Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Patent
1997-11-10
1999-09-28
Yee, Deborah
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
148600, 148593, 148594, 72200, 72201, 72226, C12D 806, C12D 810
Patent
active
059581581
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for manufacturing hot-worked elongated products, particularly bars or pipes, from high-alloy or hypereutectoid steel.
BACKGROUND
High-alloy or hypereutectoid steels, especially anti-friction bearing steels such as 100Cr6, form grain boundary carbides and pearlitic microstructural components when cooled from high temperatures (1100 to 1250.degree. C.). These formations impede mechanical workability and hardenability as well as chipless deformation. A spheroidal cementite microstructure suitable for further processing can be achieved only after long annealing processes (spheroidal cementite annealing) of 16 hours or more. Much thought has been given to the question of how to shorten the duration of this soft annealing or whether the annealing can be replace altogether.
F. Mladen and E. Hornbogen studied the influence of thermomechanical processing on the mechanical properties of 100Cr6 steel (Archiv Eisenhuettenwesen 49 (1978) No. 2, pp. 449 to 453). Austenitizing was carried out above the temperature at which Fe.sub.3 C completely dissolves which, given a 0.99 C w/o, is somewhat less than 1100.degree. C. Hot rolling began at 1100.degree. C. with simultaneous cooling to 720.degree. C. Cooling from 720.degree. C. to ambient temperature was accomplished by water quenching. The details of the deformation sequence are not discussed in the article. The thermomechanically treated microstructure displayed such a finely dispersed distribution of carbides that the resolution limits of the optical microscope were reached. The reason for this improved distribution was the increase in dislocation density and the subgrain boundaries created by dislocations, which resulted in new nucleation sites for the carbides.
A process for producing cylindrical rolled bodies from steel 0.7 to 1.2 with a carbon w/o is known from DE PS 2361330. In this process, steel wire that has been hot-rolled at 1000.degree. C. is rapidly cooled to a temperature that corresponds to its lower pearlite range. The steel wire is then isothermally transformed and brought to a hardness of 50 HRC by cold drawing without intermediate annealing. The rapid cooling of the wire and its subsequent isothermal transformation results in a microstructure of fine-lamellar pearlite. This enables the wire to be drawn, after being descaled and phosphatized, without any intervening annealing.
SUMMARY OF THE INVENTION
The object of the present invention is to describe an especially economical process for producing hot-worked elongated products, especially bars or tubes, from high-alloy steel or hypereutectoid steel, especially anti-friction bearing steel, in which a microstructure is produced that is extremely well suited, without prior soft annealing, such as to spheroidal cementite annealing, for further chipless processing and final heat treatment. A further object is to describe a process for producing a microstructure that is also suitable, without prior soft annealing, for further metal-cutting processing with a subsequent final heat treatment.
The coordinated process steps of the invention make it possible to produce the desired microstructure, whereby, in the case of the anti-friction bearing steel, a brinell hardness less than or equal to 280 HB 30, preferably less than 250 HB30, is achieved. This microstructure also makes it possible to feed hot-worked tubes directly to a processing unit, without soft annealing. The manufacturing process of the present invention is especially economical, because it omits soft annealing and the transport and work steps associated therewith. The hot-worked elongated products according to the invention can be processed by cold drawing, cold pilger rolling, cold rolling or cross rolling.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings,
FIG. 1 is a structure after a prior art procedure including spheroidal cementite annealing.
FIG. 2 is a structure after the procedure according to the invention without an annealing step.
DETAILED DESCRIPTION OF THE PREFERRED EMB
REFERENCES:
patent: 5252153 (1993-10-01), Ochi et al.
patent: 5458649 (1995-10-01), Tsukamoto et al.
Kron Heinz
Kutzenberger Karlheinz
Manig Gunther
Zouhar Gustav
Mannesmann Aktiengesellschaft
Yee Deborah
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