Isothermal normalizing process for medium-carbon bearing steel ring forgings

By employing a segmented heating, forced air cooling, and double heat preservation isothermal normalizing process, the challenges of microstructure uniformity and control in traditional isothermal normalizing processes have been solved. This process has enabled high dimensional stability and fatigue life for large bearing steel ring forgings, meeting the high requirements of main bearing rings for large tunnel boring machines.

CN122303543APending Publication Date: 2026-06-30CHINA RAILWAY CONSTR HEAVY IND
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Patent Information

Authority / Receiving Office
CN · China
Patent Type
Applications(China)
Current Assignee / Owner
CHINA RAILWAY CONSTR HEAVY IND
Filing Date
2026-04-17
Publication Date
2026-06-30

AI Technical Summary

Technical Problem

Traditional isothermal normalizing processes are difficult to control the uniformity of material microstructure and hardness in the production of large bearing steel ring forgings, and the operation and control costs during the cooling stage are high, which cannot meet the high requirements of main bearing rings of large tunnel boring machines.

Method used

The isothermal normalizing process employs segmented heating, forced air cooling, and two heat preservation stages. Segmented heating reduces the temperature difference, forced air cooling controls the cooling rate, and two heat preservation stages ensure that the supercooled austenite is completely transformed into pearlite, thus achieving uniform microstructure.

Benefits of technology

It effectively reduces ferrite precipitation, controls the uniformity of the microstructure bands, lowers production costs, improves dimensional stability and fatigue life, and meets the high requirements of the main bearing rings of large tunnel boring machines.

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Abstract

This invention belongs to the technical field of ring forging rolling, specifically providing an isothermal normalizing process for medium-carbon bearing steel ring forgings, including: heating → first holding → cooling → heating up → second holding → air cooling to room temperature. By segmenting the heating of the bearing steel ring forging, the temperature difference between the surface and core of the large ring forging is reduced during heating, avoiding excessive thermal stress in the microstructure; the first holding eliminates forging defects generated during forging; cooling reduces ferrite precipitation, obtaining as much pearlite as possible, achieving control of the banded microstructure; heating the cooled bearing steel ring forging controls the surface and core temperatures at the "nose" of the C-curve in the isothermal transformation curve; and the second holding of the heated bearing steel ring forging allows the supercooled austenite to completely transform at this temperature, resulting in a finer pearlitic microstructure.
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