The role of nitrogen in the embrittlement of steel
- PDF / 4,376,249 Bytes
- 12 Pages / 594 x 774 pts Page_size
- 65 Downloads / 246 Views
I.
INTRODUCTION
O V E R the years various pieces of evidence have been put forth which have suggested that nitrogen in its elemental form can embrittle iron and steel and thus be important in both tempered martensite embrittlement and temper embrittlement. Capus ~ reported that nitrogen-doped steels which had been heat treated to produce tempered martensite embrittlement had very low fracture energies. Hopkins and Tipler2 found that 0.01 pct nitrogen embrittled high purity iron. They found that the maximum embrittlement occurred in the temperature range of 600 to 700 ~ however, the entire embrittlement problem could be avoided if samples were slowly cooled from temperatures in the austenite range. More recently, Banerji, Feng, and McMahon 3 found that nitrogen segregated during austenitization of a commercial 4340 steel and concluded that it could be a cause of intergranular tempered martensite embrittlement in such ultra-high strength steels. A similar result was reported by Edwards, Nasim, and Wilson 4 in their study of a Cr-Mn steel. Briant, Feng, and McMahon 5 reported that nitrogen segregated to the grain boundaries of a quenched and tempered HY 130 steel during aging at 480 ~ This aging produced intergranular embrittlement, but as in the case of 4340 steel, other known grain boundary embrittlers were present. Therefore, the particular effects of nitrogen could not be discerned. Inoue 6 has provided clear evidence that elemental nitrogen causes embrittlement in steels. He studied a Si-Mn-N steel and found that if an austenitizing
C.L. BRIANT and A.M. RITTER are both Staff Metallurgists with General Electric Company, Corporate Research and Development, P.O. Box 8, Schenectady, NY 12301. S. K. BANERJI is Senior Research Metallurgist with Foote Mineral Company, Route 100, Exton, PA 29341. Manuscript submitted January 20, 1982.
METALLURGICAL TRANSACTIONS A
treatment of 930 ~ was used no embrittlement was observed. However, if the samples were austenitized at 1250 ~ severe embrittlement resulted. Auger results showed that in the latter case nitrogen was present on the grain boundaries. The sputtering profiles substantiated that the nitrogen was present in an unprecipitated state. It has also been found that nitrogen, precipitated as a nitride, can be detrimental to mechanical properties. Wright and Quarrell 7 showed that the precipitation of nitrogen along the grain boundaries of a steel as aluminum nitride could lead to very low upper shelf energies. These low energies were accompanied by intergranular ductile failure with the A1N particles serving as sites for microvoid initiation. Titanium carbo-nitrides precipitated at grain boundaries cause a similar decrease in the upper shelf energy of 18 Ni maraging steels. 8 Also, chromium nitrides precipitated at the grain boundaries of ferritic stainless steels can lead to cleavage at much higher test temperatures than expected. 9-~2 Because of the ubiquity of small amounts of nitrogen in most commercial steels, it is imperative to understand whether or not it is a
Data Loading...
