Research Papers

Effects of Workshop Fabrication Processes on the Deformation Capacity of S960 Ultra-high Strength Steel

[+] Author and Article Information
M. Amraei

School of Energy Systems,
Lappeenranta University of Technology,
P.O. Box 20,
Lappeenranta 53851, Finland
e-mail: mohsen.amraei@lut.fi

M. Dabiri, T. Björk, T. Skriko

School of Energy Systems,
Lappeenranta University of Technology,
P.O. Box 20,
Lappeenranta 53851, Finland

1Corresponding author.

Manuscript received February 23, 2016; final manuscript received June 10, 2016; published online July 25, 2016. Assoc. Editor: Gracious Ngaile.

J. Manuf. Sci. Eng 138(12), 121007 (Jul 25, 2016) (13 pages) Paper No: MANU-16-1123; doi: 10.1115/1.4033930 History: Received February 23, 2016; Revised June 10, 2016

Deformation of a direct quenched type of ultra-high strength steel (UHSS) with low-carbon content is studied in this work. Although this material, as manufactured, combines high strength and good ductility, it is highly sensitive to the workshop fabrication processes used. The presence of stress concentration due to structural discontinuity or notch effects can accentuate the effect of fabrication processes on the deformation capacity of the material. To evaluate the influence of fabrication methods on deformation capacity, a series of tensile tests are done on both pure base material (BM) and after the steel has been subjected to heat input (HI) or cold forming (CF). To study the effect of HI due to welding or other heat-based workshop fabrication processes, the surface of the material was dressed by laser beam at controlled speed and laser intensity. CF effects were studied by bending the specimens to a predetermined angle prior to subjecting the steel to tensile testing. Experimental results were compared with numerical simulation using ls-dyna simulation software. The generated results show acceptable agreement between experimental and numerical simulation outcomes.

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Fig. 1

SEM of the BM, LB, martensite (M), and autotempered martensite (AM) [26]

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Fig. 2

5 MN test machine with installed ARAMIS used for the experimental tests

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Fig. 3

(a) Schematic of test specimen with hole-diameter of 40 mm. (b) Measured engineering stress–strain curve of BM without hole.

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Fig. 4

BM under tensile loading at the fracture point. From left to right hole-size increases: (a) test specimens and (b) ARAMIS plastic deformation contour.

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Fig. 5

Measured engineering stress–strain and force–displacement curves in gauge length of 80 mm for BM

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Fig. 6

(a) Distribution of the heat and the considered areas for hardness measurement and (b) microhardness of the material at different zones

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Fig. 7

Macroscopic view toward thickness and different zones at the material after experiencing heat

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Fig. 8

Microstructure of the material experiencing heat from FZ to BM: (a) FZ, (b) CGHAZ, (c) FGHAZ, (d) ICHAZ, (e) SCHAZ, and (f) transient area

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Fig. 9

Comparison of force–displacement curves after material experienced heat and BM

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Fig. 10

HI results from ARAMIS for the specimen without hole: (a) plastic strain distribution at the failure point and (b) effective stress–strain curves till 16% strain of HAZ

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Fig. 11

Distribution of strain on HI specimens right before fracture point (cracks are pointed with array). Sample with hole of (a) 8 mm, (b) 24 mm, and (c) 40 mm.

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Fig. 12

(a) Three-point bending procedure to study the effect of CF on the behavior of the material and (b) CF specimen

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Fig. 13

Load–displacement curves after CF effect and the BM

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Fig. 14

The specimens right before the fracture point including ARAMIS results

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Fig. 21

SEM view of the fracture surface of the material after experiencing heat with hole of 40 mm

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Fig. 20

Fracture surfaces (hole-diameter of 0, 8, 24, and 40 mm from left to right): the first row is for BM and the lower one is after HI

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Fig. 19

Comparison of load–displacement curves from experimental tests and FEA after (a) HI- and (b) CF- process

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Fig. 18

Macroscopic fracture of the material after experiencing HI from both experimental and FE

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Fig. 17

Macroscopic fracture of the BM from both experimental and FE, hole-diameter (mm) from left to right: 40, 24, 8, and 0

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Fig. 16

Comparison of test and FE load–displacement curves for BM

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Fig. 15

Effective stress–plastic strain curve used for the BM

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Fig. 22

Aramis versus FE results after experiencing heat without hole

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Fig. 23

Macroscopic fracture of BM and after CF




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