esidual stress
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during processing, this residual stress has a great influence on stability. Both hot rolling and cold rolling are processes of forming steel or steel sheets, which have a great influence on the microstructure and properties of steel. The rolling of steel is mainly hot rolling, and the cold rolling is only used for producing small steel and thin steel.
In general, hot rolling ( hot rolled seamless pipe ) has better mechanical properties than cold rolling. The hot rolled steel has improved tensile strength, yield strength, ductility and toughness. In addition, it is important that heat treatment eliminates residual stresses. While cold rolling refers to the processing of steel sheets or strips into various types of steel by cold drawing, cold bending, cold drawing, etc. At normal temperature, which may result from uneven deformation of the steel andduring processing, this residual stress has a great influence on stability. Both hot rolling and cold rolling are processes of forming steel or steel sheets, which have a great influence on the microstructure and properties of steel. The rolling of steel is mainly hot rolling, and the cold rolling is only used for producing small steel and thin steel.
Hot rolling
Advantages:
The cast structure of the ingot can be destroyed, the grain of the steel can be refined, and the defects of the microstructure can be eliminated, so that the steel structure is compacted and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent; bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.
Disadvantages:
1. After hot rolling, non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and delamination (sandwich) occurs. The delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and it is possible to cause interlayer tearing when the weld is shrunk. The local strain induced by weld shrinkage often reaches several times the yield point strain and is much larger than the strain caused by the load.
2, Residual stress caused by uneven cooling. The residual stress is the internal self-phase equilibrium stress without external force. The hot-rolled steel of various sections has such residual stress. The larger the section size of the general steel, the larger the residual stress. Although the residual stress is self-phase-balanced, it still has some influence on the performance of steel members under external force. Such as deformation, stability, fatigue and other aspects may have adverse effects.
Advantages:The cast structure of the ingot can be destroyed, the grain of the steel can be refined, and the defects of the microstructure can be eliminated, so that the steel structure is compacted and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent; bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.Disadvantages:1. After hot rolling, non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and delamination (sandwich) occurs. The delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and it is possible to cause interlayer tearing when the weld is shrunk. The local strain induced by weld shrinkage often reaches several times the yield point strain and is much larger than the strain caused by the load.2, Residual stress caused by uneven cooling. The residual stress is the internal self-phase equilibrium stress without external force. The hot-rolled steel of various sections has such residual stress. The larger the section size of the general steel, the larger the residual stress. Although the residual stress is self-phase-balanced, it still has some influence on the performance of steel members under external force. Such as deformation, stability, fatigue and other aspects may have adverse effects.
Cold rolling
Advantages:
The molding speed is fast, the output is high, and the coating is not damaged, and various cross-section forms can be formed to meet the requirements of the use conditions;
Cold rolling can cause a large plastic deformation of the steel, thereby increasing the yield point of the steel.
Disadvantages:
1. Although there is no hot plastic compression during the forming process, residual stress still exists in the section, which inevitably affects the overall and local buckling characteristics of the steel.
2. The cold-rolled steel profile is generally an open section, so that the free torsional stiffness of the section is low. It is easy to twist when being bent, and it is prone to bending and torsion buckling when pressed, and the torsion resistance is poor. + Third, the wall thickness of the cold-rolled steel is small, and there is no thickening at the corners where the plates are joined, and the ability to withstand localized concentrated loads is weak.
The main differences between hot and cold rolling are:
1. Cold-rolled steel allows partial buckling of the section, so that the bearing capacity of the bar after buckling can be fully utilized; and the hot-rolled steel does not allow local buckling of the section.
Advantages:The molding speed is fast, the output is high, and the coating is not damaged, and various cross-section forms can be formed to meet the requirements of the use conditions;Cold rolling can cause a large plastic deformation of the steel, thereby increasing the yield point of the steel.Disadvantages:1. Although there is no hot plastic compression during the forming process, residual stress still exists in the section, which inevitably affects the overall and local buckling characteristics of the steel.2. The cold-rolled steel profile is generally an open section, so that the free torsional stiffness of the section is low. It is easy to twist when being bent, and it is prone to bending and torsion buckling when pressed, and the torsion resistance is poor. + Third, the wall thickness of the cold-rolled steel is small, and there is no thickening at the corners where the plates are joined, and the ability to withstand localized concentrated loads is weak.The main differences between hot and cold rolling are:1. Cold-rolled steel allows partial buckling of the section, so that the bearing capacity of the bar after buckling can be fully utilized; and the hot-rolled steel does not allow local buckling of the section.
2. The causes of residual stresses in hot-rolled and cold-rolled steels are different, so the distribution on the cross-section is also very different. The residual stress distribution on the section of the cold-formed thin-walled steel is curved, while the residual stress distribution on the section of the hot-striped steel or welded steel is a film type.
Tips: ASTM A53 Gr.B is the grade in ERW high frequency welded pipe, divided into A and B grades. ASTM is only a set of specifications. ASTM steel pipe A53 A corresponds to the Chinese standard GB raw material is 10# steel, and A53 B corresponds to the Chinese standard GB raw material 20#.
For example: ASTM (standard) A53 (grade) gr is grade (abbreviation of grade) b (grade B)
There are several grades, shapes, specifications, and finishes of steel available. Each of these steel grades has its unique properties. This is why this metal material is commonly used in vehicles, appliances, aerospace parts, electronic parts, and more. The need to understand the various steel types available brings about the hot rolled vs cold rolled steel comparison.
Optimizing the characteristics of your steel for each application is more than changing its chemical composition. Rolling is a process used to improve the shape, uniformity, and mechanical properties of steel materials. There are two main categories of rolled steel — cold rolled steel and hot rolled steel. These rolled steel types have distinct properties, making them suitable for different applications.
It is essential to understand the differences between the types of rolled steel when choosing them for your project. Such prior knowledge will help you save costs and time while avoiding additional processing. This article describes the difference between hot rolled and cold rolled steel, including their benefits, limitations, and applications.
What is Hot Rolled Steel?
Rolling refers to the specific way the steel material is produced. Hot rolled steel refers to steel produced with extreme heat treatment. That is, the production occurs at extreme temperatures. Manufacturers begin with large, rectangular metals (billets). They then heat the billets before sending them for processing — a stage where they are flattened into large rolls.
The hot-rolling process involves pressing the molten steel at high temperatures of over 926° Celsius ( degrees Fahrenheit). Such high temperatures are essential because steel ideally recrystallizes between 750 degrees to 1,300 degrees Fahrenheit, allowing easier forming and reshaping. After rolling the steel through the mill into the desired shape, it is allowed to cool down.
Properties of Hot Rolled Steel
The following properties will help you identify hot rolled steel:
Scaled surface — cooling from high temperatures leaves remnants on the steel surface to make it look scaly.
Slight distortions — cooling also produces slightly trapezoidal shapes without perfect angles.
Corners and edges are slightly rounded — this is a result of shrinkages and less precision in finishing.
Benefits of Hot Rolled Steel
Hot rolled steel offers the following benefits for your applications:
Lower Cost: The processing of hot rolled steel is much lesser than cold rolled steel, making it cheaper.
Little to No Internal Stresses: The cooling of hot rolled steel occurs at room temperature, making it essentially normalized. This means that it has little or no internal stresses due to work-hardening or quenching processes.
Easier workability: Since the hot rolling process is done at extremely high temperatures, the resulting steel is easier to shape and form. The most common shapes come from hot rolled steel, e.g., UB, UC, RHS, SHS, flats, etc.
Applications: It is ideal for applications where tolerance is not the priority.
Drawbacks of Hot Rolled Steel
Dimensional defects due to expansion during heating and shrinkage/warpage while cooling down.
It often has a rough texture on the surface that needs to be removed or bugged before any finishing process.
Slight distortions.
Common Uses of Hot Rolled Steel
As discussed earlier, hot rolled steel slightly shrinks as it cools. This causes manufacturers to have lesser control over the final shape. Therefore, the applications of hot rolled steel are usually those that do not require tight tolerances, including the following:
Automobile parts, e.g., wheel rims and frames
Agricultural equipment
Railway equipment, e.g., tracks and train components
Construction materials
What is Cold Rolled Steel?
Essentially, cold rolled steel refers to hot rolled steel that has undergone further processing. As mentioned earlier, rolling involves the range of processes involved in forming the steel, including turning, grinding, and polishing. The other operations modify an existing hot rolled steel into a more refined product. The term “cold rolled” essentially applies to steels that have undergone compression.
While making hot rolled steel only involves heating at high temperatures and cooling, cold rolled steel involves an additional process. At the cold reduction mills, the manufacturer cools the steel and re-rolls it at room temperature either by cold roll forming or press-braking. This process helps to achieve desired shape and dimensions.
Properties of Cold Rolled Steel
The following features will help you identify cold rolled steel:
Smooth surfaces usually have an oily-like touch
The surface has better finish qualities and tighter tolerances
Square bars come with well-defined edges
Tubes often possess better straightness and concentric uniformity
Benefits of Cold Rolled Steel
Here are some of the benefits you can get from using cold rolled steel:
Better Surface Properties: Parts made with cold rolled steel often have smooth and shiny surfaces void of scale or rust. Thus, making them useful when aesthetics is essential.
Greater Strength: They are typically stronger and harder (up to 20% greater strength) than hot rolled steel. This makes them useful for high-stress applications.
Higher Precision: Since cold rolled steel does not shrink while forming, it allows for the fabrication of more precise parts with consistent and accurate shapes.
Various Surface Finish: It supports an extensive range of surface finishes.
Drawbacks of Cold Rolled Steel
More expensive due to the additional processing involved.
Internal stresses occur in the material due to additional treatments leading to unpredictable warping in some cases.
Fewer shapes are available, e.g., sheets and box section shapes.
Common Uses of Cold Rolled Steel
The ideal applications for cold rolled steel are those requiring better metal surface finishing and tighter tolerances. Examples of such components include the following:
Aerospace parts
Mechanical components
Home appliances
Rods, bars, strips, and sheets
Metal furniture structures
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Cold Rolled Steel vs Hot Rolled Steel: Main Differences
After examining their forming process and various properties, you probably have an idea of the difference between hot rolled and cold rolled steel. The differences in their mechanical properties are summarized in the table below:
Properties Hot Rolled SteelCold Rolled SteelTensile Strength67,000 psi85,000 psiYield Strength45,000 psi70,000 psiElongation in 2”Reduction of AreaBrinell Hardness
Asides from the mechanical properties, the primary difference between hot rolled and cold rolled steel is their processing temperature. While the rolling of hot rolled steel occurs above the recrystallization temperature of steel, cold rolled steel is processed at room temperature.
The following details will help us further compare cold rolled steel vs hot rolled steel better:
1. Appearance and Surface Quality
The edges and surfaces of hot rolled steel are usually rough. This is because cooling from extreme temperatures leaves remnants on the steel surface, making it look scaly. Thus, such surfaces may require decarburization or other surface treatments to prepare the steel for subsequent operations.
On the other hand, cold rolled steel has a smooth and shiny surface since it does not involve using very high temperatures. Thus, cold rolled steel is ideal for use in production operations without any surface treatments.
2. Recrystallization Point
When comparing hot rolled vs cold rolled steel, one of the major points to consider is the recrystallization point. Cold rolling occurs when the metal material is able to form “new grains.” The rolling and bending of the metal often destroy old grains. Cold work on steel may reduce its strength, so manufacturers add a final step of annealing. This process involves heating the steel to 1,333 – 1,400 degrees Fahrenheit (just above the recrystallization point of steel).
Cooling of the steel occurs very slowly without bringing it to room temperature too quickly. This way, the metal can create a uniform microstructure to reset its grains. In contrast, the processing of hot rolled steel occurs at above degrees Fahrenheit, which is higher than the recrystallization point of steel. This condition is necessary for the easy forming and shaping of the metal.
3. Steel Strength and Hardness
Material strength and hardness also help mentioned earlier, the process of forming cold rolled steel gives a uniform microstructure. This process helps to create metal with higher strength and hardness. It is not too hard, however, making it easily malleable.
The hot rolling process, on the other hand, involves extreme heat and rapid cooling, preventing the stress from regaining its grains. Thus, the resulting metal has more liver strength and hardness than cold rolled steel.
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4. Internal Stresses
Steel strength and hardness significantly impart internal stresses on the material. Therefore, cold rolled steel with greater strength and hardness has greater internal stresses than hot rolled steel. It is crucial to relieve such stresses before processing the material to prevent the warping of the final product.
5. Distortions
Hot rolled steel experiences slight distortions (e.g. through sheet metal bending) because the cooling process gives slightly trapezoidal shapes and forms. Cold rolled steel has perfectly squared angles with well-defined corners and edges. The tubes formed also have excellent concentric uniformity and better straightness.
This is a video about hot rolled vs cold rolled steel:
Hot Rolled vs Cold Rolled Steel: Which is Cheaper?
Hot rolled steel is typically less expensive than cold rolled steel. The reason for this is not far-fetched. The manufacturing of this steel type does not involve any delay or further processing. There is no need for re-heating and reforming, as is the case with cold rolling. Cold finishing often consists of other processes like cold drawing, turning, grinding, and polishing. The additional production operations make cold rolled steel more expensive than hot rolled steel.
Should I choose Hot Rolled Steel or Cold Rolled Steel?
Your choice of materials for sheet metal fabrication will depend on several factors. One of the major factors to consider when deciding between cold rolled steel vs hot rolled steel is the applications of the final product. Hot rolled steel is more suitable for large structural components which do not have tight tolerances and aesthetic requirements.
However, cold rolled steel will be the best choice if you need smaller parts requiring durable and more precise qualities. Cold rolled steel is also stronger and harder than hot rolled steel. Therefore, it is more suitable for components made for use in high-stress conditions. If budget is an issue, then you should go for hot rolled steel because it is cheaper than cold rolled steel.
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Our technicians have an adequate understanding of steel parts manufacturing, and you can be sure of getting the best results. Once you upload your CAD files, our system carries out automated DfM analysis and gives you a quote within 12 hours.
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Conclusion
This article covers the fundamental comparison of hot vs cold rolled steel, highlighting the major differences. Each steel type is best suited for some applications than others. Therefore, it is essential to know their properties, benefits, and weaknesses. This knowledge will help designers and project contractors to ensure efficient and effective completion of projects. There’s no better way to get the best results than working with a top-quality manufacturing company. Contact our team of experts at RapidDirect today! We look forward to working with you.
Hot rolled steel or cold rolled steel – which to choose? One of the crucial parts of an engineer’s job is picking the right materials for their application. There’s already a lot of types of metal to choose from. Each with its own advantages and uses. Some types of steel make an excellent fit for home appliances, others for the automotive or marine industry, gas tanks, constructions, etc.
Still, there’s one more distinction to make. A material grade with the same chemical composition may have varying qualities depending on the manufacturing method. Our customers have asked for the difference. So here it is.
Hot Rolled Steel
Hot working is more widely used compared to cold working because it needs less force and energy. It is used in compressive forming methods like rolling, metal extrusion, forging, etc.
Hot Rolling Method
Hot rolling takes place in temperatures above the material’s recrystallisation temperature. In case of steel, the temperatures rise above °C.
The starting material is usually steel billets or slabs. First, they are heated above the aforementioned temperature. The next step is feeding them to the rolling machinery. Continuous rolling gives the desired final shape – a metal sheet (3 mm and upwards) or profile.
Hot Rolled Steel Properties
As it is easy to form metal in high temperatures without any extra delays, it is possible to produce it in larger quantities than cold rolled steel. This keeps the market price of hot rolled steel lower. The steel cools at room temperature. This is known as normalising. It changes the material’s microstructure in a way that results in increased ductility and toughness. Ductility is especially important when forming the material (e.g sheet metal bending) to give it the required shape for your needs.
Hot rolled steel, though, doesn’t have the best quality. It shrinks slightly during the cooling process. This leaves the metal with internal stresses. The results are non-uniform measurements and some distortions. The material’s dimensional tolerances can vary between 2…5%. Also, the surface has a scaly finish. This is a kind of oxide that forms at high temperatures, known as mill scale.
It is easy to identify hot rolled products by touching the surface because of the uneven finish but it is also lacking an oily film. With steel bars, the corners are rounded.
Hot Rolled Steel Uses
Hot rolled steel is a good choice when tight tolerances are not of utmost importance. There are many fields where that is the case. Its great advantage in price matters more than precision. Some common uses for hot rolled steel are:
Constructions
Pipes and tubes
Truck frames
Doors and shelving
Railroad tracks
Railroad car parts
Cold Rolled Steel
Cold working is a metal forming method that has many advantages over hot working. Technically, cold working includes cold rolling and cold drawing. The former is a process used with sheet metal. The latter finds use with rectangular and round bars.
Cold Rolling Method
Quaker Animation Film Steel Cold Rolling Process
As opposed to hot rolling, cold rolling occurs with the metal below its temperature of recrystallisation. This is still only half the truth. The whole process starts out like hot rolling to give the initial shape without much resistance. After that, the metal is left to cool at room temperature.
The half-products are then fed to cold reduction mills. The metal is rolled to the thickness of 0.5…3 mm in case of mild steel and 0.5…5 mm in case of stainless steel. The material is cooled by the use of oil which also acts as a lubricant during the rolling process. As the metal sheet gets thinner between the rolls, its speed increases. That would mean material wear and deformation if an oil film wasn’t there to minimise the contact. Therefore, cold rolled steel is identifiable by an oily and smooth surface.
As the working takes place in temperatures below the rescrystallisation temperature, strain hardening occurs. The rolls induce plastic deformation. Thus, the yield strength of cold rolled steel is higher than that of hot rolled steel. As an example, a hot rolled steel product may have a yield strength of 235 MPa. In comparison, a cold rolled steel product with the same chemical composition has a yield strength of 365 MPa.
The main advantages of cold working are:
Accurate finished dimensions
Clean surface
Greater strength properties
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Cold Rolled Steel Uses
Although cold rolled steel is more expensive than hot rolled steel, the aforementioned advantages make it useful for many applications. The finished products need less additional surface finishing to achieve a good result, as the surfaces are already smooth. Examples of cold rolled/cold drawn steel uses include:
Metal furniture
Structural parts
Home appliances
Water heaters
Metal containers
Fan blades
Frying pans
Computer cabinets
When choosing the right material for your product, make sure to understand the difference of these two material manufacturing methods. There is no point in spending more money on something you don’t actually need. Therefore, hot rolled steel is the better choice when the demands aren’t high. Otherwise, go with cold rolled steel. It has the answers that hot rolled steel doesn’t.
To understand the difference between hot and cold rolled steel, one must first understand the fundamental difference between hot rolled vs cold rolled steel. What distinguishes these two types of steel is the process by which each is made. These differences originate at the mills where the steel is produced and often refer to the heat treatment associated with production.
Hot rolling, as its name entails, refers to a process in which the steel is heated to temperatures above or around ⁰ F. This causes the steel to surpass the recrystallization temperature. The steel can be more easily shaped and formed in this state. Hot rolled steel is generally cheaper than cold rolled steel due to the level of difficulty and duration of the production process. Since the hot rolled steel is only heated once during this process, the manufacturers have less control over the size and shape of the finished products when compared to products that have been cold rolled or finished.
Manufacturing Process: The steel is heated, rolled, and then cooled, which can lead to slight variations in shape and size due to shrinkage.
Surface Finish: It has a rough, scaly surface due to oxidation from high temperatures.
Strength & Durability: Less precise in dimension but strong, making it ideal for structural applications.
Cost: Generally cheaper than cold rolled steel because it requires fewer processing steps.
Applications: Used in construction, bridges, railroad tracks, I-beams, sheet metal, and automotive frames.
Due to the differences in the production processes, hot rolled steel is often cheaper than cold finished steel. As stated above, manufacturers have less control over the quality and specifications of hot rolled vs cold rolled steel. Therefore, hot rolled steel bars are used when precise shapes and tolerances are not required. Some applications of hot rolled steel bars could include making I-beams, general fabrication projects, structural supports, walkways, ramps, and trailers.
Cold rolled steel has similarities in the start of its production process that align with the hot rolled steel production process. The most significant difference is that cold rolled steel is essentially hot rolled steel that has been further processed. Cold reduction mills cool the material to ambient temperatures, followed by annealing and/or tempers rolling. Controlling temperatures throughout the cold rolling process will allow for steel production with precise dimensional tolerances and a wide range of surface finishes.
Manufacturing Process: Hot rolled steel is further processed by rolling it at room temperature, which increases its strength through work hardening.
Surface Finish: It has a smooth, polished, and often oily surface, making it ideal for applications requiring a clean appearance.
Strength & Durability: Stronger and harder than hot rolled steel due to strain hardening during the rolling process.
Dimensional Accuracy: More precise and uniform in thickness, width, and length.
Cost: More expensive than hot rolled steel because of additional processing.
Applications: Used in automotive parts, appliances, furniture, metal containers, and precision components where a smooth finish and high strength are important.
Cold finished bars and their production process result in higher yield points and have four main advantages. Cold drawing increases yield and tensile strength, eliminating further expensive thermal treatments; turning removes surface imperfections; grinding narrows the original size tolerance range; and polishing improves surface finishes. These qualities make cold products superior in surface finish, tolerance, concentricity, and straightness when compared to hot rolled. The length of production and quality of finished products make cold finished bars being more expensive than hot rolled bars. Real-world applications of cold rolled steel bars may include the production of gears and shafts, oil and water well shafting, industrial buildings, and products that demand defect-free surface finishes.