Microstructure and fatigue properties of friction stir welded high-strength steel plates

Sorger, Gonçalo; Lehtimäki, Eero; Hurme, Susanna; Remes, Heikki; Vilaça, Pedro; Molter, Lars

doi:10.1080/13621718.2017.1399574

Cited by 20 publications

(13 citation statements)

References 29 publications

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“…Microstructural stability is more in acicular ferrite compared to bainite in higher temperatures. 1,40 The obtained ferrite structures in the SZ microstructures are consistent with the results reported in the literature. 41,42 The low cooling rate welds (~8.33–5.55°C/s) developed polygonal ( α p ) and allotriomorphic ferrite as the major constituents in the stir zone microstructure as depicted in Figure 6(b) to (d).…”

Section: Resultssupporting

confidence: 90%

Effect of plasma preheating on weld quality and tool life during friction stir welding of DH36 steel

Tiwari

Pankaj

Suman

et al. 2021

Proceedings of the Institution of Mechanical Engineers, Part B:

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Friction stir welding (FSW) of high strength materials is challenging due to high tool cost and low tool life. To address this issue, the present investigation deals with an alternative of plasma-assisted friction stir welding (PFSW) of DH36 steel with WC-10%Co tool. Plasma preheating current (13 A, 15 A, and 17 A) was varied by keeping other FSW parameters as constant. During the FSW and PFSW process, force measurement and thermal history aided in a deep understanding of the process, tool degradation mechanisms, accompanied by the mechanical and microstructural characterization of the welded joints. The stir zone hardness was increased from 140 HV0.5 to about 267 HV0.5. The yield and tensile strength of weld increased from 385 MPa and 514 MPa to about 391 MPa and 539 MPa, respectively. Weld joint elongation (%) was increased from ~10% of weld 1 to ~13.89% of weld 4. During PFSW, the process temperature was increased, the cooling rate was lowered, and the weld bead was widened. The results also revealed that the plasma-assisted weld resulted in polygonal ([Formula: see text]) and allotriomorphic ferrite as the major constituents in the stir zone. Pearlite dissolution and spheroidization were observed in the ICHAZ and SCHAZ, respectively. Additionally, the plasma preheating reduced the tungsten tool’s wear by 58% compared to FSW.

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Section: Resultssupporting

confidence: 90%

Effect of plasma preheating on weld quality and tool life during friction stir welding of DH36 steel

Tiwari

Pankaj

Suman

et al. 2021

Proceedings of the Institution of Mechanical Engineers, Part B:

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“…In comparison with the application of a single pass advanced welding solutions to modern TMCP HSS with a minimum yield strength of 700 MPa, as demonstrated by Sorger et al [14,15] in the application of friction stir welding with faster welding speed conditions, or Górka et al [16] in the application of hybrid laser arc welding, the multi-pass fusion welding can induce excessive decrease of impact-toughness, eventually due to the intercritically reheated domains that are formed in the HAZ [17,18]. On this scope, Hu et al [19] observed that V-N micro-alloying improved the toughness of the ICCGHAZ (inter-critically reheated coarse grained heat affected zone) by decreasing the size of M/A (martensitic/austenitic) constituents and refining the ferrite forming on the prior austenite grain boundaries [19].…”

Section: Introductionmentioning

confidence: 99%

MAG Welding Tests of Modern High Strength Steels with Minimum Yield Strength of 700 MPa

et al. 2019

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The modern high strength steel plates have an excellent combination of strength and toughness based on micro-alloying and complex microstructure. Retaining this combination of properties in the weld zone is a major challenge for applications in high-demanding structural construction. This work investigates the weldability of three different modern high strength steel plates, with a thickness of 8 mm. Two of the test materials were produced by a thermo-mechanically controlled process (TMCP) and one by a quenching and tempering method (Q&T). Two-passes MAG (metal active gas) welding was used with four different heat inputs. The tests implemented on all the materials included tensile, hardness profiles (HV5), Charpy-V impact toughness tests, and microstructure analysis using scanning electron microscope (SEM). For one of the TMCP steels, some extended tests were conducted to define how the tensile properties change along the weld line. These tests included tensile tests with digital image correlation (DIC), and 3-point bending tests. The most notable differences in mechanical properties of the welds between the materials were observed in Charpy-V impact toughness tests, mostly at the vicinity of the fusion line, with the Q&T steel more prone to embrittlement of the heat affected zone (HAZ) than the TMCP steels. Microstructural analysis revealed carbide concentration combined with coarse bainitic structures in HAZ of Q&T steel, explaining the more severe embrittlement. During the tensile tests, the DIC measurements have shown a strain localization in the softest region of the HAZ. Increasing the heat input resulted in earlier localization of the strain and less maximum strength. The tensile properties along the weld line were investigated in all welding conditions, and the results emphasize relevant and systematic differences of the yield strength at the transient zones near the start and end of the weld compared with the intermediate stationary domain.

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“…Sorger, ym. [11] vertasivat kitka-ja MAG-hitsattujen päittäisliitosten väsymiskestävyyttä S355-ja S690 -teräksillä. MAG-hitsattujen S690-teräksen päittäisliitoksille saatiin väsymisluokaksi (97,7 %) 234 MPa kaltevuuskertoimella m = 4,1, kun lämmöntuonnin mukainen jäähtymisaika t8/5 oli 5 s ja väsytyskokeissa käytettiin jännityssuhdetta R = 0,1.…”

Section: Väsymiskestävyysunclassified

“…Kirjallisuudessa on raportoitu väsytyskokeita ultralujien teräksien hitsausliitoksille ja näiden perusteella on myös kehitetty tarkempia väsymislaskentamenetelmiä [10][11][12]25]. Väsytystestauksesta poiketen tässä tutkimuksessa tarkastellaan hitsatun liitoksen poikkileikkauksia (Kuva 1.…”

Section: Loven Vaikutukset Hitsausliitoksessaunclassified

“…Kuvassa 9 esitetään myös mitoitusohjeiden mukaiset nimellistä-ja lovijännitystä vastaavat S-N -käyrät kyseiselle liitosmuodolle sekä aiempien tutkimusten väsytyskoetuloksien [10][11][12] mukaiset käyrät hitsatuille Domex 600, S690 ja S1100 teräksille. Kun verrataan hitsausliitoksen minimimurtolujuuksista määritettyjä käyriä mitoitusohjeen FAT 71 -käyrään, on murtolujuuksista laskettujen käyrien väsymisrajat 38-64 % suurempia.…”

Section: Tulosten Tarkasteluunclassified

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Hitsiliitoksen geometrian vaikutus väsymismitoituksessa

Keränen

Niskanen

2020

RakMek

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Tässä tutkimuksessa tarkasteltiin kahdella eri lämmöntuonnilla MAG-hitsattujen päittäisliitosten poikkileikkausten geometriaa sekä hitsiliitoksen geometrian vaikutusta väsymiskestävyyteen lovenvaikutuslukujen avulla S700-lujuusluokan rakenneteräksellä. Hitsiliitosten poikkileikkausten geometriat tuotiin elementtimenetelmäohjelmistoon, jossa määritettiin malli lovenvaikutuslukujen laskemiseksi. Laskettuja lovenvaikutuslukuja verrattiin kirjallisuuteen, sekä lovenvaikutuslukujen avulla määritettiin S‑N ‑käyrät, joita verrattiin mitoitusohjeiden S-N -käyriin. Lisäksi tarkasteltiin elementtikoon vaikutusta lovenvaikutuslukuun sekä alkusärön koon vaikutusta kestoikään murtumismekaniikan avulla. Tutkimuksessa havaittiin, että geometria ei yksin selitä hitsiliitoksen huonompaa väsymiskestävyyttä ehjään perusaineeseen verrattuna, vaan lähes puolet erosta johtuu muusta kuin geometriasta, esimerkiksi hitsauksen aiheuttamista mikrorakenteen muutoksista tai jäännösjännityksistä. Ainoastaan lovenvaikutusluku huomioiden saadaan hitsiliitoksille ylioptimistisia väsymiskestävyyden suuruuksia sekä kirjallisuuteen että mitoitusohjeisiin verrattuna. Elementtimenetelmää mitoituksessa hyödynnettäessä on käytettävä riittävän tiheää elementtiverkkoa, jotta rakenteen ja hitsiliitoksen geometria kuvataan oikein ja laskentajännitykset ovat todellisuutta vastaavia.

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Microstructure and fatigue properties of friction stir welded high-strength steel plates

Cited by 20 publications

References 29 publications

Effect of plasma preheating on weld quality and tool life during friction stir welding of DH36 steel

Effect of plasma preheating on weld quality and tool life during friction stir welding of DH36 steel

MAG Welding Tests of Modern High Strength Steels with Minimum Yield Strength of 700 MPa

Hitsiliitoksen geometrian vaikutus väsymismitoituksessa

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