INFLUENCE OF SUPER-FINE SUBSTRUCTURE ON TOUGHNESS OF LOW-ALLOYING ULTRA-HIGH STRENGTH STRUCTURE STEEL
低合金超高强度钢亚结构超细化对韧性的影响

A series of low--alloying ultra--high strength structure steels (LUHSSS) which contain Si, Mn as the alloying elements are developed through controlling the transformation temperature, cooling rate and tempering parameters. The observations on the microstructure by means of TEM, SEM and AFM show that LUHSSS are composed of very fine and close ferrite (F) lathes and retained austenite (AR) of thin film shape with high stability, and no blocky AR and cementite are observed in steels. The discontinuous F lathes consist of several shear units and their thickness range is 75---100 nm. During low temperature tempering, the dislocations in the shear units move and finally form a number of homogeneous cell substructures with the diameter less than 17 nm. Under the condition of ultra--high strength (σb>1400 MPa), the multi--scale, multi--level and double--phase of microstructure significantly increase the impact absorption energy (AKV≈200 J). Furthermore, the mechanism of toughness improvement caused by cell substructures is analyzed.