Crack closure and fatigue crack growth near threshold of a metastable austenitic stainless steel

Abstract

In this paper R-ratio effects on fatigue crack growth near threshold region of a metastable austenitic stainless steel (MASS) in two different conditions, i.e. annealed and cold rolled, is investigated. The authors present two approaches to correlate FCGR data for R = 0.1, 0.3, 0.5, 0.7 and K-max = 23 MPa root m using a two-parameters approach (Delta K, K-max and alpha in Kujawski's model) and crack closure model (using Elber's K-op, and in Donald's ACRn2 approaches). The K-op and ACRn2 were experimentally measured on a single edge tension specimens. The K-op measurements were performed using a modified method and based on ASTM standards. While the two driving force approaches correlate data well in the Paris region, they fail to correlate them in the threshold region. However, this correlation can be improved in the threshold region when a different alpha value from the Paris region is used. The authors indicated that two different mechanisms operate; one in the Paris region and another in the near threshold. Hence, they proposed to combine the two-parameter and crack closure approaches where Delta K is replaced by Delta K-eff (estimated by a new method proposed in this paper), which is shown to correlate the FCGR data for different stress ratios for annealed steel. The correlation for cold rolled condition shows improvement with the new approach but is not as good as for the annealed one. The author further suggests to modify K-max in the two-parameter approach. (C) 2015 Elsevier Ltd. All rights reserved.Peer ReviewedPostprint (author’s final draft

Effect of Solution Annealing on Fatigue Crack Propagation in the AISI 304L TRIP Steel

“…Other internal factors affecting the susceptibility to the strain-induced phase transformation are the grain size, their distribution and initial dislocation structure [ 11 , 18 ]. Numerous studies showed that the TRIP effect in the austenitic stainless steel can significantly reduce the fatigue crack growth rate (FCGR) [ 8 , 9 , 19 , 20 ]. Several studies were carried out, in which the austenitic stainless steels were subjected to fatigue crack propagation tests at various temperatures with respect to the martensite-start (M s ) temperature.…”

“…However, in the light of the TRIP phenomenon, the dissolution of the delta ferrite increases chromium content in the adjacent regions, and together with grain coarsening, can enhance the material susceptibility to the martensitic transformation when externally loaded. Several studies have shown differences in the near threshold FCGR between cold worked and annealed austenitic stainless steels [ 8 , 9 , 19 , 20 ]. However, most of these studies were focused on different aspects of the TRIP and FCGR processes under variable conditions.…”

The influence of combined gradient structure with residual stress on crack-growth behavior in medium carbon steel

“…Such residual stress also plays a significant role in affecting the fatigue endurance of surface strengthened materials [42][43][44][45][46][47]. Many literatures [48][49][50][51] have shown that the residual compressive stress resulted from surface mechanical treatment could effectively improve the fatigue resistance. More recently, Zhang et al [52] studied experimentally the fatigue crack-growth behavior in gradient axle steel with residual stress.…”

Toughness Behaviour in Armour Steel Welds

“…There are numerous studies of fatigue crack growth in austenitic materials, but mainly due to deformation, with only a few investigating austenitic weld metal [14]. Austenitic filler material is unstable and gets transformed into martensite during fatigue crack propagation due to plastic deformation at the crack tip [15]. During the metastable austenite deformation, two types of martensitic structures can be formed: ε -martensite with hexagonal close packed and α' -martensite, with body centered cubic crystal structure.…”