JP5111028B2 - Flux-cored wire for gas shielded arc welding - Google Patents

Description

  The present invention relates to a flux-cored wire used for gas shielded arc welding of workpieces made of mild steel and tensile strength 490 MPa class high strength steel, and good at high welding current without dripping of molten metal in vertical welding. For gas shielded arc welding, which can be welded, has excellent hot crack resistance in the first layer in single-sided welding, and can obtain weld metal with excellent low temperature toughness in high heat input welding The present invention relates to a flux-cored wire.

  Flux-cored wire for gas shielded arc welding is mainly used for welding workpieces made of mild steel and 490MPa high-strength steel, and has a better bead appearance and welding workability than solid wire, and is further welded Due to its high efficiency, its usage is increasing year by year.

  However, the flux-cored wire for gas shielded arc welding has a higher welding speed than the solid wire, and therefore there is a tendency for high-temperature cracking (solidification cracking) to occur in the first layer that forms the back bead in single-sided welding. . In addition, the wire contains a lot of metal oxides such as rutile, and they cannot completely float as slag during welding and remain as metal inclusions in the weld metal, so that the welding heat input is 30 to 60 kJ / cm. In such high heat input welding, it has been difficult to secure a weld metal having good toughness at a low temperature such as −20 ° C. In addition, when welding with the same current as that of downward welding in vertical improvement welding, there is a tendency that the molten metal tends to sag (beads tend to sag).

  These gas shield arcs are designed to simultaneously increase the current in vertical welding, improve the hot crack resistance of the first layer in single-sided welding, and improve the low temperature toughness in high heat input welding. Conventionally, no flux-cored wire for welding has been proposed.

JP-A-8-99192 Japanese Patent Laid-Open No. 11-151592 Japanese Patent Laid-Open No. 2003-311476

  Accordingly, an object of the present invention is to provide a flux-cored wire used for gas shielded arc welding of workpieces made of mild steel, 490 MPa class high-strength steel, and good at high welding current without dripping of molten metal in vertical welding. Can be welded, and is excellent in hot crack resistance in the first layer in single-sided welding. Furthermore, it is possible to obtain a weld metal excellent in low temperature toughness in large heat input welding with a large amount of welding. Another object is to provide a flux-cored wire for gas shielded arc welding.

In order to solve the above problems, the present invention takes the following technical means. The invention of claim 1 is a flux-cored wire for gas shielded arc welding formed by filling a soft steel or alloy steel outer shell with a flux, TiO ₂ : 4.5 to 7.0% by mass, Ti: 0.11-0.29 mass%, Mg: 0.30-0.70 mass%, C: 0.02-0.08 mass%, Si: 0.35-0.75 mass%, Mn: 2. 20 to 2.85% by mass, B: 0.002 to 0.010% by mass, Mg content is [Mg], and MgO content is [MgO]. The flux-cored wire for gas shielded arc welding, wherein MgO satisfies a relationship of [MgO] + [Mg] × 1.66: ≦ 2.5 mass% with respect to the amount.

The invention according to claim 2 is the flux-cored wire for gas shielded arc welding according to claim 1, further satisfying Al: ≦ 0.5 mass% (including 0) per total mass of the wire, the content and [Al], when the content of _Al 2 _{O 3} and _[Al 2 _{O 3],} relative to the content of the _{Al, [Al 2 O 3]} + [Al] × 1.89: 0 Al ₂ O ₃ is contained so as to satisfy the relationship of 0.5 to 1.0% by mass.

  The invention of claim 3 is the flux-cored wire for gas shielded arc welding according to claim 1 or 2, further comprising Ni: 0.2 to 1.0 mass% per total mass of the wire. Is.

  According to the present invention having such a feature, in a flux-cored wire used for gas shielded arc welding of a workpiece made of mild steel, 490 MPa class high-tensile steel, high welding without dripping of molten metal in vertical improvement welding is achieved. It is possible to perform welding with good current, and has excellent hot crack resistance in the first layer in single-sided welding, and weld metal with excellent low temperature toughness in high heat input welding with a large amount of welding. A flux-cored wire for gas shielded arc welding that can be obtained can be provided.

  The present invention will be described in detail below.

In order to solve the above-mentioned problems, the present inventors first attempted to increase the amount of slag mainly composed of rutile (TiO ₂ ) in order to eliminate the dripping of molten metal in the vertical improvement welding. However, although the dripping of the molten metal was eliminated by this, the hot crack resistance in the first layer in the downward single-sided welding was lowered.

  Therefore, we investigated the causes and countermeasures, determined that the cause of the high temperature cracking tendency was the increase in the amount of oxygen in the weld metal, and examined the means to reduce the amount of oxygen while maintaining the slag amount. went.

As a result, the required amount of slag generator such as TiO ₂ and SiO ₂ is not added from the beginning, but by adding an alloy component that changes to a slag component during welding, while maintaining the slag amount, welding is performed. The amount of oxygen in the metal was reduced to improve hot cracking resistance. Normally, Mn, Si, Al, Ti, Mg, etc. are used as deoxidizers in the flux-cored wire, but it has been found that the addition of Ti and Mg is effective in the present invention.

For Ti, by acting as a deoxidizer during welding, the amount of oxygen in the weld metal is reduced, thereby improving the hot crack resistance in the first layer in single-sided welding, and the resulting TiO ₂ is used as a slag component. By acting, the effect of preventing dripping of the molten metal in the vertical improvement welding is exhibited. Further, Ti slightly remains in the weld metal, thereby miniaturizing the structure of the weld metal and exhibiting the effect of improving the low temperature toughness in high heat input welding.

  On the other hand, Mg does not remain in the weld metal, and almost all acts as a deoxidizer, so that the effect of reducing the amount of oxygen in the weld metal is great, and therefore the resistance in the first layer in single-sided welding is great. Great effect to improve hot cracking. Further, MgO produced by the deoxidation action has an effect of promoting the deoxidation action by changing the equilibrium state of oxygen and the deoxidizer.

  Moreover, the low temperature toughness of the weld metal in the high heat input welding of about 30 to 60 kJ / cm can be improved by appropriately defining the contents of Mg, MgO, C, Si, Mn, and B.

The flux-cored wire for gas shielded arc welding of the present invention uses CO ₂ gas as the shielding gas. Moreover, the range of 10-18 mass% (vs. wire total mass) is suitable for the flux content rate.

  Next, the reason for limiting the composition and numerical values of the flux-cored wire for gas shielded arc welding of the present invention will be described.

[TiO ₂ : 4.5 to 7.0% by mass] TiO ₂ acts as a slag forming agent (slag forming agent). If the content of TiO ₂ is less than 4.5% by mass, it is not possible to secure an amount of slag that can support the molten metal so that it does not sag in the vertical welding, and the bead shape becomes poor. On the other hand, if it exceeds 7.0% by mass, the amount of oxygen in the weld metal increases, the hot crack resistance in the first layer in single-sided welding decreases, and the toughness at low temperatures decreases. Therefore, the content of TiO ₂ is 4.5 to 7.0 mass%.

[Ti: 0.11 to 0.29% by mass] Ti, as described above, acts as a deoxidizer to reduce the amount of oxygen in the weld metal, thereby reducing the hot crack resistance in the first layer in single-sided welding. In addition, the produced TiO ₂ acts as a slag component and has an effect of preventing the molten metal from dripping in the vertical welding. Furthermore, Ti has the effect of making the structure of the weld metal finer by remaining slightly in the weld metal and improving the toughness at low temperatures in large heat input welding. In order to exhibit such an effect, the Ti content needs to be 0.11% by mass or more. On the other hand, if it exceeds 0.29% by mass, the remaining amount in the weld metal is excessively increased and the toughness is lowered as the strength is increased. Therefore, the Ti content is 0.11 to 0.29 mass%.

  [Mg: 0.30 to 0.70% by mass] Mg acts as a deoxidizer, reduces the amount of oxygen in the weld metal, improves hot crack resistance in the first layer in single-sided welding, and weld metal Also improves the low temperature toughness. When the Mg content is less than 0.30% by mass, such an effect cannot be obtained. When the Mg content exceeds 0.70% by mass, the moisture absorption resistance of the wire decreases and the cold cracking resistance decreases. Therefore, the Mg content is set to 0.30 to 0.70 mass%.

  [[MgO] + [Mg] × 1.66: ≦ 2.5% by mass] MgO is a component that, when added, promotes oxidation due to a change in oxidation-reduction constant and enhances the deoxidation effect. However, MgO is a component that promotes dripping of the molten metal. Therefore, the content of MgO needs to be contained so as to satisfy the relationship of [MgO] + [Mg] × 1.66: ≦ 2.5 mass% with respect to the content of Mg, more preferably [MgO] + [Mg] × 1.66: ≦ 1.7% by mass is preferably satisfied. When the value of [MgO] + [Mg] × 1.66 exceeds 2.5% by mass with respect to the Mg content, the molten metal tends to sag. Further, in the transverse welding, since the solidification temperature of the slag becomes high, defects such as slag entrainment are likely to occur.

  [C: 0.02 to 0.08 mass%] C is an element necessary for ensuring the strength of the weld metal. If the C content is less than 0.02% by mass, the strength of the weld metal cannot be ensured, and the toughness at low temperatures also decreases. On the other hand, if it exceeds 0.08% by mass, the strength of the weld metal increases and the toughness at low temperature decreases. In addition, the resistance to cold cracking is reduced, and the amount of spatter generated is also increased. Therefore, the C content is 0.02 to 0.08 mass%.

  [Si: 0.35 to 0.75 mass%] Si acts as a deoxidizer and has an effect of adjusting the strength of the weld metal, and also increases the viscosity of the molten metal to improve the vertical weldability. There is also an effect. If the Si content is less than 0.35% by mass, these effects cannot be obtained. On the other hand, when it exceeds 0.75 mass%, the strength of the weld metal is increased and the toughness at low temperature is lowered. In addition, the low temperature crack resistance and the high temperature crack resistance are also lowered. Therefore, the Si content is set to 0.35 to 0.75% by mass.

  [Mn: 2.20 to 2.85 mass%] Mn acts as a deoxidizer and has the effect of improving the strength of weld metal and toughness at low temperatures. If the content of Mn is less than 2.20% by mass, such an effect is not sufficiently exhibited. If the content exceeds 2.85% by mass, the strength of the weld metal is too high, and the toughness at low temperature is lowered. Cracks are also likely to occur. Therefore, the Mn content is 2.20 to 2.85 mass%.

  [B: 0.002 to 0.010 mass%] B has an effect of improving the toughness at low temperature by refining the crystal grains of the weld metal. If the content of B is less than 0.002% by mass, a sufficient effect of improving toughness cannot be obtained. On the other hand, if the content exceeds 0.010% by mass, the hot cracking resistance decreases. Therefore, the B content is set to 0.002 to 0.010 mass%.

  [Al: ≦ 0.5 mass% (including 0)] Al becomes an oxide during welding, thereby increasing the solidification temperature of the slag, thereby preventing dripping of the molten metal in the vertical improvement welding. effective. However, Al remains slightly in the weld metal, and if the residual amount is large, the toughness of the weld metal is reduced and the amount of spatter generated increases. Therefore, the Al content needs to be regulated to 0.5% by mass or less.

[[Al ₂ O ₃ ] + [Al] × 1.89: 0.5 to 1.0% by mass] Al ₂ O ₃ has the effect of increasing the solidification temperature of the slag, thereby melting in the vertical welding. It has the effect of preventing metal dripping. Relative to the content of the _Al, the content of _Al 2 _{O 3} in the case where the value of _{[Al 2 O 3] + [} Al] × 1.89 is less than 0.5 wt%, said drool prevention The effect is not fully demonstrated. On the other hand, relative to the content of _Al, the content of _Al 2 _{O 3} in the case where the value of _{[Al 2 O 3] + [} Al] × 1.89 is more than 1.0 wt%, arc is unstable As a result, the amount of spatter generated increases and the slag becomes too hard and the slag peelability deteriorates.

  [Ni: 0.2 to 1.0% by mass] Ni has an effect of improving the toughness of the weld metal at a low temperature. When the Ni content is less than 0.2% by mass, the toughness improving effect cannot be obtained. On the other hand, even if added over 1.0% by mass, an effect proportional to the added amount cannot be obtained with respect to impact performance at about −40 ° C., and the manufacturing cost is also high because the price of Ni as a raw material is high. To rise. Therefore, the Ni content is 0.2 to 1.0 mass%.

  A flux-cored wire for gas shield arc welding with a wire diameter of 1.4 mm, which is formed by filling a flux in a skin made of mild steel (JIS G 3141 SPCC) (Example No. 1 to Example No. 18 and comparison) Example No. 19 to Comparative Example No. 57). Each wire has a flux content of 14% by mass. The chemical components of these wires are shown in Tables 1, 2 and 3.

  Using each of the produced wires, under the welding conditions shown in Table 4, (b) vertical improvement welding, (b) downward butt welding with a large heat input for evaluating low temperature toughness, and (c) hot cracking resistance Welding tests were conducted for the first layer welding of the downward butt single-sided welding for evaluating the properties and (d) the downward butt welding for evaluating the cold cracking resistance.

  In vertical improvement welding, fillet welding was performed in vertical improvement, and the degree of dripping of molten metal (the quality of the bead shape) was evaluated. In the evaluation, in welding current 180A and delta weaving, a good bead shape was not a convex shape, and “good”, and a poor bead shape was “x”. Furthermore, in 220A, delta weaving, the good bead shape was not “convex”, and “250”, and in delta weaving, the bead shape was not convex, “good”. The evaluation results are shown in Tables 5 and 6.

  In downward butt welding, the low temperature toughness of weld metal by high heat input welding was evaluated. The Charpy test piece was collected from the center position in the plate thickness direction of the welded portion, and the Charpy absorbed energy value at −40 ° C. was measured by a Charpy impact test (the test piece size and test method conform to JIS Z3111). The average value of the three Charpy test pieces was defined as -40 ° C absorbed energy. In the evaluation, the case where the absorption energy at −40 ° C. exceeds 100 J is indicated as “◎”, the case where the absorption energy is in the range of 47 J to 100 J is indicated as “◯”, and the case where the absorption energy is less than 47 J is indicated as “X”. The evaluation results are shown in Tables 5 and 6.

  In the first layer welding (constraint cracking test) of downward butt single-sided welding, the presence or absence of hot cracking was examined by a radiation transmission test after welding. In the evaluation, in the first layer welding with a welding current of 230 A, the one without hot cracking was rated as “◯”, and the one with hot cracking occurred as “x”. The evaluation results are shown in Tables 5 and 6. In the downward butt window frame restraint cracking test, the presence or absence of low temperature cracking was examined by ultrasonic flaw detection after welding. In the evaluation, “o” indicates that there is no cold cracking, and “x” indicates that cold cracking occurs. The evaluation results are shown in Tables 5 and 6.

As for the results of the comparative example, the comparative example No. 21 and no. In No. 26, since TiO ₂ exceeded the upper limit value, high temperature cracking occurred in the first layer of single-sided welding, and low temperature toughness in high heat input welding was low. Comparative Example No. 35, no. 39, no. 43 and no. In No. 51, since TiO ₂ was below the lower limit value, the bead shape was convex and poor in vertical improvement welding.

  Next, No. of the comparative example. 20 and no. In No. 33, since Ti exceeded the upper limit, the strength of the weld metal was increased and the low temperature toughness in high heat input welding was low. Comparative Example No. 19, no. 23 and no. In No. 28, since Ti was below the lower limit, hot cracking occurred in the first layer of single-sided welding, and low temperature toughness in high heat input welding was low.

Next, No. of the comparative example. 47, no. 49 and No. No. 54 had low temperature cracking because Mg exceeded the upper limit. Comparative Example No. 27 and no. In No. 30, since Mg was below the lower limit, hot cracking occurred in the first layer of single-sided welding, and low temperature toughness in high heat input welding was low. The comparative example No. In No. 27, Al and Al ₂ O ₃ were added, and the uplifting weldability was very good.

  Next, No. of the comparative example. 45 and no. In No. 53, since C exceeded the upper limit value, the strength of the weld metal was increased and the low temperature toughness in the high heat input welding was low. Moreover, cold cracking occurred. Comparative Example No. In No. 29, C was lower than the lower limit value, so the low temperature toughness in high heat input welding was low.

Next, No. of the comparative example. 44 and no. In No. 46, since Si exceeded the upper limit, high temperature cracking occurred in the first layer of single-sided welding, and low temperature toughness in high heat input welding was low. Moreover, cold cracking occurred. Comparative Example No. No. 44 had very good weldability due to the improvement in the vertical improvement since Al ₂ O ₃ and Al were added. Comparative Example No. 24, no. 36 and no. In No. 55, Si was lower than the lower limit value, so that the bead shape was convex and defective in vertical improvement welding. The comparative example No. Although Al ₂ O ₃ was added to No. 55, since Si was below the lower limit value, the bead shape was convex and poor in the vertical improvement welding.

  Next, No. of the comparative example. 41 and no. In No. 50, since Mn exceeded the upper limit, the strength of the weld metal increased, the low temperature toughness in high heat input welding was low, and low temperature cracking occurred. Comparative Example No. 25, no. 37 and no. In No. 56, since Mn was below the lower limit, low temperature toughness in high heat input welding was low. The comparative example No. Although Ni was added to No. 56, since Mn was below the lower limit, the low temperature toughness in high heat input welding was low.

  Next, No. of the comparative example. 42, no. 48 and no. In No. 57, since B exceeded the upper limit, hot cracking occurred in the first layer of single-sided welding. The comparative example No. Since No. 57 was added with Ni, the low temperature toughness in high heat input welding was good. Comparative Example No. 32 and no. No. 34 had a low temperature toughness in high heat input welding because B was below the lower limit.

Next, No. of the comparative example. 22, no. 31, no. 38, no. 40 and no. In No. 52, MgO exceeded the specified value, so that the bead shape was convex and poor in the vertical improvement welding. The comparative example No. No. 31 was added with Ni and had good low temperature toughness in high heat input welding. In addition, the comparative example No. In No. 38, since Al exceeded the upper limit, the amount of spatter was large, and the total of Al and Al ₂ O ₃ (b) exceeded the upper limit, so the arc stability and slag peelability were poor. .

  On the other hand, as shown in Table 5, Example No. 1 to Example No. No. 18 can perform good welding at high welding current without dripping of molten metal in vertical improvement welding, and is excellent in hot crack resistance in the first layer in single-sided welding. In the high heat input welding with a large amount, a weld metal excellent in low temperature toughness could be obtained. Further, the low temperature cracking resistance was also good.

Claims (3)

In a flux-cored wire for gas shielded arc welding formed by filling a mild steel or alloy steel outer sheath with flux, TiO ₂ : 4.5 to 7.0 mass%, Ti: 0.11 to 0.29 per total mass of the wire Mass%, Mg: 0.30-0.70 mass%, C: 0.02-0.08 mass%, Si: 0.35-0.75 mass%, Mn: 2.20-2.85 mass% , B: 0.002 to 0.010% by mass, Mg content is [Mg], and MgO content is [MgO]. When MgO content is MgO, [MgO] + [Mg] × 1.66: A flux-cored wire for gas shielded arc welding, which satisfies the relationship of ≦ 2.5% by mass. Further, Al: ≦ 0.5 mass% (including 0) is satisfied per total mass of the wire, the Al content is [Al], and the Al ₂ O ₃ content is [Al ₂ O ₃ ]. Then, Al ₂ O ₃ should be contained so as to satisfy the relationship of [Al ₂ O ₃ ] + [Al] × 1.89: 0.5 to 1.0 mass% with respect to the content of Al. The flux-cored wire for gas shielded arc welding according to claim 1.   Furthermore, Ni: 0.2-1.0 mass% is contained per wire total mass, The flux-cored wire for gas shield arc welding of Claim 1 or 2 characterized by the above-mentioned.