SAE 4140 Square Bars

SAE 4140 square bright bar is a cold drawn chromium-molybdenum steel bar used for keys, tool holders and machine parts.

12.7 to 55 mm Alloy steel Made to order

SQUARE BRIGHT BARS

SAE 4140 square bright bar

SAE 4140 square bright bar is an alloy steel bar of square section, cold drawn to size from the hot rolled square beside it. About 0.40 percent carbon carries the strength, while chromium and molybdenum let the bar harden right through its section rather than only at the surface, so a part machined from it is as strong at the centre as at the face. A 55 mm square hardens through in 4140 without the nickel that SAE 4340 carries for heavier sections, and it reaches a strength the lower carbon SAE 4130 cannot. Plain carbon steel of the same size machines as easily but cannot be tempered to the same strength. The same steel is written 42CrMo4 in Europe and EN 19 in the older British list.

The bar is supplied annealed, normalised, or hardened and tempered to a condition of BS 970, where condition T covers 850 to 1000 MPa tensile strength. Annealed bar machines cleanly and suits a part that is hardened after cutting; hardened and tempered bar is machined to size and used as it stands. Welding needs preheat and a temper afterwards, because the carbon and the alloy content harden the weld area, so bolted and keyed joints are the normal answer. Laxcon Steels draws the bar to order from 12.7 to 55 mm side, held to h11 under EN 10278. Work commonly made from it includes machine keys and gib heads, tool and die holders, fixture blocks, and shafts with a square drive end.

Composition limits in weight percent are carbon 0.38 to 0.43, manganese 0.75 to 1.0, sulphur 0.04 maximum, phosphorus 0.035 maximum, silicon 0.15 to 0.35, chromium 0.8 to 1.1 and molybdenum 0.15 to 0.25.

SPECIFICATION

SAE 4140 square bright bar supply conditions

Size range: 12.7 mm - 55 mm (1/2" - 2")
Length: Up to 6 metres
Tolerance: h11, k12, k13
Grit Polish: As per customer’s request
Heat treatment: Soft annealing or normalising; oil or water quenching and tempering
Bars End Finish: Deburred Ends, Plain Ends without Burrs or Sharp Edges
Grade: SAE 4140 (4140, 42CrMo4, EN 19, 1.7225)
Family: Alloy steel
Supply: Made to order in this grade; every published size of the form

Composition of SAE 4140

Element	Symbol	Minimum %	Maximum %
Carbon	C	0.38	0.43
Manganese	Mn	0.75	1.0
Sulphur	S		0.04
Phosphorus	P		0.035
Silicon	Si	0.15	0.35
Chromium	Cr	0.8	1.1
Molybdenum	Mo	0.15	0.25

Composition, weight percent, balance iron. From the Laxcon Steels grade reference.

Equivalents of SAE 4140

Standard	Designation
DIN	42CrMo4
British EN	EN 19

Equivalence means nearest counterpart, not identity: each standards body sets its own composition window, so the limits of the standard named on the order govern.

Governing standards

EN 10083-1: Steels for quenching and tempering, part 1: general technical delivery conditions for the bars, rods and sections supplied for heat treatment.
EN 10083-3: Steels for quenching and tempering, part 3: technical delivery conditions for alloy steels, 42CrMo4 and 34CrNiMo6 among them.
EN 10277: Bright steel products: technical delivery conditions for cold drawn, peeled, turned and ground carbon and alloy steel bars.
BS 970-1: Wrought steels for mechanical and allied engineering purposes, part 1: the British numbering behind the EN and M designations and the R to Z heat treatment conditions.
ASTM A29/A29M: Steel bars, carbon and alloy, hot-wrought: general requirements for delivery, the base every carbon and alloy bar order inherits.
ASTM A108: Steel bar, carbon and alloy, cold-finished: the specification for drawn, turned and ground carbon and alloy bars.
EN 10278: Dimensions and tolerances of bright steel products: the h and k tolerance classes for drawn, turned, peeled and ground bars.
EN 10059: Hot rolled square steel bars for general purposes: dimensions and tolerances on shape and dimensions.
EN 10204: Metallic products, types of inspection documents: the 2.2 test report and the 3.1 and 3.2 inspection certificates a purchase order can call for.

Tolerance by size, ISO 286

Nominal side (mm)	h11	k12	k13
over 10 to 18	0 / -0.110	0 / +0.180	0 / +0.270
over 18 to 30	0 / -0.130	0 / +0.210	0 / +0.330
over 30 to 50	0 / -0.160	0 / +0.250	0 / +0.390
over 50 to 80	0 / -0.190	0 / +0.300	0 / +0.460

Deviations in millimetres from the nominal size, ISO 286-1 and ISO 286-2. An h class permits no plus material and the full grade below nominal; the k12 and k13 classes of EN 10278, used for peeled and turned bars, permit the full grade above nominal and none below.

Weight per metre

Side (mm)	kg per metre	Metres per tonne
12.7	1.27	789.8
15	1.77	566.2
15.88	1.98	505.2
19	2.83	352.9
19.05	2.85	351.0
20	3.14	318.5
22	3.80	263.2
22.22	3.88	258.0
25	4.91	203.8
25.4	5.06	197.5
26	5.31	188.4
27	5.72	174.7
28	6.15	162.5
28.58	6.41	156.0
30	7.06	141.5
31.75	7.91	126.4
32	8.04	124.4
34	9.07	110.2
35	9.62	104.0
36	10.17	98.3
38	11.34	88.2
38.1	11.40	87.8
40	12.56	79.6
41	13.20	75.8
44	15.20	65.8
45	15.90	62.9
47	17.34	57.7
48	18.09	55.3
50	19.62	51.0
50.8	20.26	49.4
55	23.75	42.1

Density 7.85 g/cm³, plain section (side squared x 0.007850).

Ordering SAE 4140 square bright bar

An enquiry for this grade in this form names the grade and the governing standard, SAE 4140 to ASTM A29 or 42CrMo4 to EN 10083-3, the delivery condition, the side in millimetres with its tolerance class to EN 10278, the cut length, the quantity, the type of inspection document required under EN 10204, and any ultrasonic test or PMI check called for.