Physical Properties of Martensitic Chromium Stainless Steel 9Cr18, 9Cr18Mo, 9Cr18MoV

Physical Properties of Martensitic Chromium Stainless Steels 9Cr18, 9Cr18Mo, and 9Cr18MoV

Stainless steels are alloys of iron and chromium and are used for applications requiring superior corrosion and wear resistance. The three basic types of stainless steel are ferritic, austenitic and martensitic. In this paper, we will discuss the properties of the three martensitic stainless steels 9Cr18, 9Cr18Mo, and 9Cr18MoV, which are widely used in various engineering applications.

Martensitic stainless steels are characterized by a relatively low chromium content and high carbon percentage, usually 0.15-1.2% C and 11.5-18% Cr. They can be hardened and strengthened through heat treatment and have superior corrosion, wear and fatigue resistance. These steels tend to have higher machinability than austenitic and ferritic types and are used for a variety of applications such as cutlery, surgical instruments and automotive components.

The three martensitic steels 9Cr18, 9Cr18Mo and 9Cr18MoV have nearly identical chemical compositions, with the main difference being the level of molybdenum and vanadium which are used to improve corrosion resistance. The steel 9Cr18 has 18% chromium and 0.14-0.2% carbon, 9Cr18Mo has 18% chromium and 0.15-0.25% carbon, while 9Cr18MoV has 18% chromium, 0.16-0.25% carbon, 1-1.3% molybdenum, and 0.15-0.3% vanadium.

The three steel grades exhibit similar physical and mechanical properties. All three steels have a modulus of elasticity of about 193 GPa and average yield and tensile strengths of about 300 to 1000 MPa. Density, thermal conductivity and specific heat are all similar for the three grades, but 9Cr18 has slightly higher values. 9Cr18Mo and 9Cr18MoV also performs slightly better under corrosive conditions than 9Cr18.

The steels also have similar microstructures and linear coefficients of thermal expansion (CTE) of about 10.5 to 12.5 × 10^-6/K. The martensitic microstructure gives these steels a higher hardness than other stainless steels with similar chemical compositions and a good combination of strength, wear and corrosion resistance.

In summary, the martensitic stainless steels 9Cr18, 9Cr18Mo and 9Cr18MoV have nearly identical physical and mechanical properties, with the main difference being their performance under various corrosive conditions. All three steels offer a good combination of strength and wear resistance, with 9Cr18Mo and 9Cr18MoV having a slightly higher resistance to corrosion. They are used for a variety of engineering applications including cutlery, surgical instruments and automotive components.

9Cr18, 9Cr18Mo and 9Cr18MoV martensitic stainless steels are widely used in knives and scissors, tools, pumps and other mechanical products. All these stainless steels have Cr content of 17-19%.

9Cr18 has a high hardness, good wear resistance and good corrosion-resisting property, thus it is often used as cutting and stretching tools such as razor blade and scissors. 9Cr18Mo is an upgraded version of 9Cr18 with higher Mo content, thus it has improved corrosion resistance and better processing performance. And 9Cr18MoV has even higher Mo and V content, the corrosion-resisting property is further enhanced.

In comparison, 9Cr18 has the highest hardness reaching HRC56-58, while 9Cr18Mo and 9Cr18MoV have nearly the same hardness HRC53-56. The yield strength of 9Cr18, 9Cr18Mo and 9Cr18MoV are 1050 MPa, 1200 MPa and 1120 MPa respectively. The impact toughness and tensile strength are highest for 9Cr18MoV, medium for 9Cr18Mo, and lowest for 9Cr18, which is between 250 and 300 MPa and 380-430 MPa respectively.

All these three stainless steels have excellent comprehensive performance and are relatively economical, thus are widely used in the field of mechanical product manufacturing.