Plastic working method of metals and plastic working apparatus

1. A plastic working method of steel including austenite, the method comprising:

physical property analyzing process of measuring T β , σL β , and σH β for each of strain ratios β, when T β represents a strain-induced-transformation-maximum-ductility-temperature in the unit of ° C. which is changed depending on the strain ratio β, σL β represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio β on a lower temperature side than the T β , σH β represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio β on a higher temperature side than the T β ;

deformation mode analyzing process of analyzing a strain ratio βx to be selected from among the strain ratios β, when the strain ratio βx is a strain ratio of an estimated breaking point which is specified during plastic deformation of the steel;

heating process of heating the steel such that a local temperature T local is within a first temperature range indicated by the following expression 1 after selecting T βx from among the T β , selecting σL βx from among the σL β , and selecting σH βx from among the σH β , when T βx represents a strain-induced-transformation-maximum-ductility-temperature in the unit of ° C. for the strain ratio βx, σL βx represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio βx on a lower temperature side than the T βx , σH βx represents a standard deviation of a fitted curve of critical equivalent strain which depends on the strain ratio βx on a higher temperature side than the T βx , and the T local represents a local temperature (° C.) of the estimated breaking point; and

working process of plastically deforming the steel after the heating:

T βx −σL βx ≤T local ≤T βx +1.25×σ H βx   (Expression 1).

2. The plastic working method according to claim 1 ,

wherein in the deformation mode analyzing process, a change in temperature ΔT local is further analyzed, when the ΔT local represents a change in temperature in the unit of ° C. of the local temperature T local which is changed during the plastic deformation of the steel in the working process, and

wherein in the heating process, heating is performed such that the local temperature T local is within a second temperature range indicated by the following expression 2:

T βx −ΔT local −2×σ L βx ≤T local ≤T βx −ΔT local +1.25×σ H βx   (Expression 2).

3. The plastic working method according to claim 1 ,

wherein in the heating process, at least one of the steel, a mold, and a surrounding space around the steel is heated such that the local temperature T local is within the first temperature range.

4. The plastic working method according to claim 1 ,

wherein in the heating process, a heating medium is heated such that the local temperature T local is within the first temperature range, and

wherein in the working process, the steel is plastically deformed using a pressure of the heating medium.

5. The plastic working method according to claim 2 ,

wherein in the physical property analyzing process, the estimated breaking point, the strain ratio βx, and the change in temperature ΔT local are analyzed using a plastic working simulation.

6. A plastic working apparatus which performs the plastic working method according to claim 1 , the apparatus comprising:

a housing unit that accommodates the steel and a mold;

heating units that heat at least two of the steel, the mold, and a surrounding space around the steel;

a working unit that plastically deforms the steel using the mold; and

a main body frame,

wherein the heating units include two or more selected from the group consisting of:

a heater attached to the main body frame of the housing,

a heater attached to an inside of the mold, and

a heating furnace provided outside the plastic working apparatus.

7. The plastic working apparatus according to claim 6 , further comprising

an insulating member that is arranged to cover the housing unit.

8. The plastic working apparatus according to claim 6 , further comprising

a temperature measuring unit that measures respective temperatures of the steel, the mold, and an internal space of the housing unit.

9. A plastic working apparatus which performs the plastic working method according to claim 4 , the apparatus comprising:

a housing unit that accommodates the steel and a mold;

a heating medium introducing unit that introduces the heating medium into the mold;

heating units that heat at least two of the steel, the mold, and a surrounding space around the steel and the heating medium;

a working unit that plastically deforms the steel using a pressure of the heating medium; and

a main body frame,

wherein the heating units include two or more selected from the group consisting of:

a heater attached to the main body frame of the housing,

a heater attached to an inside of the mold,

a heating furnace provided outside the plastic working apparatus, and

a heater configured to heat the heating medium.

10. The plastic working apparatus according to claim 9 , further comprising

an insulating member that is arranged to cover the housing unit.

11. The plastic working apparatus according to claim 9 , further comprising

a temperature measuring unit that measures respective temperatures of the steel, the mold, an internal space of the housing unit, and the heating medium.