Longitudinal surface cracks on continuous casting slabs of P and Cu containing container steel

The fact that the amount of the mold flux components differs at differentlocations on the cracking surface indicates that the longitudinal surface cracks are initiallyformed in the mold and are enlarged in the secondary cooling zone. Based on the hot ductilitymeasurement of two typical container used steels, it is known that the steels are in severeembrittlement state in the temperature range of 825-775 deg C. By means of increasing Cr/Ni platingthickness on the upper part of the mold, reducing mold heat flux, adopting new secondary coolingpattern, etc., the occurrence of the surface longitudinal cracks on the steel CC (continuouscasting) slabs has been significantly reduced.

Longitudinal surface cracks of thin slabs

Based on the production practice of medium carbon thin slabs in the CSP plant,the reasons and influencing factors for the formation of longitudinal cracks were investigated,and some industrial measures were taken to eliminate the cracks.The results show that the efficient solutions to reduce longitudinal cracks are improving the performance of the mold powder,stabilizing the mold heat flux,and maintaining a proper taper of the mold during casting.Proper pouring temperature and secondary cooling also play important roles in preventing longitudinal surface cracks.

The optimization of mold fluxes used for casting the peritectic steel of heavy slabs at Baosteel

In order to solve the problem of the high surface longitudinal crack ratio of heavy peritectic steel slabs produced by the No. 3 continuous caster at Baosteel,the physical properties of the original mold flux and the optimized mold flux were compared in a comprehensive way by using analytical measures, such as a slag film heat-flow simulator, a thermowire molten flux crystallization tester and an X-ray diffractometer in the laboratory. The results reveal that one of the major reasons for the cracks is the poor heat transfer ability of the original mold flux. However, the optimized mold flux with a high basicity features a high crystallizing rate,low crystallization temperature and low heat-flow density. Therefore, the optimized mold flux is more suitable for casting peritectic steel by the heavy slab continuous caster. The test results show that the slabs produced by using the optimized mold flux had no surface longitudinal crack in four test casts, while the surface longitudinal crack ratio of the slabs produced by using the original mold flux was 5%. The optimized mold flux can effectively prevent slab surface longitudinal cracks from occurring.

Analysis on Surface Longitudinal Cracking of Q345D Slab

The surface longitudinal cracking of peritectic steel Q345 D slab was studied by means of metallographic microscopy and scanning electron microscopy. The results show that the surface longitudinal cracking is caused by the shell repeatedly tearing and healing under the action of stress, which is due to disruption of the steel matrix continuity with inclusion aggregation on the shell surface. The relative precautions of reducing the cracking are raised according to the practical situation.

Technology Development for Controlling Slab Transverse Corner Crack of Typical Micro-alloyed Steels

A mathematical model for simulating the fluid flow, heat transfer and solidification in the conventional mold and the chamfer mold, together with a finite element stress-strain model in the straightening process of both molds, were established for the typical niobium, vanadium, and titanium micro-alloyed steels. On the basis of both numerical analysis, the mold copper plate with an optimum chamfered shape was designed and applied in industrial tests. The predicted results from numerical simulation of fluid flow, heat transfer and solidification in the conven tional mold and the chamfer mold show that the increased chamfered angle leads to an approximately linear increase o[ the slab surface temperature, but it also causes strong flow near the slab corner. Very small chamfered length can lead to a significant increase of the temperature near the slab corner. However, with further increasing the chamfered length, the temperature of the slab corner increased slightly. The calculated results from the finite element analysis of stress-strain during the straightening process show that at the same slope width, the tangential strain on the slat） edges and corners is minimum when the chamfered angle is 30° and 45°, which is only 40° to 46° of rectangular slabs with the same cross-section area. At the same chamfered angle of 30°, when the chamfered length is controlled between 65-85 mm, the tangential strain on the part of the slab edges and corners is relatively smaller. Industrial test results show that the slab corner temperature at straightening segment increases about 100 ℃ by using chamfer mold compared to the conventional molds. The slab transverse corner cracks have been reduced more than 95° in comparison with those in the conventional mold.

Q355B宽带钢表面开裂原因

某Q355B钢边部表面发生开裂现象。采用宏观观察、化学成分分析、金相检验、扫描电镜及能谱分析等方法分析了裂纹产生的原因。结果表明:钢板表面裂纹产生于连铸工艺环节,裂纹附近存在砷、铜等有害元素富集现象;砷、铜等有害元素形成了低熔点的富集相,使钢板的塑性变差,破坏了钢基体连续性,在拉应力的作用下,钢板表面发生开裂现象。

集装箱用钢连铸坯表面纵裂纹的研究

对集装箱钢铸坯表面纵裂纹开裂面不同位置处保护渣所含成分的分析结果表明 ,纵裂纹是在结晶器内生成 ,在二冷区扩展成裂纹缺陷的。由铸坯试样高温延塑性测试结果可知 ,在 775～ 82 5℃之间 ,集装箱钢处于脆性严重的状态。通过采用增加结晶器铜板上部镀层厚度降低热流和改用新的二冷工艺等措施 。

亚包晶钢连铸板坯表面纵裂纹的研究

针对 重钢七厂 板坯连铸 的实际 生产条件 ，通过现 场试 验，研 究了 钢水 质量、结晶 器液 面状况、结晶 器保护 渣和设备 检修等 对板 坯 表面 质量 的 影响 。分 析了 板坯 表 面缺 陷的 类 型、数 量 和分布，并 提出了控 制板坯表 面质量 的措施。

CSP薄板坯连铸工艺生产SPA-H钢的表面缺陷研究

针对CSP薄板坯连铸连轧生产线生产集装箱板用钢SPA-H铸坯的实际,分析讨论了引起铸坯表面纵裂纹和缺陷的各影响因素,主要包括保护渣、钢的成分、结晶器热流密度、拉速等,据此提出将[C]控制在≤0.06%,保护渣的水分含量控制在≤0.5%,采用电磁制动技术及二次冷却工艺等措施,使得CSP生产板材用料的合格率提升了约4%。

10PCuRE耐候钢连铸坯表面纵裂纹成因分析

对10PCuRE钢典型炉号铸坯表面角部纵裂缝进行了宏观观察,采用扫描电镜、电子探针及X射线能谱对裂纹开裂表面和热轧钢带断裂面上夹杂物进行了形貌观察和微区成分分析,通过Gleeble—1500试验机对铸坯试样进行了高温力学性能测试,并且还检测了10PCuRE钢连铸结晶器的宽、窄面上的热流,得到了10PCuRE耐候钢连铸坯表面纵裂纹的主要形成原因,提出了消除10PCuRE连铸坯表面角部纵裂纹的措施。

钢中碳含量和保护渣粘度对连铸板坯表面纵裂的影响

分析了攀钢09SiVL钢连铸板坯形成表面纵裂的影响因素。结果表明，钢中碳含量是板坯形成表面纵裂的决定性因素，保护渣粘度对板坯形成表面纵裂的影响显著。要消除表面纵裂，应将钢中碳含量控制在0．08％～0．10％。当钢中碳含量为0.11％～0．13％时，使用粘度适中的保护渣能减少表面纵裂。

薄板坯纵裂及其影响因素探讨

铸坯质量问题是薄板坯连铸连轧工艺研究的核心问题。在调研的基础上,对国内现有薄板坯连铸生产线铸坯质量现状进行了分析。并提出了进一步改进薄板坯表面质量的工艺措施。

M30Mn2锚链钢连铸坯表面裂纹原因分析

莱钢特殊钢厂采用电炉短流程试制生产 M3 0 Mn2锚链钢 ,红坯热送成材后出现比较严重的表面裂纹。分析认为其主要原因是热装热送工艺不完善 ,铸坯在两相转变温度区热送 ,钢的热脆性造成了大量的裂纹源 ,在轧制成材过程中裂纹进一步扩展 ,而且带状组织没有明显得到改善。同时提出了低温热装、高温加热、轧后充分冷却等控制裂纹产生的工艺改进措施。

Q235B热轧板表面纵裂成因分析及工艺控制

Q235B钢（0.11%~0.17%C）10~20 mm热轧板的生产流程为铁水预处理-50 t转炉-吹氩-（2.00~230）mm×（900~1600）mm板坯连铸-热轧工艺。分析表明,Q235B钢热轧板表面裂纹来源于铸坯纵裂。统计分析了成分、钢水过热度、拉速、连铸二冷水量、保护渣等对连铸坯纵裂的影响。通过控制Mn/S≥40,钢水过热度15~35℃,拉速1.15 m/min,按季节调节二冷水量,采用熔点≥1100℃,粘度0.20~0.32 Pa·s,碱度≥1.10的保护渣等措施,使Q235B钢热轧板表面纵裂纹由3.51%降至≤0.96%。

优化10PCuRE炼钢工艺消除铸坯表面纵裂纹

10PCuRE钢是一种C含量较低、P含量很高的稀土钢种,浇铸时难度大,板坯容易产生裂纹和夹杂等缺陷。针对10PCuRE连铸坯表面纵裂缝问题,对原10PCuRE钢冶炼工艺进行了优化,加强了出钢过程的钢液脱氧,并用合成渣技术和强化吹氩搅拌,以改善钢包中的渣—金反应;结晶器中使用专用稀土保护渣以在浇铸过程中有效地防止钢液的二次氧化,较好地润滑初始凝固坯壳和结晶器内模壁,降低表面热裂纹的倾向。应用优化后的冶炼工艺后,钢中氧含量和硫含量得到控制,稀土利用率提高,连铸坯表面纵裂缝消失,铸坯角部裂纹和内部裂纹问题大大改善,并且成品钢成分、晶粒组织、夹杂物的级别均得到了很好的改善。

316L不锈钢冷轧板表面缺陷分析和工艺改进

316L不锈钢0.3~4.0 mm冷轧板的冶金生产流程为180 t EAF-AOD-LF-200 mm连铸板坯-热轧2.5~14.0 mm板-冷轧。通过对连铸坯、热轧卷以及冷轧板的化学成分、金相和扫描电镜及能谱检测,并对316L不锈钢冷轧板表面出现的线状缺陷进行了分析。结果表明,连铸坯表面振痕较深,有凹坑,并且存在深度≤300μm微裂纹缺陷;热轧板表面存在线状缺陷,缺陷附近存在大面积的氧化区域;冷轧板缺陷处(S含量0.001%,Cr_(当量)/Ni_(当量)=1.58)未发现较大尺寸的夹杂物。得出冷轧板线状缺陷源来自连铸坯,在加热炉中被严重氧化,最终形成冷轧板表面线状缺陷。通过将铸坯拉速从1.1 m/min降至1.0m/min,钢水过热度从45℃降至40℃,二冷比水量从1.0 kg/t降至0.9 kg/t,铸坯修磨用砂轮由16~#改为20~#等工艺措施,冷轧板表面缺陷大幅减少。

低合金钢连铸工艺研究

研究了连铸低合金钢的拉速、二冷配水 ,结晶器保护渣 ,结晶器喂稀土丝等工艺 ,解决了低合金钢连铸工艺容易产生铸坯表面裂纹 ,水口堵塞等问题 ,为攀钢 135 0板坯连铸机生产低合金钢奠定基础。

圆钢表面裂纹产生原因的遗传性试验研究

采用在铸坯表面钻孔的方法模拟铸坯划伤和针孔对圆钢表面裂纹的遗传性影响,运用金相检测、SEM等方法对工业试验样品进行了分析。结果表明,随着钻孔直径的增加,圆钢裂纹深度和长度都增加;随钻孔深度的增加,裂纹深度增加,而裂纹长度变化不明显。试验表明铸坯表面划伤和表面针孔是导致圆钢表面裂纹主要原因。

连铸板坯表面纵裂分析

对生产数据进行分析,认为钢水成分、拉速和结晶器液面波动等是造成连铸坯表面纵裂的主要原因。为此,根据结晶器专家系统进行可视化的生产指导,从钢种成分控制、生产操作等方面提出了改进措施,减少了连铸板坯表面纵裂的产生。

高层建筑用Q345GJC钢板表面裂纹成因分析

采用宏观分析、化学成分分析、金相检验、扫描电镜观察和能谱分析等方法对某批轧制后表面存在纵向裂纹的高层建筑用Q345GJC钢板的裂纹形成原因进行了分析。结果表明:钢板表面裂纹在连铸板坯上就已经存在,裂纹产生的主要原因是在连铸过程中结晶器涂层严重磨损致使铜板外露,从而使铜元素渗入到连铸板坯中,降低了钢的热塑性,导致了裂纹的产生;在随后的轧制过程中,裂纹沿轧制方向进一步扩展形成纵向裂纹。