05-06-2013, 12:53 PM
Research on Material Properties and Frictional Characteristics of 20CrMnTi Alloy at Room Temperature
Research on Material.pdf (Size: 927.77 KB / Downloads: 58)
Abstract:
20CrMnTi is a lowcarbon
alloy steel massively used in China, but the research about material properties and frictional
characteristics of 20CrMnTi alloy at room temperature has been seldom reported, thus leading to the lack of robust physical foundation
for the establishment of cold precision forming technology and the lack of basic data for numerical simulations involving 20CrMnTi
alloy. Material properties including basic mechanical properties and stressstrain
constitutive equation of 20CrMnTi alloy after
isothermal spheroidization are determined based on tensile tests at room temperature. Meanwhile, a series of ring compression tests in
combination with finite element (FE) simulations are executed in order to derive the frictional characteristics of 20CrMnTi alloy in bulk
forming under different lubrication conditions. The verification of the determined material properties and friction boundary conditions is
conducted via a case study of cold rotary forging of a 20CrMnTi alloy spur bevel gear. It is through the simulation and experiment that
this paper determines the basic mechanical properties and frictional characteristics of 20CrMnTi alloy, which can not only offer the
scientific reference basis for the reasonable establishment of cold precision forming processes of 20CrMnTi alloy, but also provide the
precision material model and friction conditions for numerical simulations relating to 20CrMnTi alloy.
Introduction
Material properties and frictional characteristics (friction
boundary conditions) are the most important basic
parameters for FE simulations, the precision of which can
considerably influence the precision of FE simulation
results. 20CrMnTi (China specification) is a lowcarbon
alloy steel massively used in China for fabricating some
typical automobile components such as transmission gears,
gear rings and gear shafts under the condition of highspeed
impact and heavy loads.
Research on Material Properties
Tensile tests
Due to the high strength and deformation resistance of
20CrMnTi alloy under delivery state, it is difficult to carry
out the cold plastic forming with large deformation.
Consequently, annealing heat treatment should be applied
in the practical production to decrease the deformation
resistance and enhance the plasticity of 20CrMnTi alloy
workpiece. In this experiment, the tensile test specimens
were all machined from the 20CrMnTi alloy bar after the
isothermal spheroidizing annealing (Fig. 1), whose
chemical composition is given in Table 1. Specimen
dimensions specified in line with the China GB/T2282002
standard were utilized, as illustrated in Fig. 2. Zwick Z100
materials testing machine with a capacity of 100 kN was
used for testing. Meanwhile, to measure accurately Young’s
modulus E, a raster extensometer was adopted in all the
tests. In addition, the experimental loading speed was well
controlled by a constant strain ratee& of 0.6 min –1 (0.01 s –1 )
in consideration of the negligible effect of e& on the
stressstrain
curves at room temperature.
Research on Frictional Characteristics
The friction at the dieworkpiece
interface in plastic
forming processes is accompanied with plastic flow of
deformed metal, which is completely different from that
among mechanical parts. Because of the highly important
nature of friction, many methods have been proposed to
analyze the friction between die and workpiece. Among
these methods, the ring compression test has gained wide
acceptance to measure the friction coefficient or friction
factor at the dieworkpiece
interface in that there is no need
for force measurement during the test, nor a knowledge of
the yield strength of the material [12–16] . As schematically
shown in Fig. 4, the ring compression test involves the
compression of a ring specimen by a simple open die.
When the ring specimen is plastically compressed between
two flat platens, the inner diameter of the ring is extremely
sensitive to friction: increasing friction results in an inward
flow of the material, while decreasing friction results in an
outward flow of the material. According to the sensitivity
of the inner diameter of the ring to friction, the
measurement of the inner diameter of a compressed ring
specimen gives a particular knowledge about the friction
coefficient or friction factor at the dieworkpiece
interface.
Conclusions
(1) Basic mechanical properties and stressstrain
constitutive equation of 20CrMnTi alloy are determined
through tensile tests at room temperature.
(2) Friction boundary conditions of 20CrMnTi alloy
lubricated with different lubricants in bulk forming are
derived by comparing the calibration curves with
experimental results obtained from ring compression
tests.
(3) The material properties and friction conditions of
20CrMnTi alloy have been successfully verified via a
case study of cold rotary forging of a 20CrMnTi alloy
spur bevel gear.
(4) The research results obtained can not only offer the
useful guidance for the reasonable establishment of cold
precision forming processes of 20CrMnTi alloy and the
proper selection of forming equipment, but also provide
the precision material model and friction boundary
conditions for numerical simulations referring to
20CrMnTi alloy.