Effects of Cu addition on formability and surface delamination phenomenon in high-strength high-Mn steels

doi:10.1016/j.jmst.2020.01.021

Abstract

Abstract:

The formability of austenitic high-Mn steels is a critical issue in automotive applications under non-uniformly-deformed environments caused by dynamic strain aging. Among austenite stabilizing alloying elements in those steels, Cu has been known as an effective element to enhance tensile properties via controlling the stacking fault energy and stability of austenite. The effects of Cu addition on formability, however, have not been sufficiently reported yet. In this study, the Cu addition effects on formability and surface characteristics in the austenitic high-Mn TRIP steels were analyzed in consideration of inhomogeneous microstructures containing the segregation of Mn and Cu. To reveal determining factors, various mechanical parameters such as total elongation, post elongation, strain hardening rate, normal anisotropy, and planar anisotropy were correlated to the hole-expansion and cup-drawing test results. With respect to microstructural parameters, roles of (Mn,Cu)-segregation bands and resultant Cu-rich FCC precipitates on the formability and surface delamination were also discussed.

Key words: High-Mn steel, Cu effects, Cu-rich FCC phase, Hole-expansion test, Formability, Stretch-flangeablity, Surface delamination

Jo Min Chul, Jisung Yoo, Jo Min Cheol, Alireza Zargaran, Sohn Seok Su, Kim Nack J., Sunghak Lee. Effects of Cu addition on formability and surface delamination phenomenon in high-strength high-Mn steels[J]. J. Mater. Sci. Technol., 2020, 43: 44-51.

Figures/Tables 11

Fig. 1. XRD analysis data of the annealed 0Cu, 1Cu, and 2Cu steels.

Fig. 2. SEM backscattered-electron (BE) images of the (a) 0Cu, (b) 1Cu and (c) 2Cu steels. (d) The EDS line profile data of the 2Cu steel along the red line in (c).

Fig. 3. (a) SEM BE image in the high-(Mn,Cu) band of the 2Cu steel. Cuboidal particles are densely formed along the high-(Mn,Cu) band. (b) TEM bright-field (BF) image, selected-area diffraction pattern along [233] zone axis, and quantitative EDS data of the particles. These particles are identified to be Cu-rich FCC-phase particles.

Fig. 4. Engineering stress-strain curves of the 0Cu, 1Cu, and 2Cu steels at room temperature. Measured tensile properties are displayed in the inset.

Fig. 5. EBSD image quality (IQ) + phase maps of the 20 %-strained (a) 0Cu, (b) 1Cu, and (c) 2Cu steels. In the 0Cu and 1Cu steels, transformed α’- and ε-martensite are observed along the longitudinal direction, whereas they are not in the 2Cu steel.

Fig. 6. Optical photographs of the tensile-fractured specimens for the (a) 0Cu, (b) 1Cu, and (c) 2Cu steels. A delamination is found in the specimen surface of 1Cu steel, and becomes severe in the 2Cu steel. This delamination occurs mainly along the longitudinal direction, and is deepened into the interior up to about 0.1 mm in the 2Cu steel.

Table 1 Hole-expansion ratio (HER) data of the 0Cu, 1Cu, and 2Cu steels.

Steel	0Cu	1Cu	2Cu
HER (%)	36.67 ± 1.31	58.05 ± 2.83	49.47 ± 3.73

Table 2 Post elongation (εpost), normal anisotropy ($\bar{r}$), planar anisotropy (???Δr?), and strain hardening exponent (n) of the 0Cu, 1Cu, and 2Cu steels.

Steel	ε_post	$\bar{r}$	???Δr?	n
0Cu	0.23 %	1.068	0.093	0.341
1Cu	1.08 %	1.060	0.067	0.415
2Cu	3.14 %	1.056	0.072	0.395

Fig. 7. The relationship between HET results and various mechanical parameters of (a) εtotal, and εpost, (b) |Δr| and $\bar{r}$, (c) n, and (d) εθ.

Fig. 8. Photographs of the cup-drawn specimens of the (a) 0Cu, (b) 1Cu, and (c) 2Cu steels after the drawing test with a drawing ratio of 1.6. In the 0Cu steel, the drawing ratio of 1.6 is not satisfied because of the edge cracking. The 1Cu and 2Cu steels do not show any edge cracking, earing, or wrinkle. A severe surface delamination occurs on inner and outer cup-specimen surfaces of the 2Cu steel.

Fig. 9. SEM (a) secondary-electron (SE) and (b) BE images of a delaminated region on the tensile-fractured specimen of the 2Cu steel. The surface delamination propagates along the longitudinal direction. EPMA (c) Mn- and (d) Cu-distribution maps of the region corresponding to (a). The surface delamination occurs in the high-(Mn,Cu) band region, and that it is closely related to the formation of Cu-rich FCC-phase particles according to Fig. 2c, d.

References

[1]	G. Frommeyer, U. Brux, P. Neumann, ISIJ Int. 43(2003) 438-446.
[2]	Y.Z. Tian, Y. Bai, L.J. Zhao, S. Gao, H.K. Yang, A. Shibata, Z.F. Zhang, N. Tsuji, Mater. Charact. 126(2017) 74-80.
[3]	K.M. Rahman, V.A. Vorontsov, D. Dye, Acta Mater. 89(2015) 247-257.
[4]	S. Kang, Y.-S. Jung, J.-H. Jun, Y.-K. Lee, Mater. Sci. Eng. A 527 (2010) 745-751.
[5]	M.I. Latypov, S. Shin, B.C. De Cooman, H.S. Kim, Acta Mater. 108(2016) 219-228.
[6]	S. Vercammen, B. Blanpain, B.C. De Cooman, P. Wollants, Acta Mater. 52(2004) 2005-2012.
[7]	A. Weidner, A. Müller, A. Weiss, H. Biermann, Mater. Sci. Eng. A 571 (2013) 68-76.
[8]	B.C. De Cooman, Y. Estrin, S.K. Kim, Acta Mater. 142(2018) 283-362.
[9]	D.B. Santos, A.A. Saleh, A.A. Gazder, A. Carman, D.M. Duarte, é.A.S. Ribeiro, B.M. Gonzalez, E.V. Pereloma, Mater. Sci. Eng. A 528 (2011) 3545-3555.
[10]	X. Liang, J.R. McDermid, O. Bouaziz, X. Wang, J.D. Embury, H.S. Zurob, Acta Mater. 57(2009) 3978-3988.
[11]	I. Gutierrez-Urrutia, D. Raabe, Acta Mater. 59(2011) 6449-6462.
[12]	Z.Y. Liang, Y.Z. Li, M.X. Huang, Scr. Mater. 112(2016) 28-31.
[13]	J.-K. Kim, B.C. De Cooman, Mater. Sci. Eng. A 676 (2016) 216-231.
[14]	M. Koyama, T. Sawaguchi, K. Tsuzaki, Philos. Mag. 92(2012) 145-152.
[15]	M.C. Jo, J.H. Choi, H. Lee, A. Zargaran, J.H. Ryu, S.S. Sohn, N.J. Kim, S. Lee, Mater. Sci. Eng.A 740-741(2019) 16-27.
[16]	S. Lee, J. Kim, S.-J. Lee, B.C. De Cooman, Scr. Mater. 65(2011) 1073-1076.
[17]	X. Peng, D.Y. Zhu, Z.M. Hu, W.F. Yi, H.J. Liu, M.J. Wang, Mater. Des. 45(2013) 518-523.
[18]	J.H. Choi, M.C. Jo, H. Lee, A. Zargaran, T. Song, S.S. Sohn, N.J. Kim, S. Lee, Acta Mater. 166(2019) 246-260.
[19]	S. Lee, J. Kim, S.J. Lee, B.C. De Cooman, Scr. Mater. 65(2011) 528-531.
[20]	J.G. Kim, S. Hong, N. Anjabin, B.H. Park, S.K. Kim, K.G. Chin, S. Lee, H.S. Kim, Mater. Sci. Eng. A 633 (2015) 136-143.
[21]	O. Bouaziz, S. Allain, C.P. Scott, P. Cugy, D. Barbier, Curr. Opin. Solid State Mater.Sci. 15(2011) 141-168.
[22]	L. Chen, J.K. Kim, S.K. Kim, G.S. Kim, K.G. Chin, B.C. De Cooman, Steel Res. Int. 8(2010) 552-568.
[23]	H. Ding, H. Ding, C.L. Qiu, Z.Y. Tang, J.M. Zeng, P. Yang, J. Iron Steel Res. Int. 18(2011) 36-40.
[24]	A.P. Bentley, G.C. Smith, Metall. Trans. A 17A (1986) 1593-1599.
[25]	S.K. Paul, J. Mater. Eng. Perform. 23(2014) 3610-3619.
[26]	F. HajyAkbary, J. Sietsma, R.H. Petrov, G. Miyamoto, T. Furuhara, M.J. Santofimia, Scr. Mater. 137(2017) 27-30.
[27]	R.A. Grange, Metall. Trans. 2(1971) 417-426.
[28]	T.F. Majka, D.K. Matlock, G. Krauss, Metall. Mater. Trans. A 33 (2002) 1627-1637.
[29]	J.S. Hayes, R. Keyte, P.B. Prangnell, Mater. Sci. Technol. 16(2000) 1259-1263.
[30]	C.Y. Yu, P.W. Kao, C.P. Chang, Acta Mater. 53(2005) 4019-4028.
[31]	S. Kang, J.-G. Jung, M. Kang, W. Woo, Y.-K. Lee, Mater. Sci. Eng. A 652 (2016) 212-220.
[32]	R. Ueji, N. Tsuchida, D. Terada, N. Tsuji, Y. Tanaka, A. Takemura, K. Kunishige, Scr. Mater. 59(2008) 963-966.
[33]	Z.H. Cai, H. Ding, R.D.K. Misra, Z.Y. Ying, Acta Mater. 84(2015) 229-236.
[34]	ASTM E 517-98, Standard Test Method for Plastic Strain Ratio R for Sheet Metal, ASTM International, 2000.
[35]	ASTM E 646-98, Standard Test Method for Tensile Strain-Hardening Exponents (n-Values) of Metallic Sheet Materials, ASTM International, 2000.
[36]	B.M. Gonzalez, C.S.B. Castro, V.T.L. Buono, J.M.C. Vilela, M.S. Andrade, J.M.D. Moraes, M.J. Mantel, Mater. Sci. Eng. A 343 (2003) 51-56.
[37]	C.G. Lee, S.-J. Kim, T.-H. Lee, S. Lee, Mater. Sci. Eng. A 371 (2004) 16-23.
[38]	S.-J. Kim, C.G. Lee, T.-H. Lee, C.-S. Oh, Scr. Mater. 48(2003) 539-544.
[39]	J.I. Yoon, H.H. Lee, J. Jung, H.S. Kim, Mater. Sci. Eng. A 735 (2018) 295-301.
[40]	K. Chung, K. Ahn, D. Yoo, K. Chung, M. Seo, S. Park, Int. J. Plast. 27(2011) 52-81.
[41]	J.I. Yoon, J. Jung, H.H. Lee, J.Y. Kim, H.S. Kim, Met. Mater. Int. 25(2019) 1161-1169.
[42]	J.H. Kim, Y.J. Kwon, T. Lee, K.-A. Lee, H.S. Kim, C.S. Lee, Met. Mater. Int. 24(2018) 187-194.
[43]	Y. Chino, H. Iwasaki, M. Mabuchi, Mater. Sci. Eng. A 466 (2007) 90-95.
[44]	J.H. Han, J.Y. Suh, K.K. Jee, J.C. Lee, Mater. Sci. Eng. A 477 (2008) 107-120.
[45]	Y. Zeng, B. Jiang, O. Shi, G. Quan, S. Al-Ezzi, F. Pan, Met. Mater. Int. 24(2018) 830-839.
[46]	C.T. Wang, G. Kinzel, T. Altan, J. Mater. Process. Technol. 53(1995) 759-780.
[47]	L. Ren, L. Nan, K. Yang, Mater. Des. 32(2011) 2374-2379.
[48]	J.Y. Yoo, W.Y. Choo, T.W. Park, Y.W. Kim, ISIJ Int. 35(1995) 1034-1040.
[49]	D. Isheim, S. Vaynman, M.E. Fine, D.N. Seidman, Scr. Mater. 59(2008) 1235-1238.
[50]	F. Pegorin, K. Pingkarawat, S. Daynes, A.P. Mouritz, Compos. Part B Eng. 78(2015) 298-307.
[51]	G. Stegschuster, K. Pingkarawat, B. Wendland, A.P. Mouritz, Compos. Part A 84 (2016) 308-315.