For examination of the characteristics of the surface cor- roded in saline media, the samples were kept immersed in an aqueous solution of 5% NaCl for 15 days and the surfaces were examined under a ‘Camscan’ scanning electron micro- scope with EDX facility.


Results & Discussion A) Phase Transformation Behavior:


The selection of the ausaging temperature is very critical be- cause the structural evolution in the alloy depends on this ag- ing temperature. Figure 3 indicates that the bulk hardness of alloy 333 reaches its maximum when the sample is tempered isochronally at 800C (1472F) for one hour.


tenite phase becomes stabilized again as revealed by the optical micrograph (Fig. 5c). Due to the presence of re- tained austenite as well as coarsening of carbide precipi- tates, the hardness falls. Thus, the ausaging temperature 800C (1472F) appears to be optimum.


The corresponding optical micrograph (Fig. 5b) reveals that the austenitic matrix (Fig. 4b) gets totally trans- formed into martensite embedded with fine precipitates of carbides. While at 700C (1292F), a few patches of untransformed austenite are observed (Fig. 5a). The aus- aging temperature of 900C (1652F) is perhaps too high above the A3


temperature of the alloy, because the aus-


The variation of ausaged hardness (HRC) with ausaging time at 800C (1472F) have been exhibited in Figure 6. After


Figure 6. Hardness vs. ausaging time curve at 800C (1472F) for alloy 333.


Figure 5. Optical micrographs of alloy 333, treated for 1 hour at: a) 700C (1292F), b) 800C (1472F) and c) 900C (1652F).


52


Figure 7. Optical micrograph of ausaged alloy 333 (5hrs. at 800C [1472F]).


International Journal of Metalcasting/Winter 11


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87