High-Cycle Fatigue Behavior of High-Mn Steel/304L Stainless Steel Welds at Room and Cryogenic Temperatures
- PDF / 4,899,804 Bytes
- 12 Pages / 593.972 x 792 pts Page_size
- 20 Downloads / 270 Views
I.
INTRODUCTION
STRONG demand has driven the energy and transportation industries to develop new materials for cryogenic applications, such as liquid natural gas (LNG) storage tanks and pipelines.[1–4] At present, the International Gas Carrier (IGC) code recommends 9 pct Ni steel, 304L austenitic stainless steels, 5000- and 6000-series Al alloys, and 36 pct Ni-Fe alloys as cryogenic structural materials. However, these all have certain limitations in terms of cost, strength, and service temperatures.[5–8] 304L austenitic stainless steels (304L), for example, are expensive with high Ni contents and low yield strengths.[9,10] High-Mn (HM) steels have been proposed as materials for LNG tankage applications because they have good combinations of strength and ductility at cryogenic temperatures.[11,12] These economical steels have therefore been actively studied to replace costly Ni-added stainless steels.[13,14] For the successful cryogenic application of HM steels, the weldability and mechanical properties of their welds must be assured, because weldments provide weak points susceptible to fracture.[13,15,16] Previously, the authors reported on the tensile and fracture behaviors of
HYOKYUNG SUNG, KWANHO LEE, DAEHO JEONG, and SANGSHIK KIM are with the Dept. of Materials Engineering and Convergence Technology, ReCAPT, Gyeongsang National University, Jinju 52828, Korea. Contact e-mail: [email protected] YOUNGJU KIM is with the Korea Institute of Geoscience and Mineral Resources, Pohang, 37559, Korea. Manuscript submitted January 25, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Fe25Mn steel welds at 298 K and 110 K; the results were compared to those of 304L.[13] 304L is well known for its excellent ultimate tensile strength and high-cycle fatigue (HCF) resistance at cryogenic temperatures.[17–19] The tensile and HCF properties of the Fe25Mn steel weld were comparable to those of the 304L weld at 110 K, and substantially better at room temperature.[13] The results showed promise for the successful structural application of newly developed HM steels at cryogenic temperatures. The HCF behavior of steel is largely determined by its deformation characteristics, microstructure, and most importantly, ultimate tensile strength.[20–23] However, predicting the HCF resistance of a weld joint is not simple because of the complexities associated with the weld profile, residual stress, and possible weld defects (i.e., inclusions, porosity, incomplete penetration, and undercutting).[24,25] These weld defects tend to reduce the cycling before crack initiation substantially, while the magnitude of stress concentration may vary with the weld profile.[24] For the successful cryogenic structural application of HM steels, they must demonstrate proper weldability with dissimilar metals. For the construction of LNG tankage in the shipbuilding and energy industries, for example, HM steels must be welded to austenitic Fe-Cr-Ni steels, such as 304L.[26] Thus, understanding the mechanical properties of weld joints between HM steel and Fe-Cr-Ni
