JP2555400B2 - Consumable nozzle electroslag welding method - Google Patents

Description

The present invention relates to a consumable nozzle type electroslag welding method.

<Prior art> This consumable nozzle type electroslag welding method is
Since it is possible to perform one-run welding even for thick plates exceeding 100 mm and the efficiency is high, it is the current situation that the range of application is desired to be expanded.

However, even if the plate thickness is 50 mm, it will be a large heat input welding of about 700 KJ / cm, so in the weld heat affected zone of the weld metal and steel plate,
The microstructure becomes coarse, deterioration of toughness or deterioration of crack resistance is unavoidable, and it is limited to about -20 ° C in use, and also from the viewpoint of crack resistance, the applicable steel type is mild steel 50 The reality is that it is limited to kilo-high-tensile steel.

However, recently, with respect to steel sheets, research on large heat input resistance has been conducted, and steel sheets with improved joint toughness have been developed even in such large heat input welding, and even lower temperature specifications or YP
It is in the stage of being studied for application to high strength steels such as 40 and YP42.

Accordingly, in the weld metal, further improvement in low temperature toughness and crack resistance have been demanded.

In response to this, many methods for converting the weld metal to Ti-B have been proposed.

For example, Japanese Examined Patent Publication (Kokoku) No. 51-3020 discloses powdery granular B alloy and Ti
There is disclosed an electroslag welding method using a composite wire (flux-cored wire) containing a metal.

Further, Japanese Patent Laid-Open No. 52-70955 discloses that in the electroslag welding method for mild steel and low alloy steel, the weld metal component is used as a component of the electrode, flux and other components coming from the base metal, etc.
A welding method is disclosed in which 002 to 0.08% Ti and 0.0004 to 0.004% B are supplied from a flux addition alloy.

Further, Japanese Patent Publication No. 51-4502 discloses a consumable nozzle type electroslag welding method in which a flux-cored electrode wire and a coated consumable nozzle in which a slag forming agent is coated on a steel pipe are used together.

<Problems to be Solved by the Invention> However, the method disclosed in Japanese Patent Publication No. 51-30020 and the method disclosed in Japanese Patent Publication No. 52-70955, and Japanese Patent Publications No. 51-450.
The weld metal formed by the method disclosed in Japanese Patent Publication No. 2 has a toughness of 0 to
At about -20 ° C, the present inventors aim to obtain -40 ° C.
At present, the weld metal toughness level is not so high.

<Means for Solving Problems> The present invention solves the above problems and provides a welding method satisfying the above-mentioned object, which means (1)% by weight, C: 0.03 〜0.09% B: 0.0003〜0.005% Mn: 0.8〜1.80% Ni: 0.10〜0.8% Ti: 0.003〜0.03% Cu: 0.10〜0.8% However, it contains Cu + Ni ≧ 0.15% and consists of other iron and inevitable components. Form a weld metal, and cool the weld metal at a cooling rate of 0.3 to 5 ° C / sec.
The first means is to continuously cool it to below 00 ° C. (2) In the first means, C: ≤ 0.15% Al: ≤ 0.07% Mn: 0.8-2.0% Ti: 0.006- 0.05% Si: ≤ 0.4% Ni: 0.3 to 1.0% Cu: 0.3 to 1.0% A steel plate composed of other iron and unavoidable components, and a wire with a built-in flux containing B: ≤ 0.020% of the wire weight. The second means is to form a weld metal by welding using (3) In the first means, C: ≤ 0.15% Al: ≤ 0.07% Mn: 0.8-2.0% Ti: 0.006 to 0.05% Si: ≤ 0.4% Steel plate composed of other iron and unavoidable components, with a built-in flux containing B: ≤ 0.020% Ni: 0.3 to 1.0% Cu: 0.3 to 1.0% of the wire weight. The third means is to form a weld metal by welding using a wire. (4) In the first means, C: ≤ 0.15% Al: ≤ 0.07% Mn: 0.8 2.0% Ti: 0.006 to 0.05% Si: ≤ 0.4% Steel sheet composed of other iron and unavoidable components, and a wire with a built-in flux containing B: ≤ 0.020% Ni: 0.3 to 1.0% relative to the weight of the wire. The fourth means is to form a weld metal by welding using (5) In the first means, C: ≤ 0.15% Al: ≤ 0.07% Mn: 0.8-2.0% Ti: 0.006 to 0.05% Si: ≤0.4% Weld steel plate consisting of other iron and unavoidable components with a wire containing a flux containing B: ≤ 0.020% Cu: 0.3 to 1.0%, based on the weight of the wire. This is a consumable-nozzle type electroslag welding method in which the fifth means is to form weld metal.

The reason why the present invention limits the components of the weld metal, the steel material, and the flux-cored wire in order to achieve these means will be described below.

It is well known in the art that the weld metal can obtain desired low temperature toughness and crack resistance when each of the above-mentioned elements is contained in respective limited ranges. However, as described above, the problem is that the desired material has not been obtained from the weld metal in this known range.

The reason for adding each element, which is desirable in the art and is also recognized by the present inventor, is as follows.

C and Mn of the weld metal both maintain strength and prevent deterioration of toughness and bendability. Ti and B maintain toughness, while Cu and Ni maintain toughness and bendability. Is.

The target material is produced from this well-known weld metal component by setting the cooling rate to a range that can prevent the formation of a hardened structure containing island-like martensite and coarse ferrite and coarse bainite structure, and the cooling stop temperature in the high temperature range. It is intended to suppress the coarse growth of the ferrite and bainite structures in (3) and to make a fine structure by utilizing low temperature transformation.

Further, in order to stably form the above-mentioned components of the weld metal and further obtain a desired material from the weld metal, the elements usually used in this field are added to the steel to be welded for the reason generally known. That is, C, Mn, and Si are both C from the viewpoint of maintaining strength and stability of toughness and weldability, and A1 is C from the viewpoint of deoxidizing and maintaining toughness.
u and Ni are added from the viewpoint of economical maintenance of toughness, Ti is added within the above range from the viewpoint of maintenance of toughness of the heat affected zone of high heat input welding, and N is added as 0.005% or less of the above Ti content. This is to include means for further stabilizing the effect of addition.

Also, Cu and Ni of the flux cored wire are C on the steel plate to be welded.
It is not necessary if u and Ni have been added in the required amounts, but if they are hardly added to the steel plate to be welded, or if the component dilution amount from the steel plate to be welded is not sufficient, supplement the shortage. From the viewpoint of adjusting the composition of the weld metal to an appropriate range, the addition condition is within the above range.

Further, B of the flux-cored wire is in the above range because it is most desirable to supply it from the flux containing the wire in order to accurately adjust the amount B of the weld metal, which is required in a small amount, to an appropriate range.

As a result, B in the weld metal prevents hardening of the weld metal due to excess B, and suppresses the formation of coarse ferrite at the austenite grain boundaries during transformation from the austenite structure to the ferrite structure in the microstructure of the weld metal. The inventors ensure high toughness and crack resistance that are the objectives.

<Operation> In order to solve the above-mentioned problems, the present inventors have conducted various experiments and studies on the consumable nozzle type electroslag welding method, and as a result, the welding method performs welding by forming a molten pool by resistance heat of the molten slag. Therefore, Ti and B first exist in the slag bath in the form of oxides and are transferred to the molten metal by the reaction between the slag and the molten metal, so that the yield is not stable and the effect of adding Ti and B is sufficient. It turned out that it was not obtained and was not suitable for practical use.

In other words, Ti has a strong affinity with oxygen and is easily oxidized and consumed.In the consumable nozzle type electroslag welding method, Ti is oxidized in the flag bath even if it is contained in a solid wire, a flux cored wire, a coated consumable nozzle or an added flux, so that the bath contact It was found that there was very little migration into the metal, and most remained in the slag as oxides.

It was also clarified that a small amount of transferred Ti does not work as a nucleus for forming fine ferrite and therefore does not contribute to the improvement of microstructure and toughness.

From these, the required Ti is diluted and melted from the welding base metal, that is, the steel plate to be welded, without externally adding and supplying it with an alloy with added flux etc. as in Japanese Patent Publication No. 51-30020 and Japanese Patent Publication No. 52-70955. We continued to experiment with the supply method and confirmed that this was the most practical Ti supply method.

Further, B, Cu, and Ni have a smaller affinity for oxygen than Ti, and relatively easily migrate to the weld metal even in the consumable nozzle type electroslag welding method. Especially, the appropriate addition range of B is extremely narrow and a trace amount. It was found that it was necessary to add B accurately, and the effect of addition of B could not be obtained depending on the addition method.

In other words, when added to the consumable nozzle, coating of the nozzle, or added flux by adding it to the flux, when these are brought into contact with a high temperature slag bath, B exists as an oxide in the slag bath,
Since it is more easily reduced than Ti, it moves into the weld metal due to the reaction between the slag and metal, but if the size of the molten pool changes due to different plate thickness or changes in welding conditions, the contact between the molten pool and the slag bath interface Since the area ratio changes, the concentration of B in the molten metal changes.

Therefore, in order to adjust the amount of B in the molten metal to the required amount, it is necessary to change the thickness of the coating in the coating nozzle or the content of B for each plate thickness. It was found that it was not practical because it was necessary to change the B content.

When adding from a solid wire, B is supplied to the relatively inside of the slag bath, but it is melted and oxidized in the slag bath and exists in the slag as an oxide, and is present in the weld metal by the slag-metal interface reaction. However, it was found to be impractical for the same reason as when it was contained in the coating nozzle.

When contained in the flux-cored wire, the outer skin of the wire first comes into contact with the hot slag in the slag bath to reach a high temperature, but the built-in flux of the wire does not have good heat conduction from the outer skin and It was found that it was supplied to the bottom of the slag bath at a relatively low temperature compared to the case.

As a result, the degree of oxidation of B in the built-in flux is small, and it easily migrates into the molten metal in an effective form, and the influence of fluctuations in conditions or fluctuations due to differences in plate thickness is small. I found that it would be possible.

Based on this finding, we continued experiments to supply the required amount of B using a flux-cored wire and confirmed that the most stable amount of B can be supplied in an extremely narrow application range.

Further, the inventors of the present invention, through the above-mentioned experiments and examinations, the dilution ratio of the steel plate to be welded due to melting during welding is usually about 30 to 60%, and the weld metal contains 20% of Ti contained in the steel plate to be welded.
It was discovered that about 50% will be transferred.

Based on this, the Ti required in the present invention is supplied only from the target steel plate to be welded, so the Ti content of the target steel plate must be 0.006 to 0.050% by weight.

In addition, in the consumable nozzle type electroslag welding method, the welding heat input is generally extremely large, so that the cooling after welding is extremely slow. Therefore, it is very difficult to secure the low temperature and high toughness because the weld metal structure is significantly coarsened. is there.

This phenomenon is due to the fact that even if the heat input amount changes corresponding to the thickness of the steel plate to be welded, in the consumable nozzle type electroslag welding, the cooling rate after welding hardly changes,
For this reason, the welding heat input amount has been paid attention to and its control has been studied, but the present inventors have found from the above experiments that it is important to control the cooling rate rather than the welding heat input amount.

Based on this knowledge, the present inventors repeated various experiments and studies for improving the coarsening of the structure, and as a result, when the C content of the weld metal was in the range of 0.03 to 0.09%, a trace amount
The presence of Cu and Ni, and by selecting the cooling rate and cooling stop temperature of the weld metal after welding within the specified range, a high toughness weld metal consisting of a fine ferrite structure and a fine bainite structure can be obtained in the weld part. Found.

The present invention constitutes the above-mentioned means based on the above findings.

<Examples> (1) Consumable nozzle type electroslag welding conditions-Welding current 450Amp-Welding voltage 46V-Welding speed 1.7cm / min-Welding heat input 730KJ / cm (2) Composition of welded steel plate (thickness 50mm) Shown in 1.

(3) Table 2 shows the flux components of the test wire.

(4) Table 3 shows the combinations of the steel plate to be welded, the test wire, and the cooling conditions, the components of the obtained weld metal and their characteristics.

As is clear from Table 3, No1 ~ 3,6,7,10,11,1
Inventive examples of 4, 15, 19, 22, 23, 25, 28, 30, and 32 all have vE-20 ° C values showing good toughness, and vE-40
Excellent low temperature toughness of 10 kgf · m or more was obtained even at ℃.

On the other hand, No is 4, 5, 8, 9, 12, 13, 16, 17, 18, 20,
The comparative examples of 21, 24, 26, 27, 29, 31, and 33 all had extremely poor toughness.

That is, the cooling rate is off 3, and the cooling rate is off 4,
Cooling stop temperature is too high 8,9, Weld metal C amount is too low 12,13, Highly deviating 16,17, Cu and Ni are supplied from welded steel and wire flux. No, it was not present in the weld metal 20, similarly there was no supply from the wire flux and there was no B in the weld metal 21,
The B of the wire flux was out of the upper limit, so the B of the weld metal was out of the upper range 24, and the Mn of the welded steel material was out of the lower limit, so the Mn of the weld metal was out of the lower range 26, and the welded steel material Ti was included. Since there was no Ti in the weld metal27, the Ti of the steel to be welded was outside the upper limit, the Ti of the weld metal was outside the upper limit29, and the Ni content of the wire flux was outside the upper limit. Therefore, Ni of the weld metal 31 was deviated to a higher degree, and similarly 33, where Cu was deviated to a higher degree, each had a part having good toughness at vE-20 ° C, but vE- which is the object of the present invention. At 40 ° C, as described above, a consumable nozzle type electroslag welded steel material having a weld metal having a toughness of 10 kgf · m or more as a target could not be obtained.

<Effects of the Invention> The present invention supplies Ti and B necessary for securing the crack resistance and toughness necessary for the welded steel material including the welded portion as described above, and Ti is diluted and supplied from the base steel material, and B is supplied. Is contained in the flux-cored wire and is supplied, so each yield is high, and since it can be supplied accurately, a strict addition range can always be maintained, and a weld metal with the target components can be reliably obtained. Since the solidification process is cooled to a predetermined cooling stop temperature at a predetermined cooling rate, it is possible to obtain a structure having a target material, improve productivity, reduce cost, and further improve toughness and crack resistance of welded steel. It has a great effect of dramatically improving the practicality of the consumable nozzle type electroslag welding method such as improvement and stabilization.

Claims (5)

(57) [Claims] 1. By weight%, C: 0.03 to 0.09% B: 0.0003 to 0.005% Mn: 0.8 to 1.80% Ni: 0.10 to 0.8% Ti: 0.003 to 0.03% Cu: 0.10 to 0.8% where Cu + Ni ≧ 0.15% And forming a weld metal containing other iron and unavoidable components, and cooling the weld metal at a cooling rate of 0.3 to 5 ° C./sec.
Consumable nozzle type electroslag welding method characterized by continuous cooling to below 00 ℃. 2. By weight%, C: ≦ 0.15% Al: ≦ 0.07% Mn: 0.8-2.0% Ti: 0.006-0.05% Si: ≦ 0.4% Ni: 0.3-1.0% Cu: 0.3-1.0% Other iron 2. A weld metal is formed by welding a steel sheet composed of a metal and an unavoidable component with a wire containing a flux containing B: ≤0.020% with respect to the weight of the wire. Consumable Nozzle Electroslag Welding Method. 3. In weight%, C: ≦ 0.15% Al: ≦ 0.07% Mn: 0.8-2.0% Ti: 0.006-0.05% Si: ≦ 0.4% Steel plate composed of other iron and inevitable components is added to the wire weight. On the other hand, the weld metal is formed by welding using a wire containing a flux containing B: ≦ 0.20% Ni: 0.3 to 1.0% Cu: 0.3 to 1.0%. Consumable Nozzle Electroslag Welding Method. 4. By weight%, C: ≦ 0.15% Al: ≦ 0.07% Mn: 0.8-2.0% Ti: 0.006-0.05% Si: ≦ 0.4% Steel plate consisting of other iron and inevitable components is added to the wire weight. On the other hand, the consumable nozzle electroslag according to claim 1, wherein a weld metal is formed by welding using a wire containing a flux containing B: ≤ 0.020% Ni: 0.3 to 1.0%. Welding method. 5. In wt%, C: ≤ 0.15% Al: ≤ 0.07% Mn: 0.8-2.0% Ti: 0.006-0.05% Si: ≤ 0.4% A steel plate containing other iron and inevitable components is added to the wire weight. On the other hand, the consumable nozzle electroslag according to claim 1, wherein a weld metal is formed by welding using a wire containing a flux containing B: ≤ 0.020% Cu: 0.3 to 1.0%. Welding method.