The Control Of Crack Healing And Carbide Precipitation During Hot Forging Of Austeniticstainless Steel

The main failure ways of large forging are internal cracks and corrosion.For large size of the forging,internal crack defect is easy appear.If the defect cannot be eliminated at the first pass of forging,it will expand during the subsequent forging process and will seriously affect the performance and service life of the forging.For large thick forgings that have eliminated defect,precipitation will exist if the cooling rate is too slow,leading to inter-granular corrosion.Therefore,it is necessary to research the internal cracks healing and intergranular corrosion prevention.In this paper,micro-structure analysis and tensile test are used to study the healing degree of internal cracks under different forging processes.And the inter-granular corrosion test and bending test are used to study the effect of cooling rate on precipitation and the inter-granular corrosion sensitivity.The results are as follows:The crack can't be healed at 900?because of the atomic activity is low and the sum of the driving force provided by the temperature and the internal driving force cannot satisfy the driving force that required for the healing of crack.At 1000?when the deformation reaches 50%,a large number of atoms are activated,and crack interface is mostly achieved bonding.When the temperature is higher than 1100?and deformation is more than 40%,atomic can diffuse at high speed and the crack can be completely healed.Compared with sample without preset crack,the strength of sample with preset crack quickly recovers to the matrix value as the deformation increases.The elongation of sample with preset crack is hard to recover at low temperature,but the elongation and the strength will reach to matrix value when the temperature is higher than 1100?and deformation is more than 40%.A small amount of M₂₃C₆ is precipitated of non-aging samples when the thickness is up to 560mm?cooling rate is 0.042?/s?.For aging samples,the precipitation also existed when the thickness is 360mm?cooling rate is 0.074?/s?.For the non-ageing sample,when the thickness reaches 660mm?cooling rate is0.032?/s?for solution treatment,the bending surface begins to crack.And for the ageing sample,the bending surface begins to crack when the thickness is 360mm?cooling rate is 0.074?/s?for solution treatment.When the thickness is 660mm for solution treatment?cooling rate is 0.032?/s?,the surface of the bending sample has serious crack defects.Therefore,it is necessary to control the cooling speed of the forging to be greater than 0.074?/s to prevent precipitation.