rolls. Regarding.

0002

[Prior Art] The surface of the body of a roll for hot rolling or cold rolling of steel materials must have good wear resistance, be resistant to surface roughness (cracks, unevenness, chipping, etc.), and be resistant to seizure with the rolled material. It is necessary to have something that is difficult to 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 prevent harsher rolling conditions and to improve roll lifespan, rolls with a sintered alloy layer having a high-speed steel chemical composition formed on the body surface by hot isostatic pressure sintering, etc. have been developed. It has also been attempted to use it (Japanese Patent Application Laid-Open No. 58-213856, JP-A No. 63-297).
510 etc.).

0003

[Problem to be solved by the invention] High-speed steel alloys are subjected to tempering heat treatment such as quenching and tempering, resulting in 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 base and the dispersion-strengthening effect of carbide particles, it has good wear resistance and surface roughening resistance, and by applying this to rolling rolls, it is possible to expect an improvement in roll life. becomes. The present invention was made for the purpose of further improving the material properties of high-speed steel-based sintered alloys.

0004

[Means and effects for solving the problems] The high speed steel sintered alloy of the present invention has C: 1.7% or less and Si: 0.6%.
Below, Mn: 0.6% or less, Cr: 3 to 8%, Mo: 3
~9%, W: 5-14%, Co: 7-14%, V, Ti
, Nb: more than 8% and 11% or less (total amount), the remainder consisting essentially of Fe, if desired,
It has a chemical composition in which a part of Fe is replaced with one or two of the following elements: 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 explained below. All percentages indicating elemental content are by weight.

C: 1.7% or less C is carbide-forming carbon, V, Ti, Nb, W, Mo
, Cr, etc., to form carbides of MC type, M6C type, M2C type, etc., and increase the hardness of the alloy. However, increasing the amount of C causes deterioration in toughness and workability of the alloy due to excessive precipitation and coarsening of carbides. For this reason, 1.
The upper limit was set at 7%.

Si: 0.6% or less Si is an element that has a deoxidizing effect and an effect of improving hardenability. This effect can be sufficiently obtained by adding up to 0.6%, and there is no need to add more than 0.6%. Also,
An increase in the amount of Si causes excessive precipitation of carbides and associated embrittlement of the alloy. For this reason, it 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 also has the effect of improving hardenability. The addition amount to obtain this effect is sufficient to be up to 0.6%, and addition of a large amount leads to coarsening of austenite grains at high temperatures, causing embrittlement of the alloy. For this reason, 0.
The upper limit was set at 6%. Preferably it is 0.2 to 0.4%.

Cr: 3-8% Cr is an element that improves the hardenability of the alloy and also contributes to improving the corrosion resistance. At least 3% is required to achieve this effect. The effect increases as the amount added 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 the amount exceeds 5%, and is particularly effective in enhancing pitting corrosion resistance. However, if a large amount is added, the impact properties and softening resistance at high temperatures will decrease.
The upper limit is %.

Mo: 3 to 9% Mo is extremely effective in improving hardenability and contributes to improving resistance to temper softening. Further, it causes fine precipitation as an M2C type carbide and causes secondary hardening. These effects are ensured by adding 3% or more. However, when it exceeds 9%, the effect is almost saturated.

W: 5 to 14% W has the effect of improving hardenability by being dissolved in solid solution during austenitization for hardening. In addition, W is a strong carbide-forming element, and upon tempering, it precipitates finely as M6C type carbide and brings about remarkable secondary hardening. It also exhibits temper softening resistance. The lower limit of the amount added is set at 5% in order to obtain sufficient secondary hardening due to the precipitation of carbides. Increasing the amount added increases the effect, but on the other hand, the toughness etc. decreases due to coarsening of precipitated carbides, so the upper limit was set at 14%.

V, Ti, Nb: more than 8% and less than 11% V, Ti, and Nb can be removed by tempering treatment after quenching.
It precipitates as fine MC type carbide and causes remarkable secondary hardening. In order to achieve this effect sufficiently, the amount added should be more than 8% (in the case of two or more types, the total amount). However, if too much is added, the toughness of the alloy will be reduced due to excessive precipitation of carbides, and the workability will also be deteriorated, so the upper limit is set at 11%.

Co: 7 to 14% Co improves hardenability, and also improves heat resistance by forming a solid solution in the matrix, contributing to improvement in high-temperature strength. These effects are 7%
Obtained by the above addition. However, if it exceeds about 14%, the effect is almost saturated, so 14% is set as the upper limit.

[0013] The sintered alloy of the present invention may optionally contain one or two of the following elements: 2% or less of B and 3% or less of Ni.

B: 2% or less B is an element that replaces C, forms carbides, and contributes to improving wear resistance. 2% B is equivalent to 1% C. It also strengthens the base by dissolving it into 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 set at 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, since an increase in the amount of austenite makes machining difficult, it should not exceed 3%. Preferably it is 0.1 to 2.5%.

Although any sintering method can be used to produce the sintered alloy of the present invention, it is preferable to use a hot isostatic pressure sintering method (
HIP sintering method) is applied. According to the HIP sintering method,
This is because a highly dense sintered alloy can be obtained under the uniform action of high pressure.

The sintered alloy of the present invention can be used for various purposes, but since wear resistance, roughness resistance, etc. are problems with the surface of the member, the sintered alloy of the present invention may be used, for example, in the body of a rolling roll. When applying a suitable metal material (for example, JIS
G 4105 Cr-Mo alloy steel, 4103
It is preferable to form a roll body having a laminated structure using a hollow or solid cylindrical body made of a Cr-Ni-Mo alloy steel as a base material and covering the outer periphery with the sintered alloy of the present invention.

To explain 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, first, a suitable encapsulant (for example, made of carbon steel) is coated around the metal base material. This is surrounded by a cylindrical body), filled with alloy powder (gas atomized powder, etc., particle size: 500 μm or less) having a predetermined chemical composition as a sintering raw material, the powder packed layer is degassed, and sealed. A sintered alloy layer is formed by hot isostatic pressure sintering. 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 bed to reduce and remove the oxide film under heating, and then the bed is degassed and sealed for sintering. The sintering process is performed at a temperature of 900 to 1200
C. and pressure: approximately 500 to 1500 kgf/cm2 for an appropriate time (approximately 2 to 4 hours). During the sintering process, a strong adhesive bond is formed at the interface between the sintered alloy layer and the metal base material. After sintering is completed, the encapsulant is removed and any necessary shape corrections are made by machining.

After forming the sintered alloy layer on the surface of the metal base material as described above, the sintered alloy layer is subjected to refining heat treatment (quenching/tempering). The quenching and tempering treatment can be carried out according to conventional methods, and the quenching temperature is about 1050-1250℃,
The temperature is preferably 1100 to 1200°C, and cooling from the same temperature can be done using an oil bath, salt bath, etc., but in order to prevent cracks and cracks in the sintered alloy layer due to thermal stress. It is preferable to use a gas (such as N2 gas) as a refrigerant and cool at a controlled cooling rate (for example, 5 to 20° C./min) in an atmosphere of approximately normal pressure or pressurization (for example, 3 to 7 kgf/cm).

[0020] The tempering treatment following quenching is approximately 500
This is achieved by heating and maintaining the temperature at ~600°C, preferably 520~580°C, and then slowly cooling (for example, air cooling) once or multiple times (for example, 2 to 4 times).

[0021] Through quenching and tempering, the sintered alloy of the present invention has fine carbides precipitated in a matrix containing martensite or bainite phase, or these phases as the main phase with a small amount of residual austenite phase mixed in. A dispersed metal structure is provided. The precipitated carbide occupies about 15 to 25% in terms of area ratio, is abundant compared to the amount of carbide in general ingot material (usually about 10 to 15%), and is uniformly dispersed. Due to the chemical composition and metal composition, the sintered alloy of the present invention has improved wear resistance, roughness resistance, seizure resistance, corrosion resistance, etc., which are desired as materials for forming the body of rolling rolls. We are prepared.

FIG. 1 shows, as a specific example of the use of the sintered alloy according to the present invention, 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). The cross-sectional structure is schematically shown. This composite member (10) has, for example, an arbor (20) separately prepared in its hollow hole.
It is used as a rolling roll by fitting. In the example shown in the figure, a sintered alloy layer (12) having a constant layer thickness is placed on a base material (11).
), but this does not necessarily have to be the case; for example, in rolls with a caliber such as round steel finishing rolls, the sintered alloy layer is formed only on the circumferential groove surface. However, it goes without saying that other parts may have a partially 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 rolling rolls, if it is too thin, the sintered alloy layer will easily peel off due to the action of shear stress due to the rolling load, so it should be approximately 3 mm or more. It is preferable because the layer thickness is . However, if it is too thick, cracks will easily occur due to thermal stress, so
It is appropriate that the length be up to about 25 mm.

[0023]

[Example] Metal powder prepared to have a predetermined chemical composition (average particle size: 200 μm) is used as a sintering raw material, hot isostatic pressure sintering is performed, and then the sintered alloy block is quenched and tempered. A sample sintered alloy was obtained by treatment. However, the sintering process is performed at a temperature of 1150°C and a pressure of 1000 kgf/cm.
2. Holding time: 3 hours, hardening treatment:
After holding the temperature at 1200°C for 1 hour in a vacuum quenching chamber, N2 gas (at normal temperature and pressure) is introduced for gas cooling.The tempering process is performed by holding the temperature at 540°C for 5 hours and allowing it to cool. The pattern was repeated three times.

Table 1 shows the chemical composition of the sintered alloys tested. For each sample sintered alloy, a hardness (Hs) measurement, an abrasion 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. 1 to 8 are invention examples, No. 101 to 105 are comparative examples.

(1) Wear test The specific wear amount Ws (mm2/kg
) Measured (i) Rotating wheel: SUJ2: hardness (HRC) 60, rotating wheel width 3.0 mm (ii) Wear rate: 3.4 m/sec (iii) Wear distance: 200 m (iv) Final load: 16.8 kg・f

(2) Corrosion test specimen (test area 35 x 35, mm) was soaked in salt water (approximately 800
The process of immersing the test piece in 69.5 g of cc+NaCl (concentration: 8%) for 24 hours and leaving it to dry in the air for 24 hours was repeated five times, and the state of occurrence of pitting corrosion on the test piece was observed with the naked eye. In Table 2, “
The numerical value in the ``Number of Pitting Corrosion'' column indicates the number of minute dents caused by pitting corrosion that occurred on the surface of the test piece.

(3) Seizure resistance test A counter material (SUS304 stainless steel) was applied to the surface of the test piece by Falex type seizing test (pressing load: 150 kg).
is pressed to measure the rotational torque, and the presence or absence of seizure between the sliding surfaces of the test piece and the mating material is determined based on the presence or absence of abnormal fluctuations in torque (test time: 5 minutes). In Table 1, "○" in the "Seizure Resistance" column means no seizure (stable low torque), and "x" means seizure occurrence (abnormal torque fluctuation).

(4) Thermal shock test A test piece (Φ25×t5, mm) was heated to 900°C for 1 hour and then placed in water to repeat the heat cycle of heating and rapid cooling.Die check the presence or absence of cracks on the surface of the test piece. In Table 2, the values in the "Thermal Shock Property" column indicate the number of heat cycle repetitions until cracking occurs, and the ○ mark indicates
This indicates that no cracking occurred after 20 repetitions.

(5) Bending test The bending strength (Kgf/mm2) was measured by the three-point bending method. Test piece size: 3 x 4 x 50, mm, span distance: 30
mm.

[0030]

[Table 1]

[0031]

[Table 2]

The test results of the above examples show that the thermally sintered alloys of the invention examples (Nos. 1 to 8) have improved wear resistance, strength, corrosion resistance, and Rough skin,
This indicates that the material has thermal shock resistance, etc.

[0033]

[Effects of the Invention] The sintered alloy of the present invention has excellent and stable wear resistance, strength, corrosion resistance, roughness resistance, seizure resistance, etc. due to its chemical composition and metal structure. By coating the surface of a 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 improving the life of the roll and reducing roll maintenance can be obtained. Stable conditions have a significant effect on improving the quality of the rolled material. The sintered alloy of the present invention is also useful as a surface-modifying material for structural members such as bearings and cylinders that require wear resistance.

[Brief explanation of the drawing]

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

[Explanation of symbols]

11 Metal base material 12 Sintered alloy layer

Claims (4)

[Claims] [Claim 1] C: 1.7% or less, Si: 0.6
% or less, Mn: 0.6% or less, Cr: 3 to 8%, Mo:
3-9%, W: 5-14%, Co: 7-14%, V, T
A high-speed steel-based sintered alloy consisting of one or more of i, Nb: more than 8% and 11% or less, and the remainder substantially consisting of Fe. [Claim 2] C: 1.7% or less, Si: 0.6% or less, Mn: 0.6% or less, Cr: 3-8%, Mo: 3-8%.
9%, W: 5-14%, Co: 7-14%, V, Ti,
One or more types of Nb: more than 8% and less than 11%,
B: High-speed steel-based sintered alloy consisting of 2% or less, the remainder substantially Fe. [Claim 3] C: 1.7% or less, Si: 0.6% or less, Mn: 0.6% or less, Cr: 3-8%, Mo: 3-8%.
9%, W: 5-14%, Co: 7-14%, V, Ti,
One or more types of Nb; more than 8% and less than 11%,
A high-speed steel-based sintered alloy consisting of Ni: 3% or less and the remainder substantially Fe. [Claim 4] C: 1.7% or less, Si: 0.6% or less, Mn: 0.6% or less, Cr: 3-8%, Mo: 3-8%.
9%, W: 5-14%, Co: 7-14%, V, Ti,
One or more types of Nb: more than 8% and less than 11%,
A high-speed steel-based sintered alloy consisting of Ni: 3% or less, B: 2% or less, and the remainder substantially Fe.