Round Steel

Round Steel is a long, solid steel bar with a round cross-section. Its specifications are expressed in millimeters of diameter, such as "50" which means round steel with a diameter of 50 mm. Round steel is divided into hot rolled, forged and cold drawn three kinds. Hot rolled round steel is 5.5-250 mm in size. Among them, 5.5-25 mm small round steel is mostly supplied in straight strips in bundles, commonly used as steel bars, bolts and various mechanical parts; Round steel larger than 25 mm, mainly used for the manufacture of mechanical parts or seamless steel blanks.

Round steel classification

1. Sort by chemical composition

Carbon steel can be divided into low carbon steel, medium carbon steel and high carbon steel according to its chemical composition (that is, carbon content).

(1) Low carbon steel

Also known as mild steel, carbon content from 0.10% to 0.30% Low carbon steel easy to accept a variety of processing such as forging, welding and cutting, often used in the manufacture of chains, rivets, bolts, shafts and so on.

(2) Medium carbon steel

Carbon content 0.25%~0.60% carbon steel. There are many kinds of products such as killed steel, semi-killed steel and boiling steel. 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. Hot working and cutting performance is good, but welding performance is poor. The strength and hardness are higher than low carbon steel, while the plasticity and toughness are lower than low carbon steel. Hot-rolled and cold-drawn materials can be used directly without heat treatment, and can also be used after heat treatment. The medium carbon steel after quenching and tempering has good comprehensive mechanical properties. The highest hardness that can be achieved is about HRC55(HB538), σb is 600~1100MPa. Therefore, in the various uses of medium strength level, medium carbon steel is the most widely used, in addition to as a building material, but also a large number of used in the manufacture of various mechanical parts.

(3) High carbon steel

Often called tool steel, carbon content from 0.60% to 1.70%, can be hardened and tempered. Hammers, crowbars, etc. are made of steel with a carbon content of 0.75%; Cutting tools such as drills, taps, reamers, etc. are manufactured from steel with a carbon content of 0.90% to 1.00%.

2. Classification by steel quality

According to the quality of steel can be divided into ordinary carbon steel and high-quality carbon steel.

(1) Ordinary carbon structural steel, also known as ordinary carbon steel, has a wide limit on carbon content, performance range and phosphorus, sulfur and other residual element content. In China and some countries, it is divided into three categories according to the guarantee conditions of delivery: Class A steel (Class A steel) is a steel that guarantees mechanical properties. Class B steel (Class B steel) is the steel that guarantees the chemical composition. Special steel (Class C steel) is a steel that guarantees both mechanical properties and chemical composition, and is often used to manufacture more important structural parts. China currently produces and uses the most A3 steel (Class A No. 3 steel) with carbon content of about 0.20%, which is mainly used for engineering structures.

Some carbon structural steels also add trace amounts of aluminum or niobium (or other carbide forming elements) to form nitrides or carbide particles to limit grain growth, strengthen steel and save steel. In China and some countries, in order to meet the special requirements of professional steel, the chemical composition and properties of ordinary carbon structural steel are adjusted, and a series of ordinary carbon structural steel professional steel (such as bridge, construction, rebar, pressure vessel steel, etc.) has been developed.

(2) Compared with ordinary carbon structural steel, the content of sulfur, phosphorus and other non-metallic inclusions is low. According to the different carbon content and use, this type of steel is roughly divided into three categories :① less than 0.25%C is low carbon steel, especially with carbon content of less than 0.10% of 08F,08Al, etc., because of its good deep drawing and weldability and is widely used as deep drawing parts such as automobiles, canning... Let's wait. 20G is the main material for making ordinary boilers. In addition, low carbon steel is also widely used as carburizing steel for machinery manufacturing. ②0.25~0.60%C is medium carbon steel, which is mostly used in the tempered state to make parts of the machinery manufacturing industry. ③ More than 0.6%C is high carbon steel, which is mostly used in the manufacture of springs, gears, rolls, etc. According to the different manganese content, it can be divided into ordinary manganese content (0.25~0.8%) and high manganese content (0.7~1.0% and 0.9~1.2%) two steel groups. Manganese can improve the hardenability of steel, strengthen ferrite, and improve the yield strength, tensile strength and wear resistance of steel. It is usually marked "Mn" after the grade of steel with high manganese content, such as 15Mn, 20Mn to distinguish it from carbon steel with normal manganese content.

3. Categorize by use

According to the use, it can be divided into carbon structural steel and carbon tool steel.

The carbon content of carbon tool steel is between 0.65 and 1.35%, and after heat treatment, high hardness and high wear resistance can be obtained, mainly used in the manufacture of various tools, cutting tools, molds and measuring tools (see tool steel).

Carbon structural steel is divided into 5 grades according to the yield strength of steel:

Q195, Q215, Q235, Q255, Q275

Each brand is divided into A, B, C, D grades due to different quality, there are four kinds at most, and some only one; There are also differences in the deoxidation methods of steel smelting.

Deoxidation method symbol:

F-- boiling steel

b-- semi-killed steel

Z-- kill steel

TZ- Special killing steel

Round steel material:

Q195, Q235, 10#, 20#, 35#, 45#, Q215, Q235, Q345, 12Cr1Mov, 15CrMo, 304, 316, 20Cr, 40Cr, 20CrMo, 35CrMo, 42CrMo, 40CrNiMo, GCr15, 65Mn, 50Mn , 50Cr, 3Cr2W8V, 20CrMnTi, 5CrMnMo, etc.

Standard: (GB699-1988, GB700-1988, GB3077-1988, GB702-1986, QJ/HG02.17-1991), the following table is the detailed standard of round steel: