JPS6317038B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solid wire for welding Cr--Mo steel, which makes it possible to obtain welds with low susceptibility to embrittlement. Cr-Mo based low alloy steel, e.g. 1Cr-1/2Mo steel,
1/1/4Cr―1/2Mo steel, 2/1/4Cr―1Mo steel, 3Cr
-1Mo steel etc. are used as industrial materials with good heat resistance.
It is widely used for applications such as high-temperature, high-pressure boilers, petroleum industry, synthetic chemical industry, and high-temperature, high-pressure hydrogen resistance. In other words, Cr-Mo based low alloy steels have traditionally been developed with a focus on improving high-temperature strength and high-temperature creep properties, and when welding them, it is common to focus on the high-temperature strength of the weld metal. The attitude was towards welding design. However, in recent years, the environment in which Cr--Mo low alloy steel is used has become more severe, and other properties must also be taken into consideration in many cases.
The first point is that the frequency of use in cold regions has increased, and therefore there has been a demand for improved low-temperature toughness. The second point is 10 years as a reaction vessel
Since it will be used for a long period of 20 years, and tempering embrittlement is unavoidable due to long-term use at high temperatures, it is necessary to form a weld metal with low susceptibility to embrittlement. It started to be done. Taking these points into consideration, the present inventors believe that in order to satisfy the above requirements, it is necessary to anticipate the increase in temper embrittlement and improve the low-temperature toughness in advance, We focused on the composition of the weld metal. As a result, from the viewpoint that allowing a sufficient amount of fine precipitates to precipitate in the weld metal is effective in improving low-temperature toughness, a sufficient amount of CrN is formed in the weld metal to refine the structure of the weld metal. By realizing this, we succeeded in satisfying the above requirements. In this respect, the fact that the steel to be welded in the present invention is a Cr-Mo low alloy steel has important significance.
[Cr] content is zero or extremely low;
For example, with 0.5Mo steel, the service temperature is relatively low, so the problem of tempering embrittlement does not occur, and at the same time [Cr]
Since it does not contain enough CrN, it is not subject to the technical effect of forming CrN. Further, high alloy steel with a high [Cr] content is excluded from the scope of the present invention because its service temperature is high and the problem of temper embrittlement does not occur. That is, the present invention targets Cr-Mo low alloy steel that can effectively utilize the effect of improving low-temperature toughness in the welding stage, and achieves the above effect by forming a necessary and sufficient amount of CrN in the weld metal, resulting in excellent properties. The purpose of this study is to establish a solid wire for welding Cr-Mo steel that forms a welded joint with good tempering and embrittlement properties. Therefore, the solid wire for welding Cr-Mo steel of the present invention (hereinafter sometimes simply referred to as wire) is as follows: 0.07%≦C≦0.19% (% means weight %, the same applies hereinafter) 0.1%≦Mn≦1.6% 0.05 %≦Si≦0.40% 0.5%≦Cr≦3.8% 0.3%≦Mo≦1.5% Al≦0.04% O≦0.01% 0.012%≦N≦0.040% Ni≦0.2% The remainder is Fe and unavoidable impurities Therein lies the gist. In the present invention, the component composition in the wire is limited as described above, and the basis for this limitation is as follows. [C] = 0.07 to 0.19% (weight %, same below) When [C] exceeds 0.19%, the cracking susceptibility of the weld metal increases, and when it is less than 0.07%, the [O] content of the weld metal increases and the strength is insufficient. and toughness cannot be obtained. [Mn] = 0.1 to 1.6% If [Mn] exceeds 1.6%, tempering embrittlement of the weld metal tends to occur. On the other hand, if it is less than 0.1%, the amount of [O] in the weld metal increases and sufficient strength and toughness cannot be obtained. [Si] = 0.05 to 0.4% If [Si] exceeds 0.4%, tempering embrittlement of the weld metal tends to occur. On the other hand, if it is less than 0.05%, the amount of [O] in the weld metal increases and sufficient strength and toughness cannot be obtained. [Cr] = 0.5 to 3.8% If [Cr] is less than 0.5%, the high-temperature strength of the weld metal will be insufficient, as well as acid resistance and corrosion resistance will decrease, and [N] must be actively added to precipitate and form CrN. The technical effect of improving the toughness cannot be obtained. On the other hand, if it exceeds 3.8%, tempering and embrittlement of the welded metal will not be a problem even when used for a long time at high temperatures, and no technical effect can be obtained by actively incorporating [N]. [Mo] = 0.3 to 1.5% If [Mo] is less than 0.3%, the high temperature strength of the weld metal will be insufficient. On the other hand, if it exceeds 1.5%, the toughness of the welded metal will be poor and tempering embrittlement will likely occur. [Al]≦0.04% If [Al] exceeds 0.04%, slag seizes onto the weld metal during submerged arc welding and deteriorates the appearance. [O]≦0.01% When [O] exceeds 0.01%, the formation of CrN precipitates in the weld metal is inhibited, and on the other hand, the formation of non-metallic inclusions becomes significant, resulting in a significant decrease in toughness. [N] = 0.012 to 0.040% If [N] is less than 0.012%, precipitation and formation of CrN in the weld metal will not be sufficient and the effect of improving toughness will not be obtained. On the other hand, if it exceeds 0.040%, welding workability will deteriorate. [Ni]≦0.2% Ni is an element that improves the toughness of weld metal, but if [Ni] exceeds 0.2%, tempering embrittlement of weld metal tends to occur. As long as the wire of the present invention satisfies the above-mentioned configuration, Ti, V, Nb, B, etc. can be added as necessary, and the effects of the present invention will not be lost depending on the welding conditions and post-weld heat treatment conditions. do not have. As a result, the low-temperature toughness after welding has improved, making it possible to keep the susceptibility to tempering embrittlement low even when used for long periods of time at high temperatures. The present invention will be explained below with reference to examples, but the technical scope of the present invention is not limited by the embodiments described in the following examples and claims. Using Cr-Mo low alloy steel wire with the composition shown in Table 1 and sintered type and melted type flux (generally commercially available) with the composition shown in Table 2, these are combined as shown in Table 3. , base material (ASTM
A387Gr.11, A387Gr.22, A387Gr.21) were submerged arc welded to obtain deposited metal with the same description.

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【table】

[Table] Next, post-heat treatment is performed using the heat pattern shown in Figure 1, and some parts are left as is, while some are artificially subjected to tempering and embrittlement heat treatment using the heat pattern shown in Figure 2.
These were compared to examine the effects of the present invention. The test pieces were a tensile test piece from section A in Figure 3, and a 2 mm V-notched ruby impact test piece from section B, and the results were summarized in Table 4. The post-heat treatment was performed using test No.T in Table 4.
1 is 650℃×3Hr, T-2, T-3, T-4, T
-5 was set to 690℃ x 8 hours. Note that SR in Table 4 represents the heat pattern shown in Figure 1, and
SR+RC represents the addition of the heat pattern shown in Figure 2 later.

[Table] Although the tensile strength and elongation of the Examples and Comparative Examples were not significantly different, and both results were good, there was a noticeable difference in the Shalpy impact value between the two. In other words, in the comparative example, the Shapey impact value was already low at the stage of post-heat treatment (SR), and even if it was high at the stage of SR, it was It becomes brittle and
It showed an extremely low value. In contrast, the examples showed extremely high impact values both at the SR stage and at the stage where SC was added thereto. As a typical example of those that showed high impact values and those that showed low impact values, when comparing the precipitates in the weld metals of test Nos. T-3 and T-4 using an electron microscope, it was found that T-
3 (Example), the fine precipitates were T-4 (Comparative example)
It was clearly more recognized than When this precipitate was subjected to electrolytic extraction and quantitative analysis, significant differences were found mainly in the amount of CrN.

[Brief explanation of the drawing]

FIG. 1 is a heat pattern for post-heat treatment, FIG. 2 is a heat pattern for temper embrittlement treatment, and FIG. 3 is an explanatory diagram showing the sampling position of a test piece.

Claims (1)

[Claims] 1 0.07%≦C≦0.19% (% means weight %, the same applies hereinafter) 0.1%≦Mn≦1.6% 0.05%≦Si≦0.40% 0.5%≦Cr≦3.8% 0.3%≦Mo A solid wire for welding Cr--Mo steel, which contains ≦1.5% Al≦0.04% O≦0.01% 0.012%≦N≦0.040% Ni≦0.2%, with the balance being Fe and inevitable impurities.