3CR12
Technical Data
Summary
3CR12
is a chromium containing corrosion resisting steel developed
as an alternative material of construction where the mechanical
properties, corrosion resistance and fabrication requirements
of other materials such as mild steel, galvanised or aluminised
steel, aluminium or pre-painted steels are unsuited.
Originally
3CR12 was not included in any international specifications.
However, a 12 per cent chromium steel developed from 3CR12
has been designated DIN type 1,4003 and ASTM/ASME 41003.
The former has been incorporated into two Euronorm Standards
viz. EN 10088 and EN 10028, 3CR12 conforms to the requirements
of the above specifications and is multi certifiable to
3CR12, 1.4003 and 41003, due to its inclusion in the above
specifications. 3CR12 vessels and tanks can be designed
in accordance to BS5500, ASME, AD Merkblatter codes and
the Euronorm design specification currently in preparation.
Although
3CR12 is recognised as the World's most specified 12%
Chromium utility steel, it is by no means universal and
should not be substituted for higher grades of stainless
steel unless detailed corrosion testing has been carried
out. Columbus Stainless can be consulted for advice in
this regard.
3CR12
was designed as a corrosion resisting steel and, as such,
will exhibit staining when exposed to aggressive atmospheric
conditions. In applications where aesthetic appearance
is important, it is recommended that 3CR12 is painted,
or a higher grade should be used.
A
long term atmospheric corrosion programme conducted over
20 years bv the CSIR has shown 3CR12 to have very good
atmospheric corrosion resistance, Stainless steels, with
their higher chromium contents, exhibited very low corrosion
rates. Because of 3CR12's inherent corrosion resistance,
it has been used successfully under wet sliding abrasion
conditions such as found in the mining and bulk handling
industries. In the case of mild or low alloy steels the
presence of moisture in the solids being transported aggravates
deterioration of the working surfaces. Not only does the
surface rust wear away rapidly exposing bare metal to
further corrosion, but corrosion of the working surface
leads to 'hang-up' and interrupted flow. 3CR12 resists
the corrosive attack and thereby improves flow and reliability,
while extending the life of the solids handling equipment.
Although
3CR12 performs very well in corrosion-abrasion applications,
no real benefit can be gained by using it under dry abrasion
conditions. 3CR12 is not especially suitable under conditions
of impact abrasion. (See: A Guide to the Use of 3CR12
in Corrosion Abrasion Applications).
3CR12
has been extensively used in aqueous environments, and
has been successful in many applications involving exposure
and/or immersion. It is important when using 3CR12 in
aqueous environments that the decision be based on a thorough
water quality analysis and microbial count. (See: A Guide
to the use of 3CR12 in Water).
3CR12
is designed with ease of fabrication in mind and its composition
and properties result in good forming, drawing, blanking
and punching characteristics. The steel is easily welded
by any of the recognised welding processes and should
be post weld pickled/cleaned and passivated.
3CR12
has been included in SABS 0162 Part 4 - Code of Practice
for the Structural Use of Steel. When replacing carbon
steel with 3CR12, it is necessary to redesign mild and
constructional steel components using the mechanical and
corrosion resisting properties of 3CR12 in order to gain
full advantage of potential material and fabrication savings.
This
document covers black (hot rolled and annealed) 3CR12
as well as pickled (No1 and 2B) material, 3CR12 is available
in the following finishes HRA, No 1, 2D and 2B, Whereas
the latter three finishes can be used for all suitable
3CR12 applications, the HRA finish should only be used
in applications where wet sliding abrasion occurs. It
should never be used in immersion conditions The mechanical
properties of the HRA material are similar to those of
the No 1 finish material. A long term atmospheric programme
conducted over 20 years by the CSIR has shown 3CR12 to
have very good atmospheric corrosion resistance.
Properties
of 3CR12
Chemical Composition
| %C |
%Ni |
%Mn |
%Si |
%P |
%S |
%Cr |
Other |
0.03
Max |
1.5
Max |
1.5
Max |
1.0
Max |
0.03
Max |
0.03
Max |
11.0
- 12,0 |
Ti
0.6 Max |
1. Mechanical
Properties
| Ultimate
Tensile Strength (Transverse) |
450
MPa Min |
0.2%
Offset Proof Strength
(Transverse) |
<
6,0 mm thick - 320 MPa Min
> 6,0
mm thick - 280 MPa Min |
| Elongation
(in 50mm) |
<
6,0 mm thick
= 20% Min |
|
> 6,0
mm thick = 18% Min |
| Hardness |
<
12.0 mm thick
- 220 Brinell Max |
|
> 12.0
mm thick - 250 Brinell Max |
| Charpy
Impact (Ambient temperature) |
35
J/cm2 Min |
2.
Fatigue
Extensive
testing has shown that 3CR12 behaves in a similar manner
to constructional steels such as BS4360 Grade 43A in terms
of fatigue. Accepted procedures when desgning for fatigue
loaded structures should be followed. BSBS7068 can be
used.
3. Physical Properties
| At
Room Temperature. |
|
|
| Density |
|
7 740
kg/m3 |
| Elastic
Modulus (Tension) |
|
200
GPa |
| Specific
Heat Capacity |
|
478
J/kg K |
| Thermal
Conductivity |
@
100oC
|
30.5
W/m K |
|
|
@
500oC
|
40.0
W/m K |
| Electrical
Resistivity |
|
66 x
10-9Wm
|
| Co-efficient
of |
0-100oC
|
11,1
mm/mK |
| thermal
expansion
|
0-300oC
|
11.7
mm/mK
|
| |
0-700oC
|
12.3
mm/mK
|
| Melting
Range |
|
1'430
- 1'510oC |
| Relative
Permeability |
|
Ferromagnetic |
4.
Corrosion Resistance
3CR12,
with chromium as its major alloying element, is not intended
as a material for use in contact with process solutions
such as acids, salts, etc. It is more suited to
applications involving ancilliary equipment on process
plants such as cable racking, stairways, flooring, handrailing,
etc. 3CR12 is a "corrosion resistant" rather than
"stainless" steel and as such, will tend to form a light,
surface rust or discolouration when exposed to aggressive
environments. This patina is superficial and does
not affect the mechanical properties of the steel.
Should aesthetic or hygienic
qualities be of prime importance, stainless steels rather
than 3CR12 should be considered, although 3CR12 can be
successfully painted with a number of paint systems.
Aqueous
Corrosion
It
is recommended that consultations be held with Columbus
Stainless technical staff on the use of 3CR12 in water.
At the design stage, efforts
must be made to avoid crevices, sedimentation, stagnancy,
high operating temperatures etc., as these facts will
have a negative impact on the performance of the steel.
3CR12 is not recommended
for use in hot water systems unless detailed testing has
previously been carried out.
Atmospheric
Corrosion
A
long term atmospheric corrosion programme conducted over
10 years by the CSIR has shown 3CR12 to have very good
atmospheric corrosion resistance. Data on the performance
of various materials at different test sites is available
from VRN Technical staff.
5.
Fabrication of 3CR12
Note:
A detailed 3CR12 fabrication guideline is available from
Columbus Stainless.
Cutting
For
general fabrication requirements, the most effective cutting
methods are:
| Abrasive
disc |
- use
dedicated discs |
|
- avoid
overheating |
|
- vitrified or resinoid aluminium oxide discs recommended
|
|
|
| Plasma |
- oxygen-free
nitrogen is the most economical primary cutting
gas.
(Other gasses can be used) |
|
- heat
discolouration must be removed prior to use in a corrosive
environment |
|
|
| Guillotine |
- use well sharpened and correctly alligned and set
blades to avoid sheared
breaks and rollover. |
|
- capacity of guillotine (rated in terms of mild steel
thickness) must be
downrated by 40% of 3CR12. |
Forming
It
is important to note that due to the higher proof strength
of 3CR12, more power is required for most forming operations,
than would be needed for mild steel.
When bending 3CR12 it is
important to maintain a minimum inner bend radius equal
to twice the material thickness. Reverse bending
at ambient temperatures is not recommended - the bend
area should be preheated to +- 150oC .
Edge cracks can be avoided by placing the cut face on
the outside radius of the bend and the sheared face on
the inside. This type of cracking can also be prevented
by grinding the outside radius point of bending into a
rounded profile, thus eliminating the natural stress concentration
point.
Welding
Manual
metal arc, metal inert gas and tungsten inert gas are
the common procedures used. All welding procedures
must ensure that heat inputs are kept to a minimum.
Down-hand welding is the preferred welding position and
bead runs rather than weaving should be used. Austenitic
stainless steel filler metals such as AWS ER 309L, 308L,
or 316L should be used.
In order to ensure adequate
corrosion resistance in weld zones, it is necessary to
remove all heat tint by pickling or by some mechanical
means and passivating with a cold 10% nitric acid solution
after cleaning. Thorough washing with clean, cold
water pickling and passivating is essential.
Machining
In
the annealed condition, 3CR12 has machining characteristics
similar to AISI 430 i.e. a machinability rating of 60.
The reduced extent of work-hardening compared to austenitic
stainless steel eliminates the need for special cutting
tools and lubricants. Slow speeds and heavy feeds
with sufficient emulsion lubricant will prevent machining
problems.
Fastening
Where
3CR12 sections are to be bolted, stainless feel fasteners
such as type 304 or 431 are preferred. If bolted
structures are to be used in humid or wet environments,
it is strongly recommended that compressible, non-absorbant
gaskets such as rubber be used.
Thermal
Processing
Annealing
3CR12 is supplied in the
annealed condition, its softest and most ductile state.
After severe cold forming operations or after hot forming
operations above 750oC, annealing may be required.
Annealing is carried out at 700-750oC
followed by air cooling.
Soaking times are 12
hours per 25mm section.
Stress
Relieving
Stress relieving is not recommended
for 3CR12. If it is essential, temperatures of not
more than 450oC should be employed.
Hot
Forming
Any hot forming should preferably
be conducted at temperatures below 750oC. The
recommended temperature range is between 600oC
and 700oC
and annealing should be performed after forming.
Info by : http://www.askzn.co.za/tech/tech_grade_3cr12.htm
