NaNO_2-KNO_3-NaNO_3熔盐体系的电导率模型研究

利用串联模型、并联模型分别估算NaNO_2-KNO_3-NaNO_3混合熔盐体系的电导率,并将其计算值与实验值相比较。结果表明:低温时,二元系和三元系电导率值较符合并联模型,电导率与组分之间较好地符合加和性原则;温度逐渐升高,实验值则逐渐靠近串联模型;当温度高于550℃时,NaNO_(3-)NaNO_2二元系则远远偏离了两种理想模型。     

Dimensionless Cooling Performance Parameter for Characterization of Quench Media

The effect of varying thermal properties and boundary heat transfer coefficients on temperature profiles inside cylindrical quench probes was simulated during immersion cooling. The results of simulation indicated that, for assessment of the cooling performance of the quench media, the ratio of the quench probe diameter to its thermal conductivity should be less than 0.0005 m²K/W. A simple dimensionless cooling parameter (D ²CR/αΔT) was proposed to assess the cooling performance of quench media.     

超快速冷却对中碳钢组织和性能的影响

利用超快速冷却装置,通过控制轧后冷却路径,对某中碳钢的显微组织和力学性能进行了系统的研究.结果表明:超快速冷却可以抑制先共析铁索体的生成,破坏原有先共析铁素体的网状分布;超快速冷却显著缩小了珠光体的片层间距;随着超快速冷却后温度的降低,实验钢的强度和室温冲击韧性同时得到了提高.高温终轧+超快速冷却工艺可以使中碳钢获得良好的力学性能,避免了低温轧制带来的轧机负荷大的弊端,提高了轧制节奏.     

中厚板冷却过程高精度温度模型

实现高满意度轧后冷却控制目标必须依赖于轧后冷却过程控制系统高精度的温度场计算模型。以钢板内部热传导、空冷及水冷换热系数为主要研究对象,建立了轧后冷却数学模型,回归了空冷和水冷换热系数,采用Crank-Nicolson有限差分法求解钢板温度场。将该模型嵌入到国内某中厚板厂轧后冷却控制系统,对不同钢种不同厚度钢板进行轧后冷却试验,试验结果表明,实际终冷温度和目标终冷温度偏差±10℃的命中率在90%以上,很好地实现了冷却过程温度控制。     

Effects of Deformation Behavior and Processing Temperature on the Fatigue Performance of Deep-Rolled Medium Carbon Bar Steels

The effects of processing temperature on the deep-rolling response of three medium carbon bar steels, a quenched and tempered 4140 alloy, a 0.34C, 1.21Mn, 0.66Si nontraditional bainitic alloy, and a 0.36C, 1.37Mn V-microalloyed ferrite plus pearlite steel, was assessed through bending fatigue. The significantly different deformation behaviors of the three alloys were characterized through standard and nonstandard quasi-static and cyclic uniaxial tension and compression tests at room temperature (RT) and in situ at temperatures up to 634?K. Deep rolling, performed at RT and at elevated temperature (HT) in the dynamic strain-aging (DSA) regime, increased measured endurance limits by 51-62?pct (RT) and 96-117?pct (HT) as compared with the baseline condition. The enhanced fatigue performance by RT deep rolling primarily reflected the effects of the introduction of favorable residual stresses. The improved fatigue performance from HT deep rolling was attributed to the enhanced resistance to strain reversal of the material deformed during deep rolling, due to a change in deformation mechanism from dislocation-interstitial interactions in the DSA regime during processing, which inhibited mechanically induced relaxation of residual stress during cyclic loading.     

合金元素对中碳硅锰钼钒钢连续冷却转变及淬透性的影响

本文用顶端淬火法测定了40、40Si₂、40Mn₂、40Mo和40Si₂Mn₂钢的连续冷却转变曲线和淬透性曲线,同时研究了硅锰钼钒钢中不同硅或锰含量对钢的淬透性的影响,通过对试样中心为半马氏体时钢的淬透性乘子的计算,相对定量地说明了硅、锰对钢的淬透性的作用规律。
通过试验表明,硅使铁素体一珠光体的转变温度上升,使连续冷却转变曲线稍向右移,当钢中加入钼或锰后,使钢的转变温度和时间有较大地降低和延缓,尤其是锰钢。当钢中同时存在有硅和锰,则硅、锰的复合作用远比单一的锰或硅要大得多,使连续冷却转变曲线更往右下方移动。单一的合金元素对钢的淬透性影响最大的是锰,其次是钼,而硅的效果最小。但硅加到40Mn钢中,大大地提高了钢的淬透性,其复合作用不是简单地单个元素作用的叠加,而是乘子关系。为了保证40硅锰钼钒钢有足够的淬透性,必须加入大于1.5％的锰,硅保持在1.3％左右,当然还应加入适量的钼。     

中厚板快速冷却过程中的温度均匀性控制

本文介绍中厚板在加速冷却过程中,沿钢板长度方向、厚度方向、宽度方向温度分布不均的原因,并针对不同问题给出了相应的处理措施。     

Influence of Temperature and Grain Size on Austenite Stability in Medium Manganese Steels

With an aim to elucidate the influence of temperature and grain size on austenite stability, a commercial cold-rolled 7Mn steel was annealed at 893 K (620 °C) for times varying between 3 minutes and 96 hours to develop different grain sizes. The austenite fraction after 3 minutes was 34.7 vol pct, and at longer times was around 40 pct. An elongated microstructure was retained after shorter annealing times while other conditions exhibited equiaxed ferrite and austenite grains. All conditions exhibit similar temperature dependence of mechanical properties. With increasing test temperature, the yield and tensile strength decrease gradually, while the uniform and total elongation increase, followed by an abrupt drop in strength and ductility at 393 K (120 °C). The Olson–Cohen model was applied to fit the transformed austenite fractions for strained tensile samples, measured by means of XRD. The fit results indicate that the parameters α and β decrease with increasing test temperature, consistent with increased austenite stability. The 7Mn steels exhibit a distinct temperature dependence of the work hardening rate. Optimized austenite stability provides continuous work hardening in the temperature range of 298 K to 353 K (25 °C to 80 °C). The yield and tensile strengths have a strong dependence on grain size, although grain size variations have less effect on uniform and total elongation.     

Improvement of Hole-Expansion Property for Medium Carbo Steels by Ultra Fast Cooling After Hot Strip Rolling

 The improvement of hole-expansion properties for medium carbon steels by ultra fast cooling (UFC) after hot strip rolling was investigated. It was found that finely dispersed spherical cementite could be formed after ultra fast cooling, coiling and annealing treatment. Tensile strength of the steel after annealing was measured to be about 440 MPa. During hole-expansion test, cracks were observed in the edge region around the punched hole because necking or cracking took place when tangential elongation exceeded the forming limit. Cracks were mainly formed by the coalescence of micro-voids. Fine and homogeneous microstructure comprised of ferrite and spheroidized cementite could increase elongation values of the tested sheets by suppressing the combination of the adjacent micro-voids, resulting in the improved hole-expansion property.     

底吹喷枪结构对熔池搅拌效果的影响特性研究

针对目前底吹熔池熔炼过程中,如何改变喷枪结构起到强化搅拌目的的难题,采用数值模拟的方法建立了底吹熔池熔炼炉多相流非稳态数学模型,构建了多层栅栏结构的氧枪模型。计算结果表明,氧气底吹过程具有周期性,可分割成大气泡形成、气流柱形成和气流冲破熔池液面三个过程,并对有无栅栏喷枪结构在这三个过程下的相图、面平均湍动能、平均压力进行比对分析,结果表明多层栅栏枪口结构有助于强化熔池内部搅拌。     

基于人工神经网络的中厚板控冷温度预测

基于BP神经网络建立轧后控制冷却主要参数和目标参量之间的关系并对模型进行训练 ,实现轧后控制冷却终冷温度和冷却速度的预测。利用现场实测数据仿真表明 ,模型有效提高了预测精度。     

唐钢150tLF供中薄板连铸钢液温度改进实践

针对唐钢150t LF供中薄板连铸中间包钢液温度过高或过低的情况,通过对影响LF和中间包钢液温降的因素分析,经过优化相关工艺制度,提高了LF供钢离站温度的灵活性及中间包温降的稳定性,实现了中间包温度较高的可控性,在提高中间包温度合格率、降低生产事故及减少铸坯质量缺陷方面取得了显著成效。     

长期时效对DD407单晶高温合金组织和中温性能的影响

研究了DD407单晶高温合金在900℃长期无应力时效过程中,组织的演变规律及其对中温性能的影响。研究结果表明：经长达3 000 h的时效后,合金的组织稳定,无有害相析出,7 6 0℃中温强度稳定,但伸长率显著提高。     

中厚板层流冷却过程温度场的有限元分析

利用ANSYS有限元分析软件对中厚板轧后控冷过程的温度场进行模拟求解,得到了钢板在控冷过程中不同阶段的温降曲线和瞬态温度场分布,与实测结果进行了对比分析,结果基本吻合。     

硅含量对低碳钢连续冷却中转变组织的影响

通过热模拟压缩实验,对C、Mn含量基本相同,w（Si）对低碳钢在850℃变形后、以30℃/s冷却到室温时的组织演变的影响。结果表明：w（Si）由O．50％增加到0．99％时,硅的增加促进了先共析铁索体的形成,而w（Si）由0．99％增加到1．41％时,硅的增加促进了粒状贝氏体的形成。同时Si对组织中先共析铁素体的晶粒尺寸以及体积分数的变化也有一定的影响。     

Effect of Si Content on Oxide Formation on Surface of Molten Fe-Cr-C Alloy Bath During Oxygen Top Blowing

Using a direct observation experimental method, the oxide formation behavior on the surface of Fe-Cr-5 mass pct C-Si alloy baths during decarburization by a top-blown Ar-O₂ mixture was studied. The effects of the initial Si and Cr content of the alloy, temperature, and oxygen feed ratio on oxide formation were investigated. The results showed that, for alloys without Si, oxide particles, unstable oxide films, and stable oxide films formed sequentially. The presence of Si in the alloy changed the formation behavior of stable oxide film, and increased the crucial C content when stable oxide film started to form. Increasing the temperature, decreasing the initial Cr content, and increasing the ratio of the diluting gas decreased the critical C content at which a stable oxide film started to form. In addition, the P _CO and \( a_{{{\text{Cr}}_{2} {\text{O}}_{3} }} \) values at which oxides started to form were estimated using Hilty’s equation and the equilibrium relation to understand the formation conditions and the role of each parameter in oxide formation.