Analysis of forging cracks in 2Cr13 forgings:
(1) Quality issues
The quality of 2Cr13 stainless steel forgings produced by a factory is unstable, cracks often occur during the forging process, and the scrap rate is sometimes as high as 50%-60%.
(2) Defect analysis
It is understood that the forging process specifications of 2Cr13 stainless steel forgings produced by the plant are as follows:
Heating (1050-1180 ° C, holding 25-50 min) a free forging billet - pickling and blowing sand - heating (1050 - 1180 ° C) - die forging - pickling - blowing sand - heating (900-1000 ° C) - Correction - Annealing (860 ° C) - pickling - blowing sand - quenching and tempering.
In order to find out the reasons and solve the above problems, three batches of tests were conducted to investigate the effects of forging heating temperature and heating time on cracks.
In the first batch of tests, two forging temperatures and two holding times were selected, which were heated in an oil furnace and free forged on a 400 kg air hammer.
It can be seen from the above test that the higher the forging heating temperature, the longer the holding time, and the greater the tendency to crack.
It can be seen from the high-magnification structure that the temperature is 1100 min at 1180 °C, the cracks extend along the grain boundary, the grains are coarse (1-3 grades, 0 grades individually), the grain boundaries are thickened, there are oxidation points, and some grain boundaries have begun to melt, and the fractures are rough. . 1120 ° C insulation lOOmin and 1180 ° C insulation 50min and lOOmin, surface decarburization is serious.
For the factory to make the test more accurate, the second batch of tests was carried out in the electric furnace, using four different temperatures and one holding time.
According to the above two batches of tests, the forging temperature is too high and the holding time is too long, which is one of the main factors causing cracks in forgings. The heating temperature is too high, causing overheating, and even the ferrite causes the plasticity of the forging to decrease; the heating time is too long, the surface oxidative decarburization is severe, and the high temperature ferrite is prematurely formed on the surface, thereby greatly reducing the plasticity of the forging surface.
(3) Preventive measures
1) Preheating (800-900 °C at the door of the furnace, heat preservation 10-15min) - heating (10501180 °C insulation 25-50min) - free forging blank - blowing sand - preheating (800-900 ° C at the furnace door, insulation 10 -15min)—heating (1050-1150°C holding 25-50min)—die forging—annealing (740°C±20°C for 3h)—correction—annealing (860°C)—acid washing.
2) Preheating (800-900 ° C at the door of the furnace, heat preservation 10-15 min) - heating (1050-1150 ° C insulation 25-50 min) - forging - blowing sand - correction - annealing (860 ° C) - pickling - blowing sand.
The new process specification 1) is suitable for two-form forgings, the new process specification 2) suitable for one-time forming forgings. Compared with the original process specifications, it can be seen that the new process specification has the following characteristics:
1) The forging and forging temperature is lowered, that is, from 1180 ° C to 1150 ° C.
2) Increase the preheating (temperature is 800-900 ° C, heat preservation 10-15 min).
3) Cancel pickling after free forging (in the case of no annealing).
4) Cancel pickling after die forging (in the case of no annealing).
5) After the die forging, the annealing is increased to eliminate the internal stress.
According to the new process specification, combined with on-site production, the third batch of tests was done. The test proved the rationality of the new specification.
C54020-01 forgings were not free forged, one-time forged forming, a total of 128 pieces were tested, two furnace numbers were not annealed, all were sandblasted, and no cracks were found.
Tests have shown that heating temperature and heating time are appropriate factors to eliminate forging cracks. The timely annealing of parts after forging is an important factor in eliminating cracks. If the 2Cr13 forging is not annealed in time and the tissue stress is removed after forging, corrosion cracking often occurs after strong acid corrosion.