What is 708M40 steel?

708M40 is a medium-carbon, 1 % chromium-molybdenum through-hardening engineering steel specified in the British Standard BS 970. It was known as EN19 under BS 970:1955 and is used where high tensile strength must combine with shock and wear resistance, typically in forged gears, shafts, spindles, collars, jigs and fixtures.

Is 708M40 the same as 42CrMo4 and AISI 4140?

They are the closest commercial equivalents and interchangeable for most applications, but not identical specifications. 708M40 allows 0.36 to 0.44 % carbon with 0.15 to 0.25 % molybdenum, while 42CrMo4 allows 0.38 to 0.45 % carbon with 0.15 to 0.30 % molybdenum and tighter phosphorus. Acceptance depends on the product standard and test requirements on the order.

What is the difference between 708M40 and 709M40?

Both are the same 1 % chromium-molybdenum steel and both are called EN19 in the trade. The difference is the specified molybdenum range, approximately 0.15 to 0.25 % for 708M40 and 0.25 to 0.35 % for 709M40. A purchase order should state the designation, standard and edition year.

What is 50HM steel and what is its equivalent?

50HM is the Polish PN designation for a 0.50 % carbon chromium-molybdenum steel. In the Polish system H denotes chromium and M denotes molybdenum, so 50HM corresponds to 50CrMo4, material number 1.7228, and to AISI 4150, 50CD4 and the Russian 50KhM.

Is 708M50 the same as AISI 4150?

For practical purposes yes. 708M50 is the higher-carbon member of the BS 970 708 series at about 0.50 % carbon against 0.40 % for 708M40, which places it alongside 50CrMo4 and AISI 4150. It reaches higher hardness and strength than 708M40 but is less tough and harder to weld.

What hardness can 708M40 reach after quenching and tempering?

Between 248 and 401 HB depending on the condition specified and the section size. Condition T at 850 to 1000 MPa tensile gives 248 to 302 HB to a limiting ruling section of 250 mm. Condition X at 1150 to 1300 MPa gives 341 to 401 HB but only in sections up to about 30 mm. Annealed hardness is 225 HB maximum.

At what temperature should 708M40 be forged?

Between 1200 and 870 degrees Celsius, or 2200 to 1600 degrees Fahrenheit. Finishing as low in that range as the press allows gives a finer grain size. The alloy should not be forged below 870 degrees Celsius and forgings must be slow cooled afterwards.

Why must 708M40 not be tempered between 200 and 420 degrees Celsius?

Tempering in that band causes temper embrittlement, a sharp loss of impact toughness with no visible change in hardness. Temper either below 200 degrees Celsius or, far more commonly, in the 540 to 680 degrees Celsius range used to set final mechanical properties.

How are 708M40, 708M50 and 50HM heat treated?

Anneal at 790 to 840 degrees Celsius and furnace cool for a machinable structure of 225 HB maximum. Normalise at 840 to 880 degrees Celsius and air cool to refine grain structure after forging. Harden at 830 to 860 degrees Celsius, quenching in oil for lighter sections or water for heavy sections. Temper at 540 to 680 degrees Celsius and air cool. Stress relieve at 30 to 50 degrees Celsius below the tempering temperature, or at 600 to 650 degrees Celsius in the annealed condition.

What forged product forms are available in 708M40, 708M50 and 50HM?

Jiangyin Jiangnan Metal Co., Ltd. supplies these grades as forged round, square, rectangular, flat and hexagonal bars, hollow bars, sleeves, bushings, pipes, barrels, casings, shells, cylinders, hubs and housings, seamless rolled rings and forged rings, blocks, discs and plates, and gear shafts, pinion shafts, spindles, ring gears and gear wheels, from 50 kg to 20 t per piece.

What is the minimum order quantity and lead time for 708M40 forgings?

Open-die forging requires no dedicated tooling, so single pieces are accepted as well as production batches. Typical lead time is four to six weeks for a normalised or annealed forging and six to eight weeks when quenching, tempering and ultrasonic inspection are included.

Can you supply EN 10204 3.1 certificates and third-party inspection?

Yes. EN 10204 3.1 certificates are issued as standard and cover heat analysis, mechanical test results, heat-treatment records and NDT reports. EN 10204 3.2 certification with witness inspection by SGS, BV, TUV or Lloyd's Register is available when specified at the order stage.

708M40, 708M50 and 50HM Alloy Steel Forgings

Open-die forged bars, hollow bars, seamless rolled rings, discs, blocks and gear shafts in 1 % Cr-Mo through-hardening steel, forged and heat treated to order at our works in Jiangyin, China.

Technical data reviewed by the metallurgical department of Jiangyin Jiangnan Metal Co., Ltd. Published 12 March 2018. Last reviewed 12 September 2026.

Summary

708M40 is a 1 % chromium-molybdenum through-hardening engineering steel specified in BS 970, formerly EN19, equivalent to 42CrMo4 (1.7225) and AISI 4140. 708M50 and the Polish grade 50HM are the higher-carbon members of the same family, equivalent to 50CrMo4 (1.7228) and AISI 4150. All three are forged between 1200 °C and 870 °C and reach 248 to 341 HB after quenching and tempering.

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Jiangyin, Jiangsu Province, China that supplies 708M40, 708M50 and 50HM as forged round, square, flat and hexagonal bars, hollow bars and sleeves, seamless rolled rings, discs, blocks, and gear and pinion shafts from 50 kg to 20 t per piece, with EN 10204 3.1 material certificates.

BS 970 / EN19 42CrMo4, 50CrMo4 AISI 4140, 4150 50 kg to 20 t per piece EN 10204 3.1 MTC

1Grade identification and equivalents

The three designations on this page cover two closely related chromium-molybdenum steels that differ mainly in carbon content. The equivalence matters on paper, because an order that names only EN19 can be filled with material of two different molybdenum ranges.

Table 1. International equivalents for 708M40, 708M50 and 50HM
Designation	Standard and country	Nominal carbon	Closest equivalents
708M40	BS 970, United Kingdom, formerly EN19	0.40 %	42CrMo4, 1.7225, AISI 4140, SCM440, 42CD4, 42KhM
709M40	BS 970:1991, United Kingdom	0.40 %	Same family, molybdenum specified 0.25 to 0.35 % instead of 0.15 to 0.25 %
708M50	BS 970, United Kingdom	0.50 %	50CrMo4, 1.7228, AISI 4150, 50CD4, SCM445
50HM	PN, Poland	0.50 %	50CrMo4, 1.7228, AISI 4150, 50KhM, 50CD4

Ordering tip. State the standard and its edition year on the purchase order, for example 708M40 to BS 970-1:1991, rather than EN19 on its own. EN19 was the BS 970:1955 name. The 1991 revision re-designated the grade, and 708M40 and 709M40 carry different molybdenum ranges. We confirm the exact specification in writing before cutting.

2Chemical composition

Composition is checked on every heat by optical emission spectrometry and reported on the mill certificate. The ranges below are specification limits. What appears on your EN 10204 3.1 certificate is the actual heat analysis, plus the product analysis where one is called for.

Table 2. Chemical composition, % by weight
Grade	C	Si	Mn	P max	S max	Cr	Mo
708M40	0.36-0.44	0.10-0.40	0.70-1.00	0.035	0.040	0.90-1.20	0.15-0.25
709M40	0.36-0.44	0.10-0.40	0.70-1.00	0.035	0.040	0.90-1.20	0.25-0.35
708M50 and 50HM	0.46-0.54	0.10-0.40	0.50-0.80	0.025	0.035	0.90-1.20	0.15-0.30
42CrMo4 (1.7225)	0.38-0.45	max 0.40	0.60-0.90	0.025	0.035	0.90-1.20	0.15-0.30
50CrMo4 (1.7228)	0.46-0.54	max 0.40	0.50-0.80	0.025	0.035	0.90-1.20	0.15-0.30

Restricted sulphur down to 0.015 % max, vacuum degassing, and limits on residual Cu, Sn, As and Sb can be written into the order for critical rotating parts. Tell us the end use and we will propose the melting route.

3Mechanical properties after quenching and tempering

These steels are supplied hardened and tempered, and properties are always quoted against a stated ruling section. The same chemistry that gives 1000 MPa in a 60 mm shaft gives much less at the core of a 250 mm one, so the ruling section belongs on the order.

Table 3. 708M40 in BS 970 heat-treatment conditions
Condition	Tensile strength R_m	Yield R_p0.2 min	Elongation min	Hardness	Limiting ruling section
T	850-1000 MPa	680 MPa	13 %	248-302 HB	250 mm
U	925-1075 MPa	755 MPa	12 %	269-331 HB	150 mm
V	1000-1150 MPa	835 MPa	12 %	293-352 HB	100 mm
W	1075-1225 MPa	910 MPa	11 %	311-375 HB	63 mm
X	1150-1300 MPa	985 MPa	10 %	341-401 HB	30 mm
Annealed	n/a	n/a	n/a	225 HB max	any

Table 4. 708M50 and 50HM (50CrMo4) quenched and tempered, by section
Ruling section	Yield R_p0.2 min	Tensile R_m	Elongation A min
up to 16 mm	900 MPa	1100-1300 MPa	9 %
16 to 40 mm	780 MPa	1000-1200 MPa	10 %
40 to 100 mm	700 MPa	900-1100 MPa	11 %
100 to 160 mm	650 MPa	850-1000 MPa	12 %
160 to 250 mm	550 MPa	800-950 MPa	13 %

Typical physical constants: density 7.85 g/cm³, modulus of elasticity 210 GPa, thermal conductivity about 42 W/m·K at 20 °C, Ac₁ near 730 °C. Charpy V-notch testing, impact testing down to −40 °C and a NACE MR0175 hardness cap of 22 HRC are available on request.

4Forging practice

708M40, 708M50 and 50HM are forged between 1200 °C and 870 °C, or 2200 to 1600 °F. A lower finishing temperature gives a finer grain size, so we plan the pass schedule to finish as low as the press load allows. These alloys should not be forged below 870 °C, and forgings are slow cooled afterwards to avoid cracking from residual transformation stresses.

Every piece is worked to a forging ratio of at least 3:1 to break down the as-cast dendritic structure and close centreline porosity. Rings are expanded on a radial-axial rolling mill so the grain flow follows the circumference. That grain flow is the reason a seamless rolled ring outperforms a ring cut from plate.

5Heat treatment

Heat treatment is carried out in our own furnaces under continuous chart recording, so the thermal history stays with the part and goes into the documentation package.

Annealing, 790 to 840 °C, furnace cool Forgings can go straight from the press into a furnace held near 815 °C, soak, then furnace cool to give a machinable structure of 225 HB or below. This suits simple shapes. Where sections vary enough that parts of a forging finish much colder than others, the structure will not come out uniform, and a spheroidising anneal near 750 °C is used instead.
Normalising, 840 to 880 °C, air cool Heating above the ferrite to austenite transformation range and cooling in air refines the structure of forgings that cooled unevenly from the press. As a conditioning treatment before hardening or carburising the upper end of the range is used. When normalising is the final treatment, the lower end is used.
Hardening, 830 to 860 °C, quench in oil or water Austenitising forms martensite on quenching, which raises strength and hardness and costs ductility. The exact temperature depends on the heat analysis, the section size and the quenchant. Lighter sections are quenched in oil, heavy sections in water.
Tempering, 540 to 680 °C, air cool Tempering relieves quenching stresses and sets the final properties. Temper as soon as the part reaches ambient temperature. Do not temper between 200 °C and 420 °C, or 400 to 790 °F, because that range causes temper embrittlement in this family of steels.
Stress relieving, 600 to 650 °C annealed, or 30 to 50 °C below the tempering temperature Applied after heavy machining or welding, then cooled in still air.
Surface hardening These grades also take nitriding and flame or induction hardening, which is the usual route for journal areas on forged shafts and for gear teeth.

6Machinability and welding

708M40, 708M50 and 50HM machine readily after annealing. The best structure for machining runs from coarse lamellar pearlite through to coarse spheroidite. In the quenched and tempered condition above roughly 300 HB, tool life drops off and the job wants rigid setups with positive rake carbide tooling.

Welding is possible with conventional processes, but not in the hardened condition without a qualified procedure. Preheat, controlled interpass temperature and post-weld heat treatment are all required. The higher-carbon 708M50 and 50HM are more crack-sensitive than 708M40.

7Forged product forms and size range

Everything below is open-die forged to order from our own stock of 708M40, 708M50 and 50HM. Open-die work carries no tooling cost, which is why it suits one-off spares and batches of a few dozen equally well.

Table 5. Forged product forms available in 708M40, 708M50 and 50HM
Product form	Size range	Typical use
Round bars and rods	80 to 1200 mm diameter, up to 12 000 mm long	Shaft blanks, machining stock
Square, rectangular, flat and hexagonal bars	30 to 600 mm thick, up to 1500 mm wide	Dies, tool holders, structural blanks
Hollow bars, sleeves, bushings and cylinders	200 to 2000 mm OD, from 100 mm ID	Casings, barrels, liners, housings
Seamless rolled rings	300 to 4000 mm OD, 50 to 500 mm wall, up to 800 mm high	Bearing races, gear rims, flanges, tyres
Discs, blocks and plates	200 to 2500 mm diameter, 50 to 800 mm thick	Tube sheets, blind flanges, gear blanks
Gear shafts, pinion shafts and spindles	80 to 1000 mm diameter, up to 12 000 mm long, stepped	Gearbox and drivetrain shafts
Ring gears and gear wheels	up to 4000 mm OD	Mill and mining drives

Weight range 50 kg to 20 t per piece. Delivery condition: as forged, normalised, annealed, or quenched and tempered. Surface: black, shot blasted, rough machined, or finish machined to your drawing.

8Applications

These alloys are used as forgings in the aerospace, oil and gas, automotive, agricultural and defence industries. The usual parts are forged gears, shafts and spindles, where deep hardenability combined with toughness at 250 to 350 HB is difficult to match at the price.

Oil and gas

Drill collars, kelly bars, valve bodies and bonnets, wellhead components, riser couplings.

Power transmission

Gear shafts, pinion shafts, ring gears, couplings and torque tubes for industrial and marine gearboxes.

Mining and heavy plant

Crusher eccentric shafts, mill pinions, track pins, hydraulic cylinder rods.

Wind and hydro

Main shafts, hub and bearing rings, pitch and yaw bearing races.

9Buying 708M40 forgings from Jiangyin Jiangnan Metal

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Jiangyin sits on the south bank of the Yangtze in the Yangtze River Delta, about 90 minutes by road from Shanghai port, which keeps inland freight short on heavy single pieces.

Forging

Hydraulic open-die presses and a radial-axial ring rolling mill. Single pieces to 20 t, minimum 3:1 forging ratio.

Heat treatment

Our own quench and temper line with chart-recorded furnaces, calibrated thermocouples, water and oil quench tanks.

Testing

Spectrometer, tensile, impact and hardness testing, ultrasonic inspection to EN 10228-3 or ASTM A388, MPI and PT.

Documentation

EN 10204 3.1 certificates as standard, 3.2 with third-party witness by SGS, BV, TUV or Lloyd's on request.

We quote from a drawing, a dimensioned sketch, or just a grade and a size. For a first enquiry send the grade, the finished dimensions and the machining allowance you want, the quantity, the delivery condition, and the certificate and inspection requirements.

Document reference. JJM-TDS-708M40, revision 4, issued 12 September 2026 by Jiangyin Jiangnan Metal Co., Ltd., No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Enquiries: sales@steelforgepieces.com, +86 189 2135 9659. Source page: https://www.steelforgepieces.com/Alloy-Steel/708M40-708M50-50HM.html

10Frequently asked questions

What is 708M40 steel?: 708M40 is a medium-carbon, 1 % chromium-molybdenum through-hardening engineering steel specified in the British Standard BS 970. It was known as EN19 under BS 970:1955. It is used where high tensile strength has to be combined with shock resistance and wear resistance, typically in forged gears, shafts, spindles, collars, jigs and fixtures.
Is 708M40 the same as 42CrMo4 and AISI 4140?: They are the closest commercial equivalents and are interchangeable for most applications, but they are not identical specifications. 708M40 allows 0.36 to 0.44 % C with Mo 0.15 to 0.25 %. 42CrMo4 allows 0.38 to 0.45 % C with Mo 0.15 to 0.30 % and tighter phosphorus. Acceptance depends on the product standard and the test requirements on your order, so check the mill certificate rather than the grade name.
What is the difference between 708M40 and 709M40?: Both are the same 1 % Cr-Mo steel and both get called EN19 in the trade. The difference is the specified molybdenum range: roughly 0.15 to 0.25 % for 708M40 and 0.25 to 0.35 % for 709M40. Both designations are in commercial use, so a purchase order should state the designation, the standard and the edition year.
What is 50HM steel and what is its equivalent?: 50HM is the Polish PN designation for a 0.50 % carbon chromium-molybdenum steel. In the Polish system H denotes chromium and M denotes molybdenum, so 50HM corresponds to 50CrMo4, material number 1.7228, and to AISI 4150, 50CD4 and the Russian 50KhM.
Is 708M50 the same as AISI 4150?: For practical purposes yes. 708M50 is the higher-carbon member of the BS 970 708 series at about 0.50 % carbon against 0.40 % for 708M40, which puts it alongside 50CrMo4 and AISI 4150. It reaches higher hardness and strength than 708M40 but is less tough and harder to weld.
What hardness can 708M40 reach after quenching and tempering?: Between 248 and 401 HB depending on the condition specified and the section size. Condition T at 850 to 1000 MPa tensile gives 248 to 302 HB and holds to a limiting ruling section of 250 mm. Condition X at 1150 to 1300 MPa gives 341 to 401 HB, but only in sections up to about 30 mm. Annealed hardness is 225 HB or lower.
At what temperature should 708M40 be forged?: Between 1200 °C and 870 °C, or 2200 to 1600 °F. Finishing as low in that range as the press allows gives a finer grain size. The alloy should not be forged below 870 °C, and forgings must be slow cooled afterwards.
Why must 708M40 not be tempered between 200 and 420 °C?: Tempering in that band causes temper embrittlement, a sharp loss of impact toughness with no visible change in hardness. Temper either below 200 °C or, far more commonly, in the 540 to 680 °C range used to set final mechanical properties.
How are 708M40, 708M50 and 50HM heat treated?: Anneal at 790 to 840 °C and furnace cool for a machinable structure of 225 HB maximum. Normalise at 840 to 880 °C and air cool to refine grain structure after forging. Harden at 830 to 860 °C, quenching in oil for lighter sections or water for heavy sections. Temper at 540 to 680 °C and air cool. Stress relieve at 30 to 50 °C below the tempering temperature, or at 600 to 650 °C in the annealed condition.
What forged product forms can you supply in these grades?: Jiangyin Jiangnan Metal supplies 708M40, 708M50 and 50HM as forged round, square, rectangular, flat and hexagonal bars; hollow bars, sleeves, bushings, pipes, barrels, casings, shells, cylinders, hubs and housings; seamless rolled rings and forged rings; blocks, discs and plates; and gear shafts, pinion shafts, spindles, ring gears and gear wheels, from 50 kg to 20 t per piece.
What is the minimum order quantity and the lead time?: Open-die forging needs no dedicated tooling, so we take single pieces as well as production batches. Typical lead time is four to six weeks for a normalised or annealed forging, six to eight weeks when quenching, tempering and ultrasonic inspection are included. Confirm current lead times with your enquiry.
Can you supply EN 10204 3.1 certificates and third-party inspection?: Yes. EN 10204 3.1 certificates are issued as standard and cover heat analysis, mechanical test results, heat-treatment records and NDT reports. EN 10204 3.2 certification with witness inspection by SGS, BV, TUV or Lloyd's Register is available when it is specified at the order stage.

Request a quotation for 708M40, 708M50 or 50HM forgings

Send a drawing or the finished dimensions, grade, quantity, delivery condition and certificate requirement. We reply with price, weight, lead time and the proposed forging and heat-treatment route.

Jiangyin Jiangnan Metal Co., Ltd. No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Telephone and WhatsApp: +86 189 2135 9659
Email: sales@steelforgepieces.com

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Data note. The values on this page are specification limits and typical results published for guidance. They are not a warranty of the properties of any particular delivery. The governing document for a supplied forging is its EN 10204 material certificate.