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20CrNi2Mo low-carbon steel

20CrNi2Mo steel is a kind of high-quality low-carbon medium. Due to its low content of alloy elements and good coordination effect of various alloy elements, it is listed as the recommended standard in the world’s major industrial countries.

20CrNi2Mo equivalent grade:

Classification of steel

Ferrous, steel and nonferrous metals
Before introducing the classification of steel, the basic concepts of ferrous metals, steel and non-ferrous metals are briefly introduced.
1. Ferrous metals are iron and its alloys. Such as steel, pig iron, ferroalloy, cast iron, etc. Steel and pig iron are based on iron, carbon as the main added element of alloy, collectively known as iron carbon alloy.
Pig iron refers to the product made by smelting iron ore in blast furnace, which is mainly used for steelmaking and casting.
Cast pig iron is melted in an iron melting furnace to obtain cast iron (liquid state), which is called cast iron casting.
Ferroalloy is an alloy composed of iron and silicon, manganese, chromium, titanium and other elements. Ferroalloy is one of the raw materials for steel-making. It is used as deoxidizer and alloy element additive in steel-making.
2. The pig iron for steelmaking is put into the steelmaking furnace and smelted according to a certain process to obtain steel. Steel products include ingots, continuous casting billets and direct casting of various steel castings. Generally speaking, steel refers to the steel rolled into various steels. Steel belongs to ferrous metal, but steel is not equal to ferrous metal.
3. Nonferrous metals, also known as non-ferrous metals, refer to metals and alloys other than ferrous metals, such as copper, tin, lead, zinc, aluminum, brass, bronze, aluminum alloys and bearing alloys. In addition, chromium, nickel, manganese, molybdenum, cobalt, vanadium, tungsten and titanium are also used in industry. These metals are mainly used as alloy additives to improve the properties of metals. Tungsten, titanium and molybdenum are mostly used to produce cemented carbide for cutting tools. These nonferrous metals are called industrial metals. In addition, there are precious metals: platinum, gold, silver, and rare metals, including radioactive uranium and radium.

Classification of steel
Steel is an iron carbon alloy with carbon content between 0.04% and 2.3%. In order to ensure its toughness and plasticity, the carbon content generally does not exceed 1.7%. Besides iron and carbon, the main elements of steel are silicon, manganese, sulfur and phosphorus. The classification methods of steel are various, and the main methods are as follows:
1. Classification by quality
(1) Ordinary steel (P ≤ 0.045%, s ≤ 0.050%)
(2) High quality steel (P, s ≤ 0.035%)

2. Classification by chemical composition
(1) Carbon steel: A. low carbon steel (C ≤ 0.25%); B. medium carbon steel (C ≤ 0.25 ~ 0.60%); C. high carbon steel (C ≤ 0.60%).
(2) Alloy steel: A. low alloy steel (total alloy element content ≤ 5%); B. medium alloy steel (total alloy element content > 5 ~ 10%); C. high alloy steel (total alloy element content > 10%).

3. Classification by  forming methods: (1) forged steel; (2) cast steel; (3) hot rolled steel; (4) cold drawn steel.

4. Classification by metallographic structure
(1) Annealed: A. hypoeutectoid steel (ferrite + pearlite); B. eutectoid steel (pearlite); C. hypereutectoid steel (pearlite + cementite); D. ledeburite steel (pearlite + cementite).
(2) Normalized: A. pearlitic steel; B. bainitic steel; C. martensitic steel; D. austenitic steel.
(3) Having no or partial transformation

5. Classification by use
(1) Construction and engineering steel: a. ordinary carbon structural steel; b. low alloy structural steel; c. reinforced steel.
(2) Structural steel
a. Mechanical manufacturing steel: (a) quenching and tempering structural steel; (b) surface hardening structural steel: including carburizing steel, ammoniating steel and surface quenching steel; (c) easy cutting structural steel; (d) cold plastic forming steel: including cold stamping steel and cold heading steel.
b. Spring steel
c. Bearing steel
(3) Tool steel: a. carbon tool steel; b. alloy tool steel; c. high speed tool steel.
(4) Special performance steel: a. stainless and acid resistant steel; b. heat resistant steel: including anti-oxidation steel, hot strength steel and air valve steel;c. electric heating alloy steel; d. wear resistant steel; e. low temperature steel; f. electrical steel.
(5) Professional steel, such as bridge steel, ship steel, boiler steel, pressure vessel steel, agricultural machinery steel, etc.

6. Comprehensive classification
(1) Ordinary steel
a. Carbon structural steel: (a) Q195; (b) Q215 (a, b); (c) Q235 (a, B, c); (d) q255 (a, b); (E) Q275.
b. Low alloy structural steel
c. General structural steels for specific applications
(2) High quality steel (including * * high quality steel)
a. Structural steel: (a) high quality carbon structural steel; (b) alloy structural steel; (c) spring steel; (d) easy cutting steel; (E) bearing steel; (f) high quality structural steel for specific purposes.
b. Tool steel: (a) carbon tool steel; (b) alloy tool steel; (c) high speed tool steel.
c. Special performance steel: (a) stainless acid resistant steel; (b) heat resistant steel; (c) electrothermal alloy steel; (d) electrical steel; (E) high manganese wear-resistant steel.

7. Classification by smelting method
(1) According to the type of furnace
a. Open hearth steel: (a) acid open hearth steel; (b) basic open hearth steel.
b. Converter steel: (a) basic converter steel. Or (a) bottom blown converter steel; (b) side blown converter steel; (c) top blown converter steel.
c. EAF steel: (a) EAF steel; (b) electroslag furnace steel; (c) induction furnace steel; (d) vacuum consumable furnace steel; (E) electron beam furnace steel.
(2) According to deoxidation degree and pouring system
a. The results show that there are three kinds of steels: rimmed steel; B. semi killed steel; C. killed steel; D. special killed steel.

18NiCrMo5 construction steel

18NiCrMo5 steel is a leading construction steel in circulation.
It is a type of steel supplied in the delivery condition “annealed”.

18NiCrMo5  equivalent steel grades:

Mechanical Properties:

Tensile Strength: ≥900

Yield Strength: ≥635

Elongation  (%): ≥10

Impact Value Kv (J): ≥35

Hardness (HB): ≥271

14NiCr14 carburizing steel

14NiCr14 is a widely used high-grade carburizing steel, which has high strength, ductility and hardenability as compared with 15Cr and 20Cr steels. Quenching and tempering at low temperature or high temperature tempering, have good mechanical properties, low temperature impact toughness, notch sensitivity, machinability and weldability is good, but the temper brittleness, white point of high sensitivity After carburizing are required for secondary quenching, special circumstances also need cold treatment.

14NiCr14 Equivalent Materials:

Mechanical properties:

Tensile strength σb (MPa): ≥930 (95)
Yield strength σs (MPa): ≥ 685 (70)
Elongation δ5 (%): ≥11
Section shrinkage ψ (%): ≥50
Impact energy Akv (J): ≥71
Impact toughness value αkv (J / cm2): ≥88 (9)

1.5217 alloy steel

1.5217 belongs to alloy steel, which is a DIN standard steel grade.

1.5217 equivalent steel grades

1.5217 Mechanical Properties

34CrNiMo6 Alloy steel

34CrNiMo6 steel can be induction hardened and it is weldable under certain conditions. Through hardenability to approch 100 mm diameter bar with oil quenching.

34CrNiMo6 steel  equivalent grades:

34CrNiMo6 steel  mechanical properties:

Hardness:36～40HRC
Tensile strength:1100 MPa
Elongation A:12%,
Impact toughness:8kg/cm2

Effect of alloying elements on tempering transformation

Alloying elements of steel can slow down the decomposition and transformation speed of the quenched steel during tempering, increase the tempering resistance and improve the tempering stability, so that the hardness of the steel decreases with the increase of tempering temperature; under the action of some carbide forming elements, even secondary hardening occurs during tempering.

Carbide forming elements, especially strong carbide forming elements, can delay the process of martensite decomposition because they slow down the diffusion of carbon. The non carbide forming element Si increases the decomposition temperature of martensite because it can inhibit the growth of ε – carbide and delay the transformation of ε – carbide to Fe3C. The non carbide forming element Ni and the weak carbide forming element Mn have little effect on the decomposition of martensite.

Alloying elements can generally increase the transformation temperature range of retained austenite. In high alloy steel with high content of carbide forming elements, the retained austenite is very stable after quenching, and it does not decompose even when heated to 500-600 ℃. Instead, it transforms into martensite during cooling, making the hardness of steel increase on the contrary. This phenomenon is called “secondary hardening”.

With the increase of tempering temperature, the alloying elements will redistribute between α solid solution and carbide. The carbide forming elements will move from α solid solution to carbide until equilibrium. Therefore, with the increase of tempering temperature, the composition of carbides changes continuously, and the type of carbides also changes accordingly. The general trend is that the carbide is more stable from the unstable one. For example, chromium steel evolves from ε carbide to (Cr, Fe) 23c6 carbide during tempering.
In high alloy steel, the special carbides of these elements will be precipitated and precipitated when Ti, V, Mo, W are tempered in the temperature range of 500-600 ℃. Therefore, the hardness does not decrease but increases again, which is the so-called “precipitation type” secondary hardening phenomenon.

The higher the tempering temperature, the stronger the aggregation of special carbides. At this time, the hardness of the steel began to decline again. The strong carbide forming elements W, Mo, V and Ti have a large affinity with carbon, which can slow down the diffusion of carbon, even if the carbide is difficult to dissolve, it also makes the carbide difficult to gather. Generally speaking, at the same tempering temperature, the carbide dispersion of the alloy steel containing carbide forming elements is larger than that of the alloy steel containing non carbide forming elements at the same tempering temperature.

Alloying elements can keep the martensite morphology of α – solid solution to a higher tempering temperature, increase the recrystallization temperature of α – solid solution, and make the steel have higher tempering stability. Among them, Mo and W are the most significant.

The disadvantage of alloying elements on mechanical properties of quenched steel after tempering is tempering brittleness. Tempering brittleness usually occurs in the temperature range of 250-400 ℃ and 550-650 ℃, which significantly reduces the toughness of steel. The former is called low-temperature temper brittleness or the first temper brittleness, and the latter is called high-temperature temper brittleness or the second temper brittleness.

Some alloy structural steels, such as those containing chromium and manganese, appear the first kind of temper brittleness after tempering in the temperature range of 250-400 ℃. This temper brittleness can not be eliminated after tempering, so it is also called irreversible temper brittleness. There is no definite conclusion about the cause of the first temper brittleness. Recent tests show that carbide flakes precipitate along the boundary of lath martensite during tempering at 250-400 ℃ for medium and low carbon steels, which may be an important reason for low temperature tempering embrittlement; impurity elements such as sulfur, phosphorus, arsenic, antimony, tin, etc., as well as hydrogen and nitrogen promote the development of the first tempering embrittlement; the appearance of 360 ℃ tempering embrittlement of silicon manganese steel is related to the segregation of phosphorus along the original austenite grain boundary.

In order to avoid the first kind of temper brittleness, it is generally not tempered within the range of embrittlement temperature; sometimes it is necessary to temper at embrittlement temperature in order to ensure the required mechanical properties, isothermal quenching method can be adopted. In addition, the steel with alloying elements (such as silicon) that can move the brittle zone to high temperature can be selected to ensure high strength and high toughness after tempering at lower temperature. Recent tests have shown that the addition of Mo (about 0.3%) to Si Mn steel can greatly reduce or even completely inhibit the temper embrittlement at 360 ℃.

It must be pointed out that high carbon steel and alloy tool steel are relatively brittle after low temperature tempering, but they can not show low temperature tempering brittleness under general impact test conditions, and only under torsion and impact torsion test conditions can they show low temperature temper brittleness obviously; moreover, the test shows that their bending strength reaches the maximum value in the tempering brittle zone. According to this, the low temperature tempering temperature of high carbon steel and alloy tool steel does not have to avoid the tempering brittle zone. For tools and dies bearing bending moment, tempering at low temperature in the temper brittle zone is not only harmless, but may be beneficial.

The second type of temper embrittlement occurs mainly in alloy structural steels (quenched and tempered steels containing chromium, nickel, manganese and silicon). The results show that the second temper brittleness is related to the segregation of Ni, Cr and impurity elements sb, P and Sn in the steel to the original austenite grain boundary. The greater the segregation degree is, the more serious the temper embrittlement is. For example, the second temper brittleness of manganese steel and chromium steel increases obviously with the increase of impurity element content. The second temper brittleness can be eliminated by reheating the steel with the second temper brittleness to 600 ℃ or above, so that the segregation elements are fully dissolved and then rapidly cooled. Therefore, the second temper brittleness is also known as reversible temper brittleness.

The key to prevent the second temper embrittlement is how to eliminate the segregation of impurity elements to the grain boundary. In order to prevent the secondary element from segregation, the second impurity should be eliminated by adding proper amount of alloying elements to the grain boundary.

25CrMo4 Alloy steel

25CrMo4 steel has high hardenability, no temper brittleness, good weldability, little tendency of cold cracking, good machinability and cold strain plasticity. It is generally used in the state of quenching and tempering or carburizing and quenching.

25CrMo4 equivalent grade

25CrMo4 steel machanical properties

Tensile strength σ B (MPA): ≥ 885 (90)
Yield strength σ s (MPA): ≥ 685 (70)
Elongation δ 5 (%): ≥ 12
Reduction of area ψ (%): ≥ 50
Impact energy Akv (J): ≥ 35
Impact toughness value α kV (J / cm2): ≥ 98 (10)
Hardness: ≤ 212hb

20NiCr14 Alloy Steel

20NiCr14 steel has good hardenability and uniform strength in a large cross-section. After quenching and tempering, it has good comprehensive mechanical properties. Good machinability, moderate cold deformation plasticity and weldability. It has the sensitivity of forming white spots and the tendency of temper brittleness in high temperature tempering.

20NiCr14 equivalent grade

20NiCr14 steel machanical properties

Tensile strength σ B (MPA): ≥ 980
Conditional yield strength σ 0.2 (MPA): ≥ 835
Elongation δ 5 (%): ≥ 10
Reduction of area ψ (%): ≥ 55
Impact toughness value α Ku (J / cm2): ≥ 98
Hardness: 341 ～ 292hb

25Cr2MoV Alloy steel

25Cr2MoV has excellent corrosion resistance and cold working stamping performance, strong corrosion resistance to oxidizing acids (such as nitric acid), alkali solution and most organic and inorganic acids.

25Cr2MoV equivalent grade

GB3077-88

25Cr2MoV steel machanical properties

Tensile strength σ B (MPA): ≧1090

Yield strength σ s (MPA): ≧1042

Elongation δ 5 (%): ≧18

Reduction of area ψ (%): ≧63

Impact toughness value α Ku (J / cm2):≧ 213

17CrNiMo6/1.6587 Alloy Steel

is is a heat treatable, low alloy steel containing nickel, chromium and molybdenum as per DIN Germany standard which is known for its toughness and capability of developing high strength in the heat treated condition while retaining good fatigue strength.

17CrNiMo6 equivalent grade

Tensile strength：650 – 880MPa

Yield strength：350 – 550MPa

Elongation：8 – 25%

Fatigue：275 – 275MPa

20CrMnSi Alloy steel

20CrMnSi  has high strength and toughness, high plasticity in cold deformation and good stamping performance. It is suitable for cold drawing, cold rolling and other cold working processes. It has good weldability, low hardenability and high temper brittleness, so it is not used for carburizing or other heat treatment. If necessary, 20CrMnSi steel can also be used after quenching and tempering.  It is generally not suitable for carburizing or other heat treatment except in some cases.

20CrMnSi equivalent grade

20CrMnSi  properties

Tensile strength σ B (MPA): ≥ 785 (80)
Yield strength σ s (MPA): ≥ 635 (65)
Elongation δ 5 (%): ≥ 12
Reduction of area ψ (%): ≥ 45
Impact energy Akv (J): ≥ 55
Impact toughness value α kV (J / cm2): ≥ 69 (7)
Brinell hardness (hbs100 / 3000) (annealed or tempered at high temperature): ≤ 207