High Temperature Mechanical Properties of 00Cr18Ni18Mo5 Austenitic Stainless Steel
High temperature mechanical properties of steels, particularly austenitic stainless steels, are of importance to the engineering industry in deciding the suitability of use of materials in service. As the temperature increases above ambient, a range of phenomena can be observed, including thermal expansion, change of mechanical properties, fatigue and the development of creep. The effect of temperature on the ductile-brittle transition of steels is also significant. Therefore, in order to better understand the high temperature properties of 00Cr18Ni18Mo5 austenitic stainless steels, the following paper will provide an overview of such properties as well as evaluating their effects on serviceability.
The major components of the 00Cr18Ni18Mo5 austenitic stainless steel are iron, chromium, nickel, molybdenum and nitrogen. These various elements provide the individual characteristics of the alloy, which make it suitable for application in high temperature service. The addition of nickel and molybdenum over conventional stainless steels provides improved creep strength, fatigue strength and chromium oxidation resistance. The presence of chromium also provides additional corrosion protection due to its high oxidation potential.
The thermal expansion of 00Cr18Ni18Mo5 austenitic stainless steel follows a linear pattern from room temperature to about 700°C. As the temperature increases beyond this, phonon-assisted transport of phonons in the crystal lattice reduces the thermal expansion rate to a lower level. The thermal expansion rate of 00Cr18Ni18Mo5 is typical of other stainless steels at temperatures up to 1000 oC.
In terms of its young modulus, 00Cr18Ni18M05 has a similar value to austenitic stainless steels at room temperature. It is higher than that of carbon steels of equivalent strength and it has been found to be insensitive to temperature up to 1000 oC. The yield strength of 00Cr18Ni18Mo5 austenitic stainless steel decreases with increasing temperature. The yield strength decreases more quickly when the temperature exceeds 800 oC. This suggests that a sufficiently high temperature would reduce the strength of the steel below that needed for service.
The creep-resistant properties of 00Cr18Ni18Mo5 austenitic stainless steel have been studied in detail. It has been found to be among the best austenitic stainless steels for use in hot service due to its relatively high creep strength. The creep strength of 00Cr18Ni18Mo5 increases with increasing temperature up to about 600°C, then slowly drops with further increase in temperature. The fatigue strength of 00Cr18Ni18Mo5 austenitic stainless steel has similar properties to the creep strength, showing an initial increase in temperature, followed by a decrease above 600°C.
In terms of its oxidation resistance, 00Cr18Ni18Mo5 austenitic stainlesssteel is superior compared to other austenitic stainless steels. It is capable of resisting corrosion also, due to its high chromium content. At temperatures up to 1000 oC, the oxide layer is protective. However, longer exposure to heat will lead to loss of sheet integrity.
In conclusion, 00Cr18Ni18Mo5 austenitic stainless steel is a suitable alloy for use in applications in high temperature service. The addition of nickel and molybdenum provides improved creep strength, fatigue strength and chromium oxidation resistance, whilst its thermal expansion properties are similar to other stainless steels. The steel shows relatively high creep and fatigue strength up to 600°C and a good oxidation resistance up to 1000°C. In order to maximise the serviceability of the material, care should be taken not to exceed this temperature for lengthy periods.
