Technical Resources

High Temperature Bolt Material Selection Guide

How to choose the right superalloy fastener: the temperature matrix and the decision path first, with the corrosion, standards and cost detail one link away.

Temperature decides most bolting specifications, so it leads here. The corrosion matrix, the ASTM / AMS / EN cross-reference, preload data and the cost-versus-lifecycle comparison continue in the full selection guide.

Section 1

Temperature-Based Material Selection

Temperature Range	Recommended Grades
< 400°C (750°F)	A-286 (GH2132), 17-4PH, Grade 660
400-650°C (750-1200°F)	A-286 (GH2132), Inconel 718 (GH4169)
650-815°C (1200-1500°F)	Inconel 718 (GH4169), Nimonic 80A (GH4080A)
815-1000°C (1500-1830°F)	Nimonic 80A (GH4080A), Waspaloy, Haynes 230
> 1000°C (> 1830°F)	Haynes 230, Haynes 188 (cobalt-based), Inconel 617

Typical applications for each band are listed in the full selection guide.

Engineering rule of thumb: select a material whose metallurgical stability limit is at least 50°C above your maximum operating temperature, and add another 50°C margin for cyclic service.

Quick Reference

Simplified Selection Decision Tree

For the most common selection scenarios, here is the decision path. For applications with multiple interacting constraints, read the full selection guide or contact our engineering team directly.

Scenario A: High temperature, dry air, moderate budget

≤650°C: A-286: best value, widely available, ASTM A453 Grade 660 standard.

650-700°C: Inconel 718: highest strength in this range, AMS 5662/5663.

>700°C: Nimonic 80A: the only standard-grade option holding strength above 700°C.

Scenario B: Corrosive environment, any temperature

Seawater, ≤300°C: Monel K-500: the marine reference material.

Acids, chlorides, ≤425°C: Hastelloy C-276: gold standard for chemical resistance.

Corrosion + heat, ≤650°C: Inconel 625: best compromise of corrosion and temperature.

Scenario C: Aerospace / rotating hardware

≤650°C, non-rotating: A-286 to AMS 5732 or 5734.

≤700°C, rotating: Inconel 718 to AMS 5663: the only choice for primary structure.

>700°C: Nimonic 80A or Waspaloy; contact our aerospace engineering team for qualification data.

Scenario D: NACE / sour service, subsea

H2S, low temperature: Hastelloy C-276 or Inconel 625: solid-solution, no hardness limits.

H2S, high strength needed: Inconel 718 at ≤40 HRC with NACE qualification testing.

Seawater, NACE, non-magnetic: Monel K-500 at ≤35 HRC, with controlled aging and hardness testing per lot.

FAQ

Frequently Asked Questions About High Temperature Bolt Selection

How do I select a high-temperature bolt material?

Start with three parameters: maximum service temperature, environment (oxidising, reducing, chloride, sulphurous), and required mechanical load. Filter candidate materials against the temperature table first, then check environmental compatibility, and finally confirm strength and standard requirements. When in doubt, contact our metallurgy team with all three parameters.

What is the difference between Inconel 718 and A-286 bolts?

Inconel 718 is a nickel-based superalloy (~53% Ni) that delivers 1275 MPa tensile strength and operates to 700degC. A-286 is an iron-based superalloy (~25% Ni) that delivers 1000 MPa and operates to 650degC. The cost ratio is roughly 2.5:1. Choose A-286 for budget-sensitive applications below 650degC; choose Inconel 718 when peak strength, fatigue life, or the extra 50degC margin matters.

How does temperature affect bolt strength?

All metals lose strength with increasing temperature, but the rate differs significantly. A-286 retains ~70% of room-temperature yield at 600degC but drops sharply above 650degC. Inconel 718 retains ~80% at 650degC before the gamma-double-prime strengthening phase over-ages. Nimonic 80A retains useful strength (300+ MPa yield) to 815degC because its gamma-prime strengthening is thermally stable.

Can I use the same bolt material for the nut?

Not always. At high temperatures, galling between like materials is a risk. Industry practice is to use a nut of the same or compatible alloy, often one hardness level below the bolt. For critical joints, consider silver-plated or MoS2-coated fasteners to prevent seizure. Our technical team can recommend nut pairings per grade.

What standards apply to high-temperature bolting?

ASTM A193 covers alloy-steel bolting materials for high-temperature service (B8, B16, etc.). ASTM B637 covers precipitation-hardened nickel alloys (Inconel 718). ASTM A453 covers A-286 bolting for high temperatures. AMS 5662/5663 covers aerospace-grade Inconel 718 bar. For European projects, EN 10269 is the primary standard. Always specify the standard on your purchase order.

What is the minimum order quantity for custom superalloy bolts?

For standard sizes (M6-M36) manufactured from our in-stock VIM+VAR bar, trial quantities from 50 pieces are accepted. For fully custom melt-to-bolt orders requiring a new heat, minimum is typically 500-1000 pieces depending on size and grade. Lead time for stock material is 2-3 weeks; custom heats take 6-8 weeks.

Do superalloy bolts require special installation procedures?

Yes. Superalloy fasteners typically require controlled lubrication (never use copper-based anti-seize on nickel alloys), calibrated torque or tensioning, and in many cases preload verification. Thermal expansion mismatch with the joint material must be accounted for in the torque specification. Our torque chart page provides grade-specific torque values for standard lubrication conditions.

How do I verify the material is genuine?

Every shipment from our facility includes material test certificates (EN 10204 3.1 as standard, 3.2 with third-party witness on request). Certificates include heat number, full chemical analysis, mechanical test results, and grain size. Positive Material Identification (PMI) using handheld XRF or OES can be performed on receipt. Our head markings trace to a specific heat lot for full supply-chain transparency.