JPH0518677B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a latent arc wire for low-temperature steel, and more specifically, in latent arc welding of low-temperature steel, it is possible to obtain a Ti-B weld metal having excellent low-temperature toughness. It concerns wires. (Prior Art) In recent years, in the development of undersea energy, construction of important structures such as oil drilling rigs has been actively carried out. Structures are becoming larger year by year, and more and more structures are being used in cold regions. Against this background, there is a demand for the development of highly efficient and excellent quality welding technology. Covered arc welding is mainly used for welding various structural steels. Gas shield welding and submerged arc welding are applied. Among these methods, the submerged arc welding method is particularly effective in increasing the welding current and is easy to apply to the multi-electrode welding method, so it is used in many fields as an extremely highly efficient method. By the way, as a typical method for improving the low-temperature toughness of weld metal, the Welding Society Journal Vol. 50. No. 2 (1973)
As shown on pages 174-181 of the February issue of
A widely used method is to add Ti-B to give the weld metal a uniform and fine ashular ferrite (hereinafter referred to as AF) structure. Furthermore, due to the recent petroleum situation, it is required that good low-temperature toughness can be obtained even in high heat input welding, which is lower than the conventional -40℃ to -60℃ and more than 45KJ/cm for double-sided single-layer and double-sided multilayer welding. More and more fabricators are doing this. (Problem to be solved by the invention) In the case of the above-mentioned high heat input welding, even if Ti-B welding material is used, the toughness is not increased in the part that is reheated in the next pass (hereinafter referred to as the reheated part). However, according to the studies conducted by the present inventors, the main cause of the decrease in toughness in the reheating section was thought to be largely due to the formation of high carbon martensite (hereinafter referred to as M*). Therefore, it was considered effective to lower the amount of C in the weld metal, which promotes the formation of martensite. In fact, it has been found that by using a submerged arc welding wire with a low C content, the toughness of the reheated zone can be improved by lowering the C content in the weld metal. However, simply C
If only the amount is lowered, the parts that remain welded (hereinafter referred to as
There is room for further improvement in this regard, as the toughness actually decreases in areas that have been reheated (hereinafter referred to as AW) and above 1050°C (hereinafter referred to as coarse-grained regions). In view of the above-mentioned circumstances, an object of the present invention is to provide a latent arc welding wire capable of producing Ti-B molten metal having excellent low-temperature toughness in both the AW part and the reheating part during latent arc welding of low-temperature steel. That is. (Means for Solving the Problems) The present inventors have developed a submerged arc welding wire for low-temperature steel welding that can obtain a weld metal with good chemical composition and low-temperature toughness throughout the welded joint. For this purpose, various observations were made on these weld metals.
As a result, the main cause of the decrease in toughness is that by lowering C, the amount of O, which is normally lowered by the deoxidation reaction of C, increases, resulting in oxidation of B, oxidation of Si and Mn, and oxidation of Ti. Ti-
It becomes impossible for B to act effectively, and the precipitation of pro-eutectoid ferrite (hereinafter referred to as PF) increases.
We also found that this is because the precipitation of AF becomes difficult. Therefore, in order for Ti-B to work effectively, O in the weld metal must be kept low. As a result of examining methods for this purpose, it was found that it is effective to add a deoxidizing agent to these wires, and after examining various effects of the deoxidizing agent, it was found that Al was the most suitable. This is because the crystalline oxides of Al, Ti, and Mn not only have adequate deoxidizing power but also act as effective oxides in the production of AF, and also have improved toughness. Seem. The present invention was made based on this knowledge, and the gist thereof is as follows: C: 0.07% or less, Si: less than 0.05%,
Al: 0.002 to 0.50% is an essential component, P: 0.020
% or less, S: 0.020% or less, N: 0.0050% or less,
O: limited to 0.0150% or less, and Mn: 0.5 to 3.0
%, Ni: 0.5-12%, Cu: 0.02-3.0%, Mo: 0.1
~2%, or further contains one or more of Ti: 0.05~0.5%, B: 0.005~0.1%, the remainder being Fe and inevitable impurities, and A Ti-B submerged arc welding wire for low-temperature steel, characterized by a CE of 0.2 to 1.0. However, CE is the carbon equivalent of IIW, CE = C + 1/6Mn + 1/15 (Cu + Ni) + 1/5
(Cr+Mo+V) (However, the calculation is performed in weight%.) That is, the wire of the present invention can be most effective when used in combination with a Ti-B type flux, that is, a flux containing Ti oxide and B oxide, but when combined with a flux that does not contain Ti oxide. One or both of Ti and B is added to the wire. (Function) First, the basic components of the wire of the present invention will be described. First of all, the lower C is, the better, but at least
Unless it is 0.07% or less, precipitation of M* in the weld metal cannot be sufficiently suppressed. Next, Si acts as a deoxidizing agent and lowers O and improves toughness, but too much Si deteriorates toughness.
Must be less than 0.05%. Also, Al has stronger deoxidizing power than Ti, Mn, Si, and B.
It has weaker deoxidizing power than REM, Mg, and Ca. For this reason,
Unlike REM, Al is not completely oxidized in the arc, but a considerable portion moves to the molten pool and then reacts with oxygen in the molten pool and oxidizes. Therefore, while keeping the amount of O in the weld metal low, the molten metal By preventing the oxidation of B in the pond and producing Al-Ti-Mn-based oxides that are effective in generating AF, the effect of Ti-B can be further demonstrated and the toughness can be further improved. If there is too much Al in the metal, only Al will not oxidize and AF will not be possible, which will deteriorate the toughness.
In addition, the appropriate range is 0.002 to 0.50%, taking into consideration that oxidized Al may be excessively retained in the weld metal and increase the zero amount. On the other hand, P segregates at grain boundaries, weakens the bond between grains, and deteriorates toughness, so it must be limited to as low as possible, but if it is below 0.020%, it is not harmful. Next, like P, S also deteriorates toughness.
It is necessary to limit it to 0.020% or less. Also, N is particularly harmful to toughness and has a content of at least 0.0050
% or less. Furthermore, O forms Ti oxide in the weld metal.
Although a certain amount of O is required to generate AF, it is not necessary to add it to the wire because it is sufficiently supplied from the molten slag in the molten pool. Since oxidation loss occurs in the interior, it is necessary to limit it to as low as possible, and it must be at least 0.0150% or less. The above are the basic components of the present invention. In the present invention, Mn, Ni, Cu, and Mo are used to maintain appropriate hardenability of the weld metal, generate a uniform fine microstructure, and improve low-temperature toughness. One or more of these must be added. First, Mn is necessary for deoxidizing and providing appropriate hardenability of the weld metal, promoting the precipitation of AF, and improving the toughness of the weld metal, and its appropriate range is 0.5 to 3.0%. Addition of less than 0.5% does not produce enough AF.
When added in excess of 3.0%, upper bainite (hereinafter referred to as
UB) is formed and the toughness deteriorates. Next, Ni is a necessary component to impart appropriate hardenability to the weld metal, strengthen the ferrite base, increase the plastic deformability of the weld metal, and improve toughness, and its appropriate range is 0.5 to 12 %. If it is less than 0.5%, the effect will be small, and if it is added in excess of 12%, there will be a greater risk of hot cracking in the weld metal. Further, Cu is a component suitable for maintaining hardenability and improving toughness without promoting the formation of M*, and its appropriate range is 0.02 to 3.0%. Addition of less than 0.02% will have little effect, and addition of more than 3.0% will increase the risk of hot cracking in the weld metal. Furthermore, Mo is an effective component for maintaining the hardenability of weld metal especially in high heat input welding, and its appropriate range is 0.1 to 2.0%. If it is less than 0.1%, the effect is not sufficient, and if it is added more than 2.0%, UB
is generated and deteriorates toughness. Furthermore, if the hardenability of the weld metal is insufficient,
If PF precipitates and the hardenability becomes excessive, UB precipitates and the toughness deteriorates. Hardenability is expressed by CE, which is the carbon equivalent of IIW, and CE is 0.2~
Must be in the range 1.0. That is, if CE
If it is less than 0.2, the hardenability of the weld metal will be insufficient and PF will occur.
is generated, and if CE exceeds 1.0, UB is generated and toughness deteriorates. However, CE is the carbon equivalent of IIW, and CE=C+1/6Mn+1/15 (Cu+Ni)+1/5
(Cr + Mo + V) (However, the calculation is performed in weight%.) In other words, part of Ti dissolves into the matrix due to redox reaction in the arc or molten pool, and the rest becomes an oxide, but this oxide Since it becomes a nucleus for AF generation and improves toughness, it is necessary to add 0.05% or more. However, Ti dissolved in the matrix
If it is too large, the toughness will deteriorate, so the amount of Ti added must be 0.5% or less. In addition, B also exists in the weld metal in the form of dissolved oxides and matrix through redox reactions in the arc and molten pool, but some of it also forms N and BN in the steel. Since it makes N harmless and improves toughness, it is added at least 0.005%. In addition, B dissolved in the matrix also segregates at grain boundaries and suppresses the formation of PF, thereby improving toughness, but in excess, it promotes the formation of M*, so the appropriate range must be 0.1% or less. . A wire having the above component composition and a flux containing Ti oxide and B oxide (in the wire
If Ti or B is added, it is not necessary to include them), C: 0.07% or less, Si: 0.1 to 0.3%, A: 0.002 to
0.05%, P: 0.020% or less, S: 0.020% or less,
N: 0.005% or less, O: 0.012 to 0.045%, and Mn: 0.5 to 2.5%, Ni: 0.2 to 6.5%, Cu: 0.02 to
Contains one or more of 1.2%, Mo: 0.03 to 0.7%,
In addition, it is possible to obtain a weld metal whose composition has a CE of 0.2 to 0.6, and the AW part of such weld metal,
Both reheated parts show excellent low-temperature toughness in impact tests at -60°C. However, CE is determined using the IIW carbon equivalent formula, which is the same as the above formula. Note that this wire can be manufactured by melting raw metal, casting, forging, rolling, drawing and plating to about 1.0 to 7.0 mm. Next, the effects of the present invention will be specifically described with reference to Examples. (Example) Table 1 shows the chemical components of the wires of the present invention and comparative examples.

[Table] Note that wires other than W2 contain more than a trace amount of Cu, but this is because ordinary wires are copper-plated to prevent rust and improve conductivity. No copper plating was experimentally applied to W2. Furthermore, the wire diameter is 4.8 mm in both cases. The flux is NB-55E with single layer welding on both sides, NB
-55L was used for double-sided multilayer welding. All of these fluxes are commercially available Ti-B bond fluxes, and F1 is a flux that does not contain Ti or B. The compositions of these fluxes are shown in Table 2.

【table】 The test steel plates are shown in Table 3.

[Table] Both P1 and P2 are controlled rolled steel, P1 is 50 kg steel and P2 is 60 kg steel. Table 4 shows welding conditions.

[Table] Figure 1 shows the sampling locations of the test pieces. In the figure, a shows the procedure for collecting specimens from a double-sided single-layer weld, and b shows the procedure for collecting specimens from a double-sided multi-layer weld. 1 is an impact test piece of the AW part, 2 is an impact test piece of the reheated part, and 3 is a specimen for chemical analysis. Show the sample. Table 5 shows the test results.

【table】

[Table] All the wires using the wire according to the present invention show good values, whereas the wire using WR1 has a high C content and no A added, so there is no M in the reheating section. *, and the impact value of the part including the reheated part is WR2. Since A is not added to the wire, the amount of O in the weld metal increases, PF precipitates, and the toughness of the AW part decreases. The value has deteriorated. Those using WR3 wire are CE
is too high, UB is generated, and the toughness of both the AW section and the reheated section is degraded. In addition, in the case of using WR4 wire, A was too high and the toughness of both the AW part and the reheated part deteriorated. (Effects of the Invention) As is clear from the above examples, according to the present invention, it is possible to provide a welding wire that can impart extremely excellent low-temperature toughness to weld metal, and the industrial effects are extremely significant.

[Brief explanation of drawings]

FIG. 1A is a diagram showing the procedure for collecting test specimens from a double-sided single-layer welded part and a double-sided multilayer welded part. 1...Sampling position of impact test piece of AW section, 2...
Collection position of reheating section test piece, 3...position of collection of sample for chemical analysis.

Claims (1)

[Claims] 1% by weight: C: 0.07% or less, Si: less than 0.05%,
Al: 0.002 to 0.50% is an essential component, P: 0.020% or less, S: 0.020% or less, N:
0.0050% or less, O: 0.0150% or less, and Mn: 0.5-3.0%, Ni: 0.5-12%, Cu:
0.02 to 3.0%, Mo: 0.1 to 2%, the remainder is Fe and inevitable impurities, and
For low temperature steel characterized by a CE of 0.2~1.0
Ti-B based submerged arc welding wire. However, CE is the carbon equivalent of IIW, CE = C + 1/6Mn + 1/15 (Cu + Ni) + 1/5
(Cr+Mo+V) (However, the calculation is done in weight%.) 2 In weight%, C: 0.07% or less, Si: less than 0.05%,
Al: 0.002 to 0.50% is an essential component, P: 0.020% or less, S: 0.020% or less, N:
0.0050% or less, O: 0.0150% or less, and Mn: 0.5-3.0%, Ni: 0.5-12%, Cu:
0.02 to 3.0%, Mo: 0.1 to 2%, and Ti: 0.05 to 0.5%, B: 0.005 to 0.1%, and the remainder is Fe and unavoidable impurities. A Ti-B based submerged arc welding wire for low-temperature steel, characterized in that the wire has a CE of 0.2 to 1.0. However, CE is the carbon equivalent of IIW, CE = C + 1/6Mn + 1/15 (Cu + Ni) + 1/5
(Cr+Mo+V) (However, calculation is performed in weight%.)