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SS 431 is a martensitic chromium steel that is rust and acid resistant and contains nickel addition. This addition results in improved toughness. The formation of chromium carbides and the associated chromium-depleted areas make this grade susceptible to intergranular corrosion.

Due to its high strength, the main area of application for this stainless steel is mechanical engineering, as stainless thrust washers, turbine blades, spindles, pump parts, piston rods or in the petroleum and petrochemical industries. Other applications of martensitic steel AISI 431 SS are in power plant construction, the automotive industry and aviation.

Overview of the most important steel

BS431S29, GOST20Ch17N2, SUS431, UNE F.3427, SS2321, UNS S43100, SAE431, AFNOR Z15CN16-02, 1.4057

Chemical composition

AISI 431
C Si Mn P S Cr Mo Ni
min. 0,12 15,0 1,50
max. 0,22 1,0 1,50 0,04 0,015 17,0 2,50

AISI 431 is available in QT800 and QT900:

QT800 QT900
Tensile strength Rm 800 – 950 N/mm2 900 – 1050 N/mm2
Brinell hardness 251 – 299 HB 284 – 331   HB


Weldability good
Machinability average 5 (1 = poor – 10 = good)
Polishing yes
Corrosion class 2 (0 = weak – 5 = good)

Special features

  • suitable for high-gloss polishing
  • can be use in a temperature range between -40°C and 400°

Heat treatment

Temperature in °C Cooling
Hot forming 1.100 – 800 Furnace, slow cooling
Heat treatment
Soft annealing (+ A) 680 – 800 Furnace, air
Tempering (+ QT)
Hardening 950 – 1050 Oil, air or polymer
Annealing QT800 750 – 800 + 650 – 700 Water or air
Annealing QT900 600 – 650 Water or air


Under certain precautions, AISI 431 steel is weldable after preheating to 100°C – 300°C. Cooling to below 200°C during welding must be avoided. Nitrogenous or hydrogenous or gas must not be used. Chemical or mechanical removal of the tempering colors is necessary.


AISI 431 must be heated slowly to 850°C for forging. This is followed by rapid heating to 1150°C – 1180°C. Forging takes place in a temperature range between 1180°C and 950°C. This is followed by slow cooling.

Cold forming

SS 431 can be formed, stamped and cold upset to a certain point.

Corrosion resistance

AISI 431 is susceptible to intergranular corrosion due to the formation of chromium carbides and thus has low corrosion resistance.


Cold forming is possible
Spent processing is possible
Cold diving not typical
Free-form and drop forging rarely

Physical Properties

Density in kg/dm3 7,0
Electr. Resistance at 20°C (Ω mm2 /m) 0,7
Thermal conductivity at 20°C in W/(m K) 25
Specific heat capacity at 20°C in J/(kg K) 460
Magnetisability present
Steel from stock

Produced to the highest Standards

Special steel quick delivery from stock

Quick delivery

Special steel from stock

From stock in US

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Karol Borycki
Phone: +1 409 2395919

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Popular steel:
ss 430f, steel 17 4ph

Important questions

Is AISI 431 a stainless steel?
AISI 431 is indeed classified as a stainless steel. It belongs to the martensitic stainless steel group, characterized by high strength, moderate corrosion resistance, and good toughness.

Is SS 431 magnetic?
Yes, SS 431 is magnetic. Martensitic stainless steels like AISI 431 are generally magnetic due to their microstructure, which consists primarily of ferrite and/or martensite phases.

Is 431 SS weldable?
431 SS can be welded, but it requires careful attention to welding procedures. Due to its high carbon content and alloying elements, AISI 431 is prone to cracking during welding if proper precautions are not taken. Preheating before welding and post-weld heat treatment are often necessary to minimize the risk of cracking and ensure satisfactory weld quality.

What does QT 800 mean?
QT 800 refers to a specific heat treatment process applied to steel. In this context, “QT” stands for quenching and tempering. The “800” indicates the approximate hardness achieved on the Brinell scale after the heat treatment process. During quenching, the steel is rapidly cooled from high temperatures to room temperature to achieve a hardened microstructure. Subsequently, tempering is performed to reduce brittleness and improve toughness while maintaining a desired level of hardness. The resulting material typically exhibits enhanced strength and toughness properties, suitable for various industrial applications.