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Hot vs cold rolled steel. WHICH DO I NEED?
If you require large structural components, you will most likely need the hot-rolled steel process to create the parts. For smaller parts that require more precise and durable qualities, then the cold-rolled steel process is the way to go. Otai special steel supply hot and cold rolled steel if you have any question about above steels, welcome and contact our experienced sales. Email: jack@otaisteel.com

Hot Rolled Steel
Hot rolling is a mill process which involves rolling the steel at a high temperature (typically at a temperature over 1700° F), which is above the steel’s recrystallization temperature. When steel is above the recrystallization temperature, it can be shaped and formed easily, and the steel can be made in much larger sizes. Hot rolled steel is typically cheaper than cold rolled steel due to the fact that it is often manufactured without any delays in the process, and therefore the reheating of the steel is not required (as it is with cold rolled). When the steel cools off it will shrink slightly thus giving less control on the size and shape of the finished product when compared to cold rolled.

Uses: Hot rolled products like hot rolled steel bars are used in the welding and construction trades to make railroad tracks and I-beams, for example. Hot rolled steel is used in situations where precise shapes and tolerances are not required.

COLD-ROLLED STEEL
As you might suspect, the manufacturing process behind cold-rolled steel is a bit different. Despite the name, this process refers to steel that is pressed with the pressure of a roller at room temperature.

Compared to hot-rolled steel, cold-rolled steel has a nearly 20% increase in strength through the use of strain hardening. It’s through a series of breakdown, semi-finishing, sizing, semi-roughing, roughing and finishing that cold-rolled steel shapes can be created.

Cold-rolling steel allows for the creation of very precise shapes. Since the process is performed at room temperature, the steel will not shrink as it cools, as it does in the hot-rolled process.

The exterior finish of cold-rolled steel is very desirable when aesthetics and visual appeal are a priority in your project. However, the applications of cold-rolled steel are somewhat limited to a couple of shapes – square, round, flat, and variations thereof.

Uses: Any project where tolerances, surface condition, concentricity, and straightness are the major factors.

Steel and renewable energy – The steel industry plays an irreplaceable role in our lives. In the coming decades, it is particularly important to realize the sustainable development of the energy structure and modernize the power supply in homes, offices, hospitals, schools and transportation networks.

In solar power generation, steel is used not only as a frame to support solar panels but also as a framework for transformers and transmission infrastructure. In tidal power generation, steel is used as an armature core for generators, steel piles for supporting power turbines, and a nacelle casing for use as a generator assembly and power plant infrastructure. The geothermal heat pump, a device for collecting geothermal energy, is made of steel. As power generation companies continue to improve their production technologies, they will further reduce the cost of generating electricity such as wind power and photovoltaics, and achieve a virtuous cycle. The rapid development of renewable energy such as wind power and photovoltaics in the future will drive the demand for steel for renewable energy engineering equipment.

Both 4340 and 4140 are relatively common steel grades. We also supply 4340 steel and 4140 steel to a large number of customers around the world. These two grade steels differ in chemical composition, performance, and application fields. Below is a chemical and mechanical properties comparison of AISI 4340 vs 4140 steel.

4340
4340 Steel is a high quality Quenched and Tempered Alloy Structural steel, It belongs to the high quality medium carbon, Oil Quenched & Tempered Hardness is 28-34 HRC.4340 Annealing delivery hardness less than 250HB.

4140
AISI/SAE 4140 grade is a versatile alloy with good atmospheric corrosion resistance and reasonable strength. It shows good overall combinations of strength, toughness, wear resistance and fatigue strength.

Chemical Composition Comparison: 4340 vs 4140 steel

Application Comparison: 4340 vs 4140 steel

4340
ASTM 4340 steel is an alloy structural steel, 4340 is used for engineering structural, Used as require good toughness, high strength, as well as the important conditioning of large size, heavy machinery such as high load of axial, turbine shaft, larger than 250 mm in diameter of helicopter rotor shaft, turbojet engine turbine shaft, blade, high load of transmission parts, fasteners of the crankshaft. Gear, etc

4140
4140 alloy steel finds many applications as forgings for the aerospace and oil and gas industries, along with myriad uses in the automotive, agricultural and defense industries, Typical uses are forged gears and shafts, spindles, fixtures, jigs, and collars.

OTAI SPECIAL STEEL is ASTM 4340 and 4140 Alloy steel stockholders and suppliers from China. we have more 16 years experience in 4340/4140 steel round bar, plate, steel flat bar, square supply.

For more detail information, you can visit these below pages:

4340 steel

4140 steel

Hot Work Tool Steel VS Cold Work Tool Steel

Tool steel contains various amounts of tungsten, molybdenum, cobalt, and vanadium to increase the heat resistance and durability of the metal. This makes them ideal when used for cutting and drilling.

Tool steel is a type of carbon alloy steel that is well-matched for tool manufacturing, such as hand tools or machine dies. Its hardness, resistance to abrasion and ability to retain shape at increased temperatures are the key properties of this material. Tool steel is typically used in a heat treated condition which provides increased hardness.

Tool Steel is divided into these six groups: water-hardening, cold- work, shock-resisting, high-speed, hot-work, and special purpose.

Hot Work Tool Steel:
Our hot work tool steel is a uniquely processed group of steel used to shape and cut other materials at high temperature. Classified with the ‘H’ prefix, ‘H-group’ steels undergo intense processing to allow them to retain strength and hardness whilst being used in high-temperature conditions.

Cold Work Tool Steel:
Cold-work classes – Is a group of three tool steels: oil-hardening, air-hardening, and high carbon-chromium. The steels in the group have high hardenability and wear resistance, with average toughness. Typically they are in the production of larger parts or parts that have a minimum distortion requirement when being hardened.

Both Oil quenching and Air-hardening both reduce the distortion and higher stress caused by the quick water quenching. Because of this, they are less likely to crack.

D-grade of tool steel in the cold-work class can contain approximately 10% to 13% chromium. This type of tool steel does retain its hardness at increased temperature (425 °C / 797 °F max). The most typical applications for this type of tool steel is in forging dies, die-casting die blocks, and drawing dies.

Special steel is generally considered to be a steel that has a special chemical composition (alloying), is produced by a special process, has special organization and properties, and can meet special needs. Special steels have higher strength and toughness, physical properties, chemical properties, biocompatibility and process properties than ordinary steel.
In fact, in our normal life, the production of finished steel products that we are in contact with is also processed through various processes. So what are the special steel processing classifications?

1.Carbon steel

Carbon steel is also commonly referred to as carbon steel, and is an iron-carbon alloy having a carbon content wc of less than 2%. Carbon steel generally contains a small amount of silicon, manganese, sulfur, and phosphorus in addition to carbon. According to the use, carbon steel can be divided into three categories: carbon structural steel, carbon tool steel and free cutting structural steel. Carbon structural steel can be divided into two types: building structural steel and machine-made structural steel. According to the carbon content, the carbon steel can be divided into low carbon steel (wc≤0.25%), medium carbon steel (wc≤0.25%-0.6%) and high carbon steel (wc>0.6%) according to phosphorus and sulfur content. Plain steel is divided into ordinary carbon steel (high in phosphorus and sulfur), high-quality carbon steel (low in phosphorus and sulfur) and high-quality steel (low in phosphorus and sulfur).

2. Carbon tool steel

Carbon tool steel is a kind of high carbon steel which is basically free of alloying elements. Its carbon content is in the range of 0.65% to 1.35%. Its production cost is low, the source of raw materials is easy to obtain, and the machinability is good. It is a widely used steel grade for high hardness and high wear resistance, and is used to manufacture various cutting tools, molds and measuring tools. However, such steels have poor red hardness, that is, when the working temperature is higher than 250 ° C, the hardness and wear resistance of the steel are drastically lowered and the working ability is lost. In addition, carbon tool steels are hard to harden if they are made into larger parts, and are prone to deformation and cracking.

3. Ordinary low alloy steel

Ordinary low alloy steel is a common alloy steel containing a small amount of alloying elements (in most cases, the total amount w is not more than 3%). The strength of the steel is relatively high, the overall performance is relatively good, and has corrosion resistance, wear resistance, low temperature resistance, good cutting performance, welding performance and the like. Under the condition of saving a lot of scarce alloying elements (such as nickel and chromium), ordinary low-alloy steel can be used in the top 1.2-1.3t carbon steel, and its service life and use range is far more than carbon steel. Ordinary low-alloy steel can be smelted in open furnaces and converters by general smelting methods, and the cost is also close to that of carbon steel.

4. Alloy steel for engineering structure

This refers to alloy steel for engineering and building structures, including weldable high-strength alloy structural steel, alloy steel, alloy steel for railways, alloy steel for pressure steel for geological oil drilling, and high-manganese wear-resistant steel.

This type of steel is used as engineering and building structural parts. In alloy steel, the total amount of such steel alloys is low, but the production and use amount is large.

Automotive steel is important, cost considerations are the key

A car is a smart machine, and there are many steel or metal parts. The car body exists as a vehicle that carries all the configurations of the entire car and cab. The body has a very large proportion of the cost for the entire car. Therefore, many car companies will do enough articles on the body to maximize cost savings and increase profit margins. So how is the car body made and manufactured?

The body-in-white is made up of several sheets of steel joined together by welding. However, the steel used in the entire body is a low alloy steel. The biggest advantage of low alloy steel is that it has good processing performance and the steel itself has high mechanical strength. At the same time, low-alloy steel has better corrosion resistance than ordinary steel. In the natural environment, a layer of brown and dense oxide layer will be formed on the surface of low-alloy steel. This layer of oxide is a good way to isolate the internal steel from the outside air. , better play a role in rust prevention.

One of the representatives of low-alloy steel is weathering steel. The biggest characteristic of weathering steel is that it is very resistant to weathering. Weathering steel is usually used at the bottom of the car body, because the bottom of the car is directly exposed, and it is closely related to the ground and the driving environment and is more likely to be corroded by the environment. Therefore, the use of weathering steel is particularly important.