Rail

Patent metadata

Field	Value
Publication number	US-10494704-B2
Application number	US-201615543805-A
Country	US
Kind code	B2
Filing date	Jan 22, 2016
Priority date	Jan 23, 2015
Publication date	Dec 3, 2019
Grant date	Dec 3, 2019

Abstract

The present invention relates to a rail which has a predetermined chemical composition and satisfies expressions of 1.00<Mn/Cr≤4.00 and 0.30≤0.25×Mn+Cr≤1.00 and in which a structure to a depth of 25 mm from an outer surface of a head portion as the origin includes 95% or greater of a pearlite structure, the hardness of the structure is in a range of Hv 350 to 480, 50 to 500 V carbonitride having an average grain size of 5 to 20 nm are present per 1.0 μm2 of an area to be inspected in a transverse cross section at a position having a depth of 25 mm from the outer surface of the head portion, and the value obtained by subtracting the hardness of the position having the depth of 25 mm from the outer surface of the head portion from the hardness of the position having a depth of 2 mm from the outer surface of the head portion is in a range of Hv 0 to Hv 40.

First claim

What is claimed is:

1. A rail comprising, as a chemical composition, in terms of mass %:
C: 0.75% to 0.85%;
Si: 0.10% to 1.00%;
Mn: 0.30% to 1.20%;
Cr: 0.20% to 0.80%;
V: 0.01% to 0.20%;
N: 0.0040% to 0.0200%;
Mo: 0% to 0.50%;
Co: 0% to 1.00%;
B: 0% to 0.0050%;
Cu: 0% to 1.00%;
Ni: 0% to 1.00%;
Nb: 0% to 0.0500%;
Ti: 0% to 0.0500%;
Mg: 0% to 0.0200%;
Ca: 0% to 0.0200%;
REM: 0% to 0.0500%;
Zr: 0% to 0.0200%;
Al: 0% to 1.00%;
P≤0.0250%;
S≤0.0250%; and
Fe and impurities as a remainder,
wherein the chemical composition of the rail satisfies the following Expressions 1 and 2,
a structure of a range between an outer surface of a head portion as an origin and a depth of 25 mm includes 95% or greater of a pearlite structure and a hardness of the structure is Hv 350 to 480,
50 to 500 V carbonitride having an average grain size of 5 to 20 nm are present per 1.0 μm 2 of an area to be inspected in a transverse cross section at a position having the depth of 25 mm from the outer surface of the head portion, and
the value obtained by subtracting a hardness of the position having the depth of 25 mm from the outer surface of the head portion from a hardness of a position having a depth of 2 mm from the outer surface of the head portion is Hv 0 to Hv 40, and
wherein when a number of carbon atoms is defined as CA and a number of nitrogen atoms is defined as NA in the V carbonitride, a ratio CA/NA which is a ratio of CA to NA is 0.70 or less,
1.00< Mn/Cr≤ 4.00  Expression 1,

0.30≤0.25× Mn+Cr≤ 1.00  Expression 2,

here, the symbols of elements described in the Expressions 1 and 2 indicate the content of each element in terms of mass %.

2. The rail according to claim 1 , comprising, in terms of mass %, at least one selected from the group consisting of:
Mo: 0.01% to 0.50%;
Co: 0.01% to 1.00%;
B: 0.0001% to 0.0050%;
Cu: 0.01% to 1.00%;
Ni: 0.01% to 1.00%;
Nb: 0.0010% to 0.0500%;
Ti: 0.0030% to 0.0500%;
Mg: 0.0005% to 0.0200%;
Ca: 0.0005% to 0.0200%;
REM: 0.0005% to 0.0500%;
Zr: 0.0001% to 0.0200%; and
Al: 0.0100% to 1.00%.

Assignees

• Nippon Steel & Sumitomo Metal Corp
• Nippon Steel Corp

Inventors

• Ueda Masaharu
• Tanahashi Takuya
• Miyazaki Teruhisa

Classifications

• 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

• C22C38/54

  with boron · CPC title

• C21D9/46

  for sheet metals · CPC title

• C22C38/06

  containing aluminium · CPC title

• C22C38/18

  containing chromium · CPC title