Fracture mode identification of low alloy steels and cast irons by electron back-scattered diffraction misorientation analysis

doi:10.1016/j.jmst.2017.03.020

Abstract

Abstract:

The fracture modes of low alloy steels and cast irons under tensile and fatigue conditions were identified by electron back-scattered diffraction (EBSD) misorientation analysis in this research. The curves of grain reference orientation deviation (GROD) distribution perpendicular to the fracture surface were obtained by EBSD observation, and the characteristics of each fracture mode were identified. The GROD value of the specimen fractured in tension decreases to a constant related to the elongation of corresponding specimen in the far field (farther than 5 mm away from the fracture surface). The peak exhibits in GROD curves of two smooth specimens and a notched specimen near the fracture surface (within 5 mm away from the fracture surface), and the formation mechanisms were discussed in detail based on the influences of specimen geometries (smooth or notched) and material toughness. The GROD value of fatigue fractured specimen is close to that at undeformed condition in the whole field, except the small area near the crack path. The loading conditions (constant stress amplitude loading or constant stress intensity factor range △K loading) and the EBSD striation formation during fatigue crack propagation were also studied by EBSD observation parallel to the crack path.

Key words: Fracture mode identification, Low alloy steels, Cast irons, Electron back-scattered diffraction (EBSD), Misorientation

Rui Shao-Shi, Shang Yi-Bo, Qiu Wenhui, Niu Li-Sha, Shi Hui-Ji, Matsumoto Shunsaku, Chuman Yasuharu. Fracture mode identification of low alloy steels and cast irons by electron back-scattered diffraction misorientation analysis[J]. J. Mater. Sci. Technol., 2017, 33(12): 1582-1595.

Figures/Tables 18

Table 1 Main chemical elements of 40Cr and cast iron (wt.%).

40Cr	0.36	0.41	1.27	1.56
	C	Si	Mn	Cr
Cast iron	C	Si	S	P
	3.41	2.89	0.01	0.03

Fig. 1. Microstructures and EBSD observational results of (a) 40Cr and (b) cast iron.

Table 2 Mechanical properties of 40Cr and cast iron.

	Yield strength (MPa)	Tensile strength (MPa)	Elongation (%)	Reduction in area (%)
40Cr	277.6	638.6	25.60	46.71
Cast iron	321.0	450.7	23.36	27.12

Fig. 2. (a) Dimension of sheet specimens and (b) EBSD observational sites in the specimens fractured in tension.

Fig. 3. (a) Dimension of CT specimens and (b) EBSD observational sites in the CA fatigue specimens.

Fig. 4. (a) Dislocations slip without obstacles in (1$\bar{1}$0) surface of body-centered cubic crystal, (b) misorientation caused by dislocations accumulation in [11$\bar{1}$] and [111] slip systems, (c) dislocations accumulation ahead of grain boundary, (d) definition of GROD and KAM.

Fig. 5. Nominal stress-strain curves of four tensile specimens.

Fig. 6. GROD ((a, b): smooth specimens; (c, d): notched specimens) and IPF ((e, f): smooth specimens; (g, h): notched specimens) maps observed perpendicularly to the tensile fracture surface.

Fig. 7. Average GROD values of various distances from the fracture surface.

Fig. 8. (a) △K value of various distances from the right edge of EBSD observational sample under CA fatigue condition, and (b) the relationship between crack propagation rate da/dN and crack tip driving force △K in low alloy steel and cast iron under logarithmic coordinates.

Fig. 9. GROD ((a): low alloy steel; (b): cast iron) and IPF ((c): low alloy steel; (d): cast iron) maps observed perpendicularly to the fracture surface of CA fatigue specimens.

Fig. 10. (a) GROD, (b) KAM and (c) IPF maps observed parallelly to the crack path at three different positions of low alloy steel CA and CK fatigue specimens.

Fig. 11. Calculation method of average GROD/KAM value near the crack path in each map.

Fig. 12. Average (a) GROD and (b) KAM distribution near the crack paths at three different positions of low alloy steel CA and CK fatigue specimens.

Fig. 13. EBSD striation observed in GROD maps of cast iron fatigue fractured specimen.

Fig. 14. Microvoids distribution in the necking zone of smooth specimens.

Fig. 15. Two kinds of plastic deformation distribution near fracture surface in (a) low alloy steel and (b) cast iron notched specimens.

Fig. 16. Grain subdivisions observed in the vicinity of the fatigue crack tip in low alloy steel specimen.

References

[1]	D. Kobayashi, M. Miyabe, Y. Kagiya, R. Sugiura, A.T. Yokobori, Metall. Mater. Trans. A, 44 (7) (2013), pp. 3123-3135
[2]	M. Calcagnotto, D. Ponge, E. Demir, D. Raabe, Mater. Sci. Eng. A, 527(2010), pp. 2738-2746
[3]	K. Kubushiro, Y. Sakakibara, T. Ohtani, Soc. Mater. Sci. Jpn., 64(2015), pp. 106-112
[4]	M. Kamaya, A.J. Wilkinson, J.M.Titchmarsh, Nucl. Eng. Des., 235(2005), pp. 713-725
[5]	M. Kamaya, Mater. Charact., 60(2009), pp. 125-132
[6]	D. Kobayashi, A. Ito, M. Miyabe, Y. Kagiya, Y. Yoshioka, ASME Turbo Expo, 2012 (2012)
[7]	D. Kobayashi, M. Miyabe, M. Achiwa, ASME Turbo Expo, 2015 (2015)
[8]	D. Kobayashi, M. Miyabe, M. Achiwa, JSMS 13th Fractographic Conference (2014)
[9]	D. Kobayashi, M. Miyabe, M. Achiwa, R. Sugiura, A.T.Yokobori, Mater. High Temp., 31(2015), pp. 326-333
[10]	D. Kobayashi, M. Miyabe, Y. Kagiya, Y. Nagumo, R. Sugiura, T. Matsuzaki, A.T.Yokobori Jr., Strength Fract.Complex., 7(2011), pp. 157-167
[11]	D. Kobayashi, M. Miyabe, Y. Kagiya, Y. Nagumo, R. Sugiura, T. Matsuzaki, A.T. Yokobori, Mater. High Temp., 29 (4) (2012), pp. 301-307
[12]	D. Kobayashi, M. Miyabe, Y. Kagiya, Y. Nagumo, R. Sugiura, T. Matsuzaki, A.T.Yokobori, Mater. Sci. Technol., 30(2014), pp. 24-31
[13]	D. Kobayashi, T. Takeuchi, M. Achiwa, JSME Annual Conference 2015 (2015)
[14]	ASTM International, PA, 2008.
[15]	ASTM International, PA, 2011.
[16]	A. Arsenlis, D.M.Parks, Acta Mater., 47(1999), pp. 1597-1611
[17]	S. Suresh,Fatigue of Materials,Cambridge University Press, Cambridge(1998)
[18]	M. Cavallini, O. Di Bartolomeo, F. Iacoviello, Eng. Fract. Mech., 75(2008), pp. 694-704
[19]	E.E. Cabezas, D.J.Celentano, Finite Elem. Anal. Des., 40(2004), pp. 555-575
[20]	J. Kadkhodapour, A. Butz, S. Ziaei Rad, Acta Mater., 59 (7) (2011), pp. 2575-2588
[21]	S.A. Sajjadi, A.T.Yokobori, Mater. Sci. Technol., 30(2014), pp. 43-49
[23]	C. Butcher, Z.T. Chen, Theor. Appl. Fract. Mech., 55 (2) (2011), pp. 140-147
[24]	X. Gong, P. Marmy, L. Qin, B. Verlinden, M. Wevers, M. Seefeldt, Mater. Sci. Eng. A, 618(2014), pp. 406-415
[25]	X. Gong, P. Marmy, A. Volodin, B. Amin-Ahmadi, L. Qin, D. Schryvers, S. Gavrilov, E. Stergar, B. Verlinden, M. Wevers, M. Seefeldt, Corros. Sci., 102(2016), pp. 137-152
[26]	X. Huang, T.E. Gibson, M. Zhang, R.W. Neu, Tribol. Int., 42 (6) (2009), pp. 875-885