347 (S34700) | BYBOLT

What is 347 stainless steel and its applications?

347 stainless steel (UNS S34700) is a niobium-stabilized austenitic grade used for heated process equipment and fabricated components. Its selection often turns on resistance to sensitization and the requirements of sustained elevated-temperature service.

Process equipment: Components exposed to heat during fabrication or operation.
Thermal systems: Heated assemblies requiring a stabilized stainless grade.
Refinery equipment: Components where thermal history and shutdown corrosion mechanisms must both be assessed.

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Engineering Application & Selection Guide

Niobium, also called columbium, binds carbon and reduces the tendency for chromium-carbide sensitization. The resulting benefit depends on condition and exposure; stabilization is not immunity to every form of intergranular or stress-corrosion attack.

347 stud bolts — For hot flange joints, specify the governing bolting grade, condition and temperature-dependent acceptance requirements.
347 hex bolts — For process-equipment supports, check relaxation and thermal expansion at the joint rather than at the process-fluid headline temperature.
347 socket head cap screws — For heated service assemblies, provide head-access constraints and the required inspection and replacement procedure.

Review 321 as the titanium-stabilized comparison. If the design specifies 347H, establish the H-grade requirements explicitly. For refinery service, include shutdown conditions in the corrosion review; operating-temperature data alone may miss the relevant damage mechanism.

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347 Composition

Selected composition limits · wt.%

ElementWeight %

Cr: 17–19%
Ni: 9–12%
Nb + Ta: 10×C–1.00%
C: ≤0.08%

ASTM / ASME specifications by product form

Finished-product requirements

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

347 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
Plate, sheet & strip · Specify grade, condition and order requirements.	ASTM A240 / ASME SA-240

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

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347 Mechanical Properties

Reference sample and condition

Data basis: Minimums quoted by producer
Test sample form: Sheet test samples
Condition: Annealed
Test temperature: Room temperature
Heat treatment: 1093°C (2000°F), air cooled.
Gauge length: 2 in (50.8 mm)

Key properties	Value
Tensile strength	≥515 MPa
0.2% yield strength	≥205 MPa
Elongation	≥40%

ATI · 321 / 347 · Technical Data Sheet · composition and room-temperature mechanical table ↗

Procurement and application guide

Specify the material and final condition

Match stabilization and heat treatment to the thermal exposure.

Material forms in the technical reference: Plate · Sheet · Strip.

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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