INDUSTRIAL METALS · MATERIAL SOURCING · FABRICATION
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METAL TOOLKIT · GLOSSARY

Steel terms, in plain English.
What the words on your enquiry actually mean.

47 terms that come up on steel enquiries, drawings, mill test certificates and shipping documents, explained without jargon, with the practical consequence for your order.

Everyday abbreviations

SS
Stainless steel. In Indian trade "SS" is followed by the grade, as in SS 304 or SS 316. It is a trade abbreviation, not a standard designation; the purchase order should carry the grade and the product standard, for example ASTM A240 Type 304.
MS
Mild steel, meaning ordinary low-carbon structural or general-purpose steel such as IS 2062 E250. It is not a grade in itself.
CR and HR
Cold rolled and hot rolled. Cold rolled material is thinner, smoother and dimensionally tighter; hot rolled is thicker, with a scaled or pickled surface. For stainless, CR sheet generally runs to about 6 mm and HR plate above it.
NB, DN and NPS
Nominal bore, diameter nominal and nominal pipe size: the nominal label for a pipe size, not a measurement. A 2" NB pipe has an outside diameter of 60.3 mm whatever its wall thickness.
OD, ID and WT
Outside diameter, inside diameter and wall thickness. Tubes are ordered by OD and wall; pipes by NB and schedule.
CRCA (full form)
Cold Rolled Close Annealed: cold rolled steel sheet that is annealed in tightly stacked coils, giving a smooth surface and good formability. Sold to IS 513 as CR1, CR2, CR3 and CR4 (equivalents DC01, DC03, DC04, SPCC).
ISMB, ISMC and ISA (full form)
Indian Standard Medium weight Beam, Indian Standard Medium weight Channel and Indian Standard Angle: the hot rolled section series listed in IS 808. Sizes are written depth × flange, for example ISMB 200 or ISMC 100.
ETP copper (full form)
Electrolytic Tough Pitch copper (C11000, Cu-ETP): 99.9% minimum copper with a little oxygen, the standard grade for busbars, cables and electrical parts.
SWG and BWG (full form)
Standard Wire Gauge and Birmingham Wire Gauge: number systems for sheet, wire and tube wall thickness. A higher number means thinner material; 16 SWG is 1.626 mm.
ERW, EFW and SMLS
Electric Resistance Welded, Electric Fusion Welded and Seamless pipe. Seamless pipe has no weld seam; ERW is made from strip welded without filler; EFW is fusion welded, often for larger stainless pipe.
OHNS and HCHCr (full form)
Oil Hardening Non-Shrinking steel (O1 tool steel) and High Carbon High Chromium steel (D2 / D3 tool steel), two common Indian names for tool steels.
MOQ
Minimum order quantity: the smallest quantity a mill or supplier will produce or sell for a given grade and size.
MTC
Mill test certificate: the document from the producing mill giving heat number, chemical composition and mechanical test results for the material supplied.

Grade suffixes and what they change

L, as in 304L and 316L
Low carbon, normally 0.030% maximum against 0.07–0.08% for the base grade. Lower carbon reduces chromium carbide formation at grain boundaries during welding, so the weld zone resists intergranular corrosion. Slightly lower strength than the base grade.
H, as in 304H and 321H
A deliberately higher and controlled carbon range for creep strength in high-temperature service, typically above about 525 °C.
Dual certified, as in 304/304L
One heat that meets both specifications at once: carbon low enough for the L grade, strength high enough for the base grade. Common for plate and pipe, and accepted on most specifications that call for either.
Ti and Cb/Nb stabilised, as in 321 and 347
Titanium or niobium is added to tie up carbon so it cannot form chromium carbides. Used where the part sits in the sensitisation range of roughly 425–815 °C for long periods.
N, as in 2205 and S31803/S32205
Nitrogen is specified to stabilise austenite and raise pitting resistance. S32205 is the tighter modern chemistry within the older S31803 range.

Alloy families and brand names

Hastelloy
A brand name for a family of nickel-molybdenum and nickel-chromium-molybdenum alloys, now owned by Haynes International. Hastelloy C276 (UNS N10276) is roughly 57% nickel with 16% molybdenum and 16% chromium, used where acids, chlorides and mixed chemical service would attack stainless steel. Hastelloy C22 (N06022) raises chromium for a wider corrosion range. "Hastelloy" is a trademark, so a specification normally names the UNS number as well.
Inconel
A brand name, now Special Metals Corporation, for nickel-chromium alloys. Inconel 625 (N06625) adds molybdenum and niobium for strength and corrosion resistance; Inconel 600 (N06600) is the plain nickel-chromium-iron grade; Inconel 718 (N07718) is age-hardenable for high-strength parts. Used in refineries, petrochemical plants, heat treatment and aerospace.
Monel
A nickel-copper alloy, about 63% nickel and 30% copper in Monel 400 (N04400). Known for sea water and hydrofluoric acid service; used for pumps, valve trim and marine fittings. Monel K500 adds aluminium and titanium so it can be age-hardened.
Incoloy
Nickel-iron-chromium alloys. Incoloy 800 and 800H are used for heat resistance; Incoloy 825 adds molybdenum and copper for acid service.
Duplex and super duplex
Stainless steels with roughly half ferrite and half austenite. Duplex 2205 has about twice the yield strength of 304 or 316 and much better chloride pitting resistance. Super duplex, such as 2507 and S32760, raises chromium, molybdenum and nitrogen further for sea water and desalination service.
18/8 and 18/10
Informal shorthand for roughly 18% chromium with 8% or 10% nickel, the composition range of SS 304. Common in kitchenware descriptions; it is not a standard designation, so ask for the grade and standard.

Finishes and surface condition

No. 1
Hot rolled, annealed and pickled. A dull, matte grey plate surface. Standard for hot rolled stainless plate.
2B
Cold rolled, annealed, pickled and given a light final pass. A smooth, mildly reflective finish and the normal supply condition for stainless sheet.
BA or 2R
Bright annealed: cold rolled and annealed in a controlled atmosphere, giving a bright, mirror-like surface without polishing.
No. 4
A brushed satin finish produced with abrasive belts, typical for kitchen equipment, lifts and architectural panels.
HL (hairline)
A long, continuous brushed grain, widely used in architectural cladding and lift panels.
Mirror (No. 8)
Polished to a reflective finish. Usually supplied with a protective film.
Black and bright bar
Black bar is hot rolled with a scaled surface; bright bar is cold drawn, ground or peeled, with a smoother surface and closer diameter tolerance. Bright bar costs more per kg.

Certificates, testing and inspection

EN 10204 3.1
A mill test certificate issued and validated by the producing mill's own independent quality department, covering the actual material supplied. This is the usual requirement on industrial orders.
EN 10204 3.2
The same test results, countersigned by an independent inspector or the buyer's nominated representative, such as SGS, Bureau Veritas, TUV or Lloyd's.
EN 10204 2.1 and 2.2
A declaration of compliance without, or with, non-specific test results. Not traceable to your heat, so most project specifications do not accept it.
Heat number
The batch identifier for the melt the material came from. It links the piece in your hand to the test certificate, and should be marked on the material.
Magnet test
Holding a magnet to the material. Annealed 304 and 316 are essentially non-magnetic, while 409, 410, 430, 17-4PH and duplex are magnetic. It is a rough sort at best: cold working makes austenitic grades slightly magnetic, and it cannot separate 304 from 316 or 202, which are all non-magnetic. It is not evidence of grade.
Spot test kit, or grade tester liquid
A chemical spot test, usually a molybdenum reagent, placed on a cleaned surface. It shows whether molybdenum is present, which separates 316 from 304 and 202, and some kits also indicate nickel. It identifies an element, not a grade, and does not replace the mill test certificate or a PMI check.
PMI
Positive material identification: an on-the-spot check of alloy composition, usually with a handheld X-ray fluorescence or optical emission analyser. It confirms the alloy family and major elements, and is used to catch mixed-up material.
IGC test (ASTM A262)
Intergranular corrosion test. Practice A, B, C or E is specified to confirm the material is not sensitised, most often on welded stainless for chemical service.
Hydro test
A pressure test with water on pipe or tube, to the pressure the product standard requires.
Ferrite number
The measured proportion of ferrite in duplex or weld metal. Specifications for duplex usually require it to fall within a band, commonly about 35–65%.
Third-party inspection
An independent agency witnesses testing and inspects the material before dispatch, then issues a release note that travels with the shipping documents.

Commercial and documentation terms

Theoretical vs actual weight
Theoretical weight is calculated from nominal size and density. Actual weight is what the material weighs on the scale. Mill tolerances mean the two differ, so a quotation should state which basis is being invoiced.
HSN code
The tariff code on Indian invoices and e-way bills. Stainless pipe, sheet, bar and fittings sit in chapters 72 and 73; nickel alloys in chapter 75; titanium in chapter 81.
FOB, CFR and CIF
Incoterms. FOB puts the goods on board at the loading port at the seller's cost; CFR adds sea freight; CIF adds marine insurance as well. The term decides who pays and who carries the risk from which point.
LC at sight
An irrevocable letter of credit paid on presentation of compliant shipping documents. Common on first export orders.
Mill, stockist and trader
A mill melts and rolls the material. A stockist holds material and sells from stock. A trader sources against the enquiry. Many Indian suppliers do more than one of these; what matters on an order is the certificate and the traceability.

Common questions

What does SS stand for in steel?

SS stands for stainless steel. In Indian trade it is written with the grade, as in SS 304, SS 316 or SS 202. It is shorthand, not a standard designation, so the purchase order should also carry the product standard, for example ASTM A240 Type 304 for sheet and plate.

What is Hastelloy and what is it made of?

Hastelloy is a brand name, owned by Haynes International, for a family of nickel-based corrosion-resistant alloys. Hastelloy C276 (UNS N10276) is about 57% nickel with roughly 16% molybdenum and 16% chromium plus tungsten and iron. It is used where chlorides, acids and mixed chemical service would attack stainless steel. Because the name is a trademark, specifications normally also give the UNS number.

What is the difference between 304 and 304L?

Carbon. SS 304L is limited to about 0.030% carbon against roughly 0.07% for SS 304. Lower carbon means less chromium carbide forms at grain boundaries when the material is welded, so the weld zone resists intergranular corrosion better. SS 304L has slightly lower strength. Dual-certified 304/304L meets both specifications in one heat.

What is the difference between 304L and 304H?

They sit on opposite sides of the carbon range. 304L limits carbon to about 0.030% for weldability and corrosion resistance after welding. 304H specifies a controlled higher carbon, roughly 0.04 to 0.10%, to retain creep strength at high temperature, generally above about 525 °C. They are not interchangeable.

What is 2B finish on stainless steel?

2B is the standard cold rolled finish: the sheet is cold rolled, annealed, pickled and given a light final pass between polished rolls. It is smooth and mildly reflective, and is the usual supply condition for stainless sheet unless a brushed No. 4, hairline or bright annealed finish is specified.

What is an MTC or EN 10204 3.1 certificate?

A mill test certificate is the producing mill's record of the chemical composition and mechanical test results for the heat the material came from. EN 10204 3.1 means it is issued and validated by the mill's own independent quality department; 3.2 means an independent inspector has countersigned it as well. The heat number on the certificate should match the marking on the material.

What is PMI testing?

Positive material identification: checking the alloy composition of a finished item with a handheld X-ray fluorescence or optical emission analyser. It confirms the alloy family and the major elements in seconds and is used to catch mixed or wrongly marked material. It does not replace the mill test certificate, which also carries mechanical properties.

What is the difference between a pipe and a tube?

A pipe is ordered by nominal bore and schedule, where the nominal size is a label and the outside diameter is fixed for that size. A tube is ordered by its actual outside diameter and wall thickness. A 2" NB pipe is 60.3 mm outside diameter; a 2" tube is 50.8 mm outside diameter.