431 stainless steel is a high chromium-low nickel high hardenability Martensitic stainless steel with high strength and good corrosion resistance, as generally supplied hardened and tempered in the tensile range 850 – 1000 Mpa (condition T) Brinell range 248 – 302.

Applications

431 has been successfully used in a variety of aircraft and general industrial applications. These include fasteners, bolts, valve components and chemical equipment.

Grade Comparison

Grade	UNS No	Old British		Euronorm		Swedish SS	Japanese JIS
		BS	En	No	Name
431	S43100	431S29	57	1.4057	X17CrNi16-2	2321	SUS 431

Chemical Composition

Grade		C	Mn	Si	P	S	Cr	Ni
431	min. max.	– 0.20	– 1	– 1	– 0.04	– 0.03	15 17	1.25 2.50

Mechanical Properties

Tempering Temperature (°C)	Tensile Strength (MPa)	Yield Strength 0.2% Proof (MPa)	Elongation (% in 50mm)	Hardness Brinell (HB)	Impact Charpy V (J)
Annealed *	862	655	20	285 max	–
204	1345	1055	20	388	50
316	1295	1035	19	375	53
427	1350	1080	19	388	#
538	1140	965	19	321	#
593	1015	770	20	293	64
650	960	695	20	277	84

Sizes

Hot Rolled Process – OD 30-500mm ; WT 3-60mm ; L 6-12meter

Cold Drawn Process – OD 10-200mm ; WT 0.5-20mm ; L 1-12meter

Cold Rolled Process – OD 6-200mm ; WT 0.1-20mm ; L 1-12meter

Surface

Acid pickling – pre-passivation process of treating stainless steel parts with an acid solution, typically hydrochloric or sulfuric acid, which can remove oxide scale and heat tint while dissolving steel flecks embedded in the part.

Polishing – P grade sandpaper: P150, P200, P250, P300, P400, P500, P600, P700, P800

Inspection

Chamical analysis / Tensile test at room temperature / flattening test / ring tensile test / drift expemdomg test / ring expanding test / leak tightness test / Tensile test at elevated temperature / impact test at room temperature / impact test at low temperature / eddy current test / ultrasonic test / magnetic flux leakage test

Corrosion Resistance

431 stainless steel have considerable resistance to salt water, but they are less resistant to tropical water when compared to that of grade 316 steels. 431 steels have overall corrosion resistance similar to, or slightly lower than, that of grade 304 steels. 431 stainless steel with a smooth surface finish perform well in tempered and hardened conditions.

Heat Resistance

431 stainless steel are resistant to scaling at temperatures of 925°C in intermittent conditions, and 870°C during continuous operations. In general, these steels are not to be used at temperatures above standard tempering temperatures, owing to loss of mechanical properties.

Low Temperature Properties

431 stainless steel is not recommended for use at sub-zero temperatures due to a substantial drop in impact properties consistent with most steels other than the austenitic steel types.

Cold Bending

In the hardened and tempered as supplied condition will be extremely difficult due to the high yield strength and is not generally recommended.

Hot Bending

In the hardened and tempered as supplied condition it is not recommended due to its affect on the mechanical properties within the heat affected zone.

Welding

Welding of grade 431 stainless steels is difficult due to the chances of cracking. It is recommended to pre-heat the materials to 200 – 300°C before welding, and carry out post-weld heat treatment at 650°C. Welding can be performed using grade 410 filler rods.

Machining

Grade 431 steels can be easily machined in their annealed state. However, it is extremely difficult to machine these steels if they are hardened above 30HRC.