Low temperature carburization under soft vacuum
AssigneeSwagelok Company
InventorsPeter C. Williams, Sunniva R. Collins, Steven V. Marx
Life of this patent
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Abstract
Low temperature carburization of stainless steel using acetylene as the carburizing specie is carried out under soft vacuum conditions in the presence of hydrogen or other companion gas. As a result, formation of soot and the undesirable thermal oxide film that normally occurs during low temperature carburization is eliminated virtually completely.
Claims31
A process for surface hardening a workpiece made from an iron, nickel or chromium based alloy by gas carburization in which the workpiece is contacted with a carburizing gas at an elevated carburization temperature to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer essentially free of carbide precipitates, wherein
- (1) the carburizing gas contains a carburizing specie comprising an unsaturated hydrocarbon,
- (2) the partial pressure of the carburizing specie in the carburizing gas is about 0.5 to 20 torr (˜67 to ˜2,666 Pa),
- (3) the total pressure of the carburizing gas is about 3.5 to 100 torr (˜500 to ˜13,000 Pa), and
- (4) the carburizing gas also contains a companion gas, the companion gas comprising a gas that will react with oxygen under the above elevated carburization temperature and total pressure but which is not an unsaturated hydrocarbon.
A process for producing a surface-hardened, corrosion-resistant stainless steel workpiece exhibiting a shiny metallic appearance without requiring removal of byproduct soot or thermal oxide from the workpiece surfaces, the process comprising contacting the workpiece with a carburizing gas under conditions of time and temperature which are sufficient to cause carbon to diffuse into the workpiece surfaces thereby forming a hardened primary surface layer essentially free of carbide precipitates but insufficient to cause byproduct soot or thermal oxide to form to any significant degree, wherein
- (1) the carburizing gas comprises acetylene and hydrogen,
- (2) the partial pressure of acetylene in the carburizing gas is about 0.5 to 20 torr (˜67 to ˜2,666 Pa), and
- (3) the total pressure of the carburizing gas is about 3.5 to 100 torr (˜500 to ˜13,000 Pa).
Dependencies are inferred from the claim text.