Low-Cr alloy high-yield-ratio steel rail and production method thereof

Abstract

The invention relates to a low-Cr alloy high-yield-ratio steel rail and a production method thereof. The steel comprises the following chemical components in percentage by weight: 0.55%-0.76% of C, 0.62%-0.68% of Si, 0.50%-1.02% of Mn, 0.01%-0.15% of Cr, 0.08%-0.15% of Ni, 0.18%-0.30% of Cu, 0.01%-0.10% of Nb, 0.005%-0.023% of V, 0.030%-0.040% of Ti, less than or equal to 0.015% of P, less than or equal to 0.010% of S and the balance of Fe and inevitable impurities. A low-Cr alloy component design mode is developed in a mode of combining alloy strengthening and heat treatment strengthening, so that the yield ratio of the steel rail is increased, the steel rail has wear resistance and contact fatigue resistance, the application requirement of a user for the long service life of the steel rail is met, the steel rail is better applied to a passenger and freight mixed transportation line, the rail replacement frequency is reduced, and the railway operation and maintenance cost is saved.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel for rail transit, and relates to a rail material, mainly a low-Cr alloy high yield ratio rail with high yield ratio, high strength and toughness for mixed passenger and freight transportation laying and its production method. Background Art

[0002] As the main component guiding the stable movement of railway vehicles, the rail bears the wear and contact impact from the wheels, and its quality directly determines whether the train can run safely. With the change of the application environment, the increase of train speed, traffic volume and transportation frequency, the strong-plasticity matching of the rail has become the focus of users' evaluation of the comprehensive service performance of the rail. If the rail has high strength, high hardness and low plasticity, it is easy to have the problem of reduced anti-peeling and chipping ability; if the rail has high plasticity and low strength, it is easy to have the problem of poor wear resistance; if the rail has high strength and high plasticity, the rail shows both wear resistance and anti-peeling and chipping ability, and can show a long service life during service. Therefore, in combination with the needs of users and the actual application of the rail, the present invention has carried out the development of rails with a high yield ratio, and formed a new technology of a low-Cr alloy high yield ratio rail and its production method.

[0003] It is found in the research that there are certain deficiencies in some disclosed related technologies. For example, CN107739806A discloses "high-toughness plastic hypereutectoid rail and its manufacturing method", and the rail involved is a hypereutectoid rail, which is significantly different from the eutectoid rail of the present invention; CN117385144A discloses "a medium-strength rail with a high yield ratio and its preparation method", and its characteristics are "C: 0.72-0.82%, Si: 0.10-1.00%, Mn: 0.70-1.25%, Cr: 0.40-0.70%, P: ≤0.02%, S: ≤0.02%, Al: ≤0.005%", but it belongs to the category of medium-high chromium steel, which is essentially different from the low-chromium steel of the present invention;

[0004] CN112301205A discloses "a pearlitic rail with a high yield ratio and its preparation method", characterized by "C: 0.65 - 0.80%, Si: 0.15 - 0.80%, Mn: 0.70 - 1.20%, V: ≤0.12%, P: ≤0.025%, S: ≤0.025%, Al: ≤0.004%", but it is a non-chromium alloyed rail, which is essentially different from the present invention; CN104195433B discloses "a high-strength and high-toughness pearlitic rail and its production method". In this technology, the tensile strength of the rail does not exceed 1120 MPa, which cannot play a good wear-resistant role for laying on mixed passenger and freight lines, and it does not contain the chromium alloying effect. CN104561816B discloses "a rail with excellent high-strength and fatigue-resistant performance and its production method". This technology shows that the tensile strength of the rail involved is between 1260 MPa and 1420 MPa, and the rail exhibits relatively high strength, but the yield ratio is insufficient. CN110592496B discloses "a pearlitic rail steel and its preparation method". The rail involved shows relatively high strength, and the silicon content of the former even reaches 1%, which will significantly reduce the toughness and plasticity of the rail and is prone to potential safety hazards under the cyclic impact of train wheels. CN107475616A discloses "a high-strength and high-toughness pearlitic rail and its manufacturing method", and CN107675083B discloses "a high-strength and high-toughness pearlitic rail and its manufacturing method". The rails involved have certain strength and hardness, but the mechanism is the combined action of chromium and microalloying elements, and the combined action of chromium and nickel-copper elements is not described.

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a low-Cr alloy high-yield ratio rail and its production method. On the basis of not significantly increasing the production cost, a high-yield ratio rail with wear resistance and anti-spalling and chipping for use on mixed passenger and freight lines is produced. Summary of the Invention

[0006] The present invention provides a low-Cr alloy high-yield ratio rail and its production method. The purpose is to develop a low-Cr alloy composition design method to improve the yield ratio of the rail through the combination of alloy strengthening and heat treatment strengthening, so that the rail has wear resistance and anti-contact fatigue performance, meets the user's demand for long-life application of the rail, is better applied to mixed passenger and freight lines, reduces the rail replacement frequency, and saves the railway operation and maintenance cost.

[0007] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0008] A low-Cr alloy steel rail with a high yield ratio, the chemical components in the steel are by weight percentage: C: 0.55% - 0.76%, Si: 0.62% - 0.68%, Mn: 0.50% - 1.02%, Cr: 0.01% - 0.15%, Ni: 0.08% - 0.15%, Cu: 0.18% - 0.30%, Nb: 0.01% - 0.10%, V: 0.005% - 0.023%, Ti: 0.030% - 0.040%, P ≤ 0.015%, S ≤ 0.010%, and the balance is Fe and unavoidable impurities.

[0009] The fracture toughness index of the steel rail is: the fracture toughness value at -20°C is 36.1 - 37.0 MPa·m 0.5 .

[0010] The tensile strength (R m ) of the steel rail at room temperature is 1230 - 1280 MPa, the yield strength (R p0.2 ) is 861 - 950 MPa, and the elongation after fracture is 13.0 - 15.0%.

[0011] The hardness of the top surface of the steel rail head is 368 - 385 HB, and the hardness of the cross-section is 355 - 375 HBW.

[0012] The selection of the addition amount (by weight percentage) of each of the above elements and its function description are as follows:

[0013] C is the basic element that improves the matrix hardness in the steel. Its function in the present invention is to strengthen the matrix and ensure that the basic hardness of the steel rail meets the heat treatment requirements. In the present invention, when the C content is less than 0.55%, even with heat treatment intervention, it is impossible to ensure that the hardness of the steel rail meets the use requirements of the passenger and freight mixed transportation lines in the exporting country, and the wear resistance and service life are significantly reduced; when the C content is higher than 0.76%, it will seriously weaken the strengthening effect of the Cr element, increase the risk of brittle fracture of the steel rail, and form abnormal retained austenite during the accelerated cooling process. Therefore, the present invention selects the C content to be 0.55% - 0.76%.

[0014] Si is a solid-solution strengthening element. Its function in the present invention is to dissolve in ferrite during pouring and cooling and dissolve in pearlite during rolling, which can improve the hardness and strength of the steel rail and replace high-cost alloy elements at the same time. When the Si content is less than 0.62%, the solid-solution strengthening effect is not obvious; when the Si content is higher than 0.68%, the toughness and plasticity of the steel rail decrease significantly, and the welding performance is seriously damaged. Therefore, the present invention selects the Si content to be 0.62% - 0.68%.

[0015] Mn is a carbide - forming element. Its function in the present invention is to increase the hardness of cementite and promote the precipitation strengthening of copper. In the present invention, when the manganese content is lower than 0.50%, the above - mentioned functions cannot be exerted; when the manganese content is higher than 1.02%, it will increase the positive segregation degree of manganese and carbon, and easily produce abnormal martensite structure. Therefore, the present invention selects the Mn content to be 0.50% - 1.02%.

[0016] Cr is an element that improves the matrix hardness. Its function in the present invention is to increase the hardenability and hardening property of the rail during the heat treatment process, and improve the wear - resistance performance of the rail. At the same time, combined with the carbon, silicon and manganese in the present invention, it can improve the strength of the rail steel, delay the pearlite transformation time, making the rail easy to be heat - treated, saving energy and reducing costs. When the chromium content is lower than 0.01%, the above - mentioned properties are significantly inhibited; when the chromium content is higher than 0.15%, it will significantly reduce the elongation after fracture of the rail. Therefore, the present invention selects the Cr content to be 0.01% - 0.15%.

[0017] P is a harmful element in rail steel, which is easy to cause segregation and "cold brittleness". The lower it is, the better under the premise of ensuring steel - making conditions, steel - making cost, etc. The present invention requires that the P content ≤ 0.015%.

[0018] S is a harmful element in rail steel. It is the main forming element of type A inclusions, and is prone to "hot brittleness" during rolling. Therefore, the lower it is, the better under the premise of not increasing unnecessary costs. The present invention requires that S ≤ 0.010%.

[0019] The functions of Cu and Ni elements in the present invention are to alleviate the problems of reduced toughness and plasticity brought by Cr element. By adding a small amount of copper and nickel elements in cooperation, the concentration of eutectoid carbon can be maintained at a relatively low level, and at the same time, it can play a good solid - solution strengthening role, improve the toughness and plasticity of the rail. Combined with the on - line heat - treatment process, it can increase the elongation after fracture by about 2% on the basis of the carbon, silicon, manganese and chromium components, and at the same time increase the yield strength by about 50 MPa (Rp 0.2 ) without reducing the tensile strength. In order to enable the rail of the present invention to obtain the above - mentioned invention effects, the Ni content is controlled at 0.08% - 0.15%, and the Cu content is controlled at 0.18% - 0.30%.

[0020] Niobium, vanadium and titanium in high - carbon rail steel synergistically improve the strength, toughness, wear - resistance and fatigue - resistance performance of the rail by refining grains, precipitation strengthening and improving the microstructure. In the present invention, the reasonable matching of the contents of niobium, vanadium and titanium elements and the control of the rolling process are one of the key technologies for manufacturing high - and low - temperature toughness rails. Too high or too low contents cannot cooperate with the process of the present invention and cannot obtain the technical effects of the present invention. Therefore, in the present invention, the content of micro - alloying elements is controlled as follows: Nb: 0.01% - 0.10%, V: 0.005% - 0.023%, Ti: 0.030% - 0.040%.

[0021] Based on the above component design, in order to achieve the effects and purposes of the present invention and produce a low-Cr alloyed high-strength and high-hardness steel rail, a smelting process, a rolling process, and an on-line heat treatment process that match the components of the present invention need to be coordinated. The entire process design is closely combined with the component design, effectively realizing the strength and hardness of the steel rail under the conditions of the present invention. The designed steel rail is an on-line heat-treated steel rail. A production method of a low-Cr alloy high yield ratio steel rail, including smelting, rolling, and on-line heat treatment, specifically includes the following contents:

[0022] 1) In the smelting process, the molten iron for smelting is subjected to desulfurization pretreatment, smelted by a converter or an electric furnace, deoxidized with ferrosilicon-aluminum, and 0.20 - 0.30 kg / t of quicklime is added during the tapping process. The purpose is to promote the floating of CaS, reduce the sulfide content in the steel, and at the same time ensure that the furnace temperature is not lost and the heating cost is reduced during the refining process. LF refining is to further purify the molten steel, precisely control each alloy component, ensure that the alloy components meet the design requirements, deoxidize with ferralium, and add 5.00 - 6.00 kg / t of quicklime and fluorite during the tapping process for 40 - 45 minutes to ensure the full floating of the slag, achieve the purity of the molten steel, and effectively control the non-metallic inclusions. VD or RH vacuum degassing is to ensure that hydrogen and oxygen are below 2 ppm and 20 ppm respectively, prevent hydrogen-induced cracks in the steel rail, and control the B-class inclusion grade below 1.0. The continuous casting billet is used for the casting billet, the cross-sectional size is not less than 280*410 mm, and the casting speed is controlled at 0.4 - 0.7 m / min to ensure the surface quality of the casting billet without cracks. Only through the above treatment methods can the beneficial effects of the present invention be realized and the high-strength and high-hardness steel rail of the present invention be obtained in cooperation with the subsequent processes.

[0023] 2) The rolling process described above includes: descaling the continuous casting billet with high-pressure water, and rolling the rail using a three-stand, five-stand or seven-stand rolling mill. The rough rolling temperature of the rail is 1132 - 1152 °C; a large number of dislocations are formed, initially breaking the austenite grains. Titanium preferentially forms high-melting-point TiC particles, which pin the austenite grain boundaries during the rolling process, inhibiting grain coarsening and thus refining the final microstructure; the medium rolling temperature is 1075 - 1095 °C; the austenite grains are refined, the dislocation density is increased, niobium forms Nb(C) compounds, which inhibit the growth of austenite grains during this rolling process and refine the original grains; the finish rolling temperature is 1030 - 1050 °C; the newly grown austenite is broken, and at the same time, copper and nickel elements promote the nucleation and growth of the newly broken austenite. Blocked by the accumulated dislocations, the grains do not grow significantly, effectively refining the austenite grains. At the same time, composite niobium-vanadium-titanium carbide (Nb, V, Ti)C is precipitated, further pinning the grain boundaries, strengthening the matrix, and improving the strength and toughness. At the same time, Cr plays a role in this process, forming alloy cementite (Fe·Cr)3C with Fe, further enhancing the matrix hardness, wear resistance and stability, laying a foundation for further strengthening in subsequent on-line heat treatment.

[0024] 3) The on-line heat treatment described above includes: after the rail rolling is completed, using the remaining rolling temperature to enter the on-line heat treatment unit. The cooling medium is air, and the on-line heat treatment unit compresses the air to complete on-line under-speed quenching; the unit is divided into 6 sections, numbered from section 1 to section 6 in sequence. In the present invention, through the synergistic effect of carbon, manganese and nickel elements, the austenite region is expanded and the eutectoid temperature is reduced. The starting cooling temperature of the rail is controlled above 860 °C. At the same time, niobium, vanadium and titanium act synergistically during the heat treatment process. In the above heat treatment process, the process of each section of the unit is defined. To obtain the high yield ratio of the present invention, the cooling rate of the rail head tread of section 1 is 3.0 - 4.0 °C / s and is maintained for 15 - 20 s, preferably 20 s; the cooling rate of the rail head tread of section 2 is 1.5 - 3.0 °C / s and is maintained for 8 - 12 s, preferably 8 s; the cooling rate of the rail head tread of section 3 is 1.0 - 1.5 °C / s and is maintained for 15 - 18 s, preferably 18 s; the cooling rate of the rail head tread of section 4 is 1.5 - 2.5 °C / s and is maintained for 8 - 11 s, preferably 8 s; the cooling rate of the rail head tread of section 5 is 1.5 - 2.0 °C / s and is maintained for 7 - 10 s, preferably 10 s; the cooling rate of the rail head tread of section 6 is 1.5 °C / s. After the rail cools, the reheat temperature is controlled at 552 - 565 °C. During the cooling process in section 1 and section 2, the un-dissolved Nb precipitates as nano-scale NbC particles, further improving the strength and toughness of the rail; during the cooling in section 3, section 4 and section 5, fine VC particles precipitate in the pearlite colonies, further improving the strength and wear resistance of the rail. At the same time, nickel and copper elements cooperate with each other to play a precipitation strengthening role, promoting the right shift of the C-curve position, reducing the critical cooling rate, improving the hardenability of the steel, and ensuring the high strength and high plasticity matching of the final rail; chromium elements play a role in strong hardenability and hardenability.

[0025] To achieve the technical effects of the present invention, the present invention integrates production technologies such as alloy composition design, steelmaking, rolling, and on-line heat treatment. In particular, it gives full play to the positive effects of conventional elements such as carbon, manganese, chromium, nickel, and copper during the rolling and heat treatment processes. The mutual cooperation of niobium and vanadium microalloying during rolling and cooling complements each other, reflecting the systematicness and innovation from design to production. According to the element characteristics, the rolling process and the sectional cooling process are designed, enabling the technical indicators of the rail to meet the design expectations and realizing mass production and application. The technological innovation advantages of the present invention are concentrated in the following aspects:

[0026] First, it meets the requirements of high yield ratio for passenger and freight mixed transportation lines. By means of technical design, the unusual effects of conventional elements are brought into play. Through the mutual cooperation of carbon, manganese, chromium, nickel, copper and microalloying elements, their respective mechanism effects in the rolling stage and heat treatment stage are exerted, ensuring the tissue properties of the rail, laying a compositional foundation for obtaining higher strength and plasticity, and reducing the alloy cost.

[0027] Second, the chromium, copper and nickel elements are effectively combined with the rolling process, that is, according to the element mechanism effect, the rolling process of the present invention is designed. Through three large deformation rollings, the initial fragmentation of austenite is realized, the dislocation density is increased, and the newly grown austenite is fragmented again, effectively refining the austenite grains and laying a foundation for fine grain strengthening. At the same time, copper and nickel elements promote the nucleation and growth of newly fragmented austenite. Blocked by the accumulation of dislocations, the grains will not grow significantly, effectively refining the austenite grains; Cr plays the role of forming alloy cementite (Fe·Cr)3C with Fe, further enhancing the matrix hardness, wear resistance and stability.

[0028] Third, the microalloying elements are effectively combined with the rolling process and the cooling process to play the mechanism role. When rough rolling at 1132 - 1152 °C, titanium preferentially forms high melting point TiC particles, which pin the austenite grain boundaries during rolling, inhibit grain coarsening, and refine the final structure; when medium rolling at 1075 - 1095 °C, niobium forms Nb(C) compounds, which inhibit the growth of austenite grains during this rolling process and refine the original grains; when finish rolling at 1030 - 1050 °C, composite niobium-vanadium-titanium carbides (Nb, V, Ti)C are precipitated, further pinning the grain boundaries, strengthening the matrix, and improving the strength and toughness. During the cooling process, when cooling in section 1 and section 2, the un-dissolved Nb precipitates as nano-scale NbC particles, further improving the strength and toughness of the rail; when cooling in section 3, section 4, and section 5, fine VC particles precipitate in the pearlite colonies, further improving the strength and wear resistance of the rail.

[0029] Fourth, the elements of carbon, manganese, nickel, chromium, and copper are effectively combined with the heat treatment process. That is, according to the mechanism of the elements, the heat treatment process of the present invention is designed. By adding carbon, manganese, and nickel elements and giving play to their synergistic effects, the austenite region is expanded, the eutectoid temperature is reduced, and the starting cooling temperature of the rail is controlled above 860 °C; during the cooling process, the nickel and copper elements cooperate with each other to play the role of precipitation strengthening, and at the same time promote the right shift of the C curve position, reduce the critical cooling rate, improve the hardenability of the steel, and ensure the high strength and toughness of the final rail; the chromium element plays a strong role in hardenability and hardening, and the temperature rise after the rail is cooled is controlled between 552 and 565 °C to prevent the occurrence of self-tempering phenomenon resulting in a decrease in the cross-sectional hardness.

[0030] Fifth, the composition design is effectively combined with the on-line heat treatment. It effectively exerts the combined strengthening effect of alloying elements and heat treatment process, reduces the alloy cost and thermal energy consumption, and jointly improves the yield ratio of the rail.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) Fracture toughness index: The fracture toughness value at -20 °C is as high as 36.1 - 37.0 MPa·m 0.5 , showing high toughness.

[0033] (2) Tensile properties: The room temperature tensile strength (R m ) is 1230 - 1280 MPa, the yield strength (Rp 0.2 ) is 861 - 950 MPa, the yield ratio reaches 74%, and the elongation after fracture is 13.0% - 15.0%, showing a good combination of high strength and plasticity and a high yield ratio.

[0034] (3) Hardness: The hardness of the rail head top surface reaches 368 - 385 HB, and the cross-sectional hardness reaches 355 - 375 HBW, showing high wear resistance.

[0035] (4) Microstructure composition: The microstructure of the rail head consists of pearlite and a small amount of ferrite. By volume percentage, the proportion of pearlite exceeds 95%. The structure is evenly transitioned and does not contain other microstructures, showing structural stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is the metallographic structure diagram of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further illustrates the specific implementation manners of the present invention in combination with embodiments. The following embodiments are used to specifically illustrate the content of the present invention. These embodiments are only general descriptions of the content of the present invention and do not limit the content of the present invention.

[0038] The present invention designs a low-Cr alloy high yield ratio steel rail through a composition design of low Cr combined with niobium, vanadium, and titanium microalloying, and through the mechanism of pure steelmaking and microalloying elements in the processes of rolling in each section and sectional heat treatment.

[0039] The production processes, tensile properties, etc. corresponding to the chemical components of the examples in the present invention are shown in Tables 1 to 4 below. The metallographic structure diagram of Example 1 is shown in Figure 1 .

[0040] Table 1 Chemical components of the examples

[0041]

[0042] Table 2 Key parameters for controlling the steelmaking process of the examples

[0043]

[0044]

[0045] Table 3 Key parameters for controlling the rolling and sectional cooling processes of the examples

[0046]

[0047] The sectional cooling time adopts the optimized time.

[0048] Table 4 Mechanical properties, hardness, fracture toughness, and microstructure of the examples

[0049]

[0050]

Claims

1. A low-Cr alloy steel rail with a high yield ratio, characterized in that: The chemical components in the steel are by weight percentage: C: 0.55% - 0.76%, Si: 0.62% - 0.68%, Mn: 0.50% - 1.02%, Cr: 0.01% - 0.15%, Ni: 0.08% - 0.15%, Cu: 0.18% - 0.30%, Nb: 0.01% - 0.10%, V: 0.005% - 0.023%, Ti: 0.030% - 0.040%, P ≤ 0.015%, S ≤ 0.010%, and the balance is Fe and unavoidable impurities.

2. A low-Cr alloy steel rail with a high yield ratio according to claim 1, characterized in that: The rail fracture toughness index is: the fracture toughness value at -20°C is 36.1 - 37.0 MPa·m 0.5 .

3. A low-Cr alloy steel rail with a high yield ratio according to claim 1, characterized in that: The tensile strength of the rail at room temperature is 1230 - 1280 MPa, the yield strength is 861 - 950 MPa, and the elongation after fracture is 13.0 - 15.0%.

4. A low-Cr alloy steel rail with a high yield ratio according to claim 1, characterized in that: The hardness of the rail head surface is 368 - 385 HB, and the hardness of the cross-section is 355 - 375 HBW.

5. A low-Cr alloy steel rail with a high yield ratio according to claim 1, characterized in that: The microstructure of the rail head consists of pearlite and a small amount of ferrite, and the proportion of pearlite exceeds 95% by volume percentage.

6. A production method of a low-Cr alloy high yield-strength ratio rail as described in any one of claims 1 - 5, including smelting, rolling, and online heat treatment, characterized in that: The rolling includes: the rough rolling temperature of the rail is 1132 - 1152 °C; the medium rolling temperature is 1075 - 1095 °C; the finish rolling temperature is 1030 - 1050 °C; The online heat treatment includes: after the rail rolling is completed, it enters the online heat treatment unit and is cooled by compressed air; the temperature after the rail cools and returns is controlled at 552 - 565 °C.

7. The production method of a low-Cr alloy high yield ratio steel rail according to claim 6, characterized in that: In the smelting process, the molten iron for smelting is subjected to desulfurization pretreatment, and 0.20 - 0.30 kg / t of quicklime is added during the tapping process.

8. The production method of a low-Cr alloy steel rail with a high yield ratio according to claim 6, characterized in that: In the smelting process, LF refining is adopted, 5.00 - 6.00 kg / t of quicklime and fluorite are added during the tapping process, refined for 40 - 45 min, and VD or RH vacuum degassing is adopted.

9. The production method of a low-Cr alloy steel rail with a high yield ratio according to claim 6, characterized in that: In the smelting process, continuous casting billets are used for the cast billets, and the casting speed is controlled at 0.4 - 0.7 m / min.

10. The production method of a low-Cr alloy high yield ratio steel rail according to claim 6, characterized in that: In the online heat treatment process, the unit is divided into 6 sections, numbered from section 1 to section 6 in sequence. The cooling rate of the rail head tread surface in section 1 is 3.0 - 4.0 °C / s and is maintained for 15 - 20 s; the cooling rate of the rail head tread surface in section 2 is 1.5 - 3.0 °C / s and is maintained for 8 - 12 s; the cooling rate of the rail head tread surface in section 3 is 1.0 - 1.5 °C / s and is maintained for 15 - 18 s; the cooling rate of the rail head tread surface in section 4 is 1.5 - 2.5 °C / s and is maintained for 8 - 11 s; the cooling rate of the rail head tread surface in section 5 is 1.5 - 2.0 °C / s and is maintained for 7 - 10 s; the cooling rate of the rail head tread surface in section 6 is 1.5 °C / s.

Images