Case-Hardened plate armor and method of making

Case-hardened plate armor comprising:

• a steel plate of rolled homogenous armor that is heat treated to provide carbonitride surfaces and a tough, ductile core;
• said carbonitride surfaces having a hardness after the heat treatment of at least 67 on the Rockwell C scale to prevent surface penetration;
• the tough, ductile core having a hardness after the heat treatment in the range of about 45 to 50 on the Rockwell C scale to prevent brittle fracture of the steel plate;
• and the steel plate having holes of the same size and shape formed therethrough in a repeating pattern prior to the case-hardening of the surfaces and the core.

Case-hardened plate armor comprising:

• a steel plate of high-hard armor that is heat treated to provide carbonitride surfaces and a tough, ductile core;
• said carbonitride surfaces having a hardness of at least 67 on the Rockwell C scale to prevent surface penetration;
• the tough, ductile core having a hardness in the range of about 52 to 54 on the Rockwell C scale to prevent brittle fracture of the plate;
• and the steel plate having holes of the same size and shape formed therethrough in a repeating pattern prior to the case-hardening of the surfaces and the core.

A method for case-hardening a steel plate to provide plate armor, said method comprising:

• a) heating the steel plate in an atmosphere of nitrogen and carbon for 1 to 3 hours at a temperature in the range of 1300.degree. F. to 1550.degree. F.;
• (b) quenching the heated steel plate;
• (c) initially tempering the quenched steel plate for 1/2 to 2 hours at a temperature in the range of 275.degree. F. to 325.degree. F.;
• (d) deep freezing the tempered steel plate for 1 to 3 hours at a temperature in the range of -50.degree. F. to -150.degree. F.;
• and
• (e) subsequently again tempering the steel plate after the deep freezing to provide hard carbonitride surfaces and a softer but tougher and more ductile core, said subsequent tempering being performed for 1/2 to 2 hours at a temperature in the range of 275.degree. F. to 325.degree. F..

A method for case-hardening a steel plate to provide plate armor, said method comprising:

• (a) heating the steel plate in an atmosphere of cracked ammonia and methane for 1 to 3 hours at a temperature in the range of 1300.degree. F. to 1550.degree. F.;
• (b) oil quenching the heated steel plate;
• (c) tempering the quenched steel plate for 1/2 to 2 hours at a temperature in the range of 275.degree. F. to 325.degree. F.;
• (d) deep freezing the tempered steel plate for 1 to 3 hours at a temperature in the range of -50.degree. F. to -150.degree. F.;
• and
• e) subsequently again tempering the steel plate after the deep freezing for 1/2 to 2 hours at a temperature in the range of 275.degree. F. to 325.degree. F. to provide hard carbonitride surfaces and a softer but tougher and more ductile core.

A method for making a case-hardened, webbed steel plate, the method comprising:

• (a) forming holes in a steel plate to provide webs between the holes;
• (b) heating the webbed steel plate in an atmosphere of cracked ammonia and methane for 1 to 3 hours at a temperature in the range of 1300.degree. F. to 1550.degree. F.;
• (c) oil quenching the heated steel plate;
• (d) tempering the quenched steel plate for 1/2 to 2 hours at a temperature in the range of 275.degree. F. to 325.degree. F.;
• (e) deep freezing the tempered steel plate for 1 to 3 hours at a temperature in the range of -50.degree. F. to -150.degree. F.;
• and
• (f) subsequently again tempering the steel plate after the deep freezing for 1/2 to 2 hours at a temperature in the range of 275.degree. F. to 325.degree. F. to provide the webbed steel plate with hard carbonitride surfaces and a softer but tougher and more ductile core.