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Fe-Zn phase evolution and cracking behavior in Zn-coated press-hardened steel.

紀錄類型:	書目-語言資料,手稿 : Monograph/item
正題名/作者:	Fe-Zn phase evolution and cracking behavior in Zn-coated press-hardened steel./
作者:	Ghanbari, Zahra N.
面頁冊數:	1 online resource (104 pages)
附註:	Source: Dissertation Abstracts International, Volume: 79-03(E), Section: B.
Contained By:	Dissertation Abstracts International79-03B(E).
標題:	Materials science. -
電子資源:	click for full text (PQDT)
ISBN:	9780355257922

Fe-Zn phase evolution and cracking behavior in Zn-coated press-hardened steel.
Ghanbari, Zahra N.

Fe-Zn phase evolution and cracking behavior in Zn-coated press-hardened steel. - 1 online resource (104 pages)

Source: Dissertation Abstracts International, Volume: 79-03(E), Section: B.

Thesis (Ph.D.)

Includes bibliographical references

Zinc coated press-hardened steel (PHS) sheet used for the production of strong, corrosion resistant parts is of interest to the automotive community, but concerns about liquid metal embrittlement (LME) remain. Specifically, mitigation of the cracking associated with LME, via better understanding of the alloyed coating microstructural features and interaction with the substrate sheet during deformation, is desired. The objective of this work was to relate the microstructural evolution in the Fe Zn coatings heat treated under single or two step thermal processing to the cracking response in specimens deformed in uniaxial tension at elevated temperature. A GleebleRTM 3500 was used to heat treat galvanized 22MnB5 samples at hold times and temperatures relevant to new processes recently implemented in some hot stamping lines. The alloying achieved during heating and isothermal holding of specimens was assessed, and used to interpret the cracking response in the coating (and substrate) of specimens deformed at high temperature.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2018

Mode of access: World Wide Web

ISBN: 9780355257922Subjects--Topical Terms:

557839
Materials science.
Index Terms--Genre/Form:

554714
Electronic books.

Fe-Zn phase evolution and cracking behavior in Zn-coated press-hardened steel.
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245 1 0 $a Fe-Zn phase evolution and cracking behavior in Zn-coated press-hardened steel.
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300 $a 1 online resource (104 pages)
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500 $a Source: Dissertation Abstracts International, Volume: 79-03(E), Section: B.
500 $a Adviser: John G. Speer.
502 $a Thesis (Ph.D.) $c Colorado School of Mines $d 2017.
504 $a Includes bibliographical references
520 $a Zinc coated press-hardened steel (PHS) sheet used for the production of strong, corrosion resistant parts is of interest to the automotive community, but concerns about liquid metal embrittlement (LME) remain. Specifically, mitigation of the cracking associated with LME, via better understanding of the alloyed coating microstructural features and interaction with the substrate sheet during deformation, is desired. The objective of this work was to relate the microstructural evolution in the Fe Zn coatings heat treated under single or two step thermal processing to the cracking response in specimens deformed in uniaxial tension at elevated temperature. A GleebleRTM 3500 was used to heat treat galvanized 22MnB5 samples at hold times and temperatures relevant to new processes recently implemented in some hot stamping lines. The alloying achieved during heating and isothermal holding of specimens was assessed, and used to interpret the cracking response in the coating (and substrate) of specimens deformed at high temperature.
520 $a Heat treatments using systematic heating rates were conducted to investigate the Fe Zn phase development during heating to elevated temperatures relevant to press-hardening. The specimen heated at the slowest rate (2 ºC/s) was comprised of the most Fe rich phases (Gamma and alphaFe(Zn)). Comparison of the compositions of these phases to the Fe Zn phase diagram at elevated temperature (775 ºC), suggested that this coating was mostly solid at elevated temperature, and thus may also have had little Zn rich liquid upon reaching target temperature. The minimized Zn-rich liquid at elevated temperature indicated that minimal soak time would have been necessary to eliminate Zn rich liquid in the coating prior to deformation at this temperature.
520 $a Specimens were also heat treated via single or two step isothermal profiles (with and without deformation), and the phases were identified and quantified to understand the state of the coating microstructure at each room and elevated temperature. Fractions of the phases developed in the alloyed coating were measured using quantitative image analysis. The fraction of delta (most Zn rich phase identified in the coatings) appeared to decrease, while the fraction of Gamma and alphaFe(Zn) appeared to increase, with increased soak time and temperature. The delta phase was not observed in specimens heat treated at the highest time/temperature combinations (850 °C for 60-120 s), suggesting that the greatest degree of alloying occurred in these specimens. The fraction of the delta+Gamma1 phases present in each specimen are suggested to contribute to the amount of Zn rich liquid present at the highest deformation temperature (700 °C), and thereby used to estimate the amount of Zn rich liquid available during elevated temperature tensile tests. The thickness of the alphaFe(Zn) layer also increased with increased hold time and temperature. The alphaFe(Zn) layer thickness in undeformed versus deformed specimens and composition gradient across the layer were measured and compared to cracking behavior of the layer. At the highest deformation temperature (700 °C), the ?Fe(Zn) layer exhibited cracks after intermediate and extended hold times (60 and 120 s); these specimens also exhibited the higher alphaFe(Zn) layer thicknesses and slightly narrower composition gradients compared to specimens deformed at the same temperature after shorter soak times.
520 $a The cracking behavior observed in the deformed specimens was related to the microstructural evolution of the coating based on the inferred amount of liquid present at elevated temperature and the relative plasticity of the alphaFe(Zn) layer. In most cases, deep cracking into the substrate sheet associated with LME was avoided. Crack mitigation during deformation was proposed to be a result of: reduction of Zn rich liquid via increased alloying or reduced deformation temperature, or retention of a continuous alphaFe(Zn) layer between the alloyed coating and substrate, that served as a barrier layer to prevent contact between the Zn rich liquid and Fe-substrate.
533 $a Electronic reproduction. $b Ann Arbor, Mich. : $c ProQuest, $d 2018
538 $a Mode of access: World Wide Web
650 4 $a Materials science. $3 557839
655 7 $a Electronic books. $2 local $3 554714
690 $a 0794
710 2 $a ProQuest Information and Learning Co. $3 1178819
710 2 $a Colorado School of Mines. $b Metallurgical and Materials Engineering. $3 1182976
773 0 $t Dissertation Abstracts International $g 79-03B(E).
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10605878 $z click for full text (PQDT)