What Is Stainless Steel? Grades, Properties & Procurement Tips

A supplier quote arrives for welded stainless steel components: your drawing specifies 1.4301, but the manufacturer proposes 1.4404 at the same price. Accept or reject? For many procurement managers, this is a decision made in the dark. The answer follows a clear logic, one that comes down to a handful of fundamentals.

In brief: Stainless steel is a collective term for corrosion-resistant steels containing at least 10.5% chromium, as defined by EN 10088. The corrosion resistance comes from a self-healing chromium oxide layer on the steel surface. The main families are austenitic (e.g., V2A, V4A), ferritic, and martensitic. In procurement, material numbers such as 1.4301 and 1.4404 are the precise communication channel between design, purchasing, and manufacturing partners.

What Is Stainless Steel and How Does It Differ from Regular Steel?

The term "stainless steel" is not a legally protected term, but in technical contexts it consistently refers to corrosion-resistant, or "rustproof," steels. The technical definition comes from EN 10088: a steel is classified as stainless if it contains at least 10.5% chromium and no more than 1.2% carbon.

Chromium is the key to corrosion resistance. It forms a chromium oxide layer (Cr₂O₃) on the steel surface, just a few nanometres thick, that shields the material against oxygen, moisture, and many chemical media. Crucially, this layer is self-repairing: if it is damaged by scratching or mechanical stress, it closes again within seconds to minutes in the presence of oxygen.

Ordinary structural steel contains little or no chromium. When exposed to moisture, it oxidises into rust (iron oxide), which does not protect the surface but progressively eats into it. Stainless steel interrupts this process reliably through its passive layer.

Alloying additions modify the properties in specific ways: nickel improves toughness and ductility, molybdenum increases resistance to chlorides and acids, and nitrogen raises strength and pitting resistance.

What Grades of Stainless Steel Are There?

EN 10088 classifies stainless steels by microstructure into four main families. This classification has direct practical implications for magnetic properties, weldability, strength, and corrosion behaviour.

Austenitic stainless steels account for roughly 70% of global stainless steel production and are the standard in general mechanical engineering, food technology, and wherever weldability and hygiene matter. Ferritic grades are the more economical choice when there is no high chloride exposure. Martensitic grades combine hardenability with adequate corrosion resistance and are indispensable for cutting tools and wear-critical components. Duplex grades combine the strengths of both crystal structures and are used in extreme corrosion environments.

For international procurement, understanding the family structure is a valuable tool for supplier qualification: not every manufacturing partner works equally well across all families. A facility that processes martensite requires different equipment and expertise from one specialising in austenite — and that distinction belongs in the pre-qualification process.

What Do Stainless Steel Material Numbers Mean?

In Europe, stainless steels are designated under DIN EN 10027-2 with a five-digit number that always begins with 1.4. The first digit (1) identifies steel; the second (4) identifies stainless steels. The final three digits encode the specific alloy composition. This system allows precise communication between design, purchasing, and supplier, independent of trade names like V2A or V4A.

The most important material numbers in mechanical component procurement:

The "L" in 304L and 316L stands for Low Carbon. The reduced carbon content prevents intergranular corrosion during welding: without this protection, carbon and chromium form local compounds in the heat-affected zone, weakening the protective chromium oxide layer.

In our experience procuring stainless steel components from international markets, we regularly see material certificates where the material number is correct but the actual alloy composition sits at the permitted limits. A thorough incoming goods inspection that cross-references the certificate against the EN standard is therefore not a bureaucratic exercise — it is a concrete quality instrument.

What Is the Difference Between V2A and V4A Stainless Steel?

V2A and V4A are historical trade names, not standard designations. The "V" stands for Versuchsschmelze (trial melt) and "A" for Austenit (austenite). Friedrich Krupp AG coined these designations from 1912 onwards, when the first austenitic trial melts were developed, as the Informationsstelle Edelstahl Rostfrei explains. Today they still appear in the trades and in specialist retail, but technical specifications should always use the material number.

The decisive difference is the molybdenum content in V4A. Molybdenum increases pitting corrosion resistance: chlorides can locally penetrate the passive layer and create pitting corrosion. Molybdenum prevents this. The Pitting Resistance Equivalent (PRE = %Cr + 3.3 × %Mo, simplified; the full formula also includes a nitrogen term with a factor of 16) quantifies this: 1.4301 achieves a PRE of about 18, 1.4404 about 24.

Rule of thumb for procurement: V2A is sufficient in most industrial environments without significant chemical loads. As soon as salts, chlorides, seawater, or acidic media are involved, V4A belongs in the specification.

Is Stainless Steel Magnetic?

The answer depends on the family, not on quality. A widespread misconception is that non-magnetic behaviour indicates "genuine" or superior stainless steel. This is not correct.

Austenitic steels (1.4301, 1.4404) are non-magnetic in their as-delivered state. Their face-centred cubic crystal structure does not support ferromagnetic ordering. However, cold working (rolling, deep drawing, bending) can partially transform the austenite into martensite, creating slight magnetic susceptibility. This is not a quality defect — it is a well-known, process-related phenomenon.

Ferritic and martensitic steels are always magnetic. Their body-centred cubic crystal structure is inherently ferromagnetic. Duplex steels contain both structures and show weak to moderate magnetic susceptibility.

For procurement purposes: if a specification requires non-magnetic behaviour (e.g., in medical technology, MRI environments, or electrical engineering), the material family is clearly defined — austenitic, preferably without significant cold working.

What Surface Treatments Are Available for Stainless Steel?

Surface finish specifications on drawings are among the most common unknowns in procurement. Three treatments are particularly relevant:

Pickling removes heat tint, weld beads, and mill scale through an acid treatment (typically nitric-hydrofluoric acid mixtures). The passive layer dissolves and reforms in the process. The result is a matte, chemically clean surface.

Passivation refers to the deliberate re-formation of the chromium oxide layer after thermal or mechanical work. It is frequently specified as a finishing step after pickling or grinding.

Electropolishing is an electrochemical process that removes surface peaks, measurably reducing surface roughness (Ra value) and increasing corrosion resistance. It is often mandatory in pharmaceutical and food-processing applications.

In Far East procurement projects, we regularly see electropolishing requirements interpreted inconsistently when no standard-compliant specification is given (e.g. per DIN EN ISO 15730). The required Ra value belongs in the drawing — not in the free-text field of a purchase order.

What Matters When Procuring Stainless Steel Components?

Several aspects are consistently underestimated in the international procurement of stainless steel components.

Use material numbers, not trade names. The terms "stainless steel" or "V2A" are too vague for a purchase specification. The full material number per DIN EN 10088 must appear in every drawing and every order. Only then is the supplier legally and technically bound to the correct material.

Request the correct material certificate. For stainless steel components, a material test report per EN 10204 is standard practice. Which type is required depends on the application:

Specify tolerances completely. Stainless steel components are frequently inspected for dimensional accuracy. General tolerances per ISO 2768 apply to linear and angular dimensions; where function demands tighter geometric requirements, geometrical tolerances per ISO 1101 apply. Specifying both correctly in the drawing eliminates ambiguity for the supplier.

Qualify suppliers before the first order. Not every manufacturing partner is equally capable across all stainless steel families. Processing duplex grades or welding thin-walled components requires specific equipment and expertise. A structured supplier audit before the first order mitigates this risk systematically.

In our procurement projects in the Far East, we see that the quality of stainless steel components depends heavily on the clarity of the specification. Suppliers who work with EN standards daily produce reliably when the requirements are unambiguous. Gaps in the specification get filled with local standards or assumptions that are not always equivalent. The risk ends up with the buyer.

Frequently Asked Questions

Which stainless steel grade is the most common?

1.4301 (AISI 304, V2A) is the most widely produced stainless steel grade worldwide. It represents the largest share of the austenitic family, which in turn accounts for approximately 70% of global stainless steel output. Its balanced combination of corrosion resistance, processability, and cost makes it the standard in industrial manufacturing.

What does the minimum 10.5% chromium content mean for stainless steel?

This value is the defining threshold of EN 10088. Below 10.5% chromium, no stable passive layer forms that reliably protects the steel against corrosion. As chromium content increases, corrosion resistance improves — which is why highly alloyed grades such as duplex steels contain up to 25% chromium. The standard has been internationally harmonised by the World Stainless Association and ISO.

Can stainless steel be welded?

Austenitic and ferritic stainless steels weld well when the correct processes and filler materials are used. For austenitic grades, the low-carbon variant (e.g., 1.4307 rather than 1.4301) is preferred to prevent intergranular corrosion in the heat-affected zone. Martensitic steels are significantly more difficult to weld and require preheating and post-weld heat treatment.

What is the difference between stainless steel and Inox?

Both terms refer to the same material. "Inox" comes from the French (acier inoxydable = non-oxidising steel) and is used primarily in Switzerland, France, and Southern Europe. In technical German-language contexts, the standard term is "nichtrostender Stahl" (non-rusting steel) per EN 10088.

What drives the price of stainless steel?

Stainless steel prices fluctuate because the key alloying elements are exchange-traded commodities. Nickel (London Metal Exchange, LME) drives prices for austenitic grades; molybdenum determines the premium for V4A grades. A 10% rise in nickel prices typically appears in supplier quotes within weeks. For procurement, this means that comparing quotes with different alloy compositions always requires a look at current commodity prices.

What is the difference between corrosion-resistant and weather-resistant steel?

In European technical usage, "stainless steel" or "nichtrostender Stahl" consistently refers to fully passive, rustproof steels per EN 10088. "Weather-resistant" (or Cor-Ten) steels develop a controlled rust patina that slows further corrosion but does not eliminate it. If a supplier from a non-EU market uses different classification systems, always verify the actual alloy composition through the material certificate.

Conclusion: Stainless Steel as a Reliable Material in Procurement

Stainless steel is not a single, homogeneous material — it is a family with clear sub-groups, precise standard designations, and specific areas of application. Buyers who understand the basic structure (austenitic or ferritic, V2A or V4A, material number instead of trade name, EN 10088 as the binding reference) can tighten purchase specifications, conduct supplier conversations from a position of knowledge, and reduce quality risks early in the process.

Global stainless steel production reached a new record of 64.2 million tonnes in 2025, according to the World Stainless Association. This material runs through global supply chains at scale. Procuring it with a precise specification is the simplest risk-reduction measure available.

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