Failed Champy impact tests
Failed Champy impact tests
(OP)
I have some engineering componments made of low carbon low alloy steels (0.13%C,0.25Si, 1.1Mn,0.6Ni,0.15Cr)
The materials are cutted from forged bar and machined into different size and shape. This is followed by heat treatments of normalising, austenlising(940C), water quenching and tempering at 650C. Time for each heat treatment is 1hr/inch.
The problem is that for componments larger then 6 inchs, the thinner sections (only 1 inch) always failed the impact tests.
Any idea of why is that?
Thanks in advance!
The materials are cutted from forged bar and machined into different size and shape. This is followed by heat treatments of normalising, austenlising(940C), water quenching and tempering at 650C. Time for each heat treatment is 1hr/inch.
The problem is that for componments larger then 6 inchs, the thinner sections (only 1 inch) always failed the impact tests.
Any idea of why is that?
Thanks in advance!





RE: Failed Champy impact tests
Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)
RE: Failed Champy impact tests
In the thick positions results are so good as: 200J, 204J, and 218J.
RE: Failed Champy impact tests
Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)
RE: Failed Champy impact tests
RE: Failed Champy impact tests
Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)
RE: Failed Champy impact tests
Using slow quench method may not be good, as the thick position still need a high strength.
Can you give me an example of how thinner sction can be insulated?
Many thanks
RE: Failed Champy impact tests
So I doubt that you got uniform microstructure. To me, the Charpy at thin sections seems reasonable to me for a tempered martensite, but not the Charpy of thick section which are more like from a majority of ferrite.
So can you heat treat the bar first and then follow the machining. Actually this way you can have better dimensional control.
RE: Failed Champy impact tests
microstructure is more uniform. But the tesile strength at the thinner section is not high enough as required.
thanks
RE: Failed Champy impact tests
I would strongly suggest before you make any process changes to have the CVN samples that exhibited low toughness and some of the CVN samples that exhibited high toughness sent to a metallurgical lab for metallographic evaluation (hardness and microstructure).
You can't afford to speculate on this, and the microstructure/hardness evaluation will be key to identifying any process changes.
RE: Failed Champy impact tests
RE: Failed Champy impact tests
RE: Failed Champy impact tests
If it is established by proper metallurgical evaluation that the prior austenite grain size is indeed too large in the thinner sections of the this component, the austenitizing hold time will either need to be optimzed or possibly as mentioned above, Q&T the forged bar and machine the components after final heat treatment.
RE: Failed Champy impact tests
Of the thick section?
What is the required hardness?
It is possible that a 40 C increase in tempering temperature will increase the impacts enough while still maintaining the required hardness.
rp