Stainless steel carburization process
View Patent ↗The present invention is directed to a process for tempering steel comprising carburizing said steel in a vacuum furnace in the presence of a hydrocarbon carburizing gas in combination with hydrogen wherein said carburizing gas/hydrogen combination is administered to the vacuum furnace by cyclically reducing the pressure in the furnace followed by the pulsed addition of the hydrocarbon carburizing gas consisting of an acetylene/hydrogen mixture is in a ratio of from about 1:1 to about 1:10 to replenish the air removed in the pressure reduction step.
1. A process for carburizing martinsitic stainless steel in a high temperature furnace comprising:
i. reducing the pressure in the furnace by removing the air therein to create a partial vacuum at a furnace atmospheric pressure of from about 300 torr to about 500 torr;
ii. contacting said steel with a hydrocarbon carburizing gas mixture consisting of acetylene and hydrogen through the intermittent pulsed injection of the gas that replaces
the air removed in the pressure reduction step at a temperature of from about 1800° F. to about 2500° F.;
iii. contacting said steel with the hydrocarbon carburizing gas for a period that allows the carbon to dissociate from the gas mixture and deposit on the surface of the steel to a specified depth of penetration; and,
iv. quenching the steel by rapidly reducing the temperature from about 1100° C. to about 500° C. at increased pressure of about 10 barr to produce a substantially hardened martinsitic base.
2. The process of claim 1 wherein the temperature within the furnace is raised in a partial pressure of hydrogen to remove any residual oxygen or other contamination from the surface of the steel.
3. The process as recited in claim 2 wherein said steel is hardened on its surface.
4. The process as recited in claim 3 wherein said acetylene/hydrogen mixture is in a ratio of from about 1:1 to about 1:10.
5. The process as recited in claim 4 wherein said acetylene/hydrogen mixture is in a ratio of from about 1:9.
6. The process as recited in claim 5 wherein said gas is introduced through an intermittent pulsed injection into a furnace atmospheric pressure of from about 300 torr to about 500 torr.
7. The process as recited in claim 6 wherein said quenched steel alloy is further stabilized in a nitrogen bath at sub-zero temperatures.
8. The process as recited in claim 7 wherein said quenched steel alloy is further stabilized in hydrogen and argon to promote uniform diffusion of the nitrogen bath throughout the alloy at sub-zero temperatures.