Steel Man: Quenched and Tempered Steel Performance Characteristics and Applications (Chapter Two)

Composition characteristics

(1) Medium carbon: the carbon mass fraction is generally between 0.25% and 0.50%, and the majority is 0.4%;

(2) Add elements to improve hardenability Cr, Mn, Ni, Si, etc. : In addition to improving hardenability, these alloy elements can also form alloy ferrite and improve the strength of steel. For example, the performance of 40Cr steel after tempering treatment is much higher than that of 45 steel;

(3) Add elements to prevent the second type of tempering brittleness: alloy tempered steel containing Ni, Cr and Mn, which is easy to produce the second type of tempering brittleness when tempered at high temperature and cooled slowly. The addition of Mo and W in steel can prevent the second type of tempering brittleness, and the appropriate content is: the mass fraction of Mo is 0.15% to 0.30%, or the mass fraction of W is 0.8% to 1.2%.

Classification and Application:

1, medium carbon steel: on behalf of steel grades 30, 35, 40, 45, ML30, ML35, ML40, ML45, has a more stable room temperature performance, for small and medium-sized structural parts, fasteners, drive shaft, gear and so on.

45 steel hot and cold processing performance is good, good mechanical properties, and low price, wide source, so widely used. Its biggest weakness is low hardenability, large cross-section size and relatively high requirements of the workpiece should not be used.

2, manganese steel: representing steel 40Mn2, 50Mn2. It has overheating sensitivity, high temperature tempering brittleness, water quenching easy cracking, and higher hardenability than carbon steel.

3, silicon manganese steel: on behalf of steel 35SiMn, 42SiMn. High fatigue strength, decarburization and overheating sensitivity and temper brittleness. It is used to manufacture gears, shafts, rotating shafts, connecting rods and worm with medium speed and medium and high load but little impact, and can also manufacture fasteners below 400℃.

4, boron steel: representing steel 40B, 45B, 50BA, ML35B. High hardenability, comprehensive mechanical properties are higher than carbon steel, and 40Cr is used for manufacturing parts and fasteners with small cross-section size.

5, manganese boron steel: representing steel 40MnB. Hardenability slightly higher than 40Cr, high strength, toughness and low temperature impact toughness, temper brittleness. 40MnB is commonly used to replace 40Cr to manufacture large-section parts and 40CrNi to manufacture small parts. 45MnB replaces 40Cr and 45Cr; 45Mn2B replaces 45Cr and partially replaces 40CrNi and 45CrNi as an important shaft, and ML35 MnB is also used for fastener production.

6, manganese vanadium boron steel: representing steel 20 MnVB, 40MnVB, The tempering performance and hardenability are better than 40Cr, the tendency to overheat is small, and there is temper brittleness. It is commonly used to replace 40Cr, 45Cr, 38CrSi, 42CrMo and 40CrNi to manufacture important tempered parts, and also used for small and medium-sized bolts below 10.9 level, ML20 MnVB.

7, manganese tungsten boron steel: representing steel 40MnWB. Good low temperature impact performance, no tempering brittleness. It is equivalent to 35CrMo and 40CrNi and is used to manufacture parts below 70mm.

8, silicon manganese molybdenum tungsten steel: representative of steel 35SiMn2MoW. High hardenability, calculated by 50% martensite, water quenching diameter 180, oil quenching diameter 100; The tendency of quenching cracking and tempering brittleness is small. It has high strength and toughness. Can replace 35CrNiMoA, 40CrNiMo, used to manufacture large section, heavy load shaft, connecting rod and bolt.

9, silicon manganese molybdenum tungsten vanadium steel: representative of steel 37SiMn2MoWVA. Water quenching diameter 100, oil quenching diameter 70; Good tempering stability, low temperature impact toughness, high high temperature strength, tempering brittleness is also small, used for manufacturing large section of shaft parts.

10, chromium steel: 40Cr and ML40Cr as representatives. Good hardenability, water quenching 28-60mm, oil quenching 15-40mm. High comprehensive mechanical properties, good low temperature impact toughness, low notch sensitivity, temper brittleness. Used in the manufacture of shafts, connecting rods, gears and bolts.

11, chromium silicon steel: on behalf of steel 38CrSi. Hardenability is better than 40Cr, the strength and low temperature impact are higher, the tempering stability is better, and the tempering brittleness tendency is larger. It is often used in the manufacture of 30-40mm shafts, bolts and gears with small modulus.

12, chromium molybdenum steel: representing steel 30CrMoA, 42CrMo, ML30CrMo, ML42CrMo. Water quenching 30-55mm, oil quenching 15-40mm; High room temperature mechanical properties and high high temperature strength, good low temperature impact; No temper brittleness. Used for manufacturing parts with large sections, high load bolts, gears and flanges and bolts below 500℃; Ducts and fasteners below 400℃. 42CrMo has higher hardenability than 30CrMoA and is used to make parts with higher strength and larger sections.

13, chromium manganese molybdenum steel: representing steel 40CrMnMo. Oil quenching diameter 80mm, with high comprehensive mechanical properties, good tempering stability. Used for manufacturing heavy load gear and shaft parts with large cross sections.

14, manganese molybdenum vanadium steel: representing steel 30Mn2MoWA. It has good hardenability: water quenching reaches 150mm, and the heart is composed of upper and lower bainite plus a small amount of martensite; Oil quenching 70mm, more than 95% of martensite in the heart; Good low temperature impact toughness, low notch sensitivity and high fatigue strength. For the manufacture of important parts under 80mm.

15, chromium manganese silicon steel: on behalf of steel 30CrMnSiA. Water quenching 40-60mm (95% martensite), oil quenching 25-40mm. High strength, impact toughness, temper brittleness. Used to manufacture high pressure blower blades, valve plates, clutch friction plates, shafts and gears.

16, chrome-nickel steel: representing steel 40CrNi and 45CrNi. Water quenching up to 40mm, oil quenching 15-25mm; Good comprehensive mechanical properties, good low temperature impact toughness, low tempering brittleness tendency. 30CrNi3A has high hardenability, good comprehensive mechanical properties, white spot sensitivity and temper brittleness. It is used to manufacture crankshaft, connecting rod, gear, shaft and bolt with large cross section.

17, chromium nickel molybdenum steel: representing steel 40CrNiMoA. It has excellent comprehensive mechanical properties, high low temperature impact toughness, low notch sensitivity and no temper brittleness. It is used to manufacture large crankshafts, shafts, connecting rods, gears, bolts and other parts with large forces and complex shapes.

18, chromium nickel molybdenum vanadium steel: on behalf of steel 45CrNiMoVA. High strength, good tempering stability, oil quenching up to 60mm (95% martensitic). It is used to manufacture elastic shafts and torsion shafts of heavy-duty vehicles under vibration loads.