Surface alloyed high temperature alloys

A method of providing a protective surface made up of a surface alloy on a base alloy containing iron, nickel, chromium and alloying additives comprising:

• depositing onto said base alloy a surface alloy comprised of about 35 to 45 wt. % aluminum, a total of about 5 to 20 wt. % of at least one of titanium and chromium, and about 40 to 55 wt. % silicon, and heat treating said base alloy with said surface alloy at a temperature in the range of 400 to 1160° C. to a desired maximum temperature for a time sufficient to generate a surface alloy consisting of an enrichment pool having a thickness in the range of 10 to 300 μm which contains 3 to 7 wt. % silicon, and 5 to 15 wt. % aluminum with the balance thereof being chromium, titanium, iron, nickel and any base alloying additives, whereby said enrichment pool is functional to reduce the deposition of catalytically formed coke thereon.

A method of providing a protective surface made up of a surface alloy on a base alloy containing iron, nickel, chromium and alloying additives comprising:

• depositing onto said base alloy a surface alloy comprised of about 40 to 50 wt % chromium and about 40 to 50 wt % silicon, the balance titanium, and heat-treating said base alloy with said surface alloy at a temperature in the range of 400 to 1160° C. at a rate of temperature rise of at least 5 Celsius degrees/min. to a desired maximum temperature for a time sufficient to generate a surface alloy consisting of an enrichment pool which contains at least 22 wt % chromium, at least 2.5 wt % silicon, 0 to 10 wt % titanium with the balance thereof being iron, nickel and any base alloying additives, whereby said enrichment pool is functional to reduce the deposition of catalytically formed coke thereon.

A surface alloyed component comprising a base stainless steel alloy containing iron, nickel, chromium and alloying additives and a surface alloy coated thereon formed by the steps of depositing onto said base alloy a surface alloy comprised of about 35 to 40 wt. % aluminum, a total of about 5 to 15 wt. % of at least one of titanium and chromium, and about 50 to 55 wt. % silicon, and heat treating said base alloy with said surface alloy at a temperature in the range of 400 to 1160° C. at a rate of temperature rise of at least 5 Celsius degrees/min to a desired maximum temperature for a time sufficient to generate a surface alloy consisting of an enrichment pool having a thickness in the range of 10 to 300 μm which contains 3 to 7 wt. % silicon, and 5 to 10 wt. % aluminum with the balance thereof being chromium, titanium, iron, nickel and any base alloying additives, whereby said enrichment pool is functional to reduce the deposition of catalytically formed coke thereon.

A surface alloyed component comprising a base stainless steel alloy containing iron, nickel, chromium and alloying additives and a surface alloy coated thereon formed by the steps of depositing onto said base alloy a surface alloy comprised of about 35 to 40 wt. % aluminum, a total of about 5 to 15 wt. % of at least one of titanium and chromium, and about 50 to 55 wt. % silicon, and heat treating said base alloy with said surface alloy at a temperature in the range of 400 to 1150° C. at a rate of temperature rise of at least 5 Celsius degrees/min to a desired maximum temperature for a time sufficient to generate a surface alloy consisting of an enrichment pool having a thickness in the range of 10 to 300 μm which contains 3 to 7 wt. % silicon, and 5 to 15 wt. % aluminum with the balance thereof being chromium, titanium, iron, nickel and any base alloying additives, and a diffusion barrier between the base alloy and the surface alloy having a thickness in the range of 10 to 300 μm containing intermetallics of the deposited elemental silicon, and one ore more of titanium, chromium or aluminum, and the base alloy elements, whereby said enrichment pool is functional to reduce the deposition of catalytically formed coke thereon.

A surface alloyed component comprising a base stainless steel alloy containing iron, nickel, chromium and alloying additives and a surface alloy thereon formed by the steps of depositing onto said base alloy a surface alloy comprised of about 40 to 50 wt. % chromium and about 40 to 50 wt. % silicon, the balance titanium, and heat treating said base alloy with said surface alloy at a temperature in the range of 400 to 1160° C. to a desired maximum temperature for a time sufficient to generate a surface alloy consisting of an enrichment pool which contains at least 22 wt. % chromium, at least 2.5 wt. % silicon, 0 to 10% titanium with the balance thereof being iron, nickel and any base alloying additives, whereby said enrichment pool is functional to reduce the deposition of catalytically formed coke thereon.

A surface alloyed component comprising a base stainless steel alloy containing iron, nickel, chromium and alloying additives and a surface alloy coated thereon, said surface alloy containing an enrichment pool having a thickness in the range of 10 to 300 μm and consisting essentially of about 3 to 7 wt. % silicon and about 5 to 10 wt. % aluminum and a diffusion barrier between the base alloy and the surface alloy having a thickness in the range of 10 to 300 μm and consisting essentially of about 6 to 20 wt. % silicon and about 20 to 85 wt. % chromium, the balance thereof being iron and nickel and any alloying additives.

A surface alloyed component comprising a base stainless steel alloy containing iron, nickel, chromium and alloying additives and a surface alloy coated thereon, said surface alloy containing an enrichment pool having a thickness in the range of 10 to 300 μm and consisting essentially of about 22 to 40 wt. % chromium and about 6 to 10 wt. % silicon the balance thereof being iron and nickel and any alloying additives.

A coking and corrosion resistant reactor tube for use in high temperature environments comprising an elongated tube formed from a high temperature stainless steel base alloy containing iron, nickel, chromium and alloying additives and a surface alloy coated thereon, said surface alloy containing an enrichment pool having a thickness in the range of 10 to 300 μm and consisting essentially of about 3 to 7 wt. % silicon and about 5 to 10 wt. % aluminum and a diffusion barrier between the base alloy and the surface alloy having a thickness in the range of 10 to 300 μm and consisting essentially of about 6 to 20 wt. % silicon and about 20 to 85 wt. % chromium, the balance thereof being iron and nickel and any alloying additives.

A furnace for the production of ethylene including a plurality of reactor tubes each comprising an elongated tube formed from a high temperature stainless steel base alloy containing iron, nickel, chromium and alloying additives and a surface alloy coated thereon, said surface alloy containing an enrichment pool having a thickness in the range of 10 to 300 μm and consisting essentially of about 3 to 7 wt. % silicon and about 5 to 10 wt. % aluminum and a diffusion barrier between the base alloy and the surface alloy having a thickness in the range of 10 to 300 μm and consisting essentially of about 6 to 20 wt. % silicon and about 20 to 85 wt. % chromium, the balance thereof being iron and nickel and any alloying additives.