PSI - Issue 14

Sourabh Shukla et al. / Procedia Structural Integrity 14 (2019) 259–264 Sourabh shukla et al./ Structural Integrity Procedia 00 (2018) 000–000

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1. Introduction High price of nickel is being the main reason for increase in demand of Cr-Mn ASS that replace Ni by Mn and Nitrogen, Sedriks (1996). Like Ni, Mn also play role by stabilizing the austenitic phase. Cr-Mn ASS are used in various applications like home appliances, home accessories, outdoor installation etc. During heat treatment, temperature between 550 °C to 850 °C, Cr-Mn ASS becomes highly sensitized and causes sensitization. In this phenomena, chromium diffusion takes place from grain to grain boundary (GB) and Cr-C precipitates formed in the vicinity of grain boundary and then it cause depletion of chromium along the grain boundary which give results in sensitization causes severe intergranular corrosion (IGC), Raghuvir (2008) and White (1992). IGC is one of the important defect in failure of Cr-Mn ASS in many industries. Cold rolling with heat treatment is one of the solution to improve the sensitization through grain refinement. Martensitic transformation induced by plastic deformation of metastable ASS is well known phenomenon depending on steel composition and deformation conditions, Maksimova OP (1999). During deformation of steels, ε-martensite and α-martensite formed. As deformation of steel increases, more α-martensite grows as it follows sequence of γ→ε→α, or γ→α, Fukuda T (2006) and Das A (2008). Strain Induced Martensite which formed during deformation, can have unfavourable effect such as delayed cracking phenomenon of deep-drawn ASS component, Berrahmoune MR (2006). Therefore, SIM in metastable ASSs has been extensively studied mainly for practical reasons. On the other hand, details of SIM transformation during ageing of the deformed metastable ASS are less known. The aging causes reversal transformation of SIM, i.e., α→γ. Due to this, grain refinement takes place which helps to increase the yield strength without impairing ductility of the material. Many studied has been done on the mechanical properties of steel due to martensitic reversal, but its effect on corrosion properties of ASS are less known. So, aim of this work is to show the effect of reverted austenite on the sensitization behavior of metastable ASSs. 2. Research Significance ASS are subjected to different levels of cold work and heat treatment during the final manufacturing stages of component for numerous application in industry. Cold work might effect the corrosion resistance and also increases degree of sensitization of stainless steel. Therefore, properties of surface can improved by changing its microstructure as well as residual stress. So, it mainly involves cold working followed by heat treatment to results in grain refinement which helps to decrease the sensitization and increases the yield strength. 3. Materials and Methods The Cr-Mn sample were solution annealed for 60 min at temperature 1050 °C followed by 25% and 45% CW. Then these two sets of samples were TA at 700 °C, and 900 °C. For optical microstructure, samples were electrochemically etched in 10 wt % oxalic solution with 1A/cm 2 current density according to practice A, A262, ASTM. Specimens of 10×10 mm were cut for X-Ray diffraction analysis. The diffraction pattern is carried out at room temperature (30 °C) using a Cu target with Kα radiation.

Table 1: chemical composition of studied base materials Materials

Chemical composition (wt. %)

AISI

C

Ni

Mn

Si

Cr

P

S

Cr-Mn

0.13

0.19

9.14

0.46

13.46

0.014

0.0104

Micro-hardness (Simadzu Mico-hardness Tester) taken on dimensions of 10×10 mm cross-section with thickness 3 mm. The volumetric fraction of SIM in the cold worked samples was estimated from peaks of XRD spectrum using following formula, Wang J. et al. (2017):