Effect of Laser Surface Melting on the Microstructure and Pitting Corrosion Resistance of 304L SS Weldment
- PDF / 3,837,084 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 25 Downloads / 218 Views
TRODUCTION
AUSTENITIC stainless steel of type 304L SS is used as construction material in Indian nuclear reprocessing and waste storage plants as they exhibit excellent corrosion resistance and good mechanical property. The excellent corrosion resistance is due to the formation of protective, stable chromium-rich passive film. However, on exposure to aggressive environments, the passive film undergoes localized breakdown making these stainless steels susceptible to localized corrosion (pitting, intergranular corrosion, stress corrosion cracking). Pitting is one of the most dangerous forms of localized attack since they occur suddenly, causing catastrophic failures. The weld region and the heat-affected zone (HAZ) are susceptible to pitting attack either during storage in coastal atmosphere or during plant operation due to
GIRIJA SURESH, ARUP DASGUPTA, T. SARAVANAN, C. MALLIKA, and U. KAMACHI MUDALI are with the Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India. Contact e-mail: [email protected] P.S.V.R.A. KISHOR is with the Andhra University College of Engineering, Visakhapatnam 533 003, India. B.N. UPADHYAY is with the Raja Ramanna Centre for Advanced Technology, Indore, India. Manuscript submitted October 10, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
chloride ingress in the process medium. Surface modification of these regions by laser surface melting (LSM) would be highly beneficial to enhance the pitting corrosion resistance. In LSM, a high-power laser beam rapidly melts and solidifies a thin layer of the surface, resulting in modification of surface microstructure, while the bulk of the material undergoes self-quenching at cooling rates of 104 to 108 K s 1 (9727 to 999999727 C s 1). The modified surface enhances corrosion and wear properties. In LSM, high solidification rates could be achieved due to rapid cooling rates and large supercooling, which results in homogenization and refinement of microstructure, dissolution and redistribution of secondary phases and inclusions. Extensive work has been reported on the beneficial effects of LSM of various metals and alloys including austenitic stainless steel of type 304 and 304L SS.[1–5] The enhancement of corrosion resistance (pitting,[1,3,6,7] cavitation[2] and IGC[1,2,4,5]) and wear resistance of stainless steels by laser surface modification has been reported by several investigators, but studies on welds and weldment are sparse. The improvement in the pitting corrosion resistance of 304L SS after LSM has been attributed to the dissolution of inclusions and promotion of preferred orientation of c-austenite along the [200] direction.[8] Kwok et al.[9] have reported that LSM of austenitic stainless steels improves the cavitation resistance and pitting corrosion resistance due to the
presence of low-volume pct d-ferrite ( 2, and its formation could
Fig. 3—Optical micrograph of (a) as received 304L SS base and (b) weld region of 304L SS weldment.
Fig. 4—Optical micrograph of various delta ferrite morphology in the weld region of 304L SS weldme
Data Loading...
