Effect of laser incident energy on microstructures and mechanical properties of 12CrNi2Y alloy steel by direct laser deposition

doi:10.1016/j.jmst.2018.10.024

Abstract

Abstract:

This work aims to establish the effect of laser energy area density (EAD) as the laser incident energy on density, microstructures and mechanical properties of direct laser deposition (DLD) 12CrNi2Y alloy steel. The results show that the density of DLD 12CrNi2Y alloy steel increases at initial stage and then decreases with an increase of EAD, the highest density of alloy steel sample is 98.95%. The microstructures of DLD 12CrNi2Y alloy steel samples are composed of bainite, ferrite and carbide. With increase of EAD, the microstructures transform from polygonal ferrite (PF) to granular bainite (GB). The martensite-austenite constituent (M-A) in GB transforms from flake-like paralleling to the bainite ferrite laths to granular morphology. It is also found that the average width of laths in finer GB can be refined from 532 nm to 302 nm, which improves the comprehensive properties of DLD 12CrNi2Y alloy steel such as high hardness of 342 ± 9 HV_0.2, yield strength of 702 ± 16 MPa, tensile strength of 901 ± 14 MPa and large elongation of 15.2%±0.6%. The DLD 12CrNi2Y material with good strength and toughness could meet the demand of alloy steel components manufacturing.

Key words: Direct laser deposition, Energy area density, 12CrNi2Y alloy steel, Microstructures, Mechanical properties

Tingting Guan, Suiyuan Chen, Xueting Chen, Jing Liang, Changsheng Liu, Mei Wang. Effect of laser incident energy on microstructures and mechanical properties of 12CrNi2Y alloy steel by direct laser deposition[J]. J. Mater. Sci. Technol., 2019, 35(2): 395-402.

Figures/Tables 12

Table 1 Chemical composition of the 12CrNi2Y alloy steel (mass fraction, %).

C	Cr	Ni	Si	Mn	Y	Fe
0.144	0.745	1.850	≤0.300	0.605	1.710	Bal

Fig. 1. (a) SEM morphology of spherical powder of 12CrNi2Y alloy steel; (b) Size distribution of 12CrNi2Y alloy steel spherical powder.

Fig. 2. (a) DLD schematic diagram of 12CrNi2Y alloy steel; (b) 3D view of the tensile test samples and geometry of DLD processed samples for tensile test.

Table 2 DLD processing parameters.

Parameters	Value
Powder feeding rate (g min^-1)	3.5
Scanning velocity (mm s^-1)	5.4
Spot diameter (mm)	1.8
Increment of axis-Z(mm)	0.4
Overlap rate (%)	50
Laser power (W)	500, 600, 700, 800

Fig. 3. (a) Densification level of DLD 12CrNi2Y alloy steel samples with different EAD; (b) Three-dimensional morphology of the deposited sample (EAD = 72.02 J/mm2).

Fig. 4. SEM morphology of DLD 12CrNi2Y alloy steel samples with different EAD: (a) EAD = 51.44 J/mm2, (b) EAD = 61.73 J/mm2, (c) EAD = 72.02 J/mm2, (d) EAD = 82.30 J/mm2.

Fig. 5. TEM morphology of DLD 12CrNi2Y alloy steel samples with different EAD: (a) EAD = 61.73 J/mm2, (b) EAD = 72.02 J/mm2, (c) EAD = 82.30 J/mm2, (d) selecting electron diffraction patterns of precipitates (EAD = 82.30 J/mm2).

Fig. 6. IPF maps and grain size distribution of DLD 12CrNi2Y alloy steel samples with different EAD: (a) and (c) EAD = 61.73 J/mm2, (b) and (d) EAD = 72.02 J/mm2, (e) and (f) EAD = 82.30 J/mm2.

Table 3 Misorientation of DLD 12CrNi2Y alloy steel with different EAD.

EAD (J/mm²)	LAGBs (%)	HAGBs (%)
61.73	21.8	40.3
72.02	23.3	45.7
82.30	11.6	65.4

Fig. 7. Vickers microhardness of DLD 12CrNi2Y alloy steel samples with different EAD.

Fig. 8. Tensile properties of the DLD 12CrNi2Y alloy steel were tested at room temperature with different EAD.

Fig. 9. Tensile fraction morphology of the DLD 12CrNi2Y alloy steel samples with different EAD: (a) EAD = 51.44 J/mm2, (b) EAD = 61.73 J/mm2, (c) EAD = 72.02 J/mm2, (d) EAD = 82.30 J/mm2.

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