JPS59179720A - Repairing method of stainless steel cast steel member by welding - Google Patents

Abstract

PURPOSE:To improve weldability in a weld zone and to provide the same strength and toughness as the strength and toughness of a base metal by welding said metal with a deposited metal having specific compsn. and combining a sub-zero treatment and tempering treatments twice under a specific condition as heat treatment after the welding. CONSTITUTION:Stainless cast steel members are welded by using a molten metal contg., by weight, 0.01-0.07% C, 0.1-1% Si, 2-7% Mn, 4-8% Ni, 11-15% Cr, 0.1-2% Mo, 0.01-0.1% N, consisting of the balance substantially Fe and contg. 10-18% in terms of Ni expressed by (Ni+30XC%+0.5XMn%+30XN%). Such deposited metal is cooled locally or the entire part of the cast steel part is cooled to an ordinary temp. or below, more preferably to about -50 deg.C by dry ice, etc. The deposited metal is then heated to the temp. higher by preferably about 50-60 deg.C than the Ac1 transformation point (500-550 deg.C) and is tempered; further, the metal is again heated to the temp. higher than the Ac1 transformation point and is tempered.

Description

[Detailed description of the invention] [Technical field of development] The present invention relates to a welding repair method, particularly for high-strength martensitic stainless steel cast members used mainly in running water, such as water turbine run guide vanes and pump impellers. Regarding a method of welding sleeves.

[Technical Background of the Invention and Part 1 Subtitle False] Hydraulic equipment components such as pump-turbine runners, guide vanes, and other pump impellers and propellers that are used for operation in high continuous flow water for 1 m in hydropower generation installations are required to have corrosion resistance. Martensitic stainless steel cast steel is generally used because it has high corrosion resistance as well as corrosion resistance. In particular, Ni was added to 3. ! ;-&% Contains b/3 Cr-based stainless steel cast steel CU Due to its relatively excellent toughness and solubility, it is currently widely used as a component of the highest quality hydraulic equipment.

By the way, large and small casting defects generally occur in the surface of cast steel parts, so if these defects become a starting point for brittle fracture during medical use, it is a good idea to It will be necessary to repair the valley contact.

As the deposited metal for this repair welding, it is conceivable to use austenitic steel, which has relatively good weldability, or martensite, which has almost the same composition as the base metal (ie, cometal).

The reason why austenitic steel has excellent weldability is that the solid solution violet of hydrogen, which causes delayed cracking, is much more abundant in the martensite structure than in the martensitic structure, so hydrogen embrittlement is less likely to occur, and the cooling process after welding Possible reasons include that transformation stress does not occur because it does not undergo transformation, and that residual stress due to thermal stress generated during the cooling process is low because of its low yield strength. However, when austenitic steel (for example, Q30 steel) is used as the weld metal, problems arise in terms of mechanical strength.

In other words, after welding repair with an austenitic welding rod, the presence of an austenitic structure in the welded metal part poses no problems in terms of corrosion resistance, strength, and toughness of the heat shadow area, and it also reduces fatigue. There is a risk of breakage. Therefore, there are some 2' fittings in which austenitic steel is used as the welding tables 1 and 4 for repair welding, especially in areas where the strength is not sufficient for repair, but in most cases, austenitic steel is used. In order to obtain a material τ which is equivalent to the main body in terms of strength, 4i1 (common metal), which has the same component as the mother iodine, is used.

However, when a matching metal is used as the molten 2R metal for welding repair of martensitic stainless cast steel members, the following problems occur.

In other words, under high temperature conditions immediately after welding, the welded part forms an austenitic structure, but this changes to a martensitic structure during the cooling process of the iron, so transformation stress is generated due to volume expansion, and the Due to the quenching effect, a Hj hardness martensitic structure is formed and hydrogen embrittlement is less likely to occur9, and cracks such as cracking and delayed cracking are more likely to occur.

As a means to prevent such weld W rubbing and improve welding and oxidation properties, a method of pre-hinning is generally used. In other words, before welding, weld the bath
The whole area, or the entire city, is heated to a temperature of, say, 100 degrees Celsius or more. However, if the hand to prepare the glass is
Moreover, even after preheating, weld cracking force
This often happens as a real problem, and
As a means of improving the weldability of rutenzite-based stainless steel casting parts, this method is neither effective nor effective.

[Purpose of the invention]

The present invention has been developed in consideration of the above points, and is a 13Cr martensitic stainless steel casting Th1.
In one-shift welding + i1 + repair, welding force ζ large rli
The purpose of the present invention is to provide a welding supplementary φ method that is improved in the welding method and that makes it possible to obtain strength and toughness that do not deteriorate with the base material of the main body.

[Summary of the invention]

In order to achieve the above object, the method for welding a martensitic stainless steel cast member of the present invention is as follows:
00/~θ; o7%, SIO, /~/%, Mn2~7
Chi, N1p-IS, Cr //~/J%, MOO,
/--2'i', No, θ/~0.1, and the remainder is substantially white) with Fe power.

N1% + 30 X C% 10,! X equivalent% +30 X
A first step of welding using a weld metal whose NL current expressed in N% is to -tg@, and a welding table 4. :
LS part locally or the entire casting saw member at a temperature L below the bath temperature (the λth machine that performs sub-zero treatment of cooling at 1 and the molten metal), A of 'A. A third step of heating to a temperature of 1 transformation point or higher and tempering, and A of the weld metal again. ! It is characterized by comprising a tempering process by heating to a temperature above the transformation point.

[Detailed Description of the Invention] The present invention will be explained in more detail below. In the following description, unless otherwise specified, "chi" indicating a composition is based on weight.

Welding Table E1 The welding metal used in the present invention consists of an F8-based alloy with seven specific compositions. The purpose of cooling each component in the alloy and the reason for limiting the composition are as follows.

Kakezu C is an effective element for promoting austenitization in the welded 1-inch Buddha shape and increasing the strength of martensite after martensite transformation, and is an effective element for increasing the strength of martensite after martensite transformation. It is said. So〃D Mayuziga o
If it is less than ,0/Z, the above effect will be poor and it will be 0.
．． If it exceeds 0.7%, the toughness of the welded part will decrease and weld cracking will easily occur.

81 is added as a deoxidizing agent, and 0.7
~/Chi is added. If it is less than 0.7%, the Himeka effect is poor, and if it is added in excess of 0.7%, carbides and the like will segregate at grain boundaries, reducing toughness.

Iori is effective as a deoxidizing agent and a desulfurizing agent, and also exhibits the same effect as Ni, which will be described below, in that it promotes the toughening and austenitization of the weld metal.

It can be used in place of relatively expensive N10.

As will be explained later, there is a balance with other components, but if it is less than 2%, the desired effect will not be obtained, while if it exceeds 7%, the amount of austenite will be too large and a brittle martensite will be formed. At the same time, blowholes increase.

N1 is the most effective ingredient for improving toughness,
Goo♂chi is added. If it is less than ps, a sufficient addition effect cannot be obtained, and if g% is added, too many austenite trays are formed, which ultimately leads to a decrease in strength.

Cr provides corrosion resistance and at the same time
It contains essential ingredients necessary to cause martensitic metamorphosis, as shown in FIG. //If it is less than iss, the effect of addition is poor, and if it is added beyond iss, δ ferrite will precipitate and the toughness will decrease.

N is an effective component that not only promotes austenitization but also strengthens martensite by forming a solid solution with C after martensite transformation.
, O/~0. / Chi included. From the viewpoint of bath adhesion, it is added as a precaution in order to keep the amount of C low. However, if it is added in excess of 0.87%, the adhesion will deteriorate.

Mo is an effective component for improving corrosion resistance, increasing yield strength, and at the same time preventing martensite from becoming brittle due to tempering during post-heat treatment after melt stretching. . 0. If the load exceeds 2%, δ ferrite will precipitate.
1 melt 21! This reduces the toughness of the parts and causes weld cracks.

Further, the molten metal rot component used in the present invention is contained within the λ phase structure of austenite and martensite, which is represented by the diagonal ridge in the Schaeffler phase diagram shown in FIG.

In other words, in this phase diagram, the horizontal axis represents the Cr equivalent, the vertical axis represents the VCNi equivalent, and various structures corresponding to their arbitrary assembly are shown. In the diagram, A is the austenite structure, and M is the Martensitic structure, F means ferrite structure. The Nj equivalent in the weld metal of the present invention is Ni %
+30XC'lb+0. ! XMn%+3oxN%
When expressed as , it is preferable that it is 10~/zata. C
Although it depends on the r equivalent, if the Ni content is less than 10%, the amount of retained austenite in the as-welded state will be small.
Conversely, if the weight exceeds 7g5t, the amount of austenite increases. In order to improve weldability, which is one of the objectives of the present invention, it is necessary that at least 30% austenite remains. However, if the N] equivalent exceeds 7 g%, the austenite becomes stabilized and Because the point described in is too low, sufficient martensitic transformation occurs even with subzero treatment.
It will disappear. It should be noted that some ferrite may coexist in the 3-coat layer where Cr is high, but this does not particularly affect the effects of the present invention.

The welding auxiliary fig method of the present invention is used as an alloy weld metal having the above-mentioned composition, and also consists of the following first to first steps.

First step Welding (#, l:) using the above-mentioned weld metal can be carried out by a normal welding method, such as breakthrough arc welding or TIG welding.The method of the present invention greatly improves weldability. Therefore, preheating before welding can be performed at a low temperature, or it is possible to perform bath welding without preheating.

After the second step of welding, a sub-zero treatment is performed in which the welded metal part is locally cooled or the entire cast steel part is cooled in an enclosure at a temperature below room temperature.

This sub-zero treatment temperature is preferably -30°C or lower. For example, by adding dry ice, it is possible to easily obtain a temperature of -70°C to -0°C. A mixture of dry ice and alcohol or ether or liquid nitrogen may also be used as a coolant.

FIG. 2 shows a cross-sectional view explaining the cooling method. That is,
As shown in this figure, it is preferable to locally cool only the weld repaired part 2 of the cast steel base material 2 with a coolant 3 such as dry ice, but it is preferable to immerse the entire cast steel member in the coolant. Good too.

Note that it is desirable to carry out sub-zero treatment as soon as possible after welding is completed.

Here, the reason for performing such subzero processing will be explained.

The h point (the temperature at which the austenitic structure at high temperature begins to transform into the martensitic structure during the cooling process) of ordinary 13Cr martensitic stainless steel is not less than XSO℃, and the Iμ point (the temperature at which martensitic transformation begins The completion temperature) is around room temperature. At room temperature, the martensitic structure becomes more than 0%. Depending on the reed component, less than 10% austenite may remain. However, as the amount of Ni and seeds added increases, Ni
As the mouse gets fatter, the points will decrease. In this regard, in the case of the welded gold horse used in the present invention, below the point idjθθ℃, to 1
Since f is below room temperature, Oma austenite of 30 or more remains at the peak temperature after welding. Although the presence of such austenite remaining is undesirable in terms of improving weldability, it poses a problem in that the strength and toughness of the austenite portion are reduced. Therefore, in order to improve this problem, it is necessary to perform a subzero treatment and cool the welded metal part to a low temperature of 0°C or lower to once allow the martinsite transformation to proceed.

After the third step sub-zero treatment, the molten x-tube metal is heated to a temperature of 1 or higher to perform tempering treatment.

By the sub-zero treatment in the second step, approximately yo% or more of the welded metal part becomes martensite m weave.Although the strength is high up to this trench, the weld metal r1 A for metal. It is necessary to temper the cymartinsite by heating it to a temperature above 1.

Through this tempering treatment, a part of martensite returns to stable austenite, and even after cooling to room temperature, this remains and is finely distributed inside the martensite fibers, increasing the yield strength to a certain level. It is possible to impart the reed ductility maintained above.

Figure 3 shows the IA between the tempering temperature and the austenite f.
A related figure is shown. As shown in this figure, there is an optimum value for the amount of austenite remaining after tempering; if this optimum value is lower, the amount of stable austenite transformation will not be sufficient; on the other hand, if it exceeds this value, the The amount of rock-unstable austenite increases and this undergoes martensitic transformation during cooling, which causes a decrease in toughness.

Normally, the heating temperature at which the toughness is maximized after tempering is about 50 to A
A temperature higher than θ℃ is preferable.

After the tempering treatment in the third step, the tempering treatment is performed again by heating to a temperature equal to or higher than the Ac1 transformation point of the weld metal under the same moxibustion conditions as in the third step.

The tempering treatment in the first step is a major feature of the present invention, and the reason for performing such tempering treatment again is [
Due to reasons.

Industrial heating temperatures for tempering are generally
It is common to provide a tolerance of about 0° C., and as a result, there is a problem that the toughness of the welded metal part varies and the material becomes unstable. As a result of various attempts to solve this problem, the inventor of the present invention found that after the tempering treatment in the third step, the welded metal part was heated again to the same temperature range. It was discovered that the toughness was further improved, the variation in the toughness was reduced, and the material became more stable. This is the reason why we repeat the tempering process again.

This is thought to be due to the increase in retained austenite and the tempering effect of martensite.

The heat treatment in this first step not only removes the residual stress that had occurred during welding, but also softens the heat-affected zone of the base metal, which had hardened and decreased toughness, and restores toughness. It is also possible to do so.

[Embodiments of the invention]

Base metals and weld metals (welding rods) of samples Nα/~6 were prepared with the compositions shown in Table 1 below.

A groove corresponding to the driving defect was created in the matrix (/J Cr-II Ni-based martenzite stainless steel cast steel) after lifting, and TIG welding was performed without preheating using each of the above 1-4n/~t weld metals. It's Bue.

Each weld was as good as a normal austenitic welding rod such as D30, and there were no defects such as weld cracks.
fi did not occur.

After completing the above step/step, the amount of austenite occupied in the weld metal structure and the hardness of the weld metal part in this welded reed were measured. Next, each of these samples was subjected to a second step of subzero treatment and a third step of tempering treatment. The sub-zero treatment was carried out by locally cooling the welded part to about -70°C using dry ice as a coolant, followed by tempering treatment by heating it to 100°C in an electric furnace. At the end of this third step, the hardness and budding value of each sample were measured.

The results obtained are shown in Table 2 below.

Table 2 Note) Impact value: Shalby, 21i11flV notch temperature 0℃ The strength of welding in the -JJ state is less than Vickers 200, except for 1. Company S, and is lower than R ma in terms of strength. .

This is determined by the large amount of austenite.

Furthermore, regarding the 1 length and 1 ml impact value after completing the second and third processes, the kite was almost the same as the mother I Δ, and the toughness was also sufficiently satisfactory. I know that there is. In addition, sample Nnj is a welding rod made of a common metal, and the impact value is low because the amount of N+ is low. , the impact value is high but the hardness is low.

On the other hand, for sample Nn J, after the sub-zero treatment, the tempering temperature in the third step was changed to 120.1°C, and the impact value was measured for the sample obtained at the same temperature. Furthermore, after that, each sample was subjected to the third tempering treatment (ie, the first step). This λ-th tempering temperature was S♂0°C and 320°C.

The negative value of each sample was measured.

The measurement results are shown in Figure 1. As is clear from Figure q,
For those obtained by only seven tempering treatments, the impact value peaks at the treatment temperature of too-t, zo℃ and shows a sharp change, but after the λ-th heating treatment, When performing this process, the impact values were averaged out and an improvement in the impact values was observed in both cases of sio ℃ and 410 ℃. Furthermore, in this case, it can be seen that the higher the initial tempering temperature is, the greater the effect of one round of tempering is.

〔Effect of the invention〕

As is clear from the results of the above examples, the method of welding and repairing a stainless steel cast part of the present invention involves welding using a deposited metal of a specific composition, and also includes subzero treatment twice as heat treatment after welding. By combining tempering treatment, weldability has been greatly improved, and at the same time, strength and
It is possible to obtain a welded part (j5) that is almost the same as the base metal in terms of toughness.

Therefore, the present invention is useful as a welding repair method for martensitic stainless steel members that require both toughness and good weldability.

[Brief explanation of the drawing]

Figure 1 is a Schiefler phase diagram showing the composition of the weld metal of the present invention. Figure 2 is a cross-sectional view explaining the sub-zero treatment method of the second step of the present invention. Figure 3 is the relationship between tempering temperature and austenite content. Figure 1 is a diagram showing the results of the Gogeki trial. C...Material of cast steel, λ...Medical repair part, 3...Cooling agent. Applicant's representative Ino J role Kiyoshi Figure 1 Bow figure 2

Claims (1)

[Claims] Weight ratio CO,0/, -0,07%, SiO,/~/
%, Heko~7%, Nl 44-1%, Cr
/ / ~/ j gb% Moa, /~λchi, NO,
0/-0, υ including /chi and the remainder being substantially Fe,
N1(o+30XcZ10,!XMn'%+30XN%
The second step involves welding using a deposited metal whose N1 equivalent is /Q~/, and the sub-zero treatment in which the weld metal is locally cooled or the entire cast steel member is cooled to a temperature 1 below room temperature. The second step is to perform A of the weld metal. It is characterized by consisting of a third step in which the weld metal is heated to a temperature higher than the Acx transformation point and tempered, and a third step in which the weld metal is heated again to a temperature higher than the Acx transformation point and tempered. , a welding repair method for martensitic stainless steel cast members.