316Ti Stainless Steel 316Ti Microstructure Analysis

316Ti Stainless Steel 316Ti Microstructure Analysis

Published: November 11, 2025 | Updated: November 11, 2025By Gangsteel Engineering Team – 25+ Years in Stainless Steel Export Excellence

In the precision domain of stainless steels compliant with ASTM A240/A240M and ASME SA240/SA240M standards, 316Ti emerges as a titanium-stabilized austenitic grade whose microstructure analysis is crucial for understanding its superior resistance to intergranular corrosion (IGC) and high-temperature stability.

As a premier producer and exporter based in China, Gangsteel has supplied thousands of tons of 316Ti stainless steel, meeting ASTM A240/A240M specs for plates and sheets, to industries like petrochemical, pharmaceutical, and marine.

If you're conducting microstructure analysis for 316Ti under ASME SA240/SA240M for a welded heat exchanger or reactor where grain boundary behavior and phase stability are critical, examining its austenitic matrix and titanium inclusions is essential. This article provides a detailed microstructure analysis of 316Ti, including grain structure, precipitates, and insights, based on ASTM A240/A240M and ASME SA240/SA240M standards and our mill metallographic data.

From our production lines, we've analyzed 316Ti's microstructure: In a 2024 U.S. chemical vessel inspection, our 316Ti plates under ASTM A240 /A240M revealed a fine-grained austenitic structure (ASTM grain size 6–8) with discrete Ti(C,N) precipitates at grain boundaries, preventing chromium depletion after 1,000 hours at 650°C, as confirmed by SEM-EDS and ASTM A262 Practice E testing. Compliant with ASME SA240/SA240M for pressure apps, 316Ti's density of 8.00 g/cm³ supports consistent microstructure. Let's delve into the analysis, from composition to micrographs, to guide your evaluation.

Summary

316Ti stainless steel microstructure under ASTM A240/A240M and ASME SA240/SA240M consists of a fully austenitic matrix (FCC γ-phase) with ASTM grain size 5–8, stabilized by finely dispersed Ti(C,N) and TiC precipitates (0.5–2 μm) at grain boundaries and within grains, preventing IGC at 425–815°C. No delta ferrite (<1%) in annealed state; twin boundaries common. Density 8.00 g/cm³, PREN 23-28. Superior to 316L in sensitization resistance; ideal for welded high-temp apps. Gangsteel stocks 1–200mm with certs and micrograph reports.

Chemical Composition: Foundation for Microstructure

The chemical composition of 316Ti, as per ASTM A240/A240M and ASME SA240/SA240M, drives its stable austenitic microstructure, with titanium forming key precipitates.

Ti/C ratio >5ensures all C is bound, preventing M23C6.

Gangsteel's melts achieve Ti(C,N) dispersion for optimal structure.

For uns stainless steel plates, microstructure verified.

Microstructure Analysis: Key Features

316Ti's microstructure, analyzed via optical microscopy (OM), SEM, and TEM per ASTM E3/E112, is defined as:

1. Matrix Phase

• 100% Austenite (γ-FCC): Equiaxed grains, no ferrite (δ <1% via Schaeffler diagram).
• Grain Size: ASTM 5–8 (20–60 μm); finer in cold-rolled (ASTM 8–10).
• Annealing Twins: Abundant; indicate low stacking fault energy.

2. Precipitates

• Ti(C,N): Cubic/rectangular, 0.5–2 μm, yellow/gold in OM; at grain boundaries and intragranular.
• TiC: Smaller (<1 μm), spherical; from excess Ti.
• No M23C6: Ti binds C, preventing Cr depletion (IGC immunity per A262).
• Rare MnS: If S high; elongated.

3. Post-Weld Microstructure

• HAZ: Grain growth to ASTM 4–6; Ti(C,N) remain stable—no sensitization.
• Weld Metal (ER316L filler): Similar γ with dispersed TiC if Ti wire used.

Micrograph Examples (Gangsteel Lab)

• Annealed Plate (100x OM): Equiaxed γ grains, twin bands, Ti(C,N) at boundaries.
• SEM-EDS (5000x): Ti-rich particles (Ti:C:N ratio ~1:0.6:0.4); no Cr depletion.

Mechanical Properties: Linked to Microstructure

316Ti's mechanicals, per ASTM A240/A240M and ASME SA240/SA240M, stem from fine γ grains and Ti precipitates.

Fine grains + Ti = high strength/ductility.

High-Temperature Microstructure Stability

At 425–815°C (sensitizing range):

• Ti(C,N) Stable: No dissolution; prevent M23C6.
• No Sigma Phase: Mo <3% limits formation <1000 hr.
• Grain Growth: Minimal; Ti pins boundaries.

Test: 650°C / 1,000 hr → No IGC (A262 E pass).

Corrosion Resistance: Microstructure-Driven

316Ti's resistance, per ASTM A240/A240M and ASME SA240/SA240M, relies on clean boundaries.

• IGC: TiC prevents Cr depletion → Pass A262 Practice A/E.
• Pitting: Mo in solution → PREN 23–28.
• Uniform: γ matrix stable.

Weldability and Fabrication: Microstructure Impact

316Ti weldable per ASTM A240/A240M; Ti maintains structure in HAZ.

Gangsteel's 316Ti SA240 Type 316Ti shows no cracks post-weld.

Applications: Where Microstructure Excels

316Ti's microstructure suits welded reactors (no IGC), heat exchangers (stable at 650°C).

In Gangsteel's supply to U.S. pharma, microstructure ensured compliance.

Equivalents: Similar Microstructure

Equivalents: EN 1.4571 (identical γ + Ti(C,N)). For A240 GR 316Ti, structure matches.

Sourcing from Gangsteel: Stock and Pricing

Gangsteel stocks 316Ti at $3,200–3,800/ton FOB. 1–200mm thick, certs with micrographs. Contact for analysis.

FAQ: 316Ti Stainless Steel Microstructure Questions Answered

Q: What is the microstructure of 316Ti stainless steel?

A: 316Ti microstructure is fully austenitic (γ-FCC) with ASTM grain size 5–8, annealing twins, and finely dispersed Ti(C,N)/TiC precipitates (0.5–2 μm) at grain boundaries and within grains, preventing IGC.

Q: What precipitates are in 316Ti microstructure?

A: Primary precipitates are Ti(C,N) (cubic, yellow in OM) and TiC (spherical), sized 0.5–2 μm; no M23C6 due to Ti binding carbon.

Q: What is the grain size of 316Ti per microstructure analysis?

A: Grain size is ASTM 5–8 (20–60 μm) in annealed plate; finer (ASTM 8–10) in cold-rolled sheet, per ASTM E112.

Q: How does welding affect 316Ti microstructure?

A: Welding causes minor grain growth in HAZ (to ASTM 4–6), but Ti(C,N) remain stable—no sensitization or IGC per ASTM A262.

Q: Is there delta ferrite in 316Ti microstructure?

A: No—316Ti has <1% delta ferrite in annealed state; fully austenitic per Schaeffler diagram due to Ni and low Cr equivalent.

Q: How does high temperature affect 316Ti microstructure?

A: At 425–815°C, Ti(C,N) prevent carbide formation; no sigma phase <1000 hr; grain growth minimal due to pinning.

Q: Where can I get 316Ti microstructure analysis reports?

A: Gangsteel provides microstructure reports (OM, SEM, grain size) with EN 10204 3.1/3.2 certs upon request for stock orders.