High impact and wear resistant steel
View Patent ↗An improved steel railroad rail, and methods for producing same, having a high-carbon content in a range from more than 0.9 to 1.1 wt % is provided that has increased wear resistance and increased fracture toughness over conventional steel rail. The high-carbon rail is characterized as having a pearlitic phase of an eutectoid nature. The average ultimate tensile strength is in a range from 204,860 to 222,120 psi, with a minimum of 174,000 psi. The average yield strength is in a range from 132,320 to 148,450 psi, with the minimum of 120,000 psi. The average percent elongation is in a range from 10.50 to 11.14, with a minimum of 10.00. The Brinell hardness on the surface at any position of the head top and upper gage corners of the rail is in a range from 390 to 440 BHN. The hardness 19 mm below the top surface is in a range from 360 to 435 BHN and 19 mm below the surface at the upper gage corners is in a range from 360 to 410 BHN. The characteristics of the steel rail produced in accordance with the present invention is a substantial improvement as compared with rail used today. The production of a fully pearlitic steel rail having a carbon content from more than 0.9 to 1.1 wt % is remarkable and unexpected. A steel rail of this type having a hardness in a range from 400 to 440 BHN and a combination of yield strength, ultimate tensile strength, elongation and surface and in-depth Brinell hardness goes beyond all expectations and results in a superior and commercially important steal rail.
1. A method for manufacturing a fully pearlitic steel rail of high toughness and high wear resistance, consisting essentially of:
forging a steel billet comprising the elements in a range from more than 0.9 to 1 .1 wt % of C, 0.26 to 0.80 by wt % of Si, 0.8 to 1.2 wt % of Mn, less than or equal to 0.35 wt % of Cr, the balance of iron and residual elements;
hot rolling the billet to a rolling finishing temperature of about 1000° C. and thereby forming a rail; and
cooling the rail at a selected cooling rate in a range from 3.3° C./sec to 4.3° C./sec. beginning substantially at said rolling finishing temperature and continuing at least until pearlite transformation-completion temperature.
2. The method according to claim 1 , wherein the steel comprises a maximum of each of the elements 0.45 wt % of Cu, 0.25 wt % of Ni, 0.05 wt % of Mo, 0.025 wt % of S, and 0.01 wt % of Al.
3. The method according to claim 1 , wherein the steel further comprises at least one element selected from the group consisting of the elements in a range from 0.005 to 0.105 wt % of Ti and 0.0 to 0.20 wt % of V.
4. The method according to claim 1 , wherein cooling the rail is performed by utilizing a line slack quench (LSQ) apparatus which uses air at a given pressure in an air-quench operation.
5. A method of manufacturing a steel rail consisting essentially of:
producing a rail form from a composition primarily of iron and minor portions of selected and residual materials and including a known carbon content within the range of more than 0.9 and not greater than 1.1%/wt, said producing of the rail form including hot rolling of the material by retaining the temperature throughout substantially above the temperature of transformation of the composition to pearlite and whereby the hot rolling finishing temperature is about 1000° C.;
immediately and without delay following completion of hot rolling said rail, applying a determined and controlled accelerated cooling rate to the formed rail;
said selected cooling rate selected from a range of cooling rates between about 3.3° C./second and about 4.3° C./per second;
and as selected, said cooling rate maintained throughout the transformation process.
6. A method consisting essentially of:
producing a rail form from a composition primarily of iron and minor portions of selected and residual materials and including a known carbon content within the range of more than 0.9 and not greater than 1.1%/wt, and further including a known titanium content within the range of 0.005 and 0.105%/wt;
said producing of the rail form including hot rolling of the composition while retaining the temperature throughout substantially above the temperature of transformation of the composition to pearlite as necessary to ensure the absence of transformation of any portion of said rail form prior to heat treat and finishing said hot rolling at a temperature of about 1000° C.; and
heat treating said rail form by applying a determined and controlled cooling rate between about 3.3° C./second and about 4.3° C./second, said cooling rate applied to said rail form from said temperature substantially immediately and without delay following completion of hot rolling said rail form, and continuing said cooling rate until completion of the transformation of the complete rail form to pearlite;
said method producing a steel rail containing no ferrite and having a minimum of 174,000 psi tensile strength, a minimum of 120,000 psi yield strength, and a minimum of 10.00% elongation with a hardness at the surface of the rail top and upper gauge corners of 390-440 BHN and at 19 mm below the top surface, a hardness of 360-435 BHN and at 19 mm below the upper gauge corner surface having a hardness in a range of 360-410 BHN.