Effect of Martensite–Austenite Constituent on Low-Temperature Toughness in YS 500 MPa Grade Steel Welds
Abstract
:1. Introduction
2. Experimental Details
3. Results and Discussion
3.1. Microstructure and Mechanical Properties of the Base Metal
3.2. Microstructure and Mechanical Properties of Simulated HAZ
3.2.1. Microstructural Behaviour for Various HAZs
3.2.2. Mechanical Properties of the Various HAZs
3.3. Properties of a Real Welded Joint Formed Using the Fabricated Steel Plate
4. Conclusions
- (1)
- The Gleeble simulator produced various HAZs including CGHAZ, FGHAZ, IRCGHAZ, and SRCGHAZ in the real welded joint. IRCGHAZ contained AF and BF microstructures, and FGHAZ contained mostly fine polygonal ferrite and AF. The microstructure of CGHAZ mainly consisted of AF, BF, and a small fraction of GBF. SRCGHAZ had the same type of microstructure as CGHAZ except for the small grain size. Therefore, various HAZs produced mostly same type of microstructure, i.e., AF, BF, and GBF.
- (2)
- The volume fractions of the M–A constituents in FGHAZ and IRCGHAZ were similar and greater than 2%. Unlike FGHAZ with massive-shaped M–A constituents that were randomly distributed in the inter-ferrite grain, both massive- and slender-shaped constituents coexisted in the IRCGHAZ primarily along the PAGB. The M–A constituent was hardly observed in SRCGHAZ. The CGHAZ contained a small amount (~0.9%) of lath-shaped M–A constituent on the PAGB and inside the BF microstructure.
- (3)
- The morphology and distribution of the M–A influenced the low-temperature impact toughness of the simulated HAZs. The FGHAZ exhibited superior toughness and showed mixed dimples and cleavage fractures due to the randomly distributed massive M–A in the inter-ferrite grain. However, the IRCGHAZ exhibited inferior toughness and typical cleavage fractures because its slender M–A located primarily along the PAGB. As a result, the low-temperature impact toughness was deteriorated as the volume fraction of M–A constituents increased and the distribution of the slender-shaped M–A constituents concentrated in the PAGB.
- (4)
- During the real submerged arc welding process, the I-side groove produced a smaller amount of the IRCGHAZ than that of the V-side groove. Therefore, the I-side of the welded groove was superior to the V-side in terms of CVN-absorbed energy tested at –40 °C. The design of multi-pass weld joints with less IRCGHAZ is recommended and can be achieved by applying optimized groove design to improve the toughness of the welds for the structure used in extreme environments.
Author Contributions
Funding
Conflicts of Interest
References
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C | Si | Mn | Ni | Cr | Cu | Mo | Ti | Nb | Ceq | |
---|---|---|---|---|---|---|---|---|---|---|
Base metal | 0.07 | 0.15 | 1.55 | 0.6 | - | 0.25 | 0.15 | 0.012 | 0.02 | 0.41 |
Filler metal | 0.08 | 0.25 | 1.55 | 0.8 | 0.03 | 0.09 | 0.46 | - | - | - |
Main Parameter | Current (A) | Voltage (V) | Travel Speed (cm/min) | Heat Input (kJ/cm) | InterpassTemperature (°C) |
---|---|---|---|---|---|
Range | 680–720 | 32–36 | 25–30 | 46–55 | ≤250 |
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Kim, I.; Nam, H.; Lee, M.; Nam, D.; Park, Y.; Kang, N. Effect of Martensite–Austenite Constituent on Low-Temperature Toughness in YS 500 MPa Grade Steel Welds. Metals 2018, 8, 638. https://doi.org/10.3390/met8080638
Kim I, Nam H, Lee M, Nam D, Park Y, Kang N. Effect of Martensite–Austenite Constituent on Low-Temperature Toughness in YS 500 MPa Grade Steel Welds. Metals. 2018; 8(8):638. https://doi.org/10.3390/met8080638
Chicago/Turabian StyleKim, In, Hyunbin Nam, Myungjin Lee, Daegeun Nam, Yeongdo Park, and Namhyun Kang. 2018. "Effect of Martensite–Austenite Constituent on Low-Temperature Toughness in YS 500 MPa Grade Steel Welds" Metals 8, no. 8: 638. https://doi.org/10.3390/met8080638