Rail and manufacturing method therefor

Patent metadata

Field	Value
Publication number	US-12312645-B2
Application number	US-202017596437-A
Country	US
Kind code	B2
Filing date	Jun 9, 2020
Priority date	Jun 20, 2019
Publication date	May 27, 2025
Grant date	May 27, 2025

Abstract

A rail comprises a predetermined chemical composition. In a hardness distribution in a region from a rail head surface to a depth of 16.0 mm, a part having higher hardness than V1 that is minimum hardness in a first internal region is present in a second internal region, and hardness of the rail head surface is HBW 400 to 520 and average hardness in the region from the rail head surface to the depth of 16.0 mm is HBW 350 or more.

First claim

The invention claimed is:

1. A rail comprising a chemical composition consisting of, in mass %,
C: 0.60% to 0.84%,
Si: 0.10% to 1.50%,
Mn: 0.20% to 1.50%,
P: 0.035% or less,
S: 0.035% or less,
Cr: 0.49% to 2.00%, and optionally
one or more selected from the group consisting of
V: 0.30% or less,
Cu: 1.0% or less,
Ni: 1.0% or less,
Nb: 0.050% or less,
Mo: 0.5% or less,
Al: 0.07% or less,
W: 1.0% or less,
B: 0.005% or less, and
Sb: 0.5% or less,
with a balance consisting of Fe and inevitable impurities,
wherein, in a hardness distribution in a region from a rail head surface to a depth of 16.0 mm:
a part having higher hardness than V1 is present in a second internal region from 10.0 mm to 16.0 mm in depth located deeper than a first internal region from 4.0 mm to 8.0 mm in depth, where V1 is minimum hardness in the first internal region; and
hardness of the rail head surface is HBW 400 to 520, and average hardness in the region from the rail head surface to the depth of 16.0 mm is HBW 350 or more.

2. The rail according to claim 1 wherein the chemical composition consists of, in mass %,
C: 0.60% to 0.84%,
Si: 0.10% to 1.50%,
Mn: 0.20% to 1.50%,
P: 0.035% or less,
S: 0.035% or less, and
Cr: 0.49% to 2.00%,
with a balance consisting of Fe and inevitable impurities.

3. The rail according to claim 2 , wherein a difference between V2 and V1 is HBW 5 or more, where V2 is average hardness in the second internal region.

4. The rail according to claim 3 , wherein hardness in the second internal region increases continuously in a depth direction from the rail head surface.

5. The rail according to claim 2 , wherein the part having higher hardness than V1 is present throughout the second internal region.

6. The rail according to claim 5 , wherein hardness in the second internal region increases continuously in a depth direction from the rail head surface.

7. The rail according to claim 2 , wherein hardness in the second internal region increases continuously in a depth direction from the rail head surface.

8. A manufacturing method for the rail according to claim 2 , the manufacturing method comprising:
subjecting a steel material having the chemical composition according to claim 2 to hot rolling to obtain a rail;
thereafter cooling the rail from a temperature not less than austenite temperature to a first cooling temperature of A−25° C. to A+25° C., at an average cooling rate of 1° C./s to 20° C./s;
thereafter holding the rail until a temperature of the rail reaches an intermediate temperature of A+30° C. to A+200° C.; and
thereafter cooling the rail at an average cooling rate of 0.5° C./s to 20° C./s for 10 sec or more,
wherein A is a temperature at an intersection point between a pearlite transformation start curve and a bainite transformation start curve in a TTT diagram of steel having the chemical composition, and the temperature of the rail and the average cooling rate are respectively a temperature and an average cooling rate at the rail head surface.

9. The rail according to claim 1 , wherein a difference between V2 and V1 is HBW 5 or more, where V2 is average hardness in the second internal region.

10. The rail according to claim 9 , wherein hardness in the second internal region increases continuously in a depth direction from the rail head surface.

11. The rail according to claim 9 , wherein the part having higher hardness than V1 is present throughout the second internal region.

12. The rail according to claim 11 , wherein hardness in the second internal region increases continuously in a depth direction from the rail head surface.

13. The rail according to claim 1 , wherein the part having higher hardness than V1 is present throughout the second internal region.

14. The rail according to claim 13 , wherein hardness in the second internal region increases continuously in a depth direction from the rail head surface.

15. The rail according to claim 3 , wherein the part having higher hardness than V1 is present throughout the second internal region.

16. The rail according to claim 15 , wherein hardness in the second internal region increases continuously in a depth direction from the rail head surface.

17. The rail according to claim 1 , wherein hardness in the second internal region increases continuously in a depth direction from the rail head surface.

18. A manufacturing method for the rail according to claim 1 , the manufacturing method comprising:
subjecting a steel material having the chemical composition according to claim 1 to hot rolling to obtain a rail;
thereafter cooling the rail from a temperature not less than austenite temperature to a first cooling temperature of A−25° C. to A+25° C., at an average cooling rate of 1° C./s to 20° C./s;
thereafter holding the rail until a temperature of the rail reaches an intermediate temperature of A+30° C. to A+200° C.; and
thereafter cooling the rail at an average cooling rate of 0.5° C./s to 20° C./s for 10 sec or more,
wherein A is a temperature at an intersection point between a pearlite transformation start curve and a bainite transformation start curve in a TTT diagram of steel having the chemical composition, and the temperature of the rail and the average cooling rate are respectively a temperature and an average cooling rate at the rail head surface.

Assignees

• Jfe Steel Corp

Inventors

• Okushiro Kenji
• Tokunaga Kazuya
• Yamaguchi Moriyasu

Classifications

• C21D8/06 Primary

  during manufacturing of rods or wires · CPC title

• C21D8/00

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• C22C38/18

  containing chromium · CPC title

• C22C38/04

  containing manganese · CPC title

• C22C38/02 Primary

  containing silicon · CPC title