EFFECT OF THE CONTROLLED ROLLING CONTROLLED COOLING ON STRENGTH AND DUCTILITY OF THE BAINITE MICRO ALLOYED ENGINEERING STEEL

The continuous cooling transformation of hot deformation austenite austenite of test steel and the effect of different processing schedules of controlled rolling and controlled cooling on the strength and ductility have been studied. The theory and the experiment base are presented for controlled rolling and controlled cooling of the SBL micro alloyed engineering steel.

Large Eddy Simulation of the Effects of Plasma Actuation Strength on Film Cooling Efficiency

In this article, numerical investigation of the effects of different plasma actuation strengths on the film cooling flow characteristics has been conducted using large eddy simulation （LES）. For this numerical research, the plasma actuator is placed downstream of the trailing edge of the film cooling hole and a phenomenological model is employed to provide the electric field generated by it, resulting in the body forces. Our results show that as the plasma actuation strength grows larger, under the downward effect of the plasma actuation, the jet trajectory near the cooling hole stays closer to the wall and the recirculation region observably reduces in size. Meanwhile, the momentum injection effect of the plasma actuation also actively alters the distributions of the velocity components downstream of the cooling hole. Consequently, the influence of the plasma actuation strength on the Reynolds stress downstream of the cooling hole is remarkable. Furthermore, the plasma actuation weakens the strength of the kidney shaped vortex and prevents the jet from lifting off the wall. Therefore, with the increase of the strength of the plasma actuation, the coolant core stays closer to the wall and tends to split into two distinct regions. So the centerline film cooling efficiency is enhanced, and it is increased by 55% at most when the plasma actuation strength is 10.

Effect of Fast Cooling Rate on the Microstructure and Mechanical Properties of Low-Carbon High-Strength Steel Annealed in the Intercritical Region

The effect of fast cooling rate on the microstructure and mechanical properties of low-carbon high-strength steel annealed in the intercritical region was investigated using a Gleeble 1500 thermomechanical simulator and a continuous annealing thermomeehanical simulator. The results showed that the microstructure consisted of ferrite and bainite as the main phases with a small amount of retained austenite and martensite islands at cooling rate of 5 and 50 ℃/s, respectively. Fast cooling after continuous annealing affected all constituents of the microstructure. The mechanical properties were improved considerably. Ultimate tensile strength （U-TS） increased and total elongation （TEL） decreased with increasing cooling rate in all specimens. The specimen 1 at a cooling rate of 5 ℃/s exhibited the maximum TEL and UTSxTEL （20% and 27 200 MPa%, respectively） because of the competition between weakening by presence of the retained austenite plus the carbon indigence by carbide precipitation, and strengthening by martensitic islands and precipitation. The maximum UTS and YS （1 450 and 951 MPa, respectively） were obtained for specimen 2 at a cooling rate of 50 ℃/s. This is attributed to the effect of dispersion strengthening of finer martensite islands and the effect of precipitation strengthening of carbide precipitates.

The Effects of Cooling Mode on the Properties of Ti–Nb Microalloyed High-strength Hot-rolled Steels

The industrial trials of two cooling modes, i e, water cooling in forepart + air cooling in later part (WAC) and air cooling in forepart + water cooling in later part (AWC), were carried out for a Ti- Nb microalloyed steel. The average cooling rates and coiling temperature were the same for two modes. The continuous cooling transformation (CCT) curve of the tested steel was drawn. The effects of the cooling mode on the microstructure, precipitates, and properties of the steels were investigated. Results show that the strength of the steel in the WAC mode is significantly larger than that in the AWC mode, mainly because the smaller the grain size, the more and finer the grain precipitates. Therefore, when the average cooling rate is constant, the fast cooling in the forepart is an effective method to increase the strength of steels. However, the increase in the strength is accompanied by the decrease in toughness, so that the toughness of the steel should be considered when changing the cooling mode.

QUANTITATIVE RESEARCH ON THE STRENGTH AND MICROSTRUCTURE IN TRACE-Ti-BEARING STRUCTURE STEEL WITH DIFFERENT COOLING TECHNIQUES

Aim: To study the strength and microstructure of trace-Ti-bearing stracture steel. Materials and Methods: The strength and microstructure of the trace Ti bearing structure steel were studied by two kinds of controlled cooling simulation testing results in the first stage cooling and the last stage cooling after hot press deformation in the traceTi-bearing structure steel. Results: It showed that the ferrite grain size, the relative contribution of the involved strength and the mechanical strength were influenced more or less by different cooling rates. Both the refinement of ferrite grain and the increase of mechanical strength could be obtained by the proper decrease of water cooling interruption temperature (WTI) and coiling temperature (CT) in the first stage cooling or the proper increase of water cooling beginning temperature (WTB) and proper decrease of coiling temperature (CT) in the last stage cooling. Conclusion: The strength, the ferrite grain refinement and the yield tensile ratio in the first stage cooling process are much better than those in the last stage cooling process.

The effect of different cooling and tempering conditions on the strength and toughness of SA533B steel

The microstmcture and mechanical properties of SA533B low-alloy steel were investigated under different cooling and tempering conditions. Steel plates cooled at 40℃/s and 25℃/min,exibited microstructures of auto-tempered martensite and bainite, respectively. During tempering, the strength of steels quenched at the two different cooling rates decreased continuously with an increase in the tempering parameter, which is defined by T （20 ＋ log t）, where T is the temperature and t is the holding time. However, the rate of change of the strength scales with the degree to which the virgin microstructure deviates from equilibrium. The strength of the martensitic steel decreased faster and finally obtained a value close to that of the bainitic steel. The ductility and toughness gradually improved during tempering, passed through a maximum value, and finally diminished. The level of maximum toughness was also found to depend on the cooling rates of SA533B steel. The high cooling rate with a microstructure of auto-tempered martensite exhibited a larger toughness and a lower ductile-brittle transition temperature than the low cooling rate with a microstructure of bainite, because the former had finer precipitated cementite particles at quenching and a slower coarsing rate during tempering.

Microstructural Transformation and Precipitation of an Ultra-high Strength Steel under Continuous Cooling

We investigated phase transition and precipitation of ultra-high strength steel（UHSS）in a new ＂short process＂ with controlled rolling and controlled cooling.Thermalexpansion test combined with metallographic observation was used to research the continuous cooling transformation（CCT）curve.Moreover,the microstructuraltransformation and precipitation law was revealed by morphologicalobservation and alloying elements by electron probe micro-analyzer（EPMA）.Transmission electron microscopy（TEM）was utilized to analyze the composition and grain orientation of microstructure.The study showed that the measured criticaltransformation temperatures of Ac1 and Ac3 were 746 and 868 ℃,respectively.The CCT curve indicated that the undercooled austenite was transformed into proeutectoid ferrite and bainite with HV 520 in a broad range of cooling rate 0.1^（-1） ℃·s^（-1）.When subjected to a cooling rate of 1 ℃·s^（-1）,the undercooled austenite was divided into small-sized blocks by formed martensite.With further increase of cooling rate,micro-hardness increased dramatically,the microstructure of specimen was mainly lathe bainite（LB）,granular bainite（GB）,lath martensite（LM）and residualaustenite.By diffraction test analysis,it was identified that there was K-S orientation relationship between martensite and austenite for {110}_α//{111}_γ,{111}_α//{101}_γ.EPMA clearly showed that carbon diffused adequately due to staying for a long time at high temperature with a lower cooling rate of 2 ℃·s-1.Phase transition drive force was lower and the residualaustenite existed in the block form of Martensite austenite island（M-A）.With the increase of cooling rate to 10 ℃·s^（-1）,the block residualaustenite reduced,the carbon content of residualaustenite increased and α phase around the residualaustenite formed into a low carbon bainite form.

Effect of Heat Sink and Cooling Mediums on Ferrite Austenite Ratio and Distortion in Laser Welding of Duplex Stainless Steel 2205

In order to control the ferrite and austenite percentage in duplex stainless steel welding, many researchers try to change the laser welding parameters and cooling medium, but ignore to study the influence of heat sink effect on weld strength. In this work, the effect of aluminium heat sink and varying cooling medium on the laser welding of duplex stainless steel (DSS) 2205 is studied. The 2 mm thick DSS sheets welded with pulsed Nd: YAG laser welding machine by varying the cooling medium (air and oil) and an aluminium plate used as a heat sink. The welded specimens tested for tensile strength, micro-hardness, distortion, microstructure and radiography analysis. The faster cooling rate in the oil quenching process enhances the ferrite percentage compared with air-cooled samples. But the faster cooling rate in oil quenching leads to more distortion and using aluminium as a heat sink influenced positively the distortion to a small extent. The lower cooling rate in air quenching leads to a higher tensile strength of the welded specimen. The objective of this work is to analyse experimentally the effect of cooling medium and heat sink in the mechanical and metallurgical properties of laser welded duplex stainless steel.

Experimental Study on Deterioration of Concrete Strength under Different Sub-high Temperature Cycles

Tests were carried out to study the strength deterioration of concrete cooled in air or by water after sub-high temperature at different level and varying with cycles. It is proved that the cross-shaped cracks turned up and extended little by little on the surface of specimen subjected to repeat sub-high temperature, the splitting failure is characterized by cross-shaped cracks after 30 cycles, the concrete strengths decrease rapidly at early stage and to be steady subsequently with the increase of the temperature cycles, the splitting-tensile strength is more sensitive to temperature cycles than the compressive strength, the decline of concrete strength is mainly controlled by the maximum temperature having reached, the ultrasonic velocity in concrete is also declined. On the basis of test results, the mechanisms of sub-high temperature to the strength deterioration of concrete are analyzed.The formulas for calculating the compressive and splitting-tensile strength of concrete relating to the variation of temperature are proposed.

Influence of temperature cycling and pore fluid on tensile strength of chalk

Calcite has a highly anisotropic thermal expansion coefficient, and repeated heating and cooling cycles can potentially destabilize chalks by breaking cement bonds between neighboring particles. Based on tensile strength measurements, we investigated how temperature cycles induce weakening of chalk.Tensile strength tests were performed on chalk specimens sampled from Kansas(USA) and Mons(Belgium), each with differing amounts of contact cement. Samples of the two chalk types were tested in dry and water-saturated states, and then exposed to 0, 15, and 30 temperature cycles in order to find out under what circumstances thermally induced tensile strength reduction occurs. The testing results show that the dry samples were not influenced by temperature cycling in either of the chalk types. However, in the water-saturated state, tensile strength is increasingly reduced with progressive numbers of temperature cycles for both chalk samples, especially for the more cemented Kansas chalk. The Kansas chalk demonstrated higher initial tensile strength compared to the less cemented Mons chalk, but the strength of both chalks was reduced by the same relative proportion when undergoing thermal cycles in the water-saturated state.

Study on temper-rapid cooling process of low carbon steel produced by CSP

On the basis of the effect of carbon precipitation on the microstructure and properties of steel products below At temperature, a new thermal treatment method （temper-rapid cooling process） was studied. By the temper-rapid cooling process, the yield strengths of the high strength low carbon （HSLC） steel ZJ330 and SPA-H produced using the compact strip production （CSP） process increased from 340 to about 410 MPa and from 410 to about 450 MPa, respectively. The results indirectly indicated that there existed nanoscaled iron-carbon precipitates that have obvious precipitation effect on low carbon steel produced by CSP. The prospect of application is discussed.

玄武岩纤维再生混凝土高温水冷损伤试验研究

为研究消防喷水灭火对纤维再生混凝土力学特性的影响,以玄武岩纤维(BF)体积掺量和历经最高温度为变化参数,共设计90个玄武岩纤维再生混凝土(BFRC)标准立方体试块,进行高温喷水冷却和抗压强度—声发射(AE)试验,探讨BF体积掺量和历经最高温度对BFRC力学性能的影响。结果表明,当温度升到1 000℃,试块表面脱落,骨料全部露出,试块的完整性遭到严重破坏;试块的剩余抗压强度在温度为200~400℃时下降趋缓,抵抗高温的效果明显;BFRC的高温喷水冷却受压损伤过程可分为初期压密与裂纹萌生阶段、裂纹扩展汇集阶段和峰后破坏阶段,各阶段的声发射振铃累计计数具有明显差异;拟合得到消防喷水灭火后BFRC抗压强度计算公式,可为评估不同BF体积掺量及历经最高温度对BFRC抗压强度的影响提供参考。

碳素钢铸坯表面横裂纹原因分析与控制

某炼轧厂碳素钢因生产工艺控制及过程参数使用不当,造成轧后表面翘皮、舌头状及指甲状结疤缺陷突出。通过去除铸坯表面氧化铁皮、边部酸蚀等方式检查轧后缺陷批次表面质量,发现铸坯表面横裂纹、角部横裂纹是造成该缺陷的主要原因。通过对该系列钢种工艺C含量、生产过程结晶器振动参数及扇形段二次冷却水强度进行优化,达到减少铸坯表面横裂纹及角部裂纹的目的,从而降低铸坯轧后结疤率。

高温喷水冷却后型钢高强混凝土黏结滑移性能试验及剩余黏结强度评估

为了研究型钢高强混凝土在不同火灾高温喷水冷却后的黏结滑移性能,设计了19个型钢高强混凝土试件并进行高温喷水冷却后的推出试验。观察试件的外观变化及受力过程中裂缝发展过程及形态,获取各个试件的荷载-滑移全曲线及极限黏结强度、残余黏结强度等特征点参数,分析历经最高温度、混凝土强度等级、恒温时长和型钢锚固长度等变化参数对型钢高强混凝土试件界面黏结强度、黏结剪切刚度、耗能能力的影响规律,提出相应的黏结滑移本构方程和剩余黏结强度评估式。结果表明:随着历经温度的升高,喷水冷却后试件的黏结强度和黏结剪切刚度波动下降,耗能能力却有所提高;随着混凝土强度等级的提高,试件的黏结强度总体上升,黏结剪切刚度波动变化,耗能能力则变化较小;随着历经最高温度的恒温时间的增长,喷水冷却后试件的黏结强度和黏结剪切刚度均变大。历经最高温度对试件的界面黏结剪切刚度和界面耗能能力影响较为显著,并且温度较低的试件,其界面黏结损伤发展较早且较为迅速。基于试验数据,所提的黏结滑移本构方程和黏结强度计算公式其计算值与实测值吻合良好。

自密实混凝土高温冷却后的抗压性能试验研究

为研究高温后自密实混凝土(简称SCC)抗压性能,制作了C35强度标准立方体混凝土试块48个,通过在不同温度下进行模拟火灾试验,分析了自然冷却和水冷却方式对高温后自密实混凝土试块的表观状态、抗压强度、峰值应力和破坏形态的影响。研究结果表明:两种冷却方式下试块的表观裂纹数目随着目标温度的升高而逐渐增多,试块在经历600℃和700℃高温后水冷却过程中,其边角出现明显剥落现象。两种冷却方式下试块的抗压强度呈现降低趋势,反常现象是300℃温度下采用自然冷却试块的抗压强度相较于100℃和200℃温度下的自然冷却试块有明显增强,增幅为8.1%和9.9%。自密实混凝土应力⁃应变曲线的峰值应力随着目标温度的升高而明显减小,所对应的峰值应变显著变大。最后,给出了自密实混凝土轴压应力⁃应变本构方程的参数取值,其拟合曲线能够与试验实测数据较好地吻合。

HMLS涤纶工业丝生产工艺探讨

以特性黏数为1.12~1.14 dL/g的大有光增黏聚对苯二甲酸乙二醇酯(PET)切片为原料,采用日本TMT公司纺丝设备生产1670 dtex/480 f高模低缩型(HMLS)涤纶工业丝,探讨了原料PET切片的特性黏数、螺杆温度、无风区高度、冷却工艺、拉伸工艺对HMLS涤纶工业丝性能的影响。结果表明:控制PET切片特性黏数在1.12~1.14 dL/g时,可确保无油丝特性黏数在0.95~0.97 dL/g;生产HMLS涤纶工业丝时,选择微孔环形分布的喷丝板,合适的螺杆温度为280~290℃,无风区高度为50 mm,采用低温冷却工艺可确保丝束能承受高的卷绕速度和较大的拉伸力;与低温冷却高温拉伸工艺相比,采用低温冷却低温拉伸工艺生产的HMLS涤纶工业丝的断裂强度略高,断裂伸长率较低,且浸胶后帘子线强力保持率高,但毛丝率要明显高于低温冷却高温拉伸工艺。

冷却速率对MarM247铸造合金组织及拉伸性能的影响

通过研究定向凝固Mar M247合金冷却速率和显微组织,显微组织同拉伸性能间的关系,推导出合金冷却速率同拉伸性能间的关系。结果表明,冷却速率0.15~2.00℃/s,随着冷却速率的增加,合金二次枝晶臂间距(λ^(2))、最大碳化物尺寸(C_(1))和共晶平均尺寸(E_(4))逐渐减小,且分别满足λ_(2)=42.68·^(■-0.2548),C_(1)=-22.95·log■+38.59,E_(4)=-11.21·log■+26.88关系式。而相同浇铸温度(1480℃)和模组结构,不同模壳温度(950℃、1000℃、1100℃、1180℃)试验浇铸所得铸件合金组织(二次枝晶臂间距、最大碳化物尺寸和共晶平均尺寸)同其屈服强度和抗拉强度也呈负相关关系。借助合金组织特征参数推导出的冷却速率和拉伸性能关系式,为利用冷却速率评估、计算铸件力学性能提供了参考。

冷却条件对高速铣削高强钢的影响研究

在切削速度300m/min、进给量0.04mm/z、轴向切深1mm条件下,对30CrNi2MoVA高强钢进行了高速平面铣削试验,研究了干式切削、风冷、雾化冷却、切削液浇注四种冷却条件对切削力、切削温度和表面粗糙度的影响。结果表明,冷却条件对切削力的影响很小,四种冷却条件下的各切削分力相差10N左右,在不同冷却条件下,切削分力均表现为径向力>切向力>轴向力;风冷较干式切削能明显降低切削温度,均表现为切削区温度>切屑温度>工件已加工表面温度,不论是干式切削还是风冷冷却,工件已加工表面温度都较低;不同冷却条件下的工件已加工表面粗糙度值为干式切削>风冷>雾化冷却>切削液浇注,不同冷却方式下的已加工表面粗糙度基本处于同一水平,均可满足Ra 0.1μm的精密加工要求。

X70管线钢生产工艺及性能研究

通过合理设计X70管线钢成分,分析研究双机架轧制工艺、控冷工艺及矫直模型,同时采取标准化参数作业指导和设备改善两方面的攻关措施,成功生产出了性能合格的X70管线钢。验证结果表明,邯钢生产出的X70管线钢以粒状贝氏体组织为主,屈服强度、抗拉强度以及冲击韧性等力学性能良好,达到了标准和用户要求,产线具备进行稳定生产的能力。

高端特殊钢分切圆刀片热处理工艺研究

对分切圆刀片国内外的工艺技术研究现状进行综述,采用Cr12Mo1V1作为刀片基体材料,针对高端特殊钢分切圆刀片的特性进行热处理工艺研究。结果表明,空冷淬火后得到的分切圆刀片具有优异的力学性能。确定Cr12Mo1V1材料分切圆刀片的最佳热处理工艺为:加热至790℃退火保温2 h,随炉冷却至500℃后出炉空冷;淬火过程分为三个阶段,先升温至600℃保温0.5 h,再升温至850℃保温0.5 h,然后升温至1050℃保温1 h,空冷至室温;一次回火工艺为200℃×2 h,随炉冷却至室温;二次回火工艺为480℃×2 h,随炉冷却至室温。