JP4837322B2 - Welding wire used for welding cast iron and stainless steel - Google Patents

Description

  The present invention relates to a welding wire used for welding cast iron and stainless steel.

A welding wire used for welding cast iron and stainless steel has been developed. For example, an exhaust manifold directly connected to an automobile engine is made of spheroidal graphite cast iron for controlling exhaust such as fuel economy, thermal efficiency, and reduction of hazardous waste. A 400 series stainless steel catalyst portion is connected to such an exhaust manifold of cast iron by welding. As welding materials used for such welding, YNi-1, YNiCr-3 specified in JIS-Z-3334, and Y309 and Y430 series welding wires specified in JIS-Z-3321 are known. Yes. Japanese Patent No. 2858037 and Japanese Patent Application Laid-Open No. 2003-58584 also propose a welding wire used for such welding. In cast iron welding, the heat-affected zone is whitened by rapid cooling and easily broken. Therefore, in general, a welding wire uses a high Ni content wire that hardly dissolves C to prevent whitening.
Japanese Patent No. 2858037 JP 2003-58584 A

  However, the conventional welding wire cannot sufficiently prevent cracks generated in the weld metal. Moreover, since Ni is expensive, the conventional welding wire with a high Ni content has a problem that the price is high.

  An object of the present invention is to provide a welding wire used for welding of inexpensive cast iron and stainless steel, which can improve the crack resistance of a weld metal.

  The welding wire used for welding the cast iron and the stainless steel of the present invention is by weight, C: 0.1 to 0.8%, Si: 0.4 to 2.0%, Mn: 0.4 to 4. 0%, P: 0.04% or less, S: 0.03% or less, Ni: 20.0-40.0%, Cr: 10.0-40.0%, Nb: 0.5-4.0 %, The balance is composed of Fe and inevitable impurities. If the welding wire of this invention is used, the crack resistance of a weld metal can be improved. In particular, the addition of Nb is considered to improve the crack resistance. Moreover, since the Ni content can be suppressed, the price of the welding wire can be suppressed. Below, the effect | action of each composition and the reason for limitation of content are demonstrated.

  C has low solubility in Ni, which is the base of the component system of the present invention, but forms carbides with Cr, Nb, which is an essential component of the present invention, and Mo, W, Ta, V, etc., which are additive elements. It is effective for securing and maintaining the strength of the steel. If C is less than 0.1%, there is no effect of securing high-temperature strength, and if it exceeds 0.8%, it becomes difficult to produce a welding wire.

  Si improves the fluidity of the weld metal in gas shielded arc welding and is effective for deoxidation and high-temperature oxidation resistance. If it is less than 0.4%, the effects of deoxidation and high-temperature oxidation resistance are reduced. Since the amount of Si in the cast iron of the base material is high, the effect is not improved even if Si exceeding 2% is added. Further, it becomes difficult to manufacture a welding wire.

  Mn is effective as a deoxidizing agent, forms MnS and is effective for hot cracking resistance, and has an effect of reducing costs by partial substitution with an austenite-forming element like Ni as the base. If it is less than 0.4%, the effect is small, and if Mn is added in an amount exceeding 4%, the effect is not improved, and it becomes difficult to produce a welding wire.

  When the content of P and S increases, the crack resistance and toughness of the weld metal deteriorate, so it is better to be less. However, considering the manufacturing cost, they were made 0.04% and 0.03% or less, respectively.

  Ni is one of the basic components of the cast iron welding material, is an austenite-forming element, and is excellent in high-temperature strength, corrosion resistance, and heat resistance. Moreover, in an alloy system with Fe, the expansion coefficient is greatly affected. In the case of dissimilar material welding of cast iron and stainless steel according to the present invention, there is a difference in the coefficient of expansion between materials to be welded. If it is less than 20%, these effects are small, and if it exceeds 40%, the cost reduction effect is small.

  Cr is a strong carbide-forming element like Nb. It is a component necessary for high-temperature strength and oxidation resistance. If it is less than 10%, these effects do not fully appear. If it exceeds 40%, it is hardened and difficult to manufacture. The balance with the amount of Ni is lost. In addition to its own price increase, manufacturing costs also increase.

  Nb is a strong carbide-forming element and is a component necessary for high-temperature strength and oxidation resistance by forming carbides like Cr. Compared with Cr, the free energy of formation is low, and it is produced prior to Cr in the solidification process of welding. In the case of gas shielded arc welding for automobile exhaust systems that are commonly used, the timing and location of Nb carbide formation are thought to strongly influence the improvement of crack resistance. It is considered that Nb carbides precipitate in the crystal grains and in the grain boundaries during the solidification process of the weld metal, which is due to strengthening of the crystals. Nb of NbC, which is Nb carbide, is stoichiometrically about 8 times that of C, and in the case of stabilized stainless steel, it is defined as 8 times or more of C. In view of the high amount and the test results, it was set to 5 times C.

  In the welding wire of the present invention, Ta: 1.0% or less, W: 1.0% or less, Mo: 0.5% or less, V: 0.5% or less, Cu: 0.5% by weight% Hereinafter, any one or more of Co: 0.5% or less can be further contained. If it does in this way, high temperature strength, corrosion resistance, and heat resistance can be raised. Below, the effect | action of each composition and the reason for limitation of content are demonstrated.

  Ta and W are components that form carbides similarly to Nb and are effective in high-temperature strength and oxidation resistance. Even if Ta and W in amounts exceeding 1% are added, the effect is not improved and it is difficult to manufacture a welding wire.

  Mo and V are components that form carbides similarly to Nb and are effective in high-temperature strength and oxidation resistance. Addition of Mo and V in amounts exceeding 0.5% does not improve the effect and makes it difficult to manufacture a welding wire.

  Cu and Co are austenitizing elements and have an effect on high-temperature strength, corrosion resistance, and heat resistance together with Ni, and Cu improves the flow of weld metal and has an effect on good bead formation. Even if Cu and Co in amounts exceeding 0.5% are added, the effect is not improved.

  % By weight, C: 0.4-0.8%, Si: 0.5-1.5%, Mn: 0.7-2.0%, P: 0.04% or less, S: 0.03 % Or less, Ni: 30.0 to 40.0%, Cr: 20.0 to 30.0%, Nb: 0.5 to 3.0%, and the balance limited to Fe and inevitable impurities, the resistance of the weld metal The cracking property can be further enhanced.

  Further, even in such a welding wire, if any one or more of Ta: 1.0% or less, Mo: 0.5% or less, and Co: 0.5% or less are further contained by weight%, Strength, corrosion resistance, and heat resistance can be increased.

  If the welding wire of this invention is used, the crack resistance of a weld metal can be improved. In particular, it is considered that the crack resistance is improved by the addition of Nb. Moreover, since the Ni content can be suppressed, the price of the welding wire can be suppressed.

In order to confirm the effect of the present invention, various welding wires were made and tested. The welding wires of Examples 1 to 11 and Comparative Examples 1 to 18 having a wire diameter of 1.2 mm having the composition shown in Table 1 were made.

  Next, the following tests were performed using the welding wires of Examples 1 to 11 and Comparative Examples 1 to 18.

(Crack resistance test 1A)
The crack resistance test 1 was performed in accordance with a T-type fillet crack test of JIS-Z-3153. Specifically, as shown in FIG. 1, a cast iron base material (shown in Table 2 below) 1 consisting of two FCD450s of 10 mm × 50 mm × 150 mm is placed in a T shape, and a test bead. Shielded arc welding was performed with each welding wire across two cast iron base materials so as to form B1 and constraining beads B2. First, 98% Ar + 2% O ₂ shielding gas was flowed at a flow rate of 15 l / min, and a restraining bead B2 was formed using the welding wire of Example 4 at a welding speed of 40 cm / min with a current of 150 A and a voltage of 23 V. . Next, a test bead B1 was formed using each welding wire shown in Table 1. The test bead B1 was welded at a welding speed of 70 cm / min, and the others were welded under the same conditions as the constraining bead B2. And the crack rate [(crack length / bead length) × 100)] of the surface of the test bead B1 excluding the crater portion was determined and evaluated. The evaluation was as follows: ◯: cracking rate 0%, Δ: cracking rate 0-30%, x: cracking rate 30% or more. Table 1 also shows the evaluation results.

From Table 1, it can be seen that if the welding wires of Examples 1 to 11 are used, the cracking rate is low and the cracking resistance is high as compared with the case where the welding wires of Comparative Examples 6 to 16 are used.

(Crack resistance test 1B)
Two cast iron base materials 1 were arranged in a T shape with a gap of 2 mm, and others were welded in the same manner as the crack resistance test 1A, and the crack rate on the surface of the test bead B1 was determined and evaluated. Table 1 also shows the evaluation results.

  From Table 1, the welding wires of Examples 2, 4 and 11 in which the respective compositions were further limited (C: 0.4 to 0.8%, Si: 0.5 to 1.5%, Mn: 0.7 to 2) 0.0%, P: 0.04% or less, S: 0.03% or less, Ni: 30.0-40.0%, Cr: 20.0-30.0%, Nb: 0.5-3. If a welding wire consisting of 0% and the balance Fe and inevitable impurities is used, the cracking rate is higher than when the welding wires of Examples 1, 3, 5 to 10 and Comparative Examples 1 to 5, 17, and 18 are used. Is low and it can be seen that the crack resistance is high.

(Crack resistance test 2A)
As shown in FIG. 2, the crack resistance test 2 was performed using a cast iron base material 3 made of FCD450 of 10 mm × 50 mm × 150 mm and a stainless steel base material 5 made of SUH409 of 1.5 mm × 50 mm × 150 mm (see Table 2 above). The test bead B3 was formed by using each welding wire shown in Table 1 at the joint portion. Welding was performed under the same conditions as the test bead B1 of the crack resistance test 1. And the crack rate [(crack length / bead length) × 100)] of the surface of the test bead B3 excluding the crater portion was determined and evaluated. The evaluation was as follows: ◯: cracking rate 0%, Δ: cracking rate 0-30%, x: cracking rate 30% or more. Table 1 also shows the evaluation results.

  From Table 1, it can be seen that when the welding wires of Examples 2, 4, and 10 are used, the cracking rate is low and the cracking resistance is high as compared with the case of using the welding wires of Comparative Examples 8, 14, and 16.

(Crack resistance test 2B)
What was welded in the crack resistance test 2 was cut in a direction perpendicular to the direction in which the test bead B3 extends at a position of 50 mm from the start and end points (crater) of the test bead B3. For example, as shown in FIG. 3 in the case of three cracks, the lengths L1, L2, L3 in the width direction of the base materials 3, 5 of the cracks C1, C2, C3 in the cross section and the test bead B3 The lengths L of the base materials 3 and 5 in the width direction were obtained. Then, the crack ratio [(total crack length: L1 + L2 + L3 / bead length: L) × 100] of the cross section of the test bead B3 was calculated and evaluated. Evaluation was the average value of the cracking rate of the cross section of each two places, (circle): Cracking rate 0%, (triangle | delta): Cracking rate 0-30%, x: Cracking rate 30% or more. Table 1 also shows the evaluation results.

  From Table 1, if the welding wires of Examples 2, 4, and 10 are used, the cracking rate is low and the cracking resistance is high compared to the case of using the welding wires of Comparative Examples 1, 8, 14, 16, and 18. I understand.

(Crack resistance test 3A, 3B)
As cast iron base material 3, FCD500 (the composition is shown in Table 2 above) having higher cracking sensitivity than FCD450 was used, and the others were performed in the same manner as in crack resistance tests 2A and 2B. Table 1 also shows the evaluation results.

  From Table 1, it can be seen that when the welding wires of Examples 2 and 4 are used, the cracking rate is low and the crack resistance is high as compared with the cases where the welding wires of Comparative Examples 1, 4, 14, and 17 are used.

(Thermal expansion coefficient test)
Temperature and thermal expansion of cast iron base material made of FCD450, stainless steel base material made of SUH409, welding wire of Example 4 and welding wires of Comparative Examples 4, 14, and 16 in the range of 200 to 800 ° C. using a thermal dilatometer. The relationship with rate was examined. FIG. 4 shows the measurement results.

  As shown in FIG. 4, the welding wire of Example 4 shows the same thermal expansion coefficient as the Inconel welding wire (welding wire of Comparative Example 4) frequently used for welding of cast iron, and is more thermally expanded than the base material (FCD450, SUH409). You can see that the rate is a little high. It is considered that the crack resistance is improved by such thermal expansion characteristics.

It is a figure for demonstrating the aspect which performs the cracking resistance test 1 using each welding wire. It is a figure for demonstrating the aspect which performs the crack resistance test 2A using each welding wire. It is a figure for demonstrating the aspect which performs the cracking resistance test 2B using each welding wire. It is a figure which shows the relationship between the temperature of a base material and each welding wire, and a thermal expansion coefficient.

Explanation of symbols

1,3 Cast iron base material 5 Stainless steel base material B1, B3 Test bead B2 Restraint bead

Claims (4)

  % By weight, C: 0.1 to 0.8%, Si: 0.4 to 2.0%, Mn: 0.4 to 4.0%, P: 0.04% or less, S: 0.03 %, Ni: 20.0 to 40.0%, Cr: 10.0 to 40.0%, Nb: 0.5 to 4.0%, the balance consisting of Fe and inevitable impurities Welding wire used for welding steel to stainless steel.   % By weight, Ta: 1.0% or less, W: 1.0% or less, Mo: 0.5% or less, V: 0.5% or less, Cu: 0.5% or less, Co: 0.5% The welding wire used for welding of cast iron and stainless steel according to claim 1, further comprising any one or more of the following.   % By weight, C: 0.4-0.8%, Si: 0.5-1.5%, Mn: 0.7-2.0%, P: 0.04% or less, S: 0.03 %, Ni: 30.0-40.0%, Cr: 20.0-30.0%, Nb: 0.5-3.0%, the balance being Fe and inevitable impurities Welding wire used for welding steel to stainless steel.   The cast iron according to claim 3, further comprising at least one of Ta: 1.0% or less, Mo: 0.5% or less, and Co: 0.5% or less by weight%. Welding wire used for welding with stainless steel.

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