通过不同热机械处理工艺, 分别获得片层珠光体、球化珠光体、超细化(α+θ)复相组织以及细晶(α+θ)复相组织等4种不同组织的共析钢. 利用室温单轴拉伸实验、SEM和TEM等手段研究了上述组织对共析钢室温加工硬化行为的影响. 结果表明: 片层珠光体组织具有抗拉强度高、屈强比小且均匀延伸率低的特点, 这与其初始加工硬化率高、加工硬化率随应变量增加而下降的程度有直接关系. 其它3种铁素体/渗碳体粒子复相组织的初始加工硬化率较低, 但下降趋势较缓, 表现出较好的塑性变形能力.与球化珠光体相比, 组织细化使超细化(α+θ)复相组织和细晶(α+θ)复相组织具有更好的强度与塑性配合.

Steels with ultrafine (α+θ) duplex structure, consisting of ferrite matrix (α) with average grainsize of about 1μm and dispersed cementite particles (θ), have been investigated widely in recent years formaking better the work-hardening capability of ultrafine-grained steels. In fact, the ratio of yield strength to tensilestrength for plain carbon steels with ultrafine (α+θ) duplex structure is commonly larger than 0.85. Forstructural material, the low ratio of yield strength to tensile strength is beneficial to absorb external energy anddelay theoccurrence of destruction. However, the ratio of yield strength to tensile strength is still relatively high for steelswith ultrafine (α+θ) duplex structure to act as the structural material. Namely, the work-hardening capability ofultrafine (α+θ) duplex steel needs further improving. It could be feasible for improving the work-hardeningcapability of ultrafine (α+θ) duplex steel to change the form, size and distribution of the cementite. Therefore, it isnecessary to investigate the work--hardening behavior of steel with different cementite states. In the present research, four different microstructures of eutectoid steel were obtained by different thermo-mechanicaltreatments, i.e., lamellar pearlite, spheroidized pearlite, ultrafine (α+θ) duplex structure and fine-grained (α+θ)duplex structure. The effect of different microstructures on the room--temperature work-hardening behavior of theeutectoid steel was analyzed using room temperature tensile tests, SEM and TEM. The results indicated that thework-hardening characters of lamellar pearlite,which initial work hardening rate is large but decreases quickly with strain, have direct relationship with its large tensile strength, small yield ratio and low uniform elongation.Although the initial work hardening rates of the three ferrite/cementite particles duplex structures are lower, theydecrease much slowly with strain comparing with that of lamellar pearlite. Therefore, three types offerrite/cementite particles duplex structures demonstrate good plastic deformation capability. In comparison withspheroidized pearlite, ultrafine (α+θ) duplex structure and fine-grained (α+θ) duplex structure demonstrate better balance between strength and plasticity due to microstructure refinement.