铝镇静钢板坯表面裂纹产生原因的分析

铝镇静钢板坯表面裂纹的产生是由于从钢锭轧制板坯时．先共析铁素体和ＡＩＮ已经沿原奥氏体晶界析出，脆化了奥氏体晶界，造成沿晶断裂。同时，由于钢锭表面冷区和中心热区之间存在热应力，以及钢中的相变应力和枝晶间显微偏析，加速这种断裂。降低加Ａｌ量，或用Ｔｉ代替部分Ａｌ脱氧，可以消除这种缺陷，最后指出，连铸板坯在大于９５０℃条件下矫直，不产生表面横向裂纹。     

中碳高强度钢焊接半熔化区晶界偏析及其对韧性的影响

均匀化热处理和未均匀化热处理的45CrNiMo1V钢试样,在HRJ-2型热模拟试验机上模拟焊接半熔化区的热循环。用金相和电子探针方法研究了焊后条件下试样原奥氏体晶界上的元素偏析。对照冲击试验结果得出下列结论:钢中偏析带是原奥氏体晶界元素偏析的极其重要原因;焊前均匀化热处理,消除钢中偏析带,可以大幅度地降低晶界偏析,提高焊接半熔化区的韧性。     

立弯式板坯连铸机中微合金钢产生横向角裂的原因

在一些立弯式板坯连铸机上生产的微合金经常可以观测到横向角裂并且极难预防。通过详细检查酸洗表面和宏观检验的板坯固定（外部）侧角通常发现这些裂纹。在最近研究中,调查了板坯表面显微构造,其结果显示裂纹形成的原因是板坯弯曲时奥氏体晶界链式析出物和膜状先共析铁素体。起初,当板坯固化后温度降低时,Nb,V或前碳化物和／或氮化物以链式方式析出,然后固定在奥氏体晶界上。此工艺阻止了晶界滑移和降低了晶界上受的力。其次,由于在弯曲操作期间基体和细小析出物之间的应力错位,晶界上析出的链式碳化物和／或氮化物增加了板坯形成的裂纹趋势。同时,在奥氏体一铁素体转变过程中沿奥氏体晶界析出的膜状先共析铁素体中断了奥氏体基体的连续性。鉴于先共析铁素体膜的强度低于奥氏体晶粒的强度这一事实,当板坯经受弯曲应力时,沿膜状先共析铁索体就产生了裂纹。     

影响含B低碳贝氏体钢冲击韧性的规律研究

对影响含硼低碳贝氏体钢冲击韧性的因素进行了对比试验和分析,总结了含硼低碳贝氏体钢冲击韧性的规律。认为影响含硼低碳贝氏体钢冲击韧性的主要原因是有效晶界与质点控制,从而通过细化轧制奥氏体获得有效晶界,通过控轧控冷来控制相变,获得不同类型的中温转变组织分割奥氏体。利用准多边形铁素体、位向不同的板条束、和粒贝等组织有效改善冲击韧性,获得良好的强韧性匹配。同时微合金元素的合理使用与钢水纯净度的控制是获得良好韧性的前提。     

45钢等径弯曲通道变形及组织细化研究

研究了等径弯曲通道(ECAP)变形后45钢中先共析铁素体及珠光体组织的演变特征.结果表明,ECAP变形4道次后,片层状的珠光体组织演变成了超细的渗碳体颗粒均匀分布于亚微晶铁素体基体的组织.先共析铁素体由原始的平均晶粒尺寸约为30 μm演变为大角度晶界分离的、平均晶粒尺寸约为0.4μm的超细晶组织.ECAP变形后,先共析铁素体首先在其内部会形成具有薄片层界面(LBs)的板条位错胞甚至亚晶组织.进一步变形时位错胞或亚晶可继续细化.再进一步变形时通过晶界滑移和晶粒旋转的方式可以获得具有大角度晶界分离的、等轴的超细晶组织.     

稀土Ce对环保型铋易切削钢热塑性的影响

利用Gleeble高温拉伸模拟实验与微观组织结构分析,研究了850～1200℃时稀土Ce对环保型铋易切削钢热塑性的影响。结果表明:稀土Ce可显著提高铋易切削钢1000℃时的热塑性,使高温变形塑性温度区间扩大50℃。稀土Ce对铋易切削钢热塑性的改善,主要与稀土Ce降低钢的动态再结晶开始温度有关。850～950℃时,铋易切削钢差的热塑性主要与晶界液态铋膜偏聚、形变奥氏体未发生动态再结晶、及沿晶先共析铁素体薄膜的析出有关。     

铸态齿轮钢16MnCr5高温区形变断裂机理的研究

通过在Ｇｌｅｅｂｌｅ—１５００热模拟试验机上进行热拉伸试验,研究了１６ＭｎＣｒ５齿轮钢在高温下形变断裂的行为与机制。结果如下：在奥氏体低温区（７５０～１０００℃）,由于晶界滑移而损害了塑性;在奥氏体高温区（１０５０～１３００℃）,动态再结晶的发生使得塑性显著改善;１３５０℃以上温度晶界发生过熔导致沿晶脆性断裂;７００℃时在奥氏体晶界处形成形变诱导铁素体膜,导致沿晶塑性断裂     

Q345E板坯热送产生的裂纹的形成机理研究

采用透射电镜、扫描电镜和能谱分析等方法对Q345E板坯热送裂纹的形成机理进行了分析,研究了Q345E铸坯热送热装工艺对板坯裂纹形成的影响,分析了轧制过程中裂纹的形成机理。结果表明:Q345E铸坯在热送过程中发生奥氏体向铁素体转变,在奥氏体晶界处形成先共析铁素体膜;Nb、Ti的碳氮化物在铁素体中析出并分布在奥氏体晶界处,造成晶界弱化;铸坯在加热炉中受热应力的作用造成Nb、Ti的碳氮化物析出相与先共析铁素体脱离,形成孔洞,为板坯热送裂纹的形成提供了条件。     

Si,V钢的珠光体相变

系统研究了单独或复合添加Ｓｉ和Ｖ对珠光体钢的相变及其显微组织的委现过共析成分（０．７７％～０．９５％Ｃ）的钢中添加Ｓｉ和Ｖ，会在奥氏体晶界附近形成非片太产物。这些产物由初始不连续的渗碳体质点和晶界铁素体组成，且在铁素体中嵌入了ＶＣ相间沉淀。碳含量进一步增加时（高达１．０５％），晶界渗碳体质点的纵横尺寸比从秋降低到２５：１。提出了容易理解来解释这些作用。还研究了合金元素对珠光体钢的显微组织的其他影响     

控制轧制低碳含铌钢铁素体混晶及其对机械性能的影响

研究了控制轧制低碳含铌钢铁素体混晶的定量评定、形成原因,影响因素以及对钢的机械性能的影响,试验结果表明,铁素体晶粒尺寸的不均匀性(即混晶)可用参数C.V_A评定.C.V_A定义为晶粒面积的标准差与平均面积之比。铁素体晶粒尺寸的C.V_A值与加热温度、轧制温度、未再结晶区的形变量及轧后冷速有关,进入未再结晶区轧前奥氏体晶粒平均直径d_A的影响最大。控轧钢中产生严重混晶的根本原因是形变未再结晶奥氏体促进γ→α转变形核不均匀性。 铁素体混晶对钢的屈服强度无明显影响,对钢的脆性转变温度的影响与平均晶粒尺寸d_(F)有关。     

Effect of Austenite Deformation on Continuous Cooling Transformation Microstructures for 22CrSH Gear Steel

 The effect of compressive deformation of austenite on continuous cooling transformation microstructures for 22CrSH gear steel has been investigated using a Gleeble 1500 thermal simulator. The experimental results show that the deformation of austenite promotes the formation of proeutectoid ferrite and pearlite, and leads to the increase of critical cooling rate of proeutectoid ferrite plus pearlite microstructure. The grain boundary allotriomorphic ferrite occupies the austenite grain surfaces when the prior deformation takes place or the cooling rate is decreased, which causes a transition from bainite to acicular ferrite. The deformation enhances the stability of transformation from austenite to acicular ferrite, which results in an increase of M/A constituent.     

Effects of thermomechanical processing on the microstructure and mechanical properties of a Ti-V-N steel

Based on studies of austenite deformation behavior and continuous-cooling-transformation behavior of a Ti-V microalloyed steel by cam plastometer and quench-deformation dilatometer, respectively, plate rolling schedules were designed to produce (i) recrystallized austenite, (ii) unrecrystallized austenite, (iii) deformed ferrite + unrecrystallized austenite. The effects of austenite condition and cooling rate on the final microstructure and mechanical properties were investigated. To rationalize the variation in final ferrite grain size with different thermomechanical processing schedules, it is necessary to consider the kinetics of ferrite grain growth in addition to the density of ferrite nucleation sites. The benefit of dilatometer studies in determining the optimum deformation schedule and cooling rate for a given steel is domonstrated. A wide range of tensile and impact properties results from the different microstructures studied. Yield strength is increased by increasing the amount of deformed ferrite, bainite, or martensite, and by decreasing the ferrite grain size. Impact toughness is most strongly influenced by ferrite grain size and occurrence of rolling plane delaminations. B. Dogan, Formerly with CANMET, Ottawa, Canada,     

C Mn Nb钢在控轧控冷条件下相变后铁素体晶粒尺寸的预测

 基于相变动力学和热力学原理，讨论了椭球形铁素体晶核在奥氏体晶界形核及长大的动力学，在模型中引入变形和冷却的作用，提出了预测C Mn Nb钢经控轧控冷后铁素体晶粒尺寸的方法。用该方法进行的计算机模拟结果和实验结果吻合良好，表明这种方法可用来模拟该相变过程。     

CSP线高强度细晶热轧板的混晶和变形拉长晶粒的成因

对CSP线生产的高强度细晶热轧板的混晶和拉长晶粒的成因进行了分析,用有限元分析法模拟了热轧带钢的变形区的剪切应变场和温度场,用Gleeble实际模拟轧制工艺和组织变化。结果表明,CSP线高强度细晶热轧板的混晶和拉长晶粒的形成与钢板轧制过程中的钢板表层的变形场及温度场有关,也与先析出铁素体的形成后再进行轧制变形的过程有关;采用奥氏体深过冷轧制,既保证得到细晶粒又避免产生混晶和被变形拉长的晶粒。新的CSP轧制工艺,成功地生产了高强度高成形性细晶粒C-Mn热轧板。     

变形晶界对低碳钢显微组织的影响

对不同温度下变形和变形后再加热到奥氏体区的低碳钢SS400的显微组织进行了研究，结果表明：变形使奥氏体和铁素体晶界呈锯齿状，锯齿状的奥氏体晶界优先成为铁素体的形核位置，锯齿状的铁素体晶界有利于铁素体再结晶核心的形成。     

Austenite Recrystallization and Controlled Rolling of Low Carbon Steels

The dynamic recrystallization and static recrystallization in a low carbon steel were investigated through single-pass and double-pass experiments. The results indicate that as the deformation temperature increases and the strain rate decreases, the shape of the stress-strain curve is changed from dynamic recovery shape to dynamic recrystallization shape. The austenite could not recrystallize within a few seconds after deformation at temperature below 900 ℃. According to the change in microstructure during deformation, the controlled rolling of low carbon steel can be divided into four stages： dynamic recrystallization, dynamic recovery, strain-induced ferrite transformation, and rolling in two-phase region. According to the microstructure after deformation, the controlled rolling of low carbon steel can be divided into five regions： non-recrystallized austenite, partly-recrystallized austenite, fully-recrystallized austenite, austenite to ferrite transformation, and dual phase.     

Effect of Controlled Cooling After Hot Rolling on Mechanical Properties of Hot Rolled TRIP Steel

A three-step cooling pattern on the runout table（ROT）was conducted for the hot rolled TRIP steel.Microstructural evolution during thermomechanical controlled processing（TMCP）was investigated.Processing condition of controlled cooling on a ROT in the laboratory rolling mill was discussed.The results indicated that the microstructure containing polygonal ferrite,granular bainite and a significant amount of the stable retained austenite can be obtained through three-step cooling on the ROT after hot rolling.TMCP led to ferrite grain refinement.Controlled cooling after hot rolling resulted in the stability of the remaining austenite and a satisfactory TRIP effect.Excellent mechanical properties were obtained through TMCP for the hot rolled TRIP steel.     

Effect of Cooling Rates on the Second‐Phase Precipitation and Proeutectoid Phase Transformation of a Nb–Ti Microalloyed Steel Slab

During the continuous casting of low‐carbon Nb–Ti microalloyed steel, control of the slab surface microstructure and the behavior of the second‐phase precipitation are significantly influenced by the cooling rate. Through confocal laser scanning microscopy, the effect of the cooling rate on the behavior of ferrite precipitation both at the grain boundary and within the austenite was observed in situ and analyzed. The relationship between the cooling rate and precipitation of the microalloying elements on the slab surface microstructure was further analyzed by transmission electron microscopy. The results showed that the effect of microalloying element precipitation on proeutectoid ferrite phase transformation is mainly manifested in two aspects: (i) the carbonitrides of microalloying elements act as inoculant particles to promote nucleation of the proeutectoid ferrite and (ii) the carbon near the grain boundary is depleted when the microalloying elements precipitate into carbonitrides, inducing a decrease in the local carbon concentration and promoting ferrite precipitation.     

Microstructural evolution during the austenite-to-ferrite transformation from deformed austenite

It is well established that the ferrite grain size of low-carbon steel can be refined by hot rolling of the austenite at temperatures below the nonrecrystallization temperature (T _nr ). The strain retained in the austenite increases the number of ferrite nuclei present in the initial stages of transformation. In this work, a C-Mn-Nb steel has been heavily deformed by torsion at temperatures below the determined T _nr for this steel. After deformation, specimens are cooled at a constant cooling rate of 1 °C/s, and interrupted quenching at different temperatures is used to observe different stages of transformation. The transformation kinetics and the evolution of the ferrite grain size have been analyzed. It has been shown that the stored energy due to the accumulated deformation is able to influence the nucleation for low undercoolings by acting on the driving force for transformation; this influence becomes negligible as the temperature decreases. At the early stages of transformation, it has been observed that the preferential nucleation sites of ferrite are the austenite grain boundaries. At the later stages, when impingement becomes important, ferrite coarsening accompanies the transformation and a significant reduction in the number of the ferrite grains per unit volume is observed. As a result, a wide range of ferrite grain sizes is present in the final microstructure, which can influence the mechanical properties of the steel.     

The role of solute segregation in promoting the hardenability of steel

The two most potent promoters of hardenability in steel are boron and phosphorus. It appears that these elements function by segregating to austenite grain boundaries and interfering with the nucleation of proeutectoid ferrite. It is suggested that this occurs by the stabilization or alteration of the structure of certain special grain boundary re-gions which serve as favored nucleation sites for ferrite. It is demonstrated how at least part of the effect of alloying elements like manganese and chromium might be ascribed to their enhancement of phosphorus segregation. Under certain conditions phosphorus could be a useful addition to increase the hardenability of low alloy steels.