3CR12 Technical Data

Summary

3CR12 is a chromium containing corrosion resisting ferritic 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

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

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 3CR12Note: A detailed 3CR12 fabrication guideline is available from Columbus Stainless.

Cutting

For general fabrication requirements, the most effective cutting methods are:

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 +- 150^oC . 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 750^oC, annealing may be required. Annealing is carried out at 700-750^oC followed by air cooling.
Soaking times are 12hours per 25mm section.

Stress Relieving

Stress relieving is not recommended for 3CR12. If it is essential, temperatures of not more than 450^oC should be employed.

Hot Forming

Any hot forming should preferably be conducted at temperatures below 750^oC. The recommended temperature range is between 600^oC and 700^oC and annealing should be performed after forming.