Deformation After Heat Treatment

Why do you not expect the material to move after heat treatment?

Do you think that the residual stresses in the steel from being stamped do not exist?

Do you think that these stresses will remain unchanged when you heat treat them?

What do you mean by heat treatment?

Temperatures and process description please.

Milo

It can be also a problem of part geometry and how it is cooled. Cooling first a narrow part could lead to bigger deformations due to the generated temperature gradient in the part itself. Could you provide a drawing, in which position it is cooled, in which medium and how the deformations look? May be a picture before and after ?

Above you can see the photos of the sheet metal part before and after heat treatement. The upper photo shows the deformation after heat treatment. The heat treatment is a quenching operation in a continuous heat treatment furnace.

The hardness becomes 50 HRc(150) after heattreatment. Therefore it is not feasible to form the part after heattreatment. I proposed a stress relief heat treatment after forming, however the heat treatment supplier refused my proposal stating that in a quenching furnace the effects of such an operation will vanish.

Thanks.

Continuous heat treatment furnace so the parts are just placed on the moving hearth?

The photo and the 40% frequency tells me that the failure of these parts to be laying flat on the hearth is a likely cause. Being stacked in a bunch means both differences in mass so differences in heating rate upon heating, resulting in parts bowing aws they are leaning and their weight pulls them down as the material is first stress relieved and finally recrystallixzes upon austenitizing.

If the parts so stacked are also entaangled going into quench that compounds he problem.

My first trial would be to hand stack the parts one layer only on the hearth and look at failure rate.

Yes I know heat treater will balk @ labor cost , but for trial, it will tell you that the process of dumping parts on moving hearth in random stack/pile is the root cause. Milo

"↑" If you consider the arrow as the moving direction of the band I would suggest you make a trial with the parts in shown 3 positions so that they fall in the quenching bath with different sides down first. The rate of deformed parts and the magnitude of deformation could give you a hint about orientation. I think but I may be wrong -as usual- that for the part geometry you should find the optimal position to enter the cooling bath. The subcontractor is right since the temperature reached in the oven is high enough to eliminate all residual strains in the material but the speed with which the temperature goes up could be a reason for a deformation. I would also look at the number of parts/stack. May be it should be lower for a better temperature uniformity considering the heating time.

Good morning Mr Revenge:

1.- Do you know and have control over the rate of heating and cooling Tem/ Time?

2.- Do you know and have control over the holding time?

3.-Do you are sure about the required PWHT Temp. for this material?

Possible you need an small procedure. Regards

Note: Not to much thickness but may be Temps/times are the trouble.