Quenching and tempering treatment of 2Cr13 steel

What is 2Cr13 steel?

2Cr13 steel is a more commonly used stainless steel, which has high thermal strength, oxidation resistance and good shock absorption. It has good corrosion resistance in weakly corrosive media, and has sufficient corrosion resistance to fresh water, sea water, steam, and air. Higher performance can be obtained after heat treatment. It is commonly used to make mechanical parts that work below 450°C and chemical and food industry containers used at room temperature. For example, transmission parts, fixed pins, tie rods, turbine blades, valve seats, valve plates, valve stems, pump parts, molds, etc. Among them, transmission parts, fixed pins, tie rods and other parts are generally used after quenching and tempering. The traditional quenching and tempering process is high temperature heating, oil quenching, and then tempering.

Critical temperature of 2Cr13 steel: AC1 820℃, AC3 950℃, Ar1 780℃. The quenching and tempering process recommended by the new national standard is: quenching 920~980℃ oil cooling, 600~750℃ tempering fast cooling. The tempering process recommended by the old standard is: 1000~1050℃ oil or water cooling, 660~770℃ tempering, oil or water or air cooling. The quenching and tempering process of the general factory is: 950~1000℃ oil quenching, 640~700℃ tempering air cooling. In the quenching and tempering process recommended by the new and old standards, the quenching temperature is somewhat different. Production practice shows that quenching at 1050°C sometimes causes overheating to make the martensite coarse, and the impact toughness decreases significantly after tempering. It is generally believed that tempering of 2Cr13 steel at 400~600℃ after quenching will reduce the corrosion resistance and impact value. The use of higher temperature tempering can ensure stable structure and performance at the use temperature, and also has a higher corrosion resistance. For cooling after tempering, some people think that any cooling speed can be used. Some people think that the steel has a tendency to temper brittleness, and it should be cooled quickly after tempering to inhibit the development of temper brittleness and obtain higher impact toughness.
20200802010529 71838 - Quenching and tempering treatment of 2Cr13 steel

Compared with the mechanical properties specified in the standard, the mechanical properties tested by the new process test showed that the tensile strength increased by about 29%, the elongation after fracture decreased by about 51%, the reduction of area increased by 22%, and the impact absorption energy increased by 33%. It should be noted that in the tensile test, the elongation after fracture of the sample with the fracture in the center is greater than that of the sample with the fracture not in the center. The fractures of the three quenched and tempered tensile specimens are all close to the head, which may be one of the reasons for the lower elongation after fracture. In any case, it can not show that the plasticity index of the material has been reduced a lot. Practice and theory have proved that the reduction of area is closer to the true strain than the elongation after fracture, so it is more reasonable to use the reduction of area in the plastic index than the elongation after fracture. The reduction of area has increased by about 22%. From this point of view, the application of the new quenching and tempering process in production is feasible. For the impact test, the “U”-shaped notched sample is used. If the Ak value in the national standard refers to the “V”-shaped notched sample, the two values cannot be compared. However, the test impact value is close to the impact value of the 40Cr steel quenched and tempered “U”-notched sample found from the data. In a comparative sense, the Ak value did not decrease. Because the quenching heating temperature of the new quenching and tempering process is lower than that of the traditional quenching and tempering treatment, the grains of the steel are finer. The impact value of steel is related to the grain size. The finer the grain, the greater the impact value. In the traditional process, there are many examples that the quenching temperature exceeds 1000℃ which causes the structure to be coarse and the impact toughness is significantly reduced after tempering. Moreover, the sub-temperature quenched undissolved ferrite of steel is fine and uniformly distributed, which has a better effect on improving toughness, and concentrates harmful impurities such as phosphorus in a small amount of freely dispersed ferrite grains, which can improve the notch toughness of steel. , Reduce cold brittle transition temperature, reduce temper brittleness, etc.

In terms of the relationship between tempering temperature and impact toughness, the traditional process has a high quenching heating temperature, and carbides are fully dissolved into austenite. Tempering at 400-600°C will precipitate carbides with high dispersion, which is not only resistant to Corrosion is reduced and impact toughness is also low. The new quenching and tempering process has a low quenching temperature and relatively little carbides are dissolved. Tempering at this temperature section will not form highly dispersed carbides and will not reduce the impact value. From the analysis of the microstructure, the traditional process has a high quenching temperature, sufficient carbides are dissolved, and the degree of alloying of the matrix structure is relatively high. Even if the high temperature tempering, the matrix structure will not be completely recrystallized, so the martensite orientation will be retained.
However, the new process has low quenching temperature and the orientation of tempered sorbite is not obvious, which may be one of the reasons why the toughness will not decrease. From the perspective of intense quenching technology, the new process quenching is changed from traditional oil cooling to water cooling. The intense cooling in the martensite transformation zone (Ms→Mf) can improve the plasticity of the material and increase the strength of the material. The service life of strongly quenched parts under alternating loads can be increased by almost an order of magnitude, and steel parts can be prevented from cracking and distortion can be reduced.
2Cr13 is a martensitic stainless steel with magnetic properties, good hardness, and welding needs to be preheated. Austenitic stainless steel electrode used for welding with Q235 does not need to be preheated, and the welding uses a smaller current. 2Cr13 welding consumables can be selected:

  • For atmospheric corrosion resistance, choose G202, G207, preheat 150-300 degrees, and temper 700-730 degrees after welding;
  • Resistance to organic acid and heat resistance: G211, need to be preheated 150-300 degrees;
  • Good plasticity: A102, A107, A202, A207, A302, A307, preheating for repair welding, preheating for thick and large parts.

Standard: GB/T 1220-2007
Corresponding Japanese brand: SUS420JI
Corresponding to German brand: X20Cr13/1.4021
Corresponding American grade: 420

Characteristic of 2Cr13

2Cr13 is a martensitic stainless steel, which is magnetic and has good hardness. It should be preheated for welding. Austenitic stainless steel electrodes for welding with Q235 do not need to be preheated, such as A302.A307.
When welding, the dilution rate of the weld is controlled, and the welding is not weaving, and a smaller current is used.
2Cr13 welding consumables can be selected:

  1. For atmospheric corrosion resistance, select G202, G207, preheating 150-300 degrees, and tempering 700-730 degrees after welding;
  2. Resistance to organic acid and heat resistance: G211, need to be preheated 150-300 degrees;
  3. Good plasticity: A102, A107, A202, A207, A302, A307, preheating for repair welding, preheating for thick and large parts.

Display method of 2Cr13

According to the GB/T “Method for Representing Steel Product Grades”, it is expressed in a combination of Chinese pinyin letters, chemical element symbols and Arabic numerals. Content: Generally, an Arabic number is used at the head of the grade to indicate the average carbon content (in parts per thousand); those with an average carbon content less than one thousandth are represented by “0”; those with a carbon content less than 0.03% are represented by ” 00″ means. Alloying element content: when the average alloying element content is less than 1.50%, only the elements are indicated in the grade, and the content is generally not indicated; the average alloying element content is 1.5%-2.49%, 2.50%-3.49%…12.50%-13.49% ,…, mark 2, 3….13… accordingly. For special purpose stainless steel, add the code representing the purpose of the steel to the head of the grade. For example: 0Cr18Ni9, Y1Cr17 (free-cutting steel).
2Cr13 stainless steel has high hardness and good corrosion resistance in quenched state. Many of them are used for making knives, which are “cutting tool grade” martensitic steels, and are also used for surgical knives, similar to the earliest stainless steel such as Brinell high chromium steel, and also used for steam turbine blades, etc., with a wide range of applications.
The density of 2Cr13 is 7.75g/cm3
Quenching hardness of 2Cr13: Generally, the quenching temperature of 2Cr13 is 980~1050℃, the hardness of 980℃ heating oil quenching is obviously lower than 1050℃ heating oil quenching, 980℃ oil quenching hardness is 45~50HRC, 1050℃ oil quenching hardness to be 2HRC higher. However, the grains of the structure obtained after quenching at 1050°C are relatively coarse and brittle. It is recommended to use 1000℃ heating and quenching to get better structure and hardness.

Chemical composition of 2Cr13

  • Carbon C: 0.16~0.25
  • Silicon Si: ≤1.00
  • Manganese Mn: ≤1.00
  • Sulfur S: ≤0.030
  • Phosphorus P: ≤0.040
  • Chromium Cr: 12.00~14.00
  • Nickel Ni: Allowed to contain ≤0.60

Mechanical properties of 2Cr13

  • Tensile strength σb (MPa): quenched and tempered, ≥635
  • Conditional yield strength σ0.2 (MPa): quenched and tempered, ≥440
  • Elongation δ5 (%): quenching and tempering, ≥20
  • Reduction of area ψ (%): quenching and tempering, ≥50
  • Impact energy Aku2(J): quenching and tempering, ≥63
  • Hardness: annealing, ≤223HB; quenching and tempering, >192HB

Heat treatment specification and metallographic structure:

Heat treatment specification:

1) Annealing, 800~900℃ slow cooling or about 750℃ fast cooling;
2) Quenching, 920~980℃ oil cooling;
3) Tempering, fast cooling at 600~750℃.
Metallographic structure: The structure is characterized by martensite.

Delivery status:

Generally, the delivery is in the heat treatment state, and the type of heat treatment is specified in the contract; if it is not specified, the delivery is in the non-heat treatment state.

Source: China Pipe Fittings Manufacturer – Yaang Pipe Industry (www.metallicsteel.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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