Finding Values Using Fe-C Diagram for Materials Engineering Assignment

• Jimmojo

Jimmojo

New user has been reminded to post schoolwork problems in the Homework Help forums
Summary:: Need help with finding values using Fe c diagram

Hi, I'm doing a materials engineering assignment. In the assignment they require us to make 3 swords being given martenistic steel bars with dimensions 40x100x1000mm with a composition of Fe-0.76wt.%C (eutectoid composition). Sword A has final microhardness (HV) value of between 350-400(avg375), sword B between 550-700(avg625) and sword C between 900-950 (avg925). Based on these we are to determine and justify proper processes for making the sword.
what I am struggling with is:
Using the Fe-c diagram, I am not sure what the carbon percentage is for each sword and what temperature it would be on the diagram, based on the HV value. I've seen some answers with:
Sword A: 4.3% and 1150 degrees Celsius
Sword B: 0.8% and 725 degrees Celsius
Sword C: 0.18% with 1493 degrees Celsius,
But I don't understand where they come from. Would anyone be able to explain?
Thanks a lot

Answers and Replies

Welcome to PF.
You will need to link to the phase diagram you are using for the assignment, or post it to this thread. We will then be able to communicate more clearly.

This is the diagram. I am just unsure how they have gotten where A, B and C are on the diagram and what the heating temperature for each sword should be. I have looked around online and can't find a relationship between the microhardness (HV value) and the Carbon percentage or a relationship between the HV value and the required temperature. If anyone could explain how based on the values we have we're supposed to find the heating temperatures and carbon percentages on the Fe c diagram.
Also a bit confused as to why the A, B and C values on this diagram from an answer I've looked at has the swords at different carbon percentage values even though the task specified the materials to be of Fe -0.76wt.%C composition.
If anyone could explain, I'd really appreciate it.
thanks a lot

One sword will be wrought, worked in air to reduce the carbon content. One will be baked in carbon to increase the carbon content. One will be left with carbon as it was.

There are approximate equivalencies between the various hardness scales.
You know graphite is soft, while ferrite is hard.
Find hardness information for the iron-carbon alloys.

Find those compositions on your diagram, close to the initial C% composition.
Mark three points on the diagram at those compositions and temperatures.