Microstructure and Mechanical Behavior in Dissimilar SAF 2205/API X52 Welded Pipes

doi:10.1007/s40195-016-0428-8

Abstract

Abstract:

The welding of a duplex stainless steel SAF 2205 DSS (UNS 31803) and high strength low alloy steel API X52 by shielded metal arc welding process was conducted using two different filler metals, the duplex E2209 and austenitic E309 grade. The microstructures of the dissimilar metal joints have been investigated by optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy (EDS) and X-ray diffraction. EDS analysis at the interface X52 weld metal showed an evident gradient variation of Cr and Ni between boundaries of fusion and type II, where the highest hardness value was recorded. Tensile strength and toughness values of the weld metal produced by E309 electrode are slightly higher than those of the weld metal produced by E2209 electrode. Potentiodynamic polarization tests of different regions of the welded joints evaluated in 3.5% NaCl solution exhibit a high corrosion resistance of both weld metals.

Key words: Dissimilar metals welding, 2205 duplex stainless steel, API X52 HSLA steel, Heat-affected zone, Mechanical properties

Brahim Belkessa, Djamel Miroud, Naima Ouali, Billel Cheniti. Microstructure and Mechanical Behavior in Dissimilar SAF 2205/API X52 Welded Pipes[J]. Acta Metallurgica Sinica (English Letters), 2016, 29(7): 674-682.

Figures/Tables 17

Table 1 Chemical composition of the base and weld metals (wt%)

Element	C	Mn	Si	P	S	Cr	Ni	Mo	N	Fe
Base metals
UNS 31830	0.029	1.7	0.46	0.02	0.012	21.58	5.27	2.96	0.2	Balance
API X-52	0.14	1.2	0.24	0.017	0.005	0.058	0.041	0.014	-	Balance
Weld metals
E2209	0.03	1.0	0.90	0.026	0.02	21.8	6.8	3.1	0.15	Balance
E309	0.04	1.4	0.56	0.03	0.02	19.9	9.8	0.8	-	Balance

Fig. 1 a Single V groove welded joint, b macrosection of dissimilar welded joint

Table 2 Welding parameters

Welding process	Filler metals	Welding voltage (V)	Welding current (A)	Electrode diameter (mm)	Welding speed (mm/min)	Flow rate (l/min)
SMAW	E2209 E309	22-28	80-110	2.5	70-90	10-12

Fig. 2 Optical micrograph of DSS: a base metal, b HAZ

Fig. 3 Optical micrograph of X52 steel: a base metal, b HAZ

Fig. 4 Optical micrograph of weld metals: a E2209 WM, b E309 WM

Fig. 5 Microstructure of X52 steel/E309 weld metal interface

Fig. 6 X-rays diffractograms of DSS base metal and both weld metals

Fig. 7 EDS line scanning across the X52 steel/E309 weld metal interface

Table 3 Tensile properties of the weld metals

Material	Tensile strength (MPa)	Elongation (%)	Failure location
2205 DSS base metal	768.15	35.81	-
API X52 base metal	673.27	19.36	-
E2209 weld metal	652.76	17.72	X52 steel base metal
E309 weld metal	669.59	18.64	X52 steel base metal

Fig. 8 Evolution of hardness in the dissimilar welded joints

Fig. 9 Microhardness profiles at the X52 steel/weld metals interface

Fig. 10 Charpy impact test values of dissimilar weld metals

Fig. 11 SEM micrograph of the fractured impact test specimens: a DSS BM, b DSS HAZ, c X52 BM, d X52 HAZ, e E309 WM, f E2209 WM

Fig. 12 Potentiodynamic polarization curves of DSS and X52 steel base metal and HAZ in 3.5% NaCl solution at room temperature

Fig. 13 Potentiodynamic polarization curves of weld metals in 3.5% NaCl solution at room temperature

Table 4 Electrochemical corrosion parameters obtained from potentiodynamic polarization curves of various specimens in 3.5% NaCl solution at room temperature

Sample	DSS BM	DSS HAZ	X52 BM	X52 HAZ	E2209 WM	E309 WM
E_corr (mV)	-339.85	-357.50	-632.34	-708.42	-430.48	-341.42
I_corr (µA)	0.284	0.292	6.860	3.370	0.367	0.226

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