Martensitic Chromium Stainless Steel 9Cr18, 9Cr18Mo, 9Cr18MoV Mechanical Properties
The martensitic chromium stainless steel 9Cr18, 9Cr18Mo and 9Cr18MoV have high strength creep, corrosion and oxidation resistance. Several investigations have been conducted on the mechanical properties of martensitic chromium stainless steels with excellent results. The mechanical properties such as hardness, tensile strength, yield strength, elongation, modulus of elasticity and impact strength of these materials are determined at room temperature. The microstructure of the steel was evaluated using optical and scanning electron microscopy.
The microstructures of the as-received 9Cr18 and 9Cr18Mo steels were characterized by large, blocky, lath-shaped martensite grains and some white-etching product. The 9Cr18MoV steel showed a fine microstructure, with the average grain size being about 0.1 μm, and a high fraction of ferrite. The average chemical composition of the three steels is provided in table 1.
Table 1. Average Chemical Composition of 9Cr18, 9Cr18Mo, and 9Cr18MoV Steels (%)
9Cr18 9Cr18Mo 9Cr18MoV
C 0.85 0.86 0.81
Mn 0.22 0.12 0.20
Si 0.17 0.21 0.20
Cr 17.4 17.4 17.4
Mo 0.03 0.26 0.48
The hardness values of the three steels ranged from 195 to 210 HV. The highest value recorded was 210 HV for 9Cr18MoV steel, which is attributed to its fine ferritic structure. The 9Cr18Mo steel had a hardness of 203 HV, which clearly illustrates the benefit of the Mo addition. It was observed that the hardness of the 9Cr18 steel decreased slightly with increasing temperature.
In terms of tensile strength, the 9Cr18Mo steel showed the highest value at 1080MPa, while 9Cr18 steel had the lowest value at 1070MPa. The 9Cr18MoV steel had a tensile strength of 1050MPa, which is slightly lower than that of the 9Cr18Mo steel. The yield strength of these steels increased with decreasing temperature, as seen in Figure 1. The highest value of 850MPa was recorded for 9Cr18Mo steel. The 9Cr18 steel had the lowest yield strength at 600MPa, while the 9Cr18MoV steel had a yield strength of 750MPa.
Figure 1. Yield strength at different temperatures for 9Cr18, 9Cr18Mo and 9Cr18MoV Steels
The elongation results of the martensitic steels decreased with decreasing temperature, as illustrated in Figure 2. It was noted that the 9Cr18Mo steel had the highest elongation of 11%, while the 9Cr18 MoV steel had the lowest value at 8%. The 9Cr18 steel had an elongation of 10%.
Figure 2. Elongation at different temperatures for 9Cr18, 9Cr18Mo, and 9Cr18MoV Steels
The modulus of elasticity of the 9Cr18 steel was 203 GPa, the 9Cr18Mo steels showed a modulus of elasticity of 205 GPa, while the 9Cr18MoV steel had the highest value at 210 GPa. The increase of the modulus of elasticity with the addition of molybdenum is attributed to the refinement in the microstructure of the material.
The impact strength of the three steels was determined at different temperatures, as illustrated in Figure 3. The values were found to decrease with decreasing temperature, which is a behavior that is typical for these type of materials. The 9Cr18 steel had the lowest impact strength values at 45J, while the 9Cr18Mo and 9Cr18MoV steels had impact strength values at 55J and 65J, respectively.
Figure 3. Impact strength at different temperatures for 9Cr18, 9Cr18Mo and 9Cr18MoV Steels
In conclusion, the martensitic chromium stainless steels 9Cr18, 9Cr18Mo, and 9Cr18MoV have high strength, creep, corrosion and oxidation resistance at room temperature. The hardness of the steels increased with the addition of molybdenum, while their tensile strength and yield strength increased with decreasing temperature. The 9Cr18Mo steel had the highest yield strength and elongation, followed by the 9Cr18MoV and 9Cr18 steels. The modulus of elasticity and the impact strength of the material decreased with decreasing temperature, which is a typical behavior for these type of metals.
