Improving the quality of high alloy CA6NM stainless steel castings

Date
2015-01-01
Authors
Ganesan, Rubesh
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Abstract

This paper describes two studies performed on CA6NM martensitic stainless steel. The goal of the first study was to investigate claims that CA6NM hardness could be held below Rockwell C (Rc) 23 as per NACE requirements using an ice water quench. This research was performed on three grades of CA6NM, namely, A487 Class A, A487 Class B and A743 in both as-received and as-cast conditions. A double tempering at 667ºC and 607ºC followed by different cooling techniques after solutionizing and tempering was employed to test the hypothesis. The holding time for each tempering step was also changed to study the changes in hardness. Hardness was found to decrease on each tempering and no special effect was found on using different cooling techniques. Lower hardness values were only found to be related to the amount of carbon in the three grades studied.

The goal of the second study was to analyze the possible use of cold spray as a means of porosity repair in CA6NM stainless steel and to determine the effect on the hardness of the material. Hardness and microstructure were studied for both the cold sprayed and substrate surfaces and it was found that while the cold sprayed material was slightly higher there was no major change in the hardness and microstructures of the substrate. However, improper bonding and cracks seen in the cold spray material raise concerns that the material may spall from the surface during use. Further study is needed to determine whether this could happen and whether cold spray is a truly viable alternative to weld repair.

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Keywords
Material Science and Engineering, CA6NM, cold spray, hardness, Stainless steel
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