Internal oxidation starting temperature estimation device, internal oxide layer thickness estimation device, internal oxidation starting temperature estimation method, and program

1 . An internal oxidation starting temperature estimation device that estimates an internal oxidation starting temperature which is a minimum temperature required for an internal oxide layer to grow on a surface of an easily oxidizable element-containing hot-rolled steel sheet including Si, Mn, or Al or any combination thereof, the internal oxidation starting temperature estimation device comprising:

an internal oxidation starting temperature estimation unit that estimates the internal oxidation starting temperature on the basis of concentrations of the Si, the Mn, and the Al included in the easily oxidizable element-containing hot-rolled steel sheet,

wherein the internal oxidation starting temperature estimation unit determines the internal oxidation starting temperature such that a correlation between a measured value of a thickness of the internal oxide layer and a cumulative temperature defined by the following Expression (1) is the highest, for each of a plurality of types of the easily oxidizable element-containing hot-rolled steel sheets in which the Si concentration, the Mn concentration, or the Al concentration or any combination thereof is different:

S

T

=

∫

t

⁢

0

t

⁢

1

(

T

-

T

⁢

c

⁢

r

)

⁢

d

⁢

t

(

1

)

wherein, in Expression (1), S T is the cumulative temperature, T is a temperature of a portion to be estimated, in which the thickness of the internal oxide layer is to be estimated, in the easily oxidizable element-containing hot-rolled steel sheet, Tcr is the internal oxidation starting temperature, t0 is an estimation start time when estimation of the thickness of the internal oxide layer is started, t1 is an estimation evaluation time, and T−Tcr is 0 in an integration interval where T−Tcr is equal to or less than 0.

2 . The internal oxidation starting temperature estimation device according to claim 1 ,

wherein the internal oxide layer is formed when the easily oxidizable element-containing hot-rolled steel sheet is cooled in a coiled state.

3 . The internal oxidation starting temperature estimation device according to claim 1 ,

wherein the internal oxidation starting temperature estimation unit determines the internal oxidation starting temperature such that a sum of squared deviations when a quadratic function of the cumulative temperature is applied to the measured value of the thickness of the internal oxide layer is minimized, for each of the plurality of types of easily oxidizable element-containing hot-rolled steel sheets in which the Si concentration, the Mn concentration, or the Al concentration or any combination thereof is different.

4 . An internal oxide layer thickness estimation device comprising:

an internal oxide layer thickness estimation unit that estimates the thickness of the internal oxide layer formed in the easily oxidizable element-containing hot-rolled steel sheet, on the basis of the internal oxidation starting temperature estimated by the internal oxidation starting temperature estimation device according to claim 1 and the following Expression (2):

H=α×S T +H 0   (2)

in Expression (2), H is the thickness of the internal oxide layer, S T is the cumulative temperature, α is a proportional constant, and H 0 is an initial value of the thickness of the internal oxide layer.

5 . An internal oxidation starting temperature estimation method that estimates an internal oxidation starting temperature which is a minimum temperature required for an internal oxide layer to grow on a surface of an easily oxidizable element-containing hot-rolled steel sheet including Si, Mn, or Al or any combination thereof, the internal oxidation starting temperature estimation method comprising:

an internal oxidation starting temperature estimation step of estimating the internal oxidation starting temperature with the internal oxidation starting temperature estimation device of claim 1 , on the basis of concentrations of the Si, the Mn, and the Al included in the easily oxidizable element-containing hot-rolled steel sheet.

6 . A program that causes a computer to estimate an internal oxidation starting temperature which is a minimum temperature required for an internal oxide layer to grow on a surface of an easily oxidizable element-containing hot-rolled steel sheet including Si, Mn, or Al or any combination thereof, the program causing the computer to execute:

an internal oxidation starting temperature estimation step of estimating the internal oxidation starting temperature on the basis of concentrations of the Si, the Mn, and the Al included in the easily oxidizable element-containing hot-rolled steel sheet,

wherein the computer is the internal oxidation starting temperature estimation device according to claim 1 .