Steel is the key element when it comes to manufacturing household, commercial, or industrial products. Besides, most of the tools used in any kind of industry are made of steel. The major reason for the importance and popularity of steel is its durability, affordability, and availability.
To start with, let’s take a look at the chemical composition of the steel.
Chemical Composition of Steel
Steel is an alloy of two common elements named iron and carbon. Usually, steel has 2 percent carbon contents. It is the most commonly used material for building massive structures.
Depending on the chemical composition, there are three notable classes of steel. These include:
- Carbon steels
- Low-alloy steels
- High-alloy steels
Normally, all these types of steel have small amounts of elements i.e. manganese, aluminum, or silicon. The traces of other metals like copper are also present. Since all these elements aren’t more than 1 percent of the steel, it is not referred to as an alloy.
Carbon steel accounts for 90% of our world’s total steel production. In fact, this type of steel is the most commonly used option. There are different types of carbon steel as per the percentage of carbon.
Depending on the chemical composition, here are the most popular types of carbon steel.
- High-carbon steels (carbon content over 0.5%)
- Medium-carbon steels (carbon content 0.2% to 0.49%)
- Low-carbon steels (carbon content 0.5% to 0.19%)
- Extra-low carbon steels (carbon content 0.015% to 0.05%)
- Ultralow-carbon steels (carbon content less than 0.015%)
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Physical Properties of Steel
Just like any other metal, steel exhibits certain properties. The physical properties of steel are completely different from iron and carbon, which are the component elements.
To help you understand how different steel behaves in terms of its physical properties, we have listed such properties as under:
- The density of steel is 7,850 kg/m3.
- Steel is a lightweight material that offers high strength.
- It offers maximum ductility. This makes it easy to mold in almost any desired shape.
- The melting point of steel is 1,510 C.
- Unlike iron, steel is corrosion resistant even if exposed to moisture for quite some time.
- The ability to cool down rapidly is one of the most prominent properties of steel.
- Electricity can pass through steel. Hence, it’s a good conductor of electricity.
Types of Steel
Talking about the types of steel, these are numerous. The number of steel grades can reach up to thousands when including the published and registered versions. All of these types have their chemical compositions.
Some steels offer durability and sturdiness while others are preferred for their versatility and ductility. Furthermore, some other features of steel relate to the finish, heat treatments, shapes, and microstructures.
Furthermore, there is a wide range of options to choose from. This aspect adds to the popularity of this metal. However, here are four of the major types of steel.
- Carbon Steel
- Stainless steel
- Alloy Steel
- Tooling Steels
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Carbon Steel
This particular type of steel consists of iron and carbon. Hence, it is known as carbon steel. This term also refers to the steel that contains less than 0.4% copper or has certain magnesium/copper contents.
Carbon steel is usually classified into three different classes i.e. high carbon steel, medium carbon steel, and low carbon steel.
High Carbon Steel
Steel that contains 0.61% to 1.50% carbon and 0.31% to 0.90% magnesium contents is referred to as carbon steel. This type of steel is hard and durable. However, it is difficult to cut, mold or weld high carbon steel.
Some of the applications of high carbon steel are as under:
- Railway tracks
- Plates
- Bars
- Spring steel
The major properties of high carbon steel include:
- A tough metal that offers maximum strength
- Low machinability
- Hard to weld
- Lower ductility level
- Exhibits less hardenability
Medium Carbon Steel
This type of carbon steel contains 0.31% to 0.60% carbon as well as its magnesium content ranges from 0.31% to 1.60%. The biggest advantage of medium carbon steel relates to its high strength. On the contrary, it offers low ductility.
Here are different applications of medium carbon steel?
- Best for machinery parts
- Railway
- Used for building huge structures
The key properties of this kind of steel include:
- Not that hard, which suggests it has an average toughness
- Offers a medium level of ductility
- The strength is of medium grade
- Relatively easy to weld
- Machinability level is average too
Low-Carbon Steel
Also known as mild carbon steel, this type of steel contains carbon up to 0.30%. It is one of the most commonly used steel. The carbon content is the lowest when compared with the other two types of carbon steel.
Low carbon steel is affordable too. Apart from this, low-carbon steel is easy to mold. It is a viable option for those applications where strength isn’t that necessary.
Another advantage of low-carbon steel is its ability to improve its properties by simply adding some elements like magnesium. It is also a perfect candidate for carburizing. This process enhances the case hardness without compromising the toughness or ductility.
Listed here are the most notable applications of low carbon steel:
- Ideal for making machinery parts
- Used for building structural components
- Best option for making pipes, bolts, and wires
- Automotive spare parts/components
- Surgical instruments
- Used in making cutlery i.e. forks, knives, spoons
Properties exhibited by low carbon steel are as under:
- Affordable and cost-effective
- Hardness level is relatively low
- Offers medium level strength
- Provides maximum toughness and ductility
- Easy to weld
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Stainless Steel
Unlike carbon steel, stainless steel contains not less than 10.5% chromium. In addition to carbon and iron, the presence of chromium provides unique properties that are associated with stainless steel.
The corrosion-resistant surface is a great benefit of stainless steel. This enhances the overall lifespan of the products made with this type of steel. Usually, stainless steel cutlery and utensils can last for years.
Hence, there is a huge demand for medical equipment, cookware, and knives made of stainless steel. There are different types of stainless steel, which are available on the market. Mentioned below are the general types of stainless steel, which are used in various industries.
Martensitic Alloys
Martensitic alloys are at the lowest grade when it comes to popularity. Meaning thereby, these are the least common alloys of stainless steel. The hardness and toughness properties of this alloy are outstanding. However, martensitic alloys have less impressive anti-corrosion properties.
Therefore, these alloys are only suitable for those applications where hardness is the most desired criterion. Among the other grades of martensitic alloy, grade-420 is relatively more common.
Austenitic Alloys
This stainless steel alloy is a commonly available option. This alloy offers much better resistance against oxidation. It has a more refined and unique appearance. Apart from few exceptions, austenitic alloys are normally non–magnetic.
Mentioned here are the general grades of austenitic alloys.
- Grade 301
- Grade 302
- Grade 303
- Grade 304
- Grade 309
- Grade 316
- Grade 321
Ferritic Alloys
Ferritic alloys are among those stainless steel alloys that are not that common. In other words, it is a semi-common alloy of stainless steel. These alloys are different from austenitic alloys, as they own magnetic properties. So, this type of stainless steel alloy is a viable choice for applications that demand magnetism.
Due to the minimum nickel content, Ferritic alloys are relatively cheaper. Grade-430 and Grade-434 are the widely used grades of ferritic alloy:
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Tooling Steels
Tooling steels is a great option for tooling activities like drilling. This type of steel contains different alloys including vanadium, cobalt, molybdenum, and tungsten. The best feature of tooling steel is its ability to resist heat. Asides, this type of steel offers required durability and strength.
Tooling steels have 6 major grades such as:
- Water-hardening
- D-type
- Shock-resisting types
- Air-hardening
- Hot-working
- Oil-hardening
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Alloy Steels
Alloy steels are versatile and diverse types of steel. Besides carbon, this alloy also contains a wide range of other alloying elements. As a result, each of these steel alloys shows some unique properties.
Although there are various types of steel alloys, we have listed here the most common ones.
- Cobalt
- Vanadium
- Chromium
- Nickel
- Molybdenum
- Tungsten
Alloying and its Effects on Steel
Alloying is a popular way to bring some changes to the properties of steel. During this process, alloying elements are added to the composition in addition to the already present carbon contents. It helps to achieve those properties that aren’t present in simple carbon steel.
Approximately, there are 20 elements that steel manufacturers use when alloying steel. Each of these elements cast its influence on the different properties of steel. These changes relate to microstructure, cooling rates, and transformation times.
In this way, it is possible to alter the transformation points, change diffusion and solution rates, and produce intermetallic compounds like nitrides and carbides. The applications of alloying steel are numerous.
The alloying procedure helps to achieve a much better weld quality without compromising the strength. This is not possible by simply using carbon and adding more strength to the steel. Carbon leaves brittle areas around the welds, which lowers the strength of a welded joint.
So, this issue is resolved by simply lowering the carbon contents in steel and adding some additional elements (nickel or manganese) to gain the required strength. The alloying elements also permit high-temperature tempering. This ensures much better ductility while maintaining the same strength and hardness.
Effects of Heat-treating on Steel
The process used for changing the mechanical properties of steel is known as heat treatment. During this process, the carbon content is adjusted to achieve the required properties. When steel takes less time to cool, the carbon atoms would not form larger carbides while moving through the lattices.
For example, if the cooling is done at a much faster pace (1,000° C per minute), it depresses the process of carbide formation. The undercooled ferrite starts to engulf the maximum number of carbon atoms. As a result, a new microstructure comes into life and that is Martensite.
The heat-treating process can take place at various holding times, temperatures, and cooling rates. Hence, this procedure is a very efficient way of controlling and managing the properties of steel.
Applications of Steel
Since steel is a versatile material, it has a wide range of applications both in industrial and residential areas. Carbon steel is the widely used type of steel, as it is capable of meeting the needs of numerous consumer sections.
The best examples of the steel’s applications include:
- Molded automobile body parts
- Low-carbon steel appliances
- Medium-carbon steels for fabrication or building structures
- High-carbon used for railway tracks
- Different types of wires containing different carbon levels
In addition, expensive alloys are combined with carbon steel to introduce some additional properties. It helps to widen the usability of steel.
Discussed below are the topmost applications of steel.
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Fabrication and Machining
The steel used for this purpose offers better machinability. Meaning thereby, it is a feasible option when it comes to fabricating screws, bolts, and nuts. The addition of 0.35 percent lead and 0.35 percent sulfur helps to achieve desired machinability properties.
These elements are essential for this type of application. This is so, as their presence helps to break the long strings of steel that are common phenomena when machining the metal into small chips.
As a result, the workplace and tools stay clean. It also helps to improve the life of tools. It also allows increasing the speed of machining procedures.
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Manufacturing of Ball Bearings and Rollers
Bearing steel is one of the most important groups of steel. This type of steel has a huge impact on the development of engineering possibilities. As the name suggests, this particular steel is a suitable option for manufacturing ball bearings and rollers.
Steel used for this purpose contains 1% carbon, 0.25% nickel, 1.2% chromium, and 0.25% molybdenum. This combination of materials gives extensive hardness to the steel once it passes through the heat-treating procedure.
Apart, these steels offer a clean, shiny, and gliding surface. These properties or features are the results of vacuum treatment, which purges all inclusions. This allows the steel to sustain even the highest stress levels.
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Electricity Generation and Transmission
Steel is an essential element, which plays a pivotal role while generating and transmitting electricity. The steel used for this purpose is the “High-Silicon Electrical Steels”. The production of electromagnets (for alternating current) involves using various thin sheets of steel.
These sheets also receive insulation to avoid or lower the flow of eddy currents. This results in minimizing the heat generation and current losses. In addition, 4.5 percent silicon is also added to the steel for sustaining electrical resistance.
Grain-oriented sheets are the popular option for electric transformers. This type of steel contains 3.5 percent silicon. Hence, it offers better magnetic flux density.
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Manufacturing of Tools for Crushers and Power Shovels
The steel used for making such heavy-duty tools is referred to as the “wear-resistant steel”. It helps to produce high-strength wear plates for the machinery used during rock processing. These include crushers and power shovels.
As per chemical composition, these are the austenitic steels containing 1.2% carbon and 12% manganese. Since magnesium is a strong austenizer, it helps to keep the steel austenitic when placed at room temperature.
The desired level of wear resistance is achieved by enhancing the hardening abilities of the steel. For this purpose, the steel receives additional pounding treatment. This process creates a wide array of disturbances in the lattices of crystals.
This results in blocking the flow of dislocations effectively and impressively. To put it simply, pounding improves the overall strength of steel.
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Cutlery Industry
When seen from a historic perspective, the Knives, spoons, and forks were made of silver. The reason for such preference was the anti-bacterial properties of silver. However, with the introduction of industrial era, steel replaced silver as a more durable, strong, and affordable metal.
Stainless steel offers the desired level of hardness, toughness, and wear resistance. Especially, this material is considered the best possible option for making all types of knives. It continues to perform at very high temperatures.
One of the major benefits of using steel is its ability to maintain general hygiene. This is essential, as forks, knives, and spoons are exposed to the foods we eat. Cutlery made of stainless steel is easy to wash and clean.
Given below are a few of the other reasons why stainless steel is a suitable choice for making cutlery.
- Heat and fire-resistant
- Offers maximum resistance against corrosion/rust
- Helps to maintain proper hygiene
- A manufacturing material that is easy to manage
- Ensures maximum strength and durability
- Aesthetically pleasing
- Offers durability and ease of use
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Production of Tools
Steel is also used for producing heavy-duty tools. However, the manufacturing of tool steel takes place in small quantities. This is so, as these steels have expensive alloy contents. The reason for using such alloys is to enhance the hardness and strength of the steel.
So, tool steels are hard, tough, wear-resistant, and capable of withstanding overheating. These steels are dimensionally stable too. Sturdy carbide formers are also present. These include:
- Tungsten
- Chromium
- Molybdenum
- Vanadium
All these options are present in the tool steel in variable quantities. Besides, nickel or cobalt are often used to enhance the performance of this steel under high-temperature conditions.
Types of Steel Treatments
Although steel can pass through a variety of treatments, the most used ones are:
- Heat-Treating
- Annealing
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Heat-Treating
In general, the process of heat-treating takes place while the steel is hot-rolled. After performing this procedure at a certain temperature, the steel is left to cool down at a particular cooling down rate. Normalizing is the simplest of all heat-treating processes.
In addition to this process, there are numerous other heat-treating procedures. The heat-treating facilities designed for this purpose help to achieve specific properties and microstructures of steel. The temperature, heating & cooling rates, and time for such procedures vary depending on the type of heat-treating operations.
This helps to obtain particular chemical compositions and properties of steel. For instance, alloy steels show much lower heat conductivity as compared to carbon steels. Hence, this type of steel undergoes a slow heat-treating process to overcome the issue of internal stress.
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Annealing
Annealing is a specific process that helps to enhance the ductility of steel. In fact, this procedure prepares the steel for subsequent molding operations. During annealing treatment, steel stays at lower than Ar1 temperature for many hours.
It promotes the precipitation of carbides and coagulates, which produce large ferrite crystals. The Cold-formed steel undergoes recrystallizing. The annealing process continues for several hours at an estimated temperature of 1,260° F (680° C).
The annealing procedure takes place in a reducing or inert atmosphere. The reason for this is to avoid any kind of oxidation. The annealing lines can be as long as 200 meters. However, the strip between recoiler and uncoiler is over one kilometer long.
The strip annealed in this manner isn’t as soft as the one made through batch-annealed steel. The former annealing procedure does have its operating advantages.
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Quenching and Tempering
This is one of the most common heat-treating options used for tubular products, plates, and rail tracks. The quenching and tempering process involves heating large plates in walking-beam or roller-type furnaces. After that, quenching of these plates takes place in special chambers.
Once done properly, the steel plates undergo a tempering process in the separate furnace under low temperatures. Both the heating and quenching processes must have uniformity. It is crucial, as uniformity helps to avoid plate distortion or wrapping issues.
The tubes used for oil drilling do face demanding situations. Hence, these tubes undergo a special heat-treating process in the walking-beam furnace. Next, these tubes pass through a specifically designed quench-and-temper mechanism.
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Surface Treating
This type of steel treatment takes place at the time of hot-rolling. This is so, as the aspects like in-line scale removal, reheating conditions, cooling rate, and rolling temperature determine the thickness and type of the steel. These factors also help to achieve better resistance and paint adhesion.
At times, the final procedures of hot-rolling create particular surface patterns. The protrusions on floor plates and reinforcing bars are examples of such patterns. On the other hand, a particular surface roughness appears within the strip during cold-rolling.
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Pickling
The hot-rolled steel undergoes a descaling process before it passes through the cold forming procedure. This process is commonly known as pickling. These scales are made of thin slices of iron oxide crystals. The structures, chemical compositions, and densities of such scales vary depending on various factors. These include:
- Steel properties
- Temperature
- Oxidizing conditions
Acids can dissolve these crystals. Hence, sulfuric or hydrochloric acid is used for this purpose. However, nitric acid is another option to consider when dealing with specific types of alloy steels. To avoid steel from dissolving completely, the use of inhibitors in the acids is also very common.
The procedure of pickling takes place at continuous pickle lines. The hot-rolled strip continuously travels up to 300 meters. Almost four to five pickling tanks pull the strips. This process takes place at a constant speed of 300 meters/minute.
Just like any other strip-processing line, the pickle lines contain entry and exit groups. This ensures constant pickling conditions throughout the procedure. After passing through the last acid tank, the strip enters the new section where it undergoes rinsing, neutralizing, drying, oiling, and inspection process.
Stainless Steel Grading System
Depending on the type of stainless steel, this material is divided into different grades. This is a way to differentiate the distinctive types of steel. Usually, the grading of stainless steel may vary from country to country.
However, food-grade steel has two major grades including “Flatware Grades” and “SAE Grades”. Both these types of grades are discussed below:
Flatware Grades
Flatware grade is a grading system widely used in the food industry. This particular system takes into account the ratio of contents when grading stainless steel. For instance, 18/0, 18/8, and 18/10 are the grades that exhibit the ratio of chromium and nickel in food-grade stainless steel.
These two elements are essential for flatware grading. This is so, as chromium and nickel can affect the different properties of steel including shine, magnetism, and resistance against corrosion.
Another flatware grade ratio is 13/0. The stainless steel of this grade is widely used in the manufacturing of kitchen knives. This type of stainless steel is relatively softer as compared to other options.
Apart from grading steel for flatware, this type of grading system can also help to grade other types of utensils like pans, pots, and pans.
SAE Grades
This particular grading system takes its authority from SAE International. This organization makes standards for various manufacturing industries. The SAE has also created a grading mechanism for distinguishing between various types of stainless steel. This grading mechanism is also popular as AISI (American Iron and Steel Institute) system.
AISI is the founding father of this system. However, SAE International is the regulatory body for this grading system. This system utilizes the whole numbers to categorize stainless steel depending on its grade.
Types of Stainless Steel Used to Make Kitchen Appliances
Food-grade stainless steel is used for manufacturing utensils, cutlery, and kitchen appliances. This type of steel meets specific standards. It is essential to understand the different grades and types of food-grade steel for those associated with the restaurant and hospitality industry.
200 Grade Stainless Steel
The 200 grade stainless steel is a low-quality option. Hence, it offers less resistance against corrosion. However, it still owns a reasonable space in the industry linked with kitchen appliances. In most usual scenarios, 200 grade stainless steel is used for manufacturing food storage containers.
304 Grade Stainless Steel
This particular grade is a great option for making kitchen appliances and utensils. The high-level contents of nickel and chromium make it a lot shinier than other options. Besides, it offers resistance against rust and corrosion. Nevertheless, it is vulnerable to corrosion when exposed to salt for an extended period.
The most common applications of 304 series stainless steel are:
- Kitchen appliances and internal parts
- Kitchen utensils
- Prep tables
- Flatware
316 Series Stainless Steel
This one stands in second place among the commonly used types of food-grade stainless steel. It contains an essential element such as molybdenum. This makes it more resistant to corrosion even when used with salt, citric acid, or vinegar.
This stainless steel is used to make the following items.
- Kitchen equipment
- Hibachi grills
- Top-quality cookware & equipment
430 Grade Stainless Steel
This grade contains small contents of nickel. However, it is less corrosion resistant as compared to the 300 series steel. It has magnetic properties. The best possible applications of this type of steel include:
- Prep tables
- Induction-ready cookware
- Medium-quality flatware
- Appliance doors
440 Grade Stainless Steel
The 440 grade stainless steel contains an additional amount of carbon. By far it is the strongest type of stainless steel used in the manufacturing of kitchen equipment. Hence, the items made of this steel are corrosion-resistant, hard, and wear-resistant.
This steel is a great choice for manufacturing these kitchen items:
- Oven door handles & internal parts
- High-end chef knives
- Cutlery
13/0 Grade Stainless Steel
This particular grade is the most suitable option for making all types of knives. 13/0 grade steel contains only chromium. Hence, this is a relatively softer type of steel. This allows the manufacturers to add serration along the edge of knives.
The applications of this kind of steel include:
- Table knives,
- Hunting knives
- Kitchen knives
18/0 Grade Stainless Steel
This one is medium-quality stainless steel. Hence, it tends to be the most affordable option for the manufacturers. It lacks impressive corrosion resistance properties. Yet it exhibits magnetic characteristics. Hence, it is a viable option for washing cutlery in dishwashers.
Due to its lower quality, the kitchen items made from this steel are commonly seen in cafeterias, dining halls, and casual restaurants.
The applications for this particular stainless steel are:
- Kitchen equipment
- Cutlery
- Utensils
18/8 Grade Stainless Steel
18/8 is a steel that is a popular choice for making flatware. The utensils made with this stainless steel offer a professional feel. In addition, 18/8 grade is corrosion resistant. It offers better shine and finish than other options. This one is a viable choice for manufacturing kitchen items like:
- Cutlery
- Kitchen equipment
- Utensils
18/10 Grade Stainless Steel
18/10 is the high-end steel that offers superior quality and anti-corrosion properties. Furthermore, the flatware made with this steel has unique and elegant engravings on its surface.
The kitchen items and cutlery made with this steel are commonly seen at upscale restaurants, banquet halls, country clubs, catering companies, and hotels.
- High-quality cutlery
- Professional-grade utensils
- Industrial quality kitchen equipment
What are the Properties of Knife Steel?
There are different types of steel used for the manufacturing of knives. Each of these types exhibits different properties. This suggests that the steel used for kitchen knives and hunting knives is not the same.
Following are the properties of knife steel, which vary depending on the type of knife.
Hardness
No doubt, hardness is among the most common properties that are found in knife steel. This feature helps to provide the required protection against stress. The level of hardness is directly proportional to the strength of the steel used.
Toughness
Talking about toughness, this relates to the capacity of a knife to resist the damages such as chips and cracks. Chipping is the worst enemy of a knife, which is almost impossible to fix. Toughness can be measured through various methods. Toughness and hardness are inversely proportional, as lower hardness levels increase the toughness of steel.
Edge Retention
This term relates to the ability of a knife to retain its sharpness. It is the most essential property of knife steel. However, there isn’t a standard unit or method to measure the edge retention property of knife steel. To get some idea, knife enthusiasts rely on the wear resistance property of the steel.
Corrosion Resistance
This property provides extensive protection against corrosion or oxidation. Hence, a knife made with corrosion-resistant steel can withstand harsh elements such as moisture, humidity, citric acid, vinegar, and salt. However, higher corrosion-resistant steel offers lower edge performance.
Wear Resistance
This type of feature helps to protect the knife from abrasive and adhesive types of wear. Abrasive wear relates to a situation when a softer surface meets a harder subject. On the other hand, adhesive wear occurs when the dislodged debris or residue transfers from one surface to another.
Usually, the degree of wear resistance depends on the steel’s hardness. However, the chemical composition of the steel also affects this property. Steel composed of larger carbides is relatively more resistant to wear.
Food Grade Stainless Steel
To put it simply, food-grade stainless steel is a type of steel that is safe to use for preparing or serving food. The grades like 18/10, 18/8, etc. are made in accordance with the approved standards. Hence, these steels are safe to use.
The grading depends on the nickel and chromium contents of the steel. For instance, 18/8 relates to grade-304. It contains 18% chromium and 8% nickel.
Advantages of Food Grade Stainless Steel
Food grade stainless steel is a common material used for manufacturing cutlery, utensils, and kitchen appliances. This type of steel has numerous benefits. Listed below are the most prominent benefits of this material.
Corrosion Resistance
This is among the most crucial benefit of stainless steel. It offers the required protection against oxidation and corrosion. Hence, the products like knives, spoons, and forks stay rust-free for a maximum period.
Besides, other types of kitchen equipment are also made of food-grade stainless steel. Since such equipment is costly, replacing it frequently won’t be a viable option. These items are easy to maintain and continue to serve for a longer than the expected duration.
Non-reactive Surface
Cutlery made of stainless steel is safe to use, as this material is non-reactive. This suggests that it won’t undergo any chemical reaction when cooking different types of food items i.e. vinegar, tomatoes, and citrus. Some other options like iron and aluminum are reactive and can change the taste of cooked food.
Easy to Clean
Food-grade stainless steel is easy to clean. This is due to the clear and shiny finish of this material. On the contrary, cutlery and utensils made from plastic or wood are hard to clean. Asides, there are openings where bacteria can penetrate and grow. Hence, stainless steel is the most appropriate material.
Strength
When it comes to strength, food-grade stainless steel is among the strongest materials. The kitchen equipment made from this material offers extended durability. This is the reason why stainless steel is the most preferred material for building kitchen shelves and storage compartments.
