【発明の詳細な説明】[Detailed description of the invention]
本発明は、溶接トーチを用いて異種鋼材を潜弧
溶接する際、特に片側が高炭素鋼、合金鋼などの
溶接割れ感受性の高い鋼材である場合の溶接割れ
を防止する溶接法に関するものである。
一般構造用鋼材の溶接において、溶接性の良い
鋼材に、高炭素鋼、合金鋼などの溶接割れ感受性
の高い鋼材を溶接する場合がある。このような場
合、溶接後、溶接割れ感受性の高い鋼材側に割れ
が生ずるか、あるいは、割れが顕在化しなくとも
溶接時の熱間割れによつて溶接部に割れが潜在す
る（以下溶接熱間割れと言う）ことが多い。溶接
後顕在する割れに対しては、溶接前の予熱か、も
しくは、溶接入熱の低減等により溶接部の熱歪を
緩和するか、あるいは、溶接後の脱水素処理によ
り拡散性水素を除くなどの対策によつて軽減でき
る場合もあるが、溶接熱間割れは、これらの処理
では、完全には防止できないのが現状である。
このように、溶接熱間割れが発生した継手部を
含む構造物を使用すれば、使用中、溶接部に潜在
する割れを起点として破壊に到る危険性がある。
そのため、一般の溶接性の良好な鋼材に高炭素鋼
合金鋼のような、溶接割れ感受性の高い鋼材を溶
接した際、溶接熱間割れが発生しない溶接施工法
が強く要望されている。
溶接部に発生する溶接熱間割れに関する研究
は、今までに数多く行われてきたが、有効な改善
策は、低炭素化、低合金化、あるいは不純物（例
えば、硫黄など）の低減など鋼材成分の変更であ
り、従つて、溶接性を改善するには、高強度等構
造物としての特性を犠性にせざるをえなかつた。
本発明の目的は、一般に溶接性の良好な鋼材に
高強度が容易に得られる高炭素鋼、合金鋼の被溶
接鋼材を溶接するに際して、溶接後の高強度を維
持し、かつ、溶接割れ（溶接熱間割れおよび溶接
後顕在する割れを含む）が発生しない鋼材の溶接
法を提供するものである。
本発明は、溶接トーチを用いて異種鋼材を潜弧
溶接するに際し、該溶接トーチを被溶接鋼材表面
の垂直方向から溶接割れ感受性の高い鋼材側に20
゜〜35゜傾斜させ、かつ開先端部の溶融長さが３
mm以下となる条件で溶接することを特徴とするも
のである。溶接性の良好な鋼材Ｂに高炭素、合金
鋼等溶接割れ感受性の高い鋼材Ａが溶接される従
来の場合を模式的に図示すると第１図のようにな
る。この場合の溶接では、鋼材１，２に対し溶接
トーチ３をほぼ垂直方向にして溶接を行う。この
ような従来法では、溶着鋼５の形状は、第１図の
ようになり、溶接割れ感受性の高い鋼材Ａ１側の
溶接境界部に凸形状６が生じ、その部分に溶接熱
間割れ７が発生する。
本発明においては、第２図に示すように、溶接
トーチ３を鋼材表面垂直方向８から鋼材Ａ１側に
角度α傾斜させて溶接を行う。トーチ傾斜角度α
は、20〜35゜とする。また、溶着鋼５が鋼材Ａ１
の開先面９を覆い、かつ、開先端１０をわずかに
乗りこえて盛り上がり、開先端部の溶融長さｌが
３mm以下になるような条件で溶接する。このよう
な溶接条件とすることにより第１図のような溶接
熱間割れ７の発生がなくなり、かつ、溶接後に顕
在する割れもなく、溶接割れを防止することがで
きる。
本発明において、溶接条件を上記の如く定めた
理由について述べる。
溶接トーチ３が鋼材１，２にほぼ垂直な場合、
すなわち、トーチ傾斜角α≒０゜の場合、他の溶
接条件を考慮しても高炭素鋼、合金鋼等溶接割れ
感受性の高い鋼材Ａ側の溶融境界部近傍に溶接熱
間割れが発生する。これを防止するため本発明で
は溶接割れ感受性の高い鋼材側へ、溶接トーチを
傾斜させる。トーチ傾斜角度αが20゜末満の場合
は、鋼材Ａの材質によつては、熱間割れが発生す
ることがあるのでαを20゜以上にする。また、ト
ーチ傾斜角度αが35゜を越えると、アーク形状が
不安定となつて、アーク切れが発生するのでトー
チ傾斜角度αの上限は35゜とする。更に、第２図
における開先端部の溶融長さｌがないと溶接欠陥
の一種である溶盛不足となり、また、ｌが３mmを
越えると、第１図の凸形状６が出現し、溶接熱間
割れ７が発生するのでｌは０を越え３mm以下とす
る。
次に本発明の実施例を示す。
被溶接鋼材の化学成分、板厚を第１表に示す。
潜弧溶接法により溶接割れ感受性の高い鋼材Ａ
側への溶接トーチ傾斜角度αを０゜〜40゜まで変
化させると共に鋼材Ａの開先端部の溶融長さｌを
０〜6.5mmまで変化させて、溶接熱間割れ発生状
況を調査した。
The present invention relates to a welding method for preventing weld cracking when dissimilar steel materials are submerged arc welded using a welding torch, especially when one side is made of a steel material that is highly susceptible to weld cracking, such as high carbon steel or alloy steel. . In welding general structural steel materials, steel materials with high weld crack susceptibility, such as high carbon steel and alloy steel, are sometimes welded to steel materials with good weldability. In such cases, after welding, cracks may occur on the steel material side that is more susceptible to weld cracking, or even if cracks do not become apparent, cracks may be latent in the weld due to hot cracking during welding (hereinafter referred to as hot welding). This is often called cracking. For cracks that appear after welding, the thermal strain of the weld zone can be alleviated by preheating before welding, or by reducing welding heat input, or by dehydrogenation treatment after welding to remove diffusible hydrogen. In some cases, hot cracking during welding can be reduced by taking measures to prevent the occurrence of hot weld cracking, but the current situation is that hot weld cracking cannot be completely prevented by these treatments. As described above, if a structure including a joint in which hot weld cracks have occurred is used, there is a risk that the cracks latent in the weld may lead to destruction during use.
Therefore, there is a strong demand for a welding method that does not cause hot weld cracks when welding a steel material with high weld crack susceptibility, such as high carbon steel alloy steel, to a general steel material with good weldability. Many studies have been conducted on weld hot cracking that occurs in welds, but effective improvement measures include reducing steel composition, reducing carbon content, reducing alloys, or reducing impurities (such as sulfur). Therefore, in order to improve weldability, the characteristics of the structure such as high strength had to be sacrificed. The purpose of the present invention is to maintain high strength after welding and prevent weld cracking when welding high carbon steel and alloy steel, which generally have good weldability and easily obtain high strength. The present invention provides a method for welding steel materials that does not cause hot welding cracks or cracks that appear after welding. When performing submerged arc welding of dissimilar steel materials using a welding torch, the present invention aims to move the welding torch from the vertical direction of the surface of the steel material to be welded to the side of the steel material with high weld crack susceptibility.
Inclined at an angle of ~35°, and the melting length of the open end is 3.
It is characterized by welding under conditions where the thickness is less than mm. A conventional case in which a steel material A with high weld crack susceptibility such as high carbon or alloy steel is welded to a steel material B with good weldability is schematically shown in FIG. 1. In this case, welding is performed with the welding torch 3 oriented substantially perpendicular to the steel materials 1 and 2. In such a conventional method, the shape of the welded steel 5 is as shown in Fig. 1, and a convex shape 6 occurs at the weld boundary on the side of the steel material A1, which is highly susceptible to weld cracking, and a weld hot crack 7 occurs in that part. Occur. In the present invention, as shown in FIG. 2, welding is performed by tilting the welding torch 3 at an angle α from a direction 8 perpendicular to the surface of the steel material toward the steel material A1. Torch tilt angle α
should be 20 to 35°. In addition, the welded steel 5 is the steel material A1
Welding is carried out under conditions such that the weld covers the groove surface 9 of the groove, and rises slightly over the groove tip 10, so that the fusion length l of the groove tip becomes 3 mm or less. By setting such welding conditions, the occurrence of weld hot cracks 7 as shown in FIG. 1 is eliminated, and no cracks appear after welding, making it possible to prevent weld cracks. In the present invention, the reason why the welding conditions are determined as described above will be described. When the welding torch 3 is almost perpendicular to the steel materials 1 and 2,
That is, when the torch inclination angle α≈0°, hot weld cracking occurs near the fusion boundary on the A side of the steel material A, which is highly susceptible to weld cracking, such as high carbon steel or alloy steel, even if other welding conditions are considered. In order to prevent this, in the present invention, the welding torch is tilted toward the steel material side that is more susceptible to weld cracking. If the torch inclination angle α is less than 20°, hot cracking may occur depending on the material of the steel material A, so set α to 20° or more. Furthermore, if the torch inclination angle α exceeds 35°, the arc shape becomes unstable and arc breakage occurs, so the upper limit of the torch inclination angle α is set to 35°. Furthermore, if there is no fusion length l at the open end in Fig. 2, insufficient welding will occur, which is a type of welding defect, and if l exceeds 3 mm, a convex shape 6 in Fig. 1 will appear, and the welding heat will be reduced. Since cracks 7 will occur, l should be greater than 0 and less than 3 mm. Next, examples of the present invention will be shown. Table 1 shows the chemical composition and plate thickness of the steel materials to be welded. Steel material A with high weld crack susceptibility due to submerged arc welding
The occurrence of hot weld cracking was investigated by varying the welding torch inclination angle α to the side from 0° to 40° and by varying the fusion length l of the open end of steel material A from 0 to 6.5 mm.
【表】
開先端部の溶融長さｌが３mm以下の場合の鋼材
Ａ側へのトーチ傾斜角度αと溶接熱間割れ発生率
との関係を第３図に示す。又鋼材Ａ側への溶接ト
ーチ傾斜角度αを30゜と一定とし、鋼材Ａの開先
端部の溶融長さｌと熱間割れ発生率の関係を第４
図に示す。
第３図、第４図から明らかな如く、溶接トーチ
傾斜角度αが20〜35゜のとき、および鋼材Ａの開
先端部の溶融長さｌが０〜3.0mmのとき溶接熱間
割れは、完全に防止できた。
以上の如く、本発明は、溶接性の良好な鋼材に
溶接熱間割れ感受性の高い鋼材Ａを溶接する際、
該鋼材Ａ側に溶接トーチを傾斜させることによつ
て鋼材Ａ側の溶接境界部に第１図のような、凸形
状６が出現するのを阻止し、溶接部に溶接熱間割
れおよび溶接後顕在する割れを発生させることが
ない。
なお、本発明でいう溶接熱間割れ感受性の高い
鋼は高炭素鋼、低合金鋼のみならず。例えば高
Ni鋼あるいは、高Cr鋼そしてステンレス鋼をも
含む。
又、本発明の溶接法は各種構造物製造におい
て、異種鋼材を溶接する際に効果があり、特にケ
ーシング用鋼管に高強度鋼からなる管継手を溶接
する際に効果を発揮する。[Table] Figure 3 shows the relationship between the torch inclination angle α toward the steel A side and the weld hot cracking incidence when the fusion length l of the open end is 3 mm or less. In addition, the welding torch inclination angle α toward the steel material A side is kept constant at 30°, and the relationship between the fusion length l of the open end of steel material A and the hot cracking incidence rate is expressed as
As shown in the figure. As is clear from FIGS. 3 and 4, when the welding torch inclination angle α is 20 to 35 degrees and the fusion length l of the open end of steel material A is 0 to 3.0 mm, weld hot cracking occurs. It was completely preventable. As described above, in the present invention, when welding steel material A with high weld hot cracking susceptibility to steel material with good weldability,
By tilting the welding torch toward the steel material A side, it is possible to prevent the appearance of a convex shape 6 as shown in FIG. No obvious cracks will occur. Note that the steels with high welding hot cracking susceptibility as used in the present invention include not only high carbon steels and low alloy steels. For example, high
Also includes Ni steel, high Cr steel and stainless steel. Further, the welding method of the present invention is effective when welding dissimilar steel materials in the manufacture of various structures, and is particularly effective when welding a pipe joint made of high-strength steel to a steel pipe for casing.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図は、従来の溶接方法およびそのビード形
状を示す断面図。第２図は、本発明に係る溶接ト
ーチ傾斜溶接方法およびそのビード形状を示す断
面図。第３図は、被溶接鋼材の開先面への溶接ト
ーチ傾斜角角度αと熱間割れ発生率の関係を示す
グラフ。第４図は、被溶接鋼材の開先端部の溶融
長さｌと熱間割れ発生率の関係を示すグラフ。
１……溶接割れ感受性の高い鋼材、２……溶接
性の良い鋼材、３……溶接トーチ、４……溶接
棒、５……溶着鋼、６……凸形状の溶接境界部、
７……熱間割れ、８……垂直方向、９……開先
面、１０……開先端。
FIG. 1 is a sectional view showing a conventional welding method and its bead shape. FIG. 2 is a sectional view showing the welding torch inclined welding method and the bead shape thereof according to the present invention. FIG. 3 is a graph showing the relationship between the welding torch inclination angle α to the groove surface of the steel material to be welded and the hot crack occurrence rate. FIG. 4 is a graph showing the relationship between the fusion length l of the open end of the steel material to be welded and the incidence of hot cracking. 1... Steel material with high weld crack sensitivity, 2... Steel material with good weldability, 3... Welding torch, 4... Welding rod, 5... Welded steel, 6... Convex welding boundary part,
7...Hot cracking, 8...Vertical direction, 9...Bevel surface, 10...Bevel tip.