Fe-base austenitic steel having single crystalline austenitic phase, method for producing of same and usage of same

An austenitic steel which has superior characteristics in resistance against stress corrosion cracking, said steel having a composition consisting essentially of

• Ni of 9-15% by weight, Cr of 16-18.5% by weight, and balance Fe of at least 45% by weight, wherein the
• amount of Cr and Ni is enough to form whole austenitic structure in the equilibrium diagram at 700.degree. C.;
• and said steel at room temperature has a metallic structure consisting essentially of an austenitic phase, which is at least 80% in area fraction, and a ferritic phase, wherein
• said austenitic phase is a single crystal.

Method for producing an austenitic steel which has superior characteristics in resistance against stress corrosion cracking and which has a composition consisting essentially of

• Ni of 9-30%, Cr of 16-18.5%, and balance Fe of at least 45% by weight, said method comprising the steps of
• forming molten metal of the austenitic steel which has whole austenitic structure in the equilibrium diagram at 700.degree. C.;
• casting the molten austenitic steel into a mold heated at a temperature between 1500.degree. C.;
• forming an initial solidified part having crystals which are oriented in one direction by cooling one end of the mold so as to solidify steel in one direction;
• keeping the molten metal in the mold in a vacuum lower than 3.times.10.sup.-3 Torr or in an inert gas atmosphere for a predetermined time;
• forming a further solidified part which is composed of an austenitic single crystal by solidifying the molten metal from the initial solidified part in a selector of the mold to form an austenitic single crystal and progressively cooling the mold in said one direction from said one end to another end progressively solidify the melt and grow said austenitic single crystal at a rate of 1-50 cm/h.

Method for producing an austenitic steel which has superior characteristics in resistance against stress corrosion cracking and which has a composition consisting essentially of

• Ni of 9-30%, Cr of 16-18.5%, and balance Fe of at least 45% by weight, said method comprising the steps of
• forming molten metal of the austenitic steel which has whole austenitic structure in the equilibrium diagram at 700.degree. C.;
• casting the molten austenitic steel into a mold heated at a temperature between 1500.degree. C. and 1650.degree. C.;
• keeping the molten metal in the mold in a vacuum lower than 3.times.10.sup.-3 Torr or in an inert gas atmosphere for a predetermined time;
• forming an initial solidified part having crystals which are oriented in one direction by cooling one end of the mold so as to solidify the steel in one direction;
• forming a further solidified part which is composed of an austenitic single crystal by solidifying the molten metal from the initial solidified part in a selector of the mold to form an austenitic single crystal and progressively cooling the mold in said one direction from said one end to another end to progressively solidify the melt and grow said austenitic single crystal at a rate of 1-50 cm/h;
• and
• performing of solution treatment to homogenize an alloy composition of the austenitic single crystalline casting by heating the casting at least once at a temperature between 1,000.degree. C. and 1,300.degree. C. after completion of the solidification.

Method for producing an austenitic steel which has superior characteristics in resistance against stress corrosion cracking and which has a composition consisting essentially of

• Ni of 9-30%, Cr of 16-18.5%, and balance Fe of at least 45% by weight, said method comprising the steps of
• forming molten metal of the austenitic steel which has whole austenitic structure in the equilibrium diagram at 700.degree. C.;
• casting the molten austenitic steel into a mold heated at a temperature between 1500.degree. C. and 1650.degree. C.;
• keeping the molten metal in the mold in a vacuum lower than 3.times.10.sup.-3 Torr or in an inert gas atmosphere for a predetermined time;
• forming an initial solidified part having crystals which are oriented in one direction by cooling one end of the mold so as to solidify the steel in one direction;
• forming a further solidified part which is composed of an austenitic single crystal by solidifying the molten metal from the initial solidified part in a selector of the mold to form an austenitic single crystal and progressively cooling the mold in said one direction from said one end to another end to progressively solidify the melt and grow said austenitic single crystal at a rate of 1-50 cm/h;
• performing cutting work on the casting;
• and
• performing of solution treatment to homogenize an alloy composition of the austenitic single crystalline casting by heating the casting at least once at a temperature between 1,000.degree. C. and 1,300.degree. C. after completion of solidification.