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Apr 19 – 22, 2022
Vienna, Austria
Europe/Vienna timezone
FR22 starts in Vienna 19 - 22 April 2022 Online Stream:

Influence of preheating temperature on delta-ferrite formation and mechanical properties of 12%Cr steel weld metals

Apr 20, 2022, 10:40 AM
Vienna, Austria

Vienna, Austria

POSTER Track 4. Fast Reactor Materials (Coolants, Structures) and Components Poster Session


Dr Dong Wu


A 12% Cr ferritic/martensitic (F/M) steel, HT-9, has been used as a primary core material for nuclear reactors. Welding is inevitably used in the nuclear structure design. Fusion welding processes such as gas tungsten arc welding (GTAW) were broadly applied for the F/M steel components. Unfortunately, in the fusion zone of F/M steel weldment, delta (δ)-ferrite is frequently produced, which is considered to decay the creep strength and impact toughness.
In this work, the fusion-zone microstructure and mechanical properties of gas tungsten arc butt welded joints of HT-9 have been explored. The fusion zone solidified with the transformation from the liquid into δ-ferrite, followed by a solid-state transformation from the δ-ferrite to the γ phase. The cooled microstructure was formed by a fresh martensite matrix and retained δ-ferrite. Two kinds of retained δ-ferrite with were observed: one was rich in Cr and depleted in C; the other one was rich in Cr、C、Mo and V. The area fractions of retained δ-ferrite decreased when a preheating treatment at 95 ℃ was applied, moreover the number and mean size of the retained δ-ferrite decreased significantly due to the preheating effect. It indicated that a slower cooling rate (e.g. conducting a preheating treatment) provided more time for the δ → γ reaction and therefore reduced the retained δ-ferrite. After the welding process, a tempered treatment was conducted with 760℃/1h. The impact toughness test for the welds in the as-tempered condition showed that the ductile-brittle transaction temperature (DBTT) of the welds with preheating treatment was lower than that without preheating treatment. The improvement of impact toughness in the welds with preheating treatment was due to the less δ-ferrite in the matrix.

Affiliation/Organization Institute of metal research, Chinese Academy of Sciences
Country/Int. organization China
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Primary author


Prof. Shanping Lu (Institute of Metal Research, Chinese Academy of Sciences) Prof. Dianzhong Li Prof. Yiyi Li ( Institute of Metal Research, Chinese Academy of Sciences)

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