Technical Highlight Vol.13

Submerged arc welding consumables produced exclusively for use with direct current

1. Preface

Submerged Arc Welding (SAW) is one of the principal arc welding processes. It accounts for about 10 % of all arc welding. By country, China consumes more than 50% of SAW consumables and is followed by Europe, North America, Russia and Japan. As for industries, SAW is used primarily in the fabrication of steel pipes, steel structures, bridges, ships and chemical plants due to the long straight welding lines that are common in these structures.

In Japan, the SAW consumption ratio by industry is nearly the same as that for the world except for steel pipe, which accounts for a much lower share of SAW consumption.

Table 1: Types and features of SAW fluxes

Flux type	Notch toughness at low temperature	Moisture absorption resistance	Diffusible hydrogen content	Flux consumption ratio	Efficiency	Kind of electric power
Fused	Average	Best	Low	Average	Average	AC
Bonded	Good	Average	Lowest	Low	Best	AC / DC
Agglomerated	Good	Good	Low	Low	Good	DC

Table 1 shows the characteristics of the three types of SAW fluxes: fused, bonded and agglomerated. In the Japanese market, SAW fluxes suitable for alternating current (AC) have been favored because of the relatively lower cost of AC power sources in comparison with direct current (DC) ones. Bonded fluxes, designed for both AC and DC, were also developed in Japan. However, while these fluxes were mainly used for large heat-input welding, the agglomerated fluxes, applied for general-high speed welding with DC, were in demand in the overseas markets.

To respond to the needs of global markets, Kobe Steel has been pursuing the development of SAW consumables designed for use exclusively with DC and is now pleased to announce the availability of agglomerated flux. Naming its first SAW flux of this type “AF,” Kobe Steel has now officially launched FAMILIARC™ AF-490E and FAMILIARC™ AF-490AS.

This article introduces the benefits and features of using AF-490E in combination with US-29 SAW wire and AF-490AS with US-36.

FAMILIARC™ US-29 FAMILIARC™ AF-490E

Table 2: Description of US-29/AF-490E

Classification	AWS A5.17 F7A2-EM12K; F6P4-EM12K
Features	Butt welding and horizontal fillet welding of medium and heavy plate
	Excellent notch toughness at low temperature down to -20℃
Polarity	DCEP
Boniszewski basicity	1.4
Shipping approval	ABS, DNV, LR, BV

US-29/AF-490E is a solid wire/flux combination for welding mild steels as well as 490 MPa class high tensile strength (HT490 class) steels. AF-490E, an aluminate-basic agglomerated flux, exhibits excellent notch toughness down to -20°C as well as weldability in combination with US-29 SAW wire. Table 2 shows the details of US-29 x AF-490E.

2-1. Properties of all weld metal

The chemistries and mechanical properties of the all weld metal are shown in Tables 3 and 4, respectively, and the bead appearance, in Figure 1. Even without the addition of any special elements, stable notch toughness can be obtained even at temperatures as low as -20°C.

Table 3: Chemical composition of all weld metal (mass %)

	C	Si	Mn	P	S
US-29 / AF-490E	0.05	0.41	1.60	0.016	0.005
Note: Welding conditions: 550A-30V-42cpm; Ext=30mm

Table 4: Mechanical properties of all weld metal

		0.2%OS (MPa)	TS (MPa)	El (%)	IV at -40℃ (J)	IV at -20℃ (J)
US-29/ AF-490E	AW*1	464	562	30	-	Avg 119 (125, 113, 118)
	PWHT (620℃ x 1hr)	380	494	35	Avg 129 (142, 124, 122)	Avg 150 (154, 153, 143)
AWS spec.(AW*1 only)		350 min	490 min	22 min	-	35 min
Note: Welding conditions: 550A-30V-42cpm; Ext=30mm *1: As-welded condition

2-2. Two-run welding of butt joint

Butt joint welding was carried out using JIS G3106 SM400B plates with a maximum thickness of 16 mm. The electrode arrangement is shown in Figure 2 . The welding conditions are shown in Table 5.

Figures 3 and 4 show the macrostructure and the bead appearance, respectively, and Table 6, the mechanical properties of the butt joint weld metal.

Table 5: Welding conditions of two-run welding

Welding sequence	Wire diameter (mm)	Welding conditions	Preheating and interpass temperature
1st	4.0	750A-32V-60cpm Ext 30mm	Room temperature
2nd		700A-32V-55cpm Ext 30mm

Table 6: Mechanical properties of weld metal by two-run welding

0.2%OS (MPa)	TS (MPa)	El (%)	IV at -20℃ (J)	IV at 0℃ (J)
419	532	34	Avg 116 (131, 121, 96)	Avg 147 (148, 146, 146)

2-3. Horizontal fillet welding

The electrode arrangement used in horizontal fillet welding is shown in Figure 5 and the macrostructure and bead appearance, in Figure 6 and 7.

The relationship between welding heat input and leg length is shown in Figure 8, in all available electrode diameters. In laboratory tests, leg lengths from 4 to 9 mm were obtained; however, users are recommended to aim for leg lengths of 6-8 mm, in consideration of groove accuracy as well as the stability of welding at actual work sites.

Table 7: Diffusible hydrogen content

	Diffusible hydrogen content (ml/100g)					Classification of shipping approval
	N=1	N=2	N=3	N=4	Avg
US-29/AF-490E	2.5	2.6	2.7	2.7	2.6	H5
Note: (1) Welding conditions: 550A-30V-42cpm; Ext=30mm (2) Test method: Gas chromatography (as per AWS A4.3)

2-4. Diffusible hydrogen content of weld metal

The diffusible hydrogen content as measured by gas chromatography as per AWS A4.3 is shown in Table 7. One may note the extremely low level of 2.5 ml/100g and almost no fluctuation.

3. FAMILIARC™ US-36 3 FAMILIARC™ AF-490AS

Table 8: Description of US-36/AF-490AS

Classification	AWS A5.17 F7A6-EH14; F7P6-EH14
Features	Butt welding of medium and heavy plate
	Multi-pass welding only
	Excellent notch toughness at low temperature down to -40℃
Polarity	DCEP
Boniszewski basicity	2.6
Shipping approval	ABS, DNV, LR, BV

US-36/AF-490AS is a solid wire/flux combination for welding mild steels as well as HT490 class steels. AF-490AS, a fluoride-basic agglomerated flux, shows superb and stable notch toughness down to -40°C as well as good usability in combination with US-36 SAW wire. Details related to US-36 x AF-490E are shown in Table 8.

3-1. Properties of all weld metal

The chemistries and mechanical properties of the all weld metal are shown in Tables 9 and 10, respectively. Impact test results in the as-welded condition as well as after Postweld Heat Treatment (PWHT) are shown in Figures 9 and 10 by the transition curves, respectively.

Designed for optimum flux basicity, AF-490AS can obtain stable and excellent notch toughness at temperatures as low as -40°C even though no special elements have been added. The bead appearance is shown in Figure 11.

Table 9: Chemical composition of all weld metal (mass %)

	C	Si	Mn	P	S
US-36 / AF-490AS	0.07	0.39	1.62	0.014	0.004
Note: Welding conditions: 550A-30V-42cpm; Ext=30mm

Table 10: Mechanical properties of all weld metal

		0.2%OS (MPa)	TS (MPa)	El (%)
US-36/ AF-490AS	As-welded	516	598	32
	PWHT (620℃ x 1hr)	547	565	32
AWS spec. (As-welded & PWHT)		375 min	490-660	22 min
Note: Welding conditions: 550A-30V-42cpm; Ext=30mm

3-2. Multi pass both side welding of butt joint

Butt joint welding was carried out using EH36 grade plates with a thickness of 20 mm. Figure 12 shows the groove configuration and pass sequence. Table 11 shows the welding conditions, Table 12, the chemistries and Table 13, the mechanical properties of the butt joint obtained via both side welding.

Table 11: Welding conditions

Side	Wire diameter (mm)	Pass	Welding parameters	Extension (mm)
Face	4.0	1	450A-30V-42cpm	30
		2-6	550A-30V-42cpm
Back		1	450A-30V-42cpm
		2-4	550A-30V-42cpm
Note: Preheating & interpass temperature: 100-150°C

Table 13: Mechanical properties of butt joint of both side welding

TS(MPa)	IV at -40C(J)	Bend test *2
559 *1	Avg 84 (81, 87, 83)	Face : Good Reverse : Good
Note: *1: Fractured position=Base metal *2: Bend test: According to Shipping Classification Rule

Table 12: Chemistries of butt joint of both side welding (mass %)

C	Si	Mn	P	S
0.09	0.39	1.55	0.014	0.004

Table 14: Diffusible hydrogen content

	Diffusible hydrogen content (ml/100g)					Classification of shipping approval
	N=1	N=2	N=3	N=4	Avg
US-36/AF-490AS	2.2	2.3	2.1	2.3	2.2	H5
Note: (1) Welding conditions: 550A-30V-42cpm; Ext=30mm (2) Test method: Gas chromatography (as per AWS A4.3)

3-3. Diffusible hydrogen content of weld metal

The diffusible hydrogen content as measured by gas chromatography as per AWS A4.3 is shown in Table 14. The extremely low level of 2.0 ml/100g and little fluctuation is notable.

4. Package specifications

Table 15: Package specifications for new SAW wires

Diameter (mm)	Type	Weight (kg)
1.6	Spool	10, 20
2.0
2.4
2.4	Coil	25
3.2
4.0		25, 75
4.8

The package specifications of US-29 and US-36 SAW wires and the AF-490E and AF-490AS SAW fluxes are shown in Tables 15 and 16, respectively.

Table 16: Package specifications for new SAW flux

Mesh size	Type	Weight (kg)
12 x 65	Bag (Aluminum laminated)	20

5. Redrying condition

Table 17: Redrying condition for new SAW fluxes

	Redrying temperature	Redrying time
AF-490E	300-350℃	1-2 hour(s)
AF-490AS

The redrying condition for AF-490E and AF-490AS are shown in Table 17.

6. Postscript

This article has described Kobe Steel’s two newly-developed agglomerated fluxes: AF-490E and AF-490AS. Used in combination with US-29 or US-36, they feature stable weld metal properties and extremely low diffusible hydrogen content. It is expected that they will be applied to offshore structures as well as shipbuilding, both of which require sound and reliable welded joints.

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