DIFFUSION TREATED HOT-DIP ALUMINUM COATED STEEL AND METHOD OR TREATING

摘要

A solid solution iron-aluminum diffusion alloy coated steel strip is formed by hot-dip aluminum coating a cold rolled low alloy low carbon steel strip preferably having all the carbon in the steel combined with titanium by hot-dip aluminum coating the steel strip and subjecting the aluminum coated low alloy steel strip to a controlled diffusion heat treatment in a non-oxidizing atmosphere for a period and at a temperature which avoids significantly increasing the grain size of the steel, and which effects diffusion of the hot-dip aluminum coating into the steel to establish a critical surface concentration of aluminum in the iron-aluminum diffusion alloy coating of at least about 8 wt. percent and below an aluminum surface concentration which results in crazing and cracking of the diffusion alloy coating when the diffusion alloy coated strip is fabricated at room temperature. A solid solution iron-aluminum diffusion alloy coated titanium containing low carbon steel strip having an aluminum surface concentration between about 8 and about 10 wt. percent does not exhibit objectionable crazing and cracking of the diffusion alloy coating when the coated steel is severely strained during fabrication at room temperature and has good high temperature oxidation resistance when the diffusion alloy coated steel strip is exposed to oxidizing gasses having temperatures between about 816 DEG C. (1500 DEG F.) and 982 DEG C. (1800 DEG F.) after being severely strained at room temperature.