Core Tip: How to deal with cracks in forgings during the forging process? Shanxi Forging Factory needs to analyze the reasons for this situation. (1) Cracks in forgings caused by defects in steel ingots are mostly caused by defects in steel ingots
How to deal with cracks in forgings during the forging process? Shanxi Forging Factory needs to analyze the reasons for this situation.
(1) Most defects in steel ingots may cause cracks in forgings during the forging process. This is because the crystallization temperature range of 6-ton steel ingots is narrow and the linear shrinkage coefficient is large. Condensation and insufficient condensation, large temperature difference between internal and external, high axial tensile stress, cracking along dendritic cracks, forming intergranular cracks on the axis of the steel ingot, and further expanding into cracks in the main shaft forging during the forging process.
(2) The sulfur in forging cracks caused by the precipitation of harmful impurities along grain boundaries in steel usually precipitates in the form of FeS along grain boundaries. Its melting point is only 982 ℃. At a forging temperature of 1200 ℃, FeS on the grain boundaries will melt. And wrap the grains in the form of liquid film, breaking the bond between grains to produce thermal brittleness, and slight forgings may rupture.
(3) The mechanical properties of forging cracks caused by heterogeneous phases in steel are usually significantly different from those of the metal matrix. Therefore, during the deformation flow, additional stress will be induced, and the plasticity of the entire process will decrease. When the bonding force between the heterogeneous phase and the matrix is exceeded, separation occurs and pores are formed. For example, oxides, nitrides, carbides, borides, sulfides, silicates, etc. in steel. Are these stages dense. Chain like distribution, especially those with weak bonding strength along grain boundaries, will rupture in high-temperature forgings.
The countermeasures of Shanxi Forging Factory are:
1) Limit the amount of aluminum added to steel, remove nitrogen from the steel or use titanium addition method to suppress the precipitation of AlN;
2) Shanxi Forging Factory adopts hot feed steel ingots and undercooled phase transformation treatment process;
3) Raise the hot delivery temperature (>900 ℃) and directly heat the forging;
4) Perform sufficient homogeneous annealing before forging to facilitate the diffusion of precipitated phases at grain boundaries.
The above is the solution for cracking in forgings produced by Shanxi Forging Factory