Simultaneous chromizing-aluminizing coating of low alloy steels by a halide-activated pack cementation process

Technical Report · Sun Nov 01 04:00:00 EST 1992

DOI:https://doi.org/10.2172/6828925· OSTI ID:6828925

Geib, F D; Rapp, R A ^[1]

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1. Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering

The simultaneous chromizing-aluminizing of low-alloy steels has achieved Kanthal-like surface compositions of 16--2lCr and 5--8 wt%Al by the use of cementation packs with a Cr-Al masteralloy and an NH[sub 4]Cl activator salt. An initial preferential deposition of Al into the alloy induces the phase transformation from austenite to ferrite at the 1150[degrees]C process temperature. The low solubility of carbon in ferrite results in the rejection of solute C into the core of the austenitic substrate, thereby preventing the formation of an external Cr-carbide layer, which would otherwise block aluminizing and chromizing. The deposition and rapid diffusion of Cr and Al into the external bcc ferrite layer follows. Parabolic cyclic oxidation kinetics for alumina growth in air were observed over a wide range of relatively low temperatures (637--923[degrees]C).

• Research Organization: Oak Ridge National Lab., TN (United States); Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering
• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6828925
• Report Number(s): ORNL/Sub-87-SB154/01; ON: DE93004699
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360101* -- Metals & Alloys-- Preparation & Fabrication
ALLOYS
ALUMINIUM
BOILERS
CHEMICAL REACTIONS
CHROMIUM
COATINGS
DEPOSITION
ELEMENTS
IRON ALLOYS
IRON BASE ALLOYS
METALS
OXIDATION
PROTECTIVE COATINGS
STEELS
TRANSITION ELEMENTS