IRON AND STEEL APPLICATIONS 



Fig. 3. Microradiograph. Iron radiation. 12% 

 Cr steel with white streaks due to Cr segregation, 

 containing dark specks due to MnS. X75. 



Mi 



Fig. 4. Same area as Fig. 3. Cobalt radiation. 

 MnS now also shows up white as well as the Cr 

 segregation. Some dark areas associated with MnS 

 may be cavities or silicate inclu.sions. X75 



examples of segregation of alloy elements 

 into one phase or another or of segregation 

 into dendrites or other cast structures have 

 been given in the literature (3, 6, 7). 



The radiations which are usually available 

 and suitable for the microradiography of 



Fig. 5. Same area as in Figs. 3 and 4. Chromium 

 radiation. MnS and associated cavities or silicates 

 are now dark. Cr segregation not revealed. White 

 specks could be due to traces of lead or other 

 heavy element. X75 



iron and steel are such that lead particles 

 always appear lighter than the matrix 

 (higher absorption) while alimiina and other 

 light inclusions appear darker (lower absorp- 

 tion) . Similarly, graphite flakes show up very 

 readily in cast iron (3, 5) and small graphite 

 particles etc. can easily be detected in 

 graphitized steels (8). Other applications in- 

 clude the study of interdiffusion between 

 metals. A particular example is described by 

 Goldschmidt (9) and concerns the changes 

 which occur during the preparation of iron- 

 chromium alloys by sintering powders. 



An effect which is important with rela- 

 tively coarse-grained ferrous materials (as 

 indeed with any kind of metallic specimen) 

 depends on diffraction. Different grains in a 

 specimen will diffract the incident radiation 

 to different degrees according to their orien- 

 tation. This effect reduces the intensity of 

 the transmitted beam and may lead to a 

 reproduction of the grain pattern on the 

 microradiograph which readily shows con- 

 trast reversals with different radiations or 



589 



