A method of dynamical adjustment for manufacturing a thermally treated steel sheet having a chemical steel composition and a microstructure mtarget comprising from 0 to 100% of at least one phase chosen among:
- ferrite, martensite, bainite, pearlite, cementite and austenite such that mtarget=Xferrite+Xmartensite+Xbainite+Xpearlite+Xcementite+Xaustenite, X being a phase fraction, in a heat treatment line, wherein a predefined thermal treatment TT including thermal treatment steps is performed on the steel sheet sequentially in the heat treatment line, such method comprising:
- performing at least one of the thermal treatment steps of the predefined thermal treatment TT on the steel sheet in the heat treatment line,
- A. a control step wherein at least one sensor detects a deviation happening in the heat treatment line during the performed at least one thermal treatment step, the deviation being such that the predefined thermal treatment TT is determined to produce a microstructure different from mtarget,
- B. a calculation step performed when the deviation is detected during the thermal treatment such that a new thermal path TPtarget, performed as at least one further heat treatment step in the heat treatment line sequentially downstream from the performed at least one thermal treatment step, is determined to reach mtarget taking the deviation into account, such calculation step comprising:
- 1) a calculation substep, wherein at least two thermal paths TPx, each performed as at least one further heat treatment step in the heat treatment line sequentially downstream from the performed at least one thermal treatment step and corresponding to one microstructure mx obtained at the end of TPx, are calculated based on TT, including the performed at least one thermal treatment step, and the microstructure mi of the steel sheet to reach mtarget, the calculation substep taking into consideration a thermal enthalpy Hx released or consumed between mi and mtarget, the thermal enthalpy Hx being calculated such that:
- Hx=(Xferrite*Hferrite)+(Xmartensite*Hmartensite)+(Xbainite*Hbainite)+(Xpearlite*Hpearlite)+(Hcementite*Xcementite)+(Haustenite*Xaustenite)
- 2) a selection substep wherein one new thermal path TPtarget to reach mtarget is selected, TPtarget being chosen from one of the at least two thermal paths TPx calculated in substep B.1) and being selected such that mx is the closest to mtarget,
- C. performing a new thermal treatment step in the heat treatment line sequentially downstream from the performed at least one thermal treatment step by modifying at least one of a time, a temperature or rate of one of the thermal treatment steps of the predefined thermal treatment sequentially downstream from the performed at least one thermal treatment step, the performing of the new thermal treatment step including performing the selected new thermal treatment path TPtarget online on the steel sheet to produce a thermally treated steel sheet having a microstructure=Xferrite+Xmartensite+Xbainite+Xpearlite+Xcementite+Xaustenite with each phase X being within a predetermined threshold of the microstructure mtarget.