What is Stainless Steel and It's Manufacturing Process

BLOGS

On June 8, 2025

Stainless steel is an iron-based alloy that contains at least 10.5% chromium and typically less than 1.2% carbon by mass. The chromium reacts with oxygen in the environment to produce a thin, transparent layer of chromium oxide on the surface a passive film that blocks further oxidation and can repair itself when scratched or abraded.

This self-healing behaviour is what separates stainless steel from ordinary steel or mild steel, which rusts quickly when exposed to moisture and air. The material is also referred to as inox (from the French inoxydable, meaning non-oxidisable) or simply rustless steel.

Beyond corrosion resistance, stainless steel delivers high tensile strength, heat resistance, impact resistance and a smooth non-porous surface that does not support bacterial growth properties that make it indispensable in construction, automotive, medical, food processing and energy infrastructure.

TL;DR

Stainless steel is an iron-based alloy containing a minimum of 10.5% chromium, which forms a self-healing chromium oxide passive film on its surface, giving the metal its characteristic resistance to rust and corrosion.
It is classified into five families austenitic, ferritic, martensitic, duplex, and precipitation hardening each suited to different environments and loads.
Manufacturing involves melting raw materials and stainless steel scrap in an electric arc furnace, refining in an AOD converter, continuous casting, hot rolling, annealing and pickling.
The material is 100% recyclable, carries an average recycled content of about 60%, and is used across construction, automotive, medical, food processing, and oil and gas sectors worldwide.

What Makes Stainless Steel Corrosion Resistant?

The corrosion resistance of stainless steel begins with its minimum chromium content of 10.5%. At that threshold, chromium atoms on the metal’s surface react with atmospheric oxygen to form a continuous, invisible layer of chromium oxide roughly 3-5 nm thick.

This passive film adheres tightly to the underlying metal and, if scratched, regenerates within seconds wherever oxygen or moisture is present a property that ordinary carbon steel entirely lacks. Carbon steel, by contrast, forms porous iron oxide (rust) that flakes away and exposes fresh metal to continued attack.

Higher chromium levels along with additions of molybdenum and nitrogen push corrosion resistance further.

Engineers use the Pitting Resistance Equivalent Number (PREN = %Cr + 3.3 × %Mo + 16 × %N) to rank a grade’s ability to resist localised pitting corrosion, the most common form of localised attack in stainless steels, particularly in the presence of chloride ions.

Increasing chromium and molybdenum content also improves resistance to reducing acids, while the addition of nitrogen boosts both pitting resistance and mechanical strength.

Despite these defences, stainless steels are not immune to all corrosive conditions.

Stress corrosion cracking (SCC) can occur when sustained tensile stress coincides with a corrosive environment especially one rich in chlorides. Chloride stress corrosion cracking is a well-documented failure mode for austenitic grades in warm chloride solutions.
Galvanic corrosion is another risk: when stainless steel is coupled with a less noble metal in a conductive electrolyte, the stainless steel acts as the cathode and accelerates attack on the other metal.

Chemical Composition of Stainless Steel

Stainless steel is, at its core, an iron-based alloy whose properties are tuned by the type and proportion of its alloying elements. The key elements chromium, nickel, carbon, molybdenum, manganese, and nitrogen each play a distinct role in determining a grade’s corrosion resistance, mechanical properties, and workability.

Element	Role	Typical Range
Chromium (Cr)	Forms the passive oxide layer; primary source of corrosion resistance	10.5-27%
Nickel (Ni)	Stabilises the austenitic microstructure; improves ductility and corrosion resistance in certain media	0-30%
Carbon (C)	Increases hardness and tensile strength; kept low (<0.08%) in grades like 304L/316L to prevent sensitisation during welding	<1.2% (often <0.08%)
Molybdenum (Mo)	Improves resistance to pitting and crevice corrosion, especially in chloride environments	0-7%
Manganese (Mn)	Improves hot working properties and can partially replace nickel as an austenite stabiliser	0-10%
Nitrogen (N)	Increases mechanical strength and pitting resistance; important in duplex and lean austenitic grades	0-0.5%

Adjusting these alloying elements allows metallurgists to produce hundreds of commercial alloys from general-purpose 304 to highly corrosion resistant grades like 2205 duplex.

Low-carbon variants (designated with an “L”, such as 304L and 316L) minimise the risk of intergranular corrosion that can occur when carbon combines with chromium at grain boundaries during welding (a phenomenon called sensitisation).

Stainless Steel Families and Common Grades

Stainless steel is classified into five families of alloys, each with a distinct crystal structure, magnetic behaviour, and set of mechanical properties. Austenitic stainless steel is by far the largest family, accounting for roughly two-thirds of all stainless steel production worldwide.

Family	Magnetic?	Corrosion Resistance	Hardenable?	Example Grades	Typical Uses
Austenitic	No	Excellent	Cold work only	304, 316	Food processing equipment, chemical tanks, cooking utensils, medical instruments
Ferritic	Yes	Good	Cold work only	430, 409	Automotive exhaust systems, kitchen sinks, industrial trim
Martensitic	Yes	Moderate	Heat treatment & cold working	410, 420	Cutlery, gun barrels, circular knives, high speed blades, stainless steel fasteners
Duplex	Yes	Very high	Limited	2205, 2507	Oil and gas industry, marine structures, chemical processing
Precipitation Hardening	Varies	Good to high	Heat treatment (ageing)	17-4PH	Aerospace, high-performance shafts, structural applications

1. Austenitic stainless steel (300 series)

It contains varying chromium (16-26%) and nickel (6-22%) with an austenitic microstructure that gives them excellent ductility and formability. Type 304 the most common stainless steel grade, with 18% chromium and 8% nickel is the workhorse of the food, chemical, and construction sectors. Type 316 adds 2-3% molybdenum for superior corrosion resistance in chloride-rich environments.

2. Ferritic stainless steel

It contains 10.5-27% chromium with very little or no nickel. They offer good corrosion resistance at lower cost but have lower ductility than austenitic grades, making them popular for automotive trim and industrial applications.

3. Martensitic stainless steel

These are magnetic and can be hardened through heat treatment and cold working. Heat treatment typically involves quenching followed by tempering to achieve the desired balance of hardness and toughness. These grades are well suited to cutlery, surgical tools, and valve components.

4. Duplex stainless steels

This has a mixed microstructure of austenite and ferrite, with higher chromium and molybdenum contents than standard austenitic alloys. They deliver better corrosion resistance especially against chloride stress corrosion cracking and roughly double the yield strength, making them the material of choice for offshore platforms and chemical processing vessels.

5. Precipitation hardening stainless steel

This can be aged to achieve superior mechanical properties high tensile strength with good corrosion resistance through controlled precipitation of intermetallic compounds within the matrix. Grade 17-4PH is a common example used in aerospace and defence.

Laxcon Steels supplies all five stainless steel families across a wide range of product forms to meet diverse engineering requirements.

How Stainless Steel is Made: Step-by-Step Process

Stainless steel production is a multi-stage manufacturing process that converts raw materials and stainless steel scrap into finished products. Here is how stainless steel is made, from melt to final inspection.

1. Melting

Selected raw materials stainless steel scrap, ferrochromium, ferronickel, and other alloying elements are charged into an electric arc furnace (EAF) or electric induction furnace (EIF). Powerful electrodes or induction coils heat the charge to around 1,500-1,600°C until the metal becomes molten steel. This stage typically takes 8-12 hours, depending on the furnace size and charge composition.

2. Refining (AOD/VOD)

The molten steel is transferred to an Argon Oxygen Decarburisation (AOD) converter or, in some plants, a Vacuum Oxygen Decarburisation (VOD) unit where argon and oxygen are blown through the melt.

This step reduces the carbon content to the required level (critical for low-carbon and ultra-low-carbon grades) while preserving expensive chromium in the bath. Final chemistry adjustments including additions of nickel, molybdenum, and other elements are made at this stage.

3. Continuous Casting

Refined molten steel is cast into semi-finished forms slabs, blooms, or billets through a continuous casting machine. The steel solidifies as it passes through water-cooled copper moulds and is cut to the desired shape and length for downstream processing.

4. Hot Rolling

Cast forms are reheated and passed through a series of rolling mills that reduce them to the desired thickness and profile: plates, coils, bars, or wire rod. Hot rolling takes place above the steel’s recrystallisation temperature, so the material can be deformed without cracking. Flame cutting or plasma jet cutting may be used to trim plates to final dimensions.

5. Annealing

Hot-rolled products are heat treated in a controlled furnace to relieve internal stresses, restore ductility, and ensure full corrosion resistance. Annealing temperatures and cooling rates are tailored to the specific steel alloy; austenitic grades, for example, are solution-annealed at 1,050-1,100°C and then rapidly cooled.

6. Pickling and Descaling

An acid bath typically a mixture of nitric and hydrofluoric acid removes the oxide scale formed during annealing and exposes the clean, bright metal surface beneath. This step is essential for the passive film to form uniformly.

7. Cold Working and Finishing (where required)

For products that demand tighter tolerances, a finer surface, or higher mechanical strength, the material undergoes cold working cold drawing, peeling, grinding, or polishing. Cold working increases tensile strength and hardness while achieving the desired shape and surface finish. Laxcon’s bright bars, for instance, go through precision cold-drawing and polishing lines to deliver tight dimensional tolerances.

8. Testing and Quality Assurance

Every batch undergoes rigorous quality checks: spectrometric chemical analysis, mechanical testing (tensile strength, hardness, elongation), and non-destructive testing (ultrasonic, magnetic particle inspection) to confirm conformance to international standards such as ASTM and AISI. Mill test certificates provide full traceability.

Key Properties and Applications of Stainless Steel

Stainless steel’s broad adoption stems from a combination of properties that few other metals can match: excellent corrosion resistance, high mechanical strength and fatigue resistance, heat resistance at temperatures exceeding 800°C in certain grades, a hygienic non-porous surface that is easy to clean and does not support bacterial growth, a bright and aesthetically pleasing finish that stays attractive over time, and complete recyclability with no loss of quality.

These properties make stainless steel the preferred material across many sectors:

Construction: Facades, roofs, bridges, rainwater recovery systems, and reinforcing bars. The material’s durability and low maintenance translate to lower life-cycle costs.
Automotive and aerospace: Exhaust systems, structural components, and stainless steel fasteners. Its strength-to-weight ratio and corrosion resistance in automotive use are increasingly valued as emissions standards tighten.
Food and beverage: Tanks, piping, food processing equipment, cooking utensils, sinks, refrigerators, and dishwashers. Stainless steel is environmentally neutral and biologically inert when in contact with water and food, meeting stringent hygiene standards.
Medical: Surgical instruments, hospital furniture, and orthopaedic implants. Its smooth surface resists bacterial adhesion and withstands repeated sterilisation.
Oil and gas: Wellhead equipment, subsea pipelines, and storage tanks. Duplex steels and super-austenitic alloys provide the mechanical strength and corrosion resistance demanded by harsh offshore environments.
Energy and pulp/paper: Power plant components, heat exchangers, and digester vessels, where the alloy’s ability to withstand high temperatures and corrosive chemicals is critical.

Learn more about Steel Manufacturing

Quality Control and Why Choose Laxcon Steels

At Laxcon Steels, every heat is sampled for spectrometric chemical analysis and every finished product undergoes mechanical testing (tensile, hardness, impact) and non-destructive examination including ultrasonic and magnetic particle inspection. All products comply with ASTM, AISI, EN, and JIS standards and ship with full mill test certificates for complete traceability.

Founded in 1978 in Gujarat, India, Laxcon Steels is one of the country’s most technologically advanced stainless steel manufacturers, exporting to 82+ destinations.

We supply austenitic and ferritic grades, martensitic stainless steels, duplex steels, and precipitation hardening alloys in product forms ranging from bright bars to PSQ bars.

Whether you need a standard grade like 304 or a custom corrosion resistant alloy for a specialised application, our metallurgical team can advise on the optimal chemical composition and heat treatment route.

Get in touch: Contact Laxcon Steels for grade recommendations, samples, or a manufacturing enquiry at laxconsteels.com.

FAQ: Stainless Steel Basics

What percentage of chromium makes steel “stainless”?

A minimum of 10.5% chromium is required. At this level, the chromium reacts with oxygen to form a protective passive film of chromium oxide that prevents rust.

What is the difference between 304 and 316 stainless steel?

Both are austenitic grades. Type 304 (18% Cr, 8% Ni) is the most common for general use. Type 316 adds 2-3% molybdenum, giving it better corrosion resistance in chloride-rich and marine environments.

Why is AOD used in stainless steel production?

The Argon Oxygen Decarburisation converter reduces carbon in molten steel to very low levels without oxidising valuable chromium. This step is essential for producing low-carbon and corrosion resistant grades.

Is stainless steel recyclable?

Yes stainless steel is 100% recyclable without any loss of quality. The average stainless steel product already contains about 60% recycled material, and end-of-life recovery rates exceed 95% globally. For expert guidance on grades and applications, reach out to the team at Laxcon Steels.

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What is Stainless Steel and How is it manufactured