Carburizing 1018 same or different as 1117?

[jsalomon]

Hello,

I'm a sales engineer at a new heat treatment plant in northern Mexico.
We've been running some tests for a big client that will keep one of our lines running 24/7; they came here to run the first carburizing test with some machined parts but the results didn't fall inside the specs.

We've been doing a simulation of the process with some 1018 bars we bought (because here in Mexico 1117 steel is not a common steel and cannot be obtained very easily) but we've obtained results in the lower spec for case depth (0.024") or even lower.

The chemical composition of 1018 and 1117 steels are:
1018: 0.15 to 0.20 C, 0.60 to 0.90 Mn, 0.040 P max, 0.050 S max
1117: 0.14 to 0.20 C, 1.00 to 1.30 Mn, 0.040 P max, 0.08 to 0.13 S

The main difference is that 1117 steel is resulfurized and that has more Mn concentration (which enhances quenchability).

My question is, is it accurate to trust the 1018 results if were falling in the lower spec (or even lower)? or would the slight changes in the chemical composition of 1117 steel would make a big difference in the results?

Thanks a lot.

 

[swall]

It is hard to answer your question without knowing the case depth spec and how case depth is defined. If you are doing a microhardness check on a cross section and defining case depth as Rc 50, you will get different results for the 1018 compared to the 1117, as you already seem to understand based on your comment about the greater hardenability of 1117 because of the Mn content. And is this straight carburizing rather than carbonitriding? I ask this because it is common to carbonitride 1117 steel.

 

[jsalomon]

Thanks for your answer.

Sorry I didn't specify the case depth spec and how it's defined.
As you mentioned a microhardness test is performed on a cross section of the part defining a case depth as 50 HRC, the hardness must be greater than 50 HRC between 0.024" and 0.034"; after the treatment the parts receive a finishing operation.

We considered the option of carbonitriding as well because it's the most common practice, but our client's client must validate the change of the process first and this might take a while, so we are testing with their current process (our client heat treats as well, but they are outsourcing part of their production in our plant) so they can validate it and later on we will run some carbonitriding tests.

Hope I made myself clear.
Thanks!