SAE 4340 Steel Alloy Bar Suppliers

AISI 4340 steel is a medium carbon, low alloy steel known for its toughness and strength in relatively large sections. AISI 4340 is also one kind of nickel chromium molybdenum steels. 4340 alloy steel is generally supplied hardened and tempered in the tensile range of 930 – 1080 Mpa.

Due to availability the ASTM 4340 grade steel is often substituted with European based standards 817M40/EN24 and 1.6511/36CrNiMo4 or Japan based SNCM439 steel. You have the detailed data of 4340 steel below:

Production 

1. AISI Alloy 4340 Steel Supply Range

4340 Steel Round Bar: diameter 8mm – 3000mm (*Dia30-240mm in stock in annealed condition, immediate shipment)

4340 Steel Plate: thickness 10mm – 1500mm x width 200mm – 3000mm

4340 Steel Grade Square: 20mm – 500mm

Surface Finish: Black, Rough Machined, Turned or as per given requirements

Production 

2. AISI 4340 Steel Specification and Relevant Standards

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

Production 

3. ASTM 4340 Steels And Equilvalents 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

Production 

4. AISI Alloy 4340 Steel Mechanical Properties

Mechannical Properties (Heat Treated Condition )	Condition	Ruling section mm	Tensile Strength MPa	Yield Strength MPa	Elong. %	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, specimen oil hardened, 600°C (1110°F) temper	12.3 µm/m°C	6.83 µin/in°F
Thermal conductivity (typical steel)	44.5 W/mK	309 BTU in/hr.ft².°F

Production 

5. Forging of 4340 Alloy Steel

Preheat the steel 4340 first, heat up to 1150°C – 1200°C maximum for forging, hold until temperature is uniform throughout the section.

Do not forge below 850 °C. 4340 has good forging characteristics but care must be taken when cooling as the steel shows susceptibility to cracking. Following forging operation the work piece should be cooled as slowly as possible. And cooling in in sand or dry lime is recommended etc.

Production 

6. AISI 4340 Steel Grade Heat Treatment

Stress Relieving

For pre-hardened steel stress relieving is achieved by heating steel 4340 to between 500 to 550°C. Heat to 600 °C – 650 °C, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm section, and cool in still air.

Annealing

A full anneal may be done at 844°C (1550 F) followed by controlled (furnace) cooling at a rate not faster than 10°C (50 F) per hour down to 315°C (600 F). From 315°C 600 F it may be air cooled.

Tempering

AISI 4340 alloy steel should be in the heat treated or normalized and heat treated condition before tempering. The tempering temperature for depends upon the strength level desired. For strength levels in the 260 – 280 ksi range temper at 232°C (450 F). For strength in the 125 – 200 ksi range temper at 510°C (950 F). And don’t temper the 4340 steels if it is in the 220 – 260 ksi strength range as tempering can result in degradation of impact resistance for this level of strength.

Tempering should be avoided if possible within the range 250 °C – 450 °C due to temper brittleness.