U.S. patent application number 16/495394 was filed with the patent office on 2020-01-09 for torsional severe plastic deformation method for metal bar, employing surface polishing to improve mechanical properties of metal.
The applicant listed for this patent is POSTECH ACADEMY-INDUSTRY FOUNDATION. Invention is credited to Seung-mi BAEK, Hyoung-seop KIM, Ji-hyun MOON, Ho-yong UM, Jae-ik YOON.
Application Number | 20200009631 16/495394 |
Document ID | / |
Family ID | 62600271 |
Filed Date | 2020-01-09 |
United States Patent
Application |
20200009631 |
Kind Code |
A1 |
KIM; Hyoung-seop ; et
al. |
January 9, 2020 |
TORSIONAL SEVERE PLASTIC DEFORMATION METHOD FOR METAL BAR,
EMPLOYING SURFACE POLISHING TO IMPROVE MECHANICAL PROPERTIES OF
METAL BAR
Abstract
The present invention relates to a torsional severe plastic
deformation method for a metal bar to which surface polishing is
applied to the metal bar to improve the mechanical properties of
the metal bar. According to an embodiment of the present invention,
there is provided a torsional severe plastic deformation method for
a metal bar, which includes: applying torsion to a metal bar; and
removing a surface defect on the surface of the metal bar, the
surface defect being caused by the applying of torsion, wherein the
removing of the surface defect is carried out in a continuous
manner in which the removing of the surface defect is performed
together with the applying of torsion or in a discontinuous manner
in which the applying of torsion is temporarily stopped and then
the applying of torsion is performed, and the removing of a surface
defect increases the amount of torsional rotation or the shear
strain applied to the metal bar.
Inventors: |
KIM; Hyoung-seop;
(Pohang-si, KR) ; MOON; Ji-hyun; (Cheonan-si,
KR) ; UM; Ho-yong; (Incheon, KR) ; YOON;
Jae-ik; (Pohang-si, KR) ; BAEK; Seung-mi;
(Incheon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POSTECH ACADEMY-INDUSTRY FOUNDATION |
Pohang-si |
|
KR |
|
|
Family ID: |
62600271 |
Appl. No.: |
16/495394 |
Filed: |
February 6, 2018 |
PCT Filed: |
February 6, 2018 |
PCT NO: |
PCT/KR2018/001541 |
371 Date: |
September 19, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B21D 11/22 20130101;
B24B 5/22 20130101; C21D 2261/00 20130101; B24B 27/033 20130101;
B21J 1/025 20130101; C21D 7/10 20130101; B21C 25/02 20130101; C21D
9/0075 20130101; B21D 11/14 20130101; B21D 43/006 20130101 |
International
Class: |
B21D 11/14 20060101
B21D011/14; B21D 11/22 20060101 B21D011/22; B21C 25/02 20060101
B21C025/02; B21D 43/00 20060101 B21D043/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 20, 2017 |
KR |
10-2017-0034782 |
Claims
1. A torsional severe plastic deformation method for a metal bar,
comprising: applying torsion to a metal bar; and removing a surface
defect on the surface of the metal bar, the surface defect being
caused by the applying of torsion, wherein the removing of the
surface defect is carried out in a continuous manner in which the
removing of the surface defect is performed together with the
applying of torsion or in a discontinuous manner in which the
applying of torsion is temporarily stopped and then the applying of
torsion is performed, and the removing of a surface defect
increases the amount of torsional rotation or the shear strain
applied to the metal bar.
2. The torsional severe plastic deformation method for a metal bar
of claim 1, wherein the removing of a surface defect comprises a
polishing process.
3. The torsional severe plastic deformation method for a metal bar
of claim 2, wherein a silicon carbide (SiC) grinding paper is used
for the polishing process.
4. The torsional severe plastic deformation method for metal bars
of claim 2, wherein the polishing process is performed by using a
polishing material that can reduce the surface roughness of the
metal bar according to the increase in the amount of torsional
rotation or shear strain.
5. The torsional severe plastic deformation method for a metal bar
of claim 4, wherein when the polishing process is performed in a
discontinuous manner, the polishing process is performed so that
the surface roughness of the metal rod is 5 um or less per torsion
process.
Description
TECHNICAL FIELD
[0001] The present invention relates to a torsional severe plastic
deformation method for a metal bar, to which surface polishing is
applied, and more particularly, to a torsional severe plastic
deformation method for a metal bar that is capable of improving the
mechanical properties of a material by forming a gradient structure
through shear deformation formed by applying a huge shear stress
through torsion while substantially maintaining the shape of the
metal bar, and by ultrafine crystallization or nano-crystallization
of fine structures of a metal pipe material.
BACKGROUND ART
[0002] When plastic deformation is applied to a metal material, a
dislocation cell structure having a small boundary angle is formed,
and a phenomenon occurs in which the greater the amount of plastic
deformation, the greater the crystal grain boundary angles of
dislocation cell sub-grains, and the finer crystal grains gradually
become. Using this, when a large plastic deformation is applied to
a material and crystal grains thereof are thereby ultrafinely
crystallized and nano-crystallized, the material has remarkably
improved mechanical properties (strength, hardness, polishing
resistance, superplasticity, etc.). Thus, there is growing
importance and demand for a processing method for producing
ultrafine/nano crystal materials, beyond a conventional material
processing method which is mainly for shape formation.
[0003] Not only an amount of plastic deformation, such as
compressive, tensile, and shear deformation, is important for the
formation of ultrafine/nano crystal grains, but also the design of
a die is important such that repeated processes capable of applying
a large amount of plastic deformation may be performed and the
shape of the material is substantially the same before and after
the process.
[0004] Severe plastic deformation methods such as an equal channel
angular pressing (ECAP) process, a high-pressure torsion (HPT)
process, an accumulative roll bonding (ARB) process, and an equal
channel angular rolling (ECAR) process, which meet the above
requirements, have been developed to date.
[0005] However, when an ultrafine/nano crystal material is formed,
the phenomenon occurs in which the strength and hardness of the
material are improved, but ductility of the material decreases. A
gradient structure of crystal grain sizes has been proposed as an
alternative for solving the phenomenon of decreasing ductility.
When a metallic material has a gradient structure of the crystal
grain sizes thereof, ductility increases in a region formed of
large crystal grains, and strength and hardness are improved by a
region formed of ultrafine/nano crystal grains, and thus, opposed
mechanical properties may both be achieved. Thus, for ultrafinely
crystallized/nano-crystallized metal materials, a gradient
structure has emerged as a solution for the ductility decrease
problem.
[0006] A gradient structure may be formed through a high-pressure
torsion (HPT) process among the existing sever plastic processing
methods, but this processing method has a disadvantage that the
size of the produced material is limited because of requiring high
pressure. Thus, a simple torsion process is being required as a
processing method for producing a bulk material having a gradient
structure.
[0007] Such a torsional extreme-plastic process is stopped by a
shear fracture phenomenon, but there is a case of being stopped
while sufficient plastic deformation is not applied, and thus, a
method for delaying a shear fracture phenomenon is being required.
A torsional processing method has a characteristic that the greater
the distance from a center axis, the greater the amount of
deformation applied. Thus, a defect is caused on the surface to
which the largest amount of deformation is applied, and a shear
fracture phenomenon proceeds at the point at which the defect
occurs while a process proceeds.
DISCLOSURE OF THE INVENTION
Technical Problem
[0008] An object of the present invention is to provide a torsional
severe plastic deformation method for a metal bar with which larger
deformation processing than existing torsional processing can be
performed by adding a surface polishing process in a process of
adding torsional severe plasticity to an existing metal bar, fine
structures may be ultrafinely crystallized or nano-crystallized,
and the mechanical properties of the metal bar may be improved by
forming a gradient structure of crystal grain sizes.
Technical Solution
[0009] According to an embodiment of the present invention, there
is provided a torsional severe plastic deformation method for a
metal bar, which includes: applying torsion to a metal bar; and
removing a surface defect on the surface of the metal bar, the
surface defect being caused by the applying of torsion, wherein the
removing of the surface defect is carried out in a continuous
manner in which the removing of the surface defect is performed
together with the applying of torsion or in a discontinuous manner
in which the applying of torsion is temporarily stopped and then
the applying of torsion is performed, and the removing of a surface
defect increases the amount of torsional rotation or the shear
strain applied to the metal bar.
Advantageous Effects
[0010] According to a torsional severe plastic deformation method
of the present invention, a gradient structure of crystal grain
sizes may be formed by applying shear deformation while maintaining
the shape of a metal bar, and fine structures may be ultrafinely
crystallized, and thus, the mechanical properties of the material
may be improved. In addition, the torsional severe plastic
deformation method of the present invention may improve the degree
of gradient and the degree of fine crystallization of fine
structures by applying a more amount of deformation than existing
torsional deformation through surface polishing. In addition, the
torsional severe plastic deformation method of the present
invention may adjust torsional deformation and mechanical
properties by adjusting a rotation speed.
[0011] In addition, the torsional severe plastic deformation method
of the present invention is capable of freely adjusting the amount
of deformation applied to a material by adjusting the rotation
speed of a die, and thus is easy to reinforce the physical
properties of metal bars and adjust fine structures of the metal
bars.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a view illustrating a torsional severe plastic
deformation method and processing equipment according to an
embodiment of the present invention.
[0013] FIG. 2 is a view illustrating a cross-sectional surface of a
specimen used in an embodiment of the present invention.
[0014] FIG. 3 is a view illustrating each of metal bars before and
after a torsional severe plastic deformation according to an
embodiment of the present invention.
[0015] FIG. 4 is a result of comparing the hardness of a metal bar
according to an embodiment of the present invention with that of an
existing metal bar.
[0016] FIG. 5 is a schematic view illustrating a region for which
an analysis has been performed on a metal bar processed according
to an embodiment of the present invention.
[0017] FIG. 6 is a result of electron back-scatter diffraction
(EBSD) analysis on a metal bar on which simple torsional processing
is completed.
[0018] FIG. 7 is a result of electron back-scatter diffraction
(EBSD) analysis on a metal bar according to an embodiment of the
present invention.
[0019] FIG. 8 is a table comparing simple torsion processing on a
metal bar and an embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0020] Hereinafter, the present invention will be described in more
detail on the basis of preferred embodiments of the invention.
However, the following embodiments are merely examples for helping
understanding of the invention, and the scope of the invention is
not reduced or limited by the embodiments.
[0021] In the present invention, it is proposed that a process of
continuously removing surface defects is added to an existing
torsion process to delay a shear fracture phenomenon, and processes
for forming ultrafine crystal grains or nanocrystal grains are
improved by applying a sufficient amount of plastic deformation to
a material.
[0022] When applying the surface treatment of the present
invention, much greater deformation by further delaying surface
fracture than existing torsional severe plastic deformation
methods, and the degree of ultrafine crystallization or nano
crystallization may be reinforced to be finer.
[0023] FIG. 1 is a view illustrating a torsional severe plastic
deformation method and processing equipment according to an
embodiment of the present invention.
[0024] FIG. 2 is a view illustrating a cross-sectional surface of a
specimen used in an embodiment of the present invention.
[0025] Referring to FIGS. 1 and 2, a torsional severe plastic
deformation method for metal bars according to an embodiment of the
present invention includes: a process of applying torsion to a
metal bar; and a process of removing surface defects caused on the
surface of the metal bar by the process of applying torsion,
wherein the process of removing the surface defects is carried out
in a continuous manner of being performed along with the process of
applying torsion or in a discontinuous manner of being performed
while temporarily stopping the process of applying torsion, and a
torsional rotation amount and a shear strain which are applied to
the metal bar may be increased.
[0026] Specifically, the process of applying torsion may include:
installing a metal bar between a pair of dies; and performing
torsion of the metal bar by rotating at least one of the pair of
dies.
[0027] For example, dies conforming to the shape of the metal bar
are attached on both upper and lower sides of the metal bar, a
surface polishing operation is performed while applying torsion to
the metal bar, and a gradient structure of crystal grain sizes may
be formed while ultrafinely crystallizing or nano-crystallizing the
fine structures of the metal bar.
[0028] Here, in the performing of torsion of the metal bar, the
gradient structure of crystal grain sizes may be formed in the
metal bar by using shear deformation formed by shear stress.
[0029] The process of removing surface defects may include a
polishing process.
[0030] Here, the polishing process may be performed by using a
silicon carbide (SiC) polishing paper or by using a polishing
material in which the greater a torsional rotation amount or a
shear strain, the smaller the surface roughness.
[0031] In addition, in the surface polishing process, the metal bar
is separated from the dies, and then the surface of the metal bar
may be polished in a discontinuous manner or the surface of the
metal bar fixed by the dies may be polished in a continuous
manner.
[0032] At this point, in the surface polishing process, a silicon
carbide (SiC) grinding paper having the size of .times.400,
.times.600, .times.800 and .times.1200 may be used. The surface
roughness of each silicon carbide grinding paper is 22 .mu.m, 15
.mu.m, 10 .mu.m or 5 .mu.m, and when surface polishing is performed
with a specific silicon carbide polishing paper, the surface
roughness of the specimen (metal bar) is formed to be the
corresponding roughness or below.
[0033] In addition, when discontinuously performing the surface
polishing process, the surface roughness of the polished surface
formed during the torsion process may be reduced through polishing
by at most approximately 5 .mu.m per one-cycle surface polishing
process.
[0034] If a procedure proceeds to a next process without polishing,
in the surface polishing process, the surface defects formed by
torsion to have a roughness of at most approximately 5 .mu.m, there
occurs a problem in that a shear fracture phenomenon proceeds from
the remaining defects and the torsion process is stopped. In
addition, when the surface polishing is excessively performed even
though the surface defects have been removed, there may occur a
problem in that the cross-sectional area of the specimen
decreases.
[0035] When proceeding the torsion process at a constant rotation
speed, the shear fracture phenomenon occurs according to the
inherent property of a material and the maximum torsional rotation
amount or the maximum shear strain at which deformation is stopped
may be different.
[0036] In the present invention, in order to increase the maximum
torsional rotation amount or the maximum shear strain of each
material by delaying the shear fracture phenomenon through the
surface polishing, the surface polishing operation may be performed
in the order of silicon carbide (SiC) polishing papers of
.times.400, .times.600, .times.800 and .times.1200 in the process
of applying torsion. Here, as approaching the maximum torsional
rotation amount or the maximum shear strain of a metal bar, surface
defects at the point to which stress (stress) is concentrated are
removed by increasing the frequency or the number of surface
polishing operations, and thus, the efficiency of increasing the
maximum torsional rotation amount or the maximum shear strain may
be maximized.
[0037] The torsional severe plastic deformation method of the
present invention applies more plastic deformation by increasing
the maximum torsional rotation amount or the maximum shear strain
than existing metal bars, and achieves improved ultrafine
crystallization or nano-crystallization and the formation of a
gradient structure of crystal grain size, whereby it is easy to
reinforce the property of the metal bar and to adjust the fine
structures of the metal bar. In addition, the torsional severe
plastic deformation method of the present invention may improve the
strength and hardness by applying more plastic shear deformation
than the existing simple torsion process through surface
polishing.
[0038] FIG. 3 is a view illustrating each of metal bars before and
after a process of applying torsion according to an embodiment of
the present invention.
[0039] FIG. 4 is a result of comparing the hardness of a metal bar
according to an embodiment of the present invention with that of an
existing metal bar. Referring to FIG. 4, it may be confirmed that a
metal bar according to an embodiment of the present invention
receives a more deformation amount by surface polishing and has an
improved hardness.
[0040] FIG. 5 is a schematic view illustrating a region for which
an analysis has been performed on a metal bar processed according
to an embodiment of the present invention.
[0041] FIG. 6 is a result of electron back-scatter diffraction
(EBSD) analysis on a metal bar on which simple torsion processing
is completed. Here, an analysis has been performed on the basis of
the position in FIG. 5.
[0042] FIG. 7 is a result of electron back-scatter diffraction
(EBSD) analysis on a metal bar according to an embodiment of the
present invention. Here, an analysis has been performed on the
basis of the position in FIG. 5.
[0043] FIG. 8 is a table showing results of comparison between
simple torsion processing on a metal bar and an embodiment of the
present invention. Referring to FIG. 8, the degree of ultrafine
crystallization or nano-crystallization on a metal bar according to
an embodiment of the present invention may be confirmed.
[0044] According to a torsional severe plastic deformation method
of the present invention, a gradient structure of the crystal grain
sizes can be formed by applying shear deformation on a material
while maintaining the shape of the metal bar, and ultrafine
crystallization of fine structures may be achieved, and thus, the
mechanical properties of the material may be improved.
[0045] In addition, the torsional severe plastic deformation method
of the present invention may improve the degree of gradient and the
degree of fine crystallization of fine structures by applying a
more amount of deformation than existing deformation through
surface polishing.
[0046] In addition, the torsional severe plastic deformation method
of the present invention may adjust torsional deformation and
mechanical properties by adjusting a rotation speed.
[0047] In addition, the torsional severe plastic deformation method
of the present invention may freely adjust the amount of
deformation applied to a material by adjusting the rotation speed
of a die, thereby easily reinforcing the physical properties of
metal bars and adjusting fine structures.
[0048] So far, the technical idea of the present invention has been
described with reference to the accompanying drawings, but this is
for merely illustrating a preferred embodiment of the present
invention rather than limiting the present invention. In addition,
it is obvious that any one skilled in the art could carry out
various modification and imitation without departing from the scope
of the technical idea of the present invention.
* * * * *