20HN3A - alloy steel

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Standards and chemical composition Specification Properties Treatment Replacements

20HN3A - chromium-nickel structural alloy steel for aviation for thermal improvement intended for the manufacture of heavy duty parts according to PN-72/H-84035.

Standards	Steel Grades
	Chemical composition %
	C:	Mn:	Si:	P:	S:	Cr:	Mo:	Ni:	V:	Ti:	Cu:	W:
PN	20HN3A
PN	0.18 - 0.24	0.30 - 0.60	0.17 - 0.37	<0.03	<0.03	0.6 - 0.9	-	2.80 - 3.20	-	-	<0.20	-
GOST	20ChN3A - 20KhN3A - 20ХН3А
GOST	0.17 - 0.24	0.30 - 0.60	0.17 - 0.37	<0.025	<0.025	0.6 - 0.9	<0.15	2.75 - 3.15	<0.05	<0.03	<0.30	<0.2
БДС	20ChN3A - 20KhN3A - 20ХН3А
БДС	0.17 - 0.24	0.30 - 0.60	0.17 - 0.37	<0.025	<0.025	0.6 - 0.9	<0.15	2.75 - 3.15	<0.05	<0.03	<0.30	<0.2
GB/T	20CrNi3 - A42202 - A 42202
GB/T	0.17 - 0.24	0.30 - 0.60	0.17 - 0.37	<0.035	<0.035	0.6 - 0.9	<0.15	2.75 - 3.15	-	-	<0.30	-
GB/T	20CrNi3A - A42203 - A 42203
GB/T	0.17 - 0.24	0.30 - 0.60	0.17 - 0.37	<0.025	<0.025	0.6 - 0.9	-	2.75 - 3.15	-	-	<0.25	-
UNS	AISI 4320 - 4320
UNS	0.17 - 0.22	0.45 - 0.65	0.15 - 0.35	<0.035	<0.04	0.4 - 0.6	0.2 - 0.3	1.65 - 2.00	-	-	-	-

20HN3A steel - specification and application

20HN3A - Nickel steel for medium hardening, carburizing and cyanidizing, designed for medium size machine parts up to approx. 50mm in cross section, with increased ductility, requiring ductile core, high durability.

Used as a steel for aviation industry for heavy-duty combustion engines parts and avionics engines, gears, shafts, bolts, rockers, screws, heavy-duty screws. Hard-welding steel requiring pre-heating, does not exhibit corrosion resistance, including atmospheric environment.

Mechanical and physical properties of 20HN3A steel

Mechanical and physical properties
General properties		Properties for individual dimensions
General properties		≤ 16mm	16 - 40mm	40 - 100mm
Tensile strength, Rm (MPa)	≥ 930	780 - 980	690 - 880	640 - 830
Yield point, Re (MPa)	≥ 780	690 - 780	590 - 690	540 - 690
Elongation, A (%)	≥ 12	10 - 16	10 - 16	11 - 18
Notch toughness, KU2	≥ 80 J
Contraction, Z	≥ 55 %
Hardness after softening	≤ 229 HB
Hardness after drawing in the softened state	≤ 229 HB
Hardness after drawing in the hardened state	≤ 277 HB (pow. 6mm)
Hardness in the tempered state	293 - 388 HB (sample ≤ 25mm)
Linear Expansion Factor, α_20-100℃	11,2⋅10⁻⁶ K⁻¹
Heat capacity, c_{p 20-100℃}	492 J ⋅ kg⁻¹ K⁻¹
Thermal conductivity, λ_20℃	~31 W ⋅ m⁻¹ K⁻¹
Density ρ	~7,85 kg/dm³

Heat treatment of 20HN3A steel

Heat treatment - Temperature and process
Softening annealing	640 - 680℃
Normalizing annealing	840 - 879℃
Carburizing	900 - 920℃
Tempering after carburization	150 - 180℃
Cyanidizing	840 - 860℃
Tempering after cyanidizing	150 - 180℃
Hardening	805 - 835℃	in oil
Tempering	450 - 550℃	in oil or water

Steel prone to flake formation and to the brittleness of tempering.

Other properties of 20HN3A

- Mechanical properties of a 25mm sample at elevated and lowered temperatures

Chemical Composition (%)				Thermal treatment	Impact resistance KM, J/cm³ (kG ⋅ m/cm²) at temperature
Chemical Composition (%)				Thermal treatment	+50℃	+20℃	0℃	-20℃	-40℃	-60℃	-70℃
C:	Mn:	Cr:	Ni:	Hardening in oil at 820℃ Tempering in oil at 500℃	101	98	98	98	95	90	88
0.20	0.57	0.76	3.17	Hardening in oil at 820℃ Tempering in oil at 500℃	(10.3)	(10,0)	(10,0)	(10,0)	(9,7)	(9,2)	(9,0)

- Resistivity of 20HN3A

Resistivity ρ and temperatures (unit μ ⋅ Ω ⋅ m) of the material after heat treatment.
20℃	100℃	200℃	300℃	400℃	500℃	600℃	700℃	800℃	900℃	1000℃	1100℃	1200℃	1300℃
0.268	0.317	0.387	0.469	0.567	0.681	0.817	0.981	1.115	1.148	1.178	1.201	1.225	1.246

- Longitudinal modulus of elasticityE

Value E ⋅ 10^-3 of the material after heat treatment (MPa)
20℃	100℃	200℃	300℃	400℃	500℃	600℃	700℃
202.0	197.0	191.5	184.6	175.7	166.4	175.7	141.8

Welding, gouging and cutting - 20HN3A

20HN3A steel can be combined using friction welding, electric welding, and resistance welding. It is best to perform the treatment on softened material. Arc-air gouging can be performed on 20HN3A steel after pre-heating on:

the product with dimensions up to 15mm - temp.: 150 - 225℃
the product with dimensions 15-25 mm - temp.: 175 - 250℃
the product with dimensions 25-50 mm - temp.: 200 - 300℃

Thermal cutting do not pose any obstacle to the user, but before the procedure the product should also be heated to a temperature of 200-275 ℃.

Materials can be cut with propane-butane-oxygen flame, acetylene-oxygen flame, or plasma arc. After the treatment the product should be cooled slowly in the air.

Welding of 20HN3A steel

20HN3A steel is difficult to weld. When using products in the 20HN3A grade, welding should be avoided and used only in exceptional circumstances. For arc welding of 20HN3A should be used either EB1.55, EB.160, EB1.70, ES18-8-6 coated electrodes, or CO₂ binding agent SpA3S1, SpG4S1. The steel must be heated to the right temperature before welding.

The condition of the product should be softened and it is recommended that relaxing annealing be used before treatment. The product after welding should be improved thermally or be subject to softening annealing, because in welded places the influence of temperature changes the state of the material.

In the absence of heat treatment, the material can be gradually cooled slowly in asbestos mats, together with the oven or in hot sand. The table below shows the temperature ranges to which the material should be heated before welding.