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Round Bar Knowledge Introduction

1. What is the classification of Round Bar?

(1) Classified by process

Round Bar is divided into three types: hot rolled, forged and cold drawn. The specification of hot-rolled round steel is 5.5-250mm. Among them: 5.5-25mm small round steel bars are mostly straight bars, often used as steel bars, bolts and various mechanical parts; Round Bar larger than 25mm is mainly used to manufacture seamless steel pipe mechanical parts and tube billets.

(2) Classified by chemical composition

Low carbon steel: also known as low carbon steel, the carbon content is between 0.10% and 0.30%. Low carbon steel is easy to accept various processing such as forging, welding and cutting. It is usually used to make chains, rivets, bolts, shafts, etc.

Medium carbon steel: carbon steel with a carbon content of 0.25% to 0.60%. Products include killed steel, semi-killed steel, rimmed steel, etc. In addition to carbon, it can also contain a small amount of manganese (0.70%~1.20%). According to product quality, it is divided into ordinary carbon structural steel and high-quality carbon structural steel.

The thermal processing and cutting performance is good, but the welding performance is poor. Strength and hardness are higher than low carbon steel, while plasticity and toughness are lower than low carbon steel. Hot rolled and cold drawn materials can be used directly without heat treatment or after heat treatment.

Quenched and tempered medium carbon steel has good comprehensive mechanical properties. The highest achievable hardness is about HRC55 (HB538), and σb is 600~1100MPa.

Therefore, medium carbon steel is the most widely used steel of various medium strength grades. In addition to being used as a building material, it is also widely used in the manufacture of various mechanical parts.

High carbon steel: usually called tool steel, with a carbon content of 0.60% to 1.70%, which can be quenched and tempered. Hammers, crowbars, etc. are made of steel with a carbon content of 0.75%; tools such as drills, taps and reamers are made of steel with a carbon content of 0.90% to 1.00%


(3) According to the quality of steel

Ordinary carbon structural steel: Ordinary carbon structural steel has broader restrictions on carbon content, performance range, and residual elements such as phosphorus and sulfur.

In China and some countries, it is divided into three categories according to the guarantee conditions of delivery: Type A steel (Type A steel) is a steel that guarantees mechanical properties. Class B steel (Class B steel) is a steel with a guaranteed chemical composition. Special steel (C steel) is a kind of steel that guarantees mechanical properties and chemical composition, and is usually used to manufacture more important structural parts. The most produced and used in China is A3 steel (A grade No. 3 steel) with a carbon content of about 0.20%, which is mainly used for engineering structures.

Some carbon structural steels also add a small amount of aluminum or niobium (or other carbide-forming elements) to form nitride or carbide particles, thereby limiting grain growth, enhancing steel strength, and saving steel.

In China and some countries, in order to meet the special requirements of professional steels, the chemical composition and performance of ordinary carbon structural steels have been adjusted to develop a series of professional steels (such as steel for bridges, buildings, steel bars, pressure vessels, etc.) .

High-quality carbon structural steel: Compared with ordinary carbon structural steel, the content of non-metallic inclusions such as sulfur and phosphorus is lower. According to the difference of carbon content and use, this kind of steel is roughly divided into three categories:

① Low carbon steel with carbon content of less than 0.25%, especially 08F, 08Al, etc. with carbon content of less than 0.10%, can be stamped due to its good depth It is widely used as deep drawing parts for automobiles, cans, automobiles and so on. . . 20G is the main material for making ordinary boilers. In addition, low carbon steel is also widely used as carburizing steel for machine manufacturing.

②0.25~0.60%C is medium carbon steel, mainly used for quenching and tempering, and used for manufacturing parts of machinery manufacturing.

③High carbon steel greater than 0.6%C is used to make springs, gears, rolls, etc. According to the difference of manganese content, it can be divided into two steel groups with ordinary manganese content (0.25~0.8%) and higher manganese content (0.7~1.0% and 0.9~1.2%).

Manganese can improve the hardenability of steel, strengthen ferrite, and increase the yield strength, tensile strength and wear resistance of steel. Usually “Mn” is added after the steel grade with high manganese content, such as 15Mn, 20Mn, to distinguish it from carbon steel with normal manganese content.


4. What is the purpose of Round Bar?

Ordinary carbon Round Bar, that is, low-carbon steel with a carbon content of less than 28%, is generally used for structures with lower tensile strength requirements, such as ordinary construction steel, ordinary standard parts, and hot-rolled steel.

Carbon bonded Round Bar, the full name of high-quality carbon structural steel, contains low content of harmful elements sulfur and phosphorus (≤0.035%). Among them, the grades of 08, 10, 15, 20, 25 are low carbon steel, with Good plasticity, easy to stretch, squeeze, stamp, forge and weld, of which 20 steel is the most widely used.

No. 30-55 belongs to medium carbon steel. After quenching and tempering, excellent mechanical properties can be obtained, and it is usually used as a more important shaft and fastener. No. 60 and above are high-carbon steel, which is used to manufacture springs and wear-resistant parts.

20CrMnTi is an important carburizing steel, suitable for important gears. 27SiMn is a high-strength, easy-to-weld steel, used in important places where welding is required. 35CrMo and 42CrMo are high-strength steels used for very important parts such as connecting rod screws and cylinder head screws for engines. Tire screws of heavy-duty vehicles, etc.



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