Hideo Yara

Fatigue Characteristics of Partially Thermal Sprayed Materials under Corrosive Environment

In order to investigate the corrosion fatigue characteristics of the coated structure materials, the rotating bending fatigue tests were conducted for carbon steel specimen with Zn, Al and paint coated layer partially under accelerated corrosive environment cycled of salt water spraying, drying with warm air and holding at room temperature.This report shows the mechanical and metallurgical properties of the coated specimens with Zn, Al and paint after corrosion fatigue tests.The results are as follows:(1) In the thermal sprayed and painted specimens, the fatigue limit under corrosive environment is the same as that of the blasted specimen tested in air.(2) The specimens partially sprayed with axial and circular direction had the almost same fatigue limit as the sprayed specimens under corrosive environment.(3) In the macrostructure of the fatigue fracture surface, the crack propagation have been observed on the specimen non-sprayed circular direction. Furthermore, the micrography of the fatigue fracture surface shows mainly dimple and striation-like pattern.

Joining between Stainless Steel and Carbon Steel with Thermal Spray Coating of Ni Based Self-Fluxing Alloy. Study on Flame Spraying (Report 5)

The joining between stainless steel (SUS304) and carbon steel (SS400) was carried out using thermal spray coating of nickel based self-fluxing alloy under atmospheric conditions for basic data. The size of joining specimen is 50 mm in length and 10 mm in diameter. After the each edged surface of SUS304 and SS400 specimens were blasted by used steel grid material sized No. 70, those were sprayed with self-fluxing alloy (S.F.A.) at the each surface of both specimens coated about 100μm in thickness.The effects of joining conditions on the structure and strength of joining were studied.The results are summarized as follows:(1) The maximum tensile strength at the joint part using R notch specimen was about 579 MPa under condition of 30 sec raising time and 60 sec holding time at 1373 K temperature.(2) The hardness gradient was not observed near the joining zone in the Vickers hardness distribution of the both materials. Furthermore, the Vickers hardness distribution near the joining zone of SUS304 was about Hv120, that was lower than base metal because of the annealing effect.(3) The microstructure near the joining zone did not indicate the martensitic structure, the carburized and the decarburized layer because of its lower cooling rate. The structure near the joining zone of SUS304 was indicated in the annealed twin at the transgranular.(4) By the EPMA line analysis across the joining zone, Cr, Ni, and B were not observed because the inserted material S.F.A. was very little diffused and the most of it was discharged out of the joining part. The elementary analysis of Fe was indicated sligthly concentrated gradient.