JPS59156599A - Submerged arc welding method - Google Patents

Abstract

PURPOSE:To provide a weld metal having a high level of low temp. toughness by specifying the component compsn. and bulk density of a flux for submerged arc welding and decreasing the content of oxygen and nitrogen in a welding wire. CONSTITUTION:A flux for submerged arc welding which contains the following components by weight % and having a bulk specific density of flux of 0.85- 1.85g/cm<2> is used: The flux contains the respective components consisting of 22-35% CaF2, 22-38% MgO, 3-12% CaO, 54-80% CaF2+MgO+CaO, 10- 25% Al2O3, 7-20% SiO2 and 0.5-3.0%>=1 kind of Na2O and K2O. A welding wire contg. <=40ppm nitrogen and <=100ppm oxygen is used. A weld metal having excellent low temp. toughness is obtd. if submerged arc welding is performed by using the above-mentioned flux and wire.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a submerged arc welding method.
A submerged arc welding method for low-temperature service steel containing 1 or 2 types, which provides a welded part with good low-temperature toughness, especially when double-sided single-layer welding with a high base metal dilution or post-weld heat treatment is performed. The present invention relates to a submerged arc welding method that allows for

For conventional Nl) and V-containing steel sheets, weld metal is TI-
Generally, a method was adopted in which low-temperature toughness was ensured by making the structure of the weld metal finer by making it B-based. However, in this method, the dilution of the base metal is extremely large (large amounts of Nb and V are added to the weld metal for double-sided welding, and MO added for the purpose of improving strength and toughness is added to the wire and base metal). When added to weld metal from flux, etc., it is possible to maintain a high level of toughness in the raw material that is not affected by heat during welding, but reheating that is affected by heat by welding the next layer or second side The toughness of the weld metal deteriorates rapidly due to precipitation hardening.Therefore, the toughness of the weld metal is not uniform and varies greatly depending on the location where the impact test piece is taken, which affects the uniformity of the welded joint and the safety of the structure after welding heat treatment. (SR, Temper,
(QT, etc.), the toughness of the weld metal deteriorates rapidly for the same reason. Furthermore, in recent years, standards that take safety into account are often adopted to prevent structures from becoming brittle and causing serious accidents. In addition to the standards for absorbed energy values in impact tests, we also adopt standards such as, for example, brittle fracture ratio of impact test pieces of 50 inches or less (referred to as daytime fracture characteristics) or δC≦0.25+nm in COD tests. It's starting to happen. These standards for fracture surface properties and COD properties are much stricter than the conventional standards for absorbed energy values, and even if the absorbed energy value satisfies the standards with a margin, it may not satisfy other standards. There were many cases. This tendency is particularly noticeable when using a steel plate containing Nb and (2).

Therefore, the inventors of the present invention have conducted repeated studies on the above-mentioned problem, and conducted experiments focusing on the oxygen content and nitrogen content in the weld metal. That is, Figure 1 shows the nitrogen content in the weld metal and -6
A graph showing the relationship with the δ0 value (COD characteristic value) at 0°C shows that the oxygen content in the weld metal is 150 to 170 PI
IIn is used, and the welded portion is subjected to post-heat treatment (stress relief annealing). As shown in the graph, the nitrogen content is 35
Good COD properties were obtained below p and the fracture surface properties were also good.

On the other hand, Fig. 2 is a graph showing the relationship between the oxygen content in the weld metal and the δ0 value at -60°C.
(stress relief annealing). As shown in the graph,
When the oxygen content was 180% or less, good C and OD properties were obtained, and the fracture surface properties were also good.

The present invention has been made based on the above findings, and has devised a flux for submerged arc welding and a wire composition that can reduce the oxygen content and nitrogen content in the weld metal. The object of the present invention is to provide a submerged arc welding method that provides a weld metal having a higher level of low-temperature toughness.

However, the submerged arc welding method of the present invention includes the following components:
And Ca'? ,, the sum of MgO and CaO is 54 to 80
%, and the bulk density of the flux is 0.85 to 1.
A flux for submerged arc welding that is 85 g/c+fl;
Nitrogen content is 404 or less, and oxygen content is 10
The gist lies in welding using a wire that is 0p or less.

CaP2122-35% MgO: 22-38% CaO: 3-12% A1+Os: 19-25% 5in2 + 7-20 Na, OlK,! 001 or 2 types; 0.5 to 3 in total
．． 0% The present inventors first attempted to reduce the oxygen content and nitrogen content in the weld metal by specifying the composition of flux for submerged arc welding.

That is, flux for submerged arc welding is composed of various oxides, and by modifying the composition of the flux, the oxygen content in the weld metal can be reduced while satisfying welding performance. In addition to devising the above-mentioned component composition, we have also succeeded in reducing the nitrogen content in the weld metal by determining an appropriate range for the bulk density of the flux. However, attempts are made to improve low-temperature toughness by suppressing precipitation hardening of Ib and V due to reheating, but as mentioned above, safety requirements for welded structures in recent years have become stricter, and the composition of flux for submerged arc welding has been improved. This cannot be fully satisfied just by doing so. In addition to the above, the inventors of the present invention succeeded in satisfying the above requirements by reducing the oxygen content and nitrogen content in the welding wire.

First, the flux for submerged arc welding according to the present invention will be specifically explained below.

Ca1F,! 22-35q6 CaF2 is a basic component and has the effect of lowering the amount of oxygen in the weld metal, as well as adjusting the fluidity of molten slag and promoting the slag-metal reaction. However, if it is less than 22 inches, the effect of reducing the amount of oxygen is not effectively exhibited, and the bead becomes convex and pock marks are likely to occur.

On the other hand, if it exceeds 35 inches, the fluidity of the slag becomes excessive, making it easy for the slag to become entangled, and at the same time, the peelability of the slag becomes poor.

MgO+22 to 38% MgO is a basic component that functions as a slag forming agent and a viscosity modifier, and also has the effect of lowering the amount of oxygen in the weld metal. If it is less than 22q6, the basicity will be insufficient and the effect of reducing the amount of oxygen will be poor, and the bead will tend to meander and undercuts will occur frequently. If it exceeds 38q6, irregularities will easily appear in the bead shape and pock marks will occur frequently.

CaO: 3-12% CaO is a basic component and functions to adjust the basicity, melting point, and viscosity of the slag. If it is less than 3 inches, the basicity will not be insufficient, but the viscosity of the slag will be too low and the bead will meander. On the other hand, if it exceeds 12q6, the arc stability will be poor and the slag removability will also deteriorate.

In addition, CaCO, is used as a substitute for CaO, and CaC0,
It is also effective to promote the release of nitrogen gas in the weld metal using CO2 gas generated by the chemical reaction -+CaO+Co2. However, in this case, unless CaCQ is added in a range of 3 to 12% in terms of CaO, welding workability will deteriorate.

AI, 0.110-25.Th Al2O,l is a substantially neutral component, and exhibits the function of adjusting the melting point and viscosity of the slag while suppressing a decrease in the basicity of the flux as much as possible. If it is less than 10L16, undercuts tend to occur and slag removability deteriorates. On the other hand, if it exceeds 25 inches, the viscosity is too high, which tends to cause slag to become entangled, and the bead becomes convex, which is undesirable.

Sin, +7 to 20% Sin, is an acidic component and serves as a slag forming agent, as well as a basicity modifier and a viscosity modifier. However, if it is less than 7%, the viscosity of the slag is insufficient, resulting in meandering beads and undercuts. On the other hand, if it exceeds 20 degrees, the basicity decreases, the amount of oxygen in the weld metal increases, the impact value deteriorates, and the removability of the lug becomes poor.

For Na and O, total amount of O + 0.5 to 3.0% Na2
O and Ni20 exhibit the function of increasing the stability of the arc and the function of adjusting the viscosity. If the total content of these components is less than 0.5%, the arc will become unstable and the unevenness and meandering of the sheave will become significant.

On the other hand, if the total content exceeds 3.0 inches, the viscosity of the slag decreases too much, resulting in poor workability, and the moisture absorption resistance of the flux deteriorates, making gas-induced defects such as pock marks and pits more likely to occur.

The total amount of CaF, , MgO and CaO is 154 to 80 cm. MgO and CaO are effective in reducing the amount of oxygen in the through-welding metal described above, but they also have a large effect on welding workability. That is, CaF2. If the total amount of MgO and CaO is less than 54%, basicity is insufficient and the amount of oxygen in the weld metal cannot be reduced. On the other hand, if the total amount exceeds 80 g, the amount of oxygen will decrease, but the viscosity and melting point of the weld metal will be too high, resulting in poor workability.

Bulk density: 0.85 to 1.85 g/c The relationship between the bulk density of the flux and the amount of nitrogen in the weld metal is the third
As shown in the figure, the larger the bulk density, the lower the amount of nitrogen in the weld metal tends to be. Bulk density is 0.85 g
If it is less than 10 f1, the effect of reducing the amount of nitrogen will not be sufficient, and the effect of improving toughness will not be effectively exhibited, but the weld metal will blow up a little more during welding. On the other hand, the bulk density is 1
If it exceeds = 856/cJ, the bulk density becomes too large, the bead width becomes narrow, and the excess buildup becomes too high, which is not preferable.

In addition to using the flux for submerged arc welding having the above-mentioned composition,
The oxygen content and nitrogen content in the welding wire were specified as follows.

Nitrogen content in the wire: 404 or below (see Figure 1) Nitrogen content in the weld metal is 3.
5111XD or less, and for that purpose, it was found that it was necessary to use the aforementioned flux for submerged arc welding and to suppress the nitrogen content in the wire to 40% or less.

Oxygen content in wire + 100pr 111 or less (see Figure 2) Oxygen content in weld metal is 180pp
It was found that it was necessary to keep the oxygen content below Ill, and for that purpose, it was necessary to use the aforementioned flux for submerged arc welding and to suppress the oxygen content in the wire to below iooppm. In other words, the oxygen content in the weld metal is determined by the slag-metal reaction during welding, so it can be reduced by welding with a highly basic flux, but if the oxygen content in the wire is very high, Even with the use of a chemical flux, it was not possible to reach the target oxygen content, so it was necessary to simultaneously control the oxygen content in the wire.

Note that the chemical components of the wire other than those listed above are preferably within the following ranges, taking into account the dilution of the base material during submerged arc welding.

c + "o, o1 ~ 0.20 Chi 81 + 0.40% or less Mn + Q. 50 ~ 2.00% N: t + 7.5% or less Cujl, 25 - or less Other impurities such as P% B, Nb, v etc. It is preferable to lower the value.

By welding using the flux and wire for submerged arc welding as described above, it is possible to obtain a weld metal that does not easily undergo precipitation hardening even after being reheated. The low-temperature toughness of the weld metal can be maintained at a high level even when it is reheated by welding the next layer during welding or by post-weld heat treatment.

If a BaO component is added as a component other than the above, the amount of nitrogen in the weld metal can be reduced.

BaO content: 110% or less Ba0% By adding at least 1s selected from the group consisting of BaC0, BaF2 and 10% or less in terms of BaO, the amount of oxygen in the weld metal can be reduced. . That is, since the impact value is improved by reducing the amount of nitrogen in the weld metal, it is preferable that the amount of nitrogen be as small as possible. By the way, there is a relationship as shown in Figure 4 between the amount of nitrogen in the weld metal and the amount of BaO added! As the 3aO equivalent amount increases, the nitrogen amount decreases, but the content is 10
If it exceeds %, it will cause pockmarks.

By the way, the preferred composition of the weld metal obtained by the method of the present invention (weld metal that does not easily undergo precipitation hardening even when reheated) is as follows.

C: 0.05 to 0.15 cm s1 + o, 4596 or less Mn + 0.75 to 1.65% Ni + 3.0 cm or less cut 0.5 cm or less Other impurities such as p and s should be kept as low as possible is good.

Since the present invention is roughly configured as described above, it is possible to obtain a weld metal with excellent low-temperature toughness (impact properties or impact performance fracture surface properties, COD properties, etc.) without impairing welding workability. It has great industrial value in the field of LPG tanks and structures for cold regions.

Examples of the present invention will be described below.

Using the flux shown in Table 1 and the wire shown in Table 2, single-layer submerged arc welding was performed on both sides of the steel plates shown in Table 3.

The groove shape and lamination state were as shown in FIG. 5, and the welding conditions were as shown below.

(Remaining Fe) (Welding conditions) First side 800A-36V-40CPM Second side 900A-38V-40CPM Tensile test piece 1 (double-dashed line in Fig. 6) and impact test piece 2 (6th dotted line) were prepared from the obtained weld metal. Each specimen (dotted chain line area in the figure) was sampled and subjected to a tensile test (J Engineering 5-z-3111), an impact test (J Engineering 5-Z-3112), and a COD test.

These results are shown in Table 4 (a) to 4) along with the welding workability and the chemical composition of the weld metal.

As is clear from Table 4 (a) to (b), there is almost no difference in tensile strength between Comparative Examples 17-19 and 27-29 and the examples, and good results were obtained in all of them. However, there are significant differences in impact test values, brittle fracture ratios, and COD test values. In Comparative Examples 17 to 19, a sample flux other than the present invention was used, and in Comparative Examples 27 to 29, a sample wire other than the present invention was used. In addition, in Comparative Examples 9 to 16, either the chemical composition of the test flux was too high or too low, resulting in poor welding workability, and satisfactory welds could not be obtained, and even tensile tests and impact tests failed. .

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the nitrogen content in the weld metal and the C0II characteristic value, Figure 2 is a graph showing the relationship between the oxygen content in the weld metal and the COD characteristic value, and Figure 3 is the graph showing the relationship between the flux bulk density and the COD characteristic value. A graph showing the relationship between the amount of nitrogen in the weld metal and a graph showing the relationship between the amount of BaO added and the amount of nitrogen in the weld metal. FIG. 6 is a sectional view showing the shape 7 and the laminated state, and FIG. 6 is an explanatory diagram showing the locations where tensile test pieces and impact test pieces are taken from the submerged arc welded portion shown in FIG. 5. Applicant: Kobe Steel, Ltd. q Ikari Sui 41 B i-Q

Claims (1)

[Claims] (1) Contains the following components, and includes CaF, , MgO and C
The sum of aO is 54 to 80 by weight (hereinafter simply referred to as "chi"), and the bulk density of the flux is 0.85 to 1.
7 lux for submerged arc welding which is 85g/c-, nitrogen content is not more than 40%, and oxygen content is 1100pr.
A submerged arc welding method characterized by welding using a wire having a temperature of I or less. CaP2122-35% MgO+22-38% CaO+3-12eI6 A120a' 10-25 q6 Sin2: 7-20% One or two of Ha, OlK, O: 05-3% in total.
0chi (2, in claim 1, BaO1BaC
O, BaF, one or more selected from the group B
A submerged arc welding method using a submerged arc welding flux containing 10 g or more in terms of aO.