Effects of heat treatment and testing temperature on fracture mechanics behavior of low-Si CA-15 stainless steel

This research studied the effects of heat treatment and testing temperature on fracture mechanics behavior of Si-modified CA-15 martensitic stainless steel (MSS), which is similar to AISI 403 grade stainless steel, which has been widely used in wall and blanket structures and in the pipe of nuclear power plant reactors, turbine blades, and nozzles. The results indicated that fracture toughness of low-Si CA-15 MSS is better than that of AISI 403. The specimens of the low-Si CA-15 MSS after austenitization at 1010 degreesC and then tempering at 300 degreesC have higher plane-strain fracture toughness (K-IC) values for both 25 degreesC and - 150 degreesC testing temperatures. However, the specimens tested at 150 degreesC cannot satisfy the plane-strain fracture toughness criteria. The fatigue crack growth rate is the slowest after austenitization at 1010 degreesC for 2 hours and tempering at 400 degreesC. Observing the crack propagation paths using a metallographic test, it was found that the cracking paths preferred orientation and branched along ferrite phase, owing to martensite-phase strengthening and grain-boundary-carbide retarding after 300 degreesC to 400 degreesC tempering. Also, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction analysis were performed to correlate the properties attained to the microstrucrural observation.