1种Mn-B系贝氏体钢连续冷却转变曲线

利用膨胀法结合金相分析在THERMECMASTOR-Z热模拟试验机上测定,获得了Mn-B钢的连续冷却转变曲线(CCT曲线),并研究了冷却速率对钢组织及硬度的影响。实验结果表明,在生产中冷却速度控制在2～15℃/s范围内,可以得到贝氏体为主、没有马氏体的组织;Mn-B钢的硬度随着冷却速率的增加逐渐增大。     

The crystallography of bainite in a medium-carbon steel containing Si,Mn, and Mo

A composite microstructure consisting of upper bainite laths and lower bainite plates, both carbide-free, plate (twinned) martensite, and carbon-enriched retained austenite, was produced by air-cooling a medium-carbon alloy steel (0.55 pct C, 1.35 pct Si, 0.78 pct Mn, 0.45 pct Mo) from 900 °C. Well-defined midribs and subunits were found to be associated with both the upper bainite laths and lower bainite plates, clearly showing that the two kinds of bainite growvia a sympathetic nucleation and growth process. The orientation relationship between the bainite and austenite, as determined by electron diffraction, showed that the close-packed planes in the two phases were separated by 0.5 deg and the close-packed directions were 1.9 apart. The habit plane determined from the midrib was (5 127)_f, about 20 deg away from the nearly parallel close-packed planes (111)_f/(011)_b. The experimentally determined orientation relation-ship and habit plane (as defined by the midrib) were in good agreement with the predictions of the phenomenological theory of martensite crystallography.     

碳含量对高性能桥梁钢组织结构和性能的影响

研究了低碳和超低碳两种成分500 MPa级高性能桥梁钢的成分设计及组织控制对性能的影响.连续冷却的实验表明,在相同冷却速度下,碳的质量分数为0.08%的微合金钢比碳的质量分数为0.04%的微合金钢容易得到更多的板条贝氏体组织.碳的质量分数为0.04%的微合金钢在一定的冷却速度范围内(1～10℃/s)均可得到低碳贝氏体组织,因此有利于大厚度钢板内部的组织均匀性.实验轧制结果显示,两种成分钢的屈服强度均能达到500 MPa,并且具有良好的伸长率和低温冲击韧性.20 mm厚钢板的断面组织均匀,为以粒状贝氏体和针状铁素体为主的低碳贝氏体组织.     

CSP生产600MPa级低碳贝氏体钢的相变

以低碳Nb、V、Ti、Mo和Cr合金化贝氏体钢为研究对象,在Formaster-Digital膨胀仪上测定了过冷奥氏体的静态CCT曲线;在Gleeble-1500热/力模拟机上,用膨胀法测定了奥氏体的动态CCT曲线;采用扫描电镜和透射电镜分析了贝氏体钢的室温组织演变规律.结果表明:合金元素抑制奥氏体向铁素体转变,在冷却速度大于10℃·s^-1的范围内,静态CCT和动态CCT的室温组织均为贝氏体,具有较高的强度;奥氏体变形促进了贝氏体转变,贝氏体转变开始温度为610~668℃,终了温度为520~551℃.     

Effect of Cooling Rate and Deformation on Microstructures and Critical Phase-Transformation Temperature of Boron-Nickel Added HSLA H-Beams

 Microstructures and critical phase-transformation temperature of boron-nickel added Nb-treated high strength low alloy (HSLA) H-beams cooled at different cooling rate, with different deformation were investigated. Continuous cooling transformation (CCT) diagram of this new type of steel was obtained by using Gleeble 1500 thermomechanical simulator. Microstructures and hardness, especially micro-hardness of the experimental steel were investigated by optical microscopy (OM), scanning electron microscope (SEM), Rockwell and Vickers hardness tests. Phase analysis was also studied by X-ray diffraction (XRD). The results indicated that with increase of cooling rate, microstructures of continuous cooled specimens gradually transformed from polygonal ferrite and pearlite, grain boundary ferrite and bainite, bainite and martensite to single martensite. The CCT diagram revealed that slow cooling was needed to avoid austenite-bainite transformation to ensure toughness of this steel. By plastic deformation of 40%, austenite-ferrite transformation temperature increased by 46 ℃, due to deformation induced ferrite transformation during continuous cooling, but Rockwell hardness has little change.     

Microstructure and mechanical properties of the hot-rolled Fe16Mn0.6C steel plate

Results presented in this study contribute to investigation of the microstructure and mechanical properties of the hot-rolled Fe16Mn0.6C steel plates.The steel plates have been produced by being hot-rolled at temperatures ranging from 1100℃ to 850℃ in seven passes to 97.5% reduction in thickness and then cooled in a furnace of 650℃.Some plates have been annealed at temperatures ranging from 300℃ to 1100℃ for 5min to 60min,and then followed by water quenching.There are annealing twins in the hot-rolled Fe16Mn0.6C steel.Fe16Mn0.6C steel presents similar ductile behavior as X-IPTM steel,but much higher elongation than commercial martensitic steel (MP) 1000,dual phase (DP) 980,and transformation induced plasticity (TRIP) 980 steels.Fe16Mn0.6C steel experiences γ→ε (-α) transformation in some local regions,but remains mostly austenite during the entire deformation process.Fe16Mn0.6C steel with special mechanical properties can be produced by using the appropriate anneal technology.Twinning induced plasticity(TWIP) effect only occurs in the Fe16Mn0.6C steel annealed at temperature higher than 900℃.     

600MPa级热轧双相钢的组织性能

 介绍了实验室使用两段式冷却工艺试制的600MPa级热轧双相钢的化学成分及相变规律,利用光学显微镜、SEM以及拉伸试验对双相钢的微观组织和力学性能进行检测分析。结果表明：试验用钢的Ac1和Ac3分别为785、940℃;经830℃终轧后,空冷10s到750℃,在750℃开始快冷至卷取温度（≤200℃）,可得到室温组织为铁素体（86.5%）+马氏体的热轧双相钢,其屈服强度为327.1MPa,抗拉强度为651.6MPa,加工硬化率高达0.235,伸长率达25.7%。     

Mn和Si对中锰热轧高强钢组织和性能的影响

为了研究Mn和Si元素对中锰热轧高强钢显微组织和力学性能的影响,设计了不同Mn、Si含量C-Si-Mn系试验用钢.利用热膨胀仪、扫描电镜、透射电镜、X射线衍射和单向拉伸等实验方法对试验用钢的相变点、显微组织、残余奥氏体含量和力学性能进行了测定与分析.结果表明：Mn和Si对中锰热轧高强钢的显微组织影响较大,对于低Si高Mn的试验钢,其显微组织主要由粒状贝氏体组成;对于高Si高Mn的试验钢,主要由贝氏体铁素体、马氏体和残余奥氏体组成;对于高Si低Mn的试验钢,则由块状铁素体、贝氏体、马氏体和残余奥氏体组成.高Si高Mn试验钢获得最高的综合力学性能,抗拉强度达1200 MPa以上,总伸长率为16%,强塑积接近20 GPa·%.分析认为,试验钢这种高强度和较高的塑性是由超细晶组织和TRIP效应共同决定的.     

Influence of titanium on transformation behaviour during continuous cooling of boron microalloyed steels

Continuous cooling transformation (CCT) characteristics and prior-austenite grains of boron microalloyed steels with and without titanium were investigated to obtain the necessary information for heat treatment of these steels. Transformation characteristics were determined by using dilatometer tests, microscopic observation, and hardness measurements. In addition, the effects of titanium addition on the sizes of prior-austenite grains and precipitates were analysed. The results show that the changes in austenite grain size are not very distinct, and adding titanium only slightly refines the austenite grains. The CCT diagrams showed that the ranges of transformation products were shifted to the right side by the addition of titanium. The ferrite transformation starting temperatures were reduced on addition of titanium. Titanium addition induced decreased critical cooling rates for bainite transformations. The hardenability of boron microallyed steel is increased by adding titanium because more boron segregate to prior-austenite grain boundaries.     

X120管线钢的试制及其相变规律

在实验室试制了X120管线钢,并绘制了X120管线钢的连续冷却转变曲线。结果表明:热轧态时试验钢的屈服强度平均值为905 MPa,抗拉强度平均值为980 MPa,伸长率平均值为17%,屈强比为0.92,-20℃的冲击功平均值为90J。经600℃回火2h后,试验钢的屈服强度平均值达到了950 MPa,抗拉强度平均值达到了1 000 MPa,伸长率平均值为18%,屈强比为0.95,-20℃的冲击功平均值为95J。经过压缩后,冷却速度为5℃/s时试验钢的组织即全部为板条贝氏体组织,而该组织为X120级管线钢中的理想组织。     

热变形及工艺参数对C-Mn钢过冷奥氏体转变的影响

以C-Mn钢SS400为研究对象,在Gleeble-1500热模拟试验机上进行了热模拟实验,测得了试验钢静、动态CCT曲线.从CCT曲线可以看出,未变形时试验钢奥氏体向铁素体开始转变温度在800～690℃之间,变形后在810～710℃之间,变形提高了Ar3点.当冷却速度比较低时(0.2～5℃/s),变形奥氏体转变后室温组织的维氏硬度值低于未变形奥氏体转变后的室温组织维氏硬度值,而当冷却速度比较高时(5～20℃/s),趋势正好相反;变形后淬火试验结果表明应变量为0.4、变形速率为1/s 时,试验钢在820℃时已经发生形变诱导铁素体相变.随着应变量的增大和变形温度的降低,原奥氏体晶界的铁素体量增多.     

等温温度对超细贝氏体钢组织演变规律的影响

通过热膨胀试验研究实验钢的等温转变动力学,采用盐浴等温淬火工艺制备超细贝氏体组织,利用扫描电镜、透射电镜和X射线衍射仪定量分析工艺参数对微观组织结构的影响.结果显示:实验钢室温组织由大量超细板条状贝氏体铁素体和板条间分布的薄膜状奥氏体的复相组织构成,210℃等温淬火得到的贝氏体板条间距细化到约60 nm,硬度约为HBW610;实验钢的最终组织特征取决于发生贝氏体转变的等温温度和等温时间,等温温度越低时贝氏体转变完成需要的等温时间越长.     

变形工艺对V、Ti微合金钢连续冷却相变的影响

采用Gleeble-1500热模拟实验机,结合显微硬度测试,建立了含V、Ti微合金钢的未变形和50%形变奥氏体的CCT曲线.利用光学显微镜、透射电镜分析研究了冷却速度、变形条件及微合金元素对显微组织的影响.结果表明,变形使铁素体 珠光体相变区左移,获得铁素体 珠光体组织的临界冷速增大.变形也使贝氏体相变温度有所提高,同时在较高的冷速下,变形可使显微组织变得更加细小.V、Ti的复合添加,提高了过冷奥氏体的稳定性,使相变温度降低,有利于得到细小的组织.     

冷速和变形对700MPa超级钢组织和性能的影响

采用Gleeble 1 5 0 0热模拟实验机及Instron试验机研究并分析了 70 0MPa超级钢的连续冷却转变曲线 (CCT曲线 )及冷却和变形工艺对实验钢性能的影响。结果表明 ,热变形显著加速钢的相变过程 ,随着冷却速度的提高 ,钢的抗拉强度提高 ,屈服强度降低     

AM对低碳贝氏体钢等温相变和显微组织的影响

摘要：设计了马氏体起始相变温度（Ms）以上和以下5个不同温度等温淬火实验,研究了Ms以上和以下温度等温淬火对低碳贝氏体钢组织和相变动力学的影响。结果表明,试样在Ms以下等温淬火时,保温前生成的先马氏体（AM）显著缩短了等温贝氏体相变孕育期,加速贝氏体形核,细化贝氏体组织。然而,Ms以下等温淬火时,总的等温贝氏体相变动力学与先马氏体的体积分数（fAM）有很大关系,当fAM较低时,AM的形成缩短了贝氏体相变孕育期,加速了贝氏体相变,当fAM过高时,又阻碍贝氏体相变,延长贝氏体总的相变时间。最后,采用Austin Rickett(AR)和Johnson Mehl Avrami Kolgomorov(JMAK)动力学模型对等温贝氏体相变动力学进行分析,结果表明,与AR模型相比,JMAK模型更适用于本研究的实验结果。     

Phase transformation behaviour in two C–Mn–Si based steels under different cooling rates

Abstract

The continuous cooling transformation (CCT) behaviour of two C–Mn–Si based steels was investigated. The effects of chemical composition and cooling rate on γ→α transformation were studied using dilatometric measurements. Quantitative phase analysis was carried out in order to determine the effect of cooling rate on the precise phase distribution after transformation. Presence of Cr and Mo in the experimental steels appears to retard pearlitic transformation and promotes formation of acicular products (combination of acicular ferrite, Widmanstatten ferrite and bainite). Martensitic transformation also starts at a perceptibly lower cooling rate in the Mo containing alloy as compared with the one without any Mo.     

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Dilatometry is a powerful technique for phase transformation analysis of solid state in iron and steel by measuring linear strain as a function of time and temperature during thermal cycle. The basic fundamentals, equipment and experimental analysis method of dilatometric analysis were introduced. Several practical examples and applications of dilatometry in iron and steel research were briefly described, with an emphasis on continuous heating transformation (CHT) and kinetic model, continuous cooling transformation (CCT) diagram and time temperature transformation (TTT) diagram.     

高温退火和添加Si对仿M10铁基烧结合金显微组织的影响

在一种仿M10粉末冶金铁基烧结合金显微组织中出现了针状碳化物,通过高温退火和添加Si元素的方式研究了针状碳化物的演变特征.采用X射线衍射和能谱分析确认了这是一种M2C型碳化物.结果表明：M2C是一种稳定性较高的亚稳相,高温退火时Mo、Cr、V元素向基体内扩散使M2C可以断裂、球化和分解.提高退火温度能加快针状碳化物形貌和结构的转变.Si元素可进入更稳定的M6C型碳化物中,抑制M2C的形成,显微组织中针状和块状碳化物共存.     

变形温度对CSP热轧65Mn带钢相变行为的影响

利用ThermecMastor-Z型热模拟试验机模拟CSP工艺条件,辅以金相显微镜(OM)、扫描电镜(SEM)和维氏硬度计等,研究65Mn钢的连续冷却转变规律及变形温度对其等温相变的影响。绘制了65Mn钢的动态CCT曲线。结果表明,当轧后冷速小于2℃/s时,试验钢可获得铁素体和珠光体组织。随着冷速的增大,试验钢中将出现贝氏体和马氏体组织,硬度增大。当冷速大于40℃/s时,试验钢中的组织全为马氏体,硬度达到678.05HV。此外,在研究不同变形温度对65Mn钢等温相变的影响时发现,第2道次变形温度为920℃时,珠光体组织多呈片层状,硬度为271.86HV;随着变形温度的降低,试验钢中铁素体含量增加,珠光体球化趋势明显,粒状珠光体含量增多。当变形温度下降至860℃时,试验钢的硬度降低至252.21HV,有利于其后续深加工。