Intergranular fracture in 4340-type steels: Effects of impurities and hydrogen
Abstract
A study has been made of the conditions which lead to intergranular brittle fracture in 4340-type steels at an ultra high yield strength level (200 ksi, 380 MPa) in both an ambi-ent environment and gaseous hydrogen. By means of Charpy impact tests on commercial and high purity steels, and by Auger electron spectroscopy of fracture surfaces, it is con-cluded that one-step temper embrittlement (OSTE or "500°F embrittlement"), and low K intergranular cracking in gaseous hydrogen are primarily the result of segregation of P to prior austenite grain boundaries. Segregation of N may also contribute to OSTE. Most, if not all, segregation apparently occurs during austenitization, rather than during tem-pering. Elimination of impurity effects by use of a high purity NiCrMoC steel results in an increase inKth for hydrogen-induced cracking by about a factor of five (to the range 130 to 140 MNm-3/2). These observations are discussed in terms of our understanding of the mechanisms of OSTE and hydrogen-assisted cracking.
- Publication:
-
Metallurgical Transactions A
- Pub Date:
- February 1978
- DOI:
- 10.1007/BF02646706
- Bibcode:
- 1978MTA.....9..237B
- Keywords:
-
- Austenite;
- Metallurgical Transaction;
- Cementite;
- Fracture Energy;
- Intergranular Fracture