Austenitic Stainless Steel hardening

Expanite Surface Hardening For a Variety of Stainless Steel Alloys Including Austenitic

Austenitic stainless steel is on of the major categories of stainless steel include Martensitic, ferritic, duplex, and precipitation hardened variants

The predominant crystalline structure is austenite, which is face-centered cubic in nature. This structure prevents steels from becoming hardenable through heat treatment and renders them essentially non-magnetic. To achieve this structure, it’s necessary to introduce sufficient austenite-stabilizing elements like nickel, manganese, and nitrogen. The Incoloy family of alloys falls within the realm of super austenitic stainless steels.

Learn More on Wikipedia

UNS S30400 / S30403 / AISI 304 / AISI 304L / 1.4301 / 1.4307

AISI 304 stainless has excellent fabricability and weldability characteristics and is the most widely used chromium-nickel austenitic stainless steel. It is nonmagnetic in the annealed condition and becomes slightly magnetic when cold worked. Nonhardenable by heat treating. The low carbon version of this alloy is known as AISI 304L.

UNS S31600 / S31603 / AISI 316 / AISI 316L / 1.4401 / 1.4404

AISI 316 stainless is a molybdenum-bearing austenitic stainless offering improved corrosion resistance in chlorides and many other environments over 304. It also has higher tensile and creep strength at elevated temperatures than the conventional 18% chromium – 8% nickel alloys. Suggested for applications requiring a moderate level of improvement in machinability for shorter runs of less complex parts, particularly at larger bar diameters. The low carbon version of this alloy is known as AISI 316L.

UNS S30300 / AISI 303 / 1.4305

AISI 303 is an 18-8 chrome-nickel free-machining stainless steel with the addition of sulfur to enhance the machinability of this ordinarily tough and difficult to machine alloy. AISI 303 steel possesses nongalling properties that make disassembly of parts easy and help to avoid scratching or galling in moving parts. It is not recommended for vessels containing gases or liquids under high pressures.

Properties of Austenitic Stainless Steels

Heat-resistant grades are designed for applications at elevated temperatures, typically exceeding 600°C (1,100°F).

These alloys must effectively withstand corrosion, primarily oxidation, while maintaining their mechanical properties, especially strength (yield stress) and resistance to creep deformation.

Chromium primarily contributes to corrosion resistance, often accompanied by the addition of silicon and aluminum. Nickel, on the other hand, is not particularly resistant to sulfur-containing environments. To address this issue, additional silicon and aluminum are incorporated, forming highly stable oxides. Additionally, the presence of rare earth elements like cerium enhances the stability of the oxide film.

EN designation	Euronorm (EN) number	AISI grade
X10CrNi18-8	1.4310	301
X5CrNi18-10	1.4301	304
X2CrNi18-9	1.4307	304L
X8CrNiS18-9	1.4305	303
X6CrNiTi18-10	1.4541	321
X5CrNiMo17-12-2	1.4401	316
X2CrNiMo17-12-2	1.4404	316L
X6CrNiMoTi17-12-2	1.4571	316Ti

The Purpose of the Process

ExpaniteHigh-T

The purpose of this process is to dissolve nitrogen in the surface of stainless steel to a depth of 1mm. Peak hardness ranges from 280HV on austenitic grades to 950HV on martensitic/ferritic grades.

ExpaniteLow-T

The purpose of this process is to dissolve nitrogen and carbon in the surface of stainless steel to a depth in the range of 5-30µm. Peak hardness ranges from 1000-1200HV on austenitic grades to 1300HV on martensitic/ferritic grades.

SuperExpanite®

The purpose of this process is to combine ExpaniteHigh-T and ExpaniteLow-T processes to achieve higher load bearing and corrosion properties. Firstly, the ExpaniteHigh-T process is applied to create a deep case depth with moderate nitrogen content. Secondly, the ExpaniteLow-T process is applied to create a high-hardness surface on top of the ExpaniteHigh-T zone. The Expanite process does not result in a coating, but a diffusion zone with an increased carbon and nitrogen content. We call this zone expanded austenite, expanded martensite or simply: Expanite.

Discover More Stainless Steel Solutions with Expanite

Expanite® surface hardening and heat treatment solutions unlock the full potential of austenitic stainless steels by improving wear resistance, eliminating galling, and extending component lifetime without compromising corrosion resistance. With our proven expertise, we help customers in demanding industries achieve superior performance and reliability.

To gain a complete overview of how Expanite can support your material choices, we also invite you to explore our dedicated pages on Duplex, Ferritic, and Martensitic stainless steels – and discover how our technology adds value across the full range of stainless steel alloys.

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