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Heat Treatment of Medium and Low Alloy Steel Castings

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

 

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 

 

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