JPH0787931B2 - Composite member with excellent pitting resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a rolling method in which a key portion of a metal substrate surface is coated with a sintered alloy having excellent pitting corrosion resistance as well as abrasion resistance, seizure resistance, etc. The present invention relates to a composite member useful as a roll or the like.

[Conventional technology]

The body surface of the roll for hot rolling or cold rolling of steel is
It is necessary to have good wear resistance, to prevent rough skin (cracks, irregularities, chips, etc.), and to prevent seizure from the rolled steel material. 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 against severer rolling conditions and a measure for improving roll durability, it has been attempted to use a roll having a sintered alloy layer having a high-speed steel-based chemical composition formed on the body surface (JP-A-58).
-213856, JP-A-63-297510, etc.).

[Problems to be Solved by the Invention]

The roll coated with the high-speed steel-based sintered alloy layer on the body surface has wear resistance and surface roughening resistance superior to cast iron rolls and forged steel rolls, and has excellent mechanical properties such as strength, There is a problem that pitting corrosion is likely to occur during use. If minute concave holes are generated due to pitting corrosion, the surface becomes rough from the minute holes and becomes a cause of impairing the surface quality of the rolled steel material. Therefore, the surface search must be repeated for a relatively short period of use.

The present invention, for the high-speed steel-based sintered alloy, the purpose is to enhance the pitting corrosion resistance without deteriorating its wear resistance, seizure resistance and the like, and to enable stable use as a roll material or the like. It is a thing.

[Means and Actions for Solving the Problems]

The composite member of the present invention has, as a coating layer, C: 2 to 3.5%, Si: 0.4% or less, Mn: 0.4% or less, Cr: 6.5 to 20 as a coating layer in a key part of the surface of the metal substrate.
%, V: 6-12%, W: 5-14%, Co: 7-14%, Mo: 3-9%,
The balance is a sintered alloy layer (high Cr layer-bonded gold layer) having a chemical composition substantially consisting of Fe, C: 2 to 3.5%, Si: 0.6 to 3.5%, Mn: 0.4% or less, Cr: 3 to 6
%, V: 6-12%, W: 5-14%, Co: 7-14%, Mo: 3-9%,
The balance is a sintered alloy layer (high Si sintered alloy layer) having a chemical composition consisting essentially of Fe, or C: 2 to 3.5%, Si: 0.6 to 3.5%, Mn: 0.4% or less, C
r: 6.5-20%, V: 6-12%, W: 5-14%, Co: 7-14%, Mo:
It is characterized in that a sintered alloy layer (high Cr high Si sintered alloy layer) having a chemical composition of 3 to 9% and the balance substantially consisting of Fe is formed.

Hereinafter, the reasons for limiting the components of the sintered alloy of the present invention will be described. %
Are all% by weight.

C: 2 to 3.5% C increases the hardness of the sintered alloy by forming a solid solution in the matrix and forming a carbide of V or W in part. The lower limit of the amount of C is set to 2%.
This is because the amount of carbides in the steel is insufficient and it is not possible to sufficiently enhance the sophistication. On the other hand, the upper limit of 3.5% is that if it exceeds that, the toughness is increased due to the coarsening of the V and W carbides. Because it will decrease.

Si: 0.6 to 3.5% (or 0.4% or less) Si is effective in improving the pitting corrosion resistance of the sintered alloy. It also has the effect of improving hardenability. The improvement of pitting corrosion resistance by Si is obtained by adding 0.6% or more, and the effect becomes large as the amount of addition increases. However, on the other hand, the thermal and mechanical impact properties of the sintered alloy tend to deteriorate, so the upper limit is 3.5%. The effect of improving the hardenability by Si can be obtained by adding a small amount, and the contribution of secondary hardening by the tempering treatment after quenching is small, and the effect of improving the high temperature hardness is small. Therefore, when only the effect of improving the hardenability is intended, addition of up to 0.4% is sufficient.

Mn: 0.4% or less Mn is an element that improves hardenability, but secondary hardening due to tempering treatment cannot be expected, so the effect of improving high-temperature hardness is small, so addition up to 0.4% is sufficient.

Cr: 6.5 to 20% (or 3 to 6%) Cr improves the hardenability of the sintered alloy and enhances the temper softening resistance. Furthermore, the effect of improving the pitting corrosion resistance is shown with the increase of the addition amount. At least 6.5% is required to obtain the effect of improving the pitting corrosion resistance by adding Cr, and the effect is increased by increasing the amount, but at the same time, the seizure resistance to the red hot steel material decreases, and the roughening resistance tends to decrease. , 20
%, Preferably 15%. The effect of improving hardenability and temper softening resistance by Cr is obtained by adding 3% or more, and addition up to 6% is sufficient.
When it is intended to improve hardenability and temper softening resistance, the addition amount is 3 to 6%.

V: 6 to 12% V is precipitated as fine MC type carbides by the tempering treatment after quenching to cause a remarkable secondary hardening phenomenon, and also exhibits tempering softening resistance. Further, it contributes to the improvement of mechanical properties such as toughness due to the refinement of the sintered alloy structure. The effect of improving the mechanical properties due to the refinement of the structure can be obtained by adding a small amount of less than 9%, but in order to obtain sufficient high hardness and high wear resistance due to the precipitation of MC type carbides, at least 6% is added. Need. Although the effect increases with an increase in the addition amount, if it is too large, mechanical properties such as toughness are deteriorated due to coarsening of precipitated carbides, and machinability is deteriorated.
The upper limit is 12%.

W: 5-14% W is a strong carbide-forming element, and can be tempered
Finely precipitates as MC type carbide and brings about a remarkable secondary hardening. It also exhibits tempering softening resistance. The lower limit of addition is 5
% Is to obtain a sufficient secondary hardening due to the precipitation of MC type carbide. Although hardening is increased by increasing the addition amount, 14% is set as the upper limit because the mechanical properties such as toughness decrease due to the coarsening of precipitated carbides.

Co: 7 to 14% Co promotes the precipitation of carbides by the tempering treatment and the strengthening of the sintered alloy by the conversion of the matrix to secondary martensite, and is effective in improving the high temperature hardness. This effect is 7
It is obtained by adding more than 100%. However, if it exceeds 14%, the effect is almost saturated, so the upper limit is 14%.

Mo: 3 to 9% Mo enhances hardenability and forms fine carbides by tempering treatment to cause remarkable secondary hardening, which is effective in maintaining high temperature hardness. This effect is obtained by adding 3% or more. However, if it exceeds 9%, the effect is almost saturated, so the limit is set to 9%.

The sintered alloy of the present invention is produced by a hot isostatic pressing method or the like, and by quenching and tempering treatment, fine MC type and / or M ₆ C type carbides are formed in a bainite or martensite phase matrix. A dispersed and precipitated structure is given. The sintered alloy is extremely hard, has high wear resistance, is excellent in seizure resistance, etc. as shown in the examples described later, has improved pitting corrosion resistance, and has a high corrosion resistance even in a corrosive environment. It does not easily cause skin roughness due to food and its development, and maintains a smooth surface condition for a long period of time.

The composite member having the sintered alloy of the present invention as a coating layer uses a metal powder adjusted to the above chemical composition as a sintering raw material, and a sintered alloy layer is formed on the surface of a metal substrate by a hot isostatic pressing method. Are formed, and then the sintered alloy layer is subjected to quenching and tempering treatments.

Explaining the manufacturing process, first, a packing layer of sintering raw material powder is formed on the surface of a metal base material by using an appropriate encapsulant, and the powder packing layer is deaerated and sealed, and hot isostatic pressing is performed. Subject to pressure sintering to form a sintered alloy layer. The sintering process is performed at a temperature of about 900-1,200 ° C and a pressure of about 500-1,500.
It is preferably achieved by holding at kgf / cm ² for a suitable time (for example, 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. When the raw material powder is accompanied by a relatively large amount of oxide film, a reducing gas may be introduced under heating to reduce and remove the oxide film before deaeration and sealing of the powder packed bed. . After the completion of sintering, the encapsulant is removed and machining is performed to correct the shape. In addition, the material of the metal base material is arbitrarily selected according to the intended use and use conditions of the composite member, and when it requires strength and toughness like a rolling roll. For this purpose, various tough steels such as SCM steel and SNCM steel are preferably used.

The quenching temperature for quenching and tempering of sintered alloys is
1,050-1,250 ℃, preferably 1,100-1,200 ℃,
Also, cooling from that temperature is gas cooling using a gas of approximately normal pressure as a refrigerant or forced gas cooling using a pressurized gas (for example, 3 to 7 kgf / cm ² ) as a refrigerant in order to prevent cracks and deformation. It is preferable to carry out.

The tempering treatment following quenching is performed by heating and holding at 500 to 600 ° C, more preferably 520 to 580 ° C, and then gradually cooling it.
It is preferably achieved by repeating one time or a plurality of times (for example, 2 to 4 times).

The above heat treatment gives the sintered alloy layer a metallic structure in which carbides are finely precipitated and dispersed in the matrix of martensite or bainite phase. The precipitated carbide occupies about 25 to 35% in area ratio, is abundant in comparison with the amount of carbide (generally about 10 to 15%) in a general ingot, and has excellent uniform dispersibility.

FIG. 1 is a schematic cross-sectional structure of a cylindrical body in which a sintered alloy layer (2) having the above chemical composition is formed on the outer peripheral surface of a metal base material (1) having a cylindrical shape, as an example of the composite member of the present invention. Is shown in. The member of this composite is used as a rolling roll, for example, by fitting an arbor (3) in its hollow hole. In the example shown, a sintered alloy layer (20) with a constant layer thickness
Is formed over the entire outer peripheral surface of the base material (10),
This does not necessarily have to be the case.For example, in a roll having a caliber such as a round steel finishing rolling roll, a sintered alloy layer is formed on the circumferential groove surface of the roll, and the other portion is a portion where the surface of the base material remains exposed. It goes without saying that a composite structure may be used.
The layer thickness of the sintered alloy layer (2) is not particularly limited,
In the case of a rolling roll, if it is too thin, peeling easily occurs due to the action of shear stress generated in the sintered alloy layer due to the rolling load, so that the layer thickness is preferably about 3 mm or more. However, if it is made too thick, the tendency of cracking due to thermal stress increases, so it is appropriate to set the upper limit to about 25 mm.

〔Example〕

Example 1 Metal powder adjusted to a predetermined chemical composition (average particle size: 200 μ)
m) was used as a sintering raw material, hot isostatic pressing was performed, and then the sintered alloy block was quenched and tempered to obtain a test sintered alloy. However, the temperature of the sintering process is 1,15
0 ° C, pressurizing force: 1,000 kgf / cm ² , holding time: 3 hours, quenching treatment is performed in a vacuum quenching chamber at 1,200
After holding at ℃ for 1 hour, Ar gas (normal temperature and normal pressure) is introduced and gas cooling is performed.
This was performed by repeating a heat pattern in which the material was heated and held for a certain time and allowed to cool three times.

Table 1 shows the chemical composition of the test sintered alloys, the hardness (Hs) obtained for each test sintered alloy, the seizure resistance test result, and the pitting corrosion test result. No. 1 to 10 are invention examples, No. 101 to 105
Is a comparative example. Of invention examples No. 1 to 10, No. 1 to 4 are high C
r Sintered alloy, No. 5 to 8 are high Si sintered alloys, No. 9 and 10 are high Si
・ High Cr sintered alloy. Comparative Examples Nos. 101 to 103 are sintered alloys having a low content of Si and Cr (contents of elements other than Si and Cr satisfy the requirements of the present invention), and Comparative Examples No. 1
04 is chilled cast iron which is a typical conventional casting roll material.

The pitting corrosion test and the seizure resistance test were conducted as follows.

(I) Pitting corrosion test Specimen (test area 35 x 35, mm) is treated with salt water (about 800cc + NaCl
The sample is soaked in 69.5 g (concentration 8%) for 24 hours, and then left to dry in the air for 24 hours. This treatment is repeated 5 times, and then the surface properties of the test piece are visually observed. The numerical value in the "pitting corrosion resistance" column in Table 1 indicates the number of minute recesses due to pitting corrosion generated on the surface of the test piece, and "rough skin" in the same column indicates that roughening due to the progress of pitting corrosion occurred. I mean.

(Ii) Seizure resistance test A flex type seizure test (pressing load: 150 kg) was used to press the mating material (SUS 304 stainless steel) against the surface of the test piece and measure the rotational torque. The presence or absence of seizure between the sliding contact surface with the mating material is determined. First
In the table, “◯” in the “Seizure resistance” column means no seizure (stable torque value low), and “x” means seizure (torque value abnormal fluctuation). Note that FIG. 2 shows the torque measurement results obtained for Invention Example No. 1, and FIG. 3 is for Comparative Example No. 104.
The torque measurement result about (chilled cast iron) is shown. The curve (a) in each figure shows the load (kg) of the mating material on the surface of the test piece, the curve (b) shows the rotational torque (kg · cm), and the one scale on the vertical axis showing the load (kg) is 50kg, 1 scale of the vertical axis showing torque (kgcm) is 10kgcm,
The horizontal axis is time (10 seconds per scale).

From the above test results, the sintered alloy of the comparative example (No. 101 ~ 10
3) has higher hardness and better seizure resistance than chilled cast iron (No.104), but pitting corrosion resistance is not sufficient,
A large number of minute concave holes are generated or roughened due to their development. On the other hand, the invention examples (No. 1 to 10) have high hardness and high seizure resistance, as well as excellent pitting corrosion resistance, and the generation and development of minute recesses even in corrosive environments. It can be seen that the surface condition is small and the surface condition can be kept smooth for a long time.

Example 2 [I] Manufacture of sample roll SCM440 steel (0.4C-0.35Si-0.75Mn-1Cu) as a metal substrate
-0.2Mo) centrifugally cast cylinder, four kinds of metal powders A, B, C and D are prepared as sintered alloy raw material powders, the encapsulant is melted and the metal powder is filled on the outer peripheral surface side of the metal base material. Then, after degassing and sealing, hot isostatic pressing is performed, and after the completion of sintering, the capsule material is removed by mechanical processing, rough processing is applied, and then the sintered alloy layer is quenched and tempered. Then, the composite members A, B, C and D having the concentric two-layer structure of the metal base material (1) and the sintered alloy layer (2) shown in FIG.
(Both are external shape: 364 mm, length: 100 mm, sintered alloy layer thickness: 7
mm).

The chemical structures of the sintered alloy layers of the composite members A, B, C and D are trial numbers (No.) in Table 1 of Example 1, respectively.
Identical to 1, 4, 9 and 101. In addition, sintering treatment,
The quenching and tempering treatment was performed under the same conditions as those in Example 1.

Each of the composite members A to D has no defects in the sintered alloy layer and the interface with the metal base material due to the die check and the ultrasonic flaw detection, and the interface is perfect over the entire circumference. It was confirmed that they were fusion-bonded to each other.

Each of the composite members A to D is used as a roll body member, an arbor is shrink-fitted in the hollow hole of the roll member, and then a finishing process required as a rolling roll is performed to obtain test rolls A to D (A, B, C:
Invention Example, D: Comparative Example) was obtained.

[II] Actual machine test As a result of using the above-mentioned test rolls A to D as flat steel finish rolling rolls, the test rolls A to C of the invention examples are higher than the high hardness ductile cast iron roll which is a typical conventional casting roll. Then
The wear rate was a fraction or less, there was no seizure with the rolled steel material, and surface roughness due to pitting was also slight. Also,
Test rolls A to C (invention example) and test roll D (comparative example)
Compared with the above, there is no substantial difference between the two in terms of wear resistance and seizure resistance, but the test rolls A to C have a low rate of pitting corrosion and progress to rough skin, resulting in rough skin due to pitting corrosion. The frequency of surface grinding required for surface repair was reduced, and as a result, the continuous service life until surface grinding was required was about 2 to 4 times that of the test roll D.

〔The invention's effect〕

The composite member of the present invention has excellent and stable wear resistance, seizure resistance, pitting corrosion resistance, etc. due to the sintered alloy layer formed on the surface of the base material. By using it in combination with arbor etc. as the material of the part, a stable service life that surpasses that of conventional rolls can be obtained, and the stable surface condition of the body part has a great effect on the quality improvement of the material to be rolled. Is obtained. The composite member of the present invention is also useful as a structural member such as a bearing and a cylinder.

[Brief description of drawings]

FIG. 1 is an axial half-cut sectional view showing an example of a composite member of the present invention, and FIGS. 2 and 3 are graphs showing changes in torque and load in a seizure resistance test. 1: Metal substrate, 2: Sintered alloy layer, 3: Arbor.

Continuation of front page (56) Reference JP-A-2-175014 (JP, A) JP-A-61-266106 (JP, A) JP-A-63-195250 (JP, A) JP-A-2-11739 (JP , A) JP-A-58-213856 (JP, A) JP-A-63-297510 (JP, A) JP-A-63-52703 (JP, A)

Claims (3)

[Claims] 1. A C: 2-3.5%, Si:
0.4% or less, Mn: 0.4% or less, Cr: 6.5 to 20%, V: 6 to 12%,
W: 5-14%, Co: 7-14%, Mo: 3-9%, balance virtually Fe
A composite member excellent in pitting corrosion resistance, characterized in that a sintered alloy layer having a chemical composition consisting of is formed. 2. C: 2 to 3.5%, Si:
0.6-3.5%, Mn: 0.4% or less, Cr: 3-6%, V: 6-12%,
W: 5-14%, Co: 7-14%, Mo: 3-9%, balance virtually Fe
A composite member excellent in pitting corrosion resistance, characterized in that a sintered alloy layer having a chemical composition consisting of is formed. 3. C: 2 to 3.5%, Si:
0.6-3.5%, Mn: 0.4% or less, Cr: 6.5-20%, V: 6-12
%, W: 5 to 14%, Co: 7 to 14%, Mo: 3 to 9%, the balance being a sintered alloy layer consisting essentially of Fe, which is excellent in pitting corrosion resistance. Composite member.