温轧低碳钢渗碳体形态对终轧组织性能的影响

Effect of cementite morphology in a warm-rolled low-carbon steel on its microstructure and properties after finish rolling

通过温轧铁素体+珠光体组织获得两种渗碳体分布形态,并在300℃变形获得不同的位错密度,结合随后的快速升温至奥氏体低温区以及快冷后单道次轧制变形获得了铁素体晶粒尺寸为200～500nm的亚微米晶钢,拉伸性能测试表明利用该工艺获得的样品除了具有很高的抗拉强度(>1000MPa)之外,其屈强比相对较低,断后总伸长率≥20%。TEM观察发现,原始组织中渗碳体弥散分布的试样更容易在上述工艺下获得等轴亚微米晶铁素体以及适量板条马氏体和孪晶马氏体组织,而原始组织中渗碳体分布集中的试样其终态组织中等轴晶铁素体的比例显著减少,且铁素体晶内位错密度要低于前者。

Different morphology of cementite distribution in a low-carbon steel was obtained by different warm-rolling processes in dual phase region of ferrite and pearlite. Microstructure with ferrite grain size of 200-500 nm was observed in the warm-rolled steel after finish rolling at relative lower temperature in austenite region. Microstructure and mechanical properties of the steel were examined by means of SEM, TEM and tensile test. The results show that both of samples have high tensile strength （〉1000 MPa）, lower yield ration and total elongation ≥20%. TEM results indicate that equiaxial ferrite grains and certain amount of lath and/or twin martensite are prone to be obtained in the sample with disperse cementite after finish rolling, while the proportion of equiaxial ferrite grains in the sample with concentrated cementite decreases significantly, and the dislocation density in ferrite grains is also less than that in the former.