According’s to Bureau of Indian Standards, steels can be designated either based on letter symbols {IS: 1962 (Part I)—1974} or based on numerals {IS: 1962 (Part II)}. Minimum number of symbols is recommended to be used in designating any steel.
Under letter symbols of designating carbon and low alloy steels could be designated on the basis of:
(a) Mechanical properties, and
(b) Chemical composition.
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The basis of mechanical property is used where the major criterion for selection of steel is its tensile strength or yield stress. Symbol Fe is used where the basis is tensile strength and Fe E where the basis is yield stress.
These symbols are followed with minimum tensile strength (yield stress) value in N/mm2, figure 00 being used if these values are not guaranteed. The next letter in the code designation is the chemical symbols for such elements whose presence characterises the steel. Finally letters are indicated at fourth place for special characteristics and at fifth place for application, if necessary.
The special characteristics at fourth place could be for:
a. Method of de-oxidation:
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R for rimming (or semi-killed) steel
K for killed steel
b. Steel quality:
It is designated by symbols Q1 to Q5 depending on whether it is non-ageing, free from flakes, controlled grain size, controlled inclusion, and guaranteed internal homogeneity respectively.
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c. Degree of purity:
It gives the maximum content of phosphorus and sulphur in ladle analysis. It is designated by letter ‘P’ followed by 100 times the maximum percentage of phosphorus and sulphur, if they are equal. Thus P 25 means the phosphorus and sulphur content are 0.025 and 0.025% respectively.
If maximum contents of phosphorus and sulphur are not same, then degree of purity is designated by SP followed by 100 times the maximum sulphur rounded off to the nearest integer and 100 times the phosphorus content rounded off to the nearest integer.
d. Weldability guarantee:
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It is represented by symbol W for fusion weldable and W1 for the steel weldable by resistance welding but not fusion weldable.
e. Resistance to brittle fracture:
Depending on the resistance to brittle fracture (as per results of charpy V-notch specimens), steels could be designated by symbols B, B0, B2 or B4.
f. Surface condition:
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For forged or rolled steel, no symbol is used. Other symbols used are S1 for deseamed or scarfed, S2 for descaled, S3 for pickled, S4 for shot or sand blasted. S5 for skinned or peeled, S6 for bright drawn or cold rolled and S7 for ground.
g. Formability (for sheet only):
It is designated by D1 for drawing quality, D2 for deep drawing quality, and D3 for extra deep drawing quality.
h. Surface finish (for sheet only):
It is designated by 14 grades from F 1 for general purpose finish to F 14 for direct annealed finish. Other symbols are F 2 (full finish), F 3 (exposed), F 4 unexposed, F 5 (Matt finish), F 6 (Bright finish), F 7 (plating finish), F 8 (unpolished finish), F 9 (polished finish), F 10 (polished and coloured blue), F 11 (polished and coloured yellow), F 12 (Mirror finish), F 13 (vitreous enamel finish).
i. Treatment:
Symbols T1 to T 14 are used to indicate the treatment given to steel. These are T1 (shot peened), T 2 (Hard drawn), T 3 (Normalised), T 4 (controlled rolled), T 5 (Annealed), T 6 (Patented), T 7 (solution treated), T 8 (solution treated and aged) T 9 (controlled cooled), T 10 (Bright annealed), T 11 (spherodised), T 12 (stress-relieved), T 13 (case hardened), and T 14 (Hardened and tempered).
j. Elevated temperature properties:
Letter H is used where elevated temperature properties are guaranteed, and letter L for guaranteed cryogenic quality.
On the basis of chemical composition, steels are designated as follows:
(a) Unalloyed steel:
(c) Unalloyed free cutting steel:
(d) Low and Medium alloy steels (total alloying elements not exceeding 10%):
The multiplying factors for various alloying elements are:
4 for Cr, Co, Ni, Mn, Si and W
10 for Al, Be, V, Pb, Cu, Nb, Ti, Ta, Zr and Mo
100 for P, S, N.
(Symbol Mn is included if its content > 1%)
(e) High alloy steels (where total alloying elements are more than 10%):
(f) Alloy tool steels:
Same method as tor (e), except that X will be substituted by T for low alloy and medium alloy tool steels, and by XT for high alloy tool steels.
(g) Free cutting steels:
Same method as for low and medium, and high alloy steels as at (d) and (e) above except that the % age of S, Se, Te and Zr will be designated by their symbols followed by 100 times their content.
Schedules for wrought steels for general engineering purposes are given in ARE: 1570 in seven parts as are under:
Part 1. Steels specified by tensile and/or yield properties.
Part 2. Carbon steels (unalloyed steels).
Section 1. Wrought products (other than wires) with specified chemical composition and related properties.
Section 2. Carbon steel wires with related properties.
Part 3. Carbon and carbon manganese free cutting steels.
Part 4. Alloy steels (constructional and spring steels) with specified chemical composition and related mechanical properties.
Part 5. Stainless and heat resisting steels.
Part 6. Alloy tool steels.
Part 7. Steels for elevated temperature services (creep resisting steels).
Steels as per BIS:
Indian standards specification IS: 1570 (on Indian Standard Wrought Steels) have standardised the plain carbon and alloy steels under the following heads:
(a) Steels specified by tensile properties but without detailed chemical composition; and
(b) Steels specified by chemical composition and these are further sub-divided as:
(i) Carbon steels.
(ii) Carbon and carbon manganese free cutting steels.
(iii) Alloy steels other than stainless and heat resisting steels.
(iv) High alloy steels (stainless and heat resisting steels).
(v) Carbon and alloy tool steels.
IS: 1871 provides a commentary on IS: 1570 and it regroups the steels given in IS: 1570 as follows:
(a) Steel specified by tensile properties but without detailed chemical composition.
(b) Carbon and low alloy steels with specified chemical composition and related mechanical properties.
(c) Carbon and carbon-manganese free cutting steels.
(d) Hardened and tempered steels.
(e) Case hardening steels (flame and induction hardening, case carburising, cyaniding, carbo-nitriding).
(f) Creep resisting steels.
(g) High alloy steels (stainless and heat resisting steels including valve steels).
(h) Carbon and alloy tool steels
IS: 1870 provides comparison of Indian and Overseas standards for wrought steels for general engineering purposes in order to enable to select the equivalent steels in Indian Standards.
The following eight equivalents are compared:
BS — British Standard
SAE — Society of Automotive Engineers
AISI — American Iron and Steel Institute
ASM — American Society of Metals
ASTM — American Society of Testing Materials
DIN — German Standards
JIS — Japanese Standards
GOST — Russian Standards.
Designation of Steel Castings and Forgings:
Five types of steel castings are designated as below by Bureau of Indian Standards:
(i) Unalloyed steel castings are designated by letter CS followed by minimum tensile strength in MPa (N/mm2).
(ii) Unalloyed special steel castings (high magnetic permeability) are designated by letters CSM followed by the minimum tensile strength in MPa (N/mm2).
(iii) Alloy steel castings are designated by letters CS followed by the minimum tensile strength in MPa and the chemical name and percentage of important alloying elements.
(iv) Heat resistant steel castings are designated by letters CSH followed by minimum tensile strength in MPa and chemical name and percentage of important alloying elements.
(v) Corrosion resistance steel castings are designated by letters CSC followed by the minimum tensile strength and chemical name and percentage of important alloying elements.