JP3464901B2 - Welding wire for high strength steel and its base wire - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength steel welding wire used for gas shielded arc welding and an original wire thereof. The present invention relates to a welding wire for high-strength steel, which exhibits excellent welding workability without defective feeding and meandering of beads, and has a strength of a deposited metal of 60 kgf / mm ² or more, and a raw wire thereof.

[0002]

2. Description of the Related Art Gas shielded arc welding is widely used for butt welding or fillet welding of various structures such as shipbuilding, vehicles, steel frames, bridges, industrial machines, etc., for the purpose of labor saving and improvement of construction efficiency. High heat input welding with a high current is aimed at, and in recent years, the strength of steel materials has been increased for the purpose of cost reduction, and the needs for high strength and high toughness welding materials have increased accordingly.

Under these circumstances, JIS Z 3312
As standardized as YGW21 in the above, a gas shielded arc welding wire for high heat input welding containing a proper amount of Ti in a low carbon steel wire rod is used to increase the strength of the deposited metal.
A welding wire to which o is added has been developed and is becoming popular as a welding wire for large heat input used for high strength steel.
The reason for adding Ti to the welding wire is to prevent deterioration of the toughness of the deposited metal due to an increase in heat input during welding.
This is for stabilizing the welding arc in the high current region.

However, a gas shielded arc welding wire for high heat input welding, in which Ti is added to the wire material for the welding wire, undergoes remarkable work hardening during wire drawing during the production of the welding wire,
Cold workability is significantly reduced, and the strength of the obtained welding wire is excessively increased, making it difficult to wind it onto a spool, etc. However, with the welding wire for high-strength steel in which Mo is added in addition to Ti, the above problems are more remarkable.

Therefore, for the purpose of improving the wire drawability and decreasing the wire strength, it is common to perform softening annealing a plurality of times after the completion of hot rolling or during the wire drawing process. However, regarding the variation in wire strength, the improvement effect by annealing was small, and rather the variation in strength was even greater in some cases by annealing.

Regarding a general-purpose welding wire for large heat input containing only Ti, a method of improving wire drawability and reducing variations in strength is described in "R & D Kobe Steel Engineering Report" (Vol. 35, No. 35). 2, pages 52 to 54) and the like, but the strength of the original wire is at a high level even if the above method is adopted, and at least once for producing a welding wire of appropriate strength. Annealing is required, and even when annealing is performed, the variation in wire strength after wire drawing is still large. Moreover, the above method is not related to the welding wire for high-strength steel to which Mo is added, and the variation in strength of the welding wire for high-strength steel to which Mo is added is very large.

On the other hand, with the progress of automation of welding work, the problems of poor feeding of wire and meandering of bead have started to be particularly emphasized, and the welding wire having excellent welding workability without causing poor feeding and meandering of bead. The needs of are increasing.

Further, as described above, since it is necessary to anneal a plurality of times at the time of manufacturing, the raw material for welding wire excellent in wire drawing workability capable of wire drawing without annealing. The development of lines was also requested.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and the first purpose thereof is to excessively increase or disperse the strength of the welding wire by adding Ti and Mo. Of the weld metal for high-strength steel, ensuring the strength and toughness of the weld metal and excellent arc stability, and at the time of welding, there is no feed failure or bead meandering. To provide welding wire for high-strength steel that exhibits excellent welding workability.

A second object of the present invention is a raw wire for the above-mentioned welding wire for high-strength steel, which is excellent in wire drawing workability and can be drawn without annealing. To provide the line.

[0011]

The welding wire for high-strength steel of the present invention which achieves the first object is a welding wire for high-strength steel containing Ti and Mo.
(Mo) / (Ti) in Carbides or Carbonitrides Containing
[However, (Mo) content of Mo (wt%), (Ti) content of Ti (wt%)] is 0.5 or less on average, and martensite content is 10 vol% or less. (Ti) / (C) [where (Ti) is the total content of Ti in the wire (wt%), (C) is the content of C (wt%)] Is recommended to be 4.0 or higher.

The composition of the above-mentioned welding wire for high strength steel is as follows: C: 0.02 to 0.12% (meaning mass%; the same applies hereinafter) Si: 0.20 to 1.50% Mn: 0. 7 to 2.3% Ti: 0.10 to 0.30% Mo: 0.01 to 0.60% is desirable, and the balance may be Fe and unavoidable impurities, but further B is 100 ppm or less. If it is contained, it is preferable because the toughness of the deposited metal in the case of high heat input welding can be increased.
It is preferable to contain 0.1% or less in total of one or more elements selected from the group consisting of 1 and Ta, because the precipitation of fine (Ti, Mo) C having a high Mo content can be suppressed.

Further, the welding wire raw wire of the present invention which has achieved the second object is a welding wire raw wire containing Ti and Mo, which is a carbide or carbonitride containing Ti and Mo. (Ti, Mo) C or (Ti, Mo) C
N: abbreviated as (Ti, Mo) C below]
The summary is that the mass ratio (Mo) / (Ti) of o is 0.5 or less on average, and the mass ratio (Ti) / (C) of Ti to C is 4.0 or more. . It has been confirmed that carbides such as TiC and composite carbides exist as carbonitrides or composite carbonitrides containing nitrogen when the wire composition contains nitrogen. Since the object of (1) is sufficiently achieved, the present invention is intended to include these cases as well, but hereinafter, the carbide will be representatively described.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted extensive studies on factors causing the strength variations of welding wires. As a result, the variation in strength is caused by uneven cooling in the dense and coarse portions of the coiled wire during Stelmore cooling after hot rolling and annealing, which causes variations in the structure within the wire. I found that it was due to a thing. Specifically, it has been found that it is caused by a combined effect of precipitation of (Ti, Mo) C in which Mo is solid-dissolved in TiC and formation of martensite. By adding Mo, in a relatively low temperature range (650 to 700 ° C.) during hot rolling and during annealing, (Ti,
Mo) C easily precipitates and the Mo content ratio is high (T
i, Mo) C is more likely to be finely precipitated than TiC and significantly strengthens the matrix. When the cooling rate is slow and the temperature is kept in this temperature region for a long time, a large amount of (Ti, Mo) C precipitates and becomes hard. On the other hand, even when the holding time in these temperature ranges is short (when the cooling rate is high), martensite is generated and becomes hard. Then, the cooling rate is appropriate, and the portion where precipitation of (Ti, Mo) C and formation of martensite are not observed becomes relatively soft.
Furthermore, when a wire rod with such a variation in structure is drawn,
Since the degree of work hardening differs depending on each structure, the variation in strength further increases, and the variation in strength of the welding wire becomes extremely large.

Therefore, the strength variation of the welding wire and its original wire is
In order to reduce the sticking, the Mo content ratio is high (Ti, M
o) Formation of martensite while suppressing precipitation of C
It is indispensable to suppress the above-mentioned phenomenon to obtain a uniform tissue state.
Specifically, the content of Mo relative to Ti in (Ti, Mo) C
Make the mass ratio (Mo) / (Ti) on average 0.5 or less, and
Move so that the amount of rutensite produced is 10% by volume or less
For example, variations in strength to the level where bead meandering does not occur
Can be reduced. 2μm for (Ti, Mo) C ² To
As the test area, (Mo) / (Ti) in (Ti, Mo) C
When the average exceeds 0.5, the strength variation becomes large.
Is required to be 0.5 or less, and 0.2 or less
Is desirable. For martensite,
Area 2000 μm² Strength varies when exceeding 10% by volume
It is necessary to make it 10% by volume or less because the size becomes large.
And is preferably 2% by volume or less.

Further, the matrix composition (Ti) / (C) is 4
The above-mentioned is desirable because it is possible to completely suppress the formation of martensite and also suppress the precipitation of (Ti, Mo) C. If the value of (Ti) / (C) is less than 4.0, the amount of C becomes excessive and martensite is likely to be generated. In addition, the two-phase temperature range of ferrite + austenite is 6
Since it is as low as about 50 to 700 ° C, (Ti, Mo) C
Is more likely to precipitate, and precipitation strengthening increases and strength variation also increases. On the other hand, (Ti) / (C) is 4.
When it is 0 or more, martensite is not formed and a ferrite single phase is formed, and the precipitation of (Ti, Mo) C is also suppressed, so that the precipitation strengthening amount and the variation are reduced. In addition, (T
When i) / (C) is set to 4.0 or more, there is an advantage that the deformation resistance during hot rolling becomes small, which enables rolling at a lower temperature and reduces the heat generation during processing, resulting in austenite grains. Growth is also suppressed and it becomes difficult to overcool, and also precipitation of (Ti, Mo) C is suppressed. (Ti) / (C)
Is 4.0 or more, the larger this value is, the more Ti
The amount of precipitation strengthening by C is small, which is desirable.
The above is more preferable. The reason is that when (Ti) / (C) is set to 4 or more, since all C is fixed by Ti, excess C is eliminated and martensite formation is suppressed, and at the same time, the two-phase temperature of ferrite + austenite This is because the region rises and the production of (Ti, Mo) C is also suppressed.

As described above, in the present invention, variation in strength is suppressed by suppressing the amount of (Ti, Mo) C having a high Mo content ratio and martensite, and preferably by controlling the value of (Ti) / (C). It is possible to obtain a welding wire for high-strength steel which has very few feeding defects and is free from bead meandering and has excellent welding workability. Hereinafter, the reason for defining the component composition of the welding wire according to the present invention will be described.

C: 0.02 to 0.12% C is an element indispensable for ensuring the strength of the weld metal as a welding wire, and at least 0.02%.
The above must be contained. From the viewpoint of increasing the strength of the deposited metal, it is desirable that the added amount be large, but if it is too large, the strength becomes too high, which not only adversely affects the wire drawability but also deteriorates the toughness of the deposited metal. Therefore, the upper limit was set to 0.12%. A more preferable range of the C content is 0.03% or more and 0.07% or less.

Si: 0.20 to 1.50% Si has the effect of strengthening the solid solution of ferrite. Therefore, it is preferable that Si is increased in order to increase the strength of the deposited metal. In order to increase the Considering the balance between strength and wire drawability, Si
Content was determined to be in the range of 0.20 to 1.50%. Si
The more preferable range of the content is 0.50% or more and 1.2%.
It is the following.

Mn: 0.7-2.3% Mn gives sufficient strength to the deposited metal.
It should be contained in an amount of 0.7% or more, but if it is too much, the hardenability increases and the toughness of the deposited metal is adversely affected, so 2.3% was made the upper limit. A more preferable range of the Mn content is 1.2% or more and 1.8% or less.

Ti: 0.10 to 0.30% Ti is an essential element for ensuring the strength, toughness and arc stability of the deposited metal, and in order to ensure arc stability,
0.10% or more is necessary, and 0.15% or more is desirable. However, if the amount of Ti is too large, the amount of slag is increased, which causes problems such as deterioration of welding workability and entrainment of slag. Therefore, it is necessary to set it to 0.30% or less.
25% or less is desirable.

Mo: 0.01 to 0.60% Mo is an essential element for increasing the strength and toughness of the deposited metal. If it is less than 0.01%, the strength of the deposited metal becomes too low, and if it is 0.60% or more, the toughness deteriorates. The desirable range of the amount of Mo is 0.20% or more and 0.40% or less.

B: 100 ppm or less B is an element which enhances the toughness of the deposited metal in the case of high heat input welding, and is effective when added in a small amount to the high heat input wire. However, if it exceeds 100 ppm, the hardenability becomes too high and the toughness deteriorates on the contrary, so it should be 100 ppm or less, preferably 50 ppm or less. The lower limit is preferably 10 ppm or more and more preferably 20 ppm or more in order to exert a sufficient effect.

V, Zr, Nb, Hf and Ta: 0.1%
Hereinafter, V, Zr, Nb, Hf and Ta are T in austenite.
It is an element that promotes the precipitation of iC and suppresses the precipitation of (Ti, Mo) C, and is effective when added in a trace amount.
These elements are effective even if added alone or in combination. However, if the total amount of added elements exceeds 0.1%, the weld metal characteristics will be deteriorated, so it should be 0.1% or less, preferably 0.05% or less. On the other hand, the lower limit is preferably 0.01% or more in order to exert the effect of addition,
More preferably, it is 0.02% or more.

Also in the welding wire raw wire according to the present invention, the same composition as that of the welding wire of the present invention is adopted, and the (Mo) / (Ti) of (Ti, Mo) C and the matrix composition are
It is important that (Ti) / (C) is controlled. By controlling in this way, excessive strength increase and variation will not increase in subsequent wire drawing process and annealing process. It is possible to obtain a welding wire having a stable wire drawability and having no trouble during spooling or the like and having excellent handleability without softening and annealing on the way. Moreover, the obtained welding wire has an appropriate strength, has little strength variation, and is excellent in welding workability. Further, the strength and toughness of the deposited metal portion obtained by using the welding wire of the present invention are comparable to or superior to those of the conventional welding wire made of Ti-added low carbon steel.

In the present invention, (Ti, Mo) C
In controlling the proportion of Mo in it, it is extremely effective to control the conditions when manufacturing the original wire of the welding wire. Usually, the welding wire raw wire is manufactured by hot rolling. The general process is that after soaking in a furnace at 1000 ° C or higher for several tens of minutes, rough rolling and finish rolling are performed, then water cooling at around 1000 ° C, and then winding in a coil shape to a Stelmore conveyor. The process of placing and gradually cooling is adopted. The temperature during soaking and heating at this time is called the heating temperature, and the maximum temperature of the billet that has risen due to the heat generated during processing during rolling is called the maximum temperature.The temperature at which the billet is placed on the Stelmore after water cooling is called the placement temperature. In other words, when the average cooling rate of the wire on the Stelmore conveyor is used as the cooling rate, it is desirable to optimally control the heating temperature, the highest attainable temperature, the mounting temperature and the cooling rate. Specifically, it is desirable that the heating temperature during hot rolling is controlled to 1000 ° C. or lower, and the maximum temperature reached when the temperature rises due to heat generated during processing during hot rolling is 1000 ° C. or lower. , The maximum temperature reached is 1000
It is sufficient if the time at which the temperature is ℃ or higher is 3 seconds or less). When the heating temperature or the maximum reaching temperature becomes high, the solid solution amount of Ti and C increases, and a large amount of fine (Ti, Mo) C having a high Mo concentration is likely to precipitate in the cooling process after hot rolling. ,
As a result, the strength is increased / varied. still,
A preferable heating temperature range is 800 to 950 ° C., and a maximum ultimate temperature is 950 ° C. or less.

If the cooling rate after hot rolling is too fast, a large amount of (Ti, Mo) C tends to precipitate, leading to an increase in strength, so it is desirable to make it as slow as possible.
C./sec or less is preferable, and 1.0.degree. C./sec or less is more preferable.

Furthermore, it is difficult to obtain the desired structure unless the mounting temperature is properly controlled. Therefore, Ae ₃ ± 3
It is desirable to set it to 0 ° C. If the mounting temperature is higher than this, re-dissolution of (Ti, Mo) C into austenite is caused, and as a result, fine (Ti, Mo) C is precipitated. If it is too low, it will be overcooled and fine (Ti, Mo) C
Is deposited. A more preferable mounting temperature is Ae ₃
± 20 ° C.

Next, the constitution and operational effects of the present invention will be explained more specifically with reference to examples. However, the present invention is not limited by the examples below, and is within a range applicable to the gist of the preceding and following. It is of course possible to carry out the modification with the above, and all of them are included in the technical scope of the present invention.

[0030]

Example 1 A steel material having the composition shown in Table 1 was hot-rolled to a finished diameter of 5.5 mm under the conditions shown in the table. Cold drawing is performed using the obtained raw wire, and the wire is φ3.4 mm or φ2.
After forming an annealed and Cu-containing plating layer in the middle of the wire diameter such as 4 mm, wire drawing to a final wire diameter of 1.2 mm,
The drawability was examined for each of them.

Regarding the strength of the original wire and the wire, 100 wires are cut at 16 cm intervals, the average of these strengths is calculated, and the maximum strength and the minimum strength of the wire are checked to determine the difference between them. It was calculated as the variation.

(Ti, Mo) in the original wire and the welding wire
When examining (Mo) / (Ti) of C, carbides were sampled with an extraction replica, 5 fields of view were observed with a transmission electron microscope at a magnification of 60,000, and (Mo) / (T of each carbide was observed by EDX.
i) was calculated and the average value was calculated.

In order to examine the amount of martensite produced in the welding wire, a sample that had been polished parallel to the drawing direction and then etched with a 2% solution of nital was used with a scanning electron microscope to observe 10 fields at a magnification of 2000 times. The amount of martensite produced was observed and the amount of martensite produced was determined by image analysis.

Regarding the wire drawability, the wire that could be drawn to φ1.2 mm without breaking during wire drawing was passed (marked with ○ in Table 2 below), and the wire that was broken during wire drawing was rejected. (X mark in Table 2 below).

Regarding the feedability, the wire which passed the wire drawing test was subjected to the feedability test by using the apparatus shown in FIG. In FIG. 1, 1 is a welding wire, 2 is a wire feeding roller, 3 is a conduit tube, 4 is a power supply tip, and 5
Indicate wire arcs, respectively.

The feeding performance was evaluated by both feeding failure and meandering of the bead. The former feeding failure was caused by feeding the wire during the 10-minute welding operation in which gas shield arc welding was performed under the following conditions. Wires that could not be fed smoothly and had arc breakage were rejected (marked with X in Table 2 below), and those that could be welded without problems passed (○ in Table 2 below, ◎ for very good) And Regarding the latter bead meandering, in the 5 m bead obtained by the above welding operation, the wire which caused the meandering of the bead was rejected (marked with X in Table 2 below), and the one in which the bead meandering was not noticeable was passed (Table below). 2 was marked with ◯, and very good one was marked with ◎). Table 2 also shows the results of whether or not the arc stability was good during the welding work. [Welding conditions] Welding method: Carbon dioxide arc welding method Welding base metal: SM570 Welding current: 300 A Welding voltage: 34 V Welding speed: 25-30 cm / min

Regarding those which have passed the feeding test,
The strength of the deposited metal is investigated based on JIS Z3312,
Those having a strength of 60 kgf / mm ² or more were accepted. Table 2 shows the measurement results of strength and the evaluation results of each property.

[0038]

[Table 1]

[0039]

[Table 2]

Comparative examples which do not satisfy any one or more of the requirements of the present invention are wire strength, wire drawability, welding workability,
At least one of arc stability, slag inclusion, and weld metal strength is inferior. On the other hand, in the examples of the present invention satisfying all the requirements of the present invention, the wire strength, wire drawability, welding workability, arc stability, slag entrainment, and weld metal strength were all appropriate and showed excellent characteristics.

4a and 4b, 10a and 10b, 11a
And 11b are comparative examples that are different only in the presence or absence of annealing, and the effect of improving wire strength, wire drawability, and poor feeding can be seen by performing annealing, but by applying annealing (Ti, Mo ) Mass ratio of Mo to Ti in C (M
o) / (Ti) has greatly increased to over 0.5, and no improvement in bead meandering has been achieved. On the other hand, 14a and 14
When b is compared, 14b has an excellent (Mo) / (Ti) value of 0.5 even after annealing, showing no bead meandering.

Further, 15a, 18a, 18b and 18c are not preferable in the temperature condition during hot rolling and (Mo) / (Ti) is 0.5.
It is the comparative example as described above, and the wire strength is too high and the welding workability is poor. On the other hand, while having the same composition,
Inventive Examples 15b, 15c, 1 in which (Mo) / (Ti) is 0.5 or less
8d had an appropriate wire strength and excellent welding workability.

[0043]

EFFECTS OF THE INVENTION Since the present invention is constituted as described above, it solves the problems of excessive increase in strength and increase in dispersion of the welding wire due to addition of Ti and Mo, and is lacking as a welding wire for high strength steel. It is possible to provide a welding wire for high-strength steel that exhibits excellent welding workability without defective feeding or bead meandering during welding, while guaranteeing strength and toughness of the weld metal that cannot be welded, and also excellent arc stability. In addition, it is possible to provide a raw wire for the above-mentioned welding wire for high-strength steel, which is excellent in wire drawing workability and can be drawn without annealing.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an apparatus used for conducting a wire feedability test.

[Explanation of symbols]

1 Welding wire 2 wire feeding roller 3 conduit tube 4 power supply chip 5 wire arc

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuhiro Yokota 100-1 Urakawachi, Miyamae, Fujisawa-shi, Kanagawa Kobe Steel Co., Ltd., Fujisawa Plant (72) Inventor, Eiichiro Kawasaki 3-36 Nagano, Fukuchiyama, Kyoto Prefecture Kobe Steel Co., Ltd., Fukuchiyama Plant (72) Inventor Toshihiko Nakano 100-1 Urakawachi, Miyamae, Fujisawa City, Kanagawa Kobe Steel Co., Ltd., Fujisawa Works (56) Reference JP-A-8-174268 (JP, A) JP-A-6-254696 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B23K 35/30 B23K 35/40

Claims (6)

(57) [Claims] 1. A welding wire for high strength steel containing Ti and Mo in a carbide or carbonitride containing Ti and Mo.
(Mo) / (Ti) [where (Mo) is the Mo content (wt%), (T
i) has a Ti content (% by weight)] of 0.5 or less on average and a martensite amount of 10% by volume or less, and a welding wire for high-strength steel. 2. (Ti) / (C) [where (Ti) is the total content of Ti (% by weight), (C) is the content of C (% by weight)] is 4.0.
The above is the welding wire according to claim 1. 3. C: 0.02 to 0.12% (meaning mass%; the same applies hereinafter) Si: 0.20 to 1.50% Mn: 0.7 to 2.3% Ti: 0.10. The welding wire according to claim 1 or 2, containing 0.30% Mo: 0.01-0.60%. 4. The welding wire according to claim 3, further containing B in an amount of 100 ppm or less. 5. Further, V, Zr, Nb, Hf and Ta
One or more elements selected from the group consisting of 0.
The welding wire according to claim 3 or 4, containing 1% or less. 6. An original wire of a welding wire containing Ti and Mo, wherein Ti in a carbide or carbonitride containing Ti and Mo.
The wire drawability is characterized in that the mass ratio of Mo to (Mo) / (Ti) is 0.5 or less on average, and the mass ratio of Ti to C (Ti) / (C) is 4.0 or more. Excellent welding wire base wire.