JP3164965B2 - Welding wire for high-strength steel with reduced preheating temperature and welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a welding material having a strength of 60 kgf / mm ² or more and 90 kgf / mm ² or less and 60 kgf / mm ² or more used for bridges, buildings and the like.
Gas to be applied to steel with 0 kgf / mm ² or less of the intensity
The present invention relates to a shielded arc welding wire and a welding method. More specifically, even if the preheating performed before welding is suppressed at least 25 ° C. lower than the temperature performed when a conventional wire having the same strength is used, it is sound. TECHNICAL FIELD The present invention relates to a welding wire and a welding method for obtaining a suitable welding metal.

[0002]

^2. Description of the Related Art For welding steel materials having a tensile strength of 60 to 90 kgf / mm ² , preheating is performed at 50 ° C. or more before welding, particularly 100 ° C. or more when the strength is 80 kgf / mm ² or more. The reason for this is that the amount of diffusible hydrogen present in the joint is released to the outside of the joint, the hardness of the material is reduced by relaxing the cooling speed after welding, and the weld heat-affected zone of the weld metal or steel (hereinafter abbreviated as HAZ). To prevent low-temperature cracking. Therefore, the preheating temperature reduction method according to the prior art includes reducing the amount of diffusible hydrogen from the welding wire to prevent cracks generated in the weld metal, and carbon equivalent of steel (for example, the following formula ( A method of securing the strength of a steel material by using a controlled rolling controlled cooling process while keeping P _cm ) low in 1) has been mainly adopted.

[0003] Cold cracking that occurs in welded joints occurs not only in weld metal but also in HAZ. As a method for preventing low-temperature cracking that occurs in the HAZ even at a low preheating temperature, a method for achieving high strength while securing a low carbon equivalent by using controlled rolling control cooling or the like is adopted. The carbon equivalent is an index for evaluating the cold cracking susceptibility. The lower the carbon equivalent, the higher the cold cracking resistance. Although the idea of this method is to compensate for the decrease in strength due to the reduction in carbon equivalent by the production conditions, it is impossible to apply this method directly to the low-temperature cracking susceptibility of the weld metal. The reason is that it is difficult to control the cooling curve after welding because of the concentrated heat source by the arc. Therefore, the properties such as the strength of the weld metal,
It is almost determined only by the component.

As a welding material for the above-mentioned steel material, for example, Japanese Patent Application Laid-Open Nos. 58-157594 and 52-129646 discloses a welding method for a high-strength steel material, a steel wire for gas shielded arc welding. Is disclosed.

As a concept of reducing the preheating temperature by adding a specific element, there is a method of utilizing, for example, V or Nb. The idea of using V or Nb is an idea of utilizing a trapping effect of diffusible hydrogen due to the formation of a precipitate in the weld metal. Due to this effect, an effect that the amount of effective diffusible hydrogen can be reduced is expected. In particular, research has been reported on the trapping effect of V. For example, Sakai et al. (“Iron and Steel”, Vol. 72 (19
86), no. 9, p. 1375) measured the hydrogen release rate of a steel material in which the V content was changed, and experimentally confirmed that a steel material with a higher V content had a greater hydrogen trapping effect.

[0006]

Of the above methods, the method of reducing the amount of diffusible hydrogen coming from the welding wire is certainly a method that can be expected to reduce the preheating. Methods such as ensuring the cleaning (for example, increasing the number of cleaning steps) and releasing hydrogen in the wire by annealing or the like after manufacturing are conceivable, but none of these methods can significantly increase the manufacturing cost. . Therefore, it is considered virtually impossible to eliminate diffusible hydrogen at all, and in addition to the wire itself, rust, moisture, oil, etc. in the groove can be considered in addition to the wire itself. The quantity must be considered to be present.

[0007] Further, since the tensile strength of the weld metal is increased due to the use of high-tensile steel, it is necessary to add a large amount of alloying elements to the welding wire. As a result, the low-temperature cracking susceptibility of the weld metal is reduced. Therefore, there is a limit in reducing the preheating temperature in the conventional technology. Regarding the improvement of the susceptibility of steel to low-temperature cracking, low-temperature cracking susceptibility can be ensured by reducing the carbon equivalent and applying a controlled rolling control cooling process to secure a predetermined strength. However, for weld metals, it is not possible to apply such a process. In order to satisfy the properties of the weld metal, it is almost always the case that the component is set to a predetermined value. In particular, there is no effective method other than the addition of alloying elements to increase the strength. With increasing strength, the susceptibility of the weld metal to low temperature cracking has steadily declined.

According to the prior art disclosed in Japanese Patent Application Laid-Open No. 58-157594, Mn, Cu, C
Alloying elements such as r, Mo, Ni, and V are added.
The purpose of adding these elements is to secure strength and toughness, and at present, there is no technology for improving the low-temperature cracking resistance.

Further, “Iron and Steel”, Vol. 72 (198
6), No. It is shown that the trap effect described in No. 9 is effective for the first time when V is 0.25% or more, and that the addition of 0.1% has almost no difference from that of no addition. It is shown. The technique described in "Iron and Steel" is to prevent a decrease in ductility of a steel material caused by hydrogen entering into the steel during operation in a Cr-Mo steel for a pressure vessel. 0.1
4-0.15%, Cr: 2.0-3.0%, Mo: 0.
9-1.0% is the effect confirmed in the component system which is essentially different from the present invention. It is not clear whether this hydrogen trapping effect can be used as a means to reduce the critical preheating temperature in high strength steel welding wires.

For the above reasons, when welding high-tensile steel, the preheating temperature tends to be determined as a temperature that does not cause low-temperature cracking in the weld metal, so that the steel itself has good low-temperature cracking resistance. However, it was difficult to reduce the actual preheating temperature. The present invention is to reduce the preheating performed before welding by 25 ° C. or lower than the temperature performed when a conventional wire having the same strength is used.
It is an object of the present invention to provide a welding wire and a welding method capable of obtaining a sound weld metal.

[0011]

The most effective method for improving the low-temperature cracking susceptibility of a weld metal is to keep the additive element of the weld metal low. However, in this method, it becomes difficult to secure predetermined characteristics, for example, joint strength. Therefore, it is necessary to find an element which does not decrease the cold cracking susceptibility even if added to the weld metal, or rather improves the cold cracking susceptibility by adding the same. Focusing on the above points, the present inventors have intensively studied the relationship between the components of the welding wire and the minimum preheating temperature capable of preventing low-temperature cracking generated in the weld metal (hereinafter referred to as the critical preheating temperature). .

The present invention has been completed on the basis of these results, and the gist of the present invention is that the tensile strength is 60k.
High tension of gf / mm ² or more and 90 kgf / mm ² or less
Gas shielding of steel with preheating temperature of steel below 50 ° C
A welding wire for performing arc welding, the weight%
And C: 0.03-0.1%, Si: 0.3-1.0
%, Mn: 0.9 to 2.5%, Mo: 0.1 to 0.6
%, Cu: 0.05 to 0.5%, P: 0.03% or less,
S: 0.03% or less, and V: 0.05-0.
A preheating temperature-reduced high-strength steel welding wire containing 20%, Nb: one or two types of 0.01 to 0.03%, and the balance consisting of iron and unavoidable impurities.

Further, the tensile strength is 60 kgf / mm.
^{2 to} 90 kgf / mm ² , and when the content in steel expressed by weight% is represented by each chemical symbol, P _cm calculated by the following formula (1) is 0.15 to 0.24% The preheating temperature of the steel material is set to 50 ° C. or less by using the steel material of (1) and the welding wire with reduced preheating temperature according to claim 1, 2 or 3.
This is a welding method characterized by performing shielded arc welding . P _cm = C + Si / 30 + (Mn + Cu + Cr) / 20 +
Mo / 15 + V / 10 + 5B (1)

[0014]

First, the technical concept of the present invention will be described. The technical idea of the present invention lies in the effective use of the precipitated elements V and Nb. That is, the carbon equivalent is increased by adding V or Nb,
The strength improvement mechanism of b utilizes the fact that it is different from hardenable elements such as Mn, Mo, and Cr.

[0015] The carbon equivalent is a cold crack susceptibility index, which is also used as a hardenability index. That is,
This suggests that there is a strong correlation between low temperature cracking susceptibility and hardenability. In this case, the preheating temperature can be kept low by reducing the temperature.

FIG. 1 is a diagram showing a limit preheating temperature for preventing low-temperature cracking when V and Nb are added to a welding wire. FIG. 1A shows the effect of V, and FIG. 1B shows the effect of Nb. As the test method, a U-groove crack test method described in JIS-Z3157 was adopted, and a mixture of 3% hydrogen and a shielding gas was used so that the influence of the components was remarkable. The welding heat input is 1.7 kJ / mm. The main components other than V and Nb are
C: 0.05%, Si: 0.46%, Mn: 1.7%,
P: 0.007%, S: 0.01%, Cu: 0.3%,
Mo: 0.15%. The present inventors have found that there is a component range in which the critical preheating temperature can be positively lowered by adding V or Nb.

FIG. 2 shows the case where 0.1% of V is added,
FIG. 4 is a diagram showing the hydrogen release rate of a weld metal when 0.3% is added as a function of the temperature of the weld metal. After the welding, a period of one month was left until the measurement, so that all the diffusible hydrogen in the weld metal was released. Assuming that hydrogen is trapped, the trapped hydrogen is detected by increasing the temperature. FIG. 2A shows the case of V: 0.1%, but the fact that hydrogen was released was not confirmed. On the other hand, in FIG.
Release of hydrogen was confirmed in the temperature range of ° C. That is, V:
At 0.1%, there is no hydrogen trapping effect, but V: 0.
At 3%, it was confirmed that there was a hydrogen trapping effect.

However, in FIG. 1, under the condition of V: 0.3%, the effect of reducing the preheating temperature by 25 ° C. or more is in a range where it can no longer be expected. That is, it is understood that the present invention does not reduce the preheating by using the hydrogen trapping effect. The reason why the effect of FIG. 1 exists is not fully understood, but the effect of using C when forming V and Nb precipitates is to reduce C in the matrix, that is, to reduce the carbon equivalent in the matrix. Can be considered.

Based on the above findings, it is possible to reduce the susceptibility of the weld metal to low-temperature cracking by lowering the other hardenable elements by utilizing the precipitation effect, as compared with the conventional temperatures. I learned that

Next, the components of the welding wire will be described. C is an element indispensable for securing strength. 0.03% of the lower limit of C was set as the minimum value necessary for securing the strength. However, excessive addition of C increases the risk of causing solidification cracks in the weld metal, so the upper limit was made 0.1%. This upper limit is also effective in preventing excessive hardenability of the weld metal.

[0021] Si is necessary to secure strength like C. Further, Si also functions as a deoxidizing element in the weld metal. Further, Si is an essential element to improve welding workability by adding Si. 0 for the lower limit.
3% was set as the minimum value at which these effects can be expected. Conversely, if excessive addition is made, the deoxidizing effect becomes excessive and the hardenability of the weld metal becomes excessive, so the upper limit is set to 1.0%.
And

P and S are impurities in the present invention. However, if each of P and S exceeds 0.03%, the toughness of the weld metal is deteriorated.
And

Mn is an element effective for ensuring strength. Mn is a hardenable element, and by using it, the strength of the weld metal can be ensured. The lower limit of 0.9% is a minimum value necessary for securing the strength.
Further, excessive addition excessively increases the hardenability of the weld metal, which is not preferable from the viewpoint of improving the low-temperature cracking susceptibility and securing the weld metal toughness. Therefore, the upper limit is set to 2.5%.

Mo is a hardenable element like Mn and is also an effective element for securing strength. This can be understood, for example, by comparing the coefficients of Mo and Mn of P _{cm in} equation (1). That is, the value of the coefficient of Mo is Mn.
Greater than that of. Therefore, it is industrially preferable to effectively use Mo. The lower limit of 0.1% is set as a minimum value at which an effect of securing strength by utilizing the hardenability of Mo can be expected. Also, the upper limit of 0.6% is
Since Mo itself is expensive, further addition is not industrially preferable, and is set in order to prevent the toughness of the weld metal from being deteriorated due to excessive increase in hardenability.

Cu is an element effective for improving the electrical conductivity by plating a welding wire and effective for welding work. Cu is also an effective element in securing strength. The lower limit of 0.05% is set as a minimum value for securing the conductivity. Also, excessive addition of Cu
Since the risk of solidification cracking in the weld metal occurs and the hardenability increases unnecessarily, the upper limit is set to 0.5%.

The addition of V and / or Nb forms the basis of the technical idea of the present invention. FIG. 1 (a)
As shown in (1), the addition to the wire positively reduces the critical preheating temperature by 25 to 50 ° C., that is, reduces the susceptibility to cold cracking. This effect differs from the component range that can be expected from the hydrogen trapping effect of V which has been reported up to now, but rather, the present inventors have found that the hydrogen trapping effect of V becomes remarkable 0.25. It has been found that in the region above%, the marginal preheating temperature reduction effect is small, and above a certain level, it is possible to require a higher preheating temperature than in the case of no addition. The lower limit of 0.05% of V was set as a minimum value at which the effect of reducing the limit preheating temperature could be expected. The upper limit of 0.20% is set because excessive addition is not preferable from the viewpoint of raising the critical preheating temperature and securing the toughness of the weld metal.

Nb, like V, is a fundamental element in the present invention. FIG. 1B shows the effect of Nb.
The present inventors have found that the addition of Nb is an element capable of reducing the critical preheating temperature by 25 ° C. as described above. Lower limit 0.0
1% was set as the minimum value at which the effect of Nb could be expected. In FIG. 1 (b), from the viewpoint of reducing the limit preheating temperature, N
The upper limit of b is not determined. However, excessive addition of Nb causes deterioration of the toughness of the weld metal, so the upper limit was made 0.03%.

Next, Ni, which is selectively added as necessary,
Cr, Ti, and B will be described. Ni is an element particularly effective for securing the toughness of the weld metal. 0.3%
Is a minimum value at which improvement in toughness of the weld metal can be expected. However, Ni is expensive, and we have N
Excessive use of i was not considered industrially effective.
Further, Ni also increases the hardenability, so that an upper limit is required in order not to make the hardenability of the weld metal excessive, and the upper limit is set to 2.5% in order to avoid these problems.

Cr is an element effective for improving hardenability like Mo. The lower limit of 0.1% was set as the minimum value at which the effect of adding Cr can be expected. However, excessive hardenability causes deterioration of weld metal toughness, so the upper limit was made 0.5%.

The addition of Ti can dramatically increase the toughness of the weld metal. Ti exists as inclusions in the weld metal and acts as nuclei for forming ferrite. By this effect, the weld metal is refined and the toughness is improved. The lower limit of 0.05% is the minimum value at which this effect can be expected. However, if Ti is added excessively, the hardness of the weld metal becomes too high, so the upper limit was made 0.35%.

B segregates at austenite grain boundaries by adding B, and has the effect of suppressing the growth of proeutectoid ferrite generated from the grain boundaries. This effect suppresses grain growth of the weld metal and prevents coarsening. Therefore, B is also an effective element for improving the toughness of the weld metal like Ti. The lower limit of 0.0005% is set as the minimum value at which this effect can be expected. However, excessive addition undesirably increases the hardenability and is not preferable from the viewpoint of low-temperature cracking susceptibility and toughness, and furthermore, there is a risk that solidification cracking occurs in an ingot material for manufacturing a welding wire. To 0.
0080%.

Next, steel materials will be described. HAZ of steel
It has been found that the cold cracking susceptibility can be almost evaluated by the carbon equivalent as shown in the equation (1). In the present invention, the improvement of the low-temperature cracking susceptibility of HAZ is based on this conventional technology. In high-strength steel, the preheating temperature of the weld joint has been determined so as not to cause low-temperature cracking in the weld metal, because the weld metal is more sensitive to cracking than HAZ. However, according to the present invention, the low-temperature crack resistance of the weld metal has been dramatically improved. Therefore, the preheating temperature can be reduced from the viewpoint of not causing cracks in the weld metal, but HAZ cracking cannot always be prevented at this preheating temperature. Therefore, it was necessary to limit the steel materials in order to prevent HAZ cracking.

The reason for limiting the tensile strength is that the tensile strength is 6
At less than 0 kgf / mm ² , the preheating was sufficiently reduced only by the conventional techniques of the conventional steel material and the conventional welding wire.
This is because it has been determined that it is not necessary to use the present invention. In addition, the upper limit of the tensile strength of 90 kgf / mm ² , if the strength exceeds this, even if the control rolling control cooling technology is used,
This is because it has been determined that it is difficult to obtain good base material toughness while maintaining strength while maintaining the low-temperature cracking resistance of the HAZ.

The reason for limiting P _cm is as follows. P
The upper limit of _cm is determined in order to sufficiently secure the low-temperature cracking resistance of HAZ. HAZ is rapidly quenched by welding heat,
The structure itself is completely different from that of the steel material before welding. Particularly, in the HAZ adjacent to the weld metal, since the maximum heating temperature reaches near the melting point of the steel material, the austenite grains become coarse, and for this reason, it is usually easy to quench and the hardness is usually harder than other parts. . Such a hardened portion is susceptible to low-temperature cracking and is heated to just below the melting point, so that the HAZ structure hardly depends on the steel structure before welding. The reason why the cold cracking susceptibility of HAZ can be evaluated only by the composition of the steel material and the P _cm calculated from the composition is because of the above background. Therefore, no matter what the production process of the steel material is, if the P _cm is less than a certain value, the HAZ can have a low temperature cracking resistance.

The upper limit 0.24% of P _cm were set in order to ensure the HAZ of low-temperature cracking sensitivity. Further, even if the P _cm is limited to 0.24% or less, the strength of the steel material can be reduced to 60 kgf / m by using a technique such as controlled rolling control cooling.
It is not particularly difficult to set the range between m ^{2 and} 90 kgf / mm ² using conventional techniques.

The lower limit of P _cm is set mainly from the viewpoint of securing the toughness of the steel material itself. That is, even if P _cm is set to a range lower than that of the present invention, it is possible to increase the strength to 60 kgf / mm ² or more with the current steel material manufacturing technology (for example, performing accelerated cooling to room temperature). However, in this case, the toughness of the steel material itself deteriorates. Considering the reliability of the entire welded structure, it is considered that using such a steel material having low toughness is not industrially preferable even if there is an advantage by reducing the preheating temperature. The lower limit of 0.15% of P _cm was set for the reasons described above.

Next, preferred ranges of the components of the steel material will be described. First, the basic components of steel are described.

C and Mn of the steel material are indispensable elements for securing the strength and toughness of the base material. However, excessive addition increases the hardenability too much, so the range is set to 0.0
It is desirable to set it to 3 to 0.1% and 0.6 to 1.4%. If the added amount of Si is too large, the HAZ toughness is degraded, so the upper limit is preferably set to 0.6%.

P and S are impurities, but the base material, HA
Since the toughness of Z is deteriorated and S forms sulfide, the upper limits are preferably set to 0.02% and 0.001%, respectively. Al is preferably set in the range of 0.01 to 0.06% from the viewpoint of the amount required for deoxidation and the amount that does not deteriorate toughness.

Next, elements which can be selectively added to the steel material, if necessary, alone or in combination of two or more will be described.

Nb is an element which can be expected to improve the strength due to the precipitation effect, but also increases the HAZ hardness.
It is desirable to set in the range of 5% to 0.04%.

Ti is effective as TiN for refining the base material and HAZ. However, excessive addition of both Ti and N deteriorates the toughness of the base material and the HAZ, so the range is 0.005 to 0.030% for Ti and 0.006% for N.
It is desirable to make the following.

Mo improves the strength and toughness of the base material. However, if the Mo content is too large, the toughness and weldability are deteriorated. Therefore, the range is desirably 0.05 to 0.5%.

Although Ni and Cu are effective elements for improving the strength and toughness, excessive addition affects the HAZ toughness. Further, Cu may cause a risk of generation of Cu cracks at the time of steel production, so that the range is limited. Each 0.1 ~
It is desirable to set it to 1.0%.

V contributes to the precipitation effect similarly to Nb, but does not perform as much as Nb, so the range is 0.01 to 0.01%.
It is desirable to set it to 0.10%.

B improves hardenability by segregating at the prior austenite grain boundaries. However, excessive addition results in excessive hardenability, deteriorating HAZ toughness and the like, so that the range is desirably 0.0005 to 0.0030%.

Next, desirable welding conditions will be described.
The welding heat input is a factor that affects the HAZ hardness, the weld metal hardness, and the like, and excessive suppression of the heat input is not desirable from the viewpoint of obtaining good joint characteristics. Therefore, within the scope of the present invention, it is desirable to set the heat input to 0.4 kJ / mm or more. However, although adopting a high heat input improves welding work efficiency, it is desirable that the heat input be 4.0 kJ / mm or less from the viewpoint of securing joint toughness.

Next, the preheating temperature will be described. Preheating is performed to release hydrogen from the weld joint. The higher the temperature, the greater the effect of preheating. However, an excessive preheating temperature imposes a heavy burden on work efficiency and is not economically preferable. The upper limit of the preheating temperature, 50 ° C., was set as a value at which economically sufficient merits could be secured. In fact, if the preheating temperature is higher than this, the present invention can obtain a sufficiently good weld metal, but it becomes equivalent to the prior art.

The absence of preheating during welding means that the temperature of the joint coincides with the outside air temperature. In this case, depending on conditions, the temperature of the joint may be below freezing, and in this case, dew condensation may occur at the joint. This causes problems such as defects such as blowholes at the time of welding and an increase in the amount of hydrogen caused by condensation. One effective means for solving these problems is preheating. In this case, it is not necessary to use an unnecessarily high preheating temperature, but it is preferable to perform preheating at 5 ° C. or more.

Next, the shielding gas will be described. The shielding gas has an effect of blocking the welding arc from the outside air. Therefore, from the sensitivity to low-temperature cracking, an effect of preventing hydrogen from entering from the outside can be expected, but in addition, the shielding gas has a preferable range since it affects the welding operation. This range corresponds to the S
Although it depends on the component amount of i, in the scope of the present invention, considering its workability, 100 g
It is desirable to set the range of% CO _{2 to} 5% CO ₂ + 95% Ar.

[0051]

EXAMPLES Table 1 shows the chemical components of the welding wire used in this example. All wire diameters are 1.2 mm.
The wire is coated with oil enough to obtain good workability. Using the wire shown in Table 1 and the shielding gas shown in Table 2, an all-deposit (all deposited metals) was produced under the condition of a heat input of 2.5 kJ / mm, and then a tensile test piece was produced by machining.

[0052]

[Table 1]

[0053]

[Table 2]

Table 2 also shows the tensile strength (TS). The wire of Table 1 has a strength of 6 as can be seen from Table 2.
It is in the range of 0 kgf / mm ² to 90 kgf / mm ² . Further, some wires having the same strength use V or Nb to secure the strength, and others do not. For example, if the strength is between 60 kgf / mm ² and 70
kgf / mm ^{2 in} the range of wires Y1, Y2, Y3,
Among Y4, Y5, Y6, and Y7, Y2, Y3, Y
5, Y7 uses V or Nb. The wire Y3
Is not included in the examples of the present invention because 0.4% of V is added.

Table 3 shows the steel materials used in this example.
I have. Base material strength is 60kgf / mm ^Two From 80kgf /
mm^Two Within the range. P_cmIs from 0.16%
0.27%, and the plate thicknesses are all 40 mm.

[0056]

[Table 3]

Using the wires shown in Table 1 and the steel materials shown in Table 3, a U-groove crack test described in JIS-Z3157 was performed to determine a critical preheating temperature. The test was performed in a room set at 20 ° C. so as to minimize the influence of the outside air temperature. The shielding gas corresponding to each wire is the same as that shown in Table 2. The diffusible hydrogen content of each wire was measured by the gas chromatography method described in JIS-Z3118. As a result, it was confirmed that each wire had a hydrogen amount of 3 cc / 100 gr. The test piece was previously preheated uniformly to a predetermined temperature in an electric furnace. Preheating temperature: no preheating (20 ° C), 50 ° C, 7
The temperature was set to 5 ° C., 100 ° C., and 125 ° C. in steps of about 25 ° C.

Table 4 shows the combinations of wires and steel materials and the critical preheating temperatures in the U-groove crack test.
The heat input amounts in Table 4 are all 1.7 kJ / mm.
In addition, the crack occurrence location is a preheating temperature one level lower than the critical preheating temperature (for example, the symbol R10 indicates a critical preheating temperature of 100
(75 ° C., which is one level lower than 1 ° C.).

[0059]

[Table 4]

Table 4 shows that the strength of the welded joint was 60 kgf / m.
The levels are divided into three levels: m ² class, 70 kgf / mm ² class, and 80 kgf / mm ² class. 60kgf / mm ²
Looking at the grade joints R1, R2, R3, R4, R5, R6, R7, all of the inventive examples (R2, R5, R7) were free of preheating, that is, cracks could be prevented by preheating at 20 ° C.
In contrast, in the comparative examples (R1, R3, R4, R6), 5
Unless preheating was performed at 0 ° C., cracking could not be prevented. The symbol "-" at the crack generation location indicates that the crack generation location could not be limited because no crack was generated without preheating.

For R8 and R9 of 70 kgf / mm ² class,
Both the present invention example (R9) and the comparative example (R8) require preheating, but the preheating temperature of the present invention example is lower by 25 ° C. 8
0kgf / mm ² class R10, R11, R12, R1
3, R14 and R15 are described in Examples of the present invention (R11, R
13, R14) were all able to prevent cracking by preheating at 50 ° C. In contrast, the comparative examples (R10, R12, R1
In 5), the critical preheating temperature is from 100 ° C to 125 ° C. In particular, in R10 and R12, it can be seen that the place where cracks occur is the weld metal, and the preheating temperature of the joint is for preventing the weld metal from cracking. In addition, since R15 has a high P _{cm of} steel of 0.27%, it can be seen that cracks are generated not only in the weld metal but also in the HAZ. R4 using the wire of the present invention using S4 having a low carbon equivalent of steel material,
In the case of R13 and R14, cracks occurred in the HAZ and the weld metal, but both cracks could be prevented by preheating at 50 ° C. That is, these wires can form a weld metal having the same low temperature cracking susceptibility as low P _cm steel.

[0062]

According to the present invention, the crack prevention limit preheating temperature of the high-strength steel wire which has been used up to now is set to 25.
° C or more, improving welding work efficiency,
The economic effects on the industry, such as improving the working environment, are significant.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of added components to a wire and the critical preheating temperature in a U-groove cracking test.
(B) shows Nb addition

FIG. 2 is a graph showing a release rate of hydrogen released from a weld metal, where (a) shows a case where V is 0.1% and (b) shows a case where V is 0.3%.

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁷ Identification code FI C22C 38/58 C22C 38/58 (72) Inventor Kunio Koyama 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development (56) References JP-A-61-115694 (JP, A) JP-A-58-159994 (JP, A) JP-A-60-158995 (JP, A) JP-A-7-276080 (JP, A) JP-A-7-195192 (JP, A) JP-A-59-163097 (JP, A) 5P. 48-49 (1992) (58) Fields surveyed (Int. Cl. ⁷ , DB name) B23K 35/30

Claims (4)

(57) [Claims] 1. A tensile strength of 60 kgf / mm ² or more and
The 90 kgf / mm ² or less of high-tensile steel, the preheating temperature of the steel
To perform gas shielded arc welding at a temperature of 50 ° C or less
A welding wire, in weight%, C: 0.03 to 0.
1%, Si: 0.3 to 1.0%, Mn: 0.9 to 2.5
%, Mo: 0.1 to 0.6%, Cu: 0.05 to 0.5
%, P: 0.03% or less, S: 0.03% or less,
And V: 0.05 to 0.20%, Nb: 0.01 to
A welding wire for a high-strength steel with a reduced preheating temperature, comprising 0.03% of one or two kinds, the balance being iron and unavoidable impurities. 2. Ni: 0.3 to 2.5% by weight.
%, Cr: 0.1 to 0.5% of one or two kinds, and the welding wire for high-tensile steel with reduced preheating temperature according to claim 1. 3. The composition according to claim 2, wherein Ti: 0.05 to 0.1% by weight.
The preheating temperature-reduced welding wire for high-tensile-strength steel according to claim 1 or 2, comprising one or two of 35% and B: 0.0005 to 0.0080%. 4. When the tensile strength is not less than 60 kgf / mm ^{2 and not} more than 90 kgf / mm ² , and the content in steel expressed by weight% is represented by each chemical symbol, it is calculated by the following equation (1). Gas shield using a steel material having a P _cm of 0.15 to 0.24% and a reduced preheating temperature type welding wire according to claim 1, 2 or 3, wherein the preheating temperature of the steel material is 50 ° C. or less.
A welding method characterized by performing arc welding . P _cm = C + Si / 30 + (Mn + Cu + Cr) / 20 +
Mo / 15 + V / 10 + 5B (1)