低于Ms温度变形对等温贝氏体相变动力学和组织的影响

摘要：变形和等温热处理是高强贝氏体钢主要生产工艺,已有研究表明低于马氏体相变起始温度（Ms）的等温热处理可以促进贝氏体相变动力学,低温奥氏体预变形也可以加速贝氏体相变。研究了低于Ms温度变形对后续等温贝氏体相变动力学和组织的影响,结果表明,并未出现预想的加速相变叠加效应,反而,变形温度低于Ms温度时,贝氏体相变动力学减弱,等温贝氏体相变孕育期延长。低于Ms温度等温相变时,贝氏体铁素体与母相奥氏体位向关系接近K-S关系,变形试样虽然获得了一部分先马氏体,且能提高贝氏体形核率,但并非所有的胚核都能发生长大,变形改变母相奥氏体取向,使贝氏体原本的位向关系遭受破坏,导致有效形核率降低。     

奥氏体预变形对等温贝氏体相变和组织影响

轧制变形会影响母相奥氏体微观结构和形貌,进而影响后续贝氏体相变。采用热模拟实验、X射线衍射(XRD)、扫描电镜观察(SEM),研究了奥氏体预变形对一种Fe-C-Mn-Si中碳贝氏体相变和组织的影响规律。设计了不同变形温度和变形程度的组合,分析了等温贝氏体相变量和室温组织残余奥氏体含量的变化。研究结果表明,300和400℃时的变形会促进等温贝氏体相变,且变形温度越低,贝氏体体积分数增加越明显。此外,残余奥氏体含量随变形程度增加而逐渐增多,且奥氏体预变形温度越低,室温组织中残余奥氏体含量越多,低温变形同时有助于奥氏体力学稳定化。     

变形工艺对Q345 GJC高建钢连续冷却相变的影响

借助Gleeble-2000型热力模拟实验机,研究了Q345GJC高建钢奥氏体连续冷却过程的相变规律,结合热膨胀法和金相法,分别构建实验钢奥氏体动态和静态连续冷却相变曲线(CCT),分析了加速冷却、热变形和工艺温度对实验钢相变的影响。结果表明,与静态CCT曲线比较,实验钢的动态CCT曲线整体向左上方移动,γ/α相变开始温度随冷却速度的增大而逐渐降低;高温变形对铁素体和珠光体组织转变有利,扩大了铁素体相变区,但阻碍了贝氏体相变;奥氏体变形对贝氏体转变是双重的,高冷速变形促进贝氏体相变,低冷速变形抑制贝氏体相变。     

12Cr2Mo1R钢相变规律研究

采用热膨胀法并结合金相组织分析及硬度变化来测定12Cr2Mo1R钢变形奥氏体的连续冷却转变温度,研究了钢的相变规律,结果表明,12Cr2Mo1R钢未变形奥氏体连续冷却转变,冷却速度<0.27 ℃/s时,组织为贝氏体+铁素体+珠光体;在0.27～8.4 ℃/s之间时,组织为贝氏体;>8.4 ℃/s时,组织为马氏体+贝氏体。变形奥氏体连续冷却转变,冷却速度<5 ℃/s时,组织为铁素体+珠光体+贝氏体;在5～20 ℃/s之间时,主要为贝氏体组织;>20 ℃/s时,得到的组织为马氏体+贝氏体。形变加速了奥氏体连续相变,使连续冷却相变温度提高。钢中Cr、Mo等合金元素,提高了过冷奥氏体的稳定性,使连续转变过程中出现了亚稳奥氏体区,提高了贝氏体的淬透性。     

合金元素和工艺参数对热轧TRIP钢动态相变的影响

利用Gleeble热模拟试验机进行单轴压缩试验,研究了C-Mn-Si TRIP钢和C-Mn-Al-Si TRIP钢过冷奥氏体形变过程的组织演变,分析了合金元素和工艺参数对过冷奥氏体动态相变的影响.与等温相变相比,C-Mn-Si钢和C-MnAl-Si钢动态相变动力学明显加快.与C-Mn-Si钢相比,用质量分数约1%的Al替代Si后,C-Mn-Al-Si钢的A₃温度明显提高,在相同变形工艺条件下C-Mn-Al-Si钢过冷奥氏体动态相变较易发生,而C-Mn-Si钢动态相变得到的铁素体晶粒比较细小.减小动态相变前奥氏体晶粒尺寸,有利于过冷奥氏体动态相变的进行.提高过冷奥氏体形变时的变形温度或应变速率均对动态相变产生一定的阻碍作用,但影响不显著.      

奥氏体化温度对高碳含硅钢等温转变的影响

 采用XRD物相分析、金相组织观察及TEM精细组织分析研究了奥氏体组织结构状态对Fe-0.88C-1.35Si-1.03Cr-0.43Mn 钢中温等温相变鼻温和孕育期的影响,以及不同温度奥氏体化后240 ℃等温20 min试样的组织结构特征。试验发现,随着奥氏体化温度的升高,中温等温开始转变的鼻温移向更低温度并且相变孕育期缩短;不同温度奥氏体化后同为240 ℃等温20 min处理,虽然均形成由贝氏体铁素体亚条平行排列构成的束状贝氏体组织,但贝氏体组织的精细结构状态不同,突出的差别在于对应低温奥氏体化贝氏体亚条端部边界具有凸起结构,而对应高温奥氏体化贝氏体亚条端部边界较为平齐且呈现楔形结构。不能简单地以马氏体切变机制认识试验钢中贝氏体组织的形成。     

纳米贝氏体钢相变加速技术开发进展

摘要：纳米贝氏体的成功开发使得常规条件下对钢铁材料组织的纳米级细化成为可能,然而奥氏体中低温转变的热动力学条件限制了纳米贝氏体的相变速率,阻碍了纳米贝氏体钢的合金范围拓展和大规模工程应用。梳理了近期国内外学者针对这一问题开发的纳米贝氏体相变加速技术,综述了化学成分、预相变、预变形、强磁场等条件下贝氏体相变加速方面的进展。综合分析表明,针对贝氏体相变需充分考虑贝氏体形核以及长大2个过程。纳米贝氏体合金和工艺的设计需充分考虑各因素对2个过程的不同影响,充分优化贝氏体相变动力学和微观组织。复合相变加速技术可以成为纳米贝氏体钢开发的新方向。     

CSP热轧TRIP钢动态再结晶行为研究

摘要：采用Gleeble-3500热模拟试验机,在温度为950~1150℃、应变速率为0.1~10s-1和变形量为65%的条件下研究了CSP热轧TRIP钢的动态再结晶行为,探讨了初始奥氏体晶粒尺寸对TRIP钢动态再结晶行为的影响。研究结果表明,初始奥氏体晶粒尺寸越小,变形温度越高,应变速率越慢时,TRIP钢中奥氏体越易发生动态再结晶。其中,粗晶试样（初始奥氏体晶粒尺寸为767.54μm）在1050~1150℃内变形时,将发生动态再结晶。其热变形激活能为361539.17J/mol,确定了Zener-Holloman参数与应变速率和温度的关系式,建立了动态再结晶临界应变模型、高温奥氏体流动应力模型和动态再结晶晶粒尺寸模型,理论模拟结果与试验结果吻合较好。     

不同锰铬含量对贝氏体钢组织转变的影响

文章利用全自动相变仪对不同锰铬含量的贝氏体钢组织转变进行了试验研究,对比分析了不同锰铬元素含量对贝氏体钢过冷奥氏体相变点的影响,并研究了不同转变温度对贝氏体钢组织转变的影响,试验结果表明贝氏体钢组织转变的最佳温度为330℃,为贝氏体钢生产工艺开发提供了理论依据。     

高温弛豫对无Nb和Ti等元素超低碳贝氏体钢的影响

 针对试验用钢重点研究经历高温弛豫试样的中温相变点特征、450 ℃等温下的物相组成、显微组织结构及硬度随等温时间变化特征,以获得高温弛豫过程对不含Nb 和Ti等合金化合物析出元素的超低碳钢贝氏体相变影响的新认识。试验结果表明,高温弛豫过程明显影响试验用钢的中温相变点,使试样的CCT曲线虽然仍具有两区特征,但相对未经历高温弛豫处理试样,在[(t,θ)]坐标系中的位置偏左上方;高温弛豫后450 ℃短时等温下形成尺寸较小的板条束状贝氏体,试样对应有较高的硬度水平,随等温时间延长,贝氏体长大,硬度随之下降;而未经历高温弛豫试样在450 ℃等温时发生变形回复与贝氏体相变2个过程,在等温时间小于30 min的较短范围内,变形回复与贝氏体相变过程对硬度影响的综合结果致使试样的硬度变化平缓。     

热形变淬火对L485QS酸性管线用钢09MnNb淬硬性的影响

对L485QS酸性管线用钢09MnNb进行不同工艺的热形变淬火试验,测试淬硬性并观察相应的组织。结果表明,试验钢在850～1 100℃进行0.2～0.8变形水淬后可获得三种类型的组织,变形温度是影响组织转变类型的主导因素,当温度≤900℃时,主要获得针状铁素体,当温度为950～1 000℃时,主要获得细条状贝氏体,当温度≥1050℃时,主要获得粗大的板条状贝氏体。增大变形量在未再结晶和部分再结晶区分别促进针状铁素体转变和细条状贝氏体转变,在完全再结晶区使板条状贝氏体组织粗细不一致。采用09MnNb钢在950～1 000℃进行ε≥0.4的热变形淬火时,可获得以细条状贝氏体为主的淬火组织,以及较高且稳定的淬硬性,并有利于后续回火性能的调控。     

Bainite Transformation of Low-carbon and Boron-containing Steel under Continuous Cooling

The effects of deformation temperature and strain on bainite transformation of low carbon steel and boroncontaining steel were investigated under continuous cooling conditions by means of dilatometric measurement and microstructure observation.The results show that with decreasing the deformation temperature from 1 000to 800 ℃and increasing strains,bainite start temperature for boron-containing low carbon steel increases,whereas it decreases for low carbon steel under the same condition.The bainite microstructures are easily obtained for boron-containing steel deformed at different temperatures and different strains compared with plain low carbon steel.With increasing the continuous cooling rate,the bainite start temperature under deformed condition is about 20 ℃ higher than that under undeformed condition for boron-containing steel,but it changes slightly when the cooling rate is 20℃/s or more.     

Bainite Transformation Under Continuous Cooling of Nb-Microalloyed Low Carbon Steel

Utilizing Gleeble-1500 thermomechanical simulator, the influences of hot deformation parameters on continuous cooling bainite transformation in Nb-microalloyed low carbon steel were investigated. The results indicate that bainite starting temperature decreases with raising cooling rate and increases with increasing deformation temperature. Deformation has an accelerative effect on the bainite transformation when the specimens are deformed at 950 ℃. When the deformation temperature increases, the effect of deformation on bainite starting temperature is weakened. The amount of bainite is influenced by strain, cooling rate, and deformation temperature. When the specimens are deformed below 900 ℃, equiaxed ferrites are promoted and the bainite transformation is suppressed.     

Effect of Thermomechanical Treatment Temperature on Structure and Properties of CFB/M Ultra-High Strength Steel

Modified CCT diagram of carbide-free bainite-martensite(CFB/M)ultra-high strength steel was established by applying controlled cooling of small samples.In addition,the influence of thermomechanical treatment temperature on the structure and properties was discussed.The experimental results showed that when deformed at 860℃ and below,ferrite transformation occurred due to strain.With the decrease of ausforming temperature,the quantity of ferrite increased and strength and toughness were deteriorated.Therefore,certain information was provided for optimizing technical parameter of ausforming process:firstly,the thermomechanical treatment temperature should not be lower than 860℃ in order to avoid ferrite formation induced by deformation;secondly,rapid cooling rate is also significant after deformation in order to avoid ferrite precipitation during subsequent cooling stage.     

Nb-V-Ti微合金化高强度钢08MnCr连续冷却转变曲线和组织

利用ThermecMaster-Z热模拟实验机测定了一种Nb-V-Ti微合金化高强度钢08MnCr(S2)在910～1 200℃不变形(静态)和变形(动态)奥氏体0.05～30℃/s冷速下连续冷却转变(CCT)曲线,并分析和观察了对应的相变及组织。实验结果表明,提高轧后的冷却速度使Ar₃降低,导致钢的晶粒进一步细化;冷却速度大于10℃/s开始出现贝氏体转变。提高加热温度时相变温度降低,变形奥氏体相变温度较不变形奥氏体相变温度高。冷速较低时,铁素体晶粒呈多边形;冷速高时,铁素体晶粒多呈尖角形。     

Effect of ausforming on isothermal bainitic transformation and microstructure

Deformation affects the microstructure and morphology of the parent austenite, which affects the subsequent bainite transformation. The effects of ausforming on bainite transformation and microstructure were investigated by means of thermal simulation experiment, TEM and SEM etc. Different deformation temperatures and deformation strains were designed. The amount of bainitic transformation during isothermal holding and the volume fraction of retained austenite at room temperature were analyzed. The results show that the isothermal bainitic transformation is promoted by the deformation at 300?? and 400??. Moreover, the lower deformation temperature leads to larger amount of bainite. In addition, the volume fraction of retained austenite increases with the increase of the deformation strain, and more retained austenite can be obtained by decrease the deformation temperature. It indicates that deformation at lower temperature contributes to the mechanical stabilization of austenite.     

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。     

Deformation of metastable austenite and resulting properties during the ausform-finishing of 1 pct carburized AlSl 9310 steel gears

The process of ausform-finishing in gears involves the deformation of metastable austenite. A critical step in optimizing the deformation process is to determine the link between material deformation behavior and final material properties, such as hardness and microstructure. To this end, uniaxial compression testing was carried out on 1 pct carburized AISI 9310 steel specimens in the low-temperature ausforming regime (85 °C to 230 °C). The work-hardening response of metastable austenite and its relation to the hardness and microstructure was determined from these experiments. High work-hardening rates (work-hardening exponent n=0.4 to 0.7) were caused by deformation-induced transformation of metastable austenite to either martensite or bainite or both. It is postulated that, at the ausforming temperatures in the neighborhood of 230 °C, bainite formed at the highest achievable strains of 50 pct while oriented martensite (loading induced) was detectable at lower strains of 20 pct. The hardness of the resulting ausformed microstructure increased with degree of straining and with reduction in temperature of ausforming. An X-ray determination of the retained austenite content showed that austenite tends to stabilize even after minimal ausforming. A transmission electron microscopy study on ausformed specimens showed the presence of microtwinning and high-dislocation densities. The effect of processing parameters on fatigue response under rolling contact conditions is discussed given current understanding and available fatigue data.     

直接热轧法制备Cu-P-Cr-Ni-Mo双相耐候钢

 在商用09CuPCrNi耐候钢化学成分的基础上,通过调整合金元素含量,研制出了可直接热轧双相化的Cu-P-Cr-Ni-Mo耐候钢。该钢种变形奥氏体的CCT曲线具有较宽的铁素体析出区,可作为热轧“可行的速度窗口”;铁素体析出区与贝氏体转变区之间存在约80℃的奥氏体亚稳区,可作为热轧“可行的卷取范围”;贝氏体转变区的右侧端部封口,可避免在卷取过程中发生贝氏体转变。根据Cu-P-Cr-Ni-Mo耐候钢的变形奥氏体的CCT曲线,制定了5种热轧双相化工艺,并采用Gleeble-3500热模拟机进行了轧制模拟,制备出了Cu-P-Cr-Ni-Mo热轧双相耐候钢。不同工艺下获得的双相耐候钢组织均为铁素体基体及其上呈岛状分布的马氏体,马氏体体积分数为17%~28%。