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SAE4340 Quenching and Tempering Forged Steel Round Bar with Polished Surface

Minimum Order Quantity	1 Ton
Price	US $720-1,430 / Ton

Product Details

Diameter Range	OD 6-630mm	Carbon Content	0.38-0.43%
Manganese Content	0.60-0.80%	Phosphorus Content	0.035%
Sulfur Content	0.040%	Silicon Content	0.15-0.35%
Nickel Content	1.65-2.00%	Chromium Content	0.70-0.90%
Molybdenum Content	0.20-0.30%	Tensile Strength	930-1080 MPa
Yield Strength	740 MPa	Elongation	12%
Impact Resistance	47 J	Brinell Hardness	269-331
Thermal Conductivity	44.5 W/mK
Highlight	SAE4340 Steel Round Bar , Quenching and Tempering Alloy Steel Bar , Polished Surface Forged Steel Bar

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Product Description

SAE4140 SAE4340 40CrNiMoA Quenching Forged Steel Bar

Material Standards: GB 40CrNiMoA, BS S535, AMS 6350, AISI 4340 Round Bar, JIS SNCM439

AISI 4340 Steel Overview

AISI 4340 steel is a medium carbon, low alloy steel renowned for its exceptional toughness and strength in large sections. As a nickel chromium molybdenum steel, it is typically supplied hardened and tempered in the tensile range of 930-1080 MPa. This material offers excellent shock and impact resistance along with superior wear and abrasion resistance in hardened conditions.

In annealed condition, AISI 4340 demonstrates good ductility for bending and forming operations. The material supports both fusion and resistance welding processes and can be machined using all conventional methods. It is particularly suitable for highly stressed components where other alloy steels lack sufficient hardenability.

International Standards and Specifications

Country	USA	Britain	Britain	Japan
Standard	ASTM A29	EN 10250	BS 970	JIS G4103
Grades	4340	36CrNiMo4/1.6511	EN24/817M40	SNCM 439/SNCM8

Chemical Composition

Standard	Grade	C	Mn	P	S	Si	Ni	Cr	Mo
ASTM A29	4340	0.38-0.43	0.60-0.80	0.035	0.040	0.15-0.35	1.65-2.00	0.70-0.90	0.20-0.30
EN 10250	36CrNiMo4/1.6511	0.32-0.40	0.50-0.80	0.035	0.035	<=0.40	0.90-1.20	0.90-1.2	0.15-0.30
BS 970	EN24/817M40	0.36-0.44	0.45-0.70	0.035	0.040	0.1-0.40	1.3-1.7	1.00-1.40	0.20-0.35
JIS G4103	SNCM 439/SNCM8	0.36-0.43	0.60-0.90	0.030	0.030	0.15-0.35	1.60-2.00	0.60-1.00	0.15-0.30

Mechanical Properties (Heat Treated Condition)

Condition	Ruling Section (mm)	Tensile Strength (MPa)	Yield Strength (MPa)	Elongation (%)	Izod Impact (J)	Brinell Hardness
T	250	850-1000	635	13	40	248-302
T	150	850-1000	665	13	54	248-302
U	100	930-1080	740	12	47	269-331
V	63	1000-1150	835	12	47	293-352
W	30	1080-1230	925	11	41	311-375
X	30	1150-1300	1005	10	34	341-401
Y	30	1230-1380	1080	10	24	363-429
Z	30	1555-	1125	5	10	444-

Thermal Properties

Properties	Metric	Imperial
Thermal expansion co-efficient (20°C/68°F)	12.3 µm/m°C	6.83 µin/in°F
Thermal conductivity	44.5 W/mK	309 BTU in/hr.ft².°F

Forging Process

Preheat AISI 4340 steel before forging, heating to 1150°C - 1200°C maximum. Maintain uniform temperature throughout the section. Do not forge below 850°C. While 4340 exhibits good forging characteristics, careful cooling is essential to prevent cracking. After forging, cool work pieces as slowly as possible, preferably in sand or dry lime.

Heat Treatment Procedures

Stress Relieving

For pre-hardened steel, stress relieving is achieved by heating to 500-550°C. Alternatively, heat to 600-650°C, hold until uniform temperature, soak for 1 hour per 25 mm section, and cool in still air.

Annealing

Perform full annealing at 844°C (1550°F) followed by controlled furnace cooling at a maximum rate of 10°C (50°F) per hour down to 315°C (600°F). From 315°C, air cooling is acceptable.

Tempering

AISI 4340 should be in heat treated or normalized condition before tempering. Temper at 232°C (450°F) for 260-280 ksi strength range, or at 510°C (950°F) for 125-200 ksi range. Avoid tempering in the 220-260 ksi range and within 250-450°C due to temper brittleness concerns.

Flame or Induction Hardening

Pre-hardened and tempered 4340 can be surface hardened using flame or induction methods, achieving case hardness exceeding Rc 50. Heat rapidly to 830-860°C austenitic range, then immediately quench in oil or water. Temper at 150-200°C to reduce case stresses. Remove all decarburized surface material before treatment.

Nitriding

Hardened and tempered 4340 can be nitrided to achieve surface hardness up to Rc 60. Heat to 500-530°C and maintain for 10-60 hours to develop case depth. Follow with slow cooling to minimize distortion. Surface hardness of 600-650 HV is achievable without affecting core tensile strength.

Machinability

Optimal machining occurs with 4340 in annealed or normalized and tempered condition. The material can be processed using all conventional methods including sawing, turning, and drilling. Machinability decreases to 25-10% of annealed condition when strength exceeds 200 ksi.

Welding Considerations

Welding hardened and tempered 4340 is not recommended due to quench cracking risks and altered mechanical properties in heat-affected zones. If welding is necessary, pre-heat to 200-300°C and maintain during welding. Immediately stress relieve at 550-650°C before hardening and tempering. For welding in hardened condition, stress relieve at 15°C below original tempering temperature after cooling to hand warm.

Industrial Applications

Aircraft Landing Gear
Automotive Components
Oil and Gas Drilling Equipment
Forging Dies and Tools
Machine Building
Power Transmission Gears and Shafts
Heavy Duty Shafts, Axles, and Spindles
Couplings, Pins, Chucks, and Molds

General Applications: Widely used in transmission systems, tractor motors, and small-to-medium automotive applications. Serves as alternative to 12CrNi3 for high-class carburization and cyanide carburizing parts including oil drilling equipment, mining claws, and cones. Commonly employed for carburized gears, pinions, shafts, bearings, piston rings, ring gears, and crankshafts.

Available Stock Sizes

Round Bar Diameter: 12-380mm

Material Forms and Conditions

Our steel materials are available in various forms including round bars, flat bars, plates, and blocks. Conditions range from pre-hardened, hot rolled, annealed, quenched and tempered to surface conditions such as black, pre-machined, grinding, and polished finishes.

Why Choose Our Steel Products

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Comprehensive Services
We provide quality special steel for all industries with flexible order sizes and fast shipping. Value-added services include metal cutting, sizing, machining (blanking, milling, grinding), heat treatment, and sawing for both small and large quantities.

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SAE4340 Quenching and Tempering Forged Steel Round Bar with Polished Surface

SAE4340 Steel Round Bar

Quenching and Tempering Alloy Steel Bar

Polished Surface Forged Steel Bar