431 (S43100) | BYBOLT

What is 431 stainless steel and its applications?

431 stainless steel (UNS S43100) is a nickel-bearing martensitic chromium steel selected for a combination of strength, toughness and corrosion resistance. It is used in machined engineering components where a specified heat-treatment condition is essential.

Industrial machinery: Loaded parts requiring controlled strength and toughness.
Transport equipment: Engineered components with defined hardness and corrosion requirements.
Mechanical assemblies: Machined hardware where section size and heat treatment affect acceptance.

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Choose your 431 product

Engineering Application & Selection Guide

Nickel modifies the properties of this hardenable martensitic grade. Quenching and tempering establish the final balance of strength and toughness, so stock condition and final-part condition should be recorded separately.

431 hex bolts — For a highly loaded connection, define hardness, tensile acceptance and any required impact testing for the actual section.
431 stud bolts — For long threaded parts, include straightness, thread inspection and heat-treatment sequence in the manufacturing review.
431 custom fasteners — For shoulders or close-fit locating sections, agree machining allowances and final dimensional checks after thermal processing.

Compare 410 or 17-4 PH using the actual condition and environment. Improved corrosion resistance within the martensitic family does not establish suitability for continuously wetted seawater or eliminate the need for a joint-specific fatigue assessment.

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431 Composition

Selected composition limits · wt.%

ElementWeight %

Cr: 15–17%
Ni: 1.5–2.5%
C: 0.12–0.20%

ASTM / ASME specifications by product form

Finished-product requirements

Specify the finished-fastener mechanical requirements, condition and inspection separately from the starting-stock specification.

431 hex bolt requirements ↗

Fasteners · dimensional references

Product	Reference
Hex bolts	ISO 4014 / ISO 4017 · ASME B18.2.1
Threaded studs	DIN 976-1 · ASME B18.31.2
Hex nuts	ISO 4032 · ASME B18.2.2
Socket head screws	ISO 4762 · ASME B18.3
Flat washers	ISO 7089 / ISO 7090 · ASME B18.21.1
Custom fasteners	Customer drawing

Raw-material specifications

Product form / scope	Reference
Bar · Specify grade, condition and order requirements.	ASTM A276 / A479
Bar · Specify grade, condition and order requirements.	EN 10088-3

Dimensions do not define material or finished-part compliance. Specify the grade, condition and applicable requirements.

How to specify round bar, plate, wire and strip ↗

431 Mechanical Properties

Reference sample and condition

Data basis: Producer condition-specific limits
Test sample form: Bar
Condition: Hardened + tempered · QT800
Gauge length: A5D

Key properties	Value
Tensile strength	880–1080 MPa
0.2% yield strength	≥690 MPa
Elongation	≥12%

Valbruna · 431 bar · Pages 1–2 · hardened and tempered QT800 row ↗

Procurement and application guide

Specify the material and final condition

Specify the hardened and tempered condition and toughness requirement.

Material forms in the technical reference: Bar.

Define the finished-part acceptance

Include the material or bolting specification, required final condition, dimensions and quantity. State the service medium, temperature and loading where known. Agree the required tests, inspection coverage and acceptance criteria for the finished part.

Start with the information you have

Send a drawing or share the product form and dimensions. Identify any undecided requirements for review rather than copying a typical property value into the purchase order.

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