Dynamic recrystallization behavior of AISI 422 stainless steel during hot deformation processes

In this work, hot compression tests were performed to investigate the dynamic recrystallization (DRX) process of a martensitic stainless steel (AISI 422) at temperatures of 950, 1000, 1050, 1100 and 1150 °C and strain rates of 0.01, 0.1 and 1 s−1. The dependency of strain-hardening rate on flow stress was used to estimate the critical stress for the onset of DRX. Accordingly, the critical stress to peak stress ratio was calculated as 0.84. Moreover, the effect of true strain was examined by fitting stress values to an Arrhenius type constitutive equation, and then considering material constants as a function of strain by using a third-order polynomial equation. Finally, two constitutive models were used to investigate the competency of the strain-dependent constitutive equations to predict the flow stress curves of the studied steel. It was concluded that one model offers better precision on the flow stress values after the peak stress, while the other model gives more accurate results before the peak stress.Preprin

Grain growth behaviour of an AISI 422 martensitic stainless steel after hot deformation process

The metadynamic softening behaviour and grain size refinement of an AISI 422 martensitic stainless steel in the temperature range of 950–1150°C was investigated by double-hit compression tests. The deformed specimens were held at deformation temperature with delay times of 5–300 s after achieving a strain of 0.3. Based on the experimental results, a model was established for estimation of a softening fraction at different deformation parameters, and the softening fraction was compared with a recrystallised fraction. A major deviation was observed at the beginning of interpass time denoting a significant contribution of recovery to the fractional softening (FS). However, by increasing the time and temperature, the difference between the FS and recrystallised fraction is reduced. The finer grain size was achieved by prior fine pre-austenite grain and lower secondary deformation temperature. The initial grain size of 53 µm decreased down to 32 and 19 µm at the deformation temperatures of 1020 and 940°C, respectively. The austenite grains have considerable growth at a temperature higher than 1020°C, while the grain coarsening is negligible at lower deformation temperatures.Peer ReviewedPostprint (author's final draft

Impact energy of functionally graded steels in crack arrester configuration

Charpy impact energy of functionally graded steels produced by electroslag remelting composed of graded ferrite and austenite layers together with bainite or martensite intermediate layer in the form of crack arrester configuration has been investigated. The results obtained in the present study indicate that the notch tip position with respect to bainite or martensite layer significantly affects the impact energy. The closer the notch tip to the tougher layer, the higher the impact energy of the composite due to increment of energy absorbed by plastic deformation zone ahead of the notch and vice versa. Empirical relationships have been determined to correlate the impact energy of functionally graded steels to the morphology of layers

The effect of hot deformation parameters on grain size refinement in a martensitic stainless steel

The grain size refinement of AISI 422 martensitic stainless steel in the temperature range of 950-1150 ºC was investigated by hot deformation tests. The deformed specimens were held at deformation temperature with delay times of 5 to 300s after achieving a strain of 0.3. The austenite grains exhibit a considerable growth at temperature higher than 1050°C, while the grain coarsening is negligible at lower deformation temperatures. Therefore, it is a difficult task to achieve a fine grain structure at these high deformation temperatures. In the second stage of this work, the grain growth behavior of the deformed alloy at temperature range of 940-1020 ºC was investigated to obtain a fine austenite grain in the final deformation step. A uniform and fine-grain structure, with average grain size less than 30 µm, can be obtained by considering the appropriate temperature and strain per pass. At 1020°C, a relatively fine and uniform recrystallized grain, mean grain size of about 28 µm, is obtained with an applied strain of 0.4, while at 980°C after strain of 0.2 a nearly equiaxed grain with the same mean grain size is achieved.Peer ReviewedPostprint (published version

The effect of hot deformation parameters on grain size refinement in a martensitic stainless steel

The grain size refinement of AISI 422 martensitic stainless steel in the temperature range of 950-1150 ºC was investigated by hot deformation tests. The deformed specimens were held at deformation temperature with delay times of 5 to 300s after achieving a strain of 0.3. The austenite grains exhibit a considerable growth at temperature higher than 1050°C, while the grain coarsening is negligible at lower deformation temperatures. Therefore, it is a difficult task to achieve a fine grain structure at these high deformation temperatures. In the second stage of this work, the grain growth behavior of the deformed alloy at temperature range of 940-1020 ºC was investigated to obtain a fine austenite grain in the final deformation step. A uniform and fine-grain structure, with average grain size less than 30 µm, can be obtained by considering the appropriate temperature and strain per pass. At 1020°C, a relatively fine and uniform recrystallized grain, mean grain size of about 28 µm, is obtained with an applied strain of 0.4, while at 980°C after strain of 0.2 a nearly equiaxed grain with the same mean grain size is achieved.Peer Reviewe

The effect of hot deformation parameters on grain size refinement in a martensitic stainless steel

The grain size refinement of AISI 422 martensitic stainless steel in the temperature range of 950-1150 ºC was investigated by hot deformation tests. The deformed specimens were held at deformation temperature with delay times of 5 to 300s after achieving a strain of 0.3. The austenite grains exhibit a considerable growth at temperature higher than 1050°C, while the grain coarsening is negligible at lower deformation temperatures. Therefore, it is a difficult task to achieve a fine grain structure at these high deformation temperatures. In the second stage of this work, the grain growth behavior of the deformed alloy at temperature range of 940-1020 ºC was investigated to obtain a fine austenite grain in the final deformation step. A uniform and fine-grain structure, with average grain size less than 30 µm, can be obtained by considering the appropriate temperature and strain per pass. At 1020°C, a relatively fine and uniform recrystallized grain, mean grain size of about 28 µm, is obtained with an applied strain of 0.4, while at 980°C after strain of 0.2 a nearly equiaxed grain with the same mean grain size is achieved.Peer Reviewe

Dynamic recrystallization behavior of AISI 422 stainless steel during hot deformation processes

In this work, hot compression tests were performed to investigate the dynamic recrystallization (DRX) process of a martensitic stainless steel (AISI 422) at temperatures of 950, 1000, 1050, 1100 and 1150 °C and strain rates of 0.01, 0.1 and 1 s−1. The dependency of strain-hardening rate on flow stress was used to estimate the critical stress for the onset of DRX. Accordingly, the critical stress to peak stress ratio was calculated as 0.84. Moreover, the effect of true strain was examined by fitting stress values to an Arrhenius type constitutive equation, and then considering material constants as a function of strain by using a third-order polynomial equation. Finally, two constitutive models were used to investigate the competency of the strain-dependent constitutive equations to predict the flow stress curves of the studied steel. It was concluded that one model offers better precision on the flow stress values after the peak stress, while the other model gives more accurate results before the peak stress

Grain growth behaviour of an AISI 422 martensitic stainless steel after hot deformation process

The metadynamic softening behaviour and grain size refinement of an AISI 422 martensitic stainless steel in the temperature range of 950–1150°C was investigated by double-hit compression tests. The deformed specimens were held at deformation temperature with delay times of 5–300 s after achieving a strain of 0.3. Based on the experimental results, a model was established for estimation of a softening fraction at different deformation parameters, and the softening fraction was compared with a recrystallised fraction. A major deviation was observed at the beginning of interpass time denoting a significant contribution of recovery to the fractional softening (FS). However, by increasing the time and temperature, the difference between the FS and recrystallised fraction is reduced. The finer grain size was achieved by prior fine pre-austenite grain and lower secondary deformation temperature. The initial grain size of 53 µm decreased down to 32 and 19 µm at the deformation temperatures of 1020 and 940°C, respectively. The austenite grains have considerable growth at a temperature higher than 1020°C, while the grain coarsening is negligible at lower deformation temperatures.Peer Reviewe