Effect of Intercritical Quenching on Microstructure and Mechanical Properties of Ultra Low Carbon Heavy Steel Plate

The Effect of intercritical quencing on microstructure and mechanical properties of ultra low carbon heavy steel plate were studied by utilizing SEM, TEM, tensile and impact tests. The specimens were firstly subjected to an annealing treatment at 930 degrees C followed by quenching to ambient temperature, then were repeatedly annealing at the temperatures being varied in the range of 600 similar to 870 degrees C, and then repeatedly quenched to ambient temperature in cold water. When the intercritical quenching was just slightly above A(c1) the strength and low temperature toughness were remarkably deteriorated attributing to the massive grain and some twins in the bainite islands. However, the more when the annealing temperature increased higher than A(c1) but still below A(c3), the more regions can be austenized, which cause the average of carbon content in the austenized regions to be relatively low. So it was difficult that these austenite regions changed into twin martensites after interctitical quenched. Then the comprehensive properties including low temperature toughness became good again.