Z21CDV12 Forgings

§01

What Z21CDV12 is, and what it is for

Z21CDV12 belongs to the group of 12 % chromium martensitic steels developed for high-temperature steam service. The chromium gives resistance to oxidation and steam attack; the molybdenum raises creep strength by solid-solution strengthening; the vanadium forms fine, stable carbides that resist coarsening during long exposure at temperature. Together they keep the tempered-martensite structure stable under sustained stress for tens of thousands of hours, which a plain chromium-molybdenum steel cannot do.

The grade is not a corrosion-resistant stainless steel in the usual sense. At 11.00–12.50 % chromium it sits on the lower boundary of the stainless range, and it is correctly described as a martensitic heat-resisting and creep-resistant steel. Where wet corrosion rather than hot steam is the governing condition, an austenitic, duplex or precipitation-hardening grade is the right answer instead.

Three characteristics drive how Z21CDV12 must be handled in a forge shop. It is air-hardening, so a section left to cool in still air after forging will transform to untempered martensite and can crack. It has a narrow hot-working window compared with carbon steel. And its final properties come almost entirely from the post-forge heat treatment rather than from the forging itself. All three are dealt with in §05 and §06.

§02

Chemical composition of Z21CDV12

Z21CDV12 to AFNOR contains 0.17–0.24 % carbon, 11.00–12.50 % chromium, 0.80–1.20 % molybdenum and 0.20–0.35 % vanadium, with the balance iron. The full specified range is given below.

Composition as published for the AFNOR grade Z 21 CDV 12. Where an order is placed to a specific national standard or customer specification, that document governs. Jiangyin Jiangnan Metal verifies chemistry by optical emission spectrometry to ASTM E415 and carbon and sulphur by infrared analysis to ASTM E1019, at the furnace and again on the finished forging.

§03

Z21CDV12 equivalent and comparable grades

Z21CDV12 sits in the same 12 % chromium martensitic family as X20CrMoV11-1 / 1.4922, and the two are normally treated as interchangeable for enquiry purposes. The other entries below are near matches rather than exact ones, and should be confirmed against the ordering specification before any substitution is made.

Cross-references are given as a purchasing aid. Grades in the same family can differ in carbon, nickel, tungsten and niobium content, in required heat treatment and in the mechanical properties they must meet. Send the governing specification with an enquiry and the correct grade will be quoted against it.

Related martensitic grades forged at the same works

• AISI 422
• 1.4057
• AISI 431
• ASTM A182 F6a
• ASTM A182 F6NM
• AISI 416

§04

Mechanical and physical properties

In the quenched and tempered condition, steels of the Z21CDV12 / X20CrMoV11-1 type typically meet a 0.2 % proof strength of at least 490 MPa and a tensile strength of 690–840 MPa, with elongation from 17 % and Charpy V-notch impact energy from 27 J at room temperature. Values depend on section size, tempering temperature and the ordering specification.

Physical property values are representative of the X20CrMoV11-1 / 1.4922 family and are given for design guidance only. Creep-rupture and long-term design values must be taken from the governing design code, not from this page. Mechanical test results for a specific order are reported on the mill certificate for the heat and section concerned.

Service temperature

Steels of this type are normally used in creep-governed service up to about 580–600 °C, with useful scaling resistance in air to roughly 750 °C. The permissible design temperature for a given component depends on the design code, the stress level and the required service life, and is set by the design engineer rather than by the grade alone.

§05

Heat treatment of Z21CDV12

The properties of a Z21CDV12 forging come from heat treatment, not from the forging operation. A typical route is soft annealing, austenitising with an oil or air quench, and a high tempering treatment that produces tempered martensite stable at service temperature.

Hold times are set by section thickness, typically a minimum of one hour per 25 mm of ruling section with a two-hour minimum at temperature for tempering. Tempering below about 650 °C is avoided in this family because it falls in a range associated with reduced toughness. The exact cycle for an order is set by the applicable specification.

§06

Forging, machining and welding practice

Forging Z21CDV12

Z21CDV12 is preheated gradually to about 850 °C, then heated more rapidly to between 1150 and 1180 °C, and forged between 950 and 1180 °C. Because the steel is air-hardening, the forging is then cooled slowly in a furnace, in dry ash or in a similar medium, rather than being left in still air. Slow cooling avoids the untempered martensite and quench cracking that a fast cool from the finishing temperature would produce. The forging is given its full heat treatment afterwards to attain the required properties.

Forging below about 950 °C risks cracking and leaves residual stress that the subsequent heat treatment may not fully remove. Heating above 1180 °C coarsens the grain and reduces toughness. Re-heating between passes is normal on heavy sections rather than pushing a single heat to the bottom of the range.

Machinability

Machinability of Z21CDV12 is directly related to its hardness, and the grade generally machines in a manner similar to carbon steels of the same hardness. Machining parameters vary with the structure and hardness of the steel, so published figures should be treated as a starting point for coated carbide tooling rather than as fixed values. In practice, rough machining is carried out in the annealed condition wherever the sequence allows, with finish machining after the final temper.

Welding

Z21CDV12 is weldable under strict control. Because the steel is air-hardening, welding normally requires preheat in the region of 300–400 °C with a controlled interpass temperature, a matching or compatible 12 % chromium filler metal, and post-weld heat treatment carried out below the tempering temperature of the parent material. A welding procedure should be qualified for the section thickness and service conditions concerned. Where welding is part of the scope, state it at enquiry stage so the delivery condition and PWHT can be planned into the route.

§07

Forged products supplied in Z21CDV12

Jiangyin Jiangnan Metal Co., Ltd. supplies Z21CDV12 as forged bars, hollow sections, seamless rolled rings, discs and blocks, rotating components and valve parts. Every item is forged from a single piece of steel melted on site. There is no casting, no welded fabrication and no purchased billet of unknown origin.

Size envelope

The limits below are set by the plant's own equipment and apply to Z21CDV12 as they do to any forged grade.

Delivery condition

Z21CDV12 forgings are supplied as-forged with machining allowance, rough-machined to a proof-machined condition suitable for ultrasonic testing, or finish-machined to drawing. Heat treatment, machining, non-destructive testing and mechanical testing are all carried out in-house before shipment.

§08

Testing, inspection and certification

Every Z21CDV12 forging is released against a documented route: melt analysis, mechanical testing on a representative test piece, non-destructive examination, dimensional inspection, then certification. Because the steel is melted at the same works, chemistry is verified at the furnace rather than taken from a supplier's certificate.

Certification. EN 10204 3.1 mill test certificates are issued as standard. EN 10204 3.2 certificates witnessed by a classification society or a third-party inspection body such as SGS or TÜV are available on request. The works holds CCS, BV, DNV, LR and NK classification society approvals. Supporting records include heat-treatment charts, NDT reports, dimensional reports and PMI records, and traceability runs from the melt number through forging, heat treatment and machining to shipment.

Order-specific tests outside the in-house scope, for example impact testing below −60 °C or bench Brinell hardness where a portable instrument is not accepted, are placed with an accredited third-party laboratory and reported alongside the mill certificate. State the requirement on the enquiry so it is scheduled before shipment.

§09

Where Z21CDV12 is used

Z21CDV12 is specified where a component carries load at temperature in steam or hot gas for a long service life. The applications below are the ones the grade is most often ordered for.

• Steam turbines. Blades, gland seal rings, sealing and guide rings, discs, rotor shafts and wheels operating in the high- and intermediate-pressure stages.
• Compressors and gas turbines. Compressor blades, impellers and rotating components in the hotter stages.
• High-temperature valves. Gate, check and control valve bodies and bonnets, stems and spindles, seats and discs for high-pressure steam lines.
• Bolting. Bolts, studs and fasteners for flanged joints and casings held at temperature, where relaxation resistance matters as much as room-temperature strength.
• Power-plant pressure parts. Casings, housings, hubs and heavy-section components in fossil and combined-cycle plant.

Forgings from this works have been exported since 1997 to customers in North America, Europe, the Middle East and Asia-Pacific, across power generation, oil and gas, shipbuilding, chemical and petrochemical processing and heavy machinery.

§10

How to request a Z21CDV12 quotation

Quotations are prepared from a drawing or a written specification, and sending the six items below in the first email usually gets a price back within two working days. Minimum order is 10 kg with no minimum piece count, and normal lead time runs 20 to 60 days.

Email a Z21CDV12 enquiry

§11

Frequently asked questions about Z21CDV12

§12

Other grades forged at this works

Alloy & quenched-and-tempered steel

• AISI 4140
• 42CrMo4
• 1.7225
• AISI 4340
• 34CrNiMo6
• 11CrMo9-10
• All alloy steel

High-temperature & nickel alloys

• Inconel 718
• Inconel 625
• Nimonic 80A
• Waspaloy
• Rene 41
• Incoloy A-286
• All nickel alloys

Product families

• Seamless rolled rings
• Forged rings
• Forged shafts
• Forged bars & blocks
• Tube sheets & discs
• Valve & wellhead parts
• Forged cylinders & pipes