Crack Analysis of 20SiMn Steel Casting

This paper proposes a crack analysis of 20SiMn castings. 20SiMn is a low alloy martensite grade steel. It is a steel material with high strength, good toughness, and low fatigue strength. Its weldability is also good. In the production of 20SiMn castings, casting defects such as cracks may occur. This paper will analyze the causes of the cracks in 20SiMn castings.

The first cause of the cracking of 20SiMn castings is the improper selection of pouring temperature and pouring speed during the casting process. The pouring temperature of 20SiMn is too high or too low, and the pouring speed is too fast or too slow. All of these factors will lead to the rapid cooling of the casting, thus forming thermal stress. The stress caused by the rapid cooling of the casting will cause the casting to crack.

The second cause is improper design. The size and shape of the castings are designed improperly. For example, if the design requires a large shrinkage allowance but a small core, the casting will be subjected to a large internal stress. Such an internal stress will cause the casting to crack.

The third cause of cracking of 20SiMn castings is the presence of shrinkage porosity. When the casting is solidified, the shrinkage porosity occurs due to the decrease of the volume of the liquid. If the shrinkage porosity is serious, the strength and toughness of the casting will be weakened, which will cause cracks in the casting.

The fourth cause of the cracking of 20SiMn castings is the presence of inclusions. Inclusions are particles or impurities contained in the molten steel, which will cause stress concentration on the surface of the casting during the solidification process. These stress concentrations will cause the surface of the casting to crack.

The fifth cause of the cracking of 20SiMn castings is poor casting structure. If the sand casting is rough and not dense, the shrinkage and deformation of the castings will be increased during the cooling and solidification process, thus forming considerable internal stress. Such internal stress can cause cracking on the surface of the casting.

The sixth cause of the cracking of 20SiMn castings is the improper operation of the cutting process. If the cutting process is not completed properly, the surface of the casting will be uneven, and the casting will be subjected to stress concentration. When the stress concentration becomes too high, it will cause the castings to crack.

In conclusion, the cracking of 20SiMn castings is caused by a combination of several factors, such as improper selection of pouring temperature and pouring speed, improper design, the presence of shrinkage porosity, the presence of inclusions, poor casting structure, and improper operation of the cutting process.

Crack Analysis of 20SiMn Castings

20 Si Mn steel is a commonly used medium-carbon low-alloyed steel, which is widely used in castings of machine tools, automobiles, tractors and other parts. The 20SiMn castings are prone to cracking, so it is necessary to analyse the cause of the crack.

In general, the cracks of 20SiMn castings can be divided into two categories: internal and external. Generally, crack formation is related to the structure of the steel. The wrong design or structure of the parts can cause bacterial stress concentration and sharp corner stress concentration, which can cause the parts to crack. In addition, casting liquid temperature, pouring system, cooling system, pouring position and other factors can cause stress concentration and cause cracks.

For the internal cracks of 20SiMn castings, most of the reasons are the embrittlement of the heat treatment process and the destruction of the surface of the casting caused by the initial flow process. For example, the parts have large wall thickness gap, and the tempering time is too long or the tempering temperature is too low, which will cause stress release and directly lead to crack formation.

For external cracks, they are mainly caused by hydrogen embrittlement. When 20SiMn steel is exposed to a humid environment such as high temperature, low temperature, vibration and impact, hydrogen can migrate into the castings, which can lead to cracks. Furthermore, the residual stress caused by creep in the smelting process can lead to internal cracks in the castings.

To sum up, for the cracks of 20SiMn castings, it is necessary to take corresponding measures according to the causes of the cracks. Only in this way can the 20SiMn castings be ensured with reliable quality and excellent mechanical properties.