Compressive stresses in induction treatment?
Compressive stresses in induction treatment?
(OP)
We manufacture a part approximately 3 mm thick (obtaine by fine blanking) with 3 zones surface hardened (high frequency treatment) for years.
We thought that this kind of treatment lead gave always a compressive state of the heat treated zones until we carried out stress measurements because of micro-crack problems.
We are now very surprise by the results : the presence of a layer of tension stress of about 10 µm depth.
Could anyone bring us his experience.... Thanks
We thought that this kind of treatment lead gave always a compressive state of the heat treated zones until we carried out stress measurements because of micro-crack problems.
We are now very surprise by the results : the presence of a layer of tension stress of about 10 µm depth.
Could anyone bring us his experience.... Thanks





RE: Compressive stresses in induction treatment?
RE: Compressive stresses in induction treatment?
RE: Compressive stresses in induction treatment?
How was the residual stress field measured?
RE: Compressive stresses in induction treatment?
Can a difference in microstructure of the present material be observed vs. material of the previously successful process?
http://www.welding-advisers.com/
RE: Compressive stresses in induction treatment?
Several things have been mentioned that are pertinent, but it is still necessary to know more about the details of the shape/geometry, and exactly how the part is induction heated and quenched. One thing to keep in mind is that the compressive residual stress pattern is produced by carburizing, but not always by induction hardening. This depends on the geometry and thickness distribution, the nature of the quench flow and impingement on the part, and how the 3 different hardening zones interact. Quite a complex problem. Are you working with your induction vendor and quench supplier?
RE: Compressive stresses in induction treatment?
The 3 zones are heat treated in 2 times but these zones are sufficiently distant to avoid any problem of thermal affected zone.
The material of the part is 65Cr3. And the treatment consists in a high frequency treatment with an inductor in the shape of 2 pins (heating from the faces), quenched with water mixed with a polymer. We use a delayed quench (1.8s)to minimize cracks problems
The part is tempered at 150°C.
The microhardness of the outermost layer is higher than the layer further inside and the microstructure is fine martensite.
RE: Compressive stresses in induction treatment?
RE: Compressive stresses in induction treatment?
RE: Compressive stresses in induction treatment?
If you have any loss of alloying elements at the surface sufficient to produce a change in Ms and Mf temperatures a thin surface can transform before the main part of the case. When the main part of the case goes through its transformation it will cause a tensile residual stress to be developed in the thin previously transformed surface layer as well as in the substrate material.
RE: Compressive stresses in induction treatment?
In fact, I beleived that the high frequency treatment was short enough to avoid any decarburation problems in depth.
But to complete the description of our problem, I have to mentionned the "toad skin" of the heat treated zone (without affected zone under skin)
RE: Compressive stresses in induction treatment?
It is interesting to note also a high compresive residual stress before the induction hardening corresponding of the fine-blanking operation (-800 MPa). Could this compressive residual field be responsible for the tension stress by repartition phenomenon?
On other point which could be very important: the part is heated from the faces and cooled perpendiculary by a double-shower ==> the angle between the heated-zone and the spray holes is about 90°. We are principaly working on this parameter and the % of the cooling polymer