Method of chromium plating

Claim 1

A METHOD FOR REDUCING THE LOSS OF FATIGUE STRENGTH FOLLOWING CHROMIUM PLATING OF AN ARTICLE OF STEEL HAVING A FATIGUE STRENGTH OF 60,000 TO 110,000 P.S.I., COMPRISING ELECTRODEPOSITING CHROMIUM ON THE ARTICLE BY PASSING A CURRENT OF 1 TO 6 A. S. I. TO SAID ARTICLE AS CATHODE IN AN AQUEOUS BATH HAVING A CRO3 CONTENT OF 500 TO 700 G./1. AND CONTAINING DISSOLVED SULFATE, SO4=, AS CATALYST AT A TEMPERATURE OF 120 TO 150* F., SAID BATH CONTAINING CALCIUM SULFATE AS THE SOURCE OF SAID DISSOLVED SULFATE, THE AMOUNT OF CALCIUM SULFATE BEING SUFFICIENT TO SATURATE THE BATH AND TO PROVIDE AN UNDISSOLVED EXCESS OF CALCIUM SULFATE, SAID BATH ALSO CONTAINING A SOLUBLE CALCIUM COMPOUND IN AN AMOUNT SUFFICIENT TO SUPPRESS THE CONCENTRATION OF DISSOLVED SULFATE FROM THE UNSUPPRESSED SATURATION CONCENTRATION OF THE LATTER TO A LOWER VALUE CORRESPONDING TO A CRO3/SO4 RATIO OF 75:1 TO 150:1, SAID BAT CONTAINING, AND BEING PARTIALLY NEUTRALIZED BY, A QUANTITY OF DISSOLVED M, WHERE M IS A METAL HAVING A BASIC REACTION AND IS SELECTED FROM THE GROUP CONSISTING OF SODIUM, POTASSIUM, AMMONIUM, AND CALCIUM, SAID QUANTITY OF DISSOLVED M BEING SUFFICIENT TO NEUTRALIZE ABOUT 10 TO 75% OF SAID BATH, PLATING CHROMIUM ON THE ARTICLE TO FORM A COATING ABOUT 2 TO 15 MILS THICK, HEATING THE PLATED ARTICLE TO A TEMPERATURE OF 350 TO 550* F. FOR ABOUT 2 HOURS, AND THEREBY PRODUCING A CHROMIUM PLATED ARTICLE OF SAID STEEL HAVING A FATIGUE STRENGTH OF AT LEAST 90% OF THAT OF THE UNPLATED ORIGINAL STEEL.

Claim 2

A METHOD FOR REDUCING THE LOSS OF FATIGUE STRENGTH FOLLOWING CHROMIUM PLATING OF AN ARTICLE OF STEEL HAVING A FATIGUE STRENGTH OF 60,000 TO 110,000 P.S.I., COMPRISING ELECTRODEPOSITING CHROMIUM ON THE ARTICLE BY PASSING A CURRENT OF 1 TO 6 A. S. I. TO SAID ARTICLE AS CATHODE IN AN AQUEOUS BATH HAVING A CRO3 CONTENT OF 500 TO 700 G./1. AND CONTAINING DISSOLVED SULFATE, SO4=, AS CATALYST AT A TEMPERATURE OF 120 TO 150* F., SAID BATH CONTAINING CALCIUM SULFATE AS THE SOURCE OF SAID DISSOLVED SULFATE, THE AMOUNT OF CALCIUM SULFATE BEING SUFFICIENT TO SATURATE THE BATH AND TO PROVIDE AN UNDISSOLVED EXCESS OF CALCIUM SULFATE, SAID BATH ALSO CONTAINING A SOLUBLE CALCIUM COMPOUND IN AN AMOUNT SUFFICIENT TO SUPPRESS THE CONCENTRATION OF DISSOLVED SULFATE FROM THE UNSUPPRESSED SATURATION CONCENTRATION OF THE LATTER TO A LOWER VALUE CORRESPONDING TO A CRO3/SO4 RATIO OF 75:1 TO 150:1, SAID BAT CONTAINING, AND BEING PARTIALLY NEUTRALIZED BY, A QUANTITY OF DISSOLVED M, WHERE M IS A METAL HAVING A BASIC REACTION AND IS SELECTED FROM THE GROUP CONSISTING OF SODIUM, POTASSIUM, AMMONIUM, AND CALCIUM, SAID QUANTITY OF DISSOLVED M BEING SUFFICIENT TO NEUTRALIZE ABOUT 10 TO 75% OF SAID BATH, PLATING CHROMIUM ON THE ARTICLE TO FORM A COATING ABOUT 2 TO 15 MILS THICK, HEATING THE PLATED ARTICLE TO A TEMPERATURE OF 350 TO 550* F. FOR ABOUT 2 HOURS, AND THEREBY PRODUCING A CHROMIUM PLATED ARTICLE OF SAID STEEL HAVING A FATIGUE STRENGTH OF AT LEAST 90% OF THAT OF THE UNPLATED ORIGINAL STEEL.