JP3160459B2 - Flux for submerged arc welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used in combination with a 12-17% Cr stainless steel electrode for submerged arc welding to obtain a build-up weld metal having excellent corrosion resistance, abrasion resistance and heat crack resistance at high temperatures. The present invention relates to a flux for submerged arc welding.

[0002]

2. Description of the Related Art Generally, guides and rolls used in continuous casting equipment and the like are exposed to a high temperature and steam environment.
Corrosion resistance at high temperatures due to repeated heating and cooling
Heat crack resistance is required. As such a roll, conventionally, 13% C is used for base rolls such as cast steel and low alloy steel.
A material that is overlaid with r-4 to 8% Ni martensitic stainless steel has been widely used. In continuous casting, the slab temperature is about 950 ° C., and when the line is stopped, the roll surface temperature rises to 700 ° C. even if the roll is water-cooled. It is also conceivable that the surface temperature of the roll reaches 720 to 750 ° C in the portion where the water cooling of the roll is insufficient. In recent years, there has been an increasing demand for higher efficiency of continuous casting, and a higher casting speed has been desired. In order to realize this high speed, there is an increasing demand to extend the allowable upper limit of the roll surface temperature, and it is also desired to extend the roll life.

[0003] Under these circumstances, the 13% Cr-4% to 8% Ni martensitic stainless steel material conventionally used for continuous casting rolls has insufficient high-temperature strength and high-temperature oxidation resistance in a high-temperature steam environment. Due to the lack of steel, the requirements for corrosion resistance, abrasion resistance, and heat crack resistance cannot be sufficiently satisfied, and materials with even higher performance have been required.

Therefore, as disclosed in Japanese Patent Publication No. 4-55791, a flux to which alloy powders such as Mo, Nb, V, W, and Cu are added in addition to Ni is used to improve the properties of the overlay weld metal. Techniques have been proposed. That is, in order to improve high-temperature strength, which leads to abrasion resistance at high temperatures, the flux contains Nb, V, W, M in addition to Mn and Mo which are usually contained.
This flux is obtained by adding a precipitation strengthening element such as o, and further adding Ni in order to strengthen the build-up weld metal and improve the high-temperature oxidation resistance.

However, Ni significantly lowers the Ac ₁ transformation point of the build-up weld metal by its addition. Therefore, when Ni is added to an amount that Ni effectively acts, the Ac ₁ transformation point becomes 70%.
Lowers to around 0 ° C. Therefore, for example, when repeatedly subjected to heating and cooling exceeding 700 ° C., cracks due to structural changes due to transformation, deterioration of mechanical properties, generation of self-transformation stress due to changes in expansion coefficient, etc., that is, heat cracks, and further mixing There is a problem that the high-temperature oxidation resistance is reduced because of the structure.

[0006]

SUMMARY OF THE INVENTION In order to solve these problems, the present invention provides a build-up weld metal having excellent corrosion resistance, abrasion resistance and heat crack resistance at high temperatures, and cracks during build-up welding. It is an object of the present invention to provide a flux for submerged arc welding for use in combination with a strip electrode of 12 to 17% Cr-based stainless steel for submerged arc welding which has no defects and has good workability.

[0007]

SUMMARY OF THE INVENTION The present invention has been completed in order to solve the above-mentioned problems by producing various welding materials on a trial basis, performing performance evaluations, and studying them. In the development of the flux for submerged arc welding according to the present invention,
For heat crack resistance, Ac ₁ transformation point of welding material, 0.2% proof stress, linear expansion coefficient and metal structure, for wear resistance, 0.2% proof stress, hardness and metal structure, for corrosion resistance, Ac ₁ transformation point Based on the knowledge that the alloy composition and the metal structure have a large effect, the Ac ₁ transformation point is high (750 ° C or higher), the 0.2% proof stress at high temperatures, the hardness is high, and the ferrite, The composition of the flux for submerged arc welding was studied with the aim of eliminating the austenite phase.

That is, the present invention relates to a 12-17Cr stainless steel.
Submerged arc welding flash used in combination with electrodes
Mixed with SiO_Two: 15-25%, MgO: 20-35%, CaO
 : 0.5-15%, CaF_Two: 2-10%, Al_TwoO _Three : 10-20%, C
O_Two Ingredient: 0.1-5%, C: 0.3-3
%, Mn: 2-6%, Mo: 0.5-2%, W: 0.5-2%, Nb, V
At least one of the following: 0.2 to 2%, Cu: 1.5 to 3%, Co:
Submer added with 1 to 5% in the form of metal powder or alloy powder
It is a flux for diarc welding.

[0009]

The reasons for limiting the components of the flux for submerged arc welding and the components of the added alloy elements in the present invention will be described below. SiO ₂ : SiO ₂ is indispensable for obtaining good bead appearance and slag releasability, and requires addition of 15% or more. However, if it exceeds 25%, local depressions are formed on the bead surface or solidification cracks are caused. for that reason,
The SiO ₂ content is limited between 15-25%. It should be noted that SiO ₂ may be added as a raw material or may be added as a binder during granulation.

MgO: MgO contributes to arc stabilization, improvement of slag peeling property and prevention of undercut. However, if less than 20%, its effect is small. Become. Therefore, the MgO content was limited to 20-35%. CaO: CaO is formulated in the form of CaCO ₃ as well as in the form of CaO, and contributes to increasing the basicity of slag. But 0.
Addition of less than 5% does not exert these effects. Also 15
%, The melting point of the slag is increased, which may cause formation of a bead. Therefore, the amount of CaO was limited to 0.5 to 15%.

CaF ₂ : Like CaO, CaF ₂ has the effect of increasing the basicity of slag, lowering the melting point of slag, and preventing bead ends from overlapping. However, addition of less than 2% does not achieve these effects. In addition, if the addition exceeds 10%, undercutting occurs, and arc stability is lost. Therefore, the amount of CaF ₂ was limited to 2 to 10%.

Al ₂ O ₃ : Al ₂ O ₃ is effective for adjusting the wave of the bead surface and maintaining the parallelism of the bead toe by adding 10% or more of the bead. Causes localized depressions on the surface and impairs bead appearance. Therefore, Al
_The amount of ₂ O ₃ was limited to 10-20%. CO ₂ component: The CO ₂ component is needed to shield the arc from the atmosphere during welding. However, the addition of less than 0.1% has no effect. On the other hand, if the addition exceeds 5%, turbulence of the molten metal is caused, which causes defects such as slag entrainment. Therefore, the amount of CO ₂
Limited to ~ 5%.

C: C combines with Nb, V, W, etc. to form carbides and has the effect of increasing the strength, and has the effect of improving the hardenability by lowering the Ms point and suppressing δ ferrite. In order to expect this effect, 0.3% or more must be added.On the other hand, if it exceeds 3%, retained austenite tends to be generated due to the balance with Mn, etc., or ferrite is generated due to the balance with Cr, Mo, and Si. Is caused to cause deterioration of heat crack resistance and corrosion resistance, and increase cracking susceptibility. Therefore, the C content was limited to 0.3 to 3%.

Mn: Mn has the effect of increasing hardenability and increasing strength, and requires addition of 2% or more. However, if it exceeds 6%, it causes deterioration of toughness and austenite formation. , Mn amount was limited to 2 to 6%. Mo: Mo forms carbides and increases the high-temperature strength of the build-up weld metal, and has the effect of increasing the hardenability and increasing the strength, similarly to Mn. This effect can be obtained by adding 0.5% or more. However, if the amount exceeds 2%, the effect obtained with respect to the added amount is small and uneconomical, so the Mo content is limited to 0.5 to 2%.

Nb, V: Nb and V form a carbide,
This has the effect of increasing the high-temperature strength of the build-up weld metal. The effect is that Nb and / or V are reduced by 0.2% in Nb + V.
It can be obtained by the above addition, but if it exceeds 2%, the effects such as ferrite formation and toughness degradation will occur.
The amount was limited to 0.2-2%. W: W forms carbide and increases the high-temperature strength of the build-up weld metal by addition of 0.5% or more. However, if it exceeds 2%, the toughness is deteriorated. Therefore, the W content is limited to 0.5 to 2%.

Cu: Cu has a great effect on improving the corrosion resistance of the build-up weld metal, particularly the corrosion resistance to steam at high temperatures, and sufficient corrosion resistance can be obtained by adding 1.5% or more. However, if the addition exceeds 3%, it causes solidification cracking during welding and causes unevenness of the corrosion-resistant oxide film due to segregation of Cu, so the Cu content was limited to 1.5 to 3%. Co: Co has almost the same effect as Ni per addition amount in increasing the high-temperature strength and hardness of the overlay weld metal and improving the corrosion resistance. Addition of both Ni and Co lowers the Ac ₁ transformation point, but the extent is that Co is about half that of Ni, and has the advantage of not impairing the oxidation resistance at high temperatures. Co is high temperature strength,
In order to increase the hardness, it is necessary to add 1% or more,
Addition of more than 5% is uneconomical because the effect does not increase despite the price rise. Therefore, the amount of Co should be 1 ~
Limited to 5%. The Co content of the build-up weld metal is preferably
It is desirable to be within the range of 1.2 to 2.5%.

Note that Mn, Mo, Nb, or V is each
As ferromagnetic iron like FeMn, FeMo, FeNb or FeV,
Further, these elements and C, W, Cu, and Co may also be added as alloy powder. The flux having the above components is
By overlay welding in combination with a 17% Cr-based strip electrode, an overlay weld metal having extremely excellent corrosion resistance, abrasion resistance and heat crack resistance at high temperatures can be obtained. Here,
As a 12-17% Cr stainless steel electrode, for example, JIS SU
SY410 (Cr: 11.50 to 13.50%), SUSY430 (Cr: 15.5%)
(0-17.00%), but the present invention is not limited to this, and the effect obtained by using a wire-shaped electrode as well as a band-shaped electrode does not change.

[0018]

EXAMPLES Overlay welding was performed using the flux shown in Table 1, and the welding workability and the mechanical properties of the overlay weld metal were evaluated. The results are also shown in Table 1.

[0019]

[Table 1]

[0020]

[Table 2]

The welding workability was evaluated mainly for slag peeling and bead shape (parallelism, appearance, presence / absence of defects, etc.). Mechanical properties include high temperature strength (evaluated by 0.2% proof stress at 600 ° C using JIS A2 tensile test specimens taken from overlay weld metal), Ac ₁ transformation point, and high temperature oxidation properties (2 (A test piece having a size of × 20 × 20 mm was exposed to high-temperature steam at 700 ° C. for 96 hours and evaluated by an increase in weight). The evaluation of the mechanical properties was performed only for those having good workability. The ○ mark as a high-temperature strength good 0.2% proof stress 450MPa of 600 ° C., the ○ mark as good or 750 ° C. for Ac ₁ transformation point, the high-temperature oxidation properties ○ mark as well less than 0.20 mg / cm ² Those that deviate from these were marked as bad and marked with a cross.

The test materials and welding conditions were as follows. Base material: JIS S25C (Chemical composition is shown in Table 2. Dimension 50
t × 200 w × 500 l) Electrode used: 13Cr steel hoop material (commercially available KWB-41, dimensions 0.
4 t × 50 w) Welding current: 650 A Welding voltage: 25 V Welding speed: 20 cm / min Preheating: None Between passes: 250 ° C or less Stacking: 3 to 10 layers Multilayer filling SR condition: 650 ° C × 2 hours

[0023]

[Table 3]

As is apparent from Table 1, in Examples 1 to 6, all the weld overlayers exhibit good welding workability, have high high-temperature strength and Ac ₁ transformation point, and have excellent high-temperature oxidation characteristics. was gotten. Table 3 shows the analytical values of the chemical composition of the build-up weld metal in Examples 1 to 6.

[0025]

[Table 4]

On the other hand, in Comparative Examples 7 and 8, the high-temperature strength was low due to the lack of C and Mn, respectively. Comparative example
Conversely, in C9 and C10, solidification cracking occurred at the end of the bead during welding due to excessive amounts of C and Mn. In Comparative Example 11, because of insufficient Mo, the high-temperature strength was insufficient, and the high-temperature oxidation characteristics were also poor. Comparative Example 12 has excellent properties, but has too much Mo, which is economically problematic. In Comparative Examples 13 and 14, W or Nb and V were insufficient, so that the high-temperature strength was low. In Comparative Examples 15 and 16, W and Nb + V were excessive, so that the slag peelability was reduced and small cracks were generated. .

In Comparative Example 17, high-temperature oxidation characteristics deteriorated due to lack of Cu, and in Comparative Example 18, solidification cracking occurred during welding due to excessive Cu. In Comparative Example 19, since the addition of Co was small, the high-temperature strength and the oxidation characteristics were deteriorated. In Comparative Example 20, the characteristics are excellent, but the addition of Co is large and the cost is high, so that adoption is not realistic. In Comparative Examples 21 and 22, where Ni was added instead of Co, the decrease in the Ac ₁ transformation point due to the addition of Ni was large.

[0028] In Comparative Example 23, 25, 26, respectively, SiO ₂ shortage,
Due to MgO deficiency and excessive MgO and CaO, the slag peeling property was reduced, the slag was seized, and the bead appearance was deteriorated. In Comparative Examples 24 and 29, local depressions occurred on the bead surface due to excessive amounts of SiO ₂ and Al ₂ O ₃ , respectively.

In Comparative Examples 27 and 28, CaF ₂ was excessive,
Undercut or occur for al ₂ O ₃ deficiency, parallelism of the bead has fallen defective shape. In Comparative Example 30, CO
_The excess of ₂ minutes caused the bead to be disturbed during welding, causing surface defects or slag entrainment.

[0030]

As described above, according to the present invention, it is possible to obtain a build-up weld metal excellent in strength, wear resistance and corrosion resistance at high temperatures, and to provide a flux with good workability. became. As a result, the performance of a roll used at a high temperature, such as a continuous casting facility, can be improved, the high-speed casting in continuous casting can be supported, and the roll life can be extended.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-56497 (JP, A) JP-A-2-151392 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 35/362

Claims (1)

(57) [Claims] 1. Use in combination with a 12-17Cr stainless steel electrode.
Flux for submerged arc welding_Two: 15-25%, MgO: 20-35%, CaO: 0.5-15%,
CaF_Two: 2-10%, Al_TwoO _Three : 10-20%, CO_Two Ingredients: 0.1 to
 5%, C: 0.3-3%, Mn: 2-6%, Mo: 0.5-2%, W: 0.5-
2%, at least one of Nb and V: 0.2 to 2%, Cu: 1.5
~ 3%, Co: 1 ~ 5%, in the form of metal powder or alloy powder
Flux for submerged arc welding.