【発明の詳細な説明】[Detailed description of the invention]
本発明は溶接用ソリツドワイヤに関し、特に溶
接時の溶滴移行性が良好でスパツタが少なく平滑
で健全な溶接ビードを得ることができるソリツド
ワイヤに関するものである。
溶接用ソリツドワイヤに要求される重要な性能
の一つとして溶接時の溶滴移行性が挙げられる。
即ち溶滴移行をスプレー状にすると、スパツタが
減少して作業性が良好になると共に溶接ビードも
平滑且つ美麗となつて溶接部の品質も向上する。
この様なところから溶滴移行性の改善を期して
種々研究が行なわれているが、そのうちワイヤ成
分組成の面からの改善策としては、ワイヤ中の非
金属介在物量（特に酸素、燐、硫黄及びこれらの
金属間化合物）を少なくする方法が有効とされて
いる。例えば特公昭52−23869号はこの種の技術
を開示するもので、酸素、燐及び硫黄の含有量を
低レベルに抑えることによつて溶滴移行性を改善
し、アークの不安定回数の減少を図つている。と
ころで上記の様な非金属介在物を抑える方法とし
ては、ワイヤ原料を溶製もしくは鋳造する段階
で、真空脱ガス溶製法や真空鋳造法等を採用する
ことによつて前記介在物を可及的に除去する方法
があるが、経済性や生産性等の点で問題があつて
ワイヤ価格が高騰するので実状にそぐわない。
本発明者等は上記の様な事情に着目し、溶滴移
行性の良好なソリツドワイヤを安価に提供すべ
く、特に酸素系の非金属介在物の含有率及び存在
位置が溶滴移行性に与える影響を定量的に把握し
ようとして研究を進めてきた。その結果、ワイヤ
全体の平均酸素濃度を低くすることによつて溶滴
移行性が改善されるという点では従来の認識と同
様の結論に達したが、従来の認識からは予測する
ことのできない異質の傾向として、ソリツドワイ
ヤ表層部の酸素濃度を積極的に高めてやれば溶滴
移行性が著しく改善されるという新たな事実を確
認した。
本発明はこの様な確認結果を元に更に研究の結
果完成されたものであつて、その構成は、軟鋼線
材の表層部酸素濃度が100〜1000ppmで、且つ全
体の平均酸素濃度が70ppm以下であるところに要
旨が存在する。
まず本発明で採用した溶滴移行性の試験法につ
いて説明する。溶接試験装置としては第１図（概
念図：図中１は供試ワイヤ、２は母材、３は通電
チツプ、４は送給ローラ、５は溶接電源、６は電
流・電圧検知素子、７は比較演算・記録装置を示
す）を用いて、例えば第２図に示す様なアーク電
圧波形（図中T1は短絡時間、T2はアーク発生時
間を示す）を得る。次いでこの波形を解析して例
えば第３図に示す様なアーク発生時間の分布をと
り、この分布から標準偏差値（σ）を求める。し
かしてこの標準偏差値（σ）が小さい程アーク発
生時間のばらつきが少なく、溶滴移行状態が良好
でアークが安定であることを意味する。
上記の方法を採用し、表層部の酸素濃度が異な
る種々の鋼製ワイヤについてアーク発生時間分布
の標準偏差を調べた。尚表層部酸素濃度の調整
は、まず、ワイヤ表面に酸化物、特にFe3O4を生
成させる。次に酸化スケールのついたワイヤを伸
線することによつて、ワイヤ表面の酸素濃度をあ
げる。表面層の酸素濃度はこの酸化スケール量を
調整することによつて行なう。また該酸素濃度の
定量は、各供試ワイヤの表層部を約0.05〜0.2mm
mmの深さに研削して0.2〜0.5ｇの試料を採取し、
インパルス炉を使つた不活性ガス中での溶融型酸
素分折法によつて酸素濃度を定量した。
結果を第４図に示す。
この結果からも明らかである様に、ワイヤ全体
の平均酸素濃度が一定（60ppm）であつても表層
部の酸素濃度によつてアーク発生時間分布の標準
偏差（σ）は著しく変わる。殊に該酸素濃度を
100ppm以上にすることによつて標準偏差値は著
しく小さくなり、アーク安定性（即ち溶滴移行
性）が極めて良好になることが分かる。この様な
結果が得られた理由としては次の様に考えること
ができる。即ち酸素には溶融金属の表面張力を低
下させる作用があるので、ワイヤ先端に懸垂する
溶滴の成長が抑えられ、規則的で且つ比較的微細
な溶滴としてクレータへ移行していく為、アーク
安定性が良くなるものと考えられる。但し表層部
の酸素濃度が1000ppmを越えるとワイヤ表面の導
電性が低下し、通電チツプでの通電性が悪化して
アーク発生不良が頻発するので好ましくない。
また第５図は、表層部酸素濃度を105ppmで一
定としワイヤ全体の平均酸素濃度を変えた場合の
同標準偏差を調べた実験グラフであり、この図か
らも明らかな様に、標準偏差値は平均酸素濃度が
約70ppmのものを境界にしてその前後で急激に変
化している。そして標準偏差値を低レベルに抑え
る為には、平均酸素濃度を70ppm以下にすべきで
あることが理解される。これはワイヤ全体の平均
酸素濃度が高すぎると、溶滴表面の導電性が不十
分になつて溶滴移行時の微小短絡が増加する為と
考えられる。
ところで酸素濃度を高めるべき表層部の肉厚
は、後述する様な表層部酸素濃度調整法によつて
若干異なるが、いずれにしても0.2mm以下にする
ことが望まれる。その理由は、0.2mmを越える深
部まで酸素濃度を高めるとワイヤ全体の平均酸素
濃度が上昇し、70ppm以下の平均酸素濃度を確保
することが困難になるからである。尚表層部の酸
素濃度を高める方法としては、原線表面に生成し
ている酸化物皮膜の除去量を調整して残存酸化物
皮膜量をコントロールした後伸線加工を行なう
か、あるいは原線表面の酸化物皮膜を一旦完全に
除去した後再度酸化物皮膜を形成して伸線加工を
行なう方法が最も一般的である。一方内部の酸素
濃度は原料鋼の溶製段階あるいは鋳造段階で調整
すればよい。即ち原線表面の酸化鉄（特にマグネ
タイト）は伸線工程でワイヤ表層部へ均一に分布
し、内部の酸素濃度は原料鋼溶製時に除去しきれ
なかつた酸素量によつて決まつてくる。従つて原
料鋼中の酸素濃度に応じて、原線表面に形成しあ
るいは残存させる酸化物皮膜の量を調整し、前記
平均酸素濃度及び表層部酸素濃度をコントロール
すればよい。
本発明は概略以上の様に構成されており、特に
酸素濃度が低ければ低い程溶滴移行性は改善され
るという従来の常識をくつがえし、表層部の酸素
濃度を積極的に高めることによつて、溶滴移行性
の良好な鋼製ソリツドワイヤを比較的安価に提供
し得ることになつた。
次に実験例を示す。
実験例
第１表に示す化学成分の鋼製ソリツドワイヤ
（1.2mmφ）を使用し、下記の条件で溶接を行なつ
た場合の溶滴移行性及び通電性を調べた。尚ワイ
ヤ全体の平均酸素濃度及び表層部の酸素濃度は、
溶製後の酸素濃度を考慮しつつ、原線表面の酸化
物皮膜を一旦完全に除去した後所定量の酸化物皮
膜を形成させる方法によつて調整した。結果を第
１表に一括して示す。
〔溶接条件〕
母 材：50キロ級高張力鋼、板厚19mm
シールドガス：CO2、20／分
溶接電流：300A
溶接電圧：30V
平均入熱：25KJ／cm
The present invention relates to a solid wire for welding, and more particularly to a solid wire that has good droplet transfer properties during welding and can produce a smooth and sound weld bead with few spatters. One of the important properties required of solid wire for welding is droplet transferability during welding.
That is, when the droplets are transferred in a spray-like manner, spatter is reduced and workability is improved, and the weld bead becomes smooth and beautiful, improving the quality of the welded part.
Various studies have been carried out with the aim of improving droplet migration from this point of view, but among these, as a measure to improve the wire component composition, the amount of nonmetallic inclusions in the wire (particularly oxygen, phosphorus, and sulfur) has been studied. and these intermetallic compounds) is considered to be effective. For example, Japanese Patent Publication No. 52-23869 discloses this type of technology, which improves droplet migration and reduces the number of unstable arcs by suppressing the contents of oxygen, phosphorus, and sulfur to low levels. We are trying to By the way, as a method for suppressing the above-mentioned nonmetallic inclusions, the inclusions can be removed as much as possible by employing a vacuum degassing melting method, a vacuum casting method, etc. at the stage of melting or casting the wire raw material. There is a method to remove the wire, but it is not suitable for the actual situation because it causes problems in terms of economy and productivity, and the price of the wire increases. The present inventors have focused on the above-mentioned circumstances, and in order to provide a solid wire with good droplet transferability at a low cost, the present inventors have investigated the effects that the content and location of oxygen-based nonmetallic inclusions have on the droplet transferability. We have been conducting research to quantitatively understand the impact. As a result, we reached the same conclusion as the conventional understanding that droplet migration is improved by lowering the average oxygen concentration throughout the wire, but there are As a trend, we confirmed a new fact that if the oxygen concentration at the surface layer of the solid wire is actively increased, the droplet transferability will be significantly improved. The present invention was completed as a result of further research based on such confirmation results, and its composition is such that the surface layer oxygen concentration of the mild steel wire rod is 100 to 1000 ppm, and the overall average oxygen concentration is 70 ppm or less. There is a gist somewhere. First, the test method for droplet migration adopted in the present invention will be explained. The welding test equipment is shown in Figure 1 (conceptual diagram: 1 is the test wire, 2 is the base material, 3 is the current carrying chip, 4 is the feed roller, 5 is the welding power source, 6 is the current/voltage detection element, 7 is the welding test device) For example, an arc voltage waveform as shown in FIG. 2 ( T1 indicates the short circuit time and T2 indicates the arc generation time) is obtained using a comparison calculation/recording device. Next, this waveform is analyzed to obtain a distribution of arc occurrence times as shown in FIG. 3, for example, and a standard deviation value (σ) is determined from this distribution. However, the smaller the standard deviation value (σ) of the lever, the less variation in arc generation time, which means that the droplet transfer state is good and the arc is stable. Using the method described above, the standard deviation of the arc generation time distribution was investigated for various steel wires with different oxygen concentrations in the surface layer. To adjust the oxygen concentration in the surface layer, first, oxides, especially Fe 3 O 4 are generated on the wire surface. Next, the wire with the oxide scale is drawn to increase the oxygen concentration on the wire surface. The oxygen concentration in the surface layer is determined by adjusting the amount of oxide scale. In addition, to quantify the oxygen concentration, measure the surface layer of each test wire by approximately 0.05 to 0.2 mm.
Grind to a depth of mm and collect a sample of 0.2 to 0.5 g.
Oxygen concentration was determined by fused oxygen spectrometry in inert gas using an impulse furnace. The results are shown in Figure 4. As is clear from this result, even if the average oxygen concentration throughout the wire is constant (60 ppm), the standard deviation (σ) of the arc generation time distribution changes significantly depending on the oxygen concentration in the surface layer. In particular, the oxygen concentration
It can be seen that by increasing the content to 100 ppm or more, the standard deviation value becomes significantly smaller, and the arc stability (ie, droplet transferability) becomes extremely good. The reason why such a result was obtained can be considered as follows. In other words, since oxygen has the effect of lowering the surface tension of molten metal, the growth of the droplets suspended at the tip of the wire is suppressed, and the droplets migrate to the crater as regular and relatively fine droplets, thereby preventing arcing. It is thought that stability will be improved. However, if the oxygen concentration in the surface layer exceeds 1000 ppm, the conductivity of the wire surface will decrease, the current conductivity at the current-carrying chip will deteriorate, and failures in arc generation will occur frequently, which is not preferable. Furthermore, Figure 5 is an experimental graph in which the standard deviation was investigated when the surface layer oxygen concentration was kept constant at 105 ppm and the average oxygen concentration of the entire wire was changed.As is clear from this figure, the standard deviation value is The average oxygen concentration is around 70 ppm, and changes rapidly around that point. It is understood that in order to keep the standard deviation value to a low level, the average oxygen concentration should be 70 ppm or less. This is thought to be because if the average oxygen concentration of the entire wire is too high, the conductivity of the droplet surface becomes insufficient, leading to an increase in micro short circuits during droplet transfer. By the way, the wall thickness of the surface layer portion in which the oxygen concentration should be increased varies slightly depending on the surface layer oxygen concentration adjustment method as described below, but in any case, it is desirable to keep it to 0.2 mm or less. The reason for this is that if the oxygen concentration is increased to a depth exceeding 0.2 mm, the average oxygen concentration of the entire wire will increase, making it difficult to ensure an average oxygen concentration of 70 ppm or less. In order to increase the oxygen concentration in the surface layer, you can adjust the amount of oxide film generated on the surface of the raw wire to be removed to control the amount of oxide film remaining, and then perform wire drawing processing, or The most common method is to once completely remove the oxide film, form the oxide film again, and perform wire drawing. On the other hand, the internal oxygen concentration may be adjusted at the melting or casting stage of the raw steel. That is, iron oxide (particularly magnetite) on the surface of the raw wire is uniformly distributed to the surface layer of the wire during the wire drawing process, and the internal oxygen concentration is determined by the amount of oxygen that cannot be removed during melting of the raw material steel. Therefore, the average oxygen concentration and surface layer oxygen concentration may be controlled by adjusting the amount of the oxide film formed or remaining on the surface of the raw wire depending on the oxygen concentration in the raw steel. The present invention is constructed as described above, and overturns the conventional wisdom that the lower the oxygen concentration, the better the droplet migration, and by actively increasing the oxygen concentration in the surface layer. Therefore, it has become possible to provide a steel solid wire with good droplet transfer properties at a relatively low cost. Next, an experimental example will be shown. Experimental Example A solid steel wire (1.2 mmφ) with the chemical composition shown in Table 1 was used to investigate the droplet transferability and electrical conductivity when welding was performed under the following conditions. The average oxygen concentration of the entire wire and the oxygen concentration of the surface layer are:
Taking into consideration the oxygen concentration after melting, the oxide film was adjusted by a method in which the oxide film on the surface of the raw wire was once completely removed and then a predetermined amount of oxide film was formed. The results are summarized in Table 1. [Welding conditions] Base material: 50 kg class high tensile steel, plate thickness 19 mm Shielding gas: CO 2 , 20/min Welding current: 300 A Welding voltage: 30 V Average heat input: 25 KJ/cm
【表】
第１表からも明らかな様に、No.１〜３は表層部
の酸素濃度が100ppm未満である為、またNo.４は
全体の平均酸素濃度が70ppmを越えると共に表層
部の酸素濃度も100ppm未満である為、何れも溶
滴移行性が悪い。またNo.８は表層部の酸素濃度が
1000ppmを越える為にワイヤーチツプ間の通電性
が悪く、且つ平均酸素濃度が70ppmを越えている
ので溶滴移行性も良くない。更にNo.９はワイヤ全
体の平均酸素濃度が70ppmを大幅に越える為、溶
滴がバブリング現象を起こして溶滴移行性が悪化
する。これらに対しNo.５〜７は本発明の要件を満
たしているので、溶滴移行性及び通電性のいずれ
も極めて良好である。[Table] As is clear from Table 1, Nos. 1 to 3 have an oxygen concentration of less than 100 ppm in the surface layer, and No. 4 has an overall average oxygen concentration of over 70 ppm, and the oxygen concentration in the surface layer is less than 100 ppm. Since the concentration is less than 100 ppm, droplet migration is poor in both cases. In addition, No. 8 has a high oxygen concentration in the surface layer.
Since the concentration exceeds 1000 ppm, the electrical conductivity between the wire chips is poor, and since the average oxygen concentration exceeds 70 ppm, the droplet migration properties are also poor. Furthermore, in No. 9, since the average oxygen concentration of the entire wire significantly exceeds 70 ppm, the droplets cause a bubbling phenomenon and the droplet transferability deteriorates. On the other hand, Nos. 5 to 7 satisfy the requirements of the present invention and are therefore extremely good in both droplet migration and electrical conductivity.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図は溶滴移行性判定の為の実険法を示す説
明略図、第２図はアーク発生時間と短絡時間の変
動パターンを示す図、第３図はアーク発生時間の
分布を示すグラフ、第４，５図は表層部酸素濃度
及びワイヤ全体の平均酸素濃度とアーク発生時間
の標準偏差との関係を示すグラフである。
１……ソリツドワイヤ、２……母材、３……通
電チツプ、５……溶接電源。
Fig. 1 is an explanatory diagram showing the actual risk method for determining droplet transferability, Fig. 2 is a diagram showing the variation pattern of arc generation time and short circuit time, Fig. 3 is a graph showing the distribution of arc generation time, 4 and 5 are graphs showing the relationship between the surface layer oxygen concentration, the average oxygen concentration of the entire wire, and the standard deviation of the arc generation time. 1...Solid wire, 2...Base metal, 3...Electricity chip, 5...Welding power source.