Ferritic alloy

Abstract

A ferritic alloy comprising the following elements in weight % C 0.01 to 0.1; N: 0.001 to 0.1; 0: <0.2; Cr 4 to 15; Al 2 to 6; Si 0.5 to 3; Mn: ≤0.4; Mo+W≤4; Y≤1.0; Sc, Ce, La and / or Yb≤0.2; Zr≤0.40; RE≤3.0; balance Fe and normal occurring impurities and also fulfilling the following equation has to be fulfilled: 0.014≤(Al+0.5SQ (Cr+10Si+0.1)≤0.022.

Description

TECHNICAL FIELD[0001]The present disclosure relates to a ferritic alloy according to the preamble of claim 1. The present disclosure further relates to use of the ferritic alloy and to objects or coatings manufactured thereof.BACKGROUND AND INTRODUCTION[0002]Ferritic alloys, such as FeCrAl-alloys comprising chromium (Cr) levels of 15 to 25 wt % and aluminium (Al) levels from 3 to 6 wt % are well known for their ability to form protective α-alumina (Al2O3), aluminium oxide, scales when exposed to temperatures between 900 and 1300° C. The lower limit of Al content to form and maintain the alumina scale varies with exposure conditions. However, the effect of a too low Al level at higher temperatures is that the selective oxidation of Al will fail and less stable and less protective scales based on chromium and iron will be formed.[0003]It is commonly agreed that FeCrAl alloys will normally not form the protective α-alumina layer if exposed to temperatures below about 900° C. There have...

AI Technical Summary

Benefits of technology

The patent text describes a new alloy that has excellent resistance to oxidation and corrosion, as well as good ductility and reduced strength. The technical effect of this alloy is achieved by balancing the content of Fe, normal impurities, and meeting a certain equation. This formula ensures that the alloy has the right combination of elements to achieve these benefits.

Problems solved by technology

However, the effect of a too low Al level at higher temperatures is that the selective oxidation of Al will fail and less stable and less protective scales based on chromium and iron will be formed.

It is commonly agreed that FeCrAl alloys will normally not form the protective α-alumina layer if exposed to temperatures below about 900° C. There have been attempts to optimize the compositions of FeCrAl alloys so that they will form the protective α-alumina at temperature below about 900° C. However, in general, these attempts have not been very successful because the diffusion of oxygen and aluminium to the oxide-metal interface will be relatively slow at lower temperatures and thereby the rate of formation of the alumina scale will be low, which means that there will be a risk of severe corrosion attacks and formation of less stable oxides.

Another problem arising at lower temperature, i.e. temperatures below 900° C., is a long term embrittlement phenomena arising from a low temperature miscibility gap for Cr in the FeCrAl alloy system.

EP 075 420 discusses Si additions in order to improve the flow properties of the alloy melt but the success was limited due to reduced ductility.

However, the obtained alloys did not provide a high temperature resistance.

Images