Strain Aging Behavior of F40 Ship Plate Steel
F40 ship plate steel after strain aging and the internal friction behavior during the aging process were studied by SEM , TEM and multifunctional internal friction instrument The structure is very stable; an internal friction peak appears at 230 °C on the internal friction temperature curve , which is caused by the free carbon atoms pinning dislocations and getting rid of dislocation pinning under this condition ; the dislocation configuration The macroscopic effect of the change and the interaction between dislocations and carbon atoms shows that the hardness increases , the toughness decreases , and the ductile-brittle transition temperature increases after strain aging .
Key words ship plate steel ; strain aging ; microstructure ; internal friction behavior
During the hull construction process , the hull steel plate is subject to cold working plastic deformation including cold straightening , roll bending , molding , curling and hemming bending . During the cold working process, the strength of the steel plate will increase due to the strain aging . Decreased plasticity and toughness ; for C - M n- type steel , during accelerated aging , for every 1 % increase in work hardening , the ductile-brittle transition temperature of the steel will increase by 5 CE. Therefore, the classification society's inspection of the strain aging performance is the An indispensable item in steel certification . In order to ensure the performance stability and safety of the steel plate during use , it is necessary to study the strain aging behavior of the steel plate . In this paper, the strain aging sensitivity of F40 ship plate steel is determined and the microscopic mechanism of strain aging behavior is discussed by studying the changes of hardness, low temperature impact energy and ductile-brittle transition temperature of F40 ship plate steel during strain aging .
1 Experimental materials and scheme
1.1 Experimental materials
F40 ship plate steel ( slab number 7409157) produced by Hunan Iron and Steel Wide and Heavy Plate Factory . The chemical composition ( mass fraction , %) of the tundish is: C 009, Si 030, Mn 1-40, p 0.010 , S 0-004, Al 0.035, Nb 0.030, Ni 0.35. The production process of F40 ship plate steel is: CR (controlled rolling), the thickness of the finished product is 40 mm , the thickness of the slab is 260 mm , the thickness of the intermediate slab is 120 mm , the pass reduction rate of the last 3 passes in the non-recrystallized area is >15% , and the final rolling temperature is 760 C. The performance test results are : ReL 495 MPa , R m = 615MPa, A =23.5%, -60°C impact energy 166J, -80°C impact energy 128J , cold bending is qualified, and the mechanical properties meet the classification society's requirements for F40 ship plate steel specification requirements .
12 experimental protocol
A transverse tensile sample of 12 mm X 12 mm X 200 mm was taken from the 1/4 part of the steel plate with a slab number of 7409157 , and the gauge length was 120 mm. It was pre-strained at 10% on the mechanical tensile testing machine of Beijing University of Science and Technology , and then Insulate in a heating furnace at 250C for 1h, then air-cool to room temperature . According to the national standard metal Charpy notched impact test method GB / T18658-2002 , standard impact samples were taken , and the test temperatures were 0 , -20 , -40 , -60 , -80 C respectively . Impact energy comparison to determine the strain aging sensitivity coefficient .
The internal friction sample was cut from the 10% pre-strained sample with a size of 70 mm X 2 mm X (0.5~1.0) mm , and the surface was polished with sandpaper and then cleaned with acetone . The internal friction measurement is carried out on the multifunctional internal friction instrument of the Institute of Solid State Physics, Chinese Academy of Sciences. The vibration mode adopts the free decay mode , and the heating rate is 4 K · min —1 , The strain amplitude is 1X10 -5 .
The steel plate tissue sample is polished and corroded with 4% nitric acid alcohol for SEM observation . The transmission electron microscope sample uses 5% perchloric acid anhydrous ethanol solution as the electrolyte , and it is used for electrolytic double-spray thinning to perforation at -20C , 50V The electron microscope is H-800 and the working voltage is 175kV .
Experimental conclusion of F40 ship plate steel
- After strain aging treatment , the hardness of F40 ship plate steel increases, the impact toughness decreases, and the ductile-brittle transition temperature increases. The sensitivity coefficient of strain aging at -60 C is 35.4 % .
- After strain aging treatment , the microstructure of F40 ship plate steel did not change significantly, and the structure stability was good .
- Nitrogen exists in a combined state and has no effect on the strain aging properties of the steel plate. The internal friction peak of the 40 ship plate steel at 230 C is due to the interaction between carbon atoms and dislocations .
Conatct us
