Banded structure elimination mechanism

Organization of low-carbon steel at room temperature deformation of ferrite and pearlite, if there is the band structure of ferrite and pearlite alternating stripes organization. Low carbon steel seamless pipe band structure, from room temperature to normalizing temperature, when the via Ac1 temperature, the eutectoid transformation occurs, pearlite transformation of austenite. In this case, the components are not homogeneous austenite, with the heating temperature exceeds Ac3, ferrite solid solution is completed, then the structure of the steel is converted to single-phase austenite, as the temperature continues to increase and normalizing temperature incubation, the austenite completely uniform.

Released from the normalizing temperature cooling After incubation, when the cooling rate of the steel to eliminate large banded structure with critical cooling rate (ie, suppression ferrite precipitate from the austenite cooling rate), the steel pipe eutectoid ferrite body is suppressed, so that the ferrite does not precipitate and removing solvent remains in the austenite, and as the temperature decreases by increasing the degree of supercooling, and will not happen again precipitated pro-eutectoid ferrite, by directly supercooled austenite decomposition product into eutectoid ferrite + cementite, but unlike eutectoid steel composition, called “pseudo-eutectoid” because “pseudo-eutectoid” no eutectoid ferrite the existence of the body, so the microstructure of steel banded structure does not exist. Pipe insulation from baked after normalizing temperature, the cooling rate is less than the band structure of the steel to eliminate the critical cooling rate of slow cooling, when the temperature is reduced to Ac3, first depleted carbon steel austenitic ferritic precipitation zone ahead ( The carbon-poor region of the parent phase about the band structure), with decreasing slow cooling and temperature eutectoid ferrite volume is gradually increased until the cold to Ac1 when austenite into pearlite, at room temperature The microstructure of the steel, it appeared ferrite and pearlite bands banded same organization.

Post time: Oct-21-2019