Method for making armor plate

A method for making armor plate which comprises commencing with a homogeneous metal plate that has been hardened. Then moving the plate into a liquid bath while applying heat to one surface of the plate. The plate is progressively moved into the bath at an angle while the heat is applied at or near the point of intersection of the plate with the bath and on a surface of the plate which is opposite that which is in contact with the bath.

PROBLEM PRESENTED TO THE INVENTOR AND PRIOR ART 
Armor plate must be very hard to be effective in resisting impacts by 
projectiles. However, if the plate is too hard the projectile, such as a 
bullet, will hit the plate and shatter the hard surface and the entire 
plate. 
One approach considered in using homogeneous material has been to 
compromise the high level and low level of hardness to arrive at a medium 
hardness to prevent shattering. This single hardness, however, requires 
that thicker material be used to achieve ballistic resistance. Another 
approach has been to use a non-homogeneous material which consists of two 
roll sheets bonded together forming a laminate of similar but different 
hardenability materials. By heat treating the bonded laminate the product 
will result in one side with high hardness and the other side with a 
relative lower hardness. The softer side of relatively lower hardness will 
support the hard side and prevent the entire plate from shattering, this 
product displays a higher ballistic resistance for a given thickness when 
compared to the above mentioned homogeneous armor. 
This would result in a desired characteristic. The problem with using this 
bonded laminate material is that while the desired characteristics are 
produced there are economic disadvantages caused by the added costs due to 
the additional processes involved to produce a good quality joint. 
Further, the non-homogeneous composite material is prone to distortions 
during a quenching process. 
The third approach is to harden one side only by current methods, all of 
which require raising only a portion of the material to above the 
austenitic temperature and quenching leaving a transition area between the 
hardened material, and the body of the material. 
INVENTOR'S SOLUTION TO THE PROBLEM 
The inventor has presented a technique for avoiding the need of the 
composite laminated material while achieving the desirable characteristics 
of having one side hard and the other side relatively ductile or soft. 
This is achieved by starting with a homogeneous hardened or hardened and 
tempered material. One side is rapidly heated to a tempering temperature 
while the other side has heat drawn from it as rapidly as possible. The 
side from which the heat is drawn is also shielded from the heating 
source. This causes the heated side to be tempered (or further tempered if 
it has previously been heated and tempered), thereby providing a softer 
yet tougher side while the opposite side retains its hard characteristics. 
This method employs a technique to progressively advance the plate at an 
angle towards a bath of water, water base solutions, gas, cool air or 
combinations of these and heat a top side to a tempering temperature while 
simultaneously submerging an opposite bottom side in the bath to prevent 
that side from increasing its temperature and avoid any reduction in the 
hardness of the bottom side. Further, as the top side advances into the 
bath it is cooled. The result will produce a differential of hardness 
between the top side and the bottom side. The top side will be tempered or 
tempered at a higher temperature and will have softer, tougher 
characteristics than the bottom side which has maintained its original 
hardness.

DESCRIPTION OF ONE EMBODIMENT OF THE METHOD 
The FIGURE shows a metal plate 10 which is progressively advanced into a 
water bath 12. The plate 10 has a top side surface 14 and bottom side 
surface 16. The plate is advanced into the bath 12 at an angle .theta. 
which is less than 90% and preferably in the range of 5.degree. and 
30.degree. between the bottom surface 16 and the top of the bath 12. An 
acetylene torch 18 applies heat to the top surface 14 at or adjacent to 
the intersection of the plate 10 with the water bath 12. 
Seven pre-hardened and tempered samples were tested. 28 PSI of oxygen and 
14 PSI of acetylene were used for each plate which was advanced at the 
rate of 18.5 inches per minute thru 23.5 inches per minute. The 
displacement d, namely the point of impingement of heat with respect to 
the intersection of the plate with the bath was zero. The distance H from 
the torch tip to the top surface 14 was 3/8". 
Tests were made starting with a steel plate 1/4" thick with thermocouples 
imbedded at various depths and readings indicated that while the maximum 
temperature of the surface exposed to the heat source reached 865.degree. 
F., the opposite side surface only reached 421.degree. F., maximum. 
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Brinell Brinell Hardness 
Sam- Hardness Material After Heating 
Flame 
ple Before Thick- Compo- Top Bottom Length 
No. Heating ness sition Surface 
Surface 
(Cone) 
______________________________________ 
1 514 1/4 4340 415 514 1/4" 
2 477 1/4 4340 388 477 3/8" 
3 418 1/4 XAR-30 321 418 1/4" 
4 418 1/4 XAR-30 302 418 3/8" 
5 444 1/4 4340 388 444 1/4" 
6 512 0.3 4350 M 401 601 3/8" 
7 477 4340 402 477 3/8" 
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Sample number 2 had a projectile fired against it and repelled military 
ball type ammunition at point blank muzzle velocities although armor 
piercing slugs did penetrate the plate. It is believed that higher face 
hardness will be able to withstand the armor piercing ammunition. 
Sample 6 was tested for military ballistic characteristics according to 
military specifications that determines the velocity at which penetration 
occurs and the velocity at which it is capable of repelling the 
projectile. This test permits rating the sample relative to established 
standards that specify various velocities for various thicknesses. This 
sample was able to withstand 30% higher velocities than standard 
homogeneous armor as specified. This test was done with standardized armor 
piercing projectiles fired at various velocities and recorded by 
electronic timing devices. It is believed that non-homogeneous metal 
plates could have their characteristics improved also.