JPH0825060B2 - Low-hydrogen coated arc welding rod - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding material for high-strength ferritic heat-resistant steel, and more specifically, 9Cr-0.5Mo-1.8W-Nb-V excellent in creep property at high temperature.
The present invention relates to a low hydrogen system coated arc welding rod for steel .

[0002]

2. Description of the Related Art Recently, in designing equipment such as a boiler operated at high temperature and high pressure, there is a movement to increase temperature and pressure during operation in order to improve pressure efficiency and thermal efficiency. As materials used for such boilers and the like, in view of oxidation resistance and high temperature strength, the steel materials are replaced with low alloy steels such as 2 and 1/4 Cr-1Mo steel, for example, 9Cr-2Mo steel and 9Cr. -1Mo-Nb-V steel, 9C
Cr-Mo such as r-0.5Mo-1.8W-Nb-V steel
Steel is being developed.

On the other hand, as a welding material for such Cr-Mo steel, for example, in Japanese Patent Application Laid-Open No. 55-30354, a large amount of austenite phase stabilizing elements such as Ni and Mn are contained in the weld metal. Although a method of reducing the coarse ferrite phase has been proposed, an excessive amount of Ni lowers the creep rupture strength for a long time, and an excessive amount of Ni or Mn lowers the crack resistance of the weld metal. No performance welded joint can be obtained.

Further, in Japanese Laid-Open Patent Publication No. 62-220300, in the welding of 9Cr steel, an appropriate amount of W is added to the welding rod, and W is allowed to coexist in a limited manner in relation to the amount of Mo, whereby it is precipitated in the weld metal. V ₄ C
₃ , NbC precipitation is suppressed for a long time, and
Furthermore, by keeping the balance of precipitation of Mo ₂ C and W ₂ C within an appropriate range, the creep rupture strength at high temperature and long time is improved. However, in order to further improve the thermal efficiency of the boiler, the steel material is oriented toward high strength, and the welded portion obtained by the above-mentioned welding rod cannot obtain joint performance comparable to that of the base material.

[0005]

The object of the present invention is to solve the above is focused on the above situation, the high-temperature strength and high temperature creep rupture strength, further decreases the coarse ferrite phase without impairing the crack resistance and the like, 9Cr- 0.5Mo-1.8W-Nb-V
It is to secure the strength, toughness, crack resistance, etc., which are comparable to those of the base metal of steel .

[0006]

[Means for Solving the Problems] The inventors of the present invention have conducted extensive research to achieve the above object. The present invention has been completed as a result of these studies, and it comprises metal carbonate: 30 to 60 weight percent, metal fluoride 10 to 30 weight percent, and other arc stabilizers, slag-forming agents, viscous agents 9Cr-0.5Mo-1.8W- formed by coating the outer circumference of the steel core wire with a coating material containing a binder so as to be 22 to 40 weight% with respect to the total weight of the welding rod.
In the coated arc welding rod for Nb-V steel , C: 0.01 to 0.11 weight percent, Si: 0, relative to the total weight of the welding rod by adjusting the composition of the coating agent and / or the steel core wire. .3 to 1.3 weight percent, Mn:
1.0 to 1.9 weight percent, Cr: 5.9 to 9.5 weight percent, Mo: 0.3 to 0.6 weight percent, Ni: 0.2 to 1.2 weight percent,
V: 0.10 to 0.40 weight percent, Nb: 0.
02 to 0.10 weight percent, W: 1.0 to 1.
9% by weight, N: 0.03 to 0.07% by weight, or Al: 0.
5 to 1.5 weight percent, B: 0.01 to 0.0
The main point is that it contains 5% by weight of the components.

That is, in the present invention, C, Si, Cr, Mo, V, Nb and W having the effect of suppressing the precipitation of coarse ferrite phase and Mn and N having the effect of stabilizing the austenite phase are used.
By appropriately containing i and N in the welding material and refining the coarse ferrite phase, the high temperature strength and the high temperature creep rupture strength are 9Cr-0.5Mo-1.8W-.
While improving the Nb-V steel to the same level as the base metal, improving the toughness,
It is possible to achieve an increase in softening resistance to post-weld heat treatment (PWHT) and the securing of excellent welding workability all at once.

The cores used in the present invention are C, Si and M.
n, Cr. Chemical components other than Mo, Ni, V, Nb, W, N, Al and B are P: 0.02 weight percent or less, S:
0.02 weight percent or less, Ti: 0.01 weight percent or less, Cu: 0.1 weight percent or less, O:
The content is 0.05% by weight or less, and the balance is Fe and inevitable impurities.

[0009]

The reason for limiting the component composition in the present invention will be described in detail below. First, the reason why the contents of the metal carbonate and the metal fluoride in the coating agent and the coverage are determined in the present invention is as follows. Metal carbonate: 30 to 60 weight percent The metal carbonate as used in the present invention means CaCO ₃ , BaCO.
₃ , MgCO _3, etc., but these metal carbonates have the effect of decomposing in the arc to generate CO ₂ gas, cutting the molten metal from the atmosphere, and lowering the hydrogen partial pressure in the arc atmosphere, It produces a basic slag.

If the addition amount is less than 30% by weight, the melting point of the slag is lowered and the encapsulation of the slag is deteriorated, so that a good bead cannot be obtained. In addition, pits and blow holes are generated because the amount of gas that cuts off the atmosphere is insufficient. On the other hand, when it is added in an amount of more than 60% by weight, the viscosity of the molten slag becomes too high, the spatter increases and the bead appearance also deteriorates.

Metal Fluoride: 10 to 30% by Weight Metal fluoride in the present invention means CaF ₂ , BaF ₂ and M.
It refers to gF ₂ , LiF, etc., but all of them lower the melting point of slag to produce slag with good fluidity. Further, the fluorine decomposed in the arc reacts with the hydrogen in the molten metal or molten slag, lowering the hydrogen partial pressure of the weld metal and producing weld metal with good crack resistance.

If the addition amount of these is less than 10% by weight, proper fluidity of the slag cannot be obtained, the bead formation is poor, and pits are generated. On the other hand, if it is added in an amount of more than 30% by weight, the viscosity of the molten slag is insufficient, the bead shape is deteriorated, and the covering cylinder is weak, resulting in poor welding workability.

Coverage: 22 to 40% by weight Coverage means the weight percentage of the coating agent relative to the total weight of the welding rod. Below 22% by weight, the function as a protective cylinder becomes insufficient and spatter increases. Or, the bead appearance deteriorates due to the lack of the amount of slag produced, while 40
When it exceeds the weight percentage, defects such as slag entrainment are likely to occur because the amount of slag becomes too large, and it becomes difficult to carry the rod when applied to a welded joint having a narrow groove width.

Next, the essential elements contained in either or both of the coating agent and the steel core wire will be described in detail. C: 0.01 to 0.11 wt% C has the effect of retaining in the weld metal to improve the strength due to the precipitation of carbides and suppressing the formation of coarse ferrite, and at least 0.01 wt% in the welding rod. It must be contained in a percentage or more. However, if too much, the weld cracking susceptibility deteriorates, so it must be suppressed to 0.11% by weight or less.

Si: 0.3 to 1.3% by weight The purpose is to deoxidize the weld metal, but it is also necessary from the viewpoint of ensuring welding workability. Content rate in welding rod is 0.3
If it is less than 1% by weight, pores are easily generated in the weld metal due to insufficient deoxidation, while if it exceeds 1.3% by weight, the toughness of the weld metal is deteriorated.

Mn: 1.0 to 1.9% by weight Like Si, it is important as a deoxidizer, and at least 1.
Must be included in an amount of 0 weight percent, but 1.9
If it exceeds the weight percentage, the fine ferrite of the weld metal disappears, the quench hardenability becomes excessive, and the weld crack susceptibility deteriorates.

Cr: 5.9 to 9.5% by weight As a base metal co-metal system, an equal amount of Cr is added, and the oxidation resistance of the weld metal is
It is an essential element for enhancing corrosion resistance and high temperature strength, and is the main component in this type of component system, and must be contained in at least 5.9 weight percent. On the other hand, 9.5
If it exceeds the weight percentage, coarse ferrite is formed and the toughness decreases.

Mo: 0.3 to 0.6% by weight As with Cr, it is necessary to add the same amount as a metallurgical system, which has an effect of improving creep rupture strength by the solid solution effect, and at least 0.3% by weight. It must be contained in a percentage or more. On the other hand, even if it exceeds 0.6% by weight, the effect of improving the creep rupture strength is not obtained and rather the weldability is significantly deteriorated. Therefore, the upper limit was made 0.6% by weight.

Ni: 0.2 to 1.2% by weight Ni suppresses the formation of coarse ferrite and is effective in stabilizing the toughness of the weld metal. If it is less than 0.2% by weight, the effect cannot be obtained. On the other hand, when it exceeds 1.2% by weight, the high temperature strength and the creep rupture strength are remarkably lowered.

[0020] V: 0.10 0.40 wt% V is an element significantly increase the high temperature strength, one other M ₂₃ C _6, M ₆ C as V ₄ C ₃ (M indicates a metal element) Part, and exerts an excellent effect of suppressing coarsening of precipitates, but if it is less than 0.10% by weight, the effect cannot be obtained. On the other hand, when it exceeds 0.40 weight percent, carbides are excessively precipitated and the toughness deteriorates.

Nb: 0.02 to 0.10 weight percent Nb enhances the high temperature strength by precipitation of NbC, M ₂₃ C
_6, M is effective in creep rupture strength improving the precipitation state of ₆ C or the like in order to control. But the amount is 0.0
If it is less than 2% by weight, the effect is not exerted, and if it exceeds 0.10% by weight, the carbides are coarsely aggregated to lower the strength.

W: 1.0 to 1.9% by weight W is an element of the same family as Cr and Mo, and is W by tempering.
₂ C precipitates, and especially in the coexistence with Mo, the effect of improving creep rupture strength at high temperature for a long time is extremely large.
However, if it is less than 1.0% by weight, the effect of coexistence with Mo cannot be obtained, and improvement in high temperature strength cannot be achieved. On the other hand, if it exceeds 1.9% by weight, the ductility of the weld metal decreases and at the same time the welding workability deteriorates, so 1.9% by weight was made the upper limit.

N: 0.03 to 0.07 wt% N is one of the austenite stabilizing elements and improves high temperature strength, creep rupture strength and toughness by precipitating fine carbonitrides. However, if it is less than 0.03% by weight, the effect is not obtained. On the other hand, if it exceeds 0.07% by weight, non-dissolved nitrogen tends to be generated as pore defects such as blowholes during solidification of the weld metal.

The kinds and optimum contents of the elements contained in the welding rod of the present invention are as described above, and the object of the present invention can be achieved as long as the above requirements are satisfied, but the functions of each element are considered comprehensively. However, in order to more effectively enhance the high temperature strength, high temperature creep rupture strength, toughness, crack resistance, etc. of the weld metal,
The following elements may also be added.

Al: 0.5 to 1.5% by weight Al reduces the amount of oxygen in the weld metal, and is effective in improving the crack resistance of the weld metal by fixing C by promoting the precipitation of fine carbide. However, if it is less than 0.5% by weight, the effect is insufficient. On the other hand, if it exceeds 1.5 weight percent, the arc is unstable, the amount of spatter increases, and the welding workability deteriorates.

B: 0.01 to 0.05% by Weight B has a function of increasing the effect of adding Mo and W in a complementary manner, but if it is less than 0.01% by weight, the effect is not effectively exhibited. On the other hand, if it exceeds 0.05% by weight, the toughness of the weld metal decreases and the welding workability also decreases.

In the coated arc welding rod of the present invention, iron powder, an alkaline component, rutile, etc. are added to the coating agent as an arc stabilizer and a slag forming agent in addition to the above-mentioned components, and the addition range is 25% by weight. The following is desirable. Further, as the binder, water glass mainly containing sodium silicate and potassium silicate is used, and SiO ₂ and Na _{2 in} the water glass are used.
It is desirable to use the molar ratio of the alkaline components such as O and K ₂ O in the range of 1.5 to 3.5. The coated arc welding rod of the present invention is manufactured by coating and coating with an ordinary welding rod coating machine and then firing at 300 to 550 ° C. to remove water.

[0028]

EXAMPLES The effects of the present invention will be more specifically described below with reference to examples. A coating agent was applied to the outer periphery of the Cr-Mo steel core wire (diameter of 3.2 mm) so that the coating rate was 27 to 29 weight percent, and the coated arc welding rod having the composition shown in Table 1 was manufactured. Using each obtained welding rod, 9Cr-0.5Mo-
Using a 1.8 W-Nb-V steel plate as a base material, AWS A5.4
Based on the above, a welding experiment was conducted and the results in Table 2 were obtained. The welding conditions are welding current of 120 amps and welding heat input of 14 kJ /
cm, the preheating pass ring temperature was 200 to 220 ° C., and the welded joint was prepared in a downward posture. 750 ° C after welding
After performing stress relief annealing for 4 hours, various physical property tests were performed.

[Table 1]

[Table 2]

As is clear from Tables 1 and 2, the welding rod No. which satisfies the requirements of the present invention. 1 to No. The welded part obtained by using No. 8 has excellent performance as compared with the comparative bar in any of room temperature strength, high temperature strength, Charpy absorbed energy and high temperature creep rupture strength. On the other hand, the welding rod No. of the comparative example. 9 has an excessive amount of Ni and thus has a low creep rupture strength. No. 10 is because the amount of B is too much,
Low toughness. No. In No. 11, since the V content is small, coarse ferrite precipitates and the high temperature strength is low. No. Since No. 12 has a small amount of W, the creep rupture strength is low. No. 13 is
Since the amount of N is small, the high temperature strength and creep rupture strength are low. No. In No. 14, since the amount of Si is too large, the toughness of the weld metal is low.

[0030]

EFFECTS OF THE INVENTION The present invention is constructed as described above, and by specifying the type and content of the alloying element contained in the coating material and the core wire, welding having physical properties comparable to that of the 9Cr base metal is obtained. A metal can be obtained, and the quality of high-temperature and high-pressure reaction equipment using this type of special steel as a base material can be greatly improved.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Aoyama 5-10-1, Fuchinobe, Sagamihara-shi, Kanagawa Inside Nippon Steel Research Laboratories, Nippon Steel Co., Ltd. (56) Reference JP-A-61-266199 (JP, A)

Claims (2)

[Claims] 1. A coating material containing 30 to 60% by weight of a metal carbonate, 10 to 30% by weight of a metal fluoride, and an arc stabilizer, a slag forming agent, and a binder other than the above with respect to the total weight of the welding rod. 9Cr-, which is coated on the outer circumference of the steel core wire so as to be 22 to 40 weight percent
In the coated arc welding rod for 0.5Mo-1.8W-Nb-V steel , C: 0.01 to 0 relative to the total weight of the welding rod by adjusting the composition of the coating agent and / or the steel core wire. .11 weight percent, Si: 0.3 to 1.3 weight percent, Mn: 1.0 to 1.9 weight percent, Cr: 5.9 to 9.5 weight percent, Mo:
0.3 to 0.6 weight percent, Ni: 0.2 to 1.2 weight percent, V: 0.10 to 0.40 weight percent, Nb: 0.02 to 0.10 weight percent, W: 1. 0 to 1.9 weight percent, N: 0.0
9Cr-0.5Mo-1.8W-Nb- characterized in that it contains 3 to 0.07% by weight of components.
Low hydrogen system coated arc welding rod for V steel . 2. In addition to the total weight of the welding rod, Al:
9. 9Cr-0.5Mo-1.8W according to claim 1 , characterized in that it contains 0.5 to 1.5% by weight and B: 0.01 to 0.05% by weight.
-Low hydrogen system coated arc welding rod for Nb-V steel .