Papers
in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(vol.44 no.505
January 2003)
Wear Resistance
and Resistance to Surface Roughening of Piercer Roll with High Carbon
Content and Low Hardness
Shoitsu SEO, Satoshi
MATSUOKA, Taro KANAYAMA and Akira YORIFUJI
(Received on December
14, 2001)
The piercer roll used
in seamless pipe manufacturing mills is expected to have wear resistance
and bite efficiency. Usually, low carbon alloyed cast steels are applied
to the piercer roll;however, low wear resistance is observed. In order to
improve the wear resistance of the piercer roll, four test samples with
high carbon content and low hardness are studied and test rolls are manufactured
based on the test results. The main results obtained are as follows:1) The
microstructure of the new piercer roll material consists of ferrite and
spheroidal carbide. 2) The carbides except spheroidal carbide cause heat
cracks by thermal shock and decrease wear resistance and surface roughness.
3) In the case of high-temperature wear resistance testing, material with
the microstructure of ferrite matrix containing much carbide shows good
wear resistance compared to material with that of pearlite matrix. 4) The
ferrite is worn by the abrasion mechanism and pearlite causes adhesion and
peeling off. 5) The low-hardness roll with excellent wear resistance consists
of spheroidal carbide and ferrite, which is gripping carbide and is worn
while keeping the effective surface roughness to bite efficiency.
Key words: tube rolling, wear test, piercer roll, low hardness, wear
resistance, bite efficiency
Detection of Damage
and Fracture of Forging Tools by Fractal Property of Acoustic Emission
Kunio HAYAKAWA,
Tamotsu NAKAMURA,
Hideki YONEZAWA and Shigekazu TANAKA
(Received on May
13, 2002)
Detection of damage
and fracture of forging tools via the fractal property of acoustic emission
(AE) is performed. First, the tensile test of tool steel SKD11 is conducted
to elucidate the fractal dimension of deformation-and fracture-induced AE
of the material. Resultant fractal dimensions are 1.97 and 1.44. Next, the
change in fractal dimension of AE from a die insert was detected under cyclic
cold forward extrusion. Workpieces processed by conversion coating were
used to eliminate the effect of friction on AE. After 300 cycles of extrusion,
no damage and wear can be observed on the die surface, and the fractal dimension
is almost constant at 2.04 on average. Then, another series of cyclic extrusion
was performed with mineral oil VG2 and stearic acid to promote the onset
of damage of the die. At 101st cycle of extrusion, a defect on the workpiece
can be observed, which results from the onset of crack on the die radius.
The former average fractal dimension, 2.01, of the onset of the crack changed
to 1.52 after the onset of the crack. From the results, the fractal dimension
can be concluded to be one of the most effective indicators of the progress
of damage to a die. Finally, a method for separating the die-induced AE
from the total AE is proposed based on the Kaiser effect.
Key words: cold forward extrusion, acoustic emission, fractal dimension,
crack, Kaiser effect
Prediction of Stress-Strain
Curves of Particulate-Reinforced Metal Matrix Composites with Voronoi
Finite-Element Polycrystal Model
Hiroshi TAKAHASHI,
Ryo KATAOKA and Takahisa OHNUKI
(Received on May
20, 2002)
Uniaxial stress-strain
behaviours of particulate-reinforced metal matrix composites are predicted
by the finite-element polycrystal model, where some elements are alumina
(Al2O3) particles and the remainder are aluminium matrix. The three-dimensional
Voronoi discretization is employed so as to ensure the morphological isotropy
of the model. Softening mechanisms such as the debonding and crushing of
particles are replaced by virtual yielding of particles. Specimens of 10%
and 20% volume contents are made by the powder liquid forging process, and
the stress-strain curves are obtained by tension and compression tests.
The numerical simulations showed good agreement with the experimental results.
Key words: particulate-reinforced metal matrix composite, powder
liquid forging, finite-element polycrystal model, Voronoi element, deformation-load
property, material design
Drawing Force and
Forming Load in Reshaping Cylindrical Steel Pipes into Square Shapes
by Draw Bench Method
Xin GUAN, Yoshitomi
ONODA, Eiji WAKAMATSU,
Sadao KIMURA and Takeo KITAWAKI
(Received on June
3, 2002)
Characteristics of the
drawing force acting on a hydraulic cylinder ram and the forming load acting
on each pair of idler rolls are experimentally investigated in a draw bench
process for reshaping cylindrical steel pipes (t0/D0=2.2~4.5%, t0=initial
wall thickness, D0=initial outer diameter) into square shapes (69*69, 72*72,
75*75mm). The results are compared with the results obtained by extroll-forming.
The drawing force is found to increase with the increase in the reduction
and the increase in the cross-sectional size ratio t0/D0 of a mother pipe.
The forming load acting on each pair of idler rolls is also found to increase
with the increase in the drawing force acting on the rolls concerned. From
these experimental results, equations for estimating the drawing force and
the forming load are formulated.
Key words: roll forming, tube forming, draw bench, extroll-forming,
cylindrical welded steel pipe, square pipe, drawing load, pushing load,
forming load, rigid-plastic FEM
Butt Bonding of
Zirconia Ceramics by Superplastic Deformation
Toshio YOKOYAMA,
Keisuke YAMAMOTO and Takashi SAYANO
(Received on June
5, 2002)
Bonding of zirconia
polycrystals(Y-TZP) was attempted by making use of superplastic compressive
deformation. The bonding method is butt bonding by longitudinal axial stress
occurring under compression in the direction perpendicular to the longitudinal
axis. Effects of compressive stress and strain on the success of solid-phase
bonding and on bonding strength were studied. Experimental conditions are
1450 Cels degrees for bonding temperature, 5 and 10 MPa for initial compressive
stress, and 0.5 to 20% for compressive strain. In addition, friction
between pressure plates and specimens appears to be the important factor
in butt bonding, so the influence of friction on butt bonding was also studied
by the use of pressure plates that had different magnitudes of surface roughness.
The friction coefficient of these plates against the Y-TZP specimen was
measured at 1450 Cels degrees by the Hill's compression test method. As a
result, the conditions for successful bonding were determined for the experimental
factors mentioned above. It was confirmed that the increase of friction
between the pressure plates and the specimen decreased the compression speed
and suppressed the elongation of the specimen in the longitudinal direction.
Bonding strength increased as the compressive strain and friction coefficient
increased.
Key words: joining, solid-phase bonding, forming property, superplasticity,
zirconia ceramics, friction test
Shot Peening Process
of Inner Surface of Machine Parts Using Rebound Shots
Yasunori HARADA,
Ken-ichiro MORI, Takehiro FUJIOKA and Seijiro MAKI
(Received on June
19, 2002)
The shot peening process
of the inner surface of machine parts using rebound shots was investigated.
In this process, a compressed air type shot peening machine was employed.
The jig used for rebound shot peening has a surface with a slope. The shots
rebounded by the rebound jig collide with the inner surface. The influence
of processing conditions on the distributions of residual stress and surface
roughness in the test pieces of pipes and coiled springs was measured. A
stress peening process for the inner surface of coiled springs using rebound
shots was also performed. The collision direction of shots was vertical
to the inner surface when the angle was 45 degrees . The influence of
shot peening increases with the increase of the kinetic energy of shots.
Using rebound shot, the coiled spring received higher compressive residual
stresses by the stress peening process. The results of the fatigue test
showed that the fatigue life of the spring was improved. It was found that
the present process was suitable for the improvement of the inner surface
of machine parts.
Key words: shot peening, rebound shot, residual stress, surface roughness,
pipe, coiled spring, stress peening
Copyright (C)1997- 2003 JSTP. All Rights Reserved.
|
|
|