阅读说明：本技术 用于制造钢轨的方法和相应的钢轨 (Method for producing a rail and corresponding rail ) 是由 何塞·阿兰孔阿尔瓦雷斯 大卫·阿尔瓦雷斯迭斯 何塞·曼努埃尔·阿蒂梅斯恩西纳 弗朗西斯卡·加西 于 2018-11-27 设计创作，主要内容包括：用于制造钢轨的方法,包括：-铸造钢以获得半成品,所述钢的组成包含0.20％≤C≤0.60％、1.0％≤Si≤2.0％、0.60％≤Mn≤1.60％和0.5≤Cr≤2.2％,任选地0.01％≤Mo≤0.3％、0.01％≤V≤0.30％,剩余部分为铁和杂质；-将所述半成品热轧成具有所述钢轨的形状并且包括头部的热轧半成品,其中最终轧制温度T<Sub>FRT</Sub>高于Ar3；-将所述头部冷却到200℃至520℃的冷却停止温度T<Sub>CS</Sub>,所述头部的随时间的温度在上边界与下边界之间,所述上边界具有由A1(0秒,780℃)、B1(50秒,600℃)和C1(110秒,520℃)限定的坐标,以及所述下边界具有由A2(0秒,675℃)、B2(50秒,510℃)和C2(110秒,300℃)限定的坐标；-将所述头部保持在300℃至520℃的温度范围内持续至少12分钟的保温时间t<Sub>保温</Sub>；以及-将所述热轧半成品冷却至室温以获得所述钢轨。(A method for manufacturing a rail, comprising: casting a steel having a composition comprising 0.20% C.ltoreq.0.60%, 1.0% Si.ltoreq.2.0%, 0.60% Mn.ltoreq.1.60%, and 0.5% Cr.ltoreq.2.2%, optionally 0.01% Mo.ltoreq.03%, V is more than or equal to 0.01% and less than or equal to 0.30%, and the balance is iron and impurities; -hot rolling the semi-finished product into a hot-rolled semi-finished product having the shape of the rail and comprising a head, wherein the final rolling temperature T FRT Above Ar 3; -cooling the head to a cooling stop temperature T of 200 ℃ to 520 ℃ CS The temperature of the head over time is between an upper boundary and a lower boundary, the upper boundary having coordinates defined by A1(0 seconds, 780 ℃), B1(50 seconds, 600 ℃) and C1(110 seconds, 520 ℃), and the lower boundary having coordinates defined by A2(0 seconds, 675 ℃), B2(50 seconds, 510 ℃) and C2(110 seconds, 300 ℃); -keeping the head in a temperature range of 300 ℃ to 520 ℃ for a holding time t of at least 12 minutes Heat preservation (ii) a And-cooling the hot rolled semi-finished product to room temperature to obtain the rail.)

1. A method for manufacturing a rail comprising a head, the method comprising the sequential steps of:

-casting a steel to obtain a semi-finished product, the chemical composition of said steel comprising, in weight%:

0.20％≤C≤0.60％，

1.0％≤Si≤2.0％，

0.60％≤Mn≤1.60％，

and 0.5-2.2% of Cr,

and optionally one or more elements selected from:

0.01％≤Mo≤0.3％，

0.01％≤V≤0.30％；

the balance being Fe and inevitable impurities resulting from the smelting;

-hot rolling the semi-finished product into a hot-rolled semi-finished product having the shape of the rail and comprising a head, wherein the final rolling temperature T_FRTAbove Ar 3;

-bringing the head of the hot-rolled semi-finished product from the final rolling temperature T_FRTCooling to a cooling stop temperature T of 200 ℃ to 520 DEG C_CSSuch that the temperature of the head of the hot-rolled semi-finished product over time is between an upper boundary having coordinates of time and temperature defined by A1(0 seconds, 780 ℃), B1(50 seconds, 600 ℃) and C1(110 seconds, 520 ℃), and a lower boundary having coordinates of time and temperature defined by A2(0 seconds, 675 ℃), B2(50 seconds, 510 ℃) and C2(110 seconds, 300 ℃);

-keeping the head of the hot-rolled semi-finished product at a temperature ranging from 300 ℃ to 520 ℃ for a holding time t of at least 12 minutes_{Heat preservation}(ii) a And

-cooling the hot rolled semi-finished product to room temperature to obtain the rail.

2. The method of claim 1, wherein the microstructure of the head of the steel rail consists of, in surface fraction:

-49% to 67% bainite;

-14% to 25% of retained austenite having an average carbon content of 0.80% to 1.44%;

-13% to 34% tempered martensite.

3. The method according to claim 2, wherein the surface fraction of bainite in the microstructure of the head is higher than or equal to 56%.

4. The method of any one of claims 2 or 3, wherein the surface fraction of retained austenite in the microstructure of the head is from 18% to 23%.

5. The method according to any one of claims 2 to 4, wherein the surface fraction of tempered martensite in the microstructure of the head is from 14.5% to 22.5%.

6. The method according to any one of claims 2 to 5, wherein the average carbon content in the retained austenite is higher than 1.3%.

7. The method of any one of claims 1 to 6, wherein the cooling stop temperature T_CSIs 300 ℃ to 520 ℃.

8. The method of any one of claims 1 to 6, wherein the cooling stop temperature T_CSIs 200 ℃ to 300 ℃, and the method is used for cooling the head part of the hot-rolled semi-finished product to the cooling stop temperature T_CSAfter the step of (a) and before the step of maintaining the head within the temperature range, further comprising the step of heating the head of the hot rolled semi-finished product up to a temperature of 300 ℃ to 520 ℃.

9. Method according to any one of claims 1 to 8, wherein the step of cooling the head of the hot rolled semi-finished product is carried out by means of water jets.

10. The method according to any one of claims 1 to 9, wherein during the step of cooling the head of the hot rolled semi-finished product, the entire hot rolled semi-finished product is cooled such that the temperature of the hot rolled semi-finished product over time is between the upper boundary and the lower boundary.

11. Method according to any one of claims 1 to 10, wherein during the step of hot rolling the semi-finished product, the semi-finished product is hot rolled from a hot rolling start temperature higher than 1080 ℃, preferably higher than 1180 ℃.

12. Method according to any one of claims 1 to 11, wherein the chemical composition of the steel comprises, in contents expressed in weight%:

0.30％≤C≤0.60％。

13. method according to any one of claims 1 to 12, wherein the chemical composition of the steel comprises, in contents expressed in weight%:

1.25％≤Si≤1.6％。

14. method according to any one of claims 1 to 13, wherein the chemical composition of the steel comprises, in contents expressed in weight%:

1.09％≤Mn≤1.5％。

15. a rail made of a steel having a chemical composition comprising, in weight%:

0.20％≤C≤0.60％，

1.0％≤Si≤2.0％，

0.60％≤Mn≤1.60％，

and 0.5-2.2% of Cr,

and optionally one or more elements selected from:

0.01％≤Mo≤0.3％，

0.01％≤V≤0.30％；

the balance being Fe and inevitable impurities resulting from the smelting;

the microstructure of the rail including the head consists of, in surface fraction:

49 to 67 percent of bainite,

14 to 25% of retained austenite, the retained austenite having an average carbon content of 0.80 to 1.44%,

13% to 34% tempered martensite.

16. The steel rail according to claim 15, wherein the microstructure of said head of said rail has a surface fraction of bainite higher than 56%.

17. The steel rail according to any one of claims 15 or 16, wherein the surface fraction of retained austenite in the microstructure of the head of the steel rail is from 18% to 23%.

18. The steel rail according to any one of claims 15 to 17, wherein the microstructure of the head of the steel rail has a surface fraction of tempered martensite of from 14.5% to 22.5%.

19. The steel rail according to any one of claims 15 to 18, wherein the average carbon content in the retained austenite is higher than 1.3%.

20. Steel rail according to any one of claims 15 to 19, wherein the chemical composition of the steel comprises, in contents expressed in% by weight:

0.30％≤C≤0.6％。

21. steel rail according to any one of claims 15 to 20, wherein the chemical composition of the steel comprises, in contents expressed in% by weight:

1.25％≤Si≤1.6％。

22. steel rail according to any one of claims 15 to 21, wherein the chemical composition of the steel comprises, in contents expressed in% by weight:

0.9％≤Mn≤1.5％。

23. a rail according to any one of claims 15 to 22, wherein the hardness of the head of the rail is from 420HB to 470HB, preferably higher than 450 HB.

24. The steel rail according to any one of claims 15 to 23, wherein the tensile strength of the head of the steel rail is 1300 to 1450 MPa.

25. The steel rail according to any one of claims 15 to 24, wherein the yield strength of the head of the steel rail is 1000 to 1150 MPa.

26. The rail according to any one of claims 15 to 25 wherein the total elongation of the head of the rail is from 13% to 18%.

Examples

The inventors of the present invention conducted the following experiments.

Steel is provided in the form of a semi-finished product having a composition (expressed in weight) according to table 1.

TABLE 1

Hot rolling the semifinished product into a hot rolled semifinished product having the shape of a rail, wherein the final rolling temperature T_FRTHigher than Ar3, then from the final rolling temperature T_FRTCooling to a cooling stop temperature T_CSWherein the cooling rate is such that, from a temperature T0 at which the initial cooling time T0 is 0 seconds, the hot-rolled semifinished product reaches the temperature T0 after 50 seconds of cooling₅₀Then reaches the temperature T after cooling for 110 seconds₁₁₀。

Then, the head of the rail is brought to a temperature equal to the cooling stop temperature T_CSTemperature T of_{Heat preservation}Keeping the temperature in the range of 300 ℃ to 520 ℃ for a holding time t_{Heat preservation}。

And finally cooling the steel rail to room temperature.

The rail manufacturing conditions are summarized in table 2 below.

TABLE 2

Chemical composition：

Samples for chemical analysis were obtained from tensile test sample locations as described in 9.1.3 of EN 13674-1:2011, which were then polished and analyzed by spark source emission spectroscopy to determine the average weight percent (% by weight.) furthermore, several 1g pins were extracted, degreased, and subjected to combustion trace element analysis in L ECO C/S and L ECO N/O analyzers to yield the percentages of N, O, S and C.

TABLE 3

Fatigue test：

Fatigue samples were taken from the head of the rail and machined according to ASTM E606-12.

Fatigue tests were carried out at room temperature on a hydraulic universal tester INSTRON 8801 with a strain control with a "peak-to-peak" amplitude of 0.00135 μm. The waveform used was a sine wave with a symmetric strain of +0.000675 μm in tension and-0.000675 μm in compression. The output (run-out) was 500 ten thousand cycles at which point the test was stopped.

Three replicates of each sample were tested.

The output was 500 ten thousand cycles at which point the test was stopped.

TABLE 4

Microstructural-optical microscopy：

Metallographic samples were obtained from the head of the rail according to line 9.1.4 in EN 13674-1: 2011.

Metallographic samples were ground, polished and etched with Nital 2% to show the microstructure of the rail samples microscopic observations were made using an L eica DMi4000 microscope.

For all samples, the overall microstructure appearance of the entire rail head was entirely bainitic, i.e., comprised of laths or plates of bainite with martensite and austenite dispersed between the laths or plates of bainite. The properties of the microstructure were analyzed in more detail by high resolution scanning electron microscopy and XR diffraction.

Characterization of microstructures by XR diffraction and high resolution scanning electron microscopy：

Detailed analysis was performed on sample 523513Y208 Electron microscopy was performed by high resolution field-emission gun electron microscopy (FEG-SEM) Zeiss Ultra Plus diffraction tests were performed on an X-ray diffractometer Bruker D8Advance using CuK α radiation.

The austenite content and its carbon content were measured by XRD according to the recommendations of the ASTM E975 standard.

The content of the M/A component was obtained on the SEM image by a manual dot counting method according to the ASTM E562 standard. The martensite content is then determined by subtracting the content of retained austenite measured by XRD from the content of the M/a component. The balance with respect to 100% consists of bainite.

The microstructure comprised 61.3% bainite, 20.20% retained austenite (carbon content 1.38%) and 18.5% martensite.

Hardness of：

In one aspect, the Brinell hardness (Brinell) was evaluated at the rolled surface of the rail head according to line 9.1.8 in EN 13674-1:2011 (average of three measurements).

On the other hand, the brinell hardness was evaluated on a section of the steel rail using an automatic hardness tester L eco L V700 AT.

Table 5 shows the average values of the hardness tests in the Rolling Surface (RS) and at different points of the cross section.

TABLE 5

Tensile test：

Tensile tests were carried out according to ISO 6892-1 using scaled circular test pieces having a diameter of 10mm according to EN 13674-1:2011, item 9.1.9. Extraction of test sample (D)₀＝10mm，L₀50mm) and tested using an Instron 600DX universal mechanical tester.

Three replicates of each sample were tested.

Table 6 shows the Yield Strength (YS), Tensile Strength (TS) and elongation (A)₅₀) The result of (1).

Sample (I)	YS(MPa)	TS(MPa)	A50(％)
				523513/Y208	1089	1440	14
523514/A208	1098	1452	14
				52351A/Y308	1052	1442	14

TABLE 6

Coefficient of linear Thermal Expansion (L inner Thermal Expansion Coefficient, L TEC)：

L TEC was measured in the rolling direction of the rail test samples (4mm diameter and 10mm length) were extracted from the center position of the tensile sample, and the coefficient of thermal expansion was evaluated by high resolution dilatometry (BAHR 805A/D) at 2 deg.C/min from-70 deg.C to 70 deg.C.

FIG. 3 depicts the relative length change of one of the three heating runs performed (d L/L)₀) And Coefficient of Thermal Expansion (CTE).

Next, table 7 shows a technique L TEC using 25 ℃ as reference temperature.

TABLE 7。