PSI - Issue 72

Aleksandra Krstevska et al. / Procedia Structural Integrity 72 (2025) 172–180

176

5. Research methodology In this paper thick pipes 32x5 mm are investigated between X10CrMoVNb9-1 martensitic steel and 12X18H12T austenitic stainless steel. As additional material is used nickel-alloy NiCr20Mn3Nb according to EN ISO 18274 (Thermanit Nicro 82). The preparation of the base materials X10CrMoVNb9-1 is shown in Table 1.

Table 1 Preparation of base material X10CrMoVNb9-1

No. of specimen

Preheating

PWHT

Specimen 1 Specimen 2 Specimen 3 Specimen 4

250°C 250°C 250°C 250°C

/ /

760°C 760°C

The martensitic base material involves buttering in one end with the chosen nickel base filler material. In all specimens a preheating was used during buttering the steel, on 250°C. After the buttering the martensitic steel was welded with the austenitic stainless steel with or without PWHT using GTAW welding process. The research methodology will include mechanical testing, static tensile test and hardness measurement. The tensile testing was designed at room temperature using Instron 600LX static tensile testing machine, according to EN ISO 4136:2022 (International Organization for Standardization: ISO 4136:2022, 2022) and EN ISO 6892-1 (International Organization for Standardization: ISО 6892 -1, 2016). The hardness measurement was conducted according to Vickers method, using hardness testing machine, according to EN ISO 6507-1 (International Organization for Standardization: ISO6507-1, 1997) and EN ISO 9015-1 (International Organization for Standardization: ISO 9015-1, 2001). Samples are made from welded pipes according to EN ISO 15614 (International Organization for Standardization, 2017). The standard defines the procedure and locations for samples intended for a certain type of mechanical testing providing insight into the welded joint characteristics. Microstructural testing is part of the research methodology, where an investigation of microstructure was conducted on the specimens according to EN ISO 17639:2013 [6]. Due to the different structures of base materials and the weld metal, different reagents are used for disclosure of the microstructure. For X10CrMoVNb9-1 was used Nital and for the 12X18H12T and weld metal is used aqua regia, mixture of nitric acid and hydrochloric acid. 6. Experimental results and discussion 6.1. Tensile test The test was conducted on ambient temperature, 20°C, requiring minimal value of ultimate tensile strength of the base material with a lower tensile strength for dissimilar metal welds. The weaker parent material for the dissimilar metal joint which is subject of this research paper is the austenitic stainless steel. The results are presented in Table 2.

Table 2 Tensile test results

No. of specimen

Preheating

PWHT R p 0.2 [MPa]

R m [MPa]

ε [%]

Fracture

Specimen 1 Specimen 2 Specimen 3 Specimen 4

250°C 250°C 250°C 250°C

/ /

326 305

544 589 617 653

11.4286 31.4286 24.2857

WM BM2 BM2 BM2

760°C 284 760°C 285

42.85

The obtained values meet the acceptance criteria and the place of fracture is the BM2 as shown in Figure 4 exception is specimen 1 where the place of fracture was the weld metal, Figure 5. The results indicate that the critical side of fracture is the side of austenitic base material. The specimen 1 fracture in the weld metal and is an example of failed welding technology.