X-RAY MICROSCOPY 



factory for steels. The preparation of speci- 

 mens can follow one of the simple established 

 procedures (1, 2, 3, 4). 



For ferrous metal specimens the possible 

 choices of radiation can be exploited to ad- 

 vantage, since a number of conventional 

 alloy elements lie in the same row of the 

 periodic table, and the usually available 

 target metals for providing Ka radiations 

 are in the same series. Thus nickel radiation 

 is most heavily absorbed by iron itself, while 

 differentiation of inclusions or other par- 

 ticles containing manganese in particular is 

 facihtated by the high absorption of Cu, Co 

 and Ni radiations and low absorption of Fe, 

 Mn, and Cr radiations. The following figvu'es 

 (2) illustrate this point and bring out the 

 possibility of reversal of contrast. 



Linear Absorption Coefficients for K 

 Radiations 



Figures 1 and 2 show microradiographs of 

 a piece of free-cutting steel which not only 

 illustrate the reversal of contrast with MnS, 

 but also bring out the ease with which the 



Fig. 1. Microradiograph with cobalt radiation 

 of free cutting steel showing manganese sulfide 

 sometimes surrounded by lead (white areas). The 

 black striations are cavities due to break up of in- 

 clusions during cold drawing. XlOO 



Fig. 2. Same region as in Fig. 1 but with chro- 

 mium radiation. MnS regions now darker than 

 matrix. Note: Lead is still represented by white 

 areas. Some lead has squeezed into the cavities in 

 the MnS. XlOO 



distribution of lead particles can be exam- 

 ined. Other examples of manganese sulfide 

 or lead distribution have been referred to in 

 the literature (1, 2, 3, 5). One of these refers 

 to the presence of MnS inclusions which lie 

 along cracks in broken fatigue specimens. 

 The over-all segregation of manganese in a 

 high manganese steel is represented by a 

 pattern of relatively darker and lighter 

 bands. 



Figs. 3, 4, 5 also happen to illustrate the 

 occurrence of manganese sulfide but are of 

 interest in that, by taking advantage of the 

 different absorption properties segregation 

 of chromium is established, and some indi- 

 cation of the presence of other inclusions is 

 obtained. These pictures illustrate a banded 

 segregation of chromium which appeared to 

 suggest that the maximum difference in chro- 

 mium content might be over 5%. 



Another kind of segregation is represented 

 by Fig. 6 a photomicrograph and Fig. 7 a 

 microradiograph of an alloy steel. The segre- 

 gation is attributed to molybdenum which 

 is present in considerably larger amounts in 

 one phase (sigma) than in the other (ferrite). 

 A notable case of this kind is shown in Fig. 

 8, the microradiograph of a high alloy steel 

 containing molybdenum and niobium. Other 



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