1.Martensite formation in P91 steel is good or harmful effect in material?
2.How we reduce martensite formation in P91 steel ?
Which process help me to reduce martensite:
1. Pre-Heat
2. PWHT
3. Any other process ?
Amount of formation of martensite depends on the cooling rate and its Ms temperature, Try to find out it and based on that you can control required martensite .
Fisrt look at CCT diagram the using it you will see the phase transformation during the cooling form A1, and you can choose the heat treatment that will help you to avoid de Ms zone
Dear Akhilesh,
P91 steel is actually a ferritic martensitic steel also known as 9Cr-1Mo steel. Other versions are Mod-P91.
The commercial manufacturing includes hot rolling and tempering to as high as 1123K, which means almost maximum tetragonality of martensite is lost in formation of carbides. The remains which you must have seen in micro-structure is the lath feature of martensite.
I would like to correct few comments here, firstly that Martensite formation actually depends on T0 locus on CCT diagram, find the lecture of Prof. Bhadeshia for more info here: https://www.youtube.com/watch?v=HPTGHzaEaXI&list=PLAE1AC30FE698EFE7
Secondly there are ways to alter the phases but then it would not be a P91 steel :)
In order to do that you can do various combinations of thermo-mechanical or just heat/thermal treatment.
You can actually end up in bainitic steel by adding Si for instance, but of course you are not going to remelt it, so at most you can do it alter Ms temperature by mechanical subzero treatment to Md.
Moreover, you can change the grain size, but as you have written PWHT, are you talking about welding, are you going to weld it? then the scenario will totally change depending on filler and which area you study, weld or HAZ, it better to mention the application you are going for or objective of your study with the question.
All the best.
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