Mechanical properties of modified cast martensitic stainless steel CA6NM with addition of molybdenum and nitrogen

Abstract

Martensitic stainless steel is widely used for geothermal turbine blade. Herein, we study the mechanical properties of cast martensitic stainless steel CA6NM as geothermal turbine blade material with addition of alloying element of molybdenum and nitrogen. Three different material were used in this experiment: (i) CA6NM with 1 wt.% of molybdenum without addition of nitrogen, (ii) CA6NM with 2 wt.% molybdenum without addition of nitrogen, (iii) CA6NM with 2 wt.% of molybdenum and 0.1 wt.% of nitrogen. Thus, materials were heat treated in two parameters: (i) single tempered process at 670°C for 3 h, (ii) double tempered process at 670 °C for 3 h and continued with 620 °C for 3 h. Tempered materials were cooled by air cooling. As cast material and heat-treated materials were tested in tension test, wear test and hardness test. The result reveal that the addition of 2 wt.% of molybdenum and 0.1 wt.% of nitrogen in CA6NM would give slightly optimization effect to the mechanical properties of the material. However, the effect of molybdenum and nitrogen addition become less effective on CA6NM mechanical properties enhancement after the material heat treated by single and double temper process.