WCB vs WCC: Carbon Steel Casting Grades for Valve Bodies

CF8M against CF3M comes down to 0.05 % of carbon. WCB against WCC comes down to manganese — and to how thick the casting is. Both are ASTM A216 carbon steel castings for valve bodies, both are painted the same colour, and both are routinely sold as "carbon steel" with no grade mentioned. The difference is a minimum yield of 36 ksi against 40 ksi.

Why "Carbon Steel" Is Not a Grade

"Carbon steel" names a family, not a specification. A DN50 gas valve and a DN600 steam valve can both be quoted as carbon steel and still be different alloys, with different strengths and different behaviour after welding.

What they have in common is that nothing is added deliberately except carbon and manganese. What they do not have in common is the grade designation cast into the body — and that mark is the only thing that tells you which chemistry the foundry melted.

What ASTM A216 Actually Covers

ASTM A216 covers carbon steel castings for valves, flanges, fittings and other pressure-containing parts for high-temperature service, of a quality suitable for fusion welding. It defines three grades: WCA, WCB and WCC — "weldable", "carbon", and a suffix running from the weakest grade to the strongest.

All three share the same residual limits: copper to 0.30 %, nickel and chromium to 0.50 %, molybdenum to 0.20 %, vanadium to 0.03 %, totalled at 1.00 % maximum. Silicon is capped at 0.60 % and phosphorus and sulphur at 0.035 % each. Nothing is deliberately alloyed; what separates the grades is carbon and manganese.

WCA is the softest: carbon to 0.25 %, manganese to 0.70 %, minimum tensile strength only 60 ksi. It exists for castings needing maximum ductility, and in valve work it is rare — a supplier offering "WCA" is usually quoting a grade the foundry does not pour.

WCB: The Default Valve Body Grade

WCB is what arrives when a buyer writes "carbon steel" and nobody asks a second question. The chemistry is deliberately loose: carbon to 0.30 %, manganese to 1.00 %, with minimum properties of 70 ksi tensile, 36 ksi yield and 22 % elongation.

It is stocked in every size and class, welded with ordinary carbon steel procedures, and cheap. For water, steam, oil, gas and general process duty across the ordinary pressure classes it is the correct first answer, and the great majority of carbon steel valves in a plant are WCB. Its wrought counterpart is A105, which is why a WCB body bolts without ceremony to forged carbon steel flanges.

WCC: What the Extra Manganese Buys

WCC holds carbon at 0.25 % or below but raises manganese to 1.20 %. That is the entire change, and it lifts the minimum yield strength from 36 ksi to 40 ksi without touching the 70–95 ksi tensile range.

Manganese raises hardenability — the ability of the steel to develop strength as it cools. A thin section cools quickly and hardenability barely matters; a thick section cools slowly, and a low-hardenability steel may never reach the yield strength the certificate promises.

That is why WCC exists: not as a general upgrade on WCB, but as the grade a foundry reaches for when the wall is too heavy for WCB to make its numbers reliably.

A216 also allows carbon to be traded for manganese: each 0.01 % of carbon held below the maximum permits 0.04 % more manganese.

WCB and WCC Side by Side

Property	WCB	WCC
A216 grade suffix	B	C
Carbon, max	0.30 %	0.25 %
Manganese, max	1.00 %	1.20 %
Tensile strength, min	70–95 ksi	70–95 ksi
Yield strength, min	36 ksi (250 MPa)	40 ksi (275 MPa)
Elongation, min	22 %	22 %
ASME B16.34 material group	1.1	1.2
Section it suits	Standard walls	Heavy walls
Relative cost	Baseline	Slight premium

Where They Sit in ASME B16.34

The two grades do not share a material group. WCB sits in Group 1.1 with forged A105 and A350 LF2. WCC sits in Group 1.2, alongside the low-temperature castings A352 LC2, LC3 and LCC.

This is not a filing detail. Group membership carries its own pressure-temperature table, and WCC's higher minimum yield buys it a higher allowable stress — modestly different at ambient temperature, more visibly different as it rises.

The consequence is that a rating table is only valid for the grade actually marked on the body. Quoting a Group 1.2 figure against a Group 1.1 valve is a real and not uncommon error.

Temperature: Where Carbon Steel Stops

Both grades are rated from −29 °C. Below that, carbon steel loses notch toughness, and the answer changes material rather than grade: A352 LCB, which is impact tested and rated to −46 °C, or LCC, which sits alongside WCC in Group 1.2.

At the top end, cast carbon steel is normally rated to 425 °C. Above that the material moves up the alloy ladder: A217 WC6 (1.25Cr-0.5Mo) to about 565 °C, then WC9 and the high-chromium C5 or C12 grades.

Between −29 °C and 425 °C the two grades share one range. Above the carbon steel band you are specifying chromium, not more manganese.

Section Size and the Real Reason WCC Exists

A216 grades are qualified on test coupons cast alongside the production casting, and the coupon cools at a rate that depends on section. The thicker the wall, the slower the cooling, the coarser the structure and the harder it is to reach the specified yield.

This is why the WCC question appears on large valves and rarely on small ones. A DN50 WCB ball valve is a comfortable casting; a DN600 gate valve body with a heavy wall is a different proposition, and a foundry quoting it may prefer WCC — or may quote WCB and hope.

If the foundry is quiet about the grade, ask which one is cast on the body and ask to see the coupon results.

Welding WCB and WCC

Both weld cleanly with ordinary carbon steel procedures, and a competent fabricator will not notice a difference on the root pass. The difference is carbon equivalent: WCC's higher carbon and manganese raise hardenability in the weld and heat-affected zone. In thin sections that changes nothing; in thick sections it brings preheat and post-weld heat treatment into the procedure and makes hydrogen cracking a live risk.

WCB typically runs a carbon equivalent of 0.45–0.48 %, which is why it is welded with the same procedures as A105 forgings. WCC sits above that, so a procedure qualified on WCB should not be assumed to cover it.

For sour service to NACE MR0175 / ISO 15156, hardness governs — 22 HRC maximum — and the weld is usually the place that fails it.

European Equivalents: GS-C25 and GP280GH

European bodies carry EN 10213 designations, and the mapping is close but not automatic. WCB corresponds to 1.0619, GP240GH — the material older drawings still call GS-C25. WCC corresponds to 1.0625, GP280GH, and the older DIN 17182 grade GS20Mn5 (now EN G20Mn5, 1.6220) is also cross-referenced to WCC.

The naming is worth knowing, because EN puts the minimum yield strength into the grade name: GP240GH is a 240 MPa material, GP280GH a 280 MPa one. Europe makes the WCB and WCC distinction visible at a glance, where the American suffix does not.

Reading the Mark and the Certificate

Carbon steel valve bodies carry cast or stamped marks giving grade, size and rating, usually with a heat number and foundry mark. On painted castings they are shallow, so read them before the valve is wrapped.

Four designations turn up and are easy to mix up: WCB and WCC are A216 castings, A105 is the forged grade, and LCB and LCC are A352 low-temperature castings.

Where the mark is unreadable, a datasheet is not evidence. Ask for a mill certificate to EN 10204 3.1 naming the grade, heat number and mechanical results, and keep it with the valve record.

Five Specification Mistakes

Writing "carbon steel" and accepting either grade. WCB arrives by default, and on a large casting that may not be what the design needed.

Assuming WCC is a corrosion upgrade. It is not. Manganese buys strength in thick sections. For corrosion you change family, not grade.

Using a WCB rating table for a WCC valve. The two sit in different ASME B16.34 material groups, with different allowable stresses.

Treating GS-C25, GP240GH and WCB as interchangeable. They are close, but the certificate must name the grade you specified.

Assuming a WCB welding procedure covers WCC. The higher carbon equivalent means a different qualified procedure.

FAQ

Is WCC stronger than WCB?

In yield strength, yes: 40 ksi minimum against 36 ksi. The tensile range, elongation and temperature range are identical. WCC is not a higher-tensile material; it is a more hardenable one.

Can I use WCB instead of WCC?

In small sizes and ordinary classes, usually yes. On a large heavy-wall casting the foundry may not meet WCB's properties from the test coupon, which is exactly what WCC solves.

What is the difference between WCB and A105?

Product form. WCB is a casting under A216, A105 the forged carbon steel grade. They share an ASME B16.34 material group and are routinely welded to each other.

Is WCB suitable for low temperature service?

To −29 °C. Below that, specify A352 LCB, impact tested to −46 °C, or LCC. Low-temperature service is a material change, not a grade change.

The Short Answer

For a standard valve in water, steam, oil or gas between −29 °C and 425 °C, WCB is the right grade and the one the market is built around.

WCC earns its premium on heavy-wall and large castings, where the extra manganese is what lets the foundry meet the yield strength at all. If you are buying a large carbon steel valve, the grade is worth one line on the enquiry — and the coupon results worth one look.