Claims
- 1. A process for hot rolling and cooling medium to high carbon steel rod in uninterrupted sequence wherein the rod issuing from rolling, is laid in spread-out rings onto a conveyor and cooled through a first, austenite effective grain growth phase, and a second austenite transformation phase, comprising the steps of:
- effectively growing the austenite grains along the length of the rod substantially throughout the first cooling phase at differing rates by forcing a gaseous cooling medium through and around the rings in a substantially continuously maintained distribution as the rings move along the conveyor to cool the rod non-uniformly whereby the austenite grains, in the rod in the areas which are more matted due to overlapping cool more slowly, and in the areas where they are less matted cool more rapidly, effectively grow at a rate which is inversely proportional to the respective cooling rates associated therewith along the rod;
- cooling the respective portions of the rod through the second cooling phase by forcing the same gaseous cooling medium through and around the rings in substantially the same continuously maintained distribution to substantially match the cooling rates of the first cooling phase whereby the respective austenite grains in the respective places along the rod cool through transformation at a rate which is substantially inversely proportional to their respective effective grain sizes, and
- maintaining the rings in substantially the same relative positions of mutual overlap and contact on the conveyor throughout the first and second cooling phases.
- 2. The process of claim 1 further characterized by:
- growing the austenite grains in the first cooling phase to a size in the range of ASTM 5 to 9 with the number of grains per unit of volume in the places where the grains are smallest being at least twice the number per unit of volume than where the grains are largest.
- 3. The process of claim 1 further characterized by:
- increasing the intensity of application of the gaseous cooling medium to the rod in the second phase substantially to compensate for the decrease in radiational cooling of the rod as the temperature of the rod decreases from rolling temperature.
- 4. The process of claim 1 further characterized by:
- applying said medium to said rings in a substantially uniform pattern across said conveyor whereby the non-uniformity of the cooling effect of said medium results substantially solely from the differences in flow paths of said medium through said rings.
- 5. The process of claim 1 further characterized by:
- applying said medium to said rod through sets of orifices along and across said conveyor spaced to provide a substantially continuous and equal application of said medium to said rod, whereby the non-uniform cooling of the rod in both cooling phases is due mainly to non-uniformity of flow paths for said medium through said rings due to their overlapped disposition.
- 6. The process of claim 1 further characterized by:
- controlling the application of the cooling medium to provide an average cooling rate which cools the rod in conformance with a curve which substantially bisects the knee of the inner curve of the continuous cooling transformation diagram of the steel in process at a grain size equal to the mean between the large and small grains resulting from the non-uniform cooling in the first cooling phase,
- whereby a structure of predominantly fine pearlite is produced having substantially less free ferrite in any part of the rod along its length than in steel rod which has been hot-rolled, cooled by water in a delivery pipe to 780.degree. C. and then after a passive, equalization of temperature period cooled rapidly by forced air in the form of spread-out rings on an open conveyor.
- 7. The process of claim 1 further characterized by:
- laying the rod on the conveyor and starting the first cooling phase at a temperature at least as high as 850.degree. C., and
- employing a cooling rate through the first cooling phase selected to bring the steel in process to the transformation temperature while a potential for effective grain growth (grain boundary reduction) still remains in the steel.
- 8. The process of claim 1 further characterized by:
- the cooling rate in said first phase selected to bring said steel to transformation temperature between about 15 seconds and 35 seconds.
- 9. The process defined in claim 1 further characterized by:
- applying a limited amount of water to the surface of the rod prior to laying said rod on said conveyor to control both the temperature and scale thereof but not to cool same below about 850.degree. C.
- 10. 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).
- 11. The apparatus defined in claim 10 further characterized by:
- said cooling conveyor including first and second conveyor sections,
- said second conveyor section being in addition to the length of 79 m, mounted adjacent to the ends of said first conveyor section and extending back toward said coiling means, and
- means for transferring said rod rings from said first to said second conveyor sections without introducing residual spring tension between said rings.
- 12. The apparatus defined in claim 10 further characterized by:
- said open conveyor arranged to move the rings alternately in the direction of rolling; and opposite to the direction of rolling.
- 13. The apparatus defined in claim 10 further characterized by:
- means for reversing the direction of travel of said rod from the rolling direction to a direction opposite thereto.
- 14. The apparatus defined in claim 11 further characterized by:
- means for collecting said rings from the end of said second section, and
- optionally operable means for collecting said rings directly from said first section.
- 15. 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.
- 16. The process defined in claim 15 further characterized by:
- (g) projecting said rings onto said collection point at a rate which is at least 25% faster axially of said conveyor than the rate of the conveyor.
- 17. The process for making steel rod defined in claim 1:
- reducing the cross-section of a billet to an intermediate size by rolling same at a temperature above about 980.degree. C., and;
- further reducing the cross-section to finished rod size and controlling the delivery temperature of the rod from the mill by cooling between roll passes prior to rolling the intermediately sized stock to finished size, but not below 850.degree. C.
- 18. The process of claim 8 further characterized by:
- regulating the average cooling rate to bring about the average start of transformation before the maximum potential for effective grain growth at temperatures approaching that of transformation has been reached.
- 19. The process of claim 17 further characterized by:
- regulating the average cooling rate to bring about the average start of transformation between about 15 to 35 seconds after coiling said rod at rolling temperature.
Parent Case Info
This application is a continuation-in-part of Ser. No. 111,122 filed Jan. 10, 1980, abandoned.
US Referenced Citations (4)
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
111122 |
Jan 1980 |
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