Hot-rolled steel plates have mechanical properties far inferior to those of cold-worked ones and are also inferior to those of forged ones, but they have better toughness and ductility

 

Cold-rolled steel plates, due to a certain degree of work hardening, have low toughness but can achieve a better yield-to-tensile ratio. They are used for cold-bending parts such as spring plates. Meanwhile, as the yield point is close to the tensile strength, there is no predictability of danger during use, and accidents are prone to occur when the load exceeds the allowable load

 

1) The cold plate is processed by cold rolling, with no oxide scale on the surface and good quality. The hot plate is processed by hot rolling, with an oxide scale on the surface and a thickness difference.

 

2) Hot-rolled plates have poor toughness and surface flatness, and are relatively inexpensive, while cold-rolled plates have good ductility and toughness, but are more expensive

 

3) Rolling is divided into cold rolling and hot rolling, with the recrystallization temperature as the distinguishing point

 

4) Cold rolling: Cold rolling is generally used for the production of strip materials, and its rolling speed is relatively high.

 

Hot rolling: The temperature of hot rolling is similar to that of forging

 

5) The surface of the hot-rolled plate without electroplating is blackish-brown, while the surface of the cold-rolled plate without electroplating is gray. After electroplating, it can be distinguished by the smoothness of the surface. The smoothness of cold-rolled plates is higher than that of hot-rolled plates.

 

6) Hot-rolled plates have relatively lower strength and poorer surface quality (with oxidation and low smoothness), but they have good plasticity and are generally medium and thick plates. Cold-rolled plates: have high strength and hardness, high surface smoothness, and are generally thin plates, which can be used as stamping plates.

 

Hot-rolled steel plates are divided into two types: thick plates (with a thickness greater than 4mm) and thin plates (with a thickness ranging from 0.35 to 4mm). Cold-rolled steel plates only come in thin plates (with a thickness ranging from 0.2 to 4mm).

 

 

 

Hot-rolled coil and cold-rolled coil

 

Cold-rolled coil is made from hot-rolled coil as raw material and is rolled under recrystallization, but it is generally understood as rolling with materials rolled at room temperature. In Europe and America, 3 to 6 continuous rolling mills are mostly used as cold rolling equipment, including plates and coils. Many domestic steel mills such as Baosteel, Wuhan Iron and Steel, and Ansteel can all produce them. Among them, those delivered in sheets are called steel plates, also known as box plates or flat plates. Those that are very long and delivered in coils are called steel strips, also known as coil plates.

 

Hot-rolled coil is made from slabs (mainly continuous casting billets) as raw materials, which are heated and then processed into strip steel by rough rolling mills and finishing rolling mills. The hot steel strip coming out of the last finishing mill is cooled by laminar flow to the set temperature and then coiled into steel strip coils by the coiler. After cooling, the steel strip coils are processed through different finishing lines (flattening, straightening, cross-cutting or longitudinal cutting, inspection, weighing, packaging and marking, etc.) according to different user requirements to become steel plates, flattening coils and longitudinal cutting steel strip products. Due to the excellent properties of hot-rolled steel plates, such as high strength, good toughness, easy processing and forming, and good weldability, they are widely used in the manufacturing industries of ships, automobiles, Bridges, construction, machinery, pressure vessels, etc.

 

With the increasing maturity of new technologies for controlling the dimensional accuracy, plate shape and surface quality of hot-rolled products, as well as the continuous emergence of new products, hot-rolled steel plates and strips have been applied more and more widely and have become increasingly competitive in the market.

 

 

 

Product Classification:

 

Hot-rolled steel plate products include steel strips (coils) and steel plates sheared from them. Steel strips (coils) can be classified into straight coils and finished coils (split coils, flat coils and longitudinal cut coils).

 

 

 

Main products:

 

Hot continuous rolling can be classified into common carbon structural steel, low alloy steel and alloy steel according to their different materials and properties.

 

According to their different uses, they can be classified as: cold-forming steel, structural steel, automotive structural steel, corrosion-resistant structural steel, mechanical structural steel, steel for welded gas cylinders and pressure vessels, pipeline steel, etc.

 

 

 

General description:

 

Hot-rolled steel plate products come in a wide variety of steel grades, specifications and types, and are widely used in various fields, from general engineering structures to the manufacturing of automobiles, Bridges, ships, boilers and pressure vessels, etc. For various uses, the requirements for the material properties, surface quality, dimensions, and shape accuracy of steel plates also vary. Therefore, it is necessary to have an understanding of the types, materials, characteristics, and applications of hot-rolled steel plate products in order to achieve economic and rational utilization.

 

The price of coil plates is calculated based on actual weight, while that of flat plates is calculated based on theoretical weight! So the price of the coil plate is high

 

 

 

Medium plate

 

Steel plate is a kind of flat steel with a large width-to-thickness ratio and a large surface area. In practical work, steel plates with a thickness of less than or equal to 20 millimeters are often referred to as medium plates, those with a thickness ranging from 20 to 60 millimeters are called thick plates, and those with a thickness greater than 60 millimeters are called extra thick plates, collectively known as medium and thick steel plates. Steel plates with relatively small widths and very long lengths are called steel strips and are classified as an independent variety.

 

Steel plates have a large covering and containment capacity and can be used as roof panels, covering materials, and for manufacturing containers, oil storage tanks, packaging boxes, train carriages, car bodies, and the shells of industrial furnaces, etc. They can be cut and combined according to usage requirements to make various structural components and mechanical parts, and can also be made into welded sections, further expanding the application range of steel plates. It can be bent and formed by stamping to make boilers, containers, stamped car bodies, household vessels and utensils, and can also be used as raw materials for welded steel pipes and cold-formed steel sections. Due to the above characteristics, it accounts for more than 50% of the total steel output. In order to meet the needs of large-scale infrastructure construction in our country, the demand for steel plates in industrial products and high-end durable consumer goods has increased sharply in the past. In order to adapt to the needs of the new situation's development, China's steel plate production has also made great progress in recent years, and a number of advanced steel plate production backbone enterprises such as Wuhan Iron and Steel have been established.

 

Steel plates are supplied in sheets or coils. The specifications of sheet steel plates are expressed in millimeters of thickness * width * length. Familiarity with the specifications of plates and strips and making full use of their width and length are of great significance for improving material utilization, reducing inappropriate leftover materials, lowering working hours and product costs. When purchasing plates and strips, it is advisable to choose specifications that are exactly twice the size of the product blank as much as possible. If it is a standardized product, when choosing plates and strips close to the fixed length, reasonable materials of fixed length or double length can be ordered, and the nesting material cutting method can be implemented, which can significantly improve the utilization rate of plates and strips. The repeated utilization of leftover materials between enterprises and industries has also been proven by practice to be an effective method for improving material utilization and saving materials.

 

 

 

Open the tablet

 

Some steel plates come out of the steel plant in rolls. The flat plates formed after these steel plates are uncoiled by machines are called "uncoiled plates". Usually, these open plates are much cheaper than the original plates (or called medium plates) that are rolled out flat.

 

The difference between open plates and medium plates

 

The internal stress level of the open plate is relatively high, so its dimensional stability is poor. With the different process parameters during the uncoiling operation, the distribution of internal stress also varies, and there will be differences in load-bearing capacity in different directions of the vertical length. Moreover, this load-bearing capacity is difficult to measure by general strength indicators.

 

Therefore, when welding the open plate, there will be significant welding deformation, which is very difficult to adjust. Therefore, components with high requirements for appearance quality cannot use open plates.

 

The difference between an open plate and an original plate

 

The original flat plate refers to the sheet material that is formed in a flat plate shape during the manufacturing process.

 

Open plate refers to a relatively thin plate that is manufactured in a rolled form. To eliminate the inconvenience caused by rolling stress in cutting and use, a flat plate machine is used to flatten the rolled plate. The flattened plate is called an open plate.

 

There is no difference in mechanical properties between the open plate and the original plate at the factory.

 

The main difference lies in the board surface of the product. The original flat plate is flatter than the open plate when leaving the factory. The open plate is made by flattening the original roll with a flattening machine and then cutting it. After a period of time, it may develop a sickle-shaped bend like the original roll. However, since the open plate is made by uncoiling, leveling and shearing the steel strip, its comprehensive mechanical properties are not as good as those of the original plate. Therefore, the original plate is used in some important occasions

 

Original plates usually have four cut edges, while open plates, unless otherwise specified, generally have two cut edges.

 

The tolerance of the thickness of the open plate can be larger than that of the original plate.

 

If the requirement for the flatness of the board surface is not very high, open plates can be used. The open plate surface is definitely not as good as the original flat plate surface, but it is also cheaper.

 

The internal stress level of the open plate is relatively high, so its dimensional stability is poor. With the different process parameters during the uncoiling operation, the distribution of internal stress also varies, and there will be differences in load-bearing capacity in different directions of the vertical length. Moreover, this load-bearing capacity is difficult to measure by general strength indicators. Therefore, when welding the open plate, there will be significant welding deformation, which is very difficult to adjust. Therefore, components with high requirements for appearance quality cannot use open plates

 

The open plate and the original plate can be distinguished by the color of the plate surface. The original open plate was made of steel strip and rolled, so it had less oxide scale. After being placed for a period of time, the colors of the open plate and the original plate were different. The original plate turned red, while the open plate turned blue.

 

 

 

Hot-rolled coil is made from slabs (mainly continuous casting billets) as raw materials, which are heated and then processed into strip steel by rough rolling mills and finishing rolling mills.

 

The hot steel strips coming out of the last finishing mill are cooled by laminar flow to the set temperature and then rolled into steel strip coils by the coiler. After cooling, the steel strip coils are processed through different finishing lines (flattening, straightening, cross-cutting or longitudinal cutting, inspection, weighing, packaging and marking, etc.) according to different user requirements to become steel plates, flattening coils and longitudinal cutting steel strip products.

 

In simple terms, when a steel billet is heated (like the red-hot steel block shown on TV), it undergoes several rolling processes, then has its edges cut and is straightened into a steel plate. This process is called hot rolling.

 

Due to the excellent properties of hot-rolled steel plates, such as high strength, good toughness, easy processing and forming, and good weldability, they are widely used in the manufacturing industries of ships, automobiles, Bridges, construction, machinery, pressure vessels, etc.

 

With the increasing maturity of new technologies for controlling the dimensional accuracy, plate shape and surface quality of hot-rolled products, as well as the continuous emergence of new products, hot-rolled steel plates and strips have been applied more and more widely and have become increasingly competitive in the market.

 

 

 

Product Classification:

 

Hot-rolled steel plate products include steel strips (coils) and steel plates sheared from them. Steel strips (coils) can be classified into straight coils and finished coils (split coils, flat coils and longitudinal cut coils).

 

 

 

Main products:

 

Hot continuous rolling can be classified into common carbon structural steel, low alloy steel and alloy steel according to their different materials and properties. According to their different uses, they can be classified as: cold-forming steel, structural steel, automotive structural steel, corrosion-resistant structural steel, mechanical structural steel, steel for welded gas cylinders and pressure vessels, pipeline steel, etc.

 

Cold rolling: Using hot-rolled steel coils as raw materials, after acid washing to remove the oxide scale, cold continuous rolling is carried out. The finished product is a hard rolled coil. Due to the cold work hardening caused by continuous cold deformation, the strength and hardness of the hard rolled coil increase, while the toughness and plasticity indicators decrease. Therefore, the stamping performance will deteriorate, and it can only be used for parts with simple deformation.

 

In simple terms, cold rolling is processed and rolled on the basis of hot-rolled sheet and coil. Generally speaking, it involves a processing procedure of hot rolling - pickling - cold rolling.

 

Cold rolling is the process of processing hot-rolled plates at room temperature. Although the steel plates will also heat up during the processing due to rolling, it is still called cold rolling. Cold rolling, which is formed through continuous cold deformation of hot rolling, has relatively poor mechanical properties and is too hard. It must be annealed to restore its mechanical properties. Those without annealing are called rolled hard coils. Hardened coils are generally used to make products that do not require bending or stretching. Those with a thickness of 1.0 or less that are hardened are lucky enough to be bent on both or all four sides.

 

Cold-rolled sheet and coil include plates and coils. Many domestic steel mills such as Baosteel, Wuhan Iron and Steel, and Ansteel can produce them. Among them, those delivered in sheets are called steel plates, also known as box plates or flat plates. Those that are very long and delivered in coils are called steel strips, also known as coil plates.

 

Cold-rolled steel plates, with a smooth surface and excellent processing, are used in household appliances such as automobiles, refrigerators and washing machines, as well as industrial equipment and various building materials. With economic development, cold-rolled steel plates have been regarded as essential materials in modern society.

 

Hard rolled coils can be used as raw materials in hot-dip galvanizing plants because all hot-dip galvanizing lines are equipped with annealing lines. The weight of the rolled hard coil is generally between 6 and 13.5 tons. The steel coil is continuously rolled from the hot-rolled pickled coil at room temperature. The inner diameter is 610mm.

 

Production process: As no heating is carried out during the production process, there are no defects such as pitting and iron oxide scale that often occur in hot rolling. The surface quality is good and the smoothness is high. Moreover, cold-rolled products have high dimensional accuracy, and their performance and structure can meet some special application requirements, such as electromagnetic performance and deep drawing performance.

 

Product features: As it has not undergone annealing treatment, its hardness is very high (HRB greater than 90), and its mechanical processing performance is extremely poor. It can only perform simple directional bending processing less than 90 degrees (perpendicular to the winding direction).

 

Performance: Mainly low-carbon steel grades are adopted, which are required to have good cold-bending and welding properties, as well as certain stamping properties.

 

Application fields: Cold-rolled sheet and strip have a wide range of uses, such as in the manufacturing of automobiles, electrical products, locomotives and vehicles, aviation, precision instruments, food cans, etc.

 

 

 

Classification of cold-rolled products:

 

Hot-rolled pickling, rolled hard coil, ordinary cold-rolled, galvanizing (electro-galvanizing, anti-fingerprint, hot-dip galvanizing), aluminized zinc, electroplated tin, color-coated, electrical steel (silicon steel sheet), etc.

 

Hot-rolled pickling

 

2. Rolled hard coil: At room temperature, the hot-rolled pickled coil is continuously rolled.

 

Product features: As it has not undergone annealing treatment, its hardness is very high (HRB greater than 90), and its mechanical processing performance is extremely poor. It can only perform simple directional bending processing less than 90 degrees (perpendicular to the winding direction).

 

 

 

Application scope:

 

(1) After annealing, it is processed into ordinary cold rolling;

 

(2) Galvanizing is processed by a galvanizing line with an annealing pretreatment device;

 

(3) Panels that basically do not require processing.

 

 

 

Common steel grades

 

CDCM-SPCC (SPCD, SPCE, ST12, ST13, ST14, BLC, BLD, BUSD, BUFD, BSUFD, etc.), but their performances are basically the same.

 

3. Common cold rolling

 

4. Galvanizing

 

5. Aluminized zinc coating: It is a process that uses a continuous melt coating to coat 55% aluminum, 43.4% zinc and 1.6% silicon onto the surface of steel plates.

 

Product Features:

 

(1) It has good durability and a longer service life compared with galvanized steel plates.

 

(2) It has good heat resistance and is less likely to discolor at high temperatures compared with galvanized steel plates.

 

(3) It has good thermal reflectivity;

 

(4) It has a magnificent silver-white surface;

 

(5) It has processing and spraying properties similar to those of galvanized steel plates;

 

(6) It has good welding performance.

 

Application scope: Industries with high requirements for the use of galvanized sheets.

 

6. Tin plating (tinplate) : Processed by the Frostein insoluble anodic tin plating process.

 

7. Color coating:

 

8. Electrical steel (silicon steel sheet).

 

Compared with hot-rolled steel plates, cold-rolled steel plates have more precise thickness, smooth and beautiful surface, and also possess various superior mechanical properties, especially in terms of processing performance. Because cold-rolled coil is relatively brittle and hard, it is not very suitable for processing. Therefore, in general, cold-rolled steel plates are required to undergo annealing, pickling and surface smoothing before being delivered to customers.

 

The national standard number of cold-rolled steel sheets

 

Cold-rolled steel sheets also come in many types. Below, I mainly list the classifications of several commonly used countries.

 

JIS standard :JISG3141-2005

 

Among them, it is mainly divided into five types:

 

SPCC stands for general cold-rolled steel strip

 

SPCD stands for stamping

 

SPCE stands for deep drawing

 

SPCF stands for Extra deep drawing

 

SPCG stands for Super Deep drawing

 

The main difference between them in terms of chemical composition lies in the content of trace elements such as C,Mn,P, and S, which decreases as time goes on. In terms of mechanical properties, the elongation rate is getting better and better.

 

The standards in Europe, the UK and Germany are basically the same :EN10130/EN10139 can both be applied with little difference.

 

It can also be roughly divided into five types