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.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates to a method for manufacturing steels, and more particularly, to a method for manufacturing prime hot rolled high tensile deformed bars with a tensile strength of 500 MPa-700 MPa.[0003]2. Description of the Related Art[0004]The deformed bar is acted as the framework and the like in the construction of buildings such as industrial factories, reservoirs and dams, road bridges, and so on. Currently, the steel billet of 20MnSi is used by the steel mills to manufacture the HRB335 grade deformed bars. However, the HRB335 deformed bar has a low tensile strength, resulting in the drawbacks of such as large dead weight of the framework structure, high project cost, and long construction period in the construction of especially major projects, and thereby, has already been abandoned for use in construction by developed countries. Nowadays, many alloy elements are added into the steel billet by the steel mill...

AI Technical Summary

Benefits of technology

[0005]In view of the above-described drawbacks, it is an objective of the present invention to provide a method for manufacturing a prime hot rolled high tensile strength deformed bars with an ultimate tensile strength of 500 MPa-700 MPa by utilizing the common 20MnSi steel billet directly so as to realize the purpose of decreasing the manufacturing cost and energy consumption, enhancing the steel strength, saving steel consumption, and decreasing project cost accordingly.

[0007]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 deformed bars with a tensile strength of 500 MPa-700 MPa. By applying the rolling process under ultra-low temperature, not only the issue of the excessive cooling intensity in the following cooling processes can be avoided so that the desirable temperature of the steel workpieces to the cooling bed can be achieved, but also the energy consumption and cost can be decreased. The pre-water cooling process is added behind the rough and intermediate rolling processes to decrease the surface temperature of the steel workpieces so as to balance the temperature of the workpieces rose in the process of finish rolling resulting from the high speed of the finish rolling mill. Finally, the steel workpieces are cooled through the water cooling process; the remained heat treatment technology is applied to improve greatly the overall mechanical performance of the steel.

[0009]As a result, the method for manufacturing the high tensile strength deformed bars in accordance with the present invention provides the following advantages:(1) compared with the HRB335 grade steel in GB1499 standard, with the same 20MnSi material, the strength index of the steel of the present invention is improved by 50% to the HRB500 grade so that the manufacture of steel having a high tensile strength and good elongation is realized.(2) by applying the rolling process under ultra-low temperature, the fuel is saved by about 15%, the manufacture cost is reduced largely, and the enterprise profitability is increased accordingly.(3) in the construction of building, the consumption of steel is saved by 15˜30%, the dead weight of the steel structure is decreased largely, the resource utilization is improved, the manufacture cost is decreased, the period of construction is shortened, the consumption of energy and the pollution to the environment is reduced, so that perfect economic and social results are realized.

Problems solved by technology

However, the HRB335 deformed bar has a low tensile strength, resulting in the drawbacks of such as large dead weight of the framework structure, high project cost, and long construction period in the construction of especially major projects, and thereby, has already been abandoned for use in construction by developed countries.

However, the addition of alloy elements complicates the steel manufacture process, and thereby, increases the manufacturing cost.

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