Grade identity and equivalent designations
Drawings reach us with at least six different names for this steel, depending on the standard they were written to. Every designation in Table 1 refers to the same 2.5 % Ni-Cr-Mo chemistry. Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders under any of them.
| Standard / country | Designation | Status |
|---|---|---|
| Werkstoff Nr. (Germany) | 1.6745 | Same material |
| DIN / EN name | 40NiCrMo10-5 (also written 40NiCrMo10 4) | Same material |
| BS 970-3 (United Kingdom) | 826M40 | Same material |
| BS 970:1955 (United Kingdom, superseded) | EN26 | Same material, obsolete name still in daily use |
| AS 1444 (Australia) | X9940 | Same material |
| IS 5517 (India) | 40Ni10Cr3Mo6 | Same material |
| EN 10083-3 (Europe) | 34CrNiMo6 (1.6582), 30CrNiMo8 (1.6580) | Nearest catalogued grades, not identical |
| AISI / SAE (USA) | 4340, E4340 | Frequently cross-referenced, not identical. See section 7 |
| GOST (Russia) | 38KhN3MFA family | Nearest. Confirm chemistry per order |
Compiled by Jiangyin Jiangnan Metal Co., Ltd. from BS 970-3, AS 1444, IS 5517 and published Werkstoff cross-reference data.
Ordering note. Where a design code, an aerospace approval or a customer specification is involved, order to a single named designation and let the mill certificate carry the others. Every heat we forge is supplied with a multi-designation material test certificate listing each specification the heat actually satisfies, so one forging can be released against 1.6745, 826M40 and EN26 at the same time.
What 1.6745 is, and when to specify it
1.6745 is a medium-carbon nickel-chromium-molybdenum steel for parts that must be strong, tough and fully hardened right through a heavy section. Nickel sits at 2.4–2.7 %, about double the AISI 4340 level. Molybdenum sits at 0.4–0.6 %, again about double. Those two levels account for most of the difference between 1.6745 and the commoner quenched and tempered grades.
Nickel raises hardenability and holds the impact transition temperature down, so the steel stays tough in sub-zero service. Molybdenum raises hardenability further, adds temper resistance and suppresses the reversible temper embrittlement that restricts how a nickel-chromium steel can be tempered. Between them, 1.6745 quenches and tempers in ruling sections up to about 250 mm and still meets the strength and elongation minima at the core. The higher strength conditions are reached by tempering between 300 °C and 550 °C, a range that would embrittle a nickel-chromium steel carrying no molybdenum.
Specify 1.6745 where
- The section is too heavy for 42CrMo4 (1.7225 / AISI 4140) or 34CrNiMo6 (1.6582) to through-harden.
- The design needs higher tensile and yield strength than 817M40 / EN24 / AISI 4340 can deliver in the same section.
- The part carries high surface pressure (gear teeth, pins, splines, journals) and carbon has to stay near 0.40 % for hardness.
- Service is at low temperature and impact values at the core matter.
- The finished part will be nitrided or induction hardened after quenching and tempering.
Consider another grade where
- The section is light and cost matters. 42CrMo4 or 34CrNiMo6 will reach the same properties for less money.
- The part must be welded into an assembly. The carbon equivalent of 1.6745 is around 0.91, which makes it a difficult weld (see section 5).
- Toughness at very heavy sections matters more than hardness. 826M31 / EN25 is the same alloy at 0.27–0.35 % carbon, softer and tougher.
Chemical composition of 1.6745
The two composition windows in Table 2 are both current and both in use. The Werkstoff 1.6745 window is slightly tighter on nickel, chromium and molybdenum than the British 826M40 window; a heat that meets 1.6745 will therefore normally also meet 826M40, but not always the reverse. Jiangyin Jiangnan Metal Co., Ltd. melts to the narrower window by default so that one heat can be certified to both.
| Element | 1.6745 min | 1.6745 max | 826M40 min | 826M40 max | Role in the steel |
|---|---|---|---|---|---|
| Carbon (C) | 0.37 | 0.43 | 0.36 | 0.44 | Sets attainable hardness and strength after quenching |
| Silicon (Si) | 0.15 | 0.35 | 0.10 | 0.35 | Deoxidiser; raises temper resistance slightly |
| Manganese (Mn) | 0.50 | 0.70 | 0.45 | 0.70 | Adds hardenability; combines with residual sulfur |
| Nickel (Ni) | 2.40 | 2.70 | 2.30 | 2.80 | The defining addition. Deep hardenability and low-temperature toughness |
| Chromium (Cr) | 0.60 | 0.80 | 0.50 | 0.80 | Hardenability and temper resistance; forms stable carbides |
| Molybdenum (Mo) | 0.40 | 0.60 | 0.45 | 0.65 | Suppresses temper embrittlement; allows tempering at 300–550 °C |
| Phosphorus (P) | — | 0.035 | — | 0.040 | Residual. Kept low for toughness |
| Sulfur (S) | — | 0.035 | — | 0.040 | Residual. Kept low for transverse ductility |
| Iron (Fe) | Balance | Base element | |||
Source: Jiangyin Jiangnan Metal Co., Ltd., 1.6745 forging specification, compiled from the Werkstoff 1.6745 window and BS 970-3: 826M40. Every heat ships with a ladle analysis on the mill certificate; product analysis on the finished forging is available on request.
Melting route
Jiangyin Jiangnan Metal Co., Ltd. melts 1.6745 by EAF + LF + VD: electric arc furnace, ladle furnace refining, then vacuum degassing. Heavy sections in this grade have to be degassed. The treatment brings hydrogen below 2 ppm and so prevents flaking, the hydrogen-induced internal cracking that shows up in large quenched and tempered Ni-Cr-Mo forgings. ESR remelting is available where a customer specification calls for improved cleanliness, tighter segregation control or aerospace-level inclusion ratings.
How to cite this page. Jiangyin Jiangnan Metal Co., Ltd. (2026). 1.6745 (40NiCrMo10-5 / EN26 / 826M40) open-die forging specification. Jiangyin, Jiangsu, China. Retrieved from https://www.steelforgepieces.com/Alloy-Steel/1.6745.html
Mechanical properties of 1.6745 forgings
1.6745 has no single set of mechanical properties. It is supplied to a condition, and the condition is chosen by the tempering temperature. BS 970-3 labels these conditions with letters from T to Z, each one a tensile band 150 MPa wide. State the condition on the enquiry, or give the strength and hardness the drawing calls for, and we set the tempering cycle to suit.
| Condition | Tensile Rm, MPa | Proof Rp0.2 min, MPa | Elongation min, % | Hardness | Max ruling section |
|---|---|---|---|---|---|
| T | 850–1000 | 665 | 13 | 248–302 HB / 24–32 HRC | 250 mm |
| U | 925–1075 | 740 | 12 | 269–321 HB / 28–34 HRC | 250 mm |
| V | 1000–1150 | 835 | 12 | 293–341 HB / 31–38 HRC | 250 mm |
| W | 1075–1225 | 925 | 11 | 311–363 HB / 33–39 HRC | 250 mm |
| X | 1150–1300 | 1005 | 10 | 341–388 HB / 37–42 HRC | 150 mm |
| Y | 1225–1375 | 1080 | 10 | 363–415 HB / 39–44 HRC | Confirm per section |
| Z | 1550 min | 1235 | 5 | 444 HB min / 47 HRC min | Confirm per section |
| Annealed | ≤ 850 | — | — | ≤ 255 HB | Any. Machining stock condition |
Source: Jiangyin Jiangnan Metal Co., Ltd., compiled from the BS 970-3 condition table for 826M40. Hardness is converted from tensile strength per ISO 18265 / ASTM A370 and is indicative, not a specified value. Condition V is the most commonly ordered condition for forged shafts and gear blanks. Proof stress and elongation minima are the values applicable at the stated limiting ruling section; for contract purposes confirm against the current edition of BS 970-3.
Impact properties
Izod impact minima to BS 970-3 for 1.6745 in condition U are 47 J at a 150 mm limiting ruling section and 34 J at 250 mm. For forgings we normally test Charpy V-notch instead, at room temperature or at a specified sub-zero temperature, with the acceptance value agreed at order entry. Nickel is what carries this grade at low temperature. The ductile-to-brittle transition sits well below that of a chromium-molybdenum steel such as 42CrMo4.
Test location and orientation
Unless the order says otherwise, Jiangyin Jiangnan Metal Co., Ltd. takes test material from a prolongation of the forging, at mid-radius or quarter-thickness, in the longitudinal direction, after the final heat treatment. Transverse and tangential testing, through-thickness testing, and testing from a sacrificial forging are all available where a specification such as EN 10250-3 or a customer standard requires them. Properties in heavy forgings fall away from surface to core, so state the section size when you ask for a condition. Condition X is realistic at 150 mm. At 400 mm it is not.
Heat treatment of 1.6745
Table 4 gives the cycles Jiangyin Jiangnan Metal Co., Ltd. runs for 1.6745 forgings. Exact temperatures and soak times are set part by part against the section size. The figures below are the working envelope.
| Operation | Temperature | Cooling | Result |
|---|---|---|---|
| Forging | 1,150–1,200 °C start, finish above 850 °C | Slow cool, then immediate post-forge anneal | Wrought grain flow following the part contour |
| Annealing | 830–850 °C | Furnace cool, about 20 °C/h to 600 °C, then air | ≤ 255 HB. Soft enough for rough machining |
| Normalising | 860–880 °C | Air | Refined, uniform grain before hardening |
| Stress relieving | 640–660 °C | Slow cool in furnace | Removes machining and welding stress without softening |
| Hardening | 820–850 °C, soak to section | Oil quench; heavy sections preheated at 400–500 °C | Full martensite through the section |
| Tempering, conditions W to Z | 300–550 °C | Air | 1075 MPa and above. Usable because molybdenum blocks temper embrittlement |
| Tempering, conditions T to V | 550–660 °C | Air | 850–1150 MPa with maximum toughness and machinability |
| Nitriding, optional | 500–530 °C after tempering | Furnace | Hard, wear-resistant case on a tough core |
| Induction or flame hardening, optional | Surface austenitising | Water or polymer spray | Local hardness on journals, teeth and wear faces |
Source: Jiangyin Jiangnan Metal Co., Ltd., 1.6745 heat treatment practice. All furnaces are calibrated and every cycle is chart-recorded; heat treatment charts are issued with the certificate on request.
Tempering practice
Temper too high and the part loses strength. Temper too low and it stays hard with reduced core toughness. Molybdenum at 0.4–0.6 % keeps the 300–550 °C window open to 1.6745, where a plain nickel-chromium steel has to avoid it, and that is why the grade gets specified over EN24 for the highest strength conditions. Put the required condition or the target hardness band on the drawing, not a tempering temperature. The shop then sets the cycle against the actual section.
Welding
The carbon equivalent of 1.6745 at mid-range composition is CE(IIW) ≈ 0.91, calculated as C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. Anything above about 0.45 is considered difficult to weld, so 1.6745 is not a fabrication steel. Welding in the hardened and tempered condition is not recommended, because the heat-affected zone will not retain the specified properties. Where welding is unavoidable, weld in the annealed condition, preheat, and stress relieve at 640–660 °C as soon as the part has cooled to hand warmth, then harden and temper the finished assembly.
Physical and derived properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 7.85 g/cm³ | 0.284 lb/in³ |
| Modulus of elasticity, 20 °C | 205–210 GPa | 29.7–30.5 × 10⁶ psi |
| Poisson's ratio | 0.29 | 0.29 |
| Mean thermal expansion, 20–100 °C | 11.5–12.5 µm/m·K | 6.4–6.9 × 10⁻⁶ in/in·°F |
| Thermal conductivity, 100 °C | approx. 40 W/m·K | approx. 277 Btu·in/ft²·h·°F |
| Specific heat, 20 °C | 460–475 J/kg·K | 0.110–0.113 Btu/lb·°F |
| Electrical resistivity, 20 °C | 0.22–0.25 µΩ·m | 132–150 Ω·circ mil/ft |
| Magnetic response | Ferromagnetic | |
Nominal values for a quenched and tempered low-alloy steel of this composition, offered for design screening. They are not certified values and do not appear on the mill certificate. Compiled by Jiangyin Jiangnan Metal Co., Ltd.
Transformation temperatures and weldability index
The values in Table 6 are calculated from Andrews' empirical equations for the mid-range 1.6745 composition (0.40 C, 0.60 Mn, 0.25 Si, 2.55 Ni, 0.70 Cr, 0.50 Mo). They are useful for setting a first-pass heat treatment cycle and for checking that a proposed austenitising temperature sits above Ac3.
| Quantity | Calculated value | Basis |
|---|---|---|
| Ac1, start of austenite formation | approx. 693 °C | Andrews (1965) linear equation |
| Ac3, end of austenite formation | approx. 770 °C | Andrews (1965) linear equation |
| Ms, martensite start | approx. 295 °C | Andrews (1965) linear equation |
| Carbon equivalent CE(IIW) | approx. 0.91 | C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 |
Calculated by Jiangyin Jiangnan Metal Co., Ltd. for the mid-range composition. Actual transformation temperatures vary with the heat analysis and with heating rate; confirm by dilatometry where a critical application demands it.
1.6745 compared with 4340, EN24, EN25 and 34CrNiMo6
These five grades get substituted for one another on enquiries every week, and three of them are close in composition. Table 7 sets out where they actually differ. 1.6745 carries about twice the nickel and twice the molybdenum of AISI 4340, which is why it hardens deeper and tempers to a higher strength in the same section.
| Criterion | 1.6745 / EN26 | AISI 4340 | 817M40 / EN24 | 826M31 / EN25 | 34CrNiMo6 / 1.6582 |
|---|---|---|---|---|---|
| Carbon, % | 0.36–0.44 | 0.38–0.43 | 0.36–0.44 | 0.27–0.35 | 0.30–0.38 |
| Nickel, % | 2.30–2.80 | 1.65–2.00 | 1.30–1.80 | 2.30–2.80 | 1.30–1.70 |
| Chromium, % | 0.50–0.80 | 0.70–0.90 | 0.90–1.40 | 0.50–0.80 | 1.30–1.70 |
| Molybdenum, % | 0.45–0.65 | 0.20–0.30 | 0.20–0.35 | 0.45–0.65 | 0.15–0.30 |
| Hardenability | Highest of the five | High | High | Highest, at lower strength | Moderate to high |
| Through-hardened section | to approx. 250 mm | to approx. 150 mm | to approx. 150 mm | to approx. 250 mm | to approx. 100–150 mm |
| Top tensile | 1550 MPa and above | approx. 1250–1400 MPa | approx. 1225–1375 MPa | approx. 1075–1225 MPa | approx. 1200 MPa |
| Temper embrittlement | Low, high Mo | Moderate | Moderate | Low, high Mo | Moderate |
| Cost | Highest | Medium-high | Medium | High | Medium |
| Specify it when | Heavy section plus highest strength, or low-temperature toughness | Drawing or code names 4340, moderate section | General high-tensile shafting, moderate section | Heavy section, toughness over hardness | Order written to EN 10083-3, moderate section |
Compiled by Jiangyin Jiangnan Metal Co., Ltd. from BS 970-3, EN 10083-3 and SAE J404 composition limits. Section and strength figures are practical guidance from our forging and heat treatment records, not standard values.
1.6745 is not AISI 4340. Cross-reference tables list them together because both are medium-carbon Ni-Cr-Mo steels, but 1.6745 carries 2.30–2.80 % nickel against 1.65–2.00 % for 4340, and 0.45–0.65 % molybdenum against 0.20–0.30 %. A 4340 heat will not meet a 1.6745 order and a 1.6745 heat will not meet a 4340 order. If a drawing says 4340 and the supplier offers 1.6745, or the reverse, that is a substitution and it needs engineering approval.
Standards and delivery conditions
| Scope | Standard | What it governs |
|---|---|---|
| Grade and condition | BS 970-3: 826M40 (formerly EN26) | Composition window, condition letters T to Z, ruling sections |
| General delivery conditions | EN 10083-1 | General technical delivery conditions for quenched and tempered steels |
| Open-die forgings | EN 10250-3 | Open-die steel forgings for general engineering, alloy special steels |
| Bar and billet | ASTM A29 / A29M | General requirements for hot-wrought alloy steel bars |
| Ultrasonic testing | EN 10228-3, SEP 1921 class C/D/E, ASTM A388 | Volumetric examination of the forging |
| Magnetic particle testing | EN 10228-1, ASTM E1444 | Surface and near-surface discontinuities |
| Mechanical testing | EN ISO 6892-1, ASTM A370, EN ISO 148-1 | Tensile, hardness and Charpy impact test methods |
| Certification | EN 10204 3.1 and 3.2 | Mill test certificate; 3.2 witnessed by a third party |
Source: Jiangyin Jiangnan Metal Co., Ltd. Where a customer specification, an NDT class or a design code differs from the list above, we work to the customer document and say so on the certificate.
Delivery conditions we supply
- Annealed. The usual condition for stock and for parts the customer will heat treat after machining. Hardness 255 HB maximum.
- Normalised, or normalised and tempered, for a uniform structure ahead of a later hardening operation.
- Quenched and tempered to a named condition T to Z, or to a hardness band you specify. Most finished forgings ship this way.
- Rough machined or finish machined to print, after heat treatment, with an agreed allowance.
1.6745 forged product forms and size capability
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory. Every item below is forged to the customer's drawing or dimensional sketch. Open-die work needs no dies, so there is no tooling charge and no piece minimum, and single prototypes are economic.
- Seamless rolled ringsRing-rolled with no weld seam. Rectangular or profiled section, for bearing races, gear rims and slew rings.
- Forged shafts and spindlesStraight, stepped and eccentric shafts, crankshafts, pinion shafts and mandrels.
- Forged flangesWeld neck, slip-on, blind, long weld neck and orifice, to ASME B16.5 / B16.47 or to drawing.
- Discs and blanksUpset forged discs for gear blanks, covers, wheels and blind ends.
- Round bars and billetsForged and peeled or rough turned, cut to length.
- Sleeves and bushingsHollow forged, trepanned or bored, thin or heavy wall.
- Tube sheetsForged and drilled tube sheets for shell-and-tube heat exchangers.
- Gear blanks and pinionsForged blanks for through-hardened or nitrided gearing.
- Forged rollsMill work rolls and back-up rolls, and rolls for paper, rubber and plastics lines.
- Valve componentsBodies, bonnets, seat rings, stems, gate and plug blanks.
| Product form | Dimensional range | Unit weight |
|---|---|---|
| Seamless rolled rings | OD 200–3,000 mm, height to 800 mm | 20–8,000 kg |
| Round bars and shafts | Ø80–800 mm, length to 6,000 mm | 20–10,000 kg |
| Discs, tube sheets, gear blanks | Ø200–2,500 mm, thickness to 600 mm | 30–12,000 kg |
| Sleeves, bushings, hollows | OD to 1,500 mm, length to 4,000 mm | 30–8,000 kg |
| Overall plant capability | 80–6,000 mm across all forms | 10–15,000 kg per piece |
Source: Jiangyin Jiangnan Metal Co., Ltd. forging capability. Machining allowance is normally 6–20 mm per surface depending on section size, unless the drawing states otherwise. Finish-machined parts to print are also supplied.
Plant and equipment
Jiangyin Jiangnan Metal Co., Ltd. operates open-die forging hammers of 1, 3, 5 and 9 tonnes together with a 5,000-tonne hydraulic press, ring rolling mills, and heat treatment and machining shops on the same site. The company employs approximately 460 people, including 9 senior engineers and 32 intermediate engineers. Raw material control, forging, heat treatment, machining, testing and inspection are all carried out in house, so one certificate covers the whole route.
How 1.6745 forgings are made
- MeltingEAF + LF + VD. Vacuum degassing brings hydrogen below 2 ppm and prevents flaking in heavy quenched and tempered Ni-Cr-Mo sections. ESR remelting where the specification calls for it.
- Ingot and billet checkHeat chemistry is verified by optical emission spectrometer against the 1.6745 window, including the nickel and molybdenum limits that define the grade, before any material is heated.
- Open-die forgingHeated to 1,150–1,200 °C and forged on hammer or press with a controlled reduction ratio, finishing above 850 °C. Rings are rolled seamless. Grain flow is developed to follow the part contour rather than being cut through by later machining.
- Post-forge annealImmediately after forging, to soften for machining, relieve forging stress and give hydrogen a route out of heavy sections.
- Rough machiningTurned, bored and faced with an agreed allowance, so that the quench sees a section close to the finished one.
- Quench and temperAustenitised at 820–850 °C, oil quenched, then tempered to the ordered condition. Charts recorded for every load.
- Non-destructive testingUltrasonic examination to EN 10228-3, SEP 1921 or ASTM A388 at the ordered class, plus magnetic particle inspection where specified.
- Mechanical testingTensile, hardness and Charpy impact from a prolongation of the forging, after final heat treatment.
- Finish machining, marking and despatchFinish machined to print if ordered, hard stamped with heat number, preserved, and packed in wooden cases or on pallets for sea or air freight.
Where 1.6745 forgings are used
| Industry | Components forged in 1.6745 |
|---|---|
| Power transmission and gearboxes | Gear blanks, pinion shafts, gear rims, slew ring blanks, spindles, cams and power transmission slide gears for wind turbine, marine and industrial drives |
| Oil and gas, onshore and offshore | Wellhead and Christmas tree components, drill collars and mandrels, subsea and deepwater production system parts, valve bodies, bonnets, seat rings and stems for ball, gate, globe, check and plug valves |
| Heavy machinery and mining | Winder parts, eccentric shafts, crusher shafts, brake pins, tie rods and tie rod ends, turnbuckles, mill and mixer components for cement, sugar and concrete plant |
| Pumps and compressors | Shafts for chemical and plunger pumps, industrial air compressors, nitrogen generators and power generators |
| Automotive and off-highway | Crankshafts, axles, differential shafts, connecting rods, push rods, main shafts, high-tensile bolts and studs |
| Aerospace and defence | Undercarriage and airframe components, ordnance parts, gun barrels and breech mechanisms, where the specification permits this grade |
| Steel and process mills | Forged mill work rolls and back-up rolls, roll necks, mandrels for tube manufacture, pinion sleeves |
| Pressure equipment | Forged tube sheets, shell flanges, nozzles, blocks and blind covers for pressure vessels, air receivers, shell-and-tube heat exchangers, columns, towers, tanks, silos and preheaters |
| Shipbuilding and marine | Propeller and intermediate shafting, rudder stocks, coupling flanges and heavy machinery forgings |
Source: Jiangyin Jiangnan Metal Co., Ltd. production experience with 1.6745 / 826M40, and published application data for the grade. Suitability for a specific duty depends on the design code and the service conditions; confirm with your own engineering review.
Most of these parts are large, heavily loaded and expected to run for years. 1.6745 gets specified when the drawing calls for a strength level that a cheaper chromium-molybdenum steel cannot reach at the required section, or when the core of a heavy part has to stay tough at low temperature. It costs more per kilogram than 42CrMo4 or 34CrNiMo6, and that extra cost only pays off in heavy sections and in the high strength conditions.
Testing, inspection and certification
- Chemical analysis. Spectrometric heat analysis on every heat, and product analysis on the finished forging on request.
- Mechanical testing. Room-temperature tensile and elongation, Brinell or Rockwell hardness, and Charpy V-notch or Izod impact, from a prolongation after final heat treatment. Sub-zero impact testing to your specified temperature.
- Ultrasonic testing. EN 10228-3, SEP 1921 class C, D or E, ASTM A388 or a customer class, on 100 % of the volume where the order requires it.
- Magnetic particle testing. EN 10228-1 or ASTM E1444 for surface and near-surface indications.
- Metallography. Grain size to ASTM E112, inclusion rating to ASTM E45 or DIN 50602, macro-etch and microstructure review on the metallographic microscope.
- Hardenability. Jominy end-quench testing where a customer specification requires a hardenability band.
- Dimensional inspection. Full dimensional report against the drawing before despatch.
- Certification. EN 10204 3.1 mill test certificate as standard, showing heat number, ladle analysis, mechanical results, heat treatment record and NDT results. EN 10204 3.2 witnessed by TUV, BV, LR, SGS or DNV on request at order entry. Full heat traceability and hard stamping throughout.
The inspection department is equipped with a universal testing machine, impact testing machine, hardness testing machine, magnetic particle flaw detector, ultrasonic flaw detector, spectrometer and metallographic microscope. Third-party witness inspection at any hold point is welcome; state the hold points on the purchase order so they can be built into the routing.
Frequently asked questions about 1.6745
What is 1.6745 steel?
1.6745 is the Werkstoff number for 40NiCrMo10-5, a medium-carbon nickel-chromium-molybdenum through-hardening alloy steel containing about 0.40 % carbon, 2.40–2.70 % nickel, 0.60–0.80 % chromium and 0.40–0.60 % molybdenum. It is the same material as the British grade 826M40, still widely called EN26. It is used for heavily loaded forgings that must be hardened right through a thick section, and it can be quenched and tempered to tensile strengths from 850 MPa to over 1550 MPa.
What is 1.6745 equivalent to?
1.6745 is the same material as 40NiCrMo10-5 (DIN/EN name), 826M40 (BS 970-3), EN26 (the superseded BS 970:1955 name still in daily use), X9940 (AS 1444, Australia) and 40Ni10Cr3Mo6 (IS 5517, India). The nearest catalogued European grades are 34CrNiMo6 (1.6582) and 30CrNiMo8 (1.6580), and the nearest American grade is AISI 4340, but none of those three is chemically identical to 1.6745.
Is 1.6745 the same as AISI 4340?
No. They are frequently cross-referenced but they are different steels. 1.6745 carries 2.30–2.80 % nickel and 0.45–0.65 % molybdenum; AISI 4340 carries 1.65–2.00 % nickel and 0.20–0.30 % molybdenum. The extra nickel and molybdenum give 1.6745 higher hardenability, so it through-hardens in about a 250 mm ruling section against roughly 150 mm for 4340, and it reaches higher tensile conditions. A 4340 heat cannot be certified against a 1.6745 order, and substituting one for the other needs engineering approval.
What tensile strength can 1.6745 forgings reach?
From 850 MPa in condition T up to 1550 MPa and above in condition Z, set by the tempering temperature. The most commonly ordered condition for forged shafts and gear blanks is condition V, 1000–1150 MPa with a 0.2 % proof stress of at least 835 MPa and a hardness of roughly 31–38 HRC. The condition that is realistically achievable depends on the section size, so state the section when you specify a condition.
What heat treatment is used for 1.6745 forgings?
Harden by austenitising at 820–850 °C and quenching in oil, with heavy sections preheated at 400–500 °C. Then temper: 550–660 °C for the lower-strength conditions T to V, or 300–550 °C for the higher-strength conditions W to Z. Annealing is at 830–850 °C with a slow furnace cool to give 255 HB maximum for machining, and stress relieving is at 640–660 °C. Because 1.6745 contains 0.4–0.6 % molybdenum, it can be tempered in the 300–550 °C range without the serious loss of impact values that this range causes in a nickel-chromium steel without molybdenum.
Can 1.6745 be welded?
It can be, but it is not a fabrication steel. The carbon equivalent CE(IIW) is approximately 0.91, well above the 0.45 threshold at which welding becomes difficult. Welding in the hardened and tempered condition is not recommended because the heat-affected zone will not hold the specified properties. Where welding is unavoidable, weld in the annealed condition with preheat, stress relieve at 640–660 °C as soon as the part cools to hand warmth, and then harden and temper the finished assembly.
Can 1.6745 be nitrided or induction hardened?
Yes. 1.6745 is well suited to both. Nitriding at 500–530 °C after quenching and tempering produces a hard, wear-resistant case on a tough core without distorting the part, and flame or induction hardening is used to raise local hardness on journals, gear teeth and wear faces. Both are carried out after the through heat treatment, so the core condition is unaffected.
What sizes of 1.6745 forgings can you supply?
Jiangyin Jiangnan Metal Co., Ltd. forges 1.6745 from 80 mm to 6,000 mm and from 10 kg to 15,000 kg per piece: seamless rolled rings to 3,000 mm outside diameter, round bars and shafts to 800 mm diameter and 6,000 mm long, and discs and tube sheets to 2,500 mm diameter and 600 mm thick. The plant runs 1, 3, 5 and 9 tonne open-die hammers and a 5,000-tonne hydraulic press. Because open-die forging needs no dies, there is no tooling charge and no minimum order quantity by piece.
Do you supply a material certificate for 1.6745 forgings?
Yes. Every 1.6745 forging ships with an EN 10204 3.1 mill test certificate as standard, showing the heat number, ladle chemical analysis, mechanical test results, heat treatment record and NDT results. EN 10204 3.2 certification witnessed by a third party such as TUV, BV, LR, SGS or DNV is available on request at the time of order. Where a heat satisfies more than one designation, the certificate lists all of them, so one forging can be released against 1.6745, 826M40 and EN26 together.
How long does a 1.6745 forging take to produce?
Lead time depends on whether the grade is in raw stock and on the size of the forging. Simple rings, discs and shafts from stock material typically run 25–40 days. Parts needing a new melt, ESR remelting, heavy machining or third-party witnessed inspection take longer. Send a drawing and we will confirm a firm date with the quotation.
Who supplies open-die forged 1.6745 parts in China?
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory located at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. It forges 1.6745 / 40NiCrMo10-5 / EN26 / 826M40 and a wide range of other alloy steels, carbon steels, tool steels, stainless steels and nickel alloys into seamless rolled rings, flanges, shafts, discs, sleeves, tube sheets and round bars, and exports worldwide. Enquiries: sales@steelforgepieces.com or +86 189 2135 9659.