Heat treatment and durability of the cutting dies, namely the final machining operation before grinding the cold cutting dies, is hardening, at which even slight deformation and distortion are unacceptable.
Step hardening of alloyed steels of the type HVG does not ensure the preservation of cross-center and other sizes of complex dies. The use of the most complex forms of X12M type steels that are quenched in air or isothermally at 450 ° C for matrices also does not provide constant sizes.
The reason for this is high carbide heterogeneity, in particular carbide line, in the direction of rolling and forging, manifested due to the high content of carbon and chromium. The difference in the thermal expansion coefficients of carbide inclusions and the base metal also leads to residual stresses .
Carbid stitchiness can be eliminated only by forging according to the mode used for high-speed steels. However, such forging is complex and not all plants can carry it out.
Were made and investigated six cut-through matrices of steel 7HG2VM (EP472), the chemical composition of which corresponded to the Chelyabinsk State Technical Institute TsNIICHM 966-63 . The peculiarity of this steel is a low score of carbide heterogeneity and the ability to quench in air to HRC 60.
Matrix forged from bars with a diameter of 60 mm. The blanks were loaded into the furnace at 1100-1150 ° С, then forged at 1150-900 ° С and annealed at 780 ° С for 1 h in bags with backfilling. After annealing, the matrix was cooled at a rate of 30 deg / h to 650 ° C, and then with a furnace in the bag, after which their hardness was HB 207-241.
The matrices were quenched in calm air from 860 ° С. To protect against the decarburization of the matrix, they were placed with a mirror down on a baking sheet with a spent carburizer. After tempering at 150-160 ° C, the matrix had a hardness of HRC 60.
Hardening did not cause changes in the size of any of the matrices studied.
The fabricated dies were transferred for operation to cut parts from solid metals. The dies, which had tested 12,000–15,000 blows, did not have chipping on the cutting edge, while the same dies under the same operating conditions, but from steel H12F1, had to be ground further.
According to available data, the durability of 7HG2BM steel dies, processed according to the specified mode, is approximately 3 times higher than the durability of dies from X12M steel.
Quenching from 860 ° С in air from steel 7ХГ2ВМ provides minimal deformation and significantly increases tool life.
I. S. KAMENICHNY, S. M. FEDOSEEV
ISSN 0026-0819. “Metallurgy and heat treatment of metals”, № 2. 1968
1. Gudremon E. Special steel. M., Metallurgizdat, 1960.
2. Yu.A. Geller. “Vestnik Mashinostroyenia”, 1963, No. 7.
This article was taken from this resource.