Alloy Steel

Definition of Alloy Steel

In addition to iron and carbon, alloy steel is called alloy steel by adding other alloying elements. An iron-carbon alloy formed by adding an appropriate amount of one or more alloying elements on the basis of ordinary carbon steel. According to the difference of added elements and appropriate processing technology, special properties such as high strength, high toughness, wear resistance, corrosion resistance, low temperature resistance, high temperature resistance, and non-magnetic properties can be obtained.

The most important and desirable changes to alloy steel are:

*Enhanced hardenability.

*Enhanced corrosion resistance.

*Maintain hardness and strength.

*Almost all alloy steels require heat treatment to achieve their optimum properties.

Generation and development of alloy steel

Alloy steel has a history of more than 100 years. More industrial use of alloy steel was about the second half of the 19th century.

In 1868, the British R.F.Mushet invented a self-hardening steel with a composition of 2.5%Mn-7%W, which increased the cutting speed to 5 m/min.

In 1870, a bridge with a span of 158.5 meters was built on the Mississippi River with chromium steel (1.5-2.0%Cr) in the United States; later, some industrial countries switched to nickel steel (3.5%Ni) to build long-span bridges, or used for Build warships.

In 1901, high carbon chromium rolling bearing steel appeared in Western Europe.

In 1910, 18W-4Cr-1V high-speed tool steel was developed, which further increased the cutting speed to 30 m/min.

After the 1920s, stainless steel and heat-resistant steel were introduced during this period.

In 1920, the German E. Maurer invented the 18-8 type stainless acid-resistant steel.

Fe-Cr-Al resistance wire appeared in the United States in 1929.

In 1939, Germany began to use austenitic heat-resistant steel in the power industry.

After World War II to the 1960s, it was mainly the era of developing high-strength steel and ultra-high-strength steel. Due to the needs of the aviation industry and the development of rocket technology, many new types of high-strength steel and ultra-high-strength steel appeared, such as Precipitation hardening high-strength stainless steel and various low-alloy high-strength steels are its representative steel grades. After the 1960s, many new metallurgical technologies, especially the out-of-furnace refining technology, were widely used, and alloy steel began to develop in the direction of high purity, high precision and ultra-low carbon, and maraging steel and ultra-pure ferrite appeared. Stainless steel and other new steel grades.

There are thousands of alloy steel grades and tens of thousands of specifications used internationally. The output of alloy steel accounts for about 10% of the total steel output. It is an important metal material widely used in national economic construction and national defense construction.

Since the 1970s, the development of alloyed high-strength steels in the world has entered a new period. Based on the controlled rolling technology and the metallurgy of microalloying, the modern low-alloyed high-strength steels, namely microalloyed steels, have been formed. new concept.

In the 1980s, a variety development involving a wide range of industrial fields and specialized material categories reached its peak with the help of achievements in metallurgical process technology. In the four-in-one relationship of chemical composition-process-structure-property of steel, the dominance of the microstructure and microstructure of steel is highlighted for the first time, and it also shows that the basic research of low-alloy steel has become mature, with unprecedented A new concept for alloy design

Classification of alloy steel

1. According to the content of alloying elements

      1) Low alloy steel - the total content of alloying elements is less than or equal to 5%

      2) Medium alloy steel - the total content of alloying elements is between 5% and 10%

      3) High alloy steel - the total content of alloying elements is greater than or equal to 10%

2. According to the type of alloying elements

      1) Chrome steel

      2) Manganese steel

      3) chrome manganese steel

      4) Chrome Nickel Steel

      5) chrome nickel molybdenum steel

      6) Silicon manganese molybdenum vanadium steel, etc.

3. According to the main purpose

      1) Structural steel

      2) Tool steel

      3) Special performance steel

There are many types of alloy steel, usually divided into low alloy steel (content <5%), medium alloy steel (content 5% ~ 10%), high alloy steel (content> 10%) according to the content of alloying elements; according to quality, it is divided into high-quality steel Alloy steel, special alloy steel; according to characteristics and uses, it is divided into alloy structural steel, stainless steel, acid-resistant steel, wear-resistant steel, heat-resistant steel, alloy tool steel, rolling bearing steel, alloy spring steel and special performance steel (such as soft magnetic steel). , permanent magnet steel, non-magnetic steel) and so on.

The alloy steel systems of various countries vary according to their respective resource conditions, production and use conditions. Some countries have developed nickel steel and steel systems in the past, while my country has found that silicon, manganese, vanadium, titanium, niobium, boron, lead, Rare earth based alloy steel system. Alloy steel accounts for about ten percent of the total output of steel, and is generally smelted in electric furnaces. Alloy steels can be divided into 8 categories according to their uses. They are: alloy structural steel, spring steel, bearing steel, alloy steel Tool steel, high-speed tool steel, stainless steel, heat-resistant non-skin steel, silicon steel for electrical use.

Our classification of alloy steels:

1. Quenched and tempered steel

    1) Medium carbon alloy steel with low alloying element content;

    2) High strength;

    3) Used for high temperature bolts, nut materials, etc. [8]

2. Spring steel

    1) The carbon content is higher than that of quenched and tempered steel;

    2) After quenching and tempering treatment, the strength is higher and the fatigue resistance is higher;

    3) For spring material.

3. Rolling bearing steel

    1) High carbon alloy steel with high alloy content;

    2) It has high and uniform hardness and wear resistance;

    3) For rolling bearings.

4. Alloy tool steel - also known as measuring tool steel

    1) High carbon alloy steel with low content of alloying elements;

    2) It has high hardness and wear resistance, good machining performance and good stability;

    3) For measuring tool materials.

5. Special performance steel

    1) Low carbon high alloy steel;

    2) Good corrosion resistance;

    3) For anti-corrosion, some can be used as heat-resistant materials.

6. Heat-resistant steel

    1) Low carbon high alloy steel;

    2) Good heat resistance; 3

For heat-resistant materials, some can be used as anti-corrosion materials.

7. Low temperature steel

    1) Low carbon alloy steel, according to the degree of low temperature resistance, the alloy elements are high or low;

    2) Good low temperature resistance;

    3) For low temperature materials (special steel is nickel steel).

Comparison table of commonly used alloy grades