SCM435 Forgings (JIS G 4053, AISI 4135, 34CrMo4)

SCM435 overview

SCM435 is a chromium-molybdenum alloy steel for machine structural use, specified in JIS G 4053. It contains 0.33-0.38% carbon, 0.90-1.20% chromium and 0.15-0.30% molybdenum and is normally used in the quenched and tempered condition. JIS G 4053 gives reference values of 930 MPa minimum tensile strength, 785 MPa minimum yield point and 15% minimum elongation, with a hardness of 269-331 HBW. The nearest foreign grades are AISI 4135 (UNS G41350), 34CrMo4 (1.7220) and 35CrMo to GB/T 3077. Their alloy ranges are close to SCM435 but not identical.

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. We forge SCM435 seamless rolled rings, shafts, spindles, discs, flanges, sleeves, gear blanks and round bars to customer drawings. The steel is melted by EAF + LF + VD and heat treated in our own plant by annealing, normalizing, or quenching and tempering. Forgings are ultrasonically tested to EN 10228-3, SEP 1921 or ASTM A388 and supplied with EN 10204 3.1 or 3.2 certificates. For a quotation, send your drawing to sales@steelforgepieces.com or call 0086-189-2135-9659.

Standard

JIS G 4053Old standard JIS G 4105, old symbol SCM 3

Carbon

0.33-0.38 %Cr 0.90-1.20 %, Mo 0.15-0.30 %

Tensile strength

≥ 930 MPaJIS reference, quenched and tempered

Yield point

≥ 785 MPaJIS reference, quenched and tempered

Hardness

269-331 HBWAbout 28-35 HRC

Density

7.85 g/cm³0.284 lb/in³

Hardening

830-880 °COil quench

Tempering

530-630 °CRapid cooling

SCM435 forged products

We make SCM435 parts by open-die forging, ring rolling, or upsetting and punching, depending on the shape of the part. Shafts, discs, blocks and other heavy sections are forged on hammers and hydraulic presses. Rings are punched and rolled on a ring rolling mill, so that the grain flow follows the circumference of the ring. Hubs, short flanges and sleeve blanks are upset and punched.

All products can be supplied annealed, normalized, or quenched and tempered, and as forged, rough machined or finish machined. The sizes above are our plant limits. In large sections the strength in the core depends on the hardenability of SCM435, so please read the notes on section size before fixing property values for a heavy part.

More product information: forging rings, forging disks, forged spindles, forged eccentric shafts, forged valve seat rings and forged steel rolls.

SCM435 grade description

SCM435 belongs to the chromium-molybdenum steels in JIS G 4053, Low-alloyed steels for machine structural use. These steels were previously covered by JIS G 4105. They are supplied as hot-rolled, hot-forged or hot-extruded material and are heat treated before use.

In the designation, S means steel, CM means chromium and molybdenum, the digit 4 is the code for the main alloy content and 35 is the nominal carbon content of 0.35%. The old symbol for the same steel is SCM 3, which still appears on some older Japanese drawings.

SCM430, SCM435 and SCM440 have the same chromium, molybdenum and manganese ranges. The main difference between them is the carbon content, so carbon is the first value to check when a drawing says "SCM435 or equivalent".

Effect of chromium and molybdenum

Chromium (0.90-1.20%) is the main addition for hardenability. With chromium, an oil quench from 830-880 °C hardens a deeper section than in a plain carbon steel with the same carbon content, such as S35C, and the steel softens more slowly during tempering. Molybdenum (0.15-0.30%) adds more hardenability and reduces temper embrittlement, the loss of toughness that occurs when Cr-Mo steels are held at, or slowly cooled through, about 350-575 °C.

Differences from AISI 4135, 34CrMo4 and 35CrMo

These grades are often treated as equivalents, but their ranges are different. AISI 4135 requires 0.70-0.90% manganese and allows only 0.80-1.10% chromium and 0.15-0.25% molybdenum. 34CrMo4 allows carbon from 0.30% and limits phosphorus to 0.025%. 35CrMo has a wider carbon range (0.32-0.40%), lower manganese (0.40-0.70%) and lower chromium and molybdenum. A heat can be made to meet SCM435, 34CrMo4 and AISI 4135 at the same time; the common range is shown in Table 4.

SCM435H

SCM435H is SCM435 ordered to JIS G 4052 with a specified hardenability band, checked by the Jominy end-quench test. It is used where the hardness after quenching has to be consistent from heat to heat, for example for gears and shafts in series production.

SCM435 equivalent grades

The table lists the designations used by our customers for SCM435 type steel. Grades marked as close can be used for most machine parts, but the chemical ranges in Table 4 should be compared before one grade is certified as another.

SCM435 chemical composition

Table 3 gives the heat analysis limits of JIS G 4053 for SCM435. We melt SCM435 by EAF + LF + VD. Lower phosphorus and sulfur limits can be agreed for heavy forgings with impact test requirements.

SCM435 also limits Ni to 0.25% max and Cu to 0.30% max. The last column is the overlap of the three standards.

A heat within the last column can be certified to SCM435, 34CrMo4 and AISI 4135 together. This is useful when the same part is supplied to customers in Japan, Europe and North America. AISI 4135 and 35CrMo only overlap at exactly 0.70% manganese, so in practice one heat cannot be certified to both of them.

SCM435 mechanical properties

The mechanical properties in JIS G 4053 are reference values. They apply to small test pieces after the reference heat treatment and are not acceptance values for forgings unless the purchase order says so. For a forging, the order should give the required values, the section size they apply to and the test location.

JIS gives the impact value in J/cm². The energy absorbed by a U-notch specimen is divided by the 0.8 cm² cross-section under the 2 mm notch, so 78 J/cm² is about 62 J. There is no conversion factor between this value and a V-notch (KV) value in joules. If your project requires KV, please specify a KV test and the test temperature.

Section size and strength

SCM435 is quenched in oil and does not harden through heavy sections. The core of a 300 mm shaft cools much more slowly than a small test bar, forms bainite or ferrite and pearlite instead of martensite, and has lower strength after tempering. JIS G 4053 has no table for this effect. EN 10083-3 gave minimum values by section size for 34CrMo4, which is a close equivalent, and the same trend applies to SCM435.

EN 10083-3:2006 was replaced by EN ISO 683-2 in 2018. For new European orders, please refer to EN ISO 683-2.

For sections over 250 mm no values are given, and the properties have to be agreed for the actual part, including test location and direction. Rough machining before quenching and tempering reduces the section size and improves the properties in the finished part. Where a heavy section needs higher strength in the core, a Ni-Cr-Mo steel such as 34CrNiMo6 or AISI 4340 is normally used.

SCM435 physical properties

Forging and heat treatment of SCM435

SCM435 has good hot workability. The main risks in production are forging below the correct temperature range, hydrogen in heavy sections and slow cooling after tempering. The temperature ranges we use for SCM435 forgings are given below.

As a starting point, the holding time at hardening temperature is about one hour per 25 mm of section thickness, checked with thermocouples on the part.

Cooling after tempering

Cr-Mo steels lose toughness when they are held at, or slowly cooled through, about 350-575 °C after tempering. Phosphorus and other trace elements collect at the prior austenite grain boundaries, and the steel breaks along these boundaries. This is called temper embrittlement. Molybdenum and a low phosphorus content reduce it, and JIS G 4053 specifies rapid cooling after tempering to prevent it. Tempering at about 250-400 °C is also avoided because it causes tempered martensite embrittlement.

Hydrogen flake control

Heavy Cr-Mo forgings can develop internal hydrogen cracks, known as flakes, after cooling. Vacuum degassing (VD) removes most of the hydrogen from the liquid steel. Slow cooling or an annealing cycle after forging allows the remaining hydrogen to diffuse out before quenching. Ultrasonic testing after the final heat treatment confirms that the forging is free from flakes.

Production process

Our production process for SCM435 forgings:

1. Melting and refining. EAF + LF + VD, heat analysis to JIS G 4053, heat number recorded and traced through all later steps.
2. Cutting. Ingots or blooms are cut to the calculated weight, with allowance for scale loss and discard.
3. Heating and forging. Heated to 1150-1200 °C, then upset and drawn on hammers or a hydraulic press. The forging ratio is at least 3:1, and the part is reheated before its temperature falls below 850 °C.
4. Ring rolling. For rings, the blank is punched and rolled to size on a radial-axial ring rolling mill.
5. Cooling and preliminary heat treatment. Slow cooling, followed by annealing or normalizing to refine the grain and remove hydrogen.
6. Rough machining. Machined for ultrasonic testing and, where the drawing allows, to a smaller section before quenching.
7. Quenching and tempering. Oil quenched from 830-880 °C, tempered at 530-630 °C and cooled rapidly. Furnace charts are recorded.
8. Testing and certification. Chemical analysis, tensile, impact and hardness tests, ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, dimensional inspection and EN 10204 3.1 or 3.2 certificate.

Welding and machining

Welding

SCM435 can be welded with a qualified welding procedure. The carbon equivalent CE (IIW) = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15 is 0.64 at the minimum and 0.87 at the maximum of the JIS G 4053 ranges, and about 0.74 for a mid-range analysis without Ni and Cu. The heat affected zone therefore hardens strongly and is sensitive to hydrogen cracking.

• Use low-hydrogen welding processes and dry consumables.
• Preheat and control the interpass temperature. Values of about 150-400 °C are used for this type of steel, depending on thickness and restraint; the actual value is given in the welding procedure specification.
• Stress relieve after welding at a temperature below the final tempering temperature, so that the strength is not reduced.
• If full strength is required across the weld, weld in the annealed or normalized condition and quench and temper the complete part afterwards.

Weld repair of forgings requires the written approval of the purchaser.

Machining

SCM435 is easiest to machine in the annealed condition. For the equivalent 34CrMo4, EN 10083-3 gives a maximum of 223 HBW in the soft annealed condition. Quenched and tempered material at 269-331 HBW can be machined with carbide tools. Parts with close tolerances are finish machined after quenching and tempering to remove heat treatment distortion. Journals and gear teeth can be induction or flame hardened locally where wear resistance is needed.

SCM435 vs SCM430 and SCM440

The three grades have the same chromium (0.90-1.20%), molybdenum (0.15-0.30%) and manganese (0.60-0.90%) ranges and the same reference heat treatment, an oil quench from 830-880 °C and tempering at 530-630 °C with rapid cooling. The difference is the carbon content.

Each 0.05% increase in carbon raises the reference tensile strength by 50-100 MPa and lowers the impact value by about a quarter. SCM435 is used when SCM430 is not strong enough and SCM440 is not tough enough for the part.

Applications of SCM435 forgings

Forging capacity

Jiangyin Jiangnan Metal Co., Ltd. has the following forging range for SCM435 and other steel grades. Please send your drawing so that we can confirm the size, weight and delivery time for your part.

Rolled ring OD

200-2,500 mmSeamless rolled rings

Ring wall

30 mmMinimum

Disc diameter

≤ 1,800 mmDiscs and flanges

Shaft length

≤ 8,000 mmShafts and spindles

Bar diameter

25-500 mmForged round bars

Single piece

≤ 8,000 kgForging weight

Melting

EAF + LF + VDVacuum degassed

Certificate

EN 102043.1 or 3.2

Standards, testing and certificates

Our quality management system is certified to ISO 9001:2015. Third-party inspection can be arranged with Lloyd's Register, DNV, Bureau Veritas, ABS, TÜV, SGS or another inspection company nominated by the customer. Customers are welcome to witness melting, forging, heat treatment and testing.

Ordering information

Please include the following information in your enquiry or purchase order:

1. Grade and standard, for example SCM435 to JIS G 4053. If a dual certificate to 34CrMo4 or AISI 4135 is required, state which standard governs.
2. Heat treatment condition (annealed, normalized, or quenched and tempered) and hardness range in HBW.
3. Section size, required tensile strength, yield strength and elongation, and test location. The JIS reference values are for small test pieces and are not suitable as acceptance values for heavy forgings.
4. Impact test type (V-notch KV in J or JIS U-notch in J/cm²), test temperature and minimum value.
5. Ultrasonic testing standard and acceptance class, for example EN 10228-3 quality class 3.
6. Phosphorus and sulfur limits, if lower than the JIS limit of 0.030%.
7. Supply condition: as forged, rough machined or finish machined.
8. Quantity, delivery date, delivery term, destination and certificate type (EN 10204 3.1 or 3.2).

MATERIAL:     SCM435 to JIS G 4053
MELTING:      EAF + LF + VD
CONDITION:    Quenched and tempered, oil quench 830-880 C,
              temper 530-630 C, rapid cooling
HARDNESS:     ___-___ HBW
TENSILE:      Rm ___ MPa min, ReH/Rp0.2 ___ MPa min, A ___ % min
              Section ___ mm, test location ___, direction ___
IMPACT:       KV ___ J min average at ___ C (ISO 148-1)
UT:           EN 10228-3 quality class ___
CERTIFICATE:  EN 10204 3.1
MARKING:      Heat number, grade, drawing number, low-stress stamps

Common errors in SCM435 orders

1. Using the JIS reference values as acceptance values for a large forging. These values cannot be reached in the core of a heavy section.
2. Using 35CrMo or SCM440 values for SCM435. A tensile strength of 980 MPa with a yield strength of 835 MPa is the GB/T 3077 minimum for 35CrMo and the JIS reference value for SCM440.
3. Requiring AISI 4135 and 35CrMo in the same heat. Their manganese ranges only meet at 0.70%.
4. Mixing impact units. JIS U-notch values in J/cm² and KV values in J come from different tests and cannot be converted with a factor.
5. Specifying only HRC for quenched and tempered forgings. Brinell hardness (HBW) is normally used; if HRC is required, state the conversion standard, ASTM E140.
6. Not stating sour service on the order. H2S service requires a maximum hardness of 22 HRC to NACE MR0175 / ISO 15156, which changes the heat treatment.

SCM435 FAQ

References

1. JIS G 4053, Low-alloyed steels for machine structural use. Japanese Industrial Standards Committee.
2. JIS G 4052, Structural steels with specified hardenability bands.
3. JIS G 3221, Chromium molybdenum steel forgings for general use.
4. EN 10083-3:2006, Steels for quenching and tempering, Part 3: Technical delivery conditions for alloy steels. CEN. Replaced by EN ISO 683-2:2018.
5. ISO 683-2, Heat-treatable steels, alloy steels and free-cutting steels, Part 2: Alloy steels for quenching and tempering. ISO.
6. SAE J404, Chemical compositions of SAE alloy steels; ASTM A29/A29M.
7. GB/T 3077, Alloy structure steels.
8. ASTM E140, Standard hardness conversion tables for metals.
9. EN 10228-3, ASTM A388/A388M, SEP 1921 and JIS G 0587, ultrasonic testing of steel forgings.
10. NACE MR0175 / ISO 15156-2, carbon and low-alloy steels for use in H2S-containing environments.
11. EN 10204, Metallic products, types of inspection documents.
12. ASM Handbook, Volume 4A: Steel Heat Treating Fundamentals and Processes. ASM International.

The values on this page are for reference. The purchase specification applies to each order.

About Jiangyin Jiangnan Metal

Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory located at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The company has 460 employees, including 9 senior engineers and 32 intermediate engineers.

Our equipment includes 1 t, 3 t, 5 t and 9 t forging hammers, 4,500 t and 5,000 t hydraulic presses and ring rolling mills up to 2,500 mm, together with heat treatment furnaces, machining workshops and a testing laboratory. Besides SCM435, we forge carbon steel, alloy steel such as AISI 4140 and 42CrMo4, tool steel, stainless steel and nickel alloys. Our quality management system is certified to ISO 9001:2015.