Accession Number : ADA319562

Title :   Investigation of Surface Intergranular Attack and Its Effects on the Fatigue Properties of AM355 Stainless Steel.

Descriptive Note : Final rept. Dec 95-Feb 96,

Corporate Author : ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD

Personal Author(s) : Grendahl, Scott ; Champagne, Victor

PDF Url : ADA319562

Report Date : NOV 1996

Pagination or Media Count : 57

Abstract : A critical flight safety component fabricated from AM355, a semiaustenitic precipitation hardenable stainless steel, from an Army attack helicopter failed catastrophically in service. The U.S. Army Research Laboratory (ARL) performed an in-depth metallurgical analysis of the broken component, which revealed that the premature failure was attributable to fatigue. Further analysis of material taken from various stages of processing revealed an intergranular surface attack that ARL determined to be caused by acid pickling during primary processing. ARL hypothesized that the surface intergranular attack may have led to premature crack initiation due to the breakdown of the protective passive layer or the stress concentration effect of the attack. This study was conducted to quantify the effects of varying degrees of surface intergranular attack on the fatigue properties of the material. Fatigue specimens were machined from actual components taken from inventory and from fielded components and were subsequently categorized into four groups which described the degree or severity of attack based on appearance and depth measurement: none, light, moderate, and heavy. Fatigue test data showed a direct relationship between the number of cycles to failure and the severity of surface intergranular attack. ARL recommended to control the amount of surface intergranular attack or to remove it altogether with a light sanding operation.

Descriptors :   *CRACKING(FRACTURING), *STAINLESS STEEL, *FATIGUE(MECHANICS), *METALLURGY, *PICKLING, ATTACK HELICOPTERS, EXPERIMENTAL DATA, ARMY RESEARCH, LAYERS, PROCESSING, FAILURE, PASSIVE SYSTEMS, PRECIPITATION, AVIATION SAFETY, HARDENING, FATIGUE TESTS(MECHANICS), ARMY AIRCRAFT, GRANULAR MATERIALS, ACIDS, STRESS CONCENTRATION.

Subject Categories : Properties of Metals and Alloys
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE