Hello,
Pls forgive me late reply. I would not expect any serious problems in this particular case becasue S235JR is rather ductile grade. Anyway, please remember that final results will depend on:
1. actual chemical composition with regard to secondary steelmaking practices(no data),
2. actual Rm to Re ratio (no data),
3. bending angle and mandrel diameter used,
4. direction of bending in relation to rolling direction (for 4mm thikcness the recommended minimum bending diameter is 5mm for transverse and 6 mm for longitudinal direction).
Under normal circumstances, the steel grades designed for cold working puropses, including bending, should have "C" letter added after the steel grade name, i.e. S235JRC in your case.
Considering your thickness 4 mm and bend radius 4mm (see tables 8 & 9 in EN10025:1990+A1:1993 version) I would not expect any problems providing the bending angle is not more than 90 degress.
You may also feel safe when bending angle is 120 degress but using the mandrel of diameter not less than
d =3 x thickness, i.e. 12mm (the statement based on my own experience).
The problems may occur when bending angle approach 180 degrees and the mandrel diameter is relatively small.
To be able to tell you more I would need to know the full chemical composition, actual mechanical proprties and direction of bending.
Best regards,
iceclass1994
