Method for manufacturing prime hot rolled high tensile strength deformed bars

Abstract

The present invention discloses a method for manufacturing high tensile strength deformed bars with an ultimate tensile strength of 500 MPa-700 MPa, comprising the steps of: (a) rolling under heavy reduction rate the common 20MnSi steel billet with an initial rolling temperature of 880˜950° C. through the rough and intermediate rolling mills having an maximum lengthening coefficient μ of 1.449; then passing the rolling workpieces through the pre-water cooling process to decrease the temperature of the workpieces to the range of 850˜950° C.; (b) rolling the workpieces through the finish rolling mill having a main motor power of 1350 KW; then cooling rapidly the surface of the workpieces through the water cooling process having a number of cooling water segments of 1˜5 and a water pressure of 0.8˜1.2 MPa so as to control the surface temperature of the workpieces to the cooling bed within the range of 550˜650° C.; (c) cooling the workpieces through the air cooling bed to cool the core portion of the workpieces; then tempering the workpieces to obtain the finished steel. In accordance with the method of the present invention, the tissue of steel is improved by rolling the common 20MnSi steel billet under heavy reduction rate to manufacture directly the high tensile strength deformed bars with a high tensile strength of 500 MPa-700 MPa so that the manufacturing cost and energy consumption are reduced and the tensile strength of steel is improved, and thereby, the construction cost is decreased.

1 . A method for manufacturing high tensile strength deformed bars with an ultimate tensile strength of at least about 500 MPa-700 MPa, comprising the steps of:
 (a) rolling under heavy reduction rate the common 20MnSi steel billet with an initial rolling temperature of 880˜950° C. through the rough and intermediate rolling mills having an maximum lengthening coefficient μ of 1.449; then passing the rolling workpieces through the pre-water cooling process to decrease the temperature of the workpieces to the range of 850˜950° C.;   (b) rolling the workpieces through the finish rolling mill having a main motor power of 1350 KW; then cooling rapidly the surface of the workpieces through the water cooling process having a number of cooling water segments of 1˜5 and a water pressure of 0.8˜1.2 MPa so as to control the surface temperature of the workpieces to the cooling bed within the range of 550˜650° C.;   (c) cooling the workpieces through the air cooling bed to cool the core portion of the workpieces; then tempering the workpieces to obtain the finished steel.   
     
     
         2 . The method of  claim 1 , wherein the number of pre-water cooling segments of said step (a) is in the range of 1˜3, and the water pressure is normal. 
     
     
         3 . The method of  claim 1 , wherein the rolling speed of said rolling mills is in the range of 4˜15 m/s.