– Micrographs of austenite grain boundaries under different annealing conditions: (a) delivery state; (b) 900 8C, 20 min; (c) 950 8C, 20 min; (d) 1000 8C, 20 min; (e) 1050 8C, 20 min; (f) 1100 8C, 20 min; Etched state, light microscope.  

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... details of heat treatment in addition to information about hardening and tempering [9]. The distribution was approximated with a logarithmic normal model. This model is similar to the distribution of austenite grains size presented in [32]. Almost 50% of the measurements are grains with a diameter of 10- 20 mm. Abnormal grains were not observed (Fig. ...

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... austenitizing process at a temperature of 900 8C caused an increase in average grain size by nearly 60%, compared to the delivery state. The size varies between 12 and 58 mm. The average value is 28.5 AE 12.8 mm. Again, abnormal grains were not observed (Fig. 4b). The measurement results are approximated with a logarithmic function. The most Fig. 3 -Austenite grain size in the delivery state and at different austenitizing ...

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... increase of austenitizing temperature to 950 8C in- creased the average size of the austenite grains by 87% with respect to the delivery state. The average grain size is 34.2 AE 18.1 mm. Grains have a regular shape (Fig. 4c). However, the measurement of grains showed that 41% of grains are in the range of 10-20 mm and 29% are in the range of 40-50 mm (Fig. 5c). This fact indicates the start of the growth of single grains. Unfortunately, the frequency of each austenite grain size is not possible to be approximated with any mathematical model. The ...

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... 8C, the minimum mea- sured grain size was approximately 13.5 mm. This value is more than 2 times higher than that measured in the delivery state (i.e. 6 mm). The average grain size is similar to the grain size obtained at 950 8C and is 35.0 AE 15.7 mm. The obtained structure is similar to the structure obtained after austenitiza- tion at 950 8C (Fig. 4d). Grains from 10 to 19 mm constitute 24% (Fig. 5d), which is almost 50% less than in the case of sample austenitizing at 950 8C. However, a higher frequency of grains in the range of approximately 60-70 mm is found (Fig. 5d). The frequency of occurrence of each austenite grain size cannot be approximated with any mathematical ...

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... in a rapid increase of the average grain size: over 2.5 times relative to the sample in the delivery state and by 85% relative to the sample after austenitizing at 1000 8C. The average grain size is 64.6 AE 35.0 mm. Almost 50% of the measured grains are in the range 27-50 mm (Fig. 5e). In the structure can be visible concentrations of fine grains (Fig. 4e). The distribution of frequency occurrence of austenite grain size was approximated by a logarithmic model. The abnormal austenite grains can be also observed in the microstructure, and they are significantly larger compared to previous samples. The measured grain size range is 27-188 ...

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... at 1100 8C caused the appearance of clearly abnormal austenite grains. Their maximum size ranged from 211 to 296 mm (Fig. 4f). They were not included in the calculation of the average grain size. Grain sizes of ranges of 50-69 mm and 107-126 mm occurred more frequently than others (Fig. 5f). The average size of the austenite grains is 93.3 AE 38.4 mm. ...

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... migration of grain boundaries can be compared to a diffusion process. So, the grain growth rate increases with increasing holding temperature. It can be seen in Fig. 4b and c that the austenite grains growth is gradual when the temperature increases from 900 to 950 8C. The abnormal grains are presented in the microstructure after heating at 1000 8C (Fig. 4d), 1050 8C (Fig. 4e) and 1100 8C (Fig. 4f) as well already presented after austenitizing at 950 8C (Fig. 4b). The ...

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... to a diffusion process. So, the grain growth rate increases with increasing holding temperature. It can be seen in Fig. 4b and c that the austenite grains growth is gradual when the temperature increases from 900 to 950 8C. The abnormal grains are presented in the microstructure after heating at 1000 8C (Fig. 4d), 1050 8C (Fig. 4e) and 1100 8C (Fig. 4f) as well already presented after austenitizing at 950 8C (Fig. 4b). The ...

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... increasing holding temperature. It can be seen in Fig. 4b and c that the austenite grains growth is gradual when the temperature increases from 900 to 950 8C. The abnormal grains are presented in the microstructure after heating at 1000 8C (Fig. 4d), 1050 8C (Fig. 4e) and 1100 8C (Fig. 4f) as well already presented after austenitizing at 950 8C (Fig. 4b). The ...