PSI - Issue 13

Valeriy Lepov et al. / Procedia Structural Integrity 13 (2018) 1201–1208 Valeriy Lepov et al/ Structural Integrity Procedia 00 (2018) 000 – 000

1203

3

1. Materials and equipment 1.1. Equipment The mechanical tests, chemical and metallography analysis were conducted, and the following machines, consumables and metals were used for the purpose of conducting the experiments:  Universal Testing Machine (UTM) Z600 Zwick Rowell used for tensile tests  Servo hydraulic machine Instron 8802 used for cycling test  Rockwell scale B hardness tester PMT-1  Metallurgical microscope Neophot-32  Scanning electron microscope (SEM) Hitachi TM3030 Plus Tabletop Microscope with Oxford Instruments Swift ED3000 microanalysis system used for defects revealing microscale  Scanning multimicroscope SMM-2000 in atomic-force mode (ASM) for defects revealing on nanoscale  Spectro analyzer «Spectroport-F» used for chemical composition definition 1.2. Materials The locomotive tires are exposed to influence of various loadings during operation. Material of the wheel of this locomotive element is merged in the complex stress state. So the internal and superficial defects are developed and damage plastic deformation and difficult tension takes place. The chemical composition of examined wheel steel is 0.6% of carbon, 0.33% of silicon, about one percent of manganese and less than two hundredth of phosphorus and sulphur. The tension test for this steel does not a great gulf fixed for mechanical properties (as yielding, breaking point, and tensile strain) at room and low temperature, but the impact toughness test reveals the ductile-brittle transition in steel (see table 1). The wheel steel structure has ferrite and pearlite mainly.

Table 1. Results of tension and impact toughness tests T,  C  Y , MPa  B , MPa  , %

KCV, J/cm 2

20

690,2 - 755,7

1037,2 - 1066,7

10,28 - 8,63

1,82 1,36 - 0,73 0,62

-20 -40 -50 -60

- -

- -

- -

Also the mechanical properties and microstructure of welded low-carbon steel St3sp probes have been studied. Arc welding includes 30 run for every probe, and a total of four different beads were achieved, such as the root run, hot pass, the filling and the capping. This welding was done on the both side of the material. All the necessary cares were taken to avoid the joint distortion and the joints were made with applying clamping fixtures. The specimens for testing were sectioned to the required sizes. The chemical composition of steel St3sp is 0.18 percent of carbon, 0.23 percent of silicon and about 0.4 percent of manganese. On Fig.1 the SEM microstructure images of locomotive tire probe surface near the impact fatigue crack at different magnification have been shown. The images analysis confirm the prospect mechanism of strain hardening crazing and impact multiply contact fractures on the tire surfaces. On Fig.1 (g-h) the face of crack and strain hardening impact fatigue peeling ply of steel have been presented. It is possible to estimate the crack size and crazing distribution also, - from 50 to 150  m with distance about 70-100  m. The result of chemical elements distribution around the crack was obtained by energy dispersion analysis by Hitachi TM-3030 attachment and has been presented on Fig.2. It is shown the segregation of impurities and admissions around the free surfaces. So the possible crack formation mechanism is the chain of non-metallic inclusions (mainly Al2O3). Also the chromium and oxygen have been presented. Last one indicate the considerable surface oxidation. 2. Microstructure study