TWI Industrial Member Report Summary 406/1989
By S M Stevens
Nitrogen in solid solution in ferritic steel, 'free nitrogen', can cause significant embrittlement by strain ageing. However, standard and common procedures for determining nitrogen in steel measure only the total content, with no indication of the proportions that are free or combined. Study has been carried out to derive a working analysis procedure that can be used on a routine basis to assess free nitrogen levels in steels.
Heating a sample in hydrogen, followed by measurement of the ammonia produced, has been used previously to determine free nitrogen. The present work examined the possibility of replacing the timc-consuming direct measurement of ammonia, and studied the possible decomposition or formation of nitrides during the extraction stage, using experimental binary and ternary alloys. The resultant procedure was evaluated using certified reference materials.