Medium and low alloy steels are a big group of alloy steels with alloying elements (mainly chemical elements such as silicon, manganese, chromium, molybdenum, nickel, copper and vanadium) content of less than 8%. Medium and low alloy steel castings have good hardenability, and good comprehensive mechanical properties can be obtained after proper heat treatment.
Heat Treatment Specifications of Low and Medium Alloy Steel Castings
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| Grade | Steel Category | Specifications of Heat Treatment | |||
| Treatment Method | Temperature / ℃ | Cooling Method | Hardness / HBW | ||
| ZG16Mn | Manganese Steel | Normalizing | 900 | Cooling in air | / |
| Tempering | 600 | ||||
| ZG22Mn | Manganese Steel | Normalizing | 880 - 900 | Cooling in air | 155 |
| Tempering | 680 - 700 | ||||
| ZG25Mn | Manganese Steel | Annealing or Tempering | / | / | 155 - 170 |
| ZG25Mn2 | Manganese Steel | 200 - 250 | |||
| ZG30Mn | Manganese Steel | 160 - 170 | |||
| ZG35Mn | Manganese Steel | Normalizing | 850 - 860 | Cooling in air | / |
| Tempering | 560 - 600 | ||||
| ZG40Mn | Manganese Steel | Normalizing | 850 - 860 | Cooling in air | 163 |
| Tempering | 550 - 600 | Cooling in furnace | |||
| ZG40Mn2 | Manganese Steel | Annealing | 870 - 890 | Cooling in furnace | 187 - 255 |
| Quenching | 830 - 850 | Cooling in oil | |||
| Tempering | 350 - 450 | Cooling in air | |||
| ZG45Mn | Manganese Steel | Normalizing | 840 - 860 | Cooling in air | 196 - 235 |
| Tempering | 550 - 600 | Cooling in furnace | |||
| ZG45Mn2 | Manganese Steel | Normalizing | 840 - 860 | Cooling in air | ≥ 179 |
| Tempering | 550 - 600 | Cooling in furnace | |||
| ZG50Mn | Manganese Steel | Normalizing | 860 - 880 | Cooling in air | 180 - 220 |
| Tempering | 570 - 640 | Cooling in furnace | |||
| ZG50Mn2 | Manganese Steel | Normalizing | 850 - 880 | Cooling in air | / |
| Tempering | 550 - 650 | Cooling in furnace | |||
| ZG65Mn | Manganese Steel | Normalizing | 840 - 860 | / | 187 - 241 |
| Tempering | 600 - 650 | ||||
| ZG20SiMn | Silico-Manganese Steel | Normalizing | 900 - 920 | Cooling in air | 156 |
| Tempering | 570 - 600 | Cooling in furnace | |||
| ZG30SiMn | Silico-Manganese Steel | Normalizing | 870 - 890 | Cooling in air | / |
| Tempering | 570 - 600 | Cooling in furnace | |||
| Quenching | 840 - 880 | Cooling in oil/water | / | ||
| Tempering | 550 - 600 | Cooling in furnace | |||
| ZG35SiMn | Silico-Manganese Steel | Normalizing | 860 - 880 | Cooling in air | 163 - 207 |
| Tempering | 550 - 650 | Cooling in furnace | |||
| Quenching | 840 - 860 | Cooling in oil | 196 - 255 | ||
| Tempering | 550 - 650 | Cooling in furnace | |||
| ZG45SiMn | Silico-Manganese Steel | Normalizing | 860 - 880 | Cooling in air | / |
| Tempering | 520 - 650 | Cooling in furnace | |||
| ZG20MnMo | Manganese Molybdenum Steel | Normalizing | 860 - 880 | / | / |
| Tempering | 520 - 680 | ||||
| ZG30CrMnSi | Chromium Manganese Silicon Steel | Normalizing | 800 - 900 | Cooling in air | 202 |
| Tempering | 400 - 450 | Cooling in furnace | |||
| ZG35CrMnSi | Chromium Manganese Silicon Steel | Normalizing | 800 - 900 | Cooling in air | ≤ 217 |
| Tempering | 400 - 450 | Cooling in furnace | |||
| Normalizing | 830 - 860 | Cooling in air | / | ||
| 830 - 860 | Cooling in oil | ||||
| Tempering | 520 - 680 | Cooling in air/furnace | |||
| ZG35SiMnMo | Silico-manganese-molybdenum steel | Normalizing | 880 - 900 | Cooling in air | / |
| Tempering | 550 - 650 | Cooling in air/furnace | |||
| Quenching | 840 - 860 | Cooling in oil | / | ||
| Tempering | 550 - 650 | Cooling in furnace | |||
| ZG30Cr | Chrome Steel | Quenching | 840 - 860 | Cooling in oil | ≤ 212 |
| Tempering | 540 - 680 | Cooling in furnace | |||
| ZG40Cr | Chrome Steel | Normalizing | 860 - 880 | Cooling in air | ≤ 212 |
| Tempering | 520 - 680 | Cooling in furnace | |||
| Normalizing | 830 - 860 | Cooling in air | 229 - 321 | ||
| Quenching | 830 - 860 | Cooling in oil | |||
| Tempering | 525 - 680 | Cooling in furnace | |||
| ZG50Cr | Chrome Steel | Quenching | 825 - 850 | Cooling in oil | ≥ 248 |
| Tempering | 540 - 680 | Cooling in furnace | |||
| ZG70Cr | Chrome Steel | Normalizing | 840 - 860 | Cooling in air | ≥ 217 |
| Tempering | 630 - 650 | Cooling in furnace | |||
| ZG35SiMo | Silicon Molybdenum Steel | Normalizing | 880 - 900 | / | / |
| Tempering | 560 - 580 | ||||
| ZG20Mo | Molybdenum Steel | Normalizing | 900 - 920 | Cooling in air | 135 |
| Tempering | 600 - 650 | Cooling in furnace | |||
| ZG20CrMo | Chrome-molybdenum steel | Normalizing | 880 - 900 | Cooling in air | 135 |
| Tempering | 600 - 650 | Cooling in furnace | |||
| ZG35CrMo | Chrome-molybdenum steel | Normalizing | 880 - 900 | Cooling in air | / |
| Tempering | 550 - 600 | Cooling in furnace | |||
| Quenching | 850 | Cooling in oil | 217 | ||
| Tempering | 600 | Cooling in furnace | |||
The Characteristics of Heat Treatment of Medium and Low Alloy Steel Castings:
1. Medium and low alloy steel castings are mostly used in machinery industries such as automobiles, tractors, trains, construction machinery, and hydraulic systems. These industries require castings with good strength and toughness. For castings requiring a tensile strength of less than 650 MPa, normalizing + tempering heat treatment is generally used; for medium and low alloy steel castings that require a tensile strength of greater than 650 MPa, quenching + high temperature tempering heat treatment is used. After quenching and tempering, the metallurgical structure of the steel casting is tempered sorbite, so as to obtain higher strength and good toughness. However, when the shape and size of the casting are not suitable for quenching, normalizing + tempering should be used instead of quenching and tempering.
2. It is better to perform normalizing or normalizing + tempering pretreatment before quenching and tempering of medium and low alloy steel castings. In this way, the crystal grain of the steel casting can be refined and the structure uniform, thereby enhancing the effect of the final quenching and tempering treatment, and also helping to avoid the adverse effects of the casting stress inside the casting.
3. After the quenching treatment, the medium and low alloy steel castings should obtain the martensite structure as much as possible. In order to achieve this goal, the quenching temperature and cooling medium should be selected according to the cast steel grade, hardenability, casting wall thickness, shape and other factors.
4. In order to adjust the quenching structure of the cast steel and eliminate the quenching stress, the medium and low alloy steel castings should be tempered immediately after quenching.
5. Under the premise of not reducing the strength of steel castings, medium-carbon low-alloy high-strength steel castings can be toughened. Toughening treatment can improve the plasticity and toughness of steel castings.
Temperature and Hardness of Low Alloy Steel after QT Heat Treatment
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| Low and Medium Alloy Steel Grade | Quenching Temperature / ℃ | Tempering Temperature / ℃ | Hardness / HBW |
| ZG40Mn2 | 830 - 850 | 530 - 600 | 269 - 302 |
| ZG35Mn | 870 - 890 | 580 - 600 | ≥ 195 |
| ZG35SiMnMo | 880 - 920 | 550 - 650 | / |
| ZG40Cr1 | 830 - 850 | 520 - 680 | / |
| ZG35Cr1Mo | 850 - 880 | 590 - 610 | / |
| ZG42Cr1Mo | 850 - 860 | 550 - 600 | 200 - 250 |
| ZG50Cr1Mo | 830 - 860 | 540 - 680 | 200 - 270 |
| ZG30CrNiMo | 860 - 870 | 600 - 650 | ≥ 220 |
| ZG34Cr2Ni2Mo | 840 - 860 | 550 -600 | 241 - 341 |
Post time: Jul-31-2021