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对出现横向断裂的Q345B钢连铸板坯的断口进行了宏观形貌分析、横向及纵向低倍分析和微观形貌分析,以研究板坯横向断裂的原因。结果表明:Q345B钢连铸板坯中存在严重的中间裂纹;断口整体表现为脆性解理形貌,断口处存在大量白点和氢致裂纹,断口的自由晶面存在碳氮析出物和含磷化合物的析出物。在钢液凝固过程中,钢液中氢原子及析出物在铸坯的中间裂纹处富集析出并产生体积变化导致了铸坯的横向断裂。通过降低钢液中H、N、O、P、S的含量和加强连铸机设备维护和检修,保持良好的对弧精度等措施可以防止铸坯断裂。 相似文献
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特厚板坯在浇铸过程中由于窄边鼓肚变形引起液相穴富集溶质钢水流动,传热不均导致严重的中心偏析和中心线状裂纹,同时增加边角部裂纹发生率。因此特厚板坯窄边鼓肚已成为了限制其质量发展的重要因素。本文结合南钢特厚板坯连铸机实际生产工艺,在生产前通过进行扇形段辊缝调整、增强了结晶器与窄边足辊的冷却强度,增加了铸坯坯壳厚度;并通过增加结晶器窄边足辊对数,进行铸坯出结晶器后窄边锥度补偿,延长对铸坯窄边的支撑,减小了钢水静压力对窄边的作用力。通过加强对生产过程中间包钢水过热度与拉速的控制,在结晶器中形成较厚坯壳,有效解决了特厚板坯460/370 mm×(1 800~2 600)mm断面窄边鼓肚现象,窄边鼓肚单侧鼓肚量控制在5 mm以内,改善了特厚板坯的表面及内部质量。相关研究结果将为未来特厚板的品种研发提供理论基础。 相似文献
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通过对天铁热轧1650mm 1^#板坯连铸机工艺流程的生产数据跟踪,针对铸坯内部中间裂纹的形成原因、机理、影响因素等进行分析,从拉速控制、杂质元素控制等几方面探讨了防止铸坯中间裂纹产生的有效措施。 相似文献
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304不锈钢2mm连铸薄带中的裂纹分布和形成分析 总被引:3,自引:0,他引:3
用扫描电镜(SEM)观察和分析了双辊连铸法生产的304不锈钢1 200 mm×2 mm铸带表面和内部裂纹的形貌和形成。由于采用导热性好的铜制结晶辊,薄带表面和内部产生了长140 mm、深0.33 mm的裂纹,薄带断面有分层现象。试验结果表明,铜制结晶辊使钢液的冷却速度达到(1~4)×103K/s,薄带接触辊面温度低,凝固区的温度梯度高达105K/m,温差产生的内应力和应力集中导致裂纹产生;MnS、MnO、Cr2O3等夹杂物是裂纹源。 相似文献
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为研究压下对连铸坯内部裂纹产生的影响,利用ABAQUS有限元软件建立了230 mm×280 mm断面大方坯压下数学模型。通过压下模型对重轨钢连铸坯压下过程进行热力耦合模拟计算,对压下过程中产生的内部裂纹进行了预测。首先,对连铸坯不同中心固相率为0.3~0.7的温度场进行计算;然后,利用压下模型计算了连铸坯中心固相率0.3~0.7时凝固前沿的等效塑性应变。研究结果表明,在连铸坯中心固相率为0.3~0.7的位置处分别施加7 mm压下量进行压下,连铸坯凝固前沿等效塑性应变未超过临界等效塑性应变(0.4%),连铸坯未出现内裂纹;同时,对连铸坯在中心固相率为0.6位置处进行了不同压下量的研究,研究结果表明,当连铸坯压下量超过7 mm时,凝固前沿的等效塑性应变超过临界塑性应变(0.4%),连铸坯出现内裂纹,并且压下量越大,连铸坯内裂纹越严重。同时,工业试验结果与模型计算结果基本吻合,验证了模型计算的准确性。 相似文献
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《钢铁研究学报(英文版)》2011,(Z2):383-388
According to the analysis of the macro and micro characteristics of the center of continuous casting blooms by acid wash, SEM, metallographic and scanning-type electron microscope, there was a serious segregation and some shrinkage cavities in the slab; Cracks occurred at the end of the columnar crystal and spread along the boundary of the primary dendrite. At the crack enriched a large number of impurity elements, carbon, phosphorus, sulfur, whose crystal boundary segregation is the internal factor of the intermediate cracks. Determining the originated location of intermediate cracks and calculating the total strain in this area during solidification process of slab, it is found that the load is the ex- ternal factor of cracks’ generation and expansion. 相似文献
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To control the halfway cracks and shrinkage cavities during bloom continuous casting (CC) process, final electromagnetic stirring (F-EMS) and soft reduction techniques have been coordinately optimised. The halfway crack and shrinkage cavity can be successfully controlled by adopting the CC technique parameters described as follows: (1) casting speed is 0.62 m min-1, (2) secondary cooling water ratio is 0.2?L?kg?1, (3) reduction amount is 18?mm; (4) reduction region ranges from 19.9?m (location of M3 roller) to 25.4?m (location of M9 roller) distance from meniscus; and (5) corresponding distributions of reduction amount for each roller are 1, 1, 2, 3, 4, 4, and 3?mm along the casting direction. As compared to origin scheme for bearing steel, the difference between the maximum and minimum segregation degrees at the strand centre can be reduced from 0.35 to 0.09 under the optimal case. 相似文献
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采用连铸圆坯冷送轧制Q345E圆钢,发现表面存在较多裂纹,裂纹长度为20 ~80 mm,呈离散型分布。经检测,裂纹两边发现较严重的脱碳层,裂纹根部存在较多高温氧化质点,未发现非金属夹杂物。理论研究表明,初生奥氏体晶界析出网状铁素体膜是导致钢材断面收缩率降低的根本原因,而Q345E中的Nb含量在特定的温度段降低了钢材的塑性,更加剧了钢材的开裂倾向性。当预热段温度较高(850~900 ℃)时,铸坯快速升温,表面局部发生α→γ的转变,体积收缩不均匀,产生拉应力。当拉应力超过钢材所能承受的极限时,产生表面裂纹。通过对铸坯的预热缓解了内外温度差,有效解决了Q345E热轧圆钢的表面裂纹问题。 相似文献
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分析钢筋混凝土现浇板产生裂缝的原因,主要论述温度-收缩应力对钢筋混凝土现浇板产生裂缝的影响。对温度-收缩应力作用产生裂缝提出预防措施。 相似文献
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Small crack size accelerates corrosion fatigue propagation through high strength 4130 steel in aqueous 3 pct NaCl. The size
effect is attributed to crack geometry dependent mass transport and electrochemical reaction processes which govern embrittlement.
For vacuum or moist air, growth rates are defined by stress intensity range independent of crack size (0.1 to 40 mm) and applied
maximum stress (0.10 to 0.95 Φys). In contrast small (0.1 to 2 mm) surface elliptical and edge cracks in saltwater grow up to 500 times faster than long (15
to 40 mm) cracks at constant δK. Small cracks grow along prior austenite grain boundaries, while long cracks propagate by
a brittle transgranular mode associated with tempered martensite. The small crack acceleration is maximum at low δK levels
and decreases with increasing crack length at constant stress, or with increasing stress at constant small crack size. Reductions
in corrosion fatigue growth rate correlate with increased brittle transgranular cracking. Crack mouth opening, proportional
to the crack solution volume to surface area ratio, determines the environmental enhancement of growth rate and the proportions
of inter- and transgranular cracking. Small cracks grow at rapid rates because of enhanced hydrogen production, traceable
to increased hydrolytic acidification and reduced oxygen inhibition within the occluded cell. 相似文献
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为了探究内部缺陷形状由裂隙至圆孔的变化对类岩体脆性材料破断模式与特征的影响,构建了含缺陷的单轴压缩力学模型,并利用水泥砂浆材料制作类岩体试样,系统地研究了缺陷形状由裂隙至圆孔变化过程中含缺陷试件的强度变化特征和裂纹演化扩展机制。结果表明:当荷载方向与缺陷长轴垂直时,缺陷周边应力集中在长短轴端点处且与缺陷无关;缺陷对试样峰值强度影响较为明显,在缺陷形状由裂隙向圆孔变化的过程,峰值强度降低幅度逐渐增大;缺陷变化对试样的裂纹起裂与裂纹扩展的影响不显著;缺陷试样的最终破坏模式可划分为剪切破坏和拉-剪混合破坏,当m值大于0.60时破坏模式为剪切破坏,当m值小于0.33时破坏模式为拉-剪混合破坏。 相似文献