Remnant tensile and creep properties of aluminized AISI 321 austenite stainless steel under prior creep–fatigue interaction

Abstract

Aluminized AISI 321 steels applied as heat exchange tube are generally subjected to creep-fatigue (C-F) exposure during service. Remaining tensile and creep performance of this steel at 620 C were therefore studied under prior C-F deformation. Results revealed that residual properties exhibit an initial increase and followed degradation with rising lifetime fraction of prior C-F.The tensile strength and creep lifespan reach highest at 30% lifetime fraction, since dislocation cell networks are well developed and secondary nanotwins are activated at substrate. Additionally, dynamic recovery and wavy slips occurred in coatings partially accommodate local plastic deformations and inhibit defect initiations, avoiding premature material fracture. On the other hand, these networks could restrain the increase in coating thicknesses. When the lifetime fraction of prior C-F increases to 80%, declined remnant properties are observed, which is attributed to the recovery of dislocation cells and carbide coarsening. Meanwhile, coating microcracks also accelerate steel failure.

Improved creep‐fatigue and remnant tensile/creep properties of 321 stainless steel by self‐healing coating

“…39 Detailed reasons can refer to our previous work. 33,34 As shown in Figure 6A,C, clear decreases in the creep strain were observed with the prior C-F lifetime increasing from 0 to 50% for the uncoated and self-healing steel at the same creep time. However, with the prior C-F lifetime further increasing to 80%, the creep strain of the sample with same creep time increased sharply but is still lower than that of the undeformed sample with prior C-F lifetime of 0%.…”

“…These results are consistent with the previous studies, [35][36][37] and detailed explanation for such phenomena can refer to our previous studies. 33,34 Clear influence of coating on the C-F behavior of 321 steel can also be observed. In detail, at the same C-F conditions, the lowest cyclic strain is shown in the self-healing 321 steel, while the highest in aluminized 321 steel.…”

“…Likewise, significant defects were commonly observed around NiAl precipitates in aluminized steel, 31 resulting in reduction in creep properties. In our previous studies, [32][33][34] it was also found that although aluminized coating improved the corrosion resistance of 321 stainless steel, it significantly decreased the mechanical properties (C-F life and UTS) of the aluminized steel due to the defects in the Fe-Al layer produced during aluminizing process. Therefore, it is crucial to develop coatings that can not only enhance corrosion resistance but also lead to higher mechanical properties (C-F life and UTS) in coated steels.…”

“…In our previous works, 33,34 the C-F behaviors of the uncoated 321 steel and the aluminized 321 steel (with aluminized coating) were studied by the same experimental routes as this work, and hence, the C-F behaviors of the present self-healing 321 steel were compared with the uncoated and aluminized 321 steel in Figure 3 to show the influence of self-healing coating. Clearly, all the cycling response curves with different creep holding time exhibit an initial hardening and subsequent softening trend until dramatical failure, as shown in Figure 3A-C.…”

Guest editorial of virtual special issue: Structural integrity in the context of carbon neutrality

“…Some authors focused on the material properties and damage mechanisms. Chen et al 8 employed microstructural characterizations to reveal remaining mechanical and creep performance of aluminized AISI 321 steels at 620°C under prior C‐F deformation. The results showed that with the increase of life fraction of prior C‐F, the residual properties increased first and then decreased.…”