A Study on the Fatigue and Fracture Toughness of GCr15Ni5Cu3Nb (15-5PH)
This study aimed to investigate the fatigue and fracture toughness behavior of GCr15Ni5Cu3Nb (15-5PH) steel, a type of martensitic stainless steel, under different loading and temperature conditions. The uniaxial tensile specimens were fabricated from the GCr15Ni5Cu3Nb steel plates and the fatigue tests were then conducted at a constant strain rate of 5x10-3 /s in the temperature range of 20 to 90°C. The investigations revealed that at temperatures of 25°C and higher, the fatigue crack propagated at a stress of approximately 2MPa, with fatigue strength stabilizing at around 3MPa as the temperature increased from 40 to 70°C. The fracture toughness was measured using the SEVNB specimens, and the results showed that the fracture toughness of the GCr15Ni5Cu3Nb steel was highest at 90°C, with a maximum value of 4MPa m1/2.
The formation and propagation of fatigue crack plays an important role in mechanical design and safety assessment of structures. It is known that the resistance to fatigue crack propagation and fracture toughness of GCr15Ni5Cu3Nb steel is closely related to its chemical composition as well as manufacturing process parameters. The fatigue and fracture behavior of the GCr15Ni5Cu3Nb steel under different temperature conditions is essential to understand its behavior during different loading scenarios.
The scanning electron microscope (SEM) was used to analyze the fracture surfaces of the fatigue specimens. It can be seen that the fracture surface at 25°C displays a fibrous nature, which indicates ductile fracture, while the fracture surface at 90°C shows a granular shape, which suggests brittle fracture. It is known that ductile fracture tends to occur in low temperatures, while brittle fracture is more likely at elevated temperatures.
Furthermore, the hardness of GCr15Ni5Cu3Nb steel was also measured under different temperature conditions. The results indicate that the hardness of the GCr15Ni5Cu3Nb steel decreases when the temperature increases from 20 to 90°C, revealing a linear relationship between the hardness and temperature of the GCr15Ni5Cu3Nb steel.
To further understand the mechanical properties of the GCr15Ni5Cu3Nb steel under different loading and temperature conditions, the tensile test was carried out. The tensile test revealed that the yield strength of the GCr15Ni5Cu3Nb steel decreases with increasing temperature from 20 to 90°C, which indicates the weakness of the material at higher temperatures.
The results of the study gave an insight into the fatigue and fracture toughness behavior of GCr15Ni5Cu3Nb (15-5PH) steel. It was found that the fatigue strength of the GCr15Ni5Cu3Nb steel shows an increase with increasing temperature from 40 to 70°C, and the fracture toughness of the steel was highest at 90°C. The hardness and yield strength of the GCr15Ni5Cu3Nb steel were found to decrease with increasing temperature, indicating the reduction in strength of the material when the temperature increases. In addition, the fracture surfaces under different temperature conditions show a different shape, suggesting the change in fracture mode from ductile to brittle. The findings of this investigation may help engineers design better equipments, reducing the failures and improving the safety of the structures made by GCr15Ni5Cu3Nb steel.
