M-1 Helmet Production Breakage IV - Metallurgy, Fabrication and Residual Stress

Big Red here with a question from "The Waco Kid"...

So, TAKE FIVE!

Kid asks,

"Big Red, I really don’t understand metallurgy but if the single draw operation and the stress it created was causing major problems making the M-1, why didn’t they use multiple draws or heat treat the steel to get rid of the stress?

Interesting thought Kid,

Here is the short of it, Time, Money and Performance. The military desperately needed helmets, they had to be economically mass producible and they had to afford a high level of protection to our soldiers and sailors.

Attempting a changeover to multiple pressings with heat treatments would require the design and manufacture of new pressing dies, the purchase and installation of a heat treatment solution and the complete reorganization of the manufacturing process.

All this would create major time delays on producing desperately needed helmets as well as incurring major expense, which would increase the cost of the helmet. Further, adding annealing heat treatments to the cold worked helmet would relieve the stress but would drastically reduce the helmets ballistic qualities.

Losses due to production breakage had increased to a level that the production engineers at McCord along with metallurgists at Carnegie-Illinois and the Army Ordnance Labs were leaving no rock unturned in their search for a solution.

During their investigation of avenues to reducing residual stress, McCord’s engineers re-visited the possibility of achieving the necessary 7-inch draw in two operations with heat treatments applied in between for stress relief but quickly discarded the idea due to the negative impact it would have on production turnaround time, cost and ballistic performance.

At the same time, Army Ordnance personnel investigated the fabrication techniques used by other countries in the manufacture of their combat helmets as well as the manufacturing techniques necessary for other potential alloy steels that could be used in place of austenitic manganese.

Watertown Arsenal Lab experiments had shown that of all the magnetic steels tested none came close to equaling the ballistic properties of austenitic manganese. McCord’s experiments concluded that multiple cold pressings of manganese drastically thinned the helmet reducing its ballistic qualities that if annealed, to remove the residual stress, would further reduce ballistic resistance by making the steel brittle.

Furthermore, Watertown Arsenal Lab reports had revealed that the next best steel options to manganese required multiple pressings and heat treatments to achieve their relatively high hardness. They also noted that heat-treating these steels for multiple draws is a delicate scientific process requiring precise supervision to avoid weak pockets in the final sheet steel whereas cold working Hadfield’s manganese to the same level of strength makes this unnecessary.

The Ordnance Department chose Hadfield’s manganese steel for helmets because, unlike other helmet steels in use, it is non-magnetic, resists corrosion, will double in strength when cold worked, and remains ductile, meaning it dented upon impact instead of fracturing, after shaping thereby meeting all requirements of performance. When successfully pressed in a single draw, without breakage losses, the manufacturing process could easily meet demand at a reasonable cost to the Government.

So, those directly involved in the development of the M-1 helmet concluded that they needed to focus their efforts on improving and ensuring the quality of helmet stock as well as reviewing manufacturing practices at the fabricator in order to get the breakage problem under control. In the meantime, it was decided to seek a supplement to the contract to compensate for the current losses due to breakage.

By the way Kid...

What's your real name?

Uh....Okay, Thanks Jim!

and remember,

Big Red Says!

FIVE'S OVER  -  MOVE OUT!