Hardenable Steel BS S155

Technical Data Sheet

BS S155 is the British aerospace equivalent of U.S. steel grade 300M (4340M / AMS 6257). It is a vacuum melted grade supplied in the normalised and tempered/softened condition to allow for final heat treatment. It has a combination of ultra high strength, good fatigue resistance and excellent transverse properties and as such finds many applications in the aerospace industry such as undercarriage components, gears and shafts.

Chemical Composition Limits
Weight% C Si Mn P + S max Cr Mo Ni
S155 0.39-0.44 1.50-1.80 0.60-0.90 P 0.015
S 0.01
1.60-2.00 0.40-0.60 3.50-4.50

Typical Mechanical Properties

Grade Condition Tensile Strength N/mm² Yield Strength N/mm² Elongation (%) Hardness (HB) Ruling Section
S155 Norm & Softened - - - 302 -
S155 Hardened & Tempered 1900-2100 1550 8 534-601 3"
S155 Hardened & Tempered 1900-2100 1550 5
(Transverse test)
534-601 3"

Alloy S155 for all stock availability contact Sales.


AMS 6257
AMS 6417
AMS 6419
SAE 4340M / 300M
BMS 7.26
DMS 1935

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Every effort is made to ensure that technical specifications are accurate. However, technical specifications included herein should be used as a guideline only. All specifications are subject to change without notice.