ATBECHDEDKESFRGBGRITLILUNLSEMCPTIESILTLVFIROMKCYALTR............................JDIM350 (Ver 2.1 Jan 2001) 1620000/01116796EUROPEAN PATENT APPLICATIONA320031217EP01300136.720010108EnEnEn200000621920000111JP20031217200351200107182001297 7C 21D 6/00 A 7C 21D 6/02 BdeTemperaturbeständiger ferritischer Stahl mit hohem Chromgehalt und Verfahren zur Wärmebehandlung desselbenenHigh chromium ferritic heat resisting steel and method of heat treatment for the samefrAcier ferritique réfractaire riche en chrome et procédé pour son traitement thermiqueNONEJAPAN as represented by NATIONAL RESEARCH INSITUTE FOR METALS0144922226.41.74741NATIONAL RESEARCH INSITUTE FOR METALS, JAPAN as represented by2-1, Sengen 1-chome, TsukubaIbaraki 300-26JPSumitomo Metal Industries Limited0208014826.41.74741Metal Industries Limited, SumitomoOte Center Bldg. 1-3, Otemachi 1-chomeChiyoda-ku, TokyoJPFujitsuna, Nobuyukic/o National Research Institute for Metals2-1 Sengen 1-chome Tsukuba-shi IbarakiJPIgarashi, Masaakic/o National Research Institute for Metals2-1 Sengen 1-chome Tsukuba-shi IbarakiJPAbe, Fujioc/o National Research Institute for Metals2-1 Sengen 1-chome Tsukuba-shi IbarakiJPCalamita, Roberto00069571Frank B. Dehn & Co., European Patent Attorneys, 179 Queen Victoria StreetLondon EC4V 4ELGBATBECHCYDEDKESFIFRGBGRIEITLILUMCNLPTSETRALLTLVMKROSI20031217200351

The invention provides a method of heat-treatment for high chromium ferritic heat resisting steel, which comprises the steps of:

(a) heat-treating for 5 seconds or longer high chromium ferritic steel containing chromium (Cr) in amount of 7-12 weight %; one or two elements of molybdenum (Mo) and tungsten (W) as a solid-solution strengthening element; and one or more of elements for forming (a) MX carbonitride(s) at a temperature higher than both solid-solution temperature of said element(s) for forming the MX carbonitride(s) and a precipitation starting temperature of δ ferrite;
(b) cooling said steel at a rate of 0.5°C/s or faster; and
(c) subsequently tempering said steel.