431 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.Characterised by very good corrosion resistance in general atmospheric corrosive environments, good resistance to mild marine and industrial atmospheres, resistant to many organic materials, nitric acid and petroleum products coupled with high tensile and high yield strength plus excellent toughness in the hardened and tempered condition. 431 due to its excellent hardenability is capable of being through hardened up to Rc44, depending upon carbon content and section size. Small sections can be air cooled and larger sections oil quenched for maximum through hardness.Pre hardened and tempered 431 will also respond readily to nitriding achieving a typical surface hardness of over Rc65. the nitriding process however reduces the corrosion resistance and is therefore not generally recommended except for critical applications where the benefit outweighs all other considerations.

Table1:

Table2:

Typical Mechanical Properties at Room Temperature - *Hardened and Tempered to Condition T

Table3:

Typical Mechanical Properties at Room Temperature - Hardened by Oil Quench at 980oC and Tempered as Indicated

*Note drop in impact properties.Tempering within the range 370oC - 565oC should be avoided.

Related Specifications

Mechanical Requirments

Mechanical Properties: Tensile strength  (MPa): quenching and tempering, min1080

Elongation 5 (%): quenching and tempering, min10

Impact energy Akv (J): quenching and tempering, min39

Hardness: annealing, min285HB

Mechanical Properties

the mechanical properties for grade 431 stainless steels are listed in the table below.the bend test is obtained around a diameter of the bend factor multiplied by the steel thickness.

^Aunless otherwise indicated,a grade designation originally assigned by the American Iron and Steel Institute(AISI).

^BYield Strength shall be determined by the offset method at 0.2% in accordance with Test Dethods and Definitions A370.unless otherwise specified (see Specification A480/A480M,paragraph 4.1.11,Ordering information),an alternative method of determining yield strength may be based on total extension under load of 0.5%.

^CEither Brinell or Rockwell B Hardness is permissible.

^DBend tests are not required for chromium steels(ferritic or martensitic) thicker than 1 in.

[25 mm] or for any austenitic or duplex(austenitic-ferritic)stainless steels regardless of thickness.

Key Properties:

the specified properties are for bar products in ASTM A276. the properties may not be necessarily similar to other forms such as forgings and plates.

Maching:

431 machines best in the hardened and tempered as supplied condition and is regarded as being readily machineable with all operations such as turning and drilling etc. Capable of being carried out satisfactorily. It does not work harden to the same extent as the 300 series austenitic stainless steels, but is more similar in this respect to the low alloy high tensile steels such as 4140 etc.Allowing therefore for its high tensile properties, all machining should be carried out as per machine manufacturers recommendations for suitable tool type, feeds and speeds.

Welding:

431 is not generally recommended for welding in either the annealed or hardened and tempered condition, due to its air hardening capability which can lead to the formation of brittle martensite, resulting in cold cracking due to contraction stresses within the weld and heat affected zone. The higher the carbon content the higher the hardening capability and the greater the risk of cracking.Pre heating and interpass temperature control during welding, plus very slow cooling and post-weld annealing is the best method to prevent cracking.

Welding Procedure:

Welding electrodes or rods should be low hydrogen types 410 or *similar when good strength is required otherwise an austenitic stainless electrode or rod such as 308 or *similar may be used resulting in a more ductile weld when strength is not so critical and post-weld annealing is not possible or intended.Pre-heat at 200oC - 300oC and maintain interpass temperature at 200oC minimum. on completion of welding cool slowly as possible until hand warm if possible: Post-weld sub-critical anneal at 620oC - 660oC, and cool in air.*Please consult your welding consumables supplier.

Applications

• · 1).Laboratory equipment
• · 2).Marine systems
• · 3).Beater bars
• · 4).Pump and propeller shafts
• · 5).Nuts and bolt.
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