Intermetallic Evolution of Al-Si-Coated Hot Stamping Steel During Modified Electrically

doi:10.1007/s40195-018-0740-6

Abstract

Abstract:

Modified electrically assisted (EA) rapid heating of Al-Si-coated hot stamping steel is suggested, and the intermetallic evolution in the coating during heating is experimentally investigated. In the modified EA rapid heating, a continuous electric current for a suitable duration is applied to a specimen to heat it to a temperature slightly below the melting temperature of the coating. The temperature of the specimen is then kept constant for a specified dwell time. The result of the microstructural analysis shows that the modified EA rapid heating could effectively increase the thickness of the intermetallic layer between the coating and steel substrate much faster than conventional furnace heating and induction heating. The effectiveness of EA rapid heating may be due to the athermal effect of the electric current on the mobility of atoms, in addition to the well-known resistance heating effect. EA rapid heating also provides a technical advantage in that partial austenization can be easily achieved by properly placing the electrodes, as demonstrated in the present study.

Key words: Hot stamping, Electrically assisted rapid heating, Partial austenization, Al-Si-coated hot stamping steel

Kieu-Anh Dinh, Sung-Tae Hong, Tien Viet Luu, Moon-Jo Kim, Heung Nam Han. Intermetallic Evolution of Al-Si-Coated Hot Stamping Steel During Modified Electrically[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(12): 1327-1333.

Figures/Tables 9

Table 1 Chemical compositions of the hot stamping steel sheet (wt%)

C	Mn	Si	Al	Ti	B	Fe
0.20-0.25	1.10-1.30	0.15-0.35	0.02-0.06	0.02-0.05	0.002-0.004	Bal.

Fig. 1 A schematic of the procedure of modified electrically assisted rapid heating

Fig. 2 A schematic of the experimental setup

Table 2 Process parameter for modified electrically assisted rapid heating

Specimen	Continuous electric current			A pulsed electric current
Specimen	Electric current density^a (A/mm²)	Duration (s)	Electric current density^a (A/mm²)	Duration (s)	Period (s)	Number of pulses
EA-0	57	3	14	2	2	0
EA-10						3
EA-25						6

Fig. 3 a Temperature history of EA-25 specimen, b temperature profile along the length of the EA-25 specimen at 1 s after the initiation of the dwell period

Fig. 4 Cross-sectional SEM-EDS micrograph of as-received specimen

Fig. 5 Cross-sectional SEM-EDS micrograph of a CH specimen, b IH specimen, c EA-0 specimen, d EA-10 specimen, e EA-25 specimen

Fig. 6 Intermetallic thickness (CH furnace heating, ID induction heating)

Table 3 Phase constituents of intermetallic layer (zone II)*

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