Dual hardness steel article

A dual-hardness steel plate, comprising:

• a first portion comprising a first nickel-molybdenum-chromium, air-hardenable steel alloy having a first hardness of at least 574 Brinell Hardness Number (BHN), wherein the first air-hardenable steel alloy comprises, in percent by weight:
• 0.42 to 0.52 carbon;
• 3.75 to 4.25 nickel;
• 1.00 to 1.50 chromium;
• 0.22 to 0.37 molybdenum;
• 0.20 to 1.00 manganese;
• 0.20 to 0.50 silicon;
• up to 0.020 phosphorus;
• up to 0.005 sulfur;
• iron;
• and
• impurities;
• and
• a second portion metallurgically-bonded to the first portion, the second portion comprising a second nickel-molybdenum-chromium, air-hardenable steel alloy having a second hardness in a range of 477 BHN to 534 BHN, inclusive.

A dual-hardness steel plate, comprising:

• a first portion comprising a first air-hardenable steel alloy having a first hardness of at least 574 Brinell Hardness Number (BHN) and comprising, in percent by weight:
• 0.42 to 0.52 carbon,
• 3.75 to 4.25 nickel,
• 1.00 to 1.50 chromium,
• 0.22 to 0.37 molybdenum,
• 0.20 to 1.00 manganese,
• 0.20 to 0.50 silicon,
• up to 0.020 phosphorus,
• up to 0.005 sulfur,
• iron, and
• impurities;
• and
• a second portion metallurgically-bonded to the first portion, the second portion comprising a second air-hardenable steel alloy having a second hardness in a range of 477 BHN to 534 BHN, inclusive, and comprising, in percent by weight:
• 0.22 to 0.32 carbon,
• 3.50 to 4.00 nickel,
• 1.60 to 2.00 chromium,
• 0.22 to 0.37 molybdenum,
• 0.80 to 1.20 manganese,
• 0.25 to 0.45 silicon,
• up to 0.020 phosphorus,
• up to 0.005 sulfur,
• iron, and
• impurities.