SCM440 Chromium-Molybdenum Steel Forgings

SCM440 steel overview

SCM440 is a medium-carbon chromium-molybdenum steel for machine structural use, specified in JIS G 4053 and intended for parts that are hardened and tempered after forging or machining. About 1% chromium and 0.2% molybdenum give it far deeper hardenability than plain carbon steels such as S45C, so a heat-treated SCM440 part keeps high strength further below its surface.

Meaning of the designation

S

Steel

CM

Chromium and molybdenum are the main alloying elements

4

Code for the main alloying element content within the SCM series

40

Nominal carbon content of 0.40%

JIS G 4105 and JIS G 4053

SCM440 was first published in JIS G 4105, the former Japanese standard for chromium-molybdenum steels. JIS G 4053 was established on 20 May 2003 to consolidate the separate Japanese standards for manganese, chromium, chromium-molybdenum, nickel-chromium and nickel-chromium-molybdenum structural steels. The current edition, JIS G 4053:2023, was issued on 22 May 2023 with reference to ISO 683-1, ISO 683-2 and ISO 683-3.

Many drawings still quote JIS G 4105. The grade name is unchanged, but older tables show a narrower manganese range of 0.60–0.85%, while JIS G 4053 allows 0.60–0.90%.

Reasons to specify SCM440

• High quenched-and-tempered strength: a JIS reference tensile strength of at least 980 MPa with 12% minimum elongation.
• Hardenability: chromium, molybdenum and manganese let moderate sections harden through, and molybdenum reduces the steel's sensitivity to temper embrittlement.
• Surface hardening: a quenched-and-tempered SCM440 core accepts induction hardening or nitriding where a wear-resistant surface is needed.
• Cost: it reaches high strength without the nickel content, and nickel cost, of Ni-Cr-Mo steels such as SNCM439 (AISI 4340).

When to choose another grade

• Very heavy sections that need high core strength: a Ni-Cr-Mo steel such as SNCM439 or 34CrNiMo6 hardens deeper.
• Corrosive service: roughly 1% chromium gives no meaningful corrosion resistance, so a stainless grade is required.
• Welded pressure-retaining parts built to a design code: use a forging grade that the code lists.

Forged products

Jiangnan Metal produces SCM440 open-die forgings and forged rings, delivered as forged or rough machined to the customer's drawing. The forging route follows the part's geometry: shafts and bars are drawn out, discs and blocks are upset, and rings are pierced and expanded so that the grain flow follows the circumference.

The practical size of an SCM440 forging depends on its geometry and on the mechanical properties it must reach at its ruling section, as the mechanical properties section explains. Send the drawing for a feasibility check before the design is fixed.

SCM440 equivalent grades

The closest equivalents of SCM440 are AISI/SAE 4140 (UNS G41400), EN 42CrMo4 (1.7225) and GB 42CrMo, but their chemistry windows are not identical. A heat can satisfy SCM440 and an equivalent at the same time only when its analysis falls inside both ranges, so the governing standard should be written on the purchase order.

GB/T 3077 limits shown are for the quality-steel class; high-grade classes (suffix A or E) have lower P and S limits.

SCM440 chemical composition

Under JIS G 4053:2023, SCM440 contains 0.38–0.43% C, 0.15–0.35% Si, 0.60–0.90% Mn, 0.030% max P, 0.030% max S, 0.25% max Ni, 0.90–1.20% Cr and 0.15–0.30% Mo, with residual copper limited to 0.30%.

Steelmaking. SCM440 for Jiangnan Metal forgings is made by electric arc furnace melting, ladle-furnace refining and vacuum degassing (EAF + LF + VD). Vacuum degassing lowers dissolved hydrogen, which reduces the risk of hydrogen flakes in heavy forgings. The heat analysis is reported on every EN 10204 certificate.

SCM440 mechanical properties

Quenched and tempered SCM440 has a JIS reference yield strength of at least 835 MPa, tensile strength of at least 980 MPa, elongation of at least 12%, reduction of area of at least 45% and hardness of 285–352 HBW, measured on a 25 mm test piece. These reference values describe the steel, not a large forging: the core of a thick part cools more slowly in the quench and reaches lower strength, as Figure 1 shows.

Test condition: 25 mm test piece, quenched from 830–880 °C in oil and tempered at 530–630 °C with rapid cooling. HRC values are approximate conversions per ASTM E140.

Effect of section size

JIS gives one set of reference values, so forging buyers usually read the section effect from the European equivalent. EN ISO 683-2 sets quenched-and-tempered requirements for 42CrMo4 by ruling diameter, and those limits are a sound guide for SCM440 forgings of the same size.

Order values. For each SCM440 forging, the required yield strength, tensile strength, elongation, reduction of area, impact energy and hardness are agreed on the drawing or purchase order to suit the ruling section, and the results are reported on the EN 10204 certificate.

Physical properties

SCM440 has a density of 7.85 g/cm³, an elastic modulus of about 205–210 GPa and a thermal conductivity of about 42 W/(m·K), typical of low-alloy Cr-Mo steels. Use the density for forging-weight estimates; treat the other values as typical data for screening.

SCM440 heat treatment

SCM440 is normally used quenched and tempered: austenitized at 830–880 °C, quenched in oil, then tempered at 530–630 °C and cooled rapidly, which are the JIS reference conditions for 285–352 HBW. Forgings are first annealed or normalized to relieve forging stresses and refine the grain, and are often rough machined before final quenching and tempering so the heat treatment acts on a section close to the finished size.

For critical parts, ask for the heat-treatment chart, showing temperature, soaking time and cooling medium, to be supplied with the material certificate.

Forging process

SCM440 is hot forged between approximately 1,200 °C and 850 °C, then cooled slowly and given a preliminary heat treatment to prevent cracking and hydrogen flakes. Forging below about 850 °C risks surface cracks and a mixed grain size, while slow cooling after forging protects heavy sections, whose hardenable core would otherwise transform under high internal stress.

For shafts and bars, a total forging ratio of at least 3:1 from the ingot is typical, and a higher ratio can be written on the order. Seamless rolled rings are pierced from an upset billet and expanded on a radial-axial ring mill, which gives circumferential grain flow and better hoop-direction fatigue and toughness than a ring cut from plate.

Manufacturing route

1. Melt. EAF + LF + VD steelmaking, with heat analysis against JIS G 4053.
2. Heat and forge. Open-die forging of shafts, bars, discs and blocks, or piercing and expanding for rings, from about 1,200 °C down to no less than 850 °C.
3. Slow cool and pre-treat. Controlled cooling, then annealing or normalizing.
4. Rough machine. Machining allowance is left according to the drawing and the ultrasonic test requirement.
5. Quench and temper. 830–880 °C oil quench, 530–630 °C temper with rapid cooling, or as the order specifies.
6. Test. Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, plus hardness, tensile, impact and dimensional checks.
7. Certify and ship. EN 10204 3.1 certificate, or 3.2 with a third-party inspector.

Machining and welding

SCM440 machines well in the annealed condition and can be welded only with a qualified procedure, because its carbon equivalent of about 0.79 makes the heat-affected zone prone to hard martensite and hydrogen cracking.

Machining

Heavy stock removal is best done on annealed or normalized material. After quenching and tempering to 285–352 HBW, SCM440 still machines with rigid set-ups, coated carbide tooling and reduced cutting speeds. Rough machining before final heat treatment and finish machining afterwards keeps both tool wear and distortion under control.

Welding

The IIW carbon equivalent is CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. Across the JIS G 4053 composition range it runs from about 0.69 to 0.92, well above the 0.40–0.45 level where preheating becomes necessary. Typical precautions are low-hydrogen consumables, preheat and interpass temperatures of about 200–300 °C (higher for thick sections), slow cooling, and stress relief about 50 °C below the tempering temperature. The procedure should be qualified on the actual section thickness.

Applications

SCM440 forgings are used for heavily loaded machine parts that need high strength and fatigue resistance after quenching and tempering, such as shafts, gears, couplings, crankshafts, rings and valve components. Jiangnan Metal supplies SCM440 forgings to the industries below; the right-hand column gives the reason for each choice.

Inspection and certification

SCM440 forgings from Jiangnan Metal are made from EAF + LF + VD steel, supplied annealed, normalized or quenched and tempered, ultrasonically tested to EN 10228-3, SEP 1921 or ASTM A388, and delivered with an EN 10204 3.1 or 3.2 inspection certificate. The table shows what the buyer chooses at each stage.

An EN 10204 3.1 certificate reports the heat analysis and the test results for the delivered forgings and is validated by the manufacturer's inspection representative, who is independent of production. A 3.2 certificate is also validated by the purchaser's authorized inspector or by an inspector named in official regulations, who usually witnesses the tests.

Ordering SCM440 forgings

A complete SCM440 forging order states the grade with its standard edition, the drawing, the heat-treatment condition, the mechanical properties with their test location, the ultrasonic acceptance class and the certificate type. Missing items are the most common cause of re-quotation and of disputes at final inspection.

1. Grade and standard: "SCM440 to JIS G 4053:2023", and whether dual certification to AISI 4140 or 42CrMo4 is acceptable.
2. Drawing and supply condition: finished dimensions with tolerances, and whether the part is delivered as forged or rough machined.
3. Heat treatment: annealed, normalized, or quenched and tempered, with the required hardness range.
4. Mechanical properties: yield strength, tensile strength, elongation, reduction of area and impact energy, with the test direction, test location and impact test temperature.
5. Ultrasonic testing: the standard and its acceptance class, for example EN 10228-3 quality class 3 or 4.
6. Certificate: EN 10204 3.1, or 3.2 with the name of the inspection body.
7. Commercial details: quantity, marking, packing and delivery destination.

Common ordering mistakes

• Quoting JIS G 4105: the standard has been replaced by JIS G 4053. Quote the current edition so that the current manganese range applies.
• Applying 25 mm reference values to a heavy section: the core of a 300 mm shaft will not reach 980 MPa. Specify properties for the ruling section, as in Table 6.
• Leaving out the test location: near-surface results are higher than mid-radius results, so the same forging can pass or fail depending on where the test piece is cut.
• Accepting a 4140 certificate as SCM440: check manganese and chromium against the JIS window first.
• Naming an ultrasonic standard without a class: EN 10228-3 and SEP 1921 each have several acceptance classes, and without one there is no pass or fail criterion.

Request a quote

To quote SCM440 forgings we need the drawing or dimensions, quantity, heat-treatment condition, mechanical and ultrasonic testing requirements, and the certificate type. Email them to sales@steelforgepieces.com or call 0086-189-2135-9659. The two tools below estimate the part weight and turn your requirements into a complete enquiry.

Contact the manufacturer

Frequently asked questions

Glossary

Quenching and tempering (Q&T)

Hardening steel by rapid cooling from the austenite range, then reheating it below the transformation range to exchange some hardness for toughness. SCM440 is normally used in this condition.

Ruling section

The section of a part that governs its cooling rate during quenching, and therefore the properties it can reach. EN ISO 683-2 lists 42CrMo4 properties by ruling diameter.

Hardenability

The depth to which a steel forms martensite on quenching, usually measured with the Jominy end-quench test. Chromium, molybdenum and manganese give SCM440 its hardenability.

Temper embrittlement

Loss of impact toughness in alloy steels held in, or cooled slowly through, roughly 375–575 °C. Phosphorus and other impurities promote it, which is why SCM440 is cooled rapidly after tempering.

Forging ratio

The ratio of cross-sectional area before and after forging. A higher ratio closes internal porosity and refines the cast structure of the ingot.

Seamless rolled ring

A ring made by piercing an upset billet and expanding it on a ring rolling mill, which gives grain flow around the circumference.

EN 10204 3.1 and 3.2 certificates

Inspection certificates with specific test results. A 3.1 certificate is validated by the manufacturer's independent inspection representative; a 3.2 certificate is also validated by the purchaser's authorized representative or an inspector named in official regulations.

Carbon equivalent (CE)

A single number that combines the effect of carbon and alloying elements on weld hardenability. The IIW formula is CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15.

Hydrogen flakes

Internal cracks caused by dissolved hydrogen in heavy alloy-steel forgings. Vacuum degassing and slow cooling after forging prevent them.

Related alloy steel forgings

SCM440 belongs to the same chromium-molybdenum family as the grades below, which Jiangnan Metal also forges.

• AISI 4140 forgings
• 42CrMo4 forgings
• 1.7225 forgings
• All alloy steel forgings
• Forging spindles
• Forged bushings

Standards and references

1. JIS G 4053:2023, Low-alloyed steels for machine structural use. Japanese Industrial Standards.
2. JIS G 4105, Chromium molybdenum steels. Japanese Industrial Standards; withdrawn and replaced by JIS G 4053.
3. EN ISO 683-2, Heat-treatable steels, alloy steels and free-cutting steels. Part 2: Alloy steels for quenching and tempering.
4. EN 10250-3, Open steel die forgings for general engineering purposes. Part 3: Alloy special steels.
5. ASTM A29/A29M, Standard Specification for General Requirements for Steel Bars, Carbon and Alloy, Hot-Wrought.
6. SAE J404, Chemical Compositions of SAE Alloy Steels.
7. GB/T 3077-2015, Alloy structure steels.
8. EN 10228-3, Non-destructive testing of steel forgings. Part 3: Ultrasonic testing of ferritic or martensitic steel forgings.
9. SEP 1921, Stahl-Eisen-Prüfblatt for the ultrasonic testing of steel bars.
10. ASTM A388/A388M, Standard Practice for Ultrasonic Examination of Steel Forgings.
11. EN 10204, Metallic products. Types of inspection documents.
12. ASTM E140, Standard Hardness Conversion Tables for Metals.
13. ISO 15156-2 (NACE MR0175), Materials for use in H2S-containing environments in oil and gas production. Part 2: Cracking-resistant carbon and low-alloy steels, and the use of cast irons.

Revision history

• 15 September 2026: page revised. Standard updated from JIS G 4105 to JIS G 4053:2023; manganese range corrected to 0.60–0.90%; phosphorus and sulfur limits corrected from 0.30% to 0.030% maximum; mechanical properties restated as JIS reference values with their test condition; section-size properties, equivalent grades, heat treatment, welding guidance, glossary and FAQ added.