Journal
METALS
Volume 11, Issue 1, Pages -Publisher
MDPI
DOI: 10.3390/met11010133
Keywords
34CrMo4; cold flow forming; hot drawing; fatigue crack growth
Funding
- National Natural Science Foundation of China [51605435]
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The fatigue crack growth behavior of 34CrMo4 steel was studied, revealing that hot-drawn and cold-flow materials exhibit better resistance to fatigue crack propagation than the base material. The FCG rates of the materials increase with higher stress ratios, while the sampling direction has little effect on the FCG rate.
The fatigue crack growth (FCG) behavior of 34CrMo4 steel, a typical material for gas cylinders, has been investigated. Specimens were taken from the base material (BM) as well as the hot-drawn (HD) cylinder and cold-flow (CF) formed cylinder along the longitudinal and transverse directions. The FCG tests were conducted under different stress ratios for different materials and directions. The main purpose of this research was to explore the influences of the mechanical and thermal processes, sampling direction and stress ratio on the FCG behavior of 34CrMo4 steel. To further reveal the mechanism of crack propagation at different stages, the microstructures and fracture modes of FCG specimens were analyzed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), respectively. The results showed that HD and CF materials exhibited better resistance to fatigue crack propagation than BM. The FCG rates of investigated materials can be accelerated by the increase in stress ratio. However, the sampling direction had little effect on the FCG rate. Finally, a driving force parameter (DFP) model was used to fit the experimental FCG data of three materials with different mechanical and thermal processes. A unified transition stage between the stable and unstable FCG stages of three materials under various experimental conditions was revealed by DFP model, playing an important role on the early warning of fatigue fracture for different types of 34CrMo4 steel.
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