奥氏体状态对 Mn-Cr 齿轮钢连续冷却相变组织的影响

使用Cleeblel500热模拟试验机研究了成分(%)为：0.23C,0.74Mn,0.90Cr 齿轮钢奥氏体晶粒尺 寸和变形(真应变量0.4)对连续冷却相变组织的影响和连续转变冷却(CCT)曲线。实验结果表明,当齿轮钢 未变形时,获得完全多边形铁素体+珠光体混合组织的临界冷速为0.5~1℃/s,冷速较快时,中温相变产物 由贝氏体及针状铁素体组成;奥氏体变形时,多边形铁素体相变开始温度升高,获得完全多边形铁素体+珠光 体混合组织冷速增大,为1~2℃/s,中温相变产物没有出现贝氏体,只有针状铁素体。     

微合金化控轧控冷钢筋纵向金相组织研究

 对微合金化控轧控冷钢筋的纵向金相组织进行了研究,并分析了不同成分试验钢纵向“条带”组织的差异及形成原因。研究结果表明：偏析元素（P、Si、Mn等）在轧制过程中沿轧制方向呈条状分布,是20MnSi、20MnSiV钢产生带状组织的原因。铌及其碳氮化物的溶质拖曳和“钉扎”作用,使20MnSiNb钢的奥氏体未再结晶轧制温度提高到1050℃,在冷却过程中,先共析铁素体在形变奥氏体晶界和内部变形带均匀析出,随后沿形变奥氏体晶界（在先共析铁素体与奥氏体的界面上）生成珠光体带,最后在形变奥氏体晶粒内部形成贝氏体条。研究条件下优势形核点的排序为：形变奥氏体晶界和形变奥氏体晶内变形带、偏析元素和夹杂、再结晶奥氏体晶界。     

Effect of Thermo‐Mechanical Process on Phase Transformation Behaviors of V–Ti–N Microalloyed Steel

Thermo‐mechanical simulation tests were performed on V–Ti–N microalloyed steel under three hot working conditions by using Gleeble‐3800 thermo‐mechanical simulator to study the effects of hot deformation and post‐deformation holding process on the continuous cooling transformation behaviors of overcooled austenite. The continuous cooling transformation diagrams (CCT diagrams) were determined by thermal dilation method and metallographic method. The effects of the hot deformation, post‐deformation holding, and cooling rate on the microstructure evolution were analyzed. The results show that deformation promotes ferrite and pearlite transformation. In addition, deformation leads to an increase in bainite start temperature, which becomes more markedly with the increase in cooling rate. The post‐deformation holding process is much favorable to promote carbonitride precipitation of the microalloying elements, which contributes to ferrite nucleation and smaller austenite grains. As a result, an increase in ferrite quantity and a decrease in ferrite grain size can be observed. And further more, the post‐deformation holding process reduces the effect of hot deformation on the bainite start temperature.     

奥氏体形变对50CrV4钢相变行为的影响

利用Thermecmastor-Z型热模拟试验机,结合金相显微镜(OM)、扫描电镜(SEM)、维氏硬度计等,系统研究了奥氏体区变形对50CrV4钢连续冷却相变和等温相变规律的影响。建立了试验钢动态CCT曲线。研究结果表明,奥氏体变形能促进连续冷却转变过程中铁素体-珠光体、贝氏体转变,但亦可提高奥氏体的机械稳定性,进而抑制马氏体转变,Ms点由331.6℃(奥氏体未变形)降低至291℃(950℃下变形50%+890℃下变形50%,变形速率均为5s-1,变形后冷速为20℃/s)。当轧后冷速小于0.5℃/s时,试验钢中可获得铁素体+珠光体组织。此外,在研究不同变形量对试验钢等温相变规律影响时发现,650℃等温时,试验钢中发生铁素体-珠光体相变。随着变形量的增加(由30%增加至50%),其等温相变动力学加快(相变完成时间由197.6s减小至136.5s),铁素体体晶粒尺寸、珠光体片层间距减小,硬度增加。     

Volume Fractions of Proeutectoid Ferrite/Pearlite and Their Dependence on Prior Austenite Grain Size in Hypoeutectoid Fe-Mn-C Alloys

It has been generally believed that pearlite transformation in hypoeutectoid steels starts when the average carbon concentration in untransformed austenite reaches the A_cm line after the formation of proeutectoid ferrite. To test this concept experimentally, volume fractions of proeutectoid ferrite/pearlite and carbon contents in the austenite being transformed into pearlite were measured for the Fe-2Mn-0.3C alloy isothermally transformed in the temperature range 848 K to 898 K (575 °C to 625 °C). It was found that lamellar pearlite can form even when the average carbon content in untransformed austenite is much lower than the A_cm line. This peculiar observation is probably due to the two-dimensional diffusion of carbon, i.e., parallel to and normal to the austenite/pearlite interface, which enables lamellar cementite to grow continuously by supplying carbon atoms to its growth front. This results in proeutectoid ferrite fractions with respect to pearlite being much lower than those predicted by the lever rule. With decreasing prior austenite grain size, proeutectoid ferrite fractions with respect to pearlite were found to increase, but the thickness of proeutectoid ferrite was constant within the range of grain size investigated. This is due to the existence of the critical α/γ interface velocity only below which pearlite (actually cementite) can be nucleated at the migrating α/γ interface. Furthermore, the upper limit temperatures for pearlite formation in the Fe-1Mn-0.33C and Fe-2Mn-0.3C alloys were found to be well between the PLE/NPLE and PE A_e1 temperatures.     

Effect of Cooling Rate on the Room Temperature Microstructure Following the Intercritical Deformation of Steel S460

The effect of final hot rolling in the intercritical (α+γ) region on microstructure and properties is very specific to the individual processing conditions and the chemical composition of a steel.S460 is a plate steel processed in this way.To reproduce at the laboratory scale,a multi-stage simulation was developed which included a high temperature austenite deformation and an isothermal hold.The effect of the applied cooling rate following intercritical deformation was investigated.At 1K/s (typical industrial cooling) the microstructure was similar to the reference sample,but included an intragranular ferrite fraction.This was due to differences in processing history,and considered to be linked to a larger prior austenite grain size.At an accelerated cooling rate (15K/s),acicular ferrite formed on shear bands within the strained austenite phase.EBSD scans have been completed to provide further information about the microstructures,with band contrast able to identify the pearlite phase at the slowest cooling rate.This is a starting point from which to focus on the ferrite morphologies.     

Modeling of Austenite Decomposition in Low Si-Mn TRIP Steel During Cooling

Transformation behavior in low carbon Si Mn TRIP steel was investigated by means of microstructural ob servation and computer modelling. A transformation model in which transformation is controlled by carbon diffusion was suggested, which well described the volume fractional change of ferrite, pearlite, and bainite during continuous cooling. The influence of Si content and austenite grain size was thoroughly investigated. The calculated results indicated that Si retards pearlite transformation, accelerates polygonal ferrite transformation, refines the austenite grain, and increases the ferrite transformation rate.     

70kg级低碳贝氏体钢相变规律研究

利用MMS-200热模拟试验机和光学显微镜研究了70kg级低碳贝氏体钢板在不同终轧温度和冷却速度下的相变规律。结果表明,随冷却速度的增大,钢中依次出现多边形铁素体、珠光体、针状铁素体、粒状贝氏体、下贝氏体和马氏体组织,奥氏体向铁素体相变温度Ar3降低,晶粒细化。随着终轧温度的降低,铁素体诱导相变明显增加,铁素体晶粒细化。     

Study on transformation behavior of hot- rolled microalloyed TRIP steel

Effects of deformation mode, deformation temperature, deformation rate, cooling rate and slow- cooling stop temperature on the transformation behavior of hot- rolled microalloyed TRIP steel were studied by means of MMS- 300 thermomechanical simulator. The results show that for the samples subjected to the single or double pass deformation, ferrite transformation area is expanded, pearlite transformation area appears, and martensite transformation area disappears in the continuous cooling transformation diagrams. Transformation temperatures of Ar3, Bs and Bf decrease, diffusional transformation is prevented and intermediate temperature transformation is promoted with the increase of deformation temperature or cooling rate. When deformation temperature is 850??, transformation temperatures of Ar3, Bs and Bf increase, the amount of ferrite also increases, and the amount of bainite decreases in the microstructure with the increase of deformation rate. With the decrease of slow- cooling stop temperature, ferrite amount increases, ferrite grains grow and retained austenite amount first increases and then decreases.     

奥氏体化温度对Ti–Zr处理钢中针状铁素体转变的影响

Ti、Zr的复合氧化物可以有效诱导针状铁素体形核,从而细化晶粒。为了研究Ti–Zr处理钢中针状铁素体转变机理,使用25 kg真空感应炉中熔炼试验所需钢种,向低合金钢中添加了质量分数为0.038%钛和0.008%锆。利用高温激光共聚焦显微镜原位观察了奥氏体化温度对针状铁素体转变行为的变化,使用扫描电镜观察了Ti–Zr处理钢种的夹杂物成分和针状铁素体在夹杂物表面形核,使用光学显微镜观察不同奥氏体化温度下的微观组织变化差异。结果表明,随着奥氏体化温度从1250 ℃增加至1400 ℃,奥氏体晶粒尺寸从125.6 μm 增加至279.8 μm,针状铁素体开始转变温度和侧板条铁素体开始转变温度先增加,在1350 ℃条件下达到最大值,后又降低,针状铁素体的体积分数由39.6%增加至83.6%;Ti–Zr处理钢中核心为Zr–Ti–O,外部为Al–Ti–Zr–O的氧化物为核心表面析出MnS的复合氧化物主要集中在1.5～3 μm,可以有效促进针状铁素体形核,贫Mn区和夹杂物与铁素体之间的良好晶格关系为该型夹杂物能够促进针状铁素体形核机理。奥氏体晶粒尺寸的增加导致多边形铁素形核位点的减少和针状铁素体的形核空间的增加,钛锆复合处理形成大量的有效诱发针状铁素体形核的夹杂物,这共同导致了针状铁素体体积分数增加。      

形变诱导铁素体逆相变过程中的组织及取向变化

 通过对普碳钢Q235在Gleeble1500热模拟机上变形后的微观组织分析,研究了组织中形变诱导的铁素体在变形后保温阶段转变为奥氏体的逆相变现象;并利用背散射电子衍射(EBSD)技术分析了晶粒取向变化。结果表明,在变形后的保温过程中,形变诱导的铁素体先逆相变为奥氏体,同时伴随着诱导铁素体晶粒的长大;然后随着变形后保温时间的延长,逆相变后的奥氏体由马氏体相变逐渐过渡到铁素体的平衡转变,相应地铁素体由具有少量亚结构的形变诱导铁素体逐渐转变为具有较多亚结构的先共析铁素体。     

NM400马氏体耐磨钢静态CCT曲线

用Gleeble3500热模拟试验机测定的连续冷却膨胀曲线,得出NM400钢临界相变点Ac1 = 719.4℃,Ac3 =847.8℃,结合金相法,利用Origin软件绘制了试验钢的过冷奥氏体连续冷却转变(CCT)曲线.结果表明,随着冷却速度增大,钢的显微硬度逐渐增大,显微组织逐渐由铁素体和珠光体过渡为贝氏体和马氏体,...     

低碳微合金管线钢的连续冷却相变及组织研究

通过Gleeble 3800热模拟试验机测定了该低碳微合金管线钢的静态（无热变形）和动态连续冷却相变曲线,并通过光学显微镜和电子显微镜对连续冷却后的组织进行了详细观察和分析。发现随着冷却速度的提高,在连续冷却转变组织中依次出现多边形铁素体（PF）、珠光体（P）、针状铁素体（AF）、粒状贝氏体（GB）和下贝氏体（LB）。在未再结晶区的热变形使C曲线发生左移,扩大了试样的针状铁素体区,并使得相变后的组织得到细化。     

低碳微合金管线钢的连续冷却相变及组织研究

通过Gleeble 3800热模拟试验机测定了该低碳微合金管线钢的静态（无热变形）和动态连续冷却相变曲线,并通过光学显微镜和电子显微镜对连续冷却后的组织进行了详细观察和分析。发现随着冷却速度的提高,在连续冷却转变组织中依次出现多边形铁素体（PF）、珠光体（P）、针状铁素体（AF）、粒状贝氏体（GB）和下贝氏体（LB）。在未再结晶区的热变形使C曲线发生左移,扩大了试样的针状铁素体区,并使得相变后的组织得到细化。     

Continuous cooling transformation behavior of hot rolled TRIP 600 steel produced by CSP process

The continuous cooling transformation behavior of hot rolled TRIP 600 steel produced by CSP process was investigated by means of Thermecmastor- Z thermal simulation testing machine, Formastor- F full automatic transformation instrument, OM, SEM and microhardness tester. The dynamic and static continuous cooling transformation (CCT) curves of the experimental steel were obtained. And the effect of deformation on phase transformation behavior was discussed. The results show that the temperature of austenite to ferrite and the volume fraction of ferrite gradually decrease with the increase of cooling rate. The transformation temperature range of the pro- eutectoid ferrite is 480-716??. Meanwhile, the transformation temperature range of pearlite is 519-647??, and the volume fraction of pearlite     

热变形和冷却对700 MPa级Mo-Nb微合金化钢组织的影响

通过Gleeble 1500热模拟试验机和光学显微镜，研究了变形及冷却对700MPa级0．04C-0．27Mo-0．047Nb微合金化钢组织和硬度的影响。得出该钢的静态(不变形)和动态(变形)奥氏体连续冷却转变(CCT)曲线，高温转变区，相变产物为先共析铁素体和粒状贝氏体；中温转变区，相变产物主要为贝氏体。热变形促进了铁素体和贝氏体相变，扩大了形成铁素体的冷却速度范围，推迟了羽毛状贝氏体的形成。     

冷作硬化非调质钢的连续冷却相变规律

钢的连续冷却相变曲线(CCT)是组织调控的基本依据,为了优化紧固件用冷作硬化非调钢热轧态的组织和力学性能,采用DIL805A相变仪测定了试验钢在0.1～50℃/s不同冷却速率下的热膨胀曲线,结合金相硬度法确定相变类型,并绘制了试验钢的CCT曲线.结果 表明,试验钢马氏体转变点(Ms)为280℃,在不同冷速范围内均有铁素...     

Microstructure and Transformation Characteristics of Acicular Ferrite in High Niobium-Bearing Microalloyed Steel

 The transformation behavior and microstructural characteristics of a low carbon high Nb-bearing microalloyed pipeline steel have been investigated by deformation dilatometry and microstructure observation. The continuous cooling transformation curves (CCT) of the tested steel was constructed. High Nb content and deformation enhancing the formation of acicular ferrite; the microstructures are range from PF, QF to AF with increasing cooling rates from 0.5 to 50℃/s and dominated by acicular ferrite in a broadened cooling rate higher than 5℃/s. The chaotic microstructure consists of non-equiaxed ferrite and interwoven ferrite laths distributed high density dislocations and sununits. The results of isothermal holding show that acicular ferrite microstructure is formed in region of 550-600℃. With the holding time or temperature increased, some low misorientations boundaries change to high misotrentationn as dislocations moving and grain boundaries coarsening.     

Isochronal Phase Transformations of Low‐Carbon High Strength Low Alloy Steel upon Continuous Cooling

Aimed to acquire optimum comprehensive properties for the oil and gas pipeline steels, thermal treatment should be controlled to achieve ideal microstructures. Effects of cooling rates on transformation kinetics and microstructures of the low‐carbon high strength low alloy (HSLA) steel were investigated to obtain an optimized thermal treatment technology. Dilatometric measurements, light microscopy, scanning electron microscopy, and transmission electron microscopy were employed in present work. The transformed microstructures contained polygonal ferrite + pearlite, acicular ferrite (AF), and bainitic ferrite (BF) due to the cooling rates increasing from 5 to 3000°C min^?1, in present investigated HSLA steel. The result shows that, the increase of cooling rate accelerates AF transformation and refines the steel's matrix. The morphology of martensite/austenite structures transformed from islands in AF to films in BF with the increase of cooling rate.     

Effects of Chromium,Vanadium and Austenite Deformation on Transformation Behaviors of High-strength Spring Steels

The phase transformation behavior during continuous cooling of high-strength spring steels containing dif-ferent amounts of Cr was studied.Furthermore,the effects of combining Cr with V as well as austenite deformation on the transformation kinetics were investigated in the method of dilatometry and metallography hardness.The re-sults showed that,with the increase of Cr,the pearlite transformation field was enlarged,the ferrite transformation field was narrowed,and the entire phase field shifted to the right.With the addition of V,the start transformation temperature of undercooling austenite (Ar3 )was gradually increased,but the ferrite and pearlite transformation fields were not affected.Besides,the minimum critical cooling rate of martensitic transformation was also reduced.In addition,the dynamic continuous cooling transformation (CCT)curve moves to the top left compared with the static CCT curve.The transformed microstructures showed that the addition of V and the deformation not only refined the overall transformed microstructures but also reduced the lamellar spacing of pearlite.The alloying elements Cr and V promoted the Vickers hardness.However,the effect of Cr on the Vickers hardness of martensite was stronger and the influence of V on that of pearlite was stronger.Moreover,the Vickers hardness affected by the austenite deform-ation was more complex and strongly depended on the transformed microstructures.