Q420D Q420MD Q420ND Q420ND-Z15 steel plate difference in heat treatment

The heat treatment process of Q420D Q420MD Q420ND Q420ND-Z15 steel plate is: hot rolling, normalizing, normalizing rolling, thermomechanical rolling, thermomechanical rolling and tempering.

The meaning of each heat treatment process:
Hot-rolled / as-rolled; AR or WAR: The condition of steel without any special rolling and/or heat treatment.

Normalizing (N): A heat treatment process in which the steel is heated to a suitable temperature above the transformation point temperature, and then cooled in air to a temperature lower than a transformation point.

Thermomechanical rolling (M): The rolling process in which the final deformation of the steel is carried out within a certain temperature range, so as to ensure that the steel obtains properties that cannot be obtained only by heat treatment. Note 1: Hot forming or post-weld heat treatment at temperatures above 580℃ that may reduce the strength value of the steel should not be applied. According to the relevant technical specifications, flame straightening is permitted to be applied. Note 2: Thermomechanical rolling may include tempering or a process of increasing the cooling rate in the untempered state. Tempering includes self-tempering but does not include direct quenching and quenching and tempering. Note 3: Also known as TMCP (Thermo-Mechanical Controlled Process), also known as "Controlled Rolling" in some publications.

Normalizing rolling (+N): The final deformation is carried out during the rolling process within a certain temperature range, so that the steel reaches a normalized state, so that the specified mechanical properties can be achieved even after normalizing. Note: For normalizing rolling, it is also called "controlled rolling" in some publications.