Damage mechanism of ladle porous plug

透气砖损毁的原因主要有4 个方面：热应力，机械磨损，机械应力，化学侵蚀。

热应力作用

在实际生产中，钢包的烘包温度为1000 ℃，钢水温度达到1600℃，两者接触时的温度差会产生较大的热应力，进而造成非常大的热震冲击。钢包处于一个周而复始的工作环境中，透气砖在接触钢水和烘包时的温度频繁变化而产生的热应力是造成透气砖损毁的一个原因。透气砖产生热应力的关键因素是温度的变化，并且透气砖的不同部位温度变化存在着差异。

机械磨损作用

卷流对透气砖的冲刷大致分三种情况：（1）透气砖高于座砖时，透气砖主要损毁的原因是钢包内钢水形成卷流对透气砖的侧面产生巨大的剪切效应和冲刷效应。因此，冲刷力是透气砖的座砖产生极大的损毁的原因之一，正常工作环境中，透气座砖使用次数也就一次，一次之后高于座砖的部分即被冲刷掉。（2）透气砖与座砖持平时，座砖对透气砖起到了保护的作用，钢水形成的卷流首先冲刷座砖致使透气砖的剪切力相应减小。（3）透气砖低于座砖时，在正常工作中该工作面上易积压冷钢，由于存留下来的冷钢的粘度相对较大，对吹气产生一定的阻碍作用，所以要满足精炼要求就需要加大吹气的压力。这样，气流对透气砖的冲刷作用力就相应加大，受到剪切、冲击强度大，更易损毁。为了达到炉外精炼对吹通率和使用寿命的要求，透气砖必须具有良好的抗冲刷能力和高温力学性能。

机械应力作用

在使用过程中，钢包底部透气砖工作面和高温钢水直接接触，在循环使用条件下，钢包中的温度一直处于变化状态，包底耐火材料使用中由高温到低温会产生温度差，耐火材料的原质层和变质层的膨胀系数存在差异，使透气砖受到剪切应力作用，导致透气砖出现横向裂缝，甚至断裂。

化学侵蚀作用

透气砖的工作层与钢渣、钢水相互接触的时间比较长，熔渣持续向透气砖中侵蚀、渗透。钢水、渣中的MnO，MgO，SiO2，FeO，Fe2O3等氧化物与透气砖中的耐火材料发生反应：12CaO+7Al2O3=12CaO·7Al2O3（1）FeO+Al2O3=FeO·Al2O3 （2）2MnO+SiO2+Al2O3=2（MnO）·SiO2·Al2O3 （3）钢水对透气砖工作层进行的熔损和剥落引起的物理蚀损，冶炼过程中钢渣和钢水对透气砖持续的渗透所产生的化学侵蚀，是透气砖损毁的最主要原因。因此，为了提高材料的抗热震冲击性能和抗渣性，需要改善透气砖的韧性和渗透性。

There are four main reasons for the damage of porous plugs : thermal stress, mechanical wear, mechanical stress, and chemical erosion.

The effect of thermal stress

In actual production, the ladle temperature is 1000℃ and the molten steel temperature reaches 1600℃. The temperature difference between the two when in contact will produce large thermal stress, which in turn causes a very large thermal shock. The ladle is in a cyclical working environment. The thermal stress generated by the frequent temperature changes of the  when they are in contact with the molten steel and the ladle is one of the reasons for the damage of the . The key factor for the thermal stress of the  is the change in temperature, and there are differences in the temperature changes of different parts of the .

The effect of mechanical wear

The scouring of the  by the vortex can be roughly divided into three situations: (1) When the  are higher than the base bricks, the main reason for the damage of the  is that the molten steel in the ladle forms a vortex that produces a huge shear effect and scouring effect on the side of the . Therefore, the scouring force is one of the reasons why the base bricks of the  are greatly damaged. In normal working environment, the  are used only once, and the part above the base bricks will be washed away after one use. (2) When the  are level with the base bricks, the base bricks play a protective role for the . The vortex formed by the molten steel first scours the base bricks, causing the shear force of the  to be reduced accordingly. (3) When the  are lower than the base bricks, cold steel is easily accumulated on the working surface during normal work. Since the viscosity of the remaining cold steel is relatively large, it has a certain obstruction effect on the blowing. Therefore, in order to meet the refining requirements, it is necessary to increase the blowing pressure. In this way, the scouring force of the air flow on the  is correspondingly increased, and the shear and impact strength is large, making it more susceptible to damage. In order to meet the requirements of the refining outside the furnace for the blowing rate and service life, the  must have good anti-scouring ability and high-temperature mechanical properties. 

Mechanical Stress

During operation, the working surface of the  at the bottom of the ladle is in direct contact with the high-temperature molten steel. Under circulating conditions, the temperature inside the ladle is constantly fluctuating. The temperature gradient between high and low temperatures in the refractory material at the bottom of the ladle occurs during use. The difference in expansion coefficients between the original and metamorphic layers of the refractory material causes shear stress on the , leading to transverse cracks and even fracture.

Chemical Attack

The working layer of the  is in contact with the slag and molten steel for a relatively long time, causing the molten slag to continuously erode and penetrate the . Oxides such as MnO, MgO, SiO2, FeO, and Fe2O3 in molten steel and slag react with the refractory materials in the breathable bricks: 12CaO+7Al2O3=12CaO·7Al2O3 (1) FeO+Al2O3=FeO·Al2O3 (2) 2MnO+SiO2+Al2O3=2(MnO)·SiO2·Al2O3 (3) Physical erosion caused by the melting and spalling of the working layer of the breathable bricks by molten steel, and chemical erosion caused by the continuous penetration of slag and molten steel into the breathable bricks during the smelting process are the main causes of damage to the breathable bricks. Therefore, in order to improve the material's resistance to thermal shock and slag, it is necessary to improve the toughness and permeability of the breathable bricks.