Effect of Heat Treatment on Microstructures and Mechanical Properties of Hot-Dip Galvanized DP Steels

doi:10.1007/s40195-014-0066-y

Abstract

Abstract:

In order to simulate the hot-dipped galvanizing of dual-phase (DP) steel (wt%) 0.15C–0.1Si–1.7Mn, the DP steels were obtained by different annealing schedules. The effects of soaking temperature, time, and cooling rate on ferrite grain, volume fraction of martensite, and the fine structure of martensite were studied. Results showed that the yield strength (YS) of DP steel is sensitive to annealing schedule, while total elongation has no noticeable dependence on annealing schedule. Increasing soaking temperature from 790 to 850 °C, the YS is the lowest at soaking temperature of 850 °C. Changing CR1 from 6 to 24 °C/s, the YS is the highest when CR1 is 12 °C/s. Increasing soaking time from 30 to 100 s, the YS is the lowest at soaking time of 100 s. Besides, it was found that sufficient movable dislocations within ferrite grains and high martensite volume fraction can eliminate yield point elongation, decrease the YS, and increase ultimate tensile strength. Through TEM observations, it was also found that increasing annealing temperature promotes austenite transformation into twin martensite, and increases volume fraction of martensite at sufficient cooling rate. With increasing the martensite volume fraction, the deformation substructure in the ferrite is well developed.

Key words: Advanced high strength steels (AHSS), Dual-phase (DP) steel, Microstructure, Annealing temperature

Enbao Pan, Hongshuang Di, Guangwei Jiang, Chengren Bao. Effect of Heat Treatment on Microstructures and Mechanical Properties of Hot-Dip Galvanized DP Steels[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(3): 469-475.

Figures/Tables 8

Fig. 1 Schematic diagram of annealing process

Table 1 Parameters for heat treatment schedules for different specimens

Specimen No.	Soaking temperature (°C)	Soaking time (s)	CR1 (°C/s)	CR2 (°C/s)
1	790	30	12	12
2	820	30	12	12
3	850	30	12	12
4	850	30	6	12
5	850	30	12	7
6	850	30	24	7
7	850	45	24	7
8	850	100	24	7

Table 2 Mechanical properties and martensite volume fractions of different specimens

Specimen No.	YS (MPa)	UTS (MPa)	YS/TS	TEL (%)	MVF (%)
1	550	800	0.69	18.5	7.0
2	485	785	0.62	18.0	15.7
3	463	840	0.55	18.0	19.6
4	413	780	0.53	17.0	12.9
5	472	775	0.61	18.0	15.9
6	440	800	0.55	21.5	13.7
7	476	840	0.57	19.5	14.6
8	369	805	0.46	20.0	15.4

Fig. 2 Variation of annealing parameters on yield and ultimate tensile strengths of DP steel: a strength vs. soaking temperature for specimens Nos. 1–3; b strength vs. cooling rate CR1 for specimens Nos. 4–6; c strength vs. soaking time of specimens Nos. 6–8

Fig. 3 Stress–strain curves of specimens Nos. 1–3

Fig. 4 Optical micrographs of the DP steel processed under different conditions: a specimen No. 1; b specimen No. 2; c specimen No. 3; d specimen No. 4; e specimen No. 5; f specimen No. 6; g specimen No. 7; h specimen No. 8

Fig. 5 TEM micrographs showing the microstructures of specimens No. 1 a, No. 2 b, No. 3 c

Fig. 6 TEM micrographs showing the deformed microstructures of specimens No. 1 a, b ; No. 3 c, d

References 26

[1]	A. Kamp, S. Celotto, D.N. Hanlon, Mater. Sci. Eng. A 538, 35(2012)10.1016/j.msea.2012.01.008
[2]	L. Chen, Y. Zhao, X. Qin, Acta Metall. Sin. (Engl. Lett.) 26, 1(2013)10.1007/s40195-012-0501-x
[3]	H. Huh, S. Kim, J. Song, J. Lim, Int. J. Mech. Sci. 50, 918(2008)10.1016/j.ijmecsci.2007.09.004
[4]	X. Sun, K.S. Choi, A. Soulami, W.N. Liu, M.A. Khaleel, Mater. Sci. Eng. A 526, 140(2009)10.1016/j.msea.2009.08.010
[5]	P. Tsipouridis, E. Werner, C. Krempaszky, E. Tragl, Steel Res. Int. 77, 654(2006)
[6]	G. Gruben, E. Fagerholt, O.S. Hopperstad, T. Borvik, Eur. J. Mech. A Solid 30, 204(2011)10.1016/j.euromechsol.2011.01.004
[7]	M.S. Rashid, Annu. Rev. Mater. Sci. 11, 245(1981)10.1146/annurev.ms.11.080181.001333
[8]	Y. Granbom, Steel Res. 79, 297(2008)
[9]	P. Movahed, S. Kolahgar, S.P.H. Marashi, M. Pouranvari, N. Parvin, Mater. Sci. Eng. A 518, 1(2009)10.1016/j.msea.2009.05.046
[10]	R.R. Mohanty, O.A. Girina, N.M. Fonstein, Metall. Mater. Trans. A 42, 3680(2011)10.1007/s11661-011-0753-5
[11]	H. Liu, F. Li, W. Shi, S. Swaminathan, Y. He, M. Rohwerder, L. Li, Surf. Coat. Technol. 206, 3428(2012)10.1016/j.surfcoat.2012.02.001
[12]	S. Alibeigi, R. Kavitha, R.J. Meguerian, J.R. McDermid, Acta Mater. 59, 3537(2011)10.1016/j.actamat.2011.02.027
[13]	R. Khondker, A. Mertens, J.R. McDermid, Mater. Sci. Eng. A 463, 157(2007)10.1016/j.msea.2006.09.116
[14]	M. Sarwar, R. Priestner, J. Mater. Sci. 31, 2091(1996)10.1007/BF00356631
[15]	M. Erdogan, J. Mater. Sci. 37, 3623(2002)10.1023/A%3A1016548922555
[16]	M. Radu, J. Valy, A. Gourgues, F.L. Strat, A. Pineau, Scr. Mater. 52, 525(2005)10.1016/j.scriptamat.2004.10.034
[17]	T. Sakaki, K. Ohnuma, K. Sugimoto, Y. Ohtakara, Int. J. Plast 6, 591(1990)10.1016/0749-6419(90)90046-H
[18]	Z. Jiang, Z. Guan, J. Lian, Mater. Sci. Eng. A 190, 55(1995)10.1016/0921-5093(94)09594-M
[19]	G. Rosenberg, I. Sinaiová, L. Juhar, Mater. Sci. Eng. A 582, 347(2013)10.1016/j.msea.2013.06.035
[20]	M. Sarwar, T. Manzoor, E. Ahmad, N. Hussain, Mater. Des. 28, 1928(2007)10.1016/j.matdes.2006.05.010
[21]	J. Kadkhodapour, S. Schmauder, D. Raabe, S. Ziaei-Rad, U. Weber, M. Calcagnotto, Acta Mater. 59, 4387(2011)10.1016/j.actamat.2011.03.062
[22]	M.H. Saleh, R. Priestner, J. Mater. Process. Technol. 113, 587(2001)10.1016/S0924-0136(01)00638-0
[23]	M. Calcagnotto, Y. Adachi, D. Ponge, D. Raabe, Acta Mater. 59, 658(2011)10.1016/j.actamat.2010.10.002
[24]	G.R.SpeichinFundamentals of Dual Phase Steels, ed. by R.A. Kot, B.L. Bramfitt(AIME, New York, 1981), pp. 3–45
[25]	P.K. Ray, R.I. Ganguly, A.K. Panda, Steel Res. 73, 347(2002)
[26]	S. Tekeli, A. Güral, Mater. Sci. Eng. A 406, 172(2005)10.1016/j.msea.2005.07.019