Effect of laser power and deposition environment on the microstructure and properties of direct laser metal-deposited 12CrNi2 steel

doi:10.1007/s40195-019-00974-4

Abstract

Abstract:

Direct laser metal deposition was used for preparing blocks of steel 12CrNi2 using four different laser powers under two different deposition environments including atmospheric environment and Ar-protected chamber. The results showed that microstructures and mechanical properties were significantly affected by different laser powers. Increasing laser power and deposition in Ar chamber will lead to a decrease in the quantity and size of the voids, which brings more elongation to the samples. Bainitic microstructure was replaced by Widmanstatten ferrite and pearlite, and the amount of proeutectoid ferrite increased with increasing laser power. Moreover, microstructures of previous layers were completely altered in high laser power. Excessive heat accumulation by using high heat input can produce equiaxed ferritic grains with the pearlites in previously deposited layers. Hardness of deposited samples increased from the bottom layer toward the top layer. By using a diode laser with a spot diameter size of 2 mm, the 900-W laser power is suitable for producing crack- and void-free samples. However, post-deposition heat treatment is necessary for obtaining homogeneous desired microstructure and grain size in the manufactured samples.

Key words: Direct laser metal deposition, Bainite, Equiaxed ferrite, Void, Steel, Microstructure, Mechanical properties, Rapid solidification

Mohamad Ebrahimnia, Yujiang Xie, Changtai Chi. Effect of laser power and deposition environment on the microstructure and properties of direct laser metal-deposited 12CrNi2 steel[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(4): 528-538.

Figures/Tables 18

Table 1 Chemical composition of 12CrNi2 steel powder (wt %)

Fig. 1 Particle size distribution of 12CrNi2 steel powder

Fig. 2 chematic illustration of the deposited sample, scanning pattern, position of the extracted tensile sample and metallographic sample

Table 2 Process parameters of DLMD samples

Fig. 3 Micrographs of the top layers of DLMD samples: a L500, b L700, c L900, d L1100. Granular bainite (GB), coalesced bainite (CB), Widmanstatten ferrite (WF), proeutectoid ferrite (F)

Fig. 4 Micrographs of the middle layers of DLMD samples: a L500, b L700, c L900, d L1100. Granular bainite (GB), proeutectoid ferrite (PF), equiaxed ferrite (F), pearlite (P)

Fig. 5 Micrographs of the top layers of DLMD samples: a AR500, b AR700, c AR900, d AR1100. Granular bainite (GB), proeutectoid ferrite (PF), Widmanstatten ferrite (WF), pearlite (P), lath bainite (LB)

Fig. 6 Micrographs of the middle layers of DLMD samples: a AR500, b AR700, c AR900, d AR1100. Granular bainite (GB), proeutectoid ferrite (PF), pearlite (P)

Fig. 7 Microstructures of different parts of sample AR1100 showing the effect of heat accumulation on the microstructure of sample

Fig. 8 Phase evolution in the steel 12CrNi2 in two different cooling rates: a 100 °C/s, b 50 °C/s

Fig. 9 SEM images of DLMD samples: a AR500, b AR700 top layer, c AR700 middle layer. Lath bainite (LB), granular bainite (GB), proeutectoid ferrite (PF), martensite (M), Widmanstatten ferrite (WF), martensite-austenite constitutes (M-A)

Fig. 10 Stress-strain curves of tensile test samples: a samples deposited in air, b samples deposited in Ar-protected chamber

Table 3 Mechanical test results of DLMD samples

Fig. 11 Vickers hardness of different samples: a atmospheric deposited samples, b Ar-protected samples

Fig. 12 Grain size measurement results for DLMD samples using intercept method

Fig. 13 Total number and area of voids in different samples

Fig. 14 Shapes and morphologies of voids in DLMD samples: a, b sample L500, c, d sample AR500. The black arrows show unmelted powder particles inside voids

Fig. 15 Fracture surfaces of tensile test samples: a sample L500 consists of ductile fracture accompanied by some holes and cleavage fracture beside holes, b sample L1100 has complete ductile fracture mode, c oxide particle leads to the void formation in the sample

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