JP4358407B2 - Welding method of thick steel plate with excellent laser weldability - Google Patents

Description

【００３１】
【表２】

【００３２】
【発明の効果】
本発明は、鋼の成分量を規制し、かつ、脱酸元素と溶接条件の適正バランスを規定することにより、鋼板のレーザー溶接性を向上させ、特に厚鋼板のレーザー溶接で最も問題となるブローホール発生の抑制を可能ならしめた。特にレーザー溶接の際の開先にレーザー切断、またはプラズマ切断、あるいはガス切断ままの切断面を適用しても耐ブローホール性に優れ、かつ、耐割れ性、耐溶け落ち性なども優れているため、今後さらに適用拡大が期待される厚鋼板のレーザー溶接において、多大な経済的メリットを享受できるものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for welding thick steel plates excellent in laser weldability, which is applied to industrial plants, machines, ships, buildings, and other steel structures.
[0002]
[Prior art]
Along with the development of high-power laser welding machines, the practical application of laser welding of thick steel plates is actively promoted. By using a laser beam with a high energy density as the welding heat source, high-speed and high-efficiency welding with deep penetration is possible, greatly reducing welding deformation, improving the shape and material of the welded part, and eliminating the use of filler metal (or This is because cost merit due to reduction in the amount of use even if used is expected.
[0003]
On the other hand, when laser welding is applied to thick steel plate welding, the generation of blow holes in the weld metal is one of the major problems in welding construction. Conventionally, in order to reduce blow holes during laser welding of thick steel plates, as disclosed in JP-A-60-206589, countermeasures such as control of the laser irradiation position have been considered. It is necessary to optimize the irradiation position every time the condition is changed, which is not practical.
[0004]
Also, in actual applications, there are many cases where welding is performed by applying to the groove surface in a state of being cut by plasma cutting, gas cutting, laser cutting, etc. In that case, blow holes are used compared to using machined grooves. The occurrence of this is more remarkable. However, when assembling a steel structure by laser welding, machining the groove is not practical in terms of construction efficiency and thus economically, and it remains in a state of being cut by plasma cutting, gas cutting, laser cutting, etc. A steel plate and a welding method that do not generate blow holes even if they are welded are desired.
On the other hand, the present inventors examined various blow hole reductions from optimization of welding conditions based on conventional knowledge, but did not lead to a significant improvement.
[0005]
[Problems to be solved by the invention]
In view of the above background, it is an object of the present invention to provide a method for welding a thick steel plate having excellent weldability that can suppress blowhole generation during laser welding.
[0006]
[Means for Solving the Problems]
The inventors have made steel sheets of various compositions and thicknesses, made laser cuts of them as butt grooves, welded them at various laser outputs and welding speeds, and investigated the occurrence of blowholes in the welds in detail. did. As a result, it was clarified that blowhole generation depends on the properties of the butted surfaces of the steel plates. In other words, the abutting surface was used from the standpoint of practical use as it was with laser cutting, but when the cutting surface is relatively flat and there is little residual oxide scale, there is relatively little blowholes, while the unevenness of the cutting surface It was concluded that the occurrence frequency of blow is high when the surface area is large and / or there are many oxide scales remaining on the surface and the cut surface is rough.
[0007]
On the other hand, when the occurrence of blowholes was analyzed from the viewpoint of the effects of steel plate components, plate thickness, and welding conditions, all of them had a strong relationship. Regarding the influence of the steel material component, it was found that the generation of blowholes decreases as the deoxidizing element, particularly Al, Ti, Mg, and Ca, is increased. In addition, under the influence of the plate thickness and welding conditions, the tendency to generate blow was stronger as the plate thickness was increased and the welding speed was increased. On the other hand, the generation tendency was lowered as the laser welding machine having a higher output was used.
[0009]
The gist of the present invention is as follows.
(1) In mass%,
C: 0.09 to 0.2%, Si: 0.05 to 0.7%,
Mn: 1.09 to 1.6%, P: 0.025% or less,
S: 0.015% or less, Al: 0.012-0.1%,
When melting and welding a thick steel plate consisting of the remaining Fe and inevitable impurities and having a plate thickness of t (mm) of 6 mm or more at a speed v (cm / min) using a laser with an output P (kW),
(% Al) + (1/10) (% Si) ≧ vt / (5000 + 150P) √P
The welding method of the thick steel plate excellent in laser weldability characterized by adjusting either or both of the welding speed v (cm / min) and the output P (kW) of the laser so as to satisfy the above.
(2) In mass%,
C: 0.09 to 0.2%, Si: 0.05 to 0.7%,
Mn: 1.09 to 1.6%, P: 0.025% or less,
S: 0.015% or less, Al: 0.012-0.1%
In addition, in mass%,
Nb: 0.001 to 0.1%, Ti: 0.001 to 0.1%,
Zr: 0.001 to 0.1%, Mg: 0.0001 to 0.02%,
Ca: 0.0001 to 0.02%, REM: 0.001 to 0.2%
It contains more than one or two, and a balance of Fe and unavoidable impurities, the speed by using a laser of plate thickness output steel plate is 6mm or more t (mm) P (kW) v (cm / min )
(% Al) + (1/10) (% Si) + (1/3) (% Ti) + (1/3) (% Zr) + (3/4) (% Mg) + (1/2) (% Ca) + (1/5) (% REM)
≧ vt / (5000 + 150P) √P
A method for welding a thick steel plate excellent in laser weldability, wherein either or both of the laser speed v (cm / min) and the output P (kW) are adjusted so as to satisfy
(3) Furthermore, in mass%,
Cu: 0.05 to 1.0%, Ni: 0.10 to 2.0%,
Cr: 0.03-3.0%, Mo: 0.05-1.0%,
V: 0.01 to 0.40%, B: 0.0002 to 0.0020%
One type or two or more types of the above are contained, and the method for welding a steel plate excellent in laser weldability according to the above (1) or (2).
(4) Of the above steel components, in mass%,
C: 0.09 to 0.18%, Si: 0.05 to 0.4%,
P: 0.010% or less, S: 0.008% or less, The method for welding a steel plate excellent in laser weldability according to any one of the above (1) to (3).
[0010]
In this case, carbon dioxide laser, YAG laser, etc. are mainly used as lasers for welding, but the present invention can be applied to all lasers as long as they can be used as welding heat sources.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
First, the reason for limiting the chemical composition of steel in the present invention will be described.
C is the most effective element for improving the strength at a low cost. However, if it exceeds 0.2%, the low temperature toughness of the base metal is inhibited and the hardening of the laser weld is remarkably promoted. .2%. On the other hand, when the C content is less than 0.04%, the solidification cracking sensitivity of the laser weld metal increases. Further, the roughness of the groove surface (hereinafter referred to as the groove surface as it is cut) provided by laser cutting, plasma cutting, or gas cutting increases, so that the generation of blowholes is promoted at the butt weld. This was found in this study . Incidentally, practically crack resistance, to ensure a sufficient resistance to blow holes, it is Nozomu Mashiku C is 0.09% or more, in order to suppress further the hardening of the welded portion in the following 0.18% It is desirable to be.
[0012]
Si is effective as a strength-enhancing element and is also useful as a deoxidizing element for cheap molten steel. However, when it exceeds 0.7%, the groove surface becomes rough as it is cut, and blow holes are generated at the butt weld. It was found to promote. On the other hand, when the content was less than that, it was weak but showed an effective tendency to suppress blowholes. This tendency was seen up to about 0.05%, and was not seen below. Therefore, it was limited to 0.05% to 0.7%. In addition, when it is used for laser welding while being cut with laser, plasma, etc. and blowhole resistance is strictly required, it is desirable to be 0.4% or less.
[0013]
Mn is a useful element that improves the strength, and it is found that the addition of more than 1.6% promotes the generation of blowholes, while it is 1.09 % or more from the necessary lower limit, and 1.09 to 1 Limited to 6%.
[0014]
P has a high segregation rate during solidification and is one of the main causes of solidification cracking in laser welds. To reduce cracking susceptibility, 0.025% or less is necessary. In order to make the cracking property very low, it is preferably 0.010% or less.
[0015]
S is an element that affects the flow of molten steel. If it is contained in excess, it will lead to dripping of the molten steel during laser welding, particularly in downward welding. Further, S, like P, needs to be suppressed to 0.015% or less in order to increase the weld cracking sensitivity during laser welding. In order to make the cracking property very low, the content is preferably 0.008% or less.
[0016]
Al is an element necessary for deoxidation and needs to be added in an amount of 0.012 % or more. The present inventor has found that the addition of Al is effective in suppressing blowholes. However, excessive addition exceeding 0.1% is limited to 0.012 to 0.1% in order to impair the toughness of the weld.
[0017]
Nb is an extremely important element that satisfies both strength and toughness of a steel sheet in TMCP steel. It also has the function of fixing C and N, which are the main factors of the curability of the weld heat affected zone (HAZ). However, addition exceeding 0.1% is harmful because it accelerates the hardening of the base material by precipitation, so it was limited to 0.001 to 0.1%.
[0018]
Ti is effective as a deoxidizing element. In addition, similarly to Nb, Ti is an important element for achieving both strength and toughness of the base material in TMCP steel. Furthermore, the present inventors have also found that addition of Ti suppresses blowhole generation and HAZ hardening. However, addition over 0.1% is harmful to the toughness of both the base metal and the welded part, so it was limited to 0.001 to 0.1%.
[0019]
Zr has almost the same deoxidizing power as Al in molten steel and can be used as a deoxidizing element, but it has also been found that solute Zr in steel sheet suppresses the formation of blowholes in laser welds, similar to Al. did. However, excessive addition impairs the weld zone toughness, so it was limited to 0.001 to 0.1%.
[0020]
Mg, Ca, and REM have a strong deoxidizing power in molten steel, and can be used as a deoxidizing element when manufacturing steel sheets and in a laser melting pool. In addition, these elements are also powerful desulfurization elements and have a function of suppressing solidification cracking of the weld metal due to segregation of S. Furthermore, the present inventors have also found that the addition of these elements has a function of suppressing the generation of blowholes during laser welding and quench hardening of the weld metal and HAZ. However, excessive addition of any element impairs the stability of the plasma in the keyhole during laser welding and also impairs the toughness of the welded portion, so the range is Mg: 0.0001 to 0.02%. , Ca: 0.0001 to 0.02%, REM: 0.001 to 0.2%.
[0021]
Furthermore, in order to reduce the carbon equivalent for the purpose of improving the strength of the base metal and improving the low temperature toughness and weldability, the alloy elements specified in the present invention according to the required quality characteristics or the size and thickness of the steel material Even if (Cu, Ni, Cr, Mo, V, B) is added from the viewpoint of improving strength, low temperature toughness and weldability, the effect of the present invention is not impaired at all.
[0022]
Next, the reason for limitation of the relational expression between the steel material component and the welding condition will be described.
As a result of analysis by the inventors of the occurrence of blow holes during laser welding from the viewpoint of the influence of steel plate components, plate thickness, and welding conditions, the more deoxidizing elements, particularly Al, Ti, Mg, and Ca, the more blow holes It has been found that the occurrence of is reduced. In addition, the influence of the plate thickness and welding conditions revealed that the greater the plate thickness, the higher the welding speed, the stronger the tendency to blow, while the more the laser welding machine with higher output was used, the lower the tendency to occur. . The results of these experiments are analyzed recursively and used as an index of steel sheet components effective for blowhole reduction.
(% Al) + (1/10) (% Si) + (1/3) (% Ti) + (1/3) (% Zr) + (3/4) (% Mg) + (1/2) (% Ca)
+ (1/5) (% REM)
Got. In other words, it was found that the larger the value, the smaller the tendency of blow generation during welding. The coefficient of each element is determined experimentally.
[0023]
On the other hand, the influence of welding conditions and plate thickness is (100 + 3P) √P / vt
I got the index. Here, P is the output (kW) of the laser welding machine, v is the welding speed (cm / min), and t is the plate thickness (mm). The larger this value, the smaller the tendency for blowholes to be generated, and the smaller the value of this index, the more pronounced blowholes were generated.
[0024]
Furthermore, by integrating the effects of both,
(% Al) + (1/10) (% Si) + (1/3) (% Ti) + (1/3) (% Zr) + (3/4) (% Mg) + (1/2) (% Ca)
+ (1/5) (% REM) ≧ (1/50) (vt / (100 + 3P) √P)
From the detailed examination of this study, it became clear that the tendency to generate blowholes is very low when In order to achieve a steel material that has good resistance to blowholes under certain laser welding conditions, the steel material component was limited as a relationship between the steel material component and the welding conditions.
[0025]
【Example】
The effects of the present invention will be described more specifically with reference to examples.
First, steel as shown in Table 1 was melted and hot-rolled by a general method to produce a thick steel plate having a predetermined thickness. In Table 1, steels A to D are examples of the present invention, steels E and F are comparative examples, this steel E has C and Mn outside the scope of the present invention, and steel F has C, P and S according to the present invention. Is out of range.
[0026]
Table 2 shows the welding conditions when these steel plates A to F are laser welded under various conditions, and the evaluation results of weldability. For laser welding, CO ₂ lasers with outputs of 15 kW and 45 kW were used. As a groove for welding, a steel plate cut by a 6 kW laser cutter was abutted to obtain an I groove. The welding posture was horizontal and horizontal, and the laser beam focus position during welding was the steel plate surface. The shielding gas is He at both the front and back, and the flow rate is 50 L / min. At the front and 20 L / min. At the back. As for the evaluation of weldability, as for the steady bead portion (1 m), confirmation of penetration (penetration / non-penetration), confirmation of the presence or absence of burn-out, blow hole by cross-sectional inspection of 10 welds at 10 cm intervals, presence or absence of solidification cracking Confirmed.
[0027]
In Examples 1 to 4 of the present invention, since the conditions of the present invention were satisfied, good welding without melting, blowholes and solidification cracks was possible.
On the other hand, compared with the invention example 1, since the welding speed is faster in Comparative Example 1, the value on the left side is smaller than the value on the right side, that is, the following equation is obtained:
(% Al) + (1/10) (% Si) + (1/3) (% Ti) + (1/3) (% Zr) + (3/4) (% Mg) + (1/2) (% Ca)
+ (1/5) (% REM) ≦ vt / (5000 + 150P) √P
A blowhole occurred. In the table, Y is the left side (* 1) and right side (* 2) of the above formula (* 1) ≥ (* 2) (invention scope), and N is (* 1) ≤ (* 2) (this It is outside the scope of the invention.
[0028]
In Comparative Example 2, the welding speed was higher than that of Invention Example 2, so that the value on the left side was smaller than the value on the right side as in Comparative Example 1, and blowholes were generated. In Comparative Example 3, compared with Invention Example 3, the laser output was reduced by 2/3, but the welding speed was reduced by 1/3. Therefore, the value on the left side was smaller than the value on the right side, and blow holes were generated. did.
In Comparative Example 4, blowholes and weld solidification cracks occurred because C and Mn were low C and high Mn steels that deviated from the present invention. Further, Comparative Example 5 was a low C, high Mn steel with C and Mn deviating from the present invention, and the value on the left side was smaller than the value on the right side, resulting in blowholes and solidification cracks.
[0029]
In Comparative Example 6, C, P, and S were high C, high P, and high S steels that deviated from the present invention, so that many weld solidification cracks occurred. In Comparative Example 7, as in Comparative Example 6, C, P, Since S was a high C, high P, and high S steel that deviated from the present invention, in the downward welding, burn-through was observed and the weld bead was defective.
[0030]
[Table 1]

[0031]
[Table 2]

[0032]
【The invention's effect】
The present invention improves the laser weldability of steel sheets by regulating the amount of steel components and defining an appropriate balance between deoxidizing elements and welding conditions. It has become possible to suppress the generation of holes. In particular, even when laser-cutting, plasma-cutting, or gas-cutting cut surfaces are applied to the groove during laser welding, it has excellent blow-hole resistance, as well as excellent crack resistance and burn-off resistance. Therefore, a great economic merit can be enjoyed in laser welding of thick steel plates, which are expected to expand further in the future.

Claims (4)

% By mass
C: 0.09 to 0.2%,
Si: 0.05 to 0.7%,
Mn: 1.09 to 1.6%
P: 0.025% or less,
S: 0.015% or less,
Al: 0.012-0.1%,
When melting and welding a thick steel plate consisting of the remaining Fe and inevitable impurities and having a plate thickness of t (mm) of 6 mm or more at a speed v (cm / min) using a laser with an output P (kW),
(% Al) + (1/10) (% Si) ≧ vt / (5000 + 150P) √P
The welding method of the thick steel plate excellent in laser weldability characterized by adjusting either or both of the welding speed v (cm / min) and the output P (kW) of the laser so as to satisfy the above. % By mass
C: 0.09 to 0.2%,
Si: 0.05 to 0.7%,
Mn: 1.09 to 1.6%
P: 0.025% or less,
S: 0.015% or less,
Al: 0.012-0.1%
In addition, in mass%,
Nb: 0.001 to 0.1%,
Ti: 0.001 to 0.1%,
Zr: 0.001 to 0.1%,
Mg: 0.0001 to 0.02%,
Ca: 0.0001 to 0.02%,
REM: 0.001 to 0.2%
It contains more than one or two, and a balance of Fe and unavoidable impurities, the speed by using a laser of plate thickness output steel plate is 6mm or more t (mm) P (kW) v (cm / min )
(% Al) + (1/10) (% Si) + (1/3) (% Ti) + (1/3) (% Zr) + (3/4) (% Mg) + (1/2) (% Ca) + (1/5) (% REM)
≧ vt / (5000 + 150P) √P
A method for welding a thick steel plate excellent in laser weldability, wherein either or both of the laser speed v (cm / min) and the output P (kW) are adjusted so as to satisfy In addition,
Cu: 0.05 to 1.0%,
Ni: 0.10 to 2.0%,
Cr: 0.03-3.0%,
Mo: 0.05-1.0%,
V: 0.01-0.40%,
B: 0.0002 to 0.0020%
The method for welding thick steel plates having excellent laser weldability according to claim 1, wherein one or more of the above are contained. Of the above steel components,
C: 0.09 to 0.18%,
Si: 0.05-0.4%
P: 0.010% or less,
S: 0.008% or less, The method for welding thick steel plates excellent in laser weldability according to any one of claims 1 to 3.