低合金超高强度钢亚结构超细化对韧性的影响

充分利用控制相变温度、冷却与回火参数,得到冲击吸收功(AKV)成倍提高的系列Si,Mn等元素合金化的低合金超高强度结构钢(LUHSSS).TEM,SEM和AFM分析表明:LUHSSS由纳米尺度的铁索体(F)板条与分布在其间的,高度稳定的膜状残余奥氏体(AR)组成,无块状不稳定AR和渗碳体析出;由若干切变单元组成的F板条不连续分布,厚度范围75-100 nm.回火过程中,板条内位错运动形成纳米尺寸(<17 nm)的均匀胞状亚结构.显微组织的多尺度、多层次与双相性保证超高强度(σb>1400 MPa)前提下,AKV大幅度提高至200 J附近.分析了胞状亚结构对LUHSSS韧性的影响机制.

INFLUENCE OF SUPER-FINE SUBSTRUCTURE ON TOUGHNESS OF LOW-ALLOYING ULTRA-HIGH STRENGTH STRUCTURE STEEL

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 (A_R) of thin film shape with high stability, and no blocky A_R 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 (σ_b>1400 MPa), the multi--scale, multi--level and double--phase of microstructure significantly increase the impact absorption energy (A_KV≈200 J). Furthermore, the mechanism of toughness improvement caused by cell substructures is analyzed.