African Fusion June 2016

Impact toughness A kv (joules)

Strength (MPA) and elongation (%)

-20 °C -40 °C Yield: σ s

Tensile: σ b

Elongation: σ 5

S890QL

40 50

942 890

988 950

15.0 15.0

UNION X 90

90

Table 2: Mechanical properties of the base metal and welding wire.

Speed: ν (cm/min)

Groove width (mm)

Current: I (A)

Voltage: U (V)

Heat input: Q (kJ/cm)

Cooling time: t 8/5 (s)

10 11 12 13

21 19 17 16

220 213 213 217

25.8 26.1 25.9 25.7

16.2 7.3/13.1* 17.6 7.8/13.6* 19.4 8.7/15.3* 20.9 10.1/15.5*

Table 3: Welding parameters (* indicates min/max measured values).

Groove width (mm)

Yield strength σ s (MPa)

Tensile Strength σ b (MPa)

Elongation A (%)

10 11 12 13

934.0 931.6 928.1 925.5

979.1 977.7 975.3 972.1

19.5 20.7 17.8 20.7

Table 4: Tensile test results of the weld joint.

Figure 2: Macrostructure and hardness distribution of the weld joint.

Groove width (mm)

Sample region

Yield strength σ s (MPa)

Tensile Strength σ b (MPa)

Elongation A (%)

10 11 12 13

Upper Lower Upper Lower

875.7 981.5 971.6

1090.2 1055.6 1120.5 1060.2

19.5 20.7 17.8 20.7

1001.0

Table 5: Tensile test results of the weld metal.

test results are 32 J, 33 J and 34 J, respectively. The average value is more than 30 J. The toughness result from the weld performed at the lowest heat input can still meet the require- ment for the Dillimax 890QL steel and DIN EN 10137-2. The hardness distribution at the welded joint Figure 2 shows the macrostructure and hardness distribution of the welded joint. The hardness of the weld metal is higher than that of HAZ and the lowest hardness is located in theHAZ, as shown in Figure 2b. Discussion The mechanical properties of the weld joint meet the EN 10025 S890QL steel T he European structural steel specification EN 10025 includes a range of high strength quenched and tempered steel grades withinSection6and thedesignationS890QLgives the composition andmechanical requirements for the steel gradewith aminimum yield strength of 890 MPa. While this steel is over three times the strength of a basic S275 structural steel, it is relatively easy to weld and fabricate and is becoming increasingly popular with engineers and designers looking to exploit its strength-to-weight ratio. S890 steel is used in applications such as cranes, aerial plat- forms, load handling equipment, bridges, and special containers.

Figure 3: The heating cycles measured at Weld pass 5 during welding.

The Charpy-V test results of theweldmetal at the centre and in the HAZ with groove width of 11 mm at -40 °C were measured at 56 J and 86 J, respectively, while at -20°C, values of 64 J and 97 J were recorded. The toughness in the HAZ is better than that of the weld metal. Three specimens from the weld joint with a groove widthof 10mmwere also testedat -40 °C. These threeCharpy-V

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June 2016

AFRICAN FUSION