JPH0716763A - Electron beam welding method of steel plate - Google Patents

Abstract

PURPOSE:To provide the electron beam welding method of steel plate capable of improving the welding efficiency of thick plate. CONSTITUTION:When a steel plate having a composition consisting of, by weight, <0.30% C, 0.1-3.0% Si, 0.05-2.0% Mn <=5X10<-5> PXN in the range of 0.0020%<=N<=0.010%, <=0.010% P, S and the balance Fe with inevitable impurities is electron beam welded; B in the weld metal is made to 0.0003-0.0050% with adding B alone or the alloy plate containing B. By this method, the toughness of electron beam weld zone is improved.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an industrial plant, machine,
In electron welding, laser welding, flash butt welding, etc. for buildings, ships, steel structures, etc.
The present invention relates to a welding method for obtaining a weld metal having excellent toughness.

[0002]

2. Description of the Related Art Electron beam welding has been rapidly developed in recent years because of its features such as high energy density and almost no need for welding material, and the economical welding of thick steel plates. By the way, in the electron beam welding, in the case of a steel material having a tensile strength of about 40 kgf / mm ² which is usually a mild steel, the requirement for toughness or strength is loose, so that the material problem is small, but the tensile strength of 50 kgf / mm ² or more is required. In the case of high-strength steel, there is a major problem in securing the material, especially improving the toughness of the weld metal.

Electron beam welding has a high energy density,
Since welding is carried out in a vacuum, there are restrictions on the composition of the weld metal, such as the generation of gases such as nitrogen and oxygen in the molten metal or evaporation of Mn. For example, latent arc welding is applied to weld metal with
Oxygen of 400 ppm was contained, and a structure containing acicular ferrite having a non-metal oxide as a nucleus as a core was obtained, and good toughness was obtained. However, since electron beam welding melts and solidifies the steel sheet itself, it is difficult to form a high oxygen weld metal.

Various methods for ensuring good toughness by electron beam welding have been studied. For example, JP-A-63-126
Japanese Patent No. 683 proposes a steel composition that ensures a good weld metal material even in low oxygen. The gist is to control the amount of Al in the weld metal to obtain acicular ferrite even with an oxygen amount of 100 ppm or less. In addition, JP-A-60
Japanese Patent Laid-Open No. 54-28787 proposes a method of ensuring a good material by adding an appropriate amount of Ni to the existing steel, which corresponds to the cooling rate during welding. Further, in JP-A-3-248787, in consideration of the deterioration of hardenability due to Mn evaporation during welding, an alloy material, preferably Ni, is added during welding, and the hardenability of the weld metal and the cooling rate during welding are considered. An electron beam welding method has been proposed in which the and are set in a specific range to obtain good toughness.

[0005]

However, even if Mn is adjusted in advance, there are some that evaporate during welding and the composition changes. Therefore, a good weld metal material cannot be secured only by the composition of the weld metal. . In addition, it is not economical to adjust the composition of the entire steel sheet only because of the toughness of the weld metal. For example, Ni is remarkably expensive as compared with iron, and it is economical to add only a necessary minimum amount to the steel plate and separately add a necessary amount to the weld metal. From this point,
The method of adding Ni during welding proposed in the above-mentioned JP-A-60-54287 is effective. However, the method described in the publication controls the amount of Ni in the plate thickness direction of the non-welded material,
The purpose is to add Ni, but simply Ni in the thickness direction.
A good weld metal material cannot be secured even if the addition amount of is changed. The reason why the amount of Ni added is changed in the plate thickness direction is that the cooling rate at the time of welding is different in the plate thickness direction, and the Ni amount suitable for each cooling rate is secured, but the hardenability of steel is Not determined only by Ni, but C, Mn or Cr, M
o, V, etc. also contribute to the hardenability of steel. Therefore, in the composition of the entire steel, the amount of Ni added must be controlled and also controlled by the cooling rate of the weld. Further, Ni is added by sandwiching a plurality of wires having different diameters on the groove surface, but Ni is a component that easily segregates, and in this method, it is possible to stably add it by providing an appropriate component analysis value. Have difficulty. Furthermore, in the method of adding Ni or an alloy plate containing Ni when welding,
Although it is possible to add an appropriate component analysis value and stably add, the level of the Charpy impact test value achieved is low, and further improvement is required.

The present invention has been made in view of the above-mentioned problems. The components of trace elements that cannot be adjusted by electron beam welding are first adjusted in steel, and an alloy component is added during electron beam welding to weld metal. The purpose of the invention is to provide an economical welding method as well as to obtain a weld metal of a good material with a proper composition.

[0007]

The subject matter of the present invention is as follows. (1) In weight%, C ≦ 0.30%, Si: 0.1-3.
0%, Mn: 0.05 to 2.0%, and 0.0020
In the electron beam welding of a steel sheet containing P and S ≦ 0.010% with P × N ≦ 5 × 10 ⁻⁵ within the range of% ≦ N ≦ 0.010% and the balance Fe and unavoidable components, When B is added, B is added alone or by an alloy plate containing B, and B in the weld metal is added in an amount of 0.0003 to 0.00% by weight.
An electron beam welding method for steel plates, which is characterized by 50%.

(2) The steel sheet further has Cu ≦ 2.5%,
Ni ≦ 9.5%, Cr ≦ 9.5%, Mo ≦ 3.5%, N
The electron beam welding method for a steel sheet according to the above item (1), which contains at least one of b ≦ 0.15% and V ≦ 0.15%.

[0009]

[Function] The weld metal structure of steel is mainly 800 to 500 ° C.
It is formed by transformation in the region of, and its composition is determined by so-called hardenability and a cooling rate of 800 to 500 ° C. Weld metal with excellent toughness depends on its structure, and there is also a method of achieving a good structure by using inclusions such as non-metal oxides as the core, but it is most necessary to secure a cooling time suitable for the composition. is there.

FIG. 1 shows the relationship between the B content and toughness of the weld metal according to the present invention. If B is not added, good toughness cannot be obtained because of the large development of upper bainite, but good weld metal toughness can be obtained when the content of B is 0.0003 to 0.0050%. In electron beam welding, Mn evaporates as described above, and there is evaporation loss of 10% or more of its content in one welding, depending on the welding conditions. In electron beam welding, when defects such as pores or solidification cracks occur, the same place may be re-welded and repaired, or welding may be performed under the condition that the beads cross each other. Sometimes welded once. In particular, the contribution of Mn to the hardenability index D _I is large, and due to evaporation of Mn due to repeated welding, D _I greatly changes toward a smaller direction.
As D _I becomes smaller, the range of conditions under which a good material for weld metal can be obtained becomes narrower.

Further, in the electron beam welding, the width of the weld metal is narrow, but the width of the weld metal tends to be wide on the incident side of the electron beam welding, and the width of the weld metal tends to be narrow on the beam exit side, that is, the back side. Therefore, as shown in Japanese Patent Laid-Open No. 60-54287, Ni having a different thickness (amount) depending on the position is used.
There is also a method of adding, but with this method, insertion positioning and N
The control of the i amount is complicated.

The B added to improve the hardenability of the weld metal is preferably added in the form of a plate. A small amount of B can significantly improve the hardenability of the weld metal. It can be used in a wide range of welding conditions even if the width of the weld metal changes depending on the welding conditions. Also, B forms a nitride,
Since a small amount may be added, it is possible to add the amount in consideration.

The addition method is a method in which a thin plate is sandwiched and welded in the groove, a method in which a linear plate is sandwiched and welded as shown in JP-A-60-54287, or a Japanese Patent Publication. As disclosed in Japanese Patent Laid-Open No. 63-32551, there is a method of adding with a filler wire. However, the method of sandwiching and adding as a line is not preferable because the position thereof is not easily determined and segregation of the additive easily occurs. Further, it is difficult to add the filler wire evenly in the welding of a thick plate that exceeds 30 mm.

The alloy containing B can be easily processed into a plate shape.
If a plate-like material is evenly attached to the welding surface and welded, it can be added uniformly. Further, since B has the effect of improving the hardenability even if the addition amount is small, there is an advantage that the plate thickness can be made thin and no defective melting occurs even if the weld metal width is narrow. Furthermore, as a result of studying the improvement of the toughness of the weld metal of the electron beam weld, it was found that coarse nitrides which precipitate in the grain and at the grain boundary in the electron beam weld significantly reduce the toughness of the electron beam weld. When the N content is high, the absolute amount of this coarse nitride increases, and the grains and the grain boundaries are embrittled.
It was also discovered that P promotes the action of N. In order to prevent this, it has been found that the contents of P and N are set within a certain range, that is, the toughness of the electron beam welded portion is remarkably improved by the superposition effect of these effects. FIG. 2 shows a correlation diagram of the amounts of N and P and the toughness of the electron beam weld. N ≦ 0.010% and P × N ≦ 5 × 1
0 it can be seen that good toughness at ^-5 range. Since such trace elements cannot be controlled by the additive, it is necessary to adjust the composition of the steel in advance.

The reasons for limiting the components will be described below. C is an element that is harmful to the toughness, and if added in excess of 0.30%, the toughness of the electron beam welded portion will significantly decrease, so the upper limit is made 0.30%. Since Si is an element necessary for steelmaking, 0.10% or more is added, but if it is added in excess of 3.0%, the low temperature toughness is significantly reduced, so the upper limit is made 3.0%.

Mn is an element that increases the strength and is at least 0.
05% is necessary, but if more than 2.0% is contained,
Not only the weldability is lowered, but also the cost is increased, which is not economical, so 2.0% was made the upper limit. As described above, P is embrittled in the grains and grain boundaries of the electron beam welded portion due to the synergistic effect with N, so it is reduced within the range of P × N ≦ 5 × 10 ⁻⁵ .

S is an element harmful to toughness, and is 0.010.
% Or less. As described above, N embrittles the grain boundaries and grain boundaries of the electron beam welded portion due to the interaction with P. Therefore, as shown in FIG. 1, P × N ≦ 5 × 10 ⁻⁵ . Lower. However, when N is added in excess of 0.010%, cracks occur in the electron beam welded portion, and with the current steelmaking capacity, decreasing N to less than 0.0020% causes an industrial cost increase. The amount of N is 0.0020-0.
It is set within the range of 010%.

Cu, Ni, Cr, Mo, Nb and V have an equivalent effect of increasing the strength of steel, and are contained as necessary, but Cu: 2.5% and N, respectively.
i: 9.5%, Cr: 9.5%, Mo: 3.5%, N
Even if the content of b: 0.15% and V: 0.15% is exceeded, the action and effect are saturated, the cost is increased, and it is not economical. The content was defined as above.

[0019]

Next, examples of the present invention will be given together with comparative examples. The test steel plates are the 10 types shown in Table 1, and the plate No. 1,
Nos. 2, 8, 9, and 10 have a plate thickness of 40 mm and plate Nos. 3, 4,
The plate thickness of 90 mm was used for 5, 6, and 7. Table 2 shows the plates used for electron beam welding, the elements added during welding, the composition of the weld metal,
Shows weld metal toughness. The additive element is B alone or B in the groove.
A thin plate of an alloy containing was sandwiched and added. The toughness was tested by collecting a Charpy impact test piece from the plate thickness center weld metal.

Electron beam welding was carried out in a horizontal position on a flat plate under the conditions shown in Table 3.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

Examples 1 to 6 show examples of the present invention, and Examples 7 to
12 shows a comparative example. In Examples 1 to 6, B was added during welding,
Shows good weld metal toughness. In Examples 7 and 8, since B was not added during welding, the weld metal toughness was low. In Example 9, B is added at the time of welding, but the addition amount is insufficient and the weld metal toughness is low. In Examples 10 and 11, B was added during welding,
Since P × N> 5 × 10 ⁻⁵ , weld metal toughness is low. Example 1
No. 2 added B during welding, but N> 0.0100%
Therefore, the weld metal toughness is low.

[0025]

The electron beam welding is particularly effective in improving the efficiency of thick plate welding. However, up to now, the tensile strength is 50 kgf /
Since it is not possible to secure an appropriate material by welding ordinary steel materials exceeding mm ² , the main application is the welding of thin materials of stainless steel or high alloy steel, and the most excellent characteristics of electron beam welding have not been fully exhibited. . However, according to the present invention, it becomes possible to economically secure a welding material having particularly good low temperature toughness, and electron beam welding can be applied to welding of a pressure vessel or a large structure. It has a great technical and economic effect.

[Brief description of drawings]

FIG. 1 is a graph showing the effect of B content on weld metal toughness.

FIG. 2 is a graph showing the influence of P and N contents on weld metal toughness.

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Claims (2)

[Claims] 1. By weight%, C ≦ 0.30%, Si: 0.1-3.0%, Mn: 0.05-2.0%, and 0.0020% ≦ N ≦ 0.010. % P within the range of P × N ≦ 5 × 10 ⁻⁵ , P ≦ S ≦ 0.010%, and in the electron beam welding of the steel plate containing the balance Fe and inevitable components, B alone or B B is added by the alloy plate containing it, and B in the weld metal is weight%
Of 0.0003 to 0.0050% by electron beam welding of a steel sheet. 2. The steel sheet further comprises Cu ≦ 2.5%, Ni ≦ 9.5%, Cr ≦ 9.5%, Mo ≦ 3.5%, Nb ≦ 0.15%, V ≦ 0.15. The electron beam welding method according to claim 1, wherein the electron beam welding method further comprises at least one of 1% and 2%.