Steel rod rolling process, product and apparatus

Apparatus for hot rolling medium to high carbon steel rod and cooling same in direct sequence comprising:

• (a) means for rolling said rod at a temperature substantially above A.sub.3 at a rod delivery rate in excess of 76 m/s;
• (b) a cooling conveyor at least 79 m in length equiped for the free passage of a gaseous cooling medium therethrough;
• (c) means positioned directly adjacent to the delivery point of said mill for coiling the rod into rings downstream of said mill while the temperature of said rod is still above 850.degree. C. and for projecting them horizontally onto said conveyor into spread out ring form;
• (d) means extending continuously along said conveyor starting immediately downstream of the point where said rings land on said conveyor for cooling said rod on said conveyor down to A.sub.3 by forcing a gaseous cooling medium through said rings in a substantially continuously maintained distribution applied to all parts of said rings to cool each point along said rod at a given rate depending upon its condition of overlap with adjacent rings so as to cool said rod non-uniformly from place-to-place along the length thereof throughout a first phase effectively to grow the austenite grains at non-uniform rates due to said non-uniform cooling;
• and
• (e) means for thereafter cooling said rod on said conveyor throughout a second, transformation, phase in substantially the same non-uniform manner at substantially the same non-uniform cooling rates as to the respective places along the rod as in the first phase, and at an average rate substantially to transform said steel at the knee of the inner curve of the continuous cooling diagram of the particular grade of steel in process at the average grain size resulting from (d).

A process for rolling and cooling medium to high carbon steel rod comprising the steps of:

• (a) rolling said rod at a temperature above 850.degree. C. at a delivery rate in excess of 76 m/s;
• (b) substantially directly upon issuance of the rod from rolling entering the rod into a laying head and forming said rod into rings;
• (c) projecting said rings onto a collection point on an open cooling conveyor and conveying the rings away from the collection point in the form of spaced overlapping rings;
• (d) while said rings are moving away from said collection point and immediately downstream thereof forcing a gaseous coolant through said rings to cool various parts along the length of said rod at differing rates and, therefore, non-uniformly, which differing rates for any part of said rod are maintained along said conveyor throughout a first cooling phase whereby the austenite grains effectively grow proportionally non-uniformly;
• (e) thereafter cooling said rings non-uniformly and continously through a second cooling phase in which the austenite transforms while maintaining a non-uniformity of cooling which is substantially inversely proportional in all parts along the length of the rod to the various austenite effective grain sizes along the length of the rod as developed by the non-uniform cooling during the first phase such that each point along the rod experiences approximately the same cooling rate through both the first and second cooling phases;
• and
• (f) regulating the average intensity of the cooling during the second phase to bisect the knee of the inner curve of the continuous cooling diagram of the particular steel in process for the average grain size thereof.