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| Longauerová M., Fedorová M., Longauer S., Kadlec J., Bořuta J., Fujda M., Janák G., Vojtko M. |
| HETEROGENEITIES OF CHEMICAL COMPOSITON IN CAST PRODUCTS |
| Keywords: Slabs|surface segregation|structure heterogeneities|centreline noncompactibilities|round blooms|central segregation| |
| No 1 (2007), p. 17-25 |
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| Hernas A., Herian J., Wylaź P. |
| MICROSTRUCTURE AND PROPERTIES OF HOT ROLLED 42CrMo4 STEEL CHARGE AND RINGS |
Abstract
The paper presents processes which determine the quality of steel cast strands and properties of rolled products. It touches upon the technology of small-size ( ? 400 – 580 mm) rings manufacture from the 42CrMo4 steel used for the production of rolling bearings and toothed rings. The most crucial problem is connected with heterogeneity of microstructure and properties on cross section and circumference of hot rolled and heat treated rings – instable mechanical properties both in the individual product and in the whole batches. Consequences of this are:
* Difficulties with machining
* Cracking during surface hardening
* Decrease of life time of final products
The quality and properties of rolled products are conditioned by three basic technological processes, including:
* the method of steel production and its off-furnace processing,
* steel casting; in the case of continuous steel casting,
* hot plastic working and heat treatment (process parameters, deformation layout and the state of stress), which conditions the product continuity, structure homogeneity and properties.
An analysis has been performed of the microstructure of bars based on their cross sections (banded ferrite – pearlite/bainite microstructure, coarrse-grained) and distribution of hardness on the hot rolled rings’ face surface as well as their cross-section structure. Heterogeneity of the bars’ microstructure as well as considerable non-uniformity of the rings’ properties have been shown. (HBmax – HB max = ca. 60 after final heat treatment.)
As a result of investigations the modification of process technology was used as follow:
* Diameter reduce of bars
* Appropriate time and temperature of heating
* Descrease temperature of the initial and final stage of rolling
* Increase of total wrought alloy up to ca. 9 (The processing degree not be lower than ?=3
* Correction of cooling conditions during hardening of rings
After corrected technology a homogeneity of microstructure and hardness at the cross section of rings was reached.
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| Keywords: Steel rings|heterogeneity|microstructure|hardness|modification of process technology| |
| No 1 (2007), p. 101-108 |
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