The influence of niobium content on austenite grain growth in microalloyed steels

Annan, Kofi Ahomkah; Siyasiya, Charles Witness; Stumpf, Waldo E.

doi:10.17159/2411-9717/2015/v115n10a12

Cited by 4 publications

(5 citation statements)

References 24 publications

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“…On contrary, by decreasing the slab temperature, as shown in Figure 1, the softening resulting from SRX becomes less pronounced, especially in the region close to homogeneous secondary precipitation of Nb(C,N). Based on [1,5,34] and the data presented in this paper, the importance of proper slab reheating temperature adjustment is revealed, as it not only influences the starting PAGS and achieved solubility of carbo-nitrides, but also affects the roughing temperature profile and with that the temperature positioning of the last roughing pass (to prevent entering into the area between RLT and RST and achieving final FRT when close to constant time delay is used. Based on [12], real deformation per pass needed for activating SRX is above 𝜀 = 0.06 (5.9% of engineering reduction), and the progress of SRX kinetics is controlled with the holding time and optimized in relation to 𝑡 50 .…”

Section: Rolling Proceduresmentioning

confidence: 98%

Hot Deformation Behavior of C-Mn Steel with Incomplete Recrystallization during Roughing Phase with and without Nb Addition

Klančnik¹,

Foder

Bradaškja

et al. 2022

Metals

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The objective of the study is to improve understanding of the practical role of niobium (Nb) in the case of industrial inconsistent rolling processes such as the rolling of heavy gauge plates where a lower stored energy rolling practice will result in a less stable and less repeatable static recrystallization (SRX) activation that prevents complete recrystallization. In the current study, these variabilities are validated by comparing the mean flow stress (MFS) indirectly determined from the rolling force measured on a reverse four-high rolling mill stand. The material resistance to deformation and grain size evolution of a C-Mn steel during hot rolling was observed and validated with and without Nb addition. The pre-defined rolling schedule was predicted to exhibit incomplete recrystallization in the roughing phase due to the limited stored energy of deformation that resulted from low rolling loads and a higher number of rolling passes. The prior austenite grain size (PAGS) distribution was predicted and compared to the measured effective ferrite grain (FG) size distribution after the completion of hot rolling and phase transformation achieved using natural air plate cooling. Both the predicted PAG and measured FG distributions revealed the presence of multimodality, and both distributions were used for grain size reduction factor determination for γ → α transformation for the current study with 1.96 for 0 Nb and 1.70 for 240 Nb. The results presented in this paper are not only limited to the rolling schedule used in this paper because instabilities resulting in incomplete austenite conditioning are also observed when evaluating the cross-sections of other heavy plates and various steel grades utilizing different processing routes with comparable compositions such as modern lean abrasion-resistant steels, regular line pipe steels, and other similar grades.

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Section: Rolling Proceduresmentioning

confidence: 98%

Hot Deformation Behavior of C-Mn Steel with Incomplete Recrystallization during Roughing Phase with and without Nb Addition

Klančnik¹,

Foder

Bradaškja

et al. 2022

Metals

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“…Very high austenitizing temperatures and long holding times may result in grain growth, distortion and loss of metal strength (Porter, et al, 1992). It has been pointed out that temperature and time greatly influence austenite grain growth and eventually the mechanical properties of the steels, with temperature being the most effective parameter (Annan, et al, 2015; Lee and Lee 2008; Zhang et al 2011). Due to the difficulty and limitations posed by in-situ measurement of grain size during heat treatments, to monitor grain growth behaviour, it has become ideal to study the grain growth behaviour of steels through the use of constitutive prediction equations.…”

Section: Introductionmentioning

confidence: 99%

Prediction of austenite grain growth during austenitization of a 0.7%C pearlitic rail steel

Khanyema

Annan

Mostert

et al. 2022

SATNT

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The prior austenite grain size of steels greatly influences the phase transformation kinetics during austenitization and the microstructure which determines the mechanical properties. The effect of temperature and time on austenite grain growth of 0.7% carbon rail steel during reheating was studied. The grain growth behaviour of this steel was investigated under different heating temperatures and holding times at a constant heating rate of 4°C/min. Samples were heated in a tube furnace at temperatures of 1150, 1200 and 1250oC and held for 0, 1800, 3600, 5400, 7200 and 9000 seconds before quenching into water. The prior austenite grains were observed using an optical microscope and austenite grain sizes were measured by the linear intercept method. The measured austenite grain sizes were used in determining the grain growth constants Q, A and n which were used in developing the constitutive equation for grain growth prediction. A good agreement was found between the actual and the predicted austenite grain size within the typical industrial soaking temperature range of 1150 and 1200oC.

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“…Hence several studies have been done on precipitation and austenite grain size during hot processing of these steels. The influence of niobium on austenite grain size was studied by K. A. Annan et al 10 the results showed that there is a linear relationship between Nb content and the activation energy for grain growth. Beata Białobrzeska et al 11 showed that the austenite grain size has a strong influence on the mechanical properties of the steel.…”

Section: Introductionmentioning

confidence: 99%

“…The basic relationship of the pinning force of grain boundaries as a function of the particle size and volume fraction is defined by Zener: 10 that alloy 1 with the highest V and S content exhibited the finest grain size res.…”

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confidence: 99%

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The influence of austenitization time and temperature on the austenite grain growth in high Ti-V HSLA steels

Rezaei

Siyayisa

Tang

et al. 2022

SATNT

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Generally, in high titanium-containing high strength low alloy (HSLA) steels, the challenge is to ensure that an adequate amount of Ti dissolves during soaking for precipitate strengthening during cooling or hot working. Therefore, this work focused on the effect of soaking time and temperature on the austenite grain growth kinetics of HSLA steels, of the three alloys containing 0.1 %Ti, and 0 to 0.12 %V. The samples were austenitized at 1150 and 1280 °C for 1, 2 and 3 hrs and quenched in a 10% NaCl brine. Thereafter, the samples were tempered at 490 °C for 72 hrs in order to reveal the prior austenite grain boundaries. The grain size was analysed by the linear intercept method. The precipitation behaviour was predicted by Thermo-Calc software and confirmed by SEM-EDS. At 1150 °C austenitizing temperature, all three steel grades exhibited the Ti (C, N) (Type 1), (Mn-Ti) (C, S) (Type 2), MnS (Type 3 (Ti4C2S2) (Type 4) and TiC (Type 5) precipitates. After escalating the temperature to 1280 °C, only the TiC dissolved. Type 4 and 5 precipitates were the finest and possibly responsible for the grain size refinement. Consequently, alloy 1 with the highest S content of 140 ppm exhibited the finest grain size at both temperatures.

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The influence of niobium content on austenite grain growth in microalloyed steels

Cited by 4 publications

References 24 publications

Hot Deformation Behavior of C-Mn Steel with Incomplete Recrystallization during Roughing Phase with and without Nb Addition

Hot Deformation Behavior of C-Mn Steel with Incomplete Recrystallization during Roughing Phase with and without Nb Addition

Prediction of austenite grain growth during austenitization of a 0.7%C pearlitic rail steel

The influence of austenitization time and temperature on the austenite grain growth in high Ti-V HSLA steels

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