Institution of Higher EducationPrydniprovs'ka State Academy of Civil Engineering and Architecture

Kseniia Salangina832-AMS group

THE INVESTIGATION OF KINETICS OF FRACTURE OF HSLA X70 STEEL WITH DIFFERENT STRUCTURE

Scientific Supervisors: Ph.D. O. Beketov

Ph.D. D. Laukhin

English Supervisor: E. Kuznetsova

Purpose:to investigate the kinetics of fracture of HSLA X70 steel in different conditions, namely: in the cold water, boiling water, oil and in the air.

Object:the low-carbon low-alloyed HSLA X70 steel micro-alloyed with niobium and vanadium. Sheets of HSLA X70 steel 18,7mm thick (for the experimental part).

Topicality:reduction of steel intensity of construction iron due to the utilization of HSLA X70 steel with a high level of running ability.

Methods of research:investigations, analysis and photos of samples were made with thehelp of Scanning Electron Microscope SEM-160I. To research thesamples structure a metallographic microscope NEOPHOT-2 was used.

BRITTLE FRACTURE DUCTILE FRACTURE

Fig.1. Schematic presentation of three characteristic features of quasi-cleavage.

Fig.2. Three main types of void coalescence:a) it occurs under the action of plastic deformation in direction of applied stresses;b) It is under the action of both the influence of plastic deformation in direction of applied load and the shear stresses in the area of maximum shear stresses;c) It is under the action of uneven plastic deformation in active direction of applied load.

X70 STEEL AFTER THE CONTROL ROLLING AND HEAT TREATMENT

Fig. 3. The microstructure of steel after cooling in the air.

Fig. 4. The microstructure of steel after cooling in the boiling water.

Fig. 5. The microstructure of steelafter cooling in the oil.

Fig. 6. The microstructure of steel after cooling in the cold water.

Fig. 8. After cooling in boiling water.

Fig. 9. After cooling in the oil. Fig.10. After cooling in cold water.

Fig. 7. After cooling in the air.

THE MICROSTRUCTURE OF FRACTURE OF HSLA X70 STEEL

FRACTURE INVESTIGATION RESULTSFracture after cooling in the air: – ductile fracture; – microvoid coalescence; – pearlite colonies have features of brittle fracture.

Fracture after cooling in the boiling water: – ductile fracture; – microvoid coalescence; – cleavage facets.

Fracture after cooling in the oil: – microvoid coalescence; – equiaxed pits.

Fracture after cooling in the cold water: – ductile fracture; – elements of brittle fracture; – martensite and bainite colonies; – quasi-cleavage; – screw dislocations.

EFFICIENCY

After checking up and analyzing of finding of the received calculations, we can make a conclusion, that substitution of elements of reinforcing cage for HSLA X70 steel is an economically sound procedure. It shows a general tendency of cost-effectiveness of high-strength steels of HSLA X70 type application and both utilization and production of construction iron of high-duty benefits from it.

Utilization of HSLA X70 steel is economical and actual nowadays because it reduces the steel intensity of construction iron due to the high level of running ability.

THANK FOR YOUR ATTENTION!