Hot Deformation Behavior and Dynamic Recrystallization Characteristics in a Low-Alloy High-Strength Ni-Cr-Mo-V Steel

doi:10.1007/s40195-018-0729-1

Abstract

Abstract:

This study presented a quantitative investigation of deformation behavior and dynamic recrystallization of low-alloy high-strength Ni-Cr-Mo-V steels during hot deformation. A series of isothermal compression experiments were performed at temperatures ranging from 800 to 1200 °C and strain rates from 0.01 to 10 s^-1 with a height reduction of 60%. A complete Arrhenius constitutive model and processing maps were developed. The results showed that the constitutive model had the ability to predict the flow stress with an average absolute relative error of <5.7%. The processing maps constructed at strains of 0.2, 0.4, and 0.8 showed that flow instability was prone to occur at higher strain. Dynamic recrystallization tended to take place at higher temperatures (900-1200 °C) and lower strain rates (0.01-1 s^-1). The critical strain for the onset of dynamic recrystallization was determined, and a kinetics model was developed. The predicted results for recrystallization volume fraction and flow stress were compared with the experimental data, which indicated that the model was accurate and reliable.

Key words: Deformation behavior, Dynamic recrystallization, Constitutive equation, Processing map, Critical strain, Recrystallization kinetics

Chuan Wu, Shuang Han. Hot Deformation Behavior and Dynamic Recrystallization Characteristics in a Low-Alloy High-Strength Ni-Cr-Mo-V Steel[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(9): 963-974.

Figures/Tables 19

Fig. 1 Experimental procedure of hot compression test for acquiring stress strain data and microstructure.

Fig. 2 Stress-strain curves of steel at strain rates from 0.01 to 10 s-1 and temperatures of a 800 °C, b 900 °C, c 1000 °C, d 1100 °C, e 1200 °C, f softening extent.

Table 1 Peak stresses and peak strains (σp/εp) at different conditions

Temperature (°C)	0.01 s^-1	0.1 s^-1	1 s^-1	10 s^-1
900	121.0/0.44	169.0/0.69	197.0/0.77	-
1000	76.4/0.22	116.0/0.43	152.0/0.71	-
1100	55.0/0.17	75.6/0.29	110.0/0.40	-
1200	40.0/0.12	55.0/0.20	75.0/0.33	-

Fig. 3 Determining values of n1 (a) and β1 (b) from Eqs. (2) and (3) .

Fig. 4 Determining value of n from Eq. (6) .

Fig. 5 Determining value of Q from Eq. (6) .

Fig. 6 Variation of material constants in Eq. (3) with strain: a α; b n; c A; d Q.

Fig. 7 Comparison of predicted flow stress with experimental data at strain rates of a 0.01 s-1, b 0.1 s-1, c 1 s-1, d 10 s-1.

Fig. 8 Correlation between experimental and predicted values.

Fig. 9 Processing maps of steel deformed at different strains of a 0.2, b 0.4, c 0.8.

Fig. 10 Typical microstructures of steel showing DRX deformed at strain rate of 0.1 s-1 and higher temperatures of a 950 °C, b 1000 °C.

Fig. 11 Microstructural evolution of steel at temperatures of a-c 800 °C, d-f 1000 °C, g-i 1200 °C and strain rates of a, d, g 0.01 s-1, b, e, h 0.1 s-1, c, f, i 1 s-1.

Fig. 12 Curves of θ-σ (a-c) and $\left( {{{ - \partial \theta } \mathord{\left/ {\vphantom {{ - \partial \theta } {\partial \sigma }}} \right. \kern-0pt} {\partial \sigma }}} \right) - \sigma$ (d-f) at strain rates of a, d 0.01 s-1, b, e 0.1 s-1, c, f 1 s-1.

Table 2 Values of critical strain and stress (σc/εc) under different deformation conditions

Temperature (°C)	0.01 s^-1	0.1 s^-1	1 s^-1	10 s^-1
900	80.0/0.07	-	-	-
1000	60.1/0.10	93.5/0.14	-	-
1100	47.8/0.09	63.0/0.11	94.6/0.20	-
1200	34.8/0.06	40.0/0.06	66.0/0.16	-

Fig. 13 Method to determine volume fraction of DRX through net softening effect.

Fig. 14 DRX kinetics at strain rates of a 0.01 s-1, b 0.1 s-1, c 1 s-1.

Fig. 15 Determining values of a k1, b k2, c βd and k3.

Fig. 16 Comparison of predicted value with experimental data at strain rates of a 0.01 s-1, b 0.1 s-1, c 1 s-1.

Fig. 17 Comparison of predicted flow stress with experimental data at strain rates of a 0.01 s-1, b 0.1 s-1, c 1 s-1.

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