【作者】 周继锋；

【导师】 荆天辅；

【作者基本信息】 燕山大学 ， 材料学， 2006， 硕士

【摘要】 本文利用Gleeble 3500热力模拟试验机,对中碳钢的马氏体(M)组织、铁素体+珠光体(F+P)组织和球化组织(S)的温变形进行了模拟实验研究,表明随变形温度提高,M组织的流变应力与F+P组织和球化组织的接近,甚至可低于F+P组织。说明M温轧与近年来流行的F轧制具有同样应用的可行性。并且M温轧后的组织更细小,力学性能更好,因此研究M温轧既具有学术价值,更具有重要的工程意义。 温压缩实验测定的流变应力表明,在350～700℃压缩,应变速率越低,M组织的流变应力越低,低于临界应变速率,高于临界温度或临界应变,M组织的流变应力低于F+P组织,但略高于球化组织。M组织的加工软化率和应变速率敏感性指数都大于F+P和球化组织。 导致M组织温变形流变应力上述特点的机制是M组织位错密度和界面密度都远高于退火组织,处于很高的能量状态,在温变形时,除降低动态回复和动态再结晶温度,加速此类软化过程外,晶界滑动和位错扩散性蠕变等其他加工软化作用比退火组织的更显著。 TEM定量观测表明,M在550～700℃压缩50%后,F动态再结晶晶粒尺寸约为0.56～1.73μm,相应的碳化物平均尺寸约为32～60 nm。而F+P组织在600℃压缩发生部分动态再结晶,650-700℃发生完全动态再结晶,700℃压缩F晶粒尺寸约为2.60μm,600～700℃压缩,碳化物尺寸为160～210 nm。 室温单轴拉伸实验结果表明,M温压缩后的屈服强度比F+P温压缩的高3.92～27.80%,比球化组织的高22.68～54.62%,而延伸率略高或相等。M温变形后组织的力学性能高于退火变形组织的原因是晶粒的细化和纳米碳化物的均匀分布。更多还原

【Abstract】 In this work, the flow curves of martensite structure (M), ferrite plus pearlite structure (F+P) and spherical structure (S) in a medium carbon steel were determined by warm compression tests performed on a Gleeble3500 machine, and the corresponding microstructures and mechanical properties at room temperature were comparatively studied by TEM, SEM, hardness and tensile tests. The results show that the flow stress of M decreases with the increase in deformation temperature, and gradually close to the flow stress of F+P and S, or even below. These imply that the M warm working has the same feasibility as ferritic rolling, which is widely used in engineering. Further more, the mechanical properties of warm deformed steel with M as starting structure are much better than that of the same steel deformed with F+P or S, due to the warm deformation of M has a stronger effect of grain refinement than that of F+P or S.The flow stresses, such as peak stress, yield stress and stable stress of M are decreased with the strain rates at the temperatures range from 350 ℃ to 700 ℃. The flow stress of M is lower than that of F+P, but little higher than that of S, when the strain rate is lower than the critical strain rate, the temperature is higher than the critical temperature, or the strain is larger than the critical strain. It is found that the strain rate sensitive index and the work-softening effect of M are the largest among the three structures.The reason of above flow behaviors of M occurred during warm compression is the high dislocation density and interface density which make the structure energy state of M very high. Besides dynamic recovery and dynamic recrystallization, grain boundary sliding and dislocation diffusional creep are more important in work-softening of M than that of F+P.The quantitative observation by TEM shows that the mean grain sizes ofdynamic recrystallized ferrite are in the range of 0.56 urn to 1.73 urn, and the mean size of the carbide is about 32 ~ 60 nm for M warm compression at temperature of 550 -700 °C. But, for F+P warm compression , local dynamic recrystallization occurred at 600 °C, entirety dynamic recrystallization occurred at 650 -700 °C. The mean grain sizes of dynamic recrystallization for ferrite warm compression are 2.63 urn at 700 °C, and the mean size of the carbide is about 160 - 210 nm in that of F+P.Uniaxial tensile tests at room temperature show the yield strength of the M warm compression sample is increased by 3.92 -27.80 % compared to that of F+P, and increased by 22.68 -54.62 % to that of S. The elongation is almost the same. The mechanical property of M is higher than that of annealing structure after warm compression, probably because of the fine ferrite grain with uniformly distributed nano-sized carbide particles.更多还原