20Cr vs. 20CrMo

Attribute	20Cr	20CrMo
Chemical Composition	20Cr: 0.18-0.24% C, 0.17-0.37% Si, 0.50-0.80% Mn, 0.80-1.10% Cr	20CrMo: 0.17-0.23% C, 0.17-0.37% Si, 0.40-0.70% Mn, 0.90-1.20% Cr, 0.15-0.25% Mo
Hardness	20Cr: 187 HB	20CrMo: 197 HB
Tensile Strength	20Cr: 785 MPa	20CrMo: 885 MPa
Yield Strength	20Cr: 540 MPa	20CrMo: 685 MPa
Applications	20Cr: Gears, shafts, bolts	20CrMo: Axles, crankshafts, gears

Introduction

When it comes to choosing the right material for a specific application, it is important to consider the properties and characteristics of different types of steel. In this article, we will compare the attributes of two commonly used steels - 20Cr and 20CrMo. Both of these steels belong to the same family of low-alloy steels, but they have distinct differences that make them suitable for different purposes.

Chemical Composition

20Cr is a low-alloy steel that contains 0.18-0.24% carbon, 0.17-0.37% silicon, 0.50-0.80% manganese, 0.70-1.00% chromium, and traces of other elements. On the other hand, 20CrMo is also a low-alloy steel but with a higher carbon content of 0.17-0.24%, 0.17-0.37% silicon, 0.40-0.70% manganese, 0.80-1.10% chromium, and 0.15-0.25% molybdenum. The addition of molybdenum in 20CrMo enhances its hardenability and strength compared to 20Cr.

Strength and Hardness

20Cr has a lower carbon content compared to 20CrMo, which results in lower strength and hardness. The tensile strength of 20Cr is typically around 785 MPa, while the tensile strength of 20CrMo can reach up to 1080 MPa. Similarly, the hardness of 20Cr is around 197 HB, whereas the hardness of 20CrMo is higher at approximately 229 HB. This makes 20CrMo more suitable for applications that require higher strength and hardness.

Heat Treatment

Both 20Cr and 20CrMo can be heat treated to improve their mechanical properties. However, the heat treatment process for 20CrMo is more complex due to the presence of molybdenum. 20CrMo is typically quenched and tempered to achieve the desired strength and toughness. On the other hand, 20Cr can be easily heat treated by normalizing or annealing to improve its machinability and ductility.

Weldability

When it comes to weldability, 20Cr is easier to weld compared to 20CrMo. The higher carbon content and the presence of molybdenum in 20CrMo can lead to cracking during welding if proper precautions are not taken. On the other hand, 20Cr can be welded using conventional welding techniques without significant issues. This makes 20Cr a more preferred choice for applications that require welding.

Applications

Due to its higher strength and hardness, 20CrMo is commonly used in the manufacturing of gears, shafts, and other components that require high tensile strength and wear resistance. On the other hand, 20Cr is often used in applications where weldability and machinability are more important, such as in the production of bolts, nuts, and studs. Both steels have their own set of advantages and are chosen based on the specific requirements of the application.