PSI - Issue 30

M.M. Kantor et al. / Procedia Structural Integrity 30 (2020) 45–52 M. М . Kantor et al. / Structural Integrity Procedia 00 (2020) 000–000

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2. Material and methods Commercial low carbon microalloyed steel sheet subjected to the controlled rolling and rapid cooling treatments was selected as an object of the investigation. Chemical composition, tensile test results and impact toughness test results are represented in Table 1 and Table 2.

Table 1. Chemical composition. Element С Si

Mn

P

S

Cr

Ni

Cu

Al

Ti

Mo

Nb

V

ω , %

0,04

0,23

1,88

0,015

0,004

0,052

0,27

0,284

0,030

0,02

0,192

0,025

<0,005

Table 2. Tensile tests results and impact toughness tests results.

σ 0,5 / σ u , not more

Document

σ 0,5 , MPa

δ , %, not less

CVN, J, not less

σ u , MPa

Requirements of ISO 3183 Quality certificate

555 ‐ 705

625 ‐ 825

0,93

10 ‐ 13

54

632

692

0,91

21

358

The steel characteristics met all the requirements for X80 strength level. For the characterization of toughness scattering in DBT region, multiple impact fracture tests with potential energy of 750 J were carried out using a Roell Amsler RKP750 (Zwick/Roell) pendulum impact test machine. At least 40 U-notch pendulum standard test specimens 55x10x10 mm were examined at 0° С , -20° С , -40° С and at least 20 at 20° С , -60° С , -80° С , -100° С . U notched standard test specimens were selected to emphasize the very phenomenon of impact toughness scattering, due to higher sensitivity to the local microstructure variations, by Shtremel (2008). A character of fracture surfaces for specimens was assessed using macro photography system consisting of rack, Canon EOS 6D equipped with Canon mp-e 65mm f/2.8 1-5x macro photo lens and commercially available image processing software. For the characterization of microcracks the specimens showing low impact toughness values at -60°C were selected. Each specimen was sectioned according to the preparation scheme, Fig.1.

Fig. 1. Specimen preparation scheme.

Procedures for mounting, grinding and polishing of metallographic specimens were standard. For the reduction of damaged surface layer, it was used 10 minutes forceless polishing with colloidal silica suspension 0,05 µm at last polishing stage.