Durehete 1055 / 950 / 900 Round Bar — Cr-Mo-V-Ti-B Steam Turbine Bolting Stock (EN 10269 20CrMoVTiB4-10 / 1.7729)

Buyers select round bar in two situations: when the OEM bolt drawing falls outside the standard bolt-up package (oversize length, non-catalogue head, integral collar) and machining from bar is the cleaner route than re-tooling a forging die; and when a turnaround maintenance contractor needs short-lead replacement studs and the bar route is faster than the forging route. Room-temperature mechanical envelope on the finished bar is UTS 900 to 1050 MPa, YS 750 to 850 MPa, elongation 14 percent minimum on 5d. Refer to EN 10269 Annex C for 0.2% proof strength and creep-rupture design curves at elevated temperature. EN 10204 type 3.1 MTC is standard; type 3.2 third-party witnessed on call-out.

Available Diameters and Lengths (12 mm to 250 mm Diameter, 1 m to 6 m Length)

Durehete round bar is rolled and Q+T treated in a standard size matrix that covers the great majority of HP turbine bolt drawings without re-rolling. Diameter steps run in 2 mm increments to 50 mm and in 5 mm steps above. Length is supplied to nominal 1 m, 2 m, 3 m, 4 m, 5 m or 6 m with a positive length tolerance length-tolerance clause. Special diameters (oversize 270 mm to 350 mm and undersize 8 mm to 10 mm) are available against project tonnage and are quoted on enquiry.

Diameter Range	Standard Steps	Length Options	Typical Application
12 to 25 mm	2 mm	1 m, 2 m, 3 m	Governor-valve studs, throttle-valve internals
26 to 50 mm	2 mm	1 m, 2 m, 3 m, 4 m	Tap studs, weld studs, body-bound studs
52 to 100 mm	5 mm	2 m, 3 m, 4 m, 5 m	HP casing flange bolts, stop-valve bonnet studs
105 to 175 mm	5 mm	3 m, 4 m, 5 m, 6 m	HP turbine casing bolts (large frame)
180 to 250 mm	10 mm	4 m, 5 m, 6 m	Heavy hex bolts for ultra-supercritical bolt-up

Surface Finish Options (Peeled+Turned, Polished, Ground, Black Scaled)

Surface condition on the supplied bar is the choice between machining allowance retention and feed-stock quality acceptance at the buyer's machine shop. Black-scaled bar carries the as-rolled oxide and is the lowest-cost route but requires a heavier first-cut on the machining floor. Peeled+turned (rough-turned) bar lands at a controlled diameter envelope and removes the decarb skin. Polished bar carries a Ra 1.6 micron surface and is preferred when the buyer dispenses with a roughing pass. Ground bar is the tightest h7/h8 dimensional envelope and is the default for studs that are NOT thread-rolled and where the un-machined shank section stays at as-supplied diameter.

• Black scaled (as Q+T): as-rolled scale retained, lowest cost, allow 3 to 5 mm diameter machining stock per side.
• Peeled and turned: rough-turned to remove decarb skin, diameter tolerance h11, default for stock-fed bolt machining.
• Polished: Ra 1.6 micron surface, tolerance h10, used when the buyer eliminates roughing pass.
• Centreless ground: Ra 0.8 micron, tolerance h7 or h8, used for un-machined shank sections on stud bolts.

Chemistry by Grade (1055, 950, 900 Side by Side)

Chemical composition is the differentiator across the three grades. Durehete 1055 carries both titanium and boron and is the highest-temperature grade. Durehete 950 carries titanium without boron and sits at 540°C. Durehete 900 is plain Cr-Mo-V and is the entry-level grade up to 510°C. Buyers specify grade by service temperature and the OEM specification call-out; the bar mill produces all three from the same primary route with the differential introduced at the alloy-addition step.

Element	Durehete 1055	Durehete 950	Durehete 900
Carbon (C)	0.20 to 0.25	0.18 to 0.25	0.18 to 0.25
Chromium (Cr)	1.00 to 1.50	1.00 to 1.50	1.00 to 1.50
Molybdenum (Mo)	0.85 to 1.25	0.85 to 1.25	0.85 to 1.25
Vanadium (V)	0.60 to 0.75	0.40 to 0.60	0.30 to 0.50
Titanium (Ti)	0.04 to 0.10	0.04 to 0.10	not specified
Boron (B)	0.005 to 0.010	not specified	not specified
Service Temperature	up for elevated-temperature service	up to 540°C	up to 510°C

Mechanical Properties on Round Bar (Rolling Direction Effect)

The mechanical envelope quoted in EN 10269 20CrMoVTiB4-10 / 1.7729 and EN 10269 is the longitudinal direction (parallel to rolling axis), measured on a test piece taken at half-radius from a bar of test-size diameter. Transverse properties on the bar fall behind the longitudinal by roughly 6 percent on tensile strength and 15 percent on elongation; this is the standard rolling-direction anisotropy of Cr-Mo-V bar and is not a quality concern. The buyer's drawing specifies the bolt axis along the rolling direction so the longitudinal numbers apply to the bolt in service. EN 10269 Annex C provides the 100,000-hour stress-rupture design curves for HP turbine casing bolts.

Property (Longitudinal)	Room Temperature	540°C	Test Method
0.2 percent proof stress (YS)	750 to 850 MPa	480 MPa	BS EN ISO 6892-2
Tensile strength (UTS)	900 to 1050 MPa	610 MPa	BS EN ISO 6892-2
Elongation on 5d	14 percent min	16 percent	BS EN ISO 6892-1
Reduction of area	45 percent min	50 percent	BS EN ISO 6892-1
Charpy V at 20°C	40 J min	not required	BS EN ISO 148-1
Hardness (Brinell)	248 to 302 HB	same	ASTM E10
100,000 h stress-rupture (EN 10269 Annex C)	not specified	280 MPa	BS EN ISO 204

Heat Treatment Condition As Supplied (Quenched and Tempered)

Round bar is supplied in the Q+T condition: austenitize 970 to 1010°C, oil quench, temper 690 to 720°C, air cool. Temper temperature is held at least 30°C above the maximum continuous service temperature so the bulk microstructure stays stable over the 100,000-hour design life. The buyer's machine shop receives the bar in finished metallurgical condition and machines the bolt blank without re-heat-treatment. Stress-relief at 650 to 680°C after final machining is performed by the buyer when the cut introduces residual stress on long studs. Microstructure is tempered bainite with the Ti-B-stabilised dispersed carbide population that carries the creep-rupture envelope. Full detail is on the heat treatment page.

Standards Compliance (EN 10269, BS 1506 671-850, ASTM A193 B16, VdTUV W350/63)

Round bar is qualified to the standards that the buyer's OEM specification calls out. The four most frequent call-outs are EN 10269 (European utility-scale, primary anchor covering 20CrMoVTiB4-10 / 40CrMoV4-6 / 42CrMoV5-6), BS 1506 671-850 (legacy UK reference for Durehete 950), ASTM A193 B16 (US bolting equivalent for Durehete 950) and VdTUV Werkstoffblatt 350 (German pressure-equipment). Each standard governs chemistry envelope, heat-treatment route, room-temperature mechanical floor and the test schedule on the bar before release.

Standard	Scope	Use Case
EN 10269 20CrMoVTiB4-10 / 1.7729	British Standard, steel forgings for pressure purposes, bolting at elevated temperature	UK and Indian power-gen procurement default
ASTM A193 B16	1.25Cr-0.5Mo-V Q+T bolting	US power-gen, plain Cr-Mo-V service to 510°C
EN 10269	Cr-Mo-V bolting (EN 10269 / ASTM A193 B16 family)	Closest US equivalent to Durehete 1055
EN 10269	Ni-Cr-Mo-V Q+T bolting, higher notch toughness	Used where Charpy toughness governs
EN 10269 21CrMoV5-7	European harmonised bolting steel	European utility-scale
VdTUV Werkstoffblatt 350	German pressure-equipment approval for bolting steels	Required for German utility-scale bolt-up

Applications — The Bar That Becomes HP Turbine Bolts

Round bar in this family is the procurement input, not the finished fastener. The buyer machines the bar into the final bolt drawing on the shop floor. Typical end-applications:

• HP Steam-Turbine Casing Bolts machined from 50 mm to 200 mm bar for European OEM steam turbines5 and US OEM steam turbines flange bolting.
• Stud Bolts from 25 mm to 100 mm bar for steam-line flange bolt-up for elevated-temperature service.
• Tap Studs from 20 mm to 60 mm bar for governor-valve and stop-valve internals.
• Weld Studs from 16 mm to 50 mm bar for casing repair and instrument-stud attachment.
• Body-Bound Studs from 30 mm to 80 mm ground bar where shear-fit governs.
• Hex Bolts and Heavy Hex Bolts from 25 mm to 150 mm bar for ultra-supercritical bolt-up.
• Threaded Rod from 12 mm to 50 mm bar for piping flange field bolting.

Frequently Asked Questions on Durehete Round Bar

What is the standard size range supplied by TorqBolt?

Diameter 12 mm to 250 mm, length 1 m to 6 m, in 2 mm steps to 50 mm and 5 mm steps above. Special diameters (8 to 10 mm and 270 mm to 350 mm) are quoted against project tonnage. Surface finish options are black-scaled, peeled+turned, polished and centreless ground.

What MTC do you supply with the bar?

EN 10204 type 3.1 by default and type 3.2 on request. Heat number, melt-shop pour record, full chemistry to EN 10269 grade called out (20CrMoVTiB4-10 / 40CrMoV4-6 / 42CrMoV5-6), room-temperature tensile, 540°C tensile, Charpy V at 20°C, hardness to ASTM E10, full Q+T heat-treatment chart with austenitize, quench and temper temperatures and dwell times, dimensional report tied to the heat lot.

What testing is performed on the finished bar?

Each heat is tested Annex test schedule schedule: chemical analysis (product analysis), tensile at room temperature, tensile at 540°C (Durehete 1055 and 950), Charpy V at 20°C, hardness, ultrasonic examination to BS EN 10228-3 quality class 3 or ASTM A388 acceptance level. PMI by handheld XRF can be performed at dispatch on request.

What is the standard lead time?

Stock diameters 25 mm to 100 mm: 6 to 8 weeks from confirmed PO including QA documentation. Diameters above 150 mm or below 20 mm: 10 to 14 weeks against project tonnage. Mill-direct heats are scheduled at confirmed PO and run from the primary mill route. Third-party witness inspection (Lloyds Register, DNV, BV, SGS, TUV Rheinland) is scheduled at PO acceptance.

How is the bar packed for export?

Bar is bundled in seaworthy wood crates, strapped with steel banding, end-painted in heat colour code by grade (Durehete 1055 = red, 950 = blue, 900 = yellow), heat number stamped on each bar, packing list and MTC bagged inside the crate. Marine wax (Tectyl 506 or equivalent) is applied to machined surfaces on request for transit longer than 60 days.