Straightening method for reducing residual stress of American-standard 115RE low-alloy high-strength heat-treated steel rail

Abstract

The invention discloses a straightening method for reducing residual stress of an American-standard 115RE low-alloy high-strength heat-treated steel rail, which comprises the following steps: heating a steel billet in a heating furnace for 3.5-4 hours at the heating temperature of more than or equal to 1200 DEG C, rolling for 13 passes by a universal rolling mill, enabling the rolling section size of the steel billet to meet the section size requirement of the American-standard 115RE steel rail, and enabling the final rolling temperature of the steel rail to be 910-930 DEG C; the steel rail enters an online heat treatment production line at the temperature of 760-810 DEG C, the steel rail is basically kept straight when being discharged from the heat treatment production line, and a guarantee is provided for subsequent light-pressure straightening; the steel rail enters a straightening machine to be subjected to pressure straightening, and the straightening pressure is that the rolling reduction of a 2 # straightening roll is 20-24 mm, the rolling reduction of a 4 # straightening roll is 10-14 mm, the rolling reduction of a 6 # straightening roll is 5-9 mm, and the rolling reduction of an 8 # straightening roll is 1-5 mm. The invention aims to realize stress release by combining heat treatment and straightening processes and optimizing temperature and straightening pressure parameters.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rail manufacturing, and particularly relates to a straightening method for reducing residual stress of AAR 115RE low-alloy high-strength heat-treated rails. BACKGROUND

[0002] Residual stress is generated in rails due to temperature gradient and plastic deformation during rolling, heat treatment, straightening and use. Residual stress can reduce the fatigue life of rails, cause deformation and even breakage, and thus threatens the safety of railway transportation. AAR 115RE low-alloy high-strength heat-treated rails are widely used in heavy-load railway construction due to their high strength and good toughness. However, the residual stress generated in the rails after heat treatment can cause deformation, fatigue and even breakage. Traditional straightening methods such as mechanical straightening, heat straightening and vibration straightening have problems such as incomplete stress relief, low efficiency or influence on material properties. SUMMARY

[0003] The purpose of the present application is to provide a straightening method for reducing residual stress of AAR 115RE low-alloy high-strength heat-treated rails, which combines heat treatment and straightening processes and realizes stress release by optimizing temperature and straightening pressure parameters.

[0004] To solve the above technical problems, the present application adopts the following technical scheme:

[0005] The present application provides a straightening method for reducing residual stress of AAR 115RE low-alloy high-strength heat-treated rails, which comprises the following steps:

[0006] The billet is heated in a heating furnace for 3.5-4 hours at a temperature of not less than 1200 DEG C, and is rolled by a universal rolling mill for 13 passes. The rolling section size of the billet meets the requirements of AAR 115RE rail section size, and the final rolling temperature of the rail is 910-930 DEG C.

[0007] The rail is put into an online heat treatment production line at a temperature of 760-810 DEG C, and the rail head and rail bottom are cooled by air blowing. The cooling speed of the rail head is 2.6-3.1 DEG C / s, and the rail head is cooled to a temperature of 500-510 DEG C. The cooling speed of the rail bottom is 2.1-2.6 DEG C / s, and the rail bottom is cooled to a temperature of 550-560 DEG C. Then, the rail is naturally air-cooled to room temperature. The rail is basically straight after being taken out of the heat treatment line, which provides a guarantee for subsequent light pressure straightening.

[0008] The rail is put into a straightening machine for pressure straightening. The roll gap of the 2# straightening roll is 20-24 mm, the roll gap of the 4# straightening roll is 10-14 mm, the roll gap of the 6# straightening roll is 5-9 mm, and the roll gap of the 8# straightening roll is 1-5 mm.

[0009] Further, the residual stress of the rail is detected. The residual stress of the rail head is not more than 150 MPa, the residual stress of the rail waist is not more than 50 MPa, and the residual stress of the rail bottom is not more than 150 MPa.

[0010] Further, the billet is heated in a heating furnace for 3.8 hours at a heating temperature of 1280 DEG C, and is rolled by a universal rolling mill for 13 passes, the rolling section size of the billet meets the section size requirement of the American standard 115RE rail, and the rail finishing rolling temperature is 922 DEG C.

[0011] Further, the rail enters an online heat treatment production line at 780 DEG C, air is sprayed to cool the rail head and the rail bottom, the cooling speed of the rail head is 2.8 DEG C / s, and the rail head is cooled to 505 DEG C, the cooling speed of the rail bottom is 2.2 DEG C / s, and the rail bottom is cooled to 553 DEG C, and then is naturally air-cooled to room temperature.

[0012] Further, the rail enters a straightening machine to be pressure straightened, the straightening pressure is 22mm for the 2# straightening roller, 12mm for the 4# straightening roller, 6mm for the 6# straightening roller, and 2mm for the 8# straightening roller.

[0013] Further, the straightness of the rail after straightening meets the requirement.

[0014] Further, the residual stress of the rail is detected, the residual stress of the rail head is 122 MPa, the residual stress of the rail waist is 45 MPa, and the residual stress of the rail bottom is 136 MPa.

[0015] Compared with the prior art, the beneficial technical effects of the present application are:

[0016] After the method of the present application, the residual stress of the rail is detected, and the American standard 115RE low-alloy high-strength heat-treated rail meets the requirements that the residual stress of the rail head is less than or equal to 150 MPa, the residual stress of the rail waist is less than or equal to 50 MPa, and the residual stress of the rail bottom is less than or equal to 150 MPa. DETAILED DESCRIPTION

[0017] The present application will be further described in detail below in combination with specific examples, so as to make the present application more clearly understood.

[0018] Example 1:

[0019] 1. The billet is heated in a heating furnace for 3.8 hours at a heating temperature of 1280 DEG C, and is rolled by a universal rolling mill for 13 passes, the rolling section size of the billet meets the section size requirement of the American standard 115RE rail, and the rail finishing rolling temperature is 922 DEG C.

[0020] 2. The rail enters an online heat treatment production line at 780 DEG C, air is sprayed to cool the rail head and the rail bottom, the cooling speed of the rail head is 2.8 DEG C / s, and the rail head is cooled to 505 DEG C, the cooling speed of the rail bottom is 2.2 DEG C / s, and the rail bottom is cooled to 553 DEG C. Subsequently, the rail is naturally air-cooled to room temperature, and the rail basically guarantees straightness after leaving the heat treatment line, thereby providing guarantee for subsequent light pressure straightening.

[0021] 3. The steel rail enters the straightener for pressure straightening, the straightening pressure is 22mm for the 2# straightening roll, 12mm for the 4# straightening roll, 6mm for the 6# straightening roll, and 2mm for the 8# straightening roll. The straightness of the straightened steel rail meets the requirements.

[0022] 4. The residual stress of the steel rail is detected, the residual stress of the rail head is 122MPa, the residual stress of the rail waist is 45MPa, and the residual stress of the rail bottom is 136MPa.

[0023] Example 2:

[0024] 1. The billet is heated in the heating furnace for 3.8 hours at a temperature of 1276℃, and is rolled by the universal mill for 13 passes. The rolled section size of the billet meets the requirements of the American standard 115RE steel rail section size, and the finishing rolling temperature of the steel rail is 918℃.

[0025] 2. The steel rail enters the online heat treatment production line at 792℃, and the rail head and the rail bottom are cooled by air blowing. The cooling speed of the rail head is 2.9℃ / s, and the cooling temperature is 506℃. The cooling speed of the rail bottom is 1.8℃ / s, and the cooling temperature is 552℃. Then, the steel rail is naturally air-cooled to room temperature, and the steel rail exists upward bending after leaving the heat treatment line, which needs to increase the straightening amount for subsequent pressure straightening.

[0026] 3. The steel rail enters the straightener for pressure straightening, the straightening pressure is 26mm for the 2# straightening roll, 16mm for the 4# straightening roll, 11mm for the 6# straightening roll, and 6mm for the 8# straightening roll. The straightness of the straightened steel rail meets the requirements.

[0027] 4. The residual stress of the steel rail is detected, the residual stress of the rail head is 189MPa, the residual stress of the rail waist is 96MPa, and the residual stress of the rail bottom is 216MPa.

[0028] Example 3:

[0029] 1. The billet is heated in the heating furnace for 3.8 hours at a temperature of 1276℃, and is rolled by the universal mill for 13 passes. The rolled section size of the billet meets the requirements of the American standard 115RE steel rail section size, and the finishing rolling temperature of the steel rail is 918℃.

[0030] 2. The steel rail enters the online heat treatment production line at 792℃, and the rail head and the rail bottom are cooled by air blowing. The cooling speed of the rail head is 2.9℃ / s, and the cooling temperature is 506℃. The cooling speed of the rail bottom is 1.8℃ / s, and the cooling temperature is 552℃. Then, the steel rail is naturally air-cooled to room temperature, and the steel rail exists upward bending after leaving the heat treatment line.

[0031] 3. The steel rail enters the straightener for pressure straightening, the straightening pressure is 22mm, the straightening pressure of the 4# straightening roll is 13mm, the straightening pressure of the 6# straightening roll is 8mm, and the straightening pressure of the 8# straightening roll is 2mm. The straightness of the steel rail does not meet the standard requirements.

[0032] 4. The residual stress of the steel rail is detected, the residual stress of the rail head is 135MPa, the residual stress of the rail waist is 47MPa, and the residual stress of the rail bottom is 142MPa.

[0033] Comparing Example 1 and Example 2, the straightness of the steel rail after the online heat treatment and straightening process meets the standard technical requirements, but the residual stress of Example 2 is higher than that of Example 1. Comparing Example 2 and Example 3, the straightness of the steel rail after the online heat treatment and straightening process meets the standard requirements, but the residual stress is too high, the straightness of Example 3 does not meet the standard requirements, and the residual stress meets the requirements. Comprehensive evaluation, the straightness and residual stress of the steel rail produced according to the control method of the present application are optimal.

[0034] The above-described embodiments are only descriptions of the preferred modes of the present application and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method of reducing residual stresses in a straightening of ASTM 115RE low alloy high strength heat treated rails, characterized in that: Comprise: The billet is heated in a heating furnace for 3.5-4 hours, the heating temperature is ≥1200℃, and the billet is rolled by a universal rolling mill for 13 passes, the rolling section size of the billet meets the section size requirement of the 115RE steel rail according to the American standard, and the final rolling temperature of the steel rail is 910-930℃; The steel rail enters an online heat treatment production line at 760-810℃, air is sprayed to cool the rail head and the rail bottom, the cooling speed of the rail head is 2.6-3.1℃ / s, and the rail head is cooled to 500-510℃, the cooling speed of the rail bottom is 2.1-2.6℃ / s, and the rail bottom is cooled to 550-560℃, and then the steel rail is naturally air-cooled to room temperature, and the steel rail is basically ensured to be straight after exiting the heat treatment line, thereby ensuring the subsequent light pressure straightening; The steel rail enters a straightening machine to be pressure-straightened, the straightening pressure is that the pressure reduction of the 2# straightening roller is 20-24mm, the pressure reduction of the 4# straightening roller is 10-14mm, the pressure reduction of the 6# straightening roller is 5-9mm, and the pressure reduction of the 8# straightening roller is 1-5mm.

2. The method of claim 1, wherein the method is for reducing residual stresses in a low alloy high strength heat treated rail according to ASTM 115RE. The residual stress of the steel rail is detected, the residual stress of the rail head is ≤150MPa, the residual stress of the rail waist is ≤50MPa, and the residual stress of the rail bottom is ≤150MPa.

3. The method of claim 1, wherein the method is for reducing residual stresses in a low alloy high strength heat treated rail according to ASTM 115RE. The billet is heated in a heating furnace for 3.8 hours, the heating temperature is 1280℃, the billet is rolled by a universal rolling mill for 13 passes, the rolling section size of the billet meets the section size requirement of the 115RE steel rail according to the American standard, and the final rolling temperature of the steel rail is 922℃.

4. The method of claim 3, wherein the method is for reducing residual stresses in a low alloy high strength heat treated rail according to ASTM 115RE. The steel rail enters an online heat treatment production line at 780℃, air is sprayed to cool the rail head and the rail bottom, the cooling speed of the rail head is 2.8℃ / s, and the rail head is cooled to 505℃, the cooling speed of the rail bottom is 2.2℃ / s, and the rail bottom is cooled to 553℃, and then the steel rail is naturally air-cooled to room temperature.

5. The method of claim 4, wherein the method is for reducing residual stresses in a low alloy high strength heat treated rail according to ASTM 115RE. The steel rail enters a straightening machine to be pressure-straightened, the straightening pressure is that the pressure reduction of the 2# straightening roller is 22mm, the pressure reduction of the 4# straightening roller is 12mm, the pressure reduction of the 6# straightening roller is 6mm, and the pressure reduction of the 8# straightening roller is 2mm.

6. The method of claim 5, wherein the method is for reducing residual stresses in a low alloy high strength heat treated rail according to ASTM 115RE. The straightness of the steel rail after straightening meets the requirement.

7. The method of claim 5 or 6, wherein the method is for reducing residual stresses in a low alloy high strength heat treated rail according to ASTM 115RE. The residual stress of the steel rail is detected, the residual stress of the rail head is 122MPa, the residual stress of the rail waist is 45MPa, and the residual stress of the rail bottom is 136MPa.