• Journal of Welding and Joining
• /
• 제6권2호
• /
• pp.40-46
• /
• 1988

The effect of heat input on the content of residual .delta.-ferrite and the hot cracking susceptibility in the austenitic stainless steel overlaid on the carbon steel was studied in the range of heat input from 7.5 to 15.1 KJ/cm. Present study shows that residual .delta.-ferrite content in the overlay is mainly determined by the dilution of the base metal (carbon steel) which is in turn affected by heat input, i.e. the amount of dilution decreases as heat input increase. Accordingly, higher heat input results in a substantial increase in Cr equivalent but a little increase in Ni equivalent due to the less dilution of carbon from base metal. This fact can explain the result obtained in this study, i, e, the higher content of .delta.-ferrite in the weld deposit made with higher heat input. This in turn causes more resistant overlaying weld metal to hot cracking.

• 한국자동차공학회논문집
• /
• 제7권8호
• /
• pp.248-261
• /
• 1999

The fatigue life of mechanical components and structures has been influenced by mechanical, material and environmental conditions. It is important to search out the load type and size for accurate cause of fracture at the damaged surface of material. The fractographic method by x-ray diffraction can utilize residual stress $\sigma$_r and half-value breadth B and find out the types and the mechanical conditions of fracture. This study showed the relationship between fracture mechanical parameters $\Delta$K, $K_{max}$ and X-ray residual stress $\sigma$_r for normalized SS41 steel with homogeneous crystal structure and M.E.F. dual phase steel(martensite encapsulated islands of ferrite). The fatigue crack propagation tests were carried out under stress ratios 0.1 and 0.5. The x-ray diffraction technique according to crack propatation direction was applied to fatigue fractured surface. Residual stress $\sigma$_r was independent on stress ratios by arrangement of $\Delta$K. The equation of $\sigma$_r$\Delta$K was established by the experimental data. Therefore, fracture mechanical parameters can be estimated can be estimated by the measurement of X-ray parameters.

• Nuclear Engineering and Technology
• /
• 제52권11호
• /
• pp.2552-2564
• /
• 2020

The crevice stress corrosion cracking (SCC) susceptibility of austenitic stainless steels was evaluated in simulated pressurized water reactor (PWR) environments. To simulate the abnormal condition in temporary clamping devices on leaking small bore pipes, crevice bent beam (CBB) tests were performed in the oxygenated as well as hydrogenated conditions. No SCC cracks were found for SS316 in both conditions. SS304 also showed good resistance in the hydrogenated condition. However, all SS304 specimens showed SCC cracks in the oxygenated condition, indicating poor crevice SCC resistance. It was found that residual ferrites were selectively dissolved because of the galvanic corrosion coupled with the neigh-bouring austenite phase, resulting in SCC initiation in SS304. Crack morphologies were mostly transgranular assisted by the damaged δ-ferrite and deformation-induced slip bands.

• 한국기계연구소 소보
• /
• 통권19호
• /
• pp.43-52
• /
• 1989

Material damage of Unifiner Change Heater: Tube used for nearly 20 years was evaluated and Mechanical tests such as tensile tests and creep-rupture tests were conducted to predict the residual life. After the investigation, any major damage or degradation was not found except the welded zone. Microstructural observation showed that most of delta-ferrite was transformed. to sigma-phase and consequently, the ductility was very much reduced. A KLA(Knife-Line Attack) crack with 60mm in length and 2.8mm in depth was found just near the welded zone, which is believed to be caused by intergranular corrosion. Creep-rupture tests, which are very essential to predict the residual life, showed that both used base and weld metals have similar results with the reference data.

• Journal of Advanced Marine Engineering and Technology
• /
• 제15권4호
• /
• pp.22-28
• /
• 1991

The crevice corrosion behavior on austenitic AISI 304 and 316L stainless steel welded by TIG, MIG, $CO_2$ and SMA was studied. The results are as follows : In 10% $FeCl_3$ solution and natural sea water sampled near Mokpo port, the base metal of 304 stainless steel showed small amount corrosion, whereas 316L stainless steel did not showed any corrosion in the test periods. The weight loss caused by crevice corrosion increased with increasing weld heat input and residual .delta. ferrite formed in welded part. The corrosion resistance of the welded part was in the order of TIG, MIG, $CO_2$ and SMA. From this tendency, it is proved that the smaller heat input gives the better corrosion resistance.