Fracture Morphologies of Advanced High Strength Steel During Deformation

doi:10.1007/s40195-014-0032-8

Abstract

Abstract:

The fracture morphologies of several advanced high-strength steels (DP590, DP780, DP980, M1180, and M1300) formed in uniaxial tension and piercing were observed by scanning electron microscope, and then quantitatively analyzed by image processing technique. The tension-induced fractographs are dominated by obvious uniform or bimodal size dimples, while shearing-induced fractographs have smooth surfaces and few dimples. The fracture zone of higher grade DP steels is smoother. As for M1180 and M1300, the fracture zones consist of very small dimples and smooth brittle surfaces. The dimple size of M1300(~1.2 μm) is smaller than that of M1180(~1.6 μm). Moreover, in the tensile fracture, the quantitative correlation between average dimple diameter (d) and tensile strength (σ) can be represented by d = 10,502.32σ^-1.21. However, the relation between dimple density and tensile strength is not monotonic due to the appearance of bimodal size dimples with increase of tensile strength. For shearing-induced fracture during piercing, the fitted empirical model between the percentage of burnish zone (f) and tensile strength can be described as f = 239.9σ^-0.36.

Key words: High strength steel, Fracture morphology, Dimple size, Burnish zone, Tensile strength

Ying Sun, Xifeng Li, Xiangyu Yu, Delong Ge, Jun Chen, Jieshi Chen. Fracture Morphologies of Advanced High Strength Steel During Deformation[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(1): 101-106.

Figures/Tables 10

Fig. 1 Geometry of the uniaxial tensile specimens (unit: mm)

Fig. 2 Schematic of experimental setup for the piercing test (unit: mm)

Fig. 3 SEM images showing the fracture surfaces and the corresponding void networks after image-processing of SEM fractographs: a, b DP590; c, d DP780

Table 1 Mechanical properties of five materials at room temperature

Steel	Yield strength (MPa)	Tensile strength (MPa)	Elongation (%)
DP590	330	594	26
DP780	497	843	21
DP980	698	1,003	15
M1180	1,075	1,300	13
M1300	1,240	1,470	12

Fig. 4 SEM images showing the fractographs of tensile fracture surface of DP980 a, M1180 b, M1300 c

Fig. 5 Variation of average dimple diameter with tensile strength

Fig. 6 Variation of dimple number density with tensile strength

Fig. 7 Photo of a specimen after the piercing test

Fig. 8 SEM images showing the fractographs of the fractured edge of the piercing sheets and the magnified images of the selected zone which marked by A, B, C, D, E: a, b DP590; c, d DP780; e, f DP980; g, h MS1180; i, j MS1300

Fig. 9 Variation of burnish zone percentage with tensile strength

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