Study of the Hard Turning Processability of Hardened Ultra-high Strength Steel 45CrNiMoVA

doi:10.12382/bgxb.2021.0757

Abstract

Abstract:

In order to avoid tensile residual stress and heavy use of highly-polluting cutting fluid, in the grinding process of hardened steel, a hard turning process is proposed. The turning process is carried out for the quenched-tempered 45CrNiMoVA steel. The cutting forces during the process are recorded, and the surface morphology, residual principal stress, and microhardness of the machined surfaces are analyzed. The results show that the cutting forces increase with the cutting depth and feed rate. However, the change in cutting speed has little effect on the cutting force. The surface roughness Ra of the workpiece after hard turning can reach 0.64 μm. The consistency of surface morphologies is also satisfying. The residual principal stress decreases with the increase of the feed rate and the cutting depth. By comparison, the residual principal stress first decreases and then increases with the increase of the cutting speed. The direction angle of the maximum residual principal stress changes steadily within the range of 37°~45° with the increase of cutting speed and cutting depth. It first increases and then maintains stable within the range of 22°~45° with the increase of feed. The surface microhardness decreases with the increase of cutting speed, and the depth of hardened layer is about 200 μm.

Key words: 45CrNiMoVA steel, hard turning, cutting force, surface morphology, residual principal stress, microhardness

DU Kai, JIAO Li, YAN Pei, YU Jianhang, WANG Yubin, QIU Tianyang, WANG Xibin. Study of the Hard Turning Processability of Hardened Ultra-high Strength Steel 45CrNiMoVA[J]. Acta Armamentarii, 2023, 44(3): 773-782.

Figures/Tables 25

Table 1 Chemical composition of 45CrNiMoVA wt.%

C	Cr	Ni	Mo	V	Si	Mn
0.42~0.49	0.80~1.10	1.30~1.80	0.20~0.30	0.10~0.20	0.17~0.37	0.50~0.80

Fig. 1 Microstructure of 45CrNiMoVA

Table 2 Mechanical parameters of 45CrNiMoVA

抗拉强度R_m/MPa	屈服强度R_p0.2/MPa	断后延伸率A / %	断面收缩率Z /%
2030	1635	13.5	52

Fig. 2 Test platform for hard turning

Table 3 Single-factor hard-turning experiment parameters

序号	切削速度 v_c / (m·min^-1)	切削深度 a_p/mm	进给量f / (mm·r^-1)
1-1	120	0.10	0.03
1-2			0.06
1-3			0.09
1-4			0.12
2-1	120	0.05	0.09
2-2		0.10
2-3		0.15
2-4		0.20
3-1	100	0.10	0.09
3-2	120
3-3	140
3-4	160

Fig. 3 Residual stress test device

Fig. 4 Measured cutting force signals

Fig. 5 Influence of feed on cutting force (vc=120 m/min, ap=0.10 mm)

Fig. 6 Influence of cutting depth on cutting force (vc = 120 m/min, f = 0.09 mm/r)

Fig. 7 Schematic diagram of the tool-workpiece contact area

Fig. 8 Influence of cutting speed on cutting force (f =0.09 mm/r, ap =0.10 mm)

Fig. 9 Surface topography of the specimens under different cutting process parameters(the above is a two-dimensional pattern map and the following is a three-dimensional morphology picture)

Fig. 10 Influence of feed rate on surface roughness (vc = 120 m/min, ap = 0.10 mm)

Fig. 11 Influence of cutting speed on surface roughness (f = 0.09 mm/r, ap = 0.10 mm)

Fig. 12 Influence of cutting depth on surface roughness (f = 0.09 mm/r, vc = 120 m/min)

Fig. 13 Schematic diagram of residual stress test

Fig. 14 Influence of feed rate on residual stress (vc = 120 m/min, ap = 0.10 mm)

Fig. 15 Influence of cutting depth on residual stress (vc = 120 m/min, f = 0.09 mm/r)

Fig. 16 Influence of cutting speed on residual stress (f = 0.09 mm/r, ap = 0.10 mm)

Fig. 17 Mohr’s circle method

Table 4 Calculation and measurement results of minimum residual principal stress

试验序号	σ_min方向角α₂/(°)	σ_min计算值/MPa	σ_min测量值/MPa	偏差/%
1-3	-45.1	-880	-912	3.64
1-4	-47.9	-929	-1027	10.49
2-3	-46.4	-934	-876	6.22
2-4	-48.6	-995	-920	7.52
3-1	-46.8	-871	-830	4.73

Fig. 18 Influence of cutting parameters on direction angle of maximum residual principal stress

Fig. 19 Influence of cutting speed on microhardness of machined surface

Fig. 20 Distribution of microhardness along the depth of subsurface layer

Table 5 Comparison of hard turning and grinding processes

工艺	Q_z /(mm³·min^-1)	Ra /μm	残余应力σ/MPa
工艺	Q_z /(mm³·min^-1)	Ra /μm	轴向	周向
硬车削	1080	0.75	-476	-474
磨削^[20]	80	0.5-0.7	-312	-249

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