Annealing of carbon steels in a pre-heated mixed ambients of nit

Details Annealing of carbon steels in a pre-heated mixed ambients of nit Annealing of carbon steels in a pre-heated mixed ambients of nit

1992-12-22

1993-10-19

Roy, Upendra

Metal treatment

Process of modifying or maintaining internal physical...

Carburizing or nitriding using externally supplied carbon or...

148206, 266 81, C21D 100

Patent

active

052541800

ABSTRACT:
An improved process for producing high-moisture containing nitrogen-based atmospheres suitable for oxide and decarburize annealing of carbon steels from non-cryogenically generated nitrogen is presented. These nitrogen-based atmospheres are produced by 1) mixing non-cryogenically generated nitrogen containing less than 5.0 vol. % residual oxygen with a specified amount of hydrogen, 2) humidifying the gaseous feed mixture, 3) feeding the gaseous mixture into the heating zone of a furnace through a diffuser, and 4) converting in-situ the residual oxygen present in it to moisture. According to the present invention, the total amount of hydrogen required for producing suitable atmospheres can be minimized by simultaneously humidifying the feed gas and controlling the residual oxygen level in it. The key features of the present invention include a) humidifying the feed gas prior to introducing it into the heating zone of a furnace operated above about 600.degree. C., b) selecting the level of residual oxygen in the feed gas in such a way that it minimizes hydrogen consumption, and c) using enough amount of hydrogen to convert completely the residual oxygen present in the feed gas to moisture and to maintain pH.sub.2 /pH.sub.2 O ratio in the heating zone of the furnace below about 2 for oxide annealing and at least 2 for decarburize annealing carbon steels.

REFERENCES:
patent: 4713124 (1987-12-01), Schmetz et al.
patent: 5069728 (1991-12-01), Rancon et al.
Stratton, P. F., Heat Treatment of Metals, 3 (1989) 63-67.

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