40Cr  SCr440 ASTM 5140 Steel Round Steel Bar

Product Introduction

40Cr steel is one of the most widely used steels in machinery manufacturing industry. After tempering, it has good comprehensive strength, good low temperature impact toughness, and low crack sensitivity. The steel has good hardenability, water quenching can be hardened to Ф28~60mm, oil quenching can be hardened to Ф15~40mm. Suitable for production of medium-sized plastic mold, shaft accessories.

40Cr steel bar Steel Chemical Composition:

Element Composition (%)
Carbon (C) 0.37~0.44
Silicon (Si) 0.17~0.37
Manganese (Mn) 0.50~0.80
Chromium (Cr) 0.80~1.10
Phosphorus (P) ≤0.35
Sulfur (S) ≤0.35
Molybdenum (Mo) 0.15~0.25
Nickel(Ni) ≤0.30



After quenching and tempering, this kind of steel is used to manufacture mechanical parts that withstand medium load and medium speed, such as steering knuckles, rear axle shafts of automobiles, gears, shafts, worms, spline shafts, top sleeves, etc. on machine tools;

After quenching and tempering at medium temperature, it is used to manufacture parts that withstand high load, impact and medium speed, such as gears, main shafts, oil pump rotors, sliders, collars, etc.;

After quenching and low-temperature tempering, it is used to manufacture parts that bear heavy loads, low impact and wear resistance, and have a solid thickness of less than 25mm on the cross-section, such as worms, spindles, shafts, collars, etc.;

After tempering and high-frequency surface quenching, it is used to manufacture parts with high surface hardness and wear resistance without great impact, such as gears, sleeves, shafts, main shafts, crankshafts, mandrels, pins, connecting rods, screws, nuts, intake valves, etc.

In addition, this steel is suitable for the manufacture of various transmission parts that undergo carbonitriding treatment, such as gears and shafts with large diameter and good low temperature toughness.


Ⅰ. Classified by process

Round steel is divided into three types: hot rolled, forged and cold drawn. The specifications of hot-rolled round steel are 5.5-250 mm. Among them: 5.5-25 mm small round steel is mostly supplied in bundles of straight strips, which are often used as steel bars, bolts and various mechanical parts; round steel larger than 25 mm is mainly used for manufacturing mechanical parts and tube blanks of seamless steel pipes wait.


Ⅱ. Classification by chemical composition

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

(1) Mild steel

Also known as mild steel, the carbon content is from 0.10% to 0.30%. Low carbon steel is easy to accept various processing such as forging, welding and cutting, and is often used to make chains, rivets, bolts, shafts, etc.

(2) Medium carbon steel

Carbon steel with a carbon content of 0.25% to 0.60%. There are killed steel, semi-killed steel, boiling steel and other products. In addition to carbon, it can also contain a small amount of manganese (0.70% to 1.20%). According to product quality, it is divided into ordinary carbon structural steel and high-quality carbon structural steel. Good thermal processing and cutting performance, poor welding performance. The strength and hardness are higher than low carbon steel, but the 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. Medium carbon steel after quenching and tempering has good comprehensive mechanical properties. The highest hardness that can be achieved is about HRC55 (HB538), and σb is 600-1100MPa. Therefore, in various uses of medium strength level, medium carbon steel is the most widely used. In addition to being used as building materials, it is also widely used in the manufacture of various mechanical parts.

(3) High carbon steel

Often called tool steel, the carbon content is from 0.60% to 1.70%, and it 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 made of steel with a carbon content of 0.90% to 1.00%.

Classified by steel quality

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

(1) Ordinary carbon structural steel, also known as ordinary carbon steel, has wide restrictions on carbon content, performance range, and content of phosphorus, sulfur and other residual elements. 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 the steel with guaranteed mechanical properties. Class B steel (Class B steel) is steel with a guaranteed chemical composition. Special steel (C-type steel) is a steel that guarantees both mechanical properties and chemical composition, and is often used to manufacture more important structural parts. The most produced and used steel in China is A3 steel (Class A No. 3 steel) with a 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 the 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 have been adjusted, thus developing a series of professional steel of ordinary carbon structural steel (such as bridges, buildings, Steel bars, steel for pressure vessels, etc.).

(2) Compared with ordinary carbon structural steel, high-quality carbon structural steel has lower content of sulfur, phosphorus and other non-metallic inclusions. According to the different carbon content and usage, this kind of steel can be roughly divided into three categories:

① Less than 0.25% C is low-carbon steel, especially 08F and 08Al with a carbon content of less than 0.10%, are widely used as deep-drawing parts such as automobiles and cans because of their good deep drawability and weldability ……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 quenched and tempered state to make parts in 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 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 improve the yield strength, tensile strength and wear resistance of steel. Usually, the mark “Mn” is added after the grade of steel with high manganese content, such as 15Mn and 20Mn, to distinguish it from carbon steel with normal manganese content.

Classification by purpose

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

Carbon tool steel The carbon content is between 0.65 and 1.35%. After heat treatment, high hardness and high wear resistance can be obtained. It is mainly used to manufacture 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, and D grades due to different quality. There are four types at most, and some have only one; in addition, there are differences in the deoxidation method of steel smelting.

Deoxygenation method symbol:

F – boiling steel

b——semi-killed steel

Z——killed steel

TZ——special killed steel


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


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