Method for hot rolling metal strip with composite metal rolls

Abstract

The object of the invention is to improve the performance of the rolls of roughing and finishing stands of a hot strip train or mill and in particular to retard as far as possible the banding phenomenon, namely the phenomenon of the incrusting of hard oxides or scale formed at the convenience rolling temperatures. For this purpose, the roll is made, at least in the working region thereof, from a chrome steel in which the ratio between the respective contents of chromium and carbon is between 7 and 12 and in which the content of equivalent carbon is between 1.5 and 1.7%. This content of equivalent carbon is calculated as the sum of the content of carbon and the content of chromium, the latter being given a coefficient 0.05.

Having now described our invention what we claim as new and desire to secure by Letters Patent is: .[.1. A mill comprising a stand including rolls operating under hot conditions, said rolls having an improved resistance to banding and each comprising a metal core and a radially outer cast chrome steel cylindrical working region, said cast chrome steel containing between 0.9 and 1.3% of carbon and between 6 and 15% of chromium, the ratio between respective contents of chromium and carbon being between 7 and 12 and the content of equivalent carbon being between 1.5 and 1.7%, said content of equivalent carbon being calculated as the sum of the content of carbon and the content of chromium with the content of chromium being given a coefficient of 0.05, said chrome steel excluding boron and tungsten apart from any traces of boron and tungsten as 
     
        impurities..]. 2. A method for hot rolling hot metal strip in a mill comprising a stand including rolls, said method comprising hot rolling the metal strip with composite metal rolls each of which rolls comprises a metal core and a radially outer cast chrome steel cylindrical working region, said cast chrome steel comprises between 0.9 and 1.3% of carbon and between 6 and 15% of chromium and wherein the ratio between respective contents of chromium and carbon is between 7 and 12 and the content of equivalent carbon is between 1.5 and 1.7%, said content of equivalent carbon being calculated as the sum of the content of carbon and the content of chromium with the content of chromium being given a coefficient of 0.05, said chrome steel excluding boron and tungsten apart from any 
     
     
        traces of boron and tungsten as impurities. 3. A method for hot rolling hot metal strip in a mill comprising a stand including rolls, said method comprising hot rolling the metal strip with composite metal rolls each of which rolls comprises a metal core and a radially outer cast chrome steel cylindrical working region, said cast chrome steel comprises between 0.9 and 1.3% of carbon and between 6 and 15% of chromium and wherein the ratio between respective contents of chromium and carbon is between 7 and 12 and the content of equivalent carbon is between 1.5 and 1.7%, said equivalent carbon being calculated as the sum of the content of carbon and the content of chromium with the content of chromium being given a coefficient 
     
     
        of 0.05. .Iadd.4.  The method according to claim 1, wherein said strip is rolled with rolls of a roughing or finishing stand of a hot strip mill. .Iaddend. .Iadd.5. The method according to claim 2, wherein said strip is rolled with rolls of a roughing or finishing stand of a hot strip mill. .Iaddend. .Iadd.6. The method according to claim 1, wherein said strip is rolled with bimetallic rolls which lack a partition wall between metallic layers thereof. .Iaddend. .Iadd.7. The method according to claim 2, wherein said strip is rolled with bimetallic rolls which lack a partition wall between metallic layers thereof. .Iaddend. .Iadd.8. The method according to claim 1, wherein said strip is rolled with rolls which have 
     
     
        been manufactured by centrifugal casting. .Iaddend. .Iadd.9.  The method according to claim 2, wherein said strip is rolled with rolls which have been manufactured by centrifugal casting. .Iaddend. .Iadd.10. The method according to claim 1, wherein said strip is rolled with rolls having a core of nodular iron. .Iaddend. .Iadd.11. The method according to claim 2, wherein said strip is rolled with rolls having a core of nodular iron. .Iaddend.