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# Cooling times (Delta T8/5) S355 till S960

Steel grade | Minimal cooling time t_{8/5} [s] |
Maximum cooling time t_{8/5} [s] |

.....S355 | ...........................8 | ..........................40 |

.....S420 | ...........................8 | ..........................40 |

.....S460 | ...........................8 | ..........................35 |

.....S500 | .........................10 | ..........................30 |

.....S550 | .........................10 | ..........................25 |

.....S620 | .........................10 | ..........................22 |

.....S690 | ...........................5 | ..........................20 |

.....S890 | ...........................5 | ..........................12 |

.....S960 | ...........................5 | ..........................10 |

**-Cooling Time:**

The cooling time between 800°C and 500°C t8/5 is the most important parameter in order to determine the welding parameters applied during welding of fine-grain structural steels

**.**In this menu you can easily calculate this cooling time by specifying the following values:

- Heat Input Q [in kJ/mm]
- Preheating temperature T
_{p}[°C] - Plate thickness d [mm]
- Welding geometry factors F
_{2}/F_{3}: For the welding geometry factors the suitable welding geometry has to be selected from a table, Moreover also a free input in the range 0 to 1.0 is possible.

From the data given above the cooling time t_{8/5 }can be calculated if a three-dimensional heat flux is assumed:

t_{8/5 }= (6700-5*T_{P})*Q* (1/(500-T_{P})-1/(800-T_{P}))*F_{3}

If the heat flux is two-dimensional the cooling time depends on the plate thickness_{ }an the following formula is used:

t_{8/5 }= (4300-4.3*T_{P})*10^{5}*Q^{2}/d^{2}* (1/(500-T_{P})^{2}-1/(800-T_{P})^{2})*F_{2}

Only the greater values obtained from the two formulas above is physically valid. Often, a transition plate thickness d_{t} is calculated, at which the transition between the two-dimensional and the three-dimensional heat flux occurs. This transition plate thickness is determined as follows:

d_{t} = SQR(((4300-4.3*T_{p})*10^{5}/(6700-5*T_{p})*Q*(1/(500-T_{P})^{2}-1/(800-T_{P})^{2})/ (1/(500-T_{P}) -1/(800-T_{P}))*F_{2}/F_{3})

Moreover it is signed whether a two- or three-dimensional heat flux occurs.

It should be considered that the assumptions underlying the formulas for the cooling time are often not perfectly fulfilled. Therefore the values calculated can deviate form the real values by up to 10 %.