Steels with high content of nitrogen is perspective materials for
substitution of steels with high content of expensive nickel for
corrosion resistance and heat resistance applications. Increasing of
nitrogen content gives the additional opportunities for strengthening
such steels by the cold working.
At present the high-nitrogen austenite steels (HNAS) are widely used
for fabrication of articles of different purposes due to a possibility
of obtaining their unique properties ( the high level of strength,
plasticity and failure viscosity, the increased corrosion stability
and absence of magnetism, etc. . In this connection the nitrogen, as
the alloying element, is used for the obtaining of steels and alloys
of different purpose. It has become of wide usage in the austenite
steel making, these steels are used in the chemical and power
engineering industry, instrument engineering, ship- and
reactorbuilding, etc.
At the same time, the search of the alloying element optimal
concentrations in HNAS and of the rational conditions for the
treatment and hardening by thermomechanical methods as well as the
high-efficient hydrostatic - working methods, which provide the
required physicomechanical and operation properties in complex, needs
the investigations be done.
The effect of strengthening may be developed by combining of heat
treatment and plastic deformation by high hydrostatic pressure
(hydroextrusion). In current investigations the relationship between
parameters of structure after heat treatment, parameters of plastic
deformation and final mechanical properties of steels with 14% wt. of
Cr, 10% of Mn, additions of Si and V at nitrogen content up to 0,45%
was investigated. It is established, that combination of thermal and
mechanical treatment allows to obtain high complex of mechanical
properties simultaneously with obtaining of needed cross-section of
extruded bars.
The hydrostatic extrusion (HE) is the effective method of forming the
optimal defect structure of metallic materials, including HNAS, which
provides the high-level mechanical properties and operating
characteristics. Under the HE the character of defect structure change
at different scale level is mainly in correspondence with the
peculiarities of defect structure or plastic deformation evolution
under the HHP. The results of the performed investigation of HE effect
on properties and parameters of the HNAS strain hardening was
summarized. The given structure changes condition mainly the
dependence of HNAS mechanical properties on percent reduction e under
the HE. It is seen that the HE results in a 2-2,5 times increase of
the yield strength, in a 1.5-1,8 times increase of the ultimate
strength with the plasticity characteristics remained at a high enough
level.
The obtained experimental results of the study of peculiarities of
HNAS structure changes, physical and mechanical properties and plastic
flow were the basic for the development of the optimal regimes of
treatment and hardening by the hydrostatic extrusion method depending
on nitrogen concentration in solid solution. After deformation
ultimate tensile strength increase in 1,5-1,8 times and yield point -
in 2 - 2,5 times in comparison with heat treatment. Plastic
characteristics keep rather high.
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