Process for the production of hardened parts of steel

Details Process for the production of hardened parts of steel Process for the production of hardened parts of steel

1999-05-17

2001-10-23

King, Roy (Department: 1742)

Metal treatment

Process of modifying or maintaining internal physical...

Heating or cooling of solid metal

C148S906000, C148S605000, C148S609000

Reexamination Certificate

active

06306230

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to improvements in a process for the production of hardened steel parts.
BACKGROUND OF THE INVENTION
The highly stressed and wear-resistant parts of ball and roller bearings, gear transmissions, etc., which are subjected to rolling fatigue must be hardened. A steel with approximately 1 wt. % of carbon, i.e., a so-called roller bearing steel (e.g., 100 Cr 6), is usually used for these parts. It is usually heated to a temperature above 1,100° C., shaped into tubes or bars, cooled, given an intermediate annealing, soft-machined, hardened, and then finish-ground.
In the production of parts of roller bearing steel (100 Cr 6), therefore, it is necessary to conduct an expensive soft annealing process between the shaping and the other operations to ensure that mechanical processing can be carried out easily and that the parts can be hardened readily. It is also known that rings of roller bearing steel can be subjected to thermo-mechanical treatments. These are processes in which shaping and a heat treatment are combined effectively with each other. These processes make it possible to harden the parts from the heat of working, so that specific material properties can be improved and/or so that the heat treatment part of the process can substitute for another, i.e. separate heat treatment. In particular, the otherwise conventional soft annealing can be omitted, which means that the amount of energy required is reduced (see, for example, the German journal Stahl und Eisen, Vol. 108, No. 12, pp. 595-603, 1988).
In these known processes, the rings are first rolled and then quenched via A
1
from the heat of working. They are then annealed (hardened and tempered) and hard-machined. In most cases, however, a soaking furnace must be placed after the working operation to achieve a higher degree of process reliability and uniformity. Quenching usually takes place in a brine or oil bath. The distortions which thus occur, however, must always be corrected by expensive hard machining.
SUMMARY OF THE INVENTION
With the foregoing in mind, it is an object of the present invention to provide an improved process for the production of hardened parts of steel which not only requires a smaller amount of energy and is therefore less expensive but also yields parts of greater dimensional accuracy, so that little or no reworking is required. This task is accomplished according to the invention by means of a process wherein the steel is an air-hardenable steel and heated to a temperature above approximately 1,100° C. The parts are then hot-worked until they reach the A
1
temperature of about 800° C. as shown on the chart. The parts are then cooled in air to about 280° C. under simultaneous thermo-mechanical sizing treatment. The parts are then cooled in air to room temperature. A stress-relief treatment is conducted at 150-250° C.; and finally the parts hard-machined if necessary.
According to another feature of the invention, a steel with the following composition (in wt. %) can be selected as a suitable air-hardening steel:
0.5-0.9% carbon (C),
0-1.0% manganese (Mn),
0-2.0% silicon (Si),
0-2.0% nickel (Ni),
0-0.7% molybdenum (Mo),
0-2.0% chromium (Cr),
0-0.3% vanadium, and
the remainder iron and the normal impurities.
It is preferred to use a steel with:
0.7% C,
0.3% Mn,
1.5% Si,
1.0% Ni, 0.17% Mo,
1.4% Cr, and
the remainder iron and the normal impurities.


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