PSI - Issue 13

Primož Štefane et al. / Procedia Structural Integrity 13 (2018) 1895 – 1900 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

1897

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2. Experimental tests 2.1. Welded joint configuration and material properties

High strength low alloyed (HSLA) steel S690 QL was selected as base material. Sample plates with 25 mm thickness, 500 mm length and 200 mm width, were joined by metal active gas (MAG) welding. Plate edges were machined to a double V-groove with a bevel angle of 60° and a root gap of 2 mm. Following weld consumables were applied in order to produce welded joints in half OM and half UM, complete OM and complete UM configurations: i) Mn4Ni2CrMO with commercial designation MIG 90 and ii) Si1 with commercial designation VAC 65. The former was applied to obtain OM weld material with mismatch factor M=1.31 while the latter was applied to obtain UM weld material with mismatch factor M=0.74. Mismatch factors were obtained through tensile testing of base and weld materials. Two kinds of tensile tests were conducted: i) standard tests in conformance with ASTM E8/E8M and ii) tests of miniature (i.e. sub-sized) tensile specimens (MTS). In case of the former, standard specimens with neck diameter D=6 mm and gauge length G=5×D=30 mm were extracted from base material and from UM and OM weld material. However, it is important to emphasize that all weld metal tensile test specimens were extracted from additional welded plates with a weld joint configuration according to ISO 15792-1 (2000) which is commonly used for all-weld metal tensile testing (AWMTT). Results of AWMTT represent average mechanical properties of multiple microstructures which are present in the welded material due to complex thermal history of the welding process. In order to characterize material properties of individual microstructures, sub-sized MTS with neck width 2 mm, thickness 0.5 mm and gauge length 8 mm were used in a similar way as in research conducted by Hertelé et al. (2016). All tensile tests were conducted in crosshead displacement control with loading rate 0.2 mm/min. Elongation was measured with extensometer in case of standard tensile specimens and with optical 3D digital image correlation (DIC) in case of MTS. This way, strain patterns on the surface of the MTS, were recorded as well. Obtained results are presented in form of characteristic values and as engineering stress-strain curves on Fig. 1.

M (-)

R m (MPa)

Material configuration

Chart code

E (GPa)

R p0,2 (MPa)

OM** UM** BM**

215 210 201 208 200 202 200 206 228 194

894 503 683 754 750 447 487 864 812 642

950 587 791 851 976 633 595 968

1.31 0.74

1

OM – As welded* OM – Reheated* UM – As welded* UM – Reheated*

1.10 1.10 0.65 0.71 1.27 1.19 0.94

HAZ – Coarse grained* HAZ – Fine grained*

1183

BM*

772

* - Obtained by MTS tensile tests ** - Obtained by AWMTT of standard ASTM E8M specimens

Figure 1 Mechanical properties obtained by tensile testing of standardised specimens and MTS.

2.2. Fracture testing of welded joints A single specimen method was used for fracture testing of single edge notched bend (SE(B)) specimens according to ASTM E1820 standard. Two sets of SE(B) specimens were extracted from welded sample plates with half UM and half OM welded joint configuration: i) with the notch positioned in OM weld material and ii) in UM weld material. Three additional sets of SE(B) specimens were extracted from welded sample plates for reference fracture tests of BM, complete UM weld configuration and complete OM weld configuration. The overview of extracted SE(B) specimens is given in table 1.