JPH0230396A - Build-up welding method - Google Patents

Abstract

PURPOSE:To render satisfactory hardness to a joining section by the addition of a small amt. of borides by feeding cermet powder obtd. by mixing stainless alloy powder, Ni alloy powder or Co alloy powder with a specified weight percentage of one or more kinds of borides such as AlB12 into plasma arc to carry out the build-up welding on a metal. CONSTITUTION:Cermet powder obtd. by mixing stainless alloy powder, Ni alloy powder or Co alloy powder with 5-60wt.% one or more kinds of borides such as AlB12, VB2, CrB, CrB2, FeB, Co2B, Ni2B, Mo2B, MoB2 and TiB2 is fed into plasma arc to carry out the build-up welding on a metal or alloy. The m.p. of each of the borides is a temp. under a prescribed temp. which is lower than that of carbide ceramics. When the cermet powder is exposed to the high temp. of plasma arc or laser beams, the alloy powder melts and the borides also melt or decompose perfectly and deposit again as borides at the time of joining by solidification. Since the borides disperse finely and uniformly, satisfactory hardness is rendered to the whole of the resulting joining section by the addition of a small amt.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" This invention relates to an overlay welding method for surface hardening.

``Prior art/problems to be solved by the invention'' Conventionally, parts such as valves, trims, and rotating machinery that require wear resistance have been manufactured using stellite alloy (1.0wt% C-28W).
We perform overlay welding for surface hardening, which is typified by t%Cr-residue Co. However, when this stellite alloy is overlaid, it is necessary to preheat the base material to be welded and slowly cool it by this preheating to prevent the occurrence of weld cracks. For this reason, strict thermal management such as preheating temperature and slow cooling time is required, which has the disadvantage that construction costs including material costs are quite high. In addition, carbon diffuses into the weld heat affected zone of the base metal due to the heat during welding, resulting in a reduction in the corrosion resistance of the base metal.

Therefore, plasma spraying and powder plasma welding, in which cermet is deposited on the surface of a metal material, have been developed as overlay welding methods that do not cause weld cracks without preheating.

However, since plasma spraying has continuous pores in the coating, there is a possibility that both the coating and the base material will be corroded by the corrosive liquid that has passed through the pores, or the adhesive strength between the coating and the base material may be insufficient. , it is not suitable as a build-up technology for corrosive and harsh environments because it cannot be applied to harsh wear environments.

On the other hand, in powder plasma welding (plasma transfer arc welding) (hereinafter referred to as rPTAJ),
Among the cermet powders that have passed through the high-temperature plasma flow, the alloy powder is completely melted, and the ceramic powder is also heated to a semi-molten or molten state, so that it is completely welded to the base material.

Additionally, there are no pores in the build-up layer, and the build-up thickness can be controlled freely, so it can be said that this technology can overcome the drawbacks of thermal spraying.

As such a cermet PTA technique, for example, a method described in Japanese Unexamined Patent Application Publication No. 55-5126 has been proposed. This applies to NbC powder, VC powder, T
A powder mixture containing at least one type of iC powder is supplied into an arc to form weld metal on the surface of a steel base material.

However, in cermets using these carbide ceramics, some of the carbides melt or decompose during plasma welding, and carbon becomes a solid solution in the molten metal, but other carbides remain unmelted in the form of almost added carbides. Remains in weld metal. Therefore, a fairly large amount of carbide is required in order to uniformly disperse the carbide to provide sufficient hardness throughout the deposited metal. In addition, carbon diffuses into the weld heat-affected zone of the base metal due to the heat during welding, which increases the susceptibility to weld cracking and significantly reduces the corrosion resistance of the base metal.

This invention was made in view of the above circumstances, and its purpose is to obtain sufficient hardness with the addition of a small amount of ceramics, do not require strict heat management, and reduce the corrosion resistance of the base material. The purpose of the present invention is to provide an overlay welding method that does not require further development.

"Means for Solving the Problem" In order to achieve the above object, the overlay welding method of the present invention:
Fe-Cr, F'e-Cr-Ni, Fe-Cr-Ni-
Stainless alloy powder represented by Mo, or Ni
-Cr, Ni-based metal powder such as Ni-Cr-Mo or CO-based metal powder such as Co-Cr, Co-Cr-W, Al2B +t, VBt, CrB, CrB
t, F eB , CotB , N iyB , Mot
The method is characterized in that cermet powder containing 5 to 60 vt% of one or more borides such as B, MoB, TiB, etc. is supplied into a plasma arc and overlay welded onto a metal or alloy. It is something.

Also, Fe-Cr, Fe-Cr-Ni, Fe-Cr-N
Stainless alloy powder represented by i-Mo, or N
Ni-based metal powder such as i-Cr, Ni-Cr-Mo or Co-based metal powder such as Co-Cr, Co-Cr-W, A12B It, V B t, CrB, CrB
t, F eB , CotB , N LB , MotB
Cermet powder containing 5 to 60 wt% of one or more borides such as MoBt, TiBt, etc. is supplied into a laser beam and overlay welded onto metal or alloy, or metal or carboxy on the alloy.
Methyl cellulose.

The cermet powder bonded with a binder such as polyvinyl alcohol is irradiated with a laser beam to perform overlay welding.

"Action" In this invention, A12B+! , VBt, CrB,
CrB x, PeB, CotB, N12
Borides such as B, MotB, MoBt, and TiB all have melting points of 300% as shown in the table below.
Since the temperature is below 0°C, which is lower than that of carbide ceramics, when cermet powder is exposed to high temperatures such as plasma arc or laser beam, not only the alloy powder but also the boride will completely melt or decompose, and then when welding and solidifying. Then, it precipitates again as a boride. The reprecipitated boride is finely and uniformly dispersed in the welded cermet.

(Left below) In addition, boride-based ceramics do not diffuse into the base material like carbon, even if they are melted or decomposed.

"Example" Hereinafter, the present invention will be specifically explained with reference to Examples.

Figure 1 shows Fe-18Cr-12Ni-2Mo(5
The hardness of the welding material and the above boride when overlay welding by PTA was performed on US316L) using cermet powder mixed with CrBt or cermet powder mixed with MoBe without heat management such as preheating and slow cooling. It is a figure showing the relationship with content. In addition, the standard hardness of the stellite alloy is also illustrated in the same figure.

In this case, the cermet powder is 5US316L powder with Cr
Bt powder or MOB! 3.5 to 65 wt% of powder was added and mixed using a rotary mixer. A spherical powder having a particle size of 50 to 330 mesh was used for each powder. Welding conditions are: Voltage = 20-30V, Current: 100-140A1, Welding speed: 100-200 mm/min.

Plasma gas flow rate = 2 to 612/11in1 weaving width: 10 to 50III. The base material is 5U with length 400IIIl x width 100mm x thickness 16mm.
A flat plate made of S316L was used.

From this figure, even if we overlay cermet powder with a CrBt content of 3.5 wt%, the hardness of the welding material is approximately 240 Hv.
This is only 40% higher than the approximately 170 Hv of weld metal not containing CrB. However, 5wt%
In the above, it is about 3508 V or more, which is about twice that of the weld metal not containing CrBt, and the lower limit hardness of the standard hardness of Stellite alloy, which is about 350 to 500 Hv, is about 350 Hv or more.

From the above results, it was found that a practically sufficient hardness can be obtained by containing 5 wt% or more of CrBt.

Furthermore, even if cermet powder with a MoB content of 3.5 wt% is deposited, the hardness of the weld material is approximately 250 Hv, compared to approximately 170 Hv of the weld metal that does not contain MoBz. It's only about 50% more expensive.

However, when it is 5wt% or more, it is about 350HvJM or higher.

The hardness was more than twice that of the weld metal not containing B, and moreover, it exceeded the lower limit of the standard hardness for stellite alloys.

From the above results, it can be seen that MoB is 5w similar to the above CrBt.
It has been found that practically sufficient hardness can be obtained if the content is t% or more.

Figure 2 shows Fe-18Cr-10Ni-2Mo(
5US316L) with 65 wt% of CrBt mixed with cermet powder, PTA overlay welding was carried out in the same manner as in Fig. 1. This is a metallographic photograph showing the results of a liquid penetrant test of a welded part. .

As is clear from this figure, weld cracking occurred in the material containing 65 wt% CrBf.

Figure 3 shows Fe-1-8Or-10Ni-2Mo
This is a photograph of the metallographic structure of a welded part when overlay welding by PTA was performed using cermet powder (5US316L) mixed with 55 wt% CrBf under the same conditions as in FIG. 1.

In this case, no weld cracking occurred.

From the above results, it was found that weld cracking does not occur even without thermal management such as preheating and slow cooling if the CrB content is 60 vt% or less.

FIG. 4 shows Fe-18Or-10Ni-2M on the sliding surface (valve body) of a gate valve made of 5US316L.

(SUS316L) with PTA overlay welding using cermet powder mixed with 50 wt% CrBt, voltage: 2
0V.

Current: 120-140A.

Welding speed + 150 mm/min, plasma gas flow rate: 2Q/min.

This is a photograph of the metallographic structure of the welded material which was finished after welding was carried out under conditions of weaving width: 10 mm.

This cermet welding material containing CrBt has excellent workability such as machinability and polishability, and has been found to be sufficiently practical as a hardfacing material.

Furthermore, N 1t B , or PeB, or CrB
.

and MoBp in a ratio of I:1 (wt%), and using cermet powder mixed with each, the above-mentioned tests were conducted in the same way, and the results were the same as above. The effect was obtained.

"Effects of the Invention" As explained above, in the overlay welding method of the present invention, A Q B re V B t , Cr B ,
CrB2, FeB.

CotB, NitB, MO2B, MOBt,
All borides such as T iB 2 have a melting point of 3
000℃ or less, it absorbs better than carbide ceramics,
When cermet powder is exposed to high temperatures such as plasma arc or laser beam, not only the alloy powder but also the boride completely melts or decomposes, and then, during welding and solidification, it precipitates again as a boride, and this The reprecipitated boride is finely and uniformly dispersed in the welded cermet, so that sufficient hardness can be obtained throughout the welded area with a smaller amount of addition than when carbide ceramics are added.

In addition, boride-based ceramics do not diffuse into the base material like carbon even if melted or decomposed, so the corrosion resistance of the base material is not reduced.

Further, if the content of the boride is 60 wt % or less, only weld cracks will occur even without heat management such as preheating and slow cooling, so workability will be improved.

Further, if the content of the boride is 5 wt% or more, practically sufficient hardness can be obtained.

Moreover, compared to NbC, which is often used as a ceramic for cermets, borides are inexpensive and, as mentioned above, have a large effect with a small amount, so they are economically advantageous.

[Brief explanation of the drawing]

1 to 4 are diagrams for explaining the present invention; FIG. 1 is a diagram showing the relationship between CrBt content or MoB content and hardness; FIGS. 2 and 3 are diagrams showing the relationship between hardness and CrBt content or MoB content; are photographs of the metallographic structure of the welded portion, and Fig. 4 is a photograph of the metallographic structure of the overlay welded gate valve.

Claims (2)

[Claims] (1) Stainless steel alloy powder or Ni-based alloy powder or Co
In the base alloy powder, AlB_1_2, VB_2, CrB, Cr
B_2, FeB, Co_2B, Ni_2B, Mo_2B
An overlay welding method characterized by supplying cermet powder containing 5 to 60 wt% of one or more borides such as , MoB_2, TiB_2 into a plasma arc and overlay welding it onto a metal or alloy. . (2) Stainless steel alloy powder or Ni-based alloy powder or Co
In the base alloy powder, AlB_1_2, VB_2, CrB, Cr
B_2, FeB, Co_2B, Ni_2B, Mo_2B
, MoB_2, TiB_2, etc., by supplying cermet powder containing 5 to 60 wt% of one or more borides, such as borides, into a laser beam and overlay welding on the metal or alloy, or An overlay welding method characterized in that overlay welding is performed by irradiating the cermet powder adhered to a laser beam with a laser beam.