超细晶粒高碳钢微复相组织及性能

在650℃采用等通道角挤压变形(ECAP)方法对原始组织为层片状珠光体的T8钢进行了Bc方式(每道次挤压后,试样按同一方向旋转90°进行下一道次挤压)的4道次变形,获得了晶粒尺寸在亚微米量级的超微细复相(α+θ)组织,其中等轴铁素体晶粒尺寸约为400 nm,球化完全的渗碳体颗粒粒径约为150 nm。微拉伸实验和SEM断口观察表明,经过4道次ECAP变形后,超微细复相组织的抗拉强度相对于原始珠光体组织而言有所下降,从867 MPa降至819 MPa,但屈服强度显著提高,由479MPa增加到664 MPa,相应的整体伸长率和断面收缩率分别从4.5%、5.2%增加到18%、31%,硬度值变化不明显;超微细复相组织的断口形貌由大量细小的韧窝构成,为典型的韧性断裂,而原始珠光体组织断口形貌则由河流花样组成,呈脆性解理断裂特征。

Microstructure and properties of microduplex（α＋θ） structure in an ultra-fine-grained high carbon steel

Extrusion deformation was performed on a T8 steel with a fully pearlitic structure by equal channel angular pressing(ECAP) through a route Bc at 650 ℃.The ultra-microduplex structure was obtained in the high carbon steel after four passes ECAP,in which the sizes of ferrite grains and cementite particles were about 400 nm and 150 nm,respectively.The mechanical properties of the steel with ultra-microduplex structure were investigated by mini-tensile tests and the morphology of fracture surfaces was observed by scanning electron microscopy(SEM).The results show that after four passes deformation,tensile strength of the steel with ultra micro duplex structure decreases slightly from 867 MPa to 819 MPa,but its yield strength obviously increases from 479 MPa to 664 MPa.Correspondingly,elongation and reduction of area of steel increase from 4.5%,5.2% to 18%,31%,respectively,which are markedly higher than those of the lamellar pearlite before ECAP.Hardness of the ultra-microduplex structure and the lamellar pearlite are almost at the same level.The tensile fracture of the ultra-microduplex structure is composed of many small dimples,which is typical ductile fracture,however,the fracture of original lamellar pearlite exhibits brittle cleavage fracture characteristics.