JPH06256885A - Corrosion resistant and wear resistant alloy - Google Patents

Abstract

PURPOSE:To improve the hydrochloric acid resistance of an alloy and furthermore to improve its wear resistance, in a chromium base alloy layer of a Cr-Ni- W or Mo allay having a specified compsn. by providing its surface with a nitriding layer. CONSTITUTION:At least the surface of a chromium base allay layer constituted of, by weight, 30.0 to 48.O% Ni and 1.5 to 15.0% W or/and 1.0 to 6.5% Mo so as to satisfy the total of W+Mo of 15.0 at the maximum, and the balance >=40.0% Cr is provided with a nitriding layer. The thickness of the nitriding layer can be formed into a suitable one by using an ordinary nitriding device and controlling the heating temp. and time. If required, the same alloy layer may furthermore be added with <=15.0% Fe or/and <=10.0% Co so as to satisfy the total of Fe and Co of 20 at the maximum or moreover be added with 0.3 to 2.0% C, 0.1 to 1.5% B and 0.1 to 3.0% Si.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromium-based alloy which has excellent corrosion resistance, particularly hydrochloric acid resistance, and wear resistance.

[0002]

2. Description of the Related Art Conventionally, Co-C represented by stellite has been used as a hard facing material having abrasion resistance and corrosion resistance.
rW alloys (hereinafter referred to as CoCr alloys) and Ni-Cr-B-Si alloys (hereinafter referred to as NiCr alloys) represented by Colmonoy are widely used, but in recent years the environment of use has become more severe, and some parts In, the wear resistance and the corrosion resistance are not satisfactory. For these reasons, there is an increasing demand for the development of hard facing materials that are more excellent in toughness, wear resistance and corrosion resistance than CoCr alloys and NiCr alloys.

The present inventors have developed Cr-Ni-W and / or M in order to meet the problems and requirements for CoCr alloys and NiCr alloys.
Focusing on alloys, we developed a chromium-based alloy for hard facings that has excellent toughness, wear resistance and corrosion resistance,
We have applied for 7 patents including Japanese Patent Application No. 3-214026. The main composition of this alloy is Ni 30.0-48.0%, W 1.5-15.0% or / and
Mo is 1.0 to 6.5%, the maximum of W and Mo is 15.0%, and the balance is 40% or more of Cr, which is a high toughness chromium-based alloy for hard facing and its powder, and if necessary, Fe 15.
Add 0% or less or / and Co 10.0% or less, and in this case, the total of Fe and Co is 20% at maximum. If necessary, C 0.3
˜2.0%, B 0.1˜1.5%, Si 0.1˜3.0% can be added alone or in combination. However, the Cr-Ni-W or / and Mo alloys (hereinafter referred to as CrNiW / Mo alloys) developed by the present inventors are
In particular, it was found in the subsequent investigation that the corrosion resistance was slightly inferior to hydrochloric acid.

[0004]

The present invention has conducted various studies to improve the hydrochloric acid corrosion resistance of the CrNiW alloy.
It was discovered that the Cr-rich phase in the Cr solid solution precipitated in the NiW alloy was corroded by hydrochloric acid, and as a solution to this, a nitride layer was provided at least on the surface to improve the hydrochloric acid resistance and further improve the wear resistance. The inventors have completed the present invention by finding improvements.

[0005]

The present invention is directed to Ni 30.
0-48.0% and W 1.5-15.0% or / and Mo 1.0-6.5%
In addition, the sum of W and Mo is 15.0% at maximum, and the balance is 40.0% or more Cr and a chromium-based alloy layer consisting of unavoidable impurities. And, if necessary, the chromium-based alloy layer can contain Fe 15.0% or less or / and Co 10.0% or less and the total of Fe and Co can be added up to 20%, and if necessary, C 0.3 to 2.0%. , B 0.1 to 1.5%, and Si 0.1 to 3.0% can be added.

[0006]

[Function] The chromium-based alloy layer forming part of the present invention is Cr,
An alloy layer composed of Ni, W, Mo, and optionally Fe, Co, C, B, and Si, which has wear resistance and corrosion resistance, is formed. The reasons for limiting each component in the chromium-based alloy layer are as follows.

(Cr) Cr constitutes the balance of the chromium-based alloy layer and forms a hard Cr solid solution containing Ni, W or / and Mo as a solid solution, and contributes to the improvement of wear resistance and corrosion resistance of the alloy. However, if the amount is 40.0% or less, the wear resistance is poor and the corrosion resistance is not improved. Therefore, Cr is set to 40.0% or more.

(Ni) Ni forms a tough Ni solid solution by forming a solid solution with W or / and Mo, but if the amount is 30.0% or less,
The Cr solid solution increases and the toughness of the alloy decreases, and if it is 48.0% or more, the toughness increases, but the desired hardness cannot be obtained, and the wear resistance decreases. For this reason, the amount of Ni was limited to 30.0-48.0%.

(W, Mo) W and / or Mo dissolve in Cr and Ni to form a solid solution to increase the strength of the alloy, but the amount of W is 1.5% or less, Mo1.
If it is 0% or less, this effect does not exist, and if W is 15.0% or more and Mo is 6.5% or more, the toughness of the alloy decreases because a σ phase having poor toughness is precipitated. Therefore, the W content is 1.5-15.0% and the Mo content is 1.0-6.5%.
Limited to%. However, if the total amount of Mo and W exceeds 15.0%, the toughness of the alloy will rather deteriorate, so the total amount was limited to 15.0% or less.

(Fe, Co) Fe or / and Co, which is added if necessary, mainly forms a solid solution in Ni and enters the Ni solid solution to increase the hardness and contribute to the improvement of the wear resistance of the alloy. If the Fe content is 15% or more, not only the toughness of the alloy tends to decrease, but also the corrosion resistance tends to decrease. If the Co content is 10.0% or more, the effect is small and the toughness of the alloy tends to decrease.
For this reason, the Fe content is limited to 15.0% or less and the Co content is limited to 10.0% or less. Furthermore, if the total content of Fe and Co exceeds 20%, the toughness of the alloy deteriorates, so the total content is up to 20%. Limited

(C) C added as necessary forms Cr carbide with Cr and contributes to further improving the wear resistance of the alloy. Cr carbide forms a eutectic with Ni solid solution on the low C side,
Crystallized as primary carbide on the high C side. The amount is 0.3%
If it is less than 2.0%, the effect of improving wear resistance is small, and if it is 2.0% or more, the toughness of the alloy decreases. Therefore, the C content is 0.3-2.0%.
Limited to.

(B) B added as necessary forms Cr boride with Cr, and contributes to further improving the wear resistance of the alloy. Cr boride forms a eutectic with Ni solid solution, but if the amount is less than 0.1%, the effect of improving wear resistance is small, and
%, The toughness of the alloy decreases. Therefore, the amount of B is
Limited to 0.1-1.5%.

(Si) Si, which is added if necessary, mainly forms a solid solution in Ni and enters the Ni solid solution to increase its hardness, contribute to the improvement of the wear resistance of the alloy, and deoxidize during hard facing. It acts as a material and improves the solubility of the alloy. If the amount is 0.1% or less, these effects cannot be obtained and 3.0%
Above all, the toughness of the alloy is reduced.
Limited to ~ 3.0%.

The above chromium-based alloy layer is composed of a Ni solid solution having excellent toughness and a Cr solid solution having excellent wear resistance.
One of the Cr solid solutions, during the cooling process, becomes a Cr-rich phase.
Although it separates and precipitates into the Ni-rich phase, this reaction is presumed to be due to the eutectoid transformation. As a result of a corrosion test, it was discovered that the Cr-rich phase in the Cr solid solution had a slightly poor corrosion resistance to hydrochloric acid and was selectively corroded by hydrochloric acid, which deteriorated the hydrochloric acid resistance of the entire alloy. In order to improve this, in the course of various investigations, it was found that if a nitride layer is provided on at least the surface of the chromium-based alloy layer, hydrochloric acid resistance is improved and wear resistance is further improved.

The nitride layer referred to in the present invention can improve the corrosion resistance and wear resistance even if it exists inside the chromium-based alloy layer, but it must exist at least on the surface of the chromium-based alloy layer. This nitride layer is considered to be mainly a chromium nitride, but the presence of this nitride prevents the Cr-rich layer from being corroded by hydrochloric acid. The presence of this nitrided layer also improves the wear resistance of the alloy.
The thickness of the nitriding layer is not particularly specified, but it is desirable that the thickness is at least about 1 μm, because if it is 1 μm or less, the effect of improving corrosion resistance decreases in a short time.

As a method for forming the nitrided layer, a normal nitriding apparatus is used not only when the chromium-based alloy layer is a built-up layer but also when it is a sintered product, a casting, a finish-polished product after thermal spraying, or the like. By adjusting the heating temperature and time, it is possible to form a nitride layer having an appropriate thickness on the surface of the chromium-based alloy layer. Further, when forming a nitride layer inside the chromium-based alloy layer, the chromium-based alloy is processed into a powder, and a nitride layer is formed on the powder surface by forming a sprayed layer by plasma spraying using nitrogen gas, By laminating this inside the thermal sprayed layer, a nitrided layer is formed inside and at the same time a nitrided layer is also formed on the surface. Similarly, a nitride layer can also be formed by overlaying a chromium-based alloy powder by a plasma transfer arc overlay method using nitrogen gas.

[0017]

EXAMPLES Next, examples of the present invention will be specifically described together with comparative examples. Example 1 A sample mixed with Cr 55%, Ni 41%, Mo 2.5%, B 0.5%, and Si 1.0% was melted in an argon stream using a normal electric furnace, and a 15 mm × 15 mm × 50 mm square column shell type was used. After casting, the cast piece was processed into a square column with dimensions of 10 mm × 10 mm × 20 mm, and the surface was subjected to ion nitriding treatment using discharge in a nitrogen gas atmosphere under reduced pressure, and a hydrochloric acid corrosion test was performed as a sample. And the hardness of the alloy was measured. Hydrochloric acid corrosion test
Immerse it in 5% hydrochloric acid solution heated to 60-65 ℃
The corrosion weight loss of the sample after holding for 1 hour was measured. The hardness was measured by using a part of the above sample using a Vickers hardness meter.

The wear test was carried out using a pin-on-disc type wear tester with a test load of 10 Kgf, a friction speed of 0.1 m / sec, and a friction distance.
The amount of pin wear was measured after 2 m without lubrication. The pins and disks used for this were prepared as follows.
The pin is cast from an alloy of the above composition in a shell shape, and is φ8 × 20 mm
After processing to a dimension of (hemispherical tip), an ion nitriding treatment was performed under the same conditions as the sample of the corrosion test. The disc is pulverized by the gas atomization method using the argon alloy gas of the above composition, and cooled in an argon gas atmosphere as it is to prepare a chromium-based alloy powder.
One surface of 60 mm in thickness and 10 mm in thickness was overlaid by plasma transfer arc (PTA), the surface was polished, and then ion nitriding treatment was performed under the same conditions as the sample of the corrosion test.

Table 1 shows the results of the above hydrochloric acid corrosion test, hardness test and abrasion test. For comparison, Table 1 also shows the results of the hydrochloric acid corrosion test, hardness test, and abrasion test of the sample not subjected to the ion nitriding treatment.

[0020]

[Table 1]

As is clear from Table 1, the alloy having the nitrided layer has improved corrosion resistance, higher hardness, and improved wear resistance as compared with the alloy having no nitrided layer of the comparative example. Example 2 Next, in order to confirm the effect of the nitriding layer by changing each composition within the composition range of the CrNiW / Mo alloy, 10 kinds of alloys having the compositions shown in Table 2 were prepared and subjected to hydrochloric acid corrosion under the same conditions as in Example 1. A sample subjected to nitriding treatment used for the test was prepared and a hydrochloric acid corrosion test was conducted. The hydrochloric acid corrosion test was carried out by immersing the sample in a 5% hydrochloric acid aqueous solution heated to 60 to 65 ° C. and observing whether or not hydrogen gas was generated from the surface of the sample 1 minute after the immersion. The results are shown in Table 2.
Shown in. For comparison, a sample of the CrNiW / Mo alloy prepared in Example 1 which is not subjected to nitriding treatment is shown in Table 2 as a comparative example.
Shown at the same time.

[0022]

[Table 2]

From the results shown in Table 2, it is understood that the hydrochloric acid corrosion resistance is good when the nitride layer is formed within the composition range of the chromium-based alloy forming part of the present invention.

[0024]

As described above, the alloy of the present invention having a nitrided layer has improved hydrochloric acid corrosion resistance and wear resistance as compared with a CrNiW / Mo alloy having no nitrided layer. Therefore, it can be applied to a portion requiring higher corrosion resistance and wear resistance.

Claims (5)

[Claims] 1. Ni 30.0-48.0% and W 1.5-15.0% by weight
% Or / and Mo 1.0-6.5%, the maximum of W and Mo is 15.0
%, And the balance is 40.0% or more of Cr and a chromium-based alloy layer consisting of unavoidable impurities, and a nitride layer is provided on at least the surface of the corrosion-resistant and wear-resistant alloy. 2. The chromium-based alloy layer according to claim 1.
Fe 15.0 wt% or less and / or Co 10.0 wt% or less, Fe
A corrosion-resistant and wear-resistant alloy characterized by containing a maximum of 20% by weight of Co and Co. 3. A corrosion-resistant and wear-resistant alloy, characterized in that the chromium-based alloy layer according to claim 1 or 2 contains 0.3 to 2.0% by weight of C. 4. The chromium-based alloy layer according to any one of claims 1, 2 and 3, wherein B is 0.1 to 1.5% by weight.
A corrosion-resistant and wear-resistant alloy characterized by containing 5. The chromium-based alloy according to claim 1, claim 2, claim 3 or claim 4, wherein Si 0.1 to
Corrosion and wear resistant alloy characterized by containing 3.0% by weight.