不同形变速率条件下低碳钢过冷奥氏体形变过程铁素体超细化

研究了低碳钢过冷奥氏体在760℃,形变速率为l s^-1和10 s^-1变形时组织演变规律.结果表明,形变速率为1 s^-1时真应力-应变曲线双峰特征为形变强化相变和铁索体动态再结晶的表征,相变形核集中在铁素体/奥氏体相界前沿奥氏体高畸变区,晶粒长大在时间和空间上受到限制,细化能力较高;形变速率提高到10 s^-1时,相变动力学提前,曲线只表现为形变强化相变的单峰特征,相变形核除了在上述铁素体/奥氏体相界前沿奥氏体高畸变区,还分布到奥氏体晶内各处,晶粒间约束有所减小,尺寸稍大.通过形变强化相变和铁素体动态再结晶可以获得平均晶粒尺寸为(1.98±1.07)μm和(2.33±1.01)μm(10 s^-1)左右的微细铁素体晶粒.     

碳、锰含量对低碳(锰)钢过冷奥氏体形变过程中铁素体形核率的影响

研究了碳、锰含量对低碳(锰)钢形变强化铁素体晶粒数目变化的影响.结果表明,形变使低碳(锰)钢过冷奥氏体内部形核位置增加,铁素体形核率显著提高,晶粒大大细化.碳、锰含量提高有利于钢中过冷奥氏体累积变形的增加,形变强化相变晶粒细化能力增强,而碳的促进作用尤为显著.     

低碳钢过冷奥氏体形变过程组织演变机制

低碳钢过冷奥氏体形变过程将发生形变强化相变及铁素体的动态再结晶,导致晶粒超细化.与未形变的过冷奥氏体等温转变相比,形变极大地促进了奥氏体向铁素体的转变,使铁素体形核率急剧升高,铁素体晶粒尺寸显著降低.形变强化相变是一以形核为主的过程.在形变后期,当形变强化相变铁素体转变基本完成后,将发生铁素体的动态回复和动态再结晶.比较不同应变速率对组织演变影响的结果表明,应变速率较低条件下,易形成铁素体与第2组织层状分布的条带特征;应变速率较高时,组织的条带特征不显著.     

碳锰含量对低碳钢超细铁素体组织退火过程的影响

对08钢和20Mn形变强化相变后退火过程的组织演变的观察表明，超细铁素体退火时的长大是应变能及晶界能共同驱动的正常长大，长大阻力是第二组织的钉扎。形变使奥氏体以离异方式加速分解。在所用应变量下，08钢中的超细铁素体快冷到600℃以下不会有明显长夫。碳锰含量的提高降低了形变强化相变进行的程度，使随后的铁素体长大受到相变驱动力的作用并加大了带状组织特征，铁素体难以正常长大。20Mn中第二组织的增多提供了形变强化相变后调整第二组织的空间及必要性。总结了碳锰含量、退火温度、形变量等因素影响的超细铁素体退火时的组织演变规律。     

低碳微量铌钢过冷奥氏体形变过程中的碳氮化物析出

利用透射电镜研究了低碳微量铌钢过冷奥氏体形变过程中的碳氮化物析出,运用Gladman晶粒粗化机制讨论了析出相颗粒的平均直径、体积分数和铁素体晶粒尺寸的关系.实验结果表明:实验用钢中的微量Nb在1200℃时完全固溶,并在760℃变形前的冷却过程中无Nb(CN)析出.在形变过程中Nb(CN)的析出同样需要孕育期,但与等温过程相比大大提前.当变形量积累到一定值(本实验条件下ε=0.69)时,大量动态析出的Nb(CN)颗粒弥散分布在晶界以及位错线上.Nb(CN)析出随着应变量的增加而增加,但颗粒长大不明显,计算得到的铁素体晶粒平均截径与实际测得的铁素体晶粒吻合得较好.     

Effect of Niobium on Transformations From Austenite to Ferrite in Low Carbon Steels

Niobium has an important effect on the transformation behaviour,grain size refinement and precipitation strengthening during hot rolling and subsequent cooling in low carbon steels,with even a low content of niobium having a strong effect on the transformation rate from austenite to ferrite.However,the effects of niobium on transformation behaviour have not been fully characterised and understood to date.This paper examines in detail austenite grain growth as a function of austenitisation time in high strength low alloy (HSLA) steels with three different niobium contents,together with the effect of niobium on the isothermal transformation kinetics from austenite to ferrite as a function of temperature.It is shown that austenite has the slowest grain growth rate in the steel with the highest niobium content.When austenite grain sizes are consistent,the steel with the highest niobium content was found to have the slowest transformation rate from austenite to ferrite.     

Influence of Prior Austenite Deformation and Non-Metallic Inclusions on Ferrite in Low Carbon Steels

 Abstract Effects of prior austenite deformation and non-metallic inclusions on the ferrite nucleation and grain refinement of two kinds of low carbon steels have been studied. The ferrites nucleation on MnS and V(C,N) is observed. The combination of thermal-mechanical processes with adequate amounts of non-metallic inclusions formed in low carbon steels could effectively refine the grain size and the microstructure. Ferrite nucleated on the single MnS or V(C,N) inclusions and complex MnS+V(C,N) inclusion. The proper addition of elements S and V could effectively promote the formation of ferrite and further refinement of ferrite grains.     

应变诱发铁素体相变对低碳钢晶粒细化的影响

研究了在奥氏体低温区变形时显微组织的变化,并测试了其变形抗力。结果表明：在Ar3以上温度变形会产生应变诱发铁素体相变,使变形抗力下降。通过降低变形温度,铁素体晶粒得到细化。     

Transformation Behavior of Low Carbon Steels Containing Two Different Si Contents

 Continuous cooling transformation behaviors of low carbon steels with two Si contents (050% and 135%) were investigated under undeformed and deformed conditions. Effects of Si contents, deformation, and cooling rates on γ transformation start temperature (Ar3), phase microstructures, and hardness were studied. The results show that, in the case of the deformation with the true strain of 04, the length of bainitic ferrite laths is significantly decreased in low Si steel, whereas, the M/A constituent becomes more uniform in high Si steel. An increase in cooling rates lowers the Ar3 greatly. The steel with higher level of Si exhibits higher Ar3, and higher hardness both under undeformed and deformed conditions compared with the steel with a lower Si content. Especially, the influence of Si on Ar3 is dependent on deformation. Such effects are more significant under the undeformed condition. The hardness of both steels increases with the increase of cooling rates, whereas, the deformation involved in both steels reduces the hardness.     

Influence of Mn Content and Hot Deformation on Transformation Behavior of C-Mn Steels

The hot deformation behaviors and the microstructural evolution of plain C-Mn steels with similar contents of C and Si but different contents of Mn have been investigated by compressive processing using Gleeble-1500 mechanical simulator.Influence of Mn and hot deformation on continuous cooling transformation of steels has been studied.The experimental results showed that deformation in austenite region accelerated transformation process,and the extent is dependent on the hot deformation and cooling conditions.The hot deformation would promote transformation process,but the increase of transformation temperature is dependent on Mn contents.The results have also shown that the effect of deformation on ferrite transformation becomes more obvious with the increase of Mn content at relatively low cooling rate.     

低碳钢Q235奥氏体的动态再结晶与动态相变

对成分为0.18C-0.22Si-0.60Mn(质量分数)的低碳钢在1 100～750 ℃之间的奥氏体动态再结晶及动态相变行为进行了研究.确定了此钢奥氏体发生动态再结晶的临界应变条件及完全动态再结晶后的晶粒尺寸.计算表明,在奥氏体低温区大变形以致使奥氏体发生完全动态再结晶时,可得到6～9 μm 的奥氏体晶粒尺寸.在Ae3以下,变形可以引发动态相变.但奥氏体快速冷却明显推迟了动态相变的发生.与相同温度下单一奥氏体变形相比,有动态相变发生时应力值不增加或降低,其降低程度随变形温度的下降而增加.     

Effects of Deformation on Bainite Transformation During Continuous Cooling of Low Carbon Steels

ted alot of interests of metallurgical researchers.Aswell known,the steels with ultra-fine grains havepoor work hardening ability and high yield ratio[1].This problem can be solved through complexstrengthening mechanism in which some bainite isintroduced to ferrite matrix with suitable grain size.So it is necessaryto studythe transformation of aus-tenite to bainite inlowcarbon steels during continu-ous cooling after deformation.Most of the research works[2-4]about the trans-formation fromauste…