What are stainless steels?
Stainless steels are iron alloys, which contain at least about 11 % chrome. Chromium is a key alloying element of stainless steels. Chromium with a content of more 11 % forms “tenacious” protective film on any fresh surface, which is a protective barrier against corrosion.
Selection criteria for stainless steel
The selection of a stainless steel grade for a product or construction application is usually based on several criteria., including
- fulfillment of functional requirements
- the cost.
Stainless steels have the following fundamental advantages:
- Corrosion resistance and overall high durability. Stainless steels have high corrosion resistance in contact with many types of media, gaseous, liquid and solid.
- High mechanical strength at high temperatures and good strength and ductility at low temperatures. Stainless steels have high strength, plasticity and viscosity over a wide temperature range, from cryogenic temperatures to 1000 ºS.
- Attractive appearance. Stainless steel is a modern material, one of the main properties of which is the preservation of an attractive appearance for a long time.
- Ease of processing: Corrosion-proof easily lends itself to various types of molding (hood, stamping, etc.. P.) and connections (welding, gluing, etc.. P.).
- Stainless steel does not change the taste of food. This property of stainless steels is very important for agricultural production., food and beverage production.
- Stainless steels are very easy to clean, disinfection and sterilization. They are also highly resistant to reagents, which are used for these purposes (eg, high pressure steam for sterilization).
- Low overall cost (taking into account the entire life cycle). Considering the cost of delivery of the equipment plus the cost of its maintenance over its entire life cycle, then stainless steel is a cost-effective material.
- Scrap recycling. Stainless steel scrap can be recycled to 100 % with stainless steel production of the same quality level, like the source material .
Application of stainless steels
The combination of the above criteria provides stainless steels with widespread use in agricultural production., food and processing industry, including the production of the following products:
- fruit juices,
Stainless steels are widely used:
- in transport engineering (railway passenger cars and tanks, tank trucks, refrigerated containers, bus bodies),
- in chemical and petrochemical engineering,
- in the oil industry,
- in the electronics industry (eg, non-magnetic components),
- in the construction industry (curtain facades, elevator cabins, escalators, roof, chimneys, outdoor equipment).
This list is by no means exhaustive.. Stainless steels are used in a wide variety of everyday objects, of which "silver" coins are a good example.
Stainless steel grades
Based on the above criteria, Below is a list of the applications of the respective stainless steel grades. These grades belong to one of the five "families" of stainless steels:
- duplex austenitic-ferritin
- hot austenite
Austenitic stainless steels
What are austenitic stainless steels?
These steels are the most popular stainless steel grades due to their high formability and high corrosion resistance.. Due to the presence of alloying elements, which stabilize austenite, especially nickel, these stainless steels have a face-centered cubic austenitic structure. These steels are not hardened by heat treatment, but can increase their strength due to cold deformation processing, that is, auto-fretting.
Picture 1 – Austenitic face-centered grating
Picture 2 – Austenitic stainless steel pump housing
0,015-0,1 % FROM; 17-20 % Cr; 7-25 % Ni; 0-4 % Mo
- Milk storage tanks
– X5CrNiMo18-10 / 1.4301
- Storage tanks for white wines
– X2CrNiMo17-12-2 /1.4404
- Beer cakes
- Catering equipment, hospitals, food storage and preparation
- Kitchen sinks and related drainage equipment
- Dishwashers: tanks and inner walls
- Cutlery and plates
- Bodies of buses and wagons
- Smoke ducts
depending on technology (tough, flexible, single or double wall, condensing or non-condensing, fuel type, etc.. P.)
- Hot water tanks
Ferritic stainless steels
What are ferritic stainless steels?
Ferritic stainless steels have a low carbon content (≤ 0,08 %). For this reason, they do not show significant hardening after quenching.. The ferrite structure has a cubic body-centered lattice (picture 3). Ferritic stainless steels are magnetic.
Picture 3 – Ferritic cubic body-centered lattice
Ferritic steels are characterized by reduced toughness in the zone of influence of welding due to significant grain growth during welding..
0,02-0,06 % FROM; 11-29 % Sr.
- Household equipment: dishwashers and dryers, dishwasher tanks
- Sinks and drains
- Cutlery, plates, pot lids
- Automotive Hose Clamps
- Decorative car trim
- Dishwasher tanks
- Hot water tanks
- Automotive exhaust systems
- Superheated steam pipes for power plants
- Sugar production equipment pipes
- Smoke suction
- Pipes of seawater desalination plants
- Conveyor chains
- Building elements, container frames, freight cars, bunkers, bodies of buses and coaches
– X6Cr17 Low Carbon
Duplex austenitic-ferritic steels
What are Duplex Austenitic Ferritic Steels?
The microstructure of duplex stainless steels consists of a mixture of austenite and ferrite. These steels exhibit the characteristics of both these phases in terms of strength and ductility.. Compared to austenitic steels, duplex steels show higher strength and markedly higher corrosion resistance in chloride solutions.
Most popular brand
X2CrNiMo22-5-3: 0,02 % FROM - 22 % Cr – 5,5 % Ni – 3 % Mo
- Chemical equipment:
– heat exchangers
– equipment for working with organic acids
– tanks and pipes
- Equipment for the production of paper:
– pressure tanks
– car traps
- Equipment for offshore and coastal structures:
– suture spiral pipes
– fire resistant walls
Picture 4 – Duplex Stainless Steel Chemical Tank Panels
Martensitic stainless steels
What are martensitic stainless steels?
Martensitic stainless steels have the highest carbon content (to 1,2 %). Their mechanical properties can be improved by quenching. Martensitic stainless steels are magnetic.
FROM > 0,1 %; 12-14 % Cr
Like many common carbon steels, these stainless steels are hardened and tempered.. This gives the final product a hardness, which is necessary for its intended use. Depending on the used brand, The main uses for martensitic stainless steels are as follows:
- Knife steel (knife blades):
- Industrial scissor blades for the paper industry:
- Compressor membranes, springs
- Surgical Instruments:
Picture 5 – Professional kitchen knife with martensitic stainless steel blade
Heat-resistant austenitic stainless steels
These grades of the iron-chromium-nickel system have high strength at elevated temperatures and resistance to carburizing atmospheres.. The basic chromium content rises to 20-25 %, and the nickel content ranges from 10 to 35 %. All brands, which are optimized for high temperature applications, have a high carbon content.
- Furnace components, heat exchangers:
- Stove casings:
- Car exhaust pipes: