Stainless steel

In the context of demolition, deconstruction, and cutting technology, stainless steel is a versatile material: corrosion-resistant, dimensionally stable, and, depending on the alloy, very tough. In applications such as concrete demolition and special deconstruction, strip-out and cutting, as well as rock demolition and tunnel construction, stainless steel appears as a construction material, as a material to be cut, and as a constituent of hydraulic components. Properties of stainless steel also matter for tools such as concrete demolition shears, stone and concrete splitters, steel shears, multi cutters, combination shears, or tank cutters – be it when cutting stainless steel sheets and profiles or in the corrosion-resistant design of individual components of Darda GmbH attachments.

Key point: Selection and processing depend on alloy, microstructure, and environmental exposure. Cold cutting methods and contamination control support safety, preserve the passive layer, and improve lifecycle performance in deconstruction workflows.

Definition: What is meant by stainless steel?

Stainless steel denotes steels of special purity and defined composition. The term itself does not inherently indicate corrosion resistance. In everyday usage, stainless steel is often understood to mean corrosion-resistant grades. Corrosion-resistant stainless steels generally contain at least about 10.5% chromium. This chromium content forms a thin, self-healing passive layer of chromium oxide that protects the material against corrosion. Alloying elements such as nickel, molybdenum, nitrogen, or titanium influence strength, toughness, weldability, and resistance to pitting and crevice corrosion.

• Designation systems: In Europe, EN material numbers are common; international practice also references UNS and, for corrosion-resistant grades, compositional groupings aligned with EN 10088 or comparable standards.
• Terminology: Corrosion resistance depends on composition and condition (surface state, heat tint, cleanliness), not on the label stainless alone.

Material classes and alloys

Stainless steels are metallurgically differentiated by their microstructure. This classification helps with selection, processing, and assessment of in-service behavior, for example when separating with steel shears, multi cutters, or tank cutters, as well as during deconstruction with concrete demolition shears.

Austenitic steels

Austenites (e.g., 1.4301, 1.4404) are tough, readily cold-formable, and widely used. They are generally non-magnetic and exhibit very good corrosion resistance. Molybdenum-containing variants show increased resistance to chlorides (seawater, de-icing salts). They tend to work harden during machining and cutting, which increases cutting forces.

Ferritic steels

Ferrites are usually magnetic, contain less nickel, and are more economical, but are generally less tough than austenitic grades. They show good resistance to stress corrosion cracking but are more demanding in welding.

Martensitic steels

Martensites are hardenable and achieve high strengths and hardness. Corrosion resistance is lower than that of austenitic grades but sufficient for many applications. Typical uses include cutting edges and blades – relevant when the cutter knives of steel shears or combination shears are made from hard, corrosion-resistant steels.

Duplex and super duplex steels

Duplex steels combine austenitic and ferritic microstructural constituents. They offer high strength, good toughness, and very good resistance to chloride-induced corrosion. In maritime deconstruction environments or in tunnel construction with high humidity, they are found as construction materials for equipment and tanks that have to be cut.

Precipitation-hardening (PH) steels

These stainless steels are strengthened by precipitation hardening. They combine corrosion resistance with high strength, which can be attractive for highly loaded components in hydraulic systems when corrosion plays a central role.

• Effect of alloying: Chromium builds passivity; molybdenum improves pitting resistance; nickel stabilizes austenite; nitrogen raises strength; titanium and niobium can stabilize against intergranular corrosion.

Properties and materials science at a glance

The passive layer of chromium oxide is the key to corrosion resistance. It regenerates in the presence of oxygen. Chlorides (e.g., in spray water, seawater, concrete pore solution with de-icing salt ingress) can locally attack the passive layer and trigger pitting corrosion. The Pitting Resistance Equivalent Number (PREN) is a parameter for pitting resistance.

• Strength and toughness: Austenites are tough and ductile; duplex offers high yield strength; martensites are hard.
• Magnetism: Austenites are mostly non-magnetic, ferrites and martensites are magnetic.
• Thermal expansion: Austenitic stainless steels have higher thermal expansion than unalloyed steels; this must be considered for precision cuts and fits.
• Thermal conductivity: Lower than unalloyed steels; local heating dissipates more slowly.
• Electrical conductivity: Lower; influences thermal separation processes.

Implication for separation: Reduced thermal conductivity and work hardening favor cold cutting strategies, defined cutting clearances, and sufficient machine stiffness to maintain edge quality.

Processing: Cutting, splitting, and separating stainless steel

In deconstruction and strip-out, stainless steel sheets, pipes, tanks, and profiles are often separated cold. Steel shears, multi cutters, combination shears, and tank cutters from Darda GmbH provide controlled, low-spark processes. Where concrete components are opened with concrete demolition shears, stainless steel may appear as reinforcement (rare, but found, for example, in structures with high chloride exposure) or as an embedded component. Stone and concrete splitters are primarily designed for brittle, compression-resistant materials; stainless steel as a ductile material is cut, not split.

Cutting forces, edge quality, and tool selection

Stainless steel tends to work harden. This increases cutting pressure and requires sharp edges and suitable geometries. For clean cut surfaces, precise cutting clearance, sufficient power reserves, and a defined feed are important. When separating austenitic sheets with steel shears or tank cutters, the rule is: low heat input, controlled bite, minimized burr formation.

• Blade materials: Highly wear-resistant, tough tool steels or hard-coated edges are advantageous.
• Cutting clearance: Too small a clearance promotes buildup and work hardening; too large a clearance causes burrs and tearing.
• Pre-deformation: Avoid it, as hardened zones markedly increase cutting forces.
• Clamping and support: Rigid support near the cut reduces vibration, improves edge integrity, and lowers burr height.
• Lubrication and cooling: Where permitted, micro-lubrication reduces friction and the tendency to galling.

Cold cutting instead of thermal separation

In sensitive environments (e.g., tanks, piping, systems with residual media), cold separation is preferred. Hydraulically operated tank cutters minimize spark generation and reduce heat-affected zones, which preserves the material properties of stainless steel and lessens impairment of the passive layer.

Additional benefits: Cold cutting reduces distortion, avoids heat tint, and simplifies subsequent passivation. It also limits fume formation and supports safe work in areas with potential flammable atmospheres, provided all safety requirements are met.

Corrosion behavior, passivation, and contamination

Stainless steel corrodes primarily when the passive layer is damaged or contaminated by foreign particles (iron debris). When working with concrete demolition shears or stone and concrete splitters, steel particles from reinforcement or tools can be generated. If such particles deposit on stainless steel surfaces, flash rust can occur. After separating stainless steel, appropriate cleaning and post-treatment measures are therefore important.

• Cleaning: Use suitable, low-chloride agents; do not use carbon-steel wire brushes.
• Pickling and passivation: Removes heat tint and regenerates the passive layer after thermal influence.
• Separation of stainless and carbon steel: Minimize tool contact and chip transfer; use dedicated tools where possible.
• Contamination hotspots: Handling equipment, abrasives, and grinding dust are common sources for iron particles on stainless surfaces.
• Water quality: Prefer low-chloride rinse water; residual chlorides can undermine passivity on warm surfaces.

Stainless steel in hydraulic power units and attachments

In corrosion-exposed environments (tunnel construction with splash water, offshore deconstruction, chemical plants), selected components made of stainless steel are used on Darda GmbH power units and tools. Typical examples include fasteners, housings of smaller subassemblies, quick couplings, filter housings, and lines. In hydraulic cylinders, corrosion-resistant piston rods or coatings are used to protect seals and guides over the long term.

• Hydraulic power units: Stainless-steel components on media paths and exposed add-on parts reduce corrosion risks.
• Concrete demolition shears and combination shears: Screws, covers, couplings, and protective parts can be made of stainless steel where moisture and chlorides are present.
• Tank cutters: For cutting stainless tanks, kinematics, blade materials, and feed are tailored to tough materials.
• Interfaces and fasteners: Isolate galvanic pairs, apply suitable pastes, and observe torque to prevent galling and crevice corrosion.

Maintenance and care in service

Regular flushing of couplings, removal of salt spray and dust, and inspection of passivated surfaces extend service life. Pay attention to seal compatibility of cleaning agents. Screw joints made of stainless steel should be assembled with suitable mounting pastes to prevent galling.

• Intervals: Shorten inspection intervals in high-chloride or abrasive environments.
• Surface checks: Look for discoloration, pitting, or deposits and restore passivity where required.

Welding, drilling, and mechanical finishing

When welding stainless steel, suitable filler metals, controlled heat input, and interpass temperatures are important to avoid sensitization and intergranular corrosion. During drilling and sawing, low cutting speeds, high feeds, and sharp tools help limit work hardening. Any heat tint formed should be post-treated to maintain corrosion resistance.

• Welding hygiene: Use dedicated stainless tools and clean joint preparation; remove oxides and spatter.
• Thermal control: Keep heat input moderate; back-purge for root protection on tubulars where applicable.
• Machining: Apply firm feed, avoid rubbing; use sharp, cobalt-alloyed HSS or carbide with appropriate geometry.
• Coolants: Use sulfurized or EP-enhanced lubricants where compatible to reduce built-up edge and galling.

Standards, designations, and quality assurance

For stainless steels, material numbers according to the EN system are commonly used (examples: 1.4301, 1.4404, 1.4462). Quality-relevant documents include mill certificates, inspection certificates, and specifications of surface condition (e.g., ground, pickled, polished). In deconstruction, clear identification facilitates selection of the appropriate separation method, particularly when using steel shears, multi cutters, or tank cutters.

• Certificates: Typical formats include EN 10204 3.1 or 3.2 for traceability and composition.
• PMI and sorting: Positive material identification via XRF or OES avoids mixing stainless and carbon steels during dismantling.
• Surface notation: Define roughness and finish to align corrosion and hygiene expectations with processing steps.

Selection criteria for projects in concrete demolition and rock demolition

Whether stainless steel plays a role as a material to be cut or as a component in the equipment depends on medium, environment, and safety requirements. In special operations with elevated humidity, chloride exposure, or potentially flammable residual media, cold separation processes and corrosion-resistant components are advantageous. When opening reinforced concrete with concrete demolition shears, check whether reinforcement is made of stainless steel – in infrastructures with high de-icing salt exposure this can occur and influences cutting strategy and tool selection.

1. Environment: Chlorides, temperature, humidity, chemical media.
2. Component: Wall thickness, accessibility, geometry, residual stresses.
3. Process: Prefer cold cutting where sparks and heat input must be avoided.
4. Tool: Sufficient cutting force, wear-resistant blades, precise cutting clearance.

• Operational constraints: Noise, vibration, and dust limits can favor specific cutting sequences and tool classes.
• Risk assessment: Consider media residues, ignition sources, and required permits for confined spaces.

Typical sources of error and how to avoid them

In practice, small oversights lead to material damage and follow-up issues. These include incorrect tool selection, surface contamination with foreign particles, insufficient post-treatment, and improper assembly.

• Avoid galvanic pairs: Do not couple stainless steel unprotected with carbon steel in the presence of moisture.
• Galling: Assemble stainless-steel threads with suitable pastes; observe tightening torques.
• Heat input: Remove heat tint after thermal processing; ensure passivation.
• Burr formation: Deburr after cutting to reduce notch effects and corrosion attack.
• Storage and handling: Use non-ferrous contact surfaces and dedicated slings to prevent iron transfer.

Surfaces, cleaning, and post-treatment

The surface influences corrosion behavior and hygiene. Smooth, dense surfaces are more resistant to pitting. After separation or welding, heat tint should be removed and the passive layer restored by suitable procedures. Avoid chloride-containing cleaners. Mechanical cleaning is performed with stainless-steel brushes to prevent iron debris.

• Finish and roughness: Lower roughness reduces deposit formation; specify finish where crevice risk is high.
• Chemical passivation: Apply verified procedures and sufficient dwell times; rinse thoroughly with low-chloride water.

Sustainability and recycling

Stainless steel is high-value and nearly fully recyclable. In deconstruction, stainless-steel components are recorded by grade, which facilitates material recycling. This reduces resource consumption and supports circular project delivery in concrete demolition, strip-out, and special operations.

• Segregation: Keep stainless grades separate from carbon steel scrap to retain alloy value.
• Documentation: Record alloy IDs and weight for efficient recycling logistics and compliance reporting.