PSI - Issue 5

Valeriy Lepov et al. / Procedia Structural Integrity 5 (2017) 777–784 Valeriy Lepov et al / Structural Integrity Procedia 00 (2017) 000 – 000

780

4

Table 3 shows the average values of chemical elements in welded steel probes.

Table 1. Results of standard tensile test T,  C  T , MPa  B , MPa

 , %

20

690,16 755,74

1037,2 1066,67

10,28

-50

8,63

Table 2. Results of test for impact toughness KCV T,  C 20 -20 -40

-60

2,29 1,75 1,69 1,72 1,64 1,82

0,70 0,58 0,74 0,51 0,67 0,62

1,33 1,37 1,38

0,71 0,54 0,96

KCV, J/cm2

Average

1,36

0,73

Table 3. Result of chemical analysis of material, %

Fe

C

Si

Mn

P

S

Cr

Mo

Ni

Al

Co

Cu .04

Nb

Ti

V

Zr

As

98.9

.183

.236

.397

.004

.32

.029

.011

.034

.046

.006

.002

.002

.002

.002

.005

Analysis of the microstructure of the base metal, weld metal and heat affected zone of the sample numbered by 7 was performed using metallographic optical microscope. Composition of pearlite and ferrite was seen with the print of the indenter of the micro hardness test. The formation of pearlite and ferrite in base metal is composed of 20/80 respectively. For weld zone and HAZ it changes due to thermal processes. So the microstructure analysis shows that the base metal is a ferrite and pearlite having a grain size of 11-12 on a scale corresponding to an average grain diameter ≈ 7 microns (see Fig . 2c). The structure of the weld metal is also made up of ferrite and pearlite (see Fig. 2a) with columnar crystals of cast metal. The HAZ is made up of Widmanstätten figures (see Fig. 2b). The width of the HAZ zone is about 1,5 mm. In different areas of heat affected zone is observed fine-grained ferrite-pearlite structure with a high degree of dispersion [9]. Fig. 2b shows a micro crack with the length 1,7 mm in the HAZ of sample number 7. In the weld zone of this probe 1,2 mm length micro crack was revealed also.

50 mkm

50 mkm

50 mkm

A

B C Fig. 2. (a) Microstructure of the weld; (b) HAZ and (c) base metal in the probe, ×250.

The un-notched smooth tensile specimens were prepared to evaluate transverse tensile properties of the joints such as tensile strength and yield strength (see Table 4). One result was removed due to very low strength. Also the un-notched smooth cyclic loading specimens were prepared to evaluate fatigue properties under low cyclic loading. Two points were obtainable from the tensile test results like the average tensile loading Rm and the average