Method for joining steel rails with controlled weld heat input
A method for creating a welded joint between ends of two steel rails, wherein the two steel rails have a substantially pearlitic microstructure. The method includes a first heating step, an upsetting step, a first cooling step, and a second heating step and provides a means to influence a microstructure and hardness of an austenitic region of a heat affected zone (HAZ) and/or an extent of softening in a softened region of a HAZ.
1. A method for creating a welded joint between ends of two steel rails, wherein the two steel rails have a substantially pearlitic microstructure, the method comprising:
a first heating step wherein the ends of the two steel rails are heated to obtain within the two steel rails:
an austenitic region comprising a microstructure substantially of austenite, the austenitic region being within and/or adjacent to the ends of the two steel rails,
a softened region adjacent to the austenitic region, the softened region comprising a microstructure substantially of softened, annealed, spheroidized, and/or degenerate pearlite, and
an unaffected region adjacent to the softened region, the unaffected region comprising a microstructure that has not been substantially altered as compared to a starting microstructure of the two rails;
an upsetting or forging step wherein the ends of the two steel rails are forced together to obtain:
a weld bond between the ends of the two steel rails,
a remaining austenitic region on both sides of the weld bond,
a remaining softened region on both sides of the weld bond, and
a remaining unaffected region on both sides of the weld bond;
a cooling step wherein a temperature of the austenitic region on at least one side of the weld bond is below an A1 temperature; and
a second heating step wherein
heat is applied directly to the weld bond and to the austenitic region on at least one side of the weld bond via an external source to maintain the temperature of the weld bond and the at least said austenitic region on at least one side of the weld bond in a temperature range below said A1 temperature,
no additional austenite is formed, and
a hardness of the austenitic region on at least one side of the weld bond after the second heating step is less than or equal to a hardness in the austenitic region on at least one side of the weld bond without the second heating step.
2. The method of claim 1 , wherein
during the second heating step:
the temperature range below said A1 temperature is a transformation temperature range that is maintained for a transformation hold time, and
at least some of the austenite in at least said austenitic region transforms to another microstructure.
3. The method of claim 2 , wherein
during the first cooling step, the temperature in the austenitic region of at least one of the two steel rails is reduced to below the A1 temperature and above a Bs temperature, and
during the second heating step, the transformation temperature range is higher than said Bs temperature but lower than said A1 temperature, and the transformation hold time is sufficiently long such that at least said austenitic region achieves a microstructure containing a pearlite content of at least 80% and a (pearlite+ferrite) content of at least 95%.
4. The method of claim 2 , wherein
during the first cooling step, the temperature in the austenitic region of at least one of the two steel rails is below a Bs temperature and above an Ms temperature,
during the second heating step, the transformation temperature range is higher than said Ms temperature and lower than said A1 temperature, and the transformation hold time is sufficiently long such that at least said austenitic region achieves a microstructure containing a (bainite+pearlite+ferrite) content of at least 95%, and
during the first cooling step and/or the second heating step, at least some austenite in at least said austenitic region transforms to bainite.
5. The method of claim 2 , wherein the austenitic region of at least one of the two steel rails contains a microstructure with an austenite content of at least 5% at a time when the second heating step is initiated.
6. The method of claim 2 , wherein during the second heating step, heat is applied to at least a web of the austenitic region of at least one of the two steel rails.
7. The method of claim 2 , wherein hardness in the austenitic region of at least one of the two steel rails resulting from the second heating step is less than or equal to a hardness in the austenitic region without the second heating step.
8. The method of claim 2 , wherein a longitudinal distance (Lh) is a distance between an outer extent of an austenitic region in one of the two steel rails to an outer extent of the austenitic region in the other of the two steel rails, a weld joint centerline is halfway between outer extents of the austenitic regions of the two steel rails, and during the second heating step, heat is applied to the austenitic region of at least one of the two steel rails within a distance of 0.2Lh from the weld joint centerline.
9. The method of claim 2 , wherein during the second heating step, heat is also applied to the weld bond, the softened region and/or the unaffected region on one or both sides of the weld bond.
10. The method of claim 9 , wherein during the second heating step, the heat is also applied to at least a web of the weld bond, softened region and/or the unaffected region of one or both sides of the weld bond.
11. The method of claim 2 , wherein a means of applying heat to achieve the first heating step is also applied during and/or for up to 10 seconds after the upsetting step.
12. The method of claim 2 , wherein during the first cooling step, heat is applied to the weld bond, one austenitic region, and/or both austenitic regions, and a rate of heat input is lower than a rate of cooling, such that a temperature of at least one austenitic region decreases with time.
13. The method of claim 2 , wherein during the first heating step, the heat is applied using electric flashing, electric resistance, induction, friction, laser beam, convection, radiation, and/or exothermic reaction, applied individually, sequentially, or simultaneously.
14. The method of claim 2 , wherein natural cooling is used during the first cooling step.
15. The method of claim 2 , wherein during the first cooling step, the cooling is achieved at least in part by flowing a cooling media over the weld bond and/or the austenitic region, softened region, and/or unaffected region on one or both sides of the weld bond.
16. The method of claim 2 , wherein during the second heating step, the heat is applied using electric resistance, induction, convection, and/or radiation, applied individually, sequentially, or simultaneously.
17. The method of claim 2 , further comprising a step of partially or fully removing an upset material that protrudes beyond an original profile of the two rails after the upsetting step and before the second heating step.
18. The method of claim 2 , further comprising a step of partially or fully removing an upset material that protrudes beyond an original profile of the two rails after the second heating step.
19. The method of claim 2 , further comprising a second cooling step after the second heating step, wherein the weld bond and the austenitic regions, softened regions, and unaffected regions on both sides of the weld bond are cooled to ambient temperature.
20. The method of claim 19 , wherein natural cooling is used during the second cooling step.
21. The method of claim 19 , wherein during the second cooling step, the cooling is achieved at least in part by flowing a cooling media over the weld bond and/or the austenitic region, softened region, and/or unaffected region on one or both sides of the weld bond.
22. The method of claim 2 , wherein an alignment of the two rails and/or the welded joint are altered after the upsetting step.
23. The method of claim 1 , wherein
during the first cooling step wherein said temperature below an A1 temperature is below an Ms temperature, such that at least some martensite is formed from austenite in at least said austenitic region; and
during the second heating step:
the temperature range below said A1 temperature is also above the Ms temperature, and
the temperature range is maintained between the A1 temperature and the Ms temperature for a predetermined time such that at least said austenitic region achieves a microstructure containing at least some tempered martensite and a (tempered martensite+bainite+pearlite+ferrite) content of at least 95%, and wherein
tempered martensite is martensite with a hardness less than or equal to 600 Hv.
24. The method of claim 23 , wherein the austenitic region of at least one of the two steel rails contains a microstructure with an austenite content of at least 5% at a time when the second heating step is initiated.
25. The method of claim 23 , wherein during the second heating step, heat is applied to at least a web of the austenitic region of at least one of the two rails.
26. The method of claim 23 , wherein hardness in the austenitic region of at least one of the two steel rails resulting from the second heating step is less than or equal to a hardness in the austenitic region without the second heating step.
27. The method of claim 23 , wherein a longitudinal distance (Lh) is a distance between an outer extent of an austenitic region in one of the two steel rails to an outer extent of the austenitic region in the other of the two steel rails, a weld joint centerline is halfway between outer extents of the austenitic regions of the two steel rails, and during the second heating step, heat is applied to the austenitic region of at least one of the two steel rails within a distance of 0.2Lh from the weld joint centerline.
28. The method of claim 23 , wherein during the second heating step, heat is also applied to the weld bond, the softened region and/or the unaffected region on one or both sides of the weld bond.
29. The method of claim 28 , wherein during the second heating step, the heat is also applied to at least a web of the weld bond, softened region and/or the unaffected region of one or both sides of the weld bond.
30. The method of claim 23 , wherein a means of applying heat to achieve the first heating step is also applied during and/or for up to 10 seconds after the upsetting step.
31. The method of claim 23 , wherein during the first cooling step, heat is applied to the weld bond, one austenitic region, and/or both austenitic regions, and a rate of heat input is lower than a rate of cooling, such that a temperature of at least one of the austenitic regions decreases with time.
32. The method of claim 23 , wherein during the first heating step, the heat is applied using electric flashing, electric resistance, induction, friction, laser beam, convection, radiation, and/or exothermic reaction, applied individually, sequentially, or simultaneously.
33. The method of claim 23 , wherein natural cooling is used during the first cooling step.
34. The method of claim 23 , wherein during the first cooling step, the cooling is achieved at least in part by flowing a cooling media over the weld bond and/or the austenitic region, softened region, and/or unaffected region on one or both sides of the weld bond.
35. The method of claim 23 , wherein during the second heating step, the heat is applied using electric resistance, induction, convection, and/or radiation, applied individually, sequentially, or simultaneously.
36. The method of claim 23 , further comprising a step of partially or fully removing an upset material that protrudes beyond an original profile of the two steel rails after the upsetting step and before the second heating step.
37. The method of claim 23 , further comprising a step of partially or fully removing an upset material that protrudes beyond an original profile of the two steel rails after the second heating step.
38. The method of claim 23 , further comprising a second cooling step after the second heating step, wherein the weld bond and the austenitic regions, softened regions, and unaffected regions on both sides of the weld bond are cooled to ambient temperature.
39. The method of claim 38 , wherein natural cooling is used during the second cooling step.
40. The method of claim 38 , wherein the during the second cooling step, the cooling is achieved at least in part by flowing a cooling media over weld bond and/or the austenitic region, softened region, and/or unaffected region on one or both sides of the weld bond.
41. The method of claim 23 , wherein an alignment of the two steel rails and/or the welded joint are altered after the upsetting step.