Hot Deformation Behavior and Constitutive Modeling of H13-Mod Steel

Abstract

The H13-mod steel optimized by composition and heat treatment has reached the performance index of the shield machine hob. The hot deformation behavior of the H13-mod steel was investigated by compression tests in the temperature range from 900 to 1150 • C and the strain rate range from 0.01 to 10 s −1 . The true stress-strain curve showed that the rising stress at the beginning of deformation was mainly caused by work hardening. After the peak stress was attained, the curve drop and the flow softening phenomenon became more obvious at low strain rates. The flow behavior of the H13-mod steel was predicted by a strain-compensated Arrhenius-type constitutive equation. The relationship between the material constant in the Arrhenius-type constitutive equation and the true strain was established by a sixth-order polynomial. The correlation coefficient between the experimental value and the predicted value reached 0.987, which indicated that the constitutive equation can accurately estimate the flow stress during the deformation process. A good linear correlation was achieved between the peak stress (strain), critical stress (strain) and the Zener-Hollomon parameters. The processing maps of the H13-mod steel under different strains were established. The instability region was mainly concentrated in the high-strain-rate region; however, the microstructure did not show any evidence of instability at high temperatures and high strain rates. Combined with the microstructure and electron backscattered diffraction (EBSD) test results under different deformations, the optimum hot working parameters were concluded to be 998-1026 • C and 0.01-0.02 s −1 and 1140-1150 • C and 0.01-0.057 s −1 . mechanical properties of H13 steel by optimizing the composition and heat-treatment conditions and applying surface treatments [7][8][9][10][11][12][13]. However, the H13 steel prepared by these processes does not demonstrate a good match between strength and toughness and cannot be used under complex geological conditions. Therefore, the development of a hob material with both strength and toughness is important.An increase in the carbon content of steel is well known to increase its strength and decrease its plastic toughness. However, an excessively high carbon content causes an increase in the brittleness of the steel. Therefore, we strictly controlled the carbon content in the range from 0.48% to 0.52%, optimized the content of other major alloying elements, reduced the impurity content and controlled the shape and size of inclusions to improve the performance of steel. The modified H13 steel, hereafter referred to as H13-mod, was developed by optimizing the heat-treatment conditions. Its hardness reaches 57 HRC and its impact toughness is 15 J/cm 2 , which fully satisfies the performance requirements of the shield hob.H13-mod exhibits excellent mechanical properties. However, whether it can be processed into a qualified part product is not only determined by the material's characteristics but also by the processing technology. At the ...

Microstructural Evolution during Homogenization and Hot Deformation for As‐Cast H13 Steel

“…[ 25 ] With an increasing strain to 0.6 and 0.8, more energy was applied to recrystallization, and the formed fine recrystallization grains swallowed each other and grown. [ 13 ] Consequently, the area of grain boundary gradually decreased, and the amount of precipitates decreased correspondingly.…”

“…By quantitative analysis, the average grain size is about 75 μm (Figure 9a), 35 μm (Figure 9b), and 28 μm (Figure 9d), and the grain size in Figure 9d is the smallest than those in Figure 9a,b, indicating that it is easier to obtain small equiaxed grains at high strain rate than at low strain rate. [ 13,17 ] However, the grain size distribution is heterogeneous at a strain rate of 0.1 s −1 in Figure 9a, where the size of large grains is to 200 μm and that of small grains is to 20 μm. It is noted that the microstructure in Figure 9c is in a seriously distorted state.…”

“…In our previous study, [ 9 ] it reported that the grain size increased with the increase in homogenization time, and the grain size was 240 μm at 1200 °C for 20 h. Ma et al, [ 10 ] Lu et al, [ 11 ] and Torkar et al [ 12 ] reported that, utilizing sufficient high‐temperature homogenization treatment (1200–1300 °C) of ingot prior to hot forging, the performance of H13 steel was obviously improved. Li et al, [ 13 ] Zhao et al, [ 14 ] Fan et al, [ 15 ] and Liang et al [ 16 ] reported that it was easier to obtain small and uniform equiaxed grains at high strain rates than at low strain rates. The results all indicated that, to date, the homogenization is still considered to be proceeded sufficiently in practical forging examples, and the study on the effect of the dendrite segregation on the microstructural evolution during hot deformation is still absent.…”

Flow Stress and Hot Deformation Activation Energy of 6082 Aluminium Alloy Influenced by Initial Structural State

“…Using the value of Qp = 98.6 kJ•mol −1 , the strain ep [-] corresponding to the peak stress in dependence on the Z parameter has been described for the extruded state. The commonly used type of power function [47,48] was applied for regression analysis of the peak strain data. = 0.0053 ⋅ .…”

Constitutive Equation and Hot Processing Map of a Nitrogen-Bearing Martensitic Stainless Steel

“…Moreover, a processing map (PM), proposed by Prasad et al and based on DMM, is a convenient and powerful tool to optimize the process parameters and evaluate the deformation mechanisms during the hot deformation process [18]. This technique has been successfully adopted in many metals, such as alloys of magnesium, titanium, nickel-based alloys and steels [19][20][21]. In recent years, many researchers have studied the hot deformation behavior of stainless steels including AISI 304, AISI 410, AISI 420, etc., [22][23][24] by using PM technology based on a hot compression test.…”