FORMING AND WELDING INNOVATIONS FOR ARMOR STEELS

This paper reviews research that has been conducted to develop inductively assisted localized hot forming bending technologies, and to use standardized welding tests to assess the practicality and potential benefits of adopting stainless based consumables to weld both existing and evolving armor alloys.

For the titanium alloy Ti6Al4V it was determined that warming the plate to circa 600°F would improve the materials ductility (as measured by reduction of area) from ~18 to 40% without exposing the material to a temperature at which atmospheric contamination would be significantly deleterious.

For the commercial alloy BB and class 1 armor alloy it was found that there was little effect on the charpy impact toughness and the proof strength as a result of processing at 900 °F with either air cool or water quench and there was an added benefit of lower residual stresses in the finished bends compared to cold formed bends. Heating “alloy BB” to 1600 °F followed by water quench resulted in mechanical properties that were equivalent to those of the parent plate with the exception of a strip of material in the transition hot zone whose temperature, before quench, was between 900 °F and 1600 °F. Heating class 1 armor to 1600°F followed by water quench increased the ultimate tensile strength.

Further work is recommended for alloy BB and class 1 armor, using a higher induction power, to determine how narrow the transition hot zone, in which lower charpy impact toughness was noted, can be made.

The weldability study indicated that grade 309LHF stainless steel is the least likely to crack when making single pass welds in “alloy BB”. It was not possible to make a similar assessment based on the available data for the class 1 RHA when using stainless steel consumables. When using ferrous consumables it was apparent that preheat was beneficial and that LA100 performed better than ER70S-6. It is recommended that the weldability study be repeated with a statistically significant number of Tekken or restrained T joint solidification cracking tests at different travel speeds to examine the significance of weld bead profile.