In this study, the effect of initial microstructure on change of mechanical properties was investigated by warm caliber rolling (WCR) of high carbon steel. Experiments were carried out with two different kinds of initial microstructures of pearlite and tempered martensite at the temperature of 500 °C. For comparison, the microstructure of austenite phase obtained from the conventional hot rolling at the temperature of 900 °C up to about 83% of the accumulative reduction in area was assumed to be a reference case. It was found that the WCR provided better mechanical properties in terms of strength and toughness compared to the conventional hot rolling based on experimental results of micro-hardness, tension, and Charpy impact tests.

http://www.sciencedirect.com/science/article/pii/S0921509311...

13. Inoue T, Yin F, Kimura Y, Tsuzaki K, Ochiai S. Delamination Effect on Impact Properties of Ultrafine-Grained Low-Carbon Steel Processed by Warm Caliber Rolling. Metallurgical and Materials Transactions A. 2010;41(2):341–355.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4599616/

The paper presents research data demonstrating the effect of warm caliber rolling on the martensite transformation temperatures, shape memory effect, and superelasticity in Ti49.2Ni50.8 (at %). The experimental values of inelastic strain in coarse-grained and microcrystalline Ti49.2Ni50.8 (at %) specimens exceed the theoretical limit of recoverable strain or maximum lattice strain for TiNi-based alloys.

https://worldwidescience.org/topicpages/w/warm caliber rolli...

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Note added at 4 hrs (2017-09-22 17:27:10 GMT)
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The industrial manufacturing process resulted in four products. The first two were obtained by caliber rolling. The third and fourth products were obtained by the combination of caliber and flat rolling processes. In order to improve the quality of the surface and the dimensional accuracy in addition to increasing the strength of the rods, further cold rolling was performed.

https://www.researchgate.net/publication/303840742_MODELLING...

Research and projects

Currently, the prospects of a combination of caliber-rolling and mirco-rolling to produce shaped micro strips are explored. A micro rolling mill fabricated by Bühler is also available at IBF.

http://www.ibf.rwth-aachen.de/en/research-development/long-p...

Ultrafine grained steel long products by Multi-Pass Warm Caliber Rolling Technology
The aim of this project is to produce submicron ultrafine grain (UFG) long steel products (ferrite-cementite microstructure) with high strength and adequate ductility for automotive and mechanical applications that can be further processed by cold forming or direct machining.
The idea consists in producing UFG bars by multi-pass warm caliber rolling in the temperature range 500-700°C, exploiting as refining mechanism the dynamic recrystallization or recovery of ferrite induced by accumulation of strain during multipass deformation.

https://ec.europa.eu/research/industrial_technologies/pdf/rf...

I've been trying to find a clear explanation of the caliber rolling process but I haven't been lucky. However, while I was searching I found some more references, which I've decided to add to my answer.

If you google "caliber rolls" you'll see that they aren't flat.