PSI - Issue 68

3

D. Tomerlin et al./ Structural Integrity Procedia 00 (2025) 000–000

D. Tomerlin et al. / Procedia Structural Integrity 68 (2025) 1237–1244

1239

2. Materials and methods 2.1. HSS material

The material investigated in this study is a High Strength Steel (HSS) S690QL grade (2022), used for various demanding structural applications. It is manufactured using the Quenching and Tempering (QT) process, with fine grained microstructure. It presents a yield strength of R p0.2 ≥ 700 MPa and a tensile strength R m between 770 and 940 MPa. In this work was used 10 mm thick plate supplied in hot rolled condition, according to EN 10025-6 (2004) standard. Gleeble test specimens were extracted by waterjet cutting. According to EN 1011-2 (2001) for S690QL grade, the optimal Δ t 8/5 cooling time to achieve quality mechanical properties is in the range of 10-20 s, while the acceptable Δ t 8/5 cooling time is in the range of 5-25 s. 2.2. Gleeble thermo-mechanical simulations In order to solve the previously mentioned problem of conventional mechanical testing of welded samples, and their characteristic HAZ regions having small material volume, a different approach is required. In this research, the authors have used Gleeble ® 3800 (Dynamic System Inc., USA) thermo-mechanical simulator. The thermo mechanical simulations are used for research of material behavior during welding. The Gleeble thermo-mechanical simulations, are able to successfully reproduce thermal history (e.g. welding thermal cycle) and subsequently characteristic HAZ microstructures, in a sufficiently large volume, having homogeneous material properties, that can later be tested using the conventional specimens for tensile and fracture mechanics investigations. Two consecutive thermal cycles recreate the conditions of the two-pass welding process, with peak temperatures relevant to specific HAZ microstructures as shown in Fig 1. Δ t 8/5 cooling times in the range from 8 to 20 s are obtained for all thermally treated specimens. The 1 st thermal cycle reached the peak temperature of 1250 °C for all specimens, while the 2 nd cycles reached the peak temperatures of 590 °C (Spec. 2 and 2C), 740 °C (Spec. 3 and 3C), 890 °C (Spec. 4 and 4C) and 1250 °C (Spec. 5 and 5C), as shown in Table 1. Two different tests were carried out: a series with free longitudinal displacement to simulate free shrinkage of metal during cooling and a series with constrained displacement during cooling in the 2 nd thermal cycle to simulate constrained shrinkage, Table 1. The specimens are waterjet cut from 10 mm S690QL plate in the form of 10x10 mm square section bars. Two different specimen types are used: 10x10x110 mm bars for unconstrained testing and 10x10x130 mm with M10 threaded ends for 2 nd cycle constrained testing.

Table 1. Gleeble experiment matrix

1 st cycle

2 nd cycle

microstructure

Specimen

constrained

T max [°C]

constrained

T max [°C]

1 2 3 4 5

Free Free Free Free Free Free Free Free Free

1250 1250 1250 1250 1250 1250 1250 1250 1250

Free Free Free Free Free

-

-

Ac1>T (590)

A (SC CGHAZ) B (IC CGHAZ)

Ac1

Ac3

C (FGHAZ) D (CGHAZ)

1250

2C 3C 4C 5C

Constrained Constrained Constrained Constrained

Ac1>T (590)

A (SC CGHAZ) B (IC CGHAZ)

Ac1

Ac3

C (FGHAZ) D (CGHAZ)

1250