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. 2021 Nov 18;14(22):6995.
doi: 10.3390/ma14226995.

Surface Integrity and Corrosion Resistance of 42CrMo4 High-Strength Steel Strengthened by Hard Turning

Qingzhong Xu  1   2 , Yan Liu  1 , Haiyang Lu  3 , Jichen Liu  1 , Gangjun Cai  1
Affiliations

Surface Integrity and Corrosion Resistance of 42CrMo4 High-Strength Steel Strengthened by Hard Turning

Qingzhong Xu et al. Materials (Basel). .

Abstract

To improve the surface corrosion resistance of 42CrMo4 high-strength steel used in a marine environment, this article studied the effects of hard turning on the surface integrity and corrosion resistance of 42CrMo4 high-strength steel through the single factor experimental method, namely hard turning, polarization corrosion, electrochemical impedance spectroscopy, potentiodynamic polarization curve, and salt spray tests. The results indicated that the surface integrity was modified by the hard turning, with a surface roughness lower than Ra 0.8 μm, decreased surface microhardness, fine and uniform surface microstructure, and dominant surface residual compressive stress. The hard turning process was feasible to strengthen the surface corrosion resistance of 42CrMo4 high-strength steel. The better corrosion resistance of the surface layer than that of the substrate material can be ascribed to the uniform carbides and compact microstructure. The corrosion resistance varied with cutting speeds as a result of the changed surface microhardness and residual compressive stress, varied with feed rates as a result of the changed surface roughness, and varied with cutting depths as a result of the changed surface residual compressive stress, respectively. The surface integrity with smaller surface roughness and microhardness and bigger surface residual compressive stress was beneficial for corrosion resistance.

Keywords: 42CrMo4 steel; corrosion resistance; hard cutting; surface integrity.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Photographic view of hard turning experiment.
Figure 2
Figure 2
(a) Model of tool and workpiece and (b) residual stress distribution.
Figure 3
Figure 3
Surface roughness of samples machined under different cutting parameters: (a) cutting speed, (b) feed rate, and (c) cutting depth.
Figure 4
Figure 4
Cutting forces obtained under different cutting parameters: (a) cutting speed, (b) feed rate, and (c) cutting depth.
Figure 5
Figure 5
Cutting vibrations obtained under different cutting parameters: (a) cutting speed, (b) feed rate, and (c) cutting depth.
Figure 6
Figure 6
Microhardness of samples machined under different cutting parameters: (a) cutting speed, (b) feed rate, and (c) cutting depth.
Figure 7
Figure 7
Cutting temperatures obtained under different cutting parameters: (a) cutting speed, (b) feed rate, and (c) cutting depth.
Figure 8
Figure 8
Metallographic structures of machined sample: (a) overall view and (b) local enlarged view.
Figure 9
Figure 9
SEM morphologies of (a) surface layer, (b) subsurface layer, and (c) substrate.
Figure 10
Figure 10
Surface residual stresses of samples obtained under different cutting parameters: (a) cutting speed, (b) feed rate, and (c) cutting depth.
Figure 11
Figure 11
(a,b) Polarization corrosion morphologies of sample cross section and detail views of (c) substrate, (d) surface layer, and (e) subsurface layer.
Figure 12
Figure 12
Nyquist plots and Bode plots of machined surfaces for samples machined under different cutting parameters: (a) cutting speed, (b) feed rate, and (c) cutting depth; and (d) equivalent circuit model of electrochemical impedance.
Figure 13
Figure 13
Charge transfer resistances of machined surfaces for samples machined under different cutting parameters: (a) cutting speed, (b) feed rate, and (c) cutting depth.
Figure 14
Figure 14
Annual corrosion rates of samples machined under different cutting parameters: (a) cutting speed, (b) feed rate, and (c) cutting depth.
Figure 15
Figure 15
Nyquist plots and Bode plots of samples obtained in comparative experiments: (a) #5 and #6, (b) #1 and #10, and (c) #9 and #10.
Figure 16
Figure 16
Polarization curves of samples obtained in comparative experiments: (a) #5 and #6, (b) #1 and #10, and (c) #9 and #10.
Figure 17
Figure 17
3D morphologies of samples obtained in (a) Experiment #5 and (b) Experiment #6.
Figure 18
Figure 18
Morphologies of samples obtained in (a) Experiment #5 and (b) Experiment #6 under salt spray corrosion for 30 min.
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