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Understanding Low Alloy Steels
Time: 2023-12-28
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Low alloy steels are an important part of the modern industrial world. With their unique properties, they play an important role in a variety of engineering and manufacturing applications. In this blog, we will delve into the basics of low alloy steels, including what they are, common grades, and applications.

Definition of low alloy steel:

Alloy steels with less than 3.5% total alloying elements are called low alloy steels. Low alloy steel is relative to carbon steel, is based on carbon steel, in order to improve one or more properties of steel, and intentionally add one or more alloying elements to the steel. The amount of alloy added over the normal production method of carbon steel has a general content, the steel is called alloy steel.

When the total amount of alloy is less than 3.5 per cent, the steel is called low alloy steel. Alloy content between 3.5 and 10 per cent is called medium-alloyed steel; greater than 10 per cent is called high-alloyed steel.

Common Low Alloy Steels

Ⅰ High Strength Low Alloy Steels

One of the common grades of low alloy steel is high strength low alloy steel (HSLA). It is a steel formed by adding a small amount of alloying elements on the basis of low carbon steel. The steel Wc ≤ 0.2%, often added alloying elements are silicon, manganese, titanium, niobium, vanadium, etc., the total content of W < 3%.
HSLA steel is mostly supplied in the hot rolled and normalised condition, and is generally no longer heat-treated when in use.

Advantages of HSLA steel:

  1. High strength
  2. Good plasticity and toughness
  3. Good weldability and cold deformability
  4. Good corrosion resistance
  5. Low tough-brittle transition temperature, low cost, suitable for cold forming and welding.

The production process of HSLA steel mainly includes conventional rolling and controlled rolling and cooling technology. The properties of HSLA steels can be further optimised by adjusting the rolling process and alloying element content.

HSLA steels are commonly used in structural applications requiring reduced weight and increased strength, and are therefore widely used in bridges, vehicles, ships, boilers, high-pressure vessels, oil pipelines, and components that operate at low temperatures. Other commonly used low alloy high-strength structural steels include Q295, Q345, Q390, Q420, Q460, and others.

application Low Alloy Steels

Ⅱ Free Cutting Structural Steel

The grade of free cutting structural steel is composed of two digits after “Y”. The two digits indicate the average carbon content of 10,000, if the steel contains high manganese marked “Mn”. For example, Y40Mn indicates that the average Wc = 0.40%, high manganese content of free-cutting structural steel.

Free-cutting structural steel is added to the steel to make the steel brittle elements, so that the steel cutting easy to break into chips, thus helping to improve the cutting speed and extend the tool life of a steel. At the same time, this steel can be carburised, quenched or tempered, surface quenching and other heat treatment to improve its performance. All cutting structure of the forging performance and welding performance is not good, selection should be noted.

Specific grades are: Y12, Y12Pb, Y15, Y15Pb, Y20, Y30, Y35, Y40Mn, Y45Ca nine grades. Often used in mass production, for the mechanical properties of small parts that do not require high.

Ⅲ Low alloy high weather resistance steel

The grade of low alloy cast steel consists of “ZG” followed by two digits plus the element symbol and number.

The first two digits represent the average carbon content in low-alloy cast steel, the element symbol represents the alloying elements contained in low-alloy cast steel, and the number after the element symbol represents the percentage of the average content of the alloying element (if the average content is <1.5 %, no number is marked after the element symbol; if the average content is 1.5%~2.4%, 2.5%~3.5%…, then 2, 3… are marked after the corresponding alloy element symbol, and so on). For example, ZG35SiMn represents low alloy cast steel with average Wc=0.35%, WSi<1.5%, and WMn<1.5%.

Low Alloy Steel


The comprehensive mechanical properties of low-alloy cast steel are significantly higher than that of non-alloy structural steel. It is generally used for mechanical parts that bear heavy loads, impact loads and friction, such as various high-strength gears, hydraulic press working cylinders, high-speed train couplers, etc.
Commonly used low alloy cast steels include: ZG40Cr, ZG40Mn, ZG35SiMn, ZG35CrMnSi, ZG35CrMo, ZG35SiMnMo, ZG35CrMnMo, ZG34CrNiMo, etc.

In summary, understanding low alloy steels is critical to understanding their importance in industry. With its unique composition and exceptional properties, low-alloy steel offers a wide range of advantages, making it an indispensable material in a variety of engineering and manufacturing applications. From increasing the strength of structural components to improving the performance of machinery, low-alloy steels continue to play a vital role in driving technological innovation across different industries.

Quanshuo Metal Materials is a manufacturer that has passed ISO9001:2015, TUV, SGS, and CE certification. It mainly produces Carbon Steel, etc., with an annual output of 300,000 tons. Looking forward to your inquiry.

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