TECHNICAL FIELD OF THE INVENTION
The present invention relates to a low cost corrosion resistant
stainless steel. More particularly, the invention is concerned about
a stainless steel composition for alleviating corrosion in gas
cleaning units of integrated steel plants.
BACKGROUND AND THE PRIOR ART
Conventional plain carbon mild steels were used extensively for
structural applications and engineering components owing to their
low cost, easy availability and fabricability. Mild steels are also
extensively used in corrosive environments, inspite of their
relatively poor corrosion resistance. Often the inadequate corrosion
resistance of carbon steels is comprehended by providing greater
allowances for corrosion in steel structures.
However the present invention relates to the corrosion resistant
stainless steel composition for alleviating corrosion in gas
cleaning units of integrated steel plants.
US 6299833 describes a steel composition consisting essentially of
Carbon 0.50-0.70 weight %, Silicon up to 0.40 weight %, Manganese
0.55-1.00 weight %, Phosphorus 0.030-0.070 weight %, Sulfur 0.055 to
0.110 weight %, Chromium up to 0.50 weight %, Molybdenum up to 0.10
weight %, Nickel up to 0.5 weight %, Copper up to 0.50 weight %,
Aluminium up to 0.050 weight %. Optionally, Vanadium sufficient to
maintain yield strength, Nitrogen up to 0.030 weight %, together
with, optionally, lead up to 0.4 weight %, and unavoidable
impurities, the balance being iron. This steel composition exhibits
mechanical properties which are suitable for use in connecting rods
but which provide both good fracture splitting performance and good

machinability when compared to C70S6 alloys. The application also
refers to a fracture splittable steel including between 0.50 to 0.70
wt % C, 0.55 to 1.00 wt % Mn, 0.030 to 0.070 wt % P and 0.055 to
0.110 wt % S, and with an elongation of 25% or less, a reduction of
area below 25%, and a V.sub.20 machinability (m/min) satisfying the
equation: where H is the HV30 hardness of the steel. However, a
corrosion resistant stainless steel for alleviating corrosion in gas
cleaning units in integrated steel plants, which is a low-cost
material as well was not known from this prior art.
Thus there is a need to provide a corrosion resistant stainless
steel for gas cleaning plant (CRSGCP).
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a corrosion
resistant stainless steel.
Another object of the present invention is to provide a corrosion
resistant stainless steel composition.
It is yet another object of the present invention to provide a
resistant stainless steel composition for alleviating corrosion in
gas cleaning units of integrated steel plants.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a
corrosion resistant stainless steel composition for alleviating
corrosion in gas cleaning units of integrated steel plants, said
composition comprising :
0.02 - 0.035 wt % C;
0.50 - 1.20 wt % Mn;

0.2 - 0.6 wt % Si;
0.02 - 0.04 wt % P;
0.005 - 0.02 wt % S;
10.0 - 13.0 wt % Cr;
0.03 - 0.50 wt % Ni; and
0.001 - 0.20 wt % Ti.
The other objects and advantages of the present invention will be
apparent from the description provided hereinbelow with reference to
the accompanying figures and detailed description provided herein
below.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly the present invention relates to stainless steel
composition for alleviating corrosion in gas cleaning units of
integrated steel plants. The present invention further overcomes the
drawbacks of carbon steel structure in the gas cleaning plants by
replacing the same with corrosion resistant steel.
The corrosion resistant stainless steel for gas cleaning plant
(CRSGCP) was selected for fabrication of bag house structure in gas
cleaning plant, considering its acceptable corrosion resistance is
achieved by utilizing the minimum Cr (10%-13%) content and techno-
economic aspects. Further the thickness of CRSGCP was 3.15 mm. This
was annealed at 750°C after hot rolling.
The composition (in wt%) of CRSGCP comprises 0.02-0.035 % C; 0.50 -
1.20 wt % Mn;0.2 - 0.6 % wt Si; 0.02 - 0.04 wt % P; 0.005 - 0.02 wt
% S; 0.005 - 0.02 wt % S; 10.0 - 13.0 wt % Cr; 0.03 - 0.50 wt % Ni;
and 0.001 - 0.2 0 wt % Ti. Cr content ranges preferably from 11.0 -
13.0 wt % and more preferably from 11.5 - 13.0 wt %.

The preferable amounts of carbon is 0.034 wt%, manganese is 0.79 wt
%, silicon is 0.31 wt %, nickel is 0.37 wt %, titanium is 0.003 wt %
and sulfur is 0.011 wt %. The average chemical composition of CRSGCP
is further illustrated in table 1 in comparison with AISI 430, AISI
304, AISI 316 and carbon steel.
Table-1: The average chemical compositions in wt % of CRSGCP, AISI
430, AISI 304, AISI 316 and carbon steel.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 describes the complex plane impedance plots for AISI 430,
carbon steel and CRSGCP in 0.5N H2SO4
Figure 2 describes complex plane impedance plots of AISI 304 and
AISI 316 stainless steels in 0.5N H2SO4
Figure 3 describes potentiodynamic polarization plots of carbon
steel, 409M, AISI 304 and AISI 316 stainless steels in 0.5N H2SO4
Figure 4 shows the light optical photomicrograph of base metal of
CRSGCP along transverse cross section direction revealing elongated
ferritic grains

Figures 5 (a) and 5 (b) show SE image of HAZ immediately adjacent to
weld interface and away from weld interface respectively
Figures 5 (c) and5 (d) show X-ray mapping of Cr and C respectively.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows the complex plane impedance (Nyquist) plots for AISI
430, carbon steel and CRSGCP and that for AISI 316 and AISI 304
stainless steels in Figure 2 in 0.5N H2SO4. Equivalent electrical
circuit modeling with R[(QR)] circuit revealed polarization
resistance of 21 Ω .cm2 for CRSGCP steel is 2 times higher than
carbon steel (9 Ω .cm2) and nearly similar to that AISI 430
stainless steel (24 Ω .cm2), which contains 16.6 % Cr (Table 1),
much higher than that of CRSGCP. Polarization resistances of AISI
304 and AISI 316 steels were found to be markedly higher at 11600
and 6080 Ω .cm2 respectively, due to presence of other costly
alloying elements Ni and Mo, and higher Cr content.
Figure 3 shows the potentiodynamic polarization plots of the above
steels in 0.5 H2SO4. All stainless steel along with CRSGCP exhibited
active to passive transition while carbon steel corroded actively.
Comparative corrosion rates and passive current densities obtained
from potentiodynamic plots are provided in table 2 as below. While
the corrosion rate of CRSGCP (10mm/y) is two times higher than that
of AISI 430, it is about three times lower than that of carbon steel
(28 mm/y) . The significantly lower corrosion rate of AISI 304 and
AISI 316, is due to the presence of Ni, Mo and higher Cr content.
The CRSGCP exhibits a passive current density almost similar to that
of AISI 430, AISI 304 and AISI 316 stainless steels. Therefore,
although the initial higher corrosion rate has been noticed for

CRSGCP, with the passage of time, it attains passivity and corrosion
current decreases significantly to a level almost similar to that of
other costly stainless steel materials like AISI 430, AISI 304 and
AISI 316.
Table 2: Corrosion rates and passive current densities for
investigated steels in 0.5N H2SO4 as determined
from potentiodynamic plots

Corrosion rate was also obtained from the weight loss method after
immersing the samples in 0.5N H2SO4 solution for 0.5 hour and 1
hour. As provided in Table 3, the corrosion rate of CRSGCP is much
less than that of carbon steel.

Table 3: Initial and final area, surface area, time of immersion of
samples in 0.5N H2SO4 solution and corrosion rate obtained during
immersion test

Accordingly figure 4 shows the light optical photomicrograph of the
base metal of CRSGCP taken along the transverse cross-section
direction revealed elongated ferritic grains.
Illustrative examples:
Further investigations were conducted to study the sensitization
effect of the CRSGCP steel. Sensitization effect is very common in
stainless steel during thermomechanical processing and welding. The
welding was performed using flux-coated 3.15 mm diameter AISI 309 L
electrode by single pass, shielded metal arc welding (SMAW) process.
The weld joints as well as base metals were sectioned in the
transverse investigated by optical microscopy and EPMA after etching
with Marble's reagent (4 g CuSO4 + 20 ml HCl + 20 ml water). The X-
ray elemental mappings were performed in EPMA on both HTHAZ (high

temperature heat affected zone) and LTHAZ (low temperature heat
affected zone) to locate carbide-enriched region.
The secondary electron photomicrograph of immediately adjacent to
weld interface (figure 5a), and that farther from the weld interface
(figure 5b), did not reveal any precipitate. The X-ray elemental
mapping for Chromium (figure 5c) and carbon (figure 5d) , at the
location near to weld interface (figure 5a), did not show any
enrichment of Cr or C. similarly enrichment of Cr or C was not
noticed from the X-ray mapping of these elements at the location
farther from the weld interface (figure 5b), i.e., these locations
did not reveal any M23C6 type carbide precipitation. Hence
sensitization of CRSGCP did not occur during single pass arc
welding.
Further the CRSGCP exhibited low corrosion rate in comparison to
plain carbon steel, and the corrosion rate and passive density is
comparable with that of AISI 430. Moreover application of CRSGCP
steel containing 11-13% Cr in severely corrosive environments in
steel plants, particularly, in gas cleaning plant, will provide
acceptable corrosion resistant and life span of gas cleaning plant
will be much higher than that of AISI 430 and hence, cost effective
as well as AISI 430 contain higher Cr content.
Corrosion rate obtained from the weight loss test after immersing
the samples in 0.5N H2SO4 solution for 0.5 hour and 1 hour have
provided. However, the low ipass value of CRSGCP, which is similar to
that of other costly stainless steel is an important observation.

WE CLAIM
1. A low-cost corrosion resistant stainless steel composition for
alleviating corrosion in gas cleaning units of integrated steel
plants, said composition comprising :
0.02 - 0.035 wt % C;
0.50 - 1.20 wt % Mn;
0.2 - 0.6 % wt Si;
0.02 - 0.04 wt % P;
0.005 - 0.02 wt % S;
10.0 - 13.0 wt % Cr;
0.03 - 0.50 wt % Ni; and
0.001 - 0.20 wt % Ti.
2. Composition as claimed in claim 1 wherein the Cr content ranges
preferably from 11.0 - 13.0 wt %.
3. Composition as claimed in claims 1 and 2 wherein the Cr content
ranges more preferably from 11.5 - 13.0 wt %.
4. Composition as claimed in claim 1 wherein the carbon content is
preferably 0.034 wt%, manganese content is preferably 0.79 wt
%, silicon content is preferably 0.31 wt %, nickel content is
preferably 0.37 wt %, titanium content is preferably 0.003 wt %
and sulfur content is preferably 0.011 wt %.
5. Composition as claimed in claims 1 to 4 comprising passive
current density of 0.23 pA/cm2 .
6. Composition as claimed in claims 1 to 4 comprising corrosion
rate of 10.00 mm/year.

7. Composition as claimed in claims 1 to 4 comprising corrosion
current density of 87 6 uA/cm2.
8. Composition as claimed in any of the preceding claims further
comprises elongated ferritic grains.

A low-cost corrosion resistant stainless steel composition for alleviating corrosion in gas cleaning units of integrated steel plants, said composition comprising 0.02 - 0.035 wt % C;0.50 - 1.20 wt % Mn;0.2 - 0.6 % wt Si; 0.02 - 0.04 wt % P;0.005 - 0.02 wt % S;10.0 - 13.0 wt % Cr; 0.03 - 0.50 wt % Ni; and 0.001 - 0.20 wt %
Ti.