What Is Low Alloy Steel?

Low alloy steel refers to alloy steel with less than 5% total alloying elements. Compared with carbon steel, low alloy steel is based on carbon steel. In order to improve the performance of steel, intentionally add one or more alloying elements to the steel. When the amount of alloy added exceeds the normal content of normal production methods of carbon steel, this steel is called alloy steel. When the total amount of alloy is less than 5%, it is called low alloy steel, ordinary alloy steel is generally below 3.5%, alloy content between 5-10% is called medium alloy steel, and more than 10% is called high alloy steel.

China's steel output has exceeded 600 million tons. The quantity of steel is no longer a major contradiction, and the contradiction of the irrational structure of steel varieties is very prominent. The main task of the current industry is to strive to improve the market competitiveness of products, stand on a new starting point for sustainable development, and include vigorous development of low-alloy steel as an important part of the development strategy. Many ordinary steel companies have realized that the production of low-alloy steel is the key to improve the technical content and added value of products in the adjustment of the steel variety structure and the development of science and technology development plans. They have countless problems in the development of low-alloy steel. Management cadres felt that "all low-alloy steels are successful, and low-alloy steels are also failures", and they urgently require a comprehensive understanding of low-alloy steels.

The current production of ordinary low alloy steel in China can be summarized as follows:

1. It is low-carbon in terms of carbon content, which is generally less than 0.20%;

2. In terms of alloys, primary steel and binary steel occupy a larger proportion;

3. In terms of supply status, most of them are delivered in the hot rolled state;

4. Many steel types add rare earth elements to improve comprehensive performance;

5. Most ordinary low alloy steels are of the ferrite + pearlite type.

1. Make full use of China's rich resources and take the path of "independence and self-reliance".

China's ordinary low-alloy steel is an independent low-alloy steel system developed by making full use of China's abundant resources and getting rid of the constraints of nickel and chromium. Nowadays, not only has China produced high-quality low-alloy steels that do not contain nickel and chromium, but also made use of China's abundant resources to create many new steel grades with excellent properties, creating a new situation in the development of steel grades.

2. Strongly supported national defense construction.

Ordinary low-alloy steel has high strength and good comprehensive performance. The weapons and equipment manufactured with it have the characteristics of light weight, fast speed, and good performance, and have played a great role in national defense construction.

3 Vigorously promoted the revolution in design, technology and products in all industrial sectors.

In addition to good mechanical properties, ordinary low-alloy steels also have special properties such as resistance to medium temperature, low temperature, abrasion and corrosion, which have greatly changed the chemical industry, petroleum, ships, boilers, vehicles, bridges, and railways. The appearance of steel in construction, construction, mining, etc. has provided a material basis for the design revolution in some industrial sectors, and also created conditions for some industrial production to further develop at high temperatures, pressures, and speeds, and further strengthen and innovate production processes. With the improvement of materials, the volume, weight, performance and service life of many industrial products have also undergone fundamental changes. Therefore, the development of ordinary low-alloy steels has, to a certain extent, created conditions for many industrial sectors to carry out design, process and product revolutions and surpass the advanced world level.

4 Saving steel, improving service life, easy mass production, low cost, easy to popularize and use, is a good way to develop the steel industry quickly and efficiently.

The equipment made of ordinary low alloy steel has a longer service life than carbon steel, especially when it is used in severe corrosion or abrasion conditions such as chemical industry, petroleum, mining, etc., its service life is several times to dozens of times longer than carbon steel. Because ordinary low alloy steel is produced by ordinary steelmaking, rolling equipment and ordinary smelting and rolling processes, and the cost is similar to that of carbon steel, it can be widely used in various industrial sectors. ^[2]

Classification of low alloy steel

According to international standards, steel is divided into two categories: non-alloy steel and alloy steel. Non-alloy steel is a large type of steel usually called carbon steel. In addition to iron and carbon, the steel also contains a small amount of alloying elements Mn, Si, Al brought by the charge, impurity elements P, S, and gases N, H, O. Wait. Alloy steel is another type of steel that intentionally adds a certain amount of alloying elements Cr, Ni, Mo, V, etc., in order to obtain certain physical, chemical or mechanical properties, and controls impurities and harmful elements.

In principle, alloy steel is divided into low alloy steel, medium alloy steel and high alloy steel. As the name suggests, it is distinguished by the total amount of alloying elements. The total amount is less than 5% is called low alloy steel, 5-10% is medium alloy steel, and more than 10% is high alloy steel. In domestic customs, carbon steel and alloy steel of special quality are called special steel, and 31 special steel companies nationwide specialize in producing this type of steel. Such as high-quality carbon structural steel, alloy structural steel, carbon tool steel, alloy tool steel, high-speed tool steel, carbon spring steel, alloy spring steel, bearing steel, stainless steel, heat-resistant steel, electrical steel, including high-temperature alloys, Corrosion-resistant alloys and precision alloys, etc.

Alloying elements in low alloy steel

The most common alloying elements in low alloy steels are manganese, silicon, chromium and nickel. If corrosion resistance must be improved, add copper to the steel. These elements (except chromium and nickel) can increase the strength limit, make the plasticity slightly change, and reduce the impact toughness.

The content of nickel in low alloy steel does not exceed 1%. This element does not enhance the steel sufficiently, but it has a good impact on the plasticity and impact toughness, and can improve the brittle fracture resistance of the steel. Nickel content is often limited due to its scarcity.

In the case of multiple alloying, chromium can increase the strength of steel and have a good effect on low temperature stability. Chromium has no adverse effect on weldability under the general content of low alloy steel (0.9%).

Low alloy steel is usually added with 0.3% copper. At this content, copper can improve corrosion resistance and improve strength properties. In addition, such copper content has no adverse effect on the weldability of steel, and does not cause red brittleness.

The future efforts of metallurgical workers are to develop steel grades with relatively high strength, good weldability, and low cold brittleness temperature. When a small amount of boron, molybdenum, vanadium, niobium, titanium and other elements are used for single alloying or multiple alloying in strict proportions, new steel types can be made. ^[3]