초록 ▼

The invention relates to a composition and heat treatment for a high-temperature, titanium alloyed, 9 Cr-1 Mo steel exhibiting improved creep strength and oxidation resistance at service temperatures up to 650° C. The novel combination of composition and heat treatment produces a heat treated materi

The invention relates to a composition and heat treatment for a high-temperature, titanium alloyed, 9 Cr-1 Mo steel exhibiting improved creep strength and oxidation resistance at service temperatures up to 650° C. The novel combination of composition and heat treatment produces a heat treated material containing both large primary titanium carbides and small secondary titanium carbides. The primary titanium carbides contribute to creep strength while the secondary titanium carbides act to maintain a higher level of chromium in the finished steel for increased oxidation resistance, and strengthen the steel by impeding the movement of dislocations through the crystal structure. The heat treated material provides improved performance at comparable cost to commonly used high-temperature steels such as ASTM P91 and ASTM P92, and requires heat treatment consisting solely of austenization, rapid cooling, tempering, and final cooling, avoiding the need for any hot-working in the austenite temperature range.

대표청구항 ▼

1. A method of producing a heat treated 9 Cr-1 Mo material, comprising the following steps in the order named: austenizing a 9 Cr-1 Mo alloy comprising 0.05-0.15 wt. % carbon, 8.0-13.0 wt. % chromium, 0.5-1.5 wt. % molybdenum, 0.1-1.0 wt. % silicon, 0.2-1.0 wt. % manganese, 0.1-0.4 wt. % vanadium, 0

1. A method of producing a heat treated 9 Cr-1 Mo material, comprising the following steps in the order named: austenizing a 9 Cr-1 Mo alloy comprising 0.05-0.15 wt. % carbon, 8.0-13.0 wt. % chromium, 0.5-1.5 wt. % molybdenum, 0.1-1.0 wt. % silicon, 0.2-1.0 wt. % manganese, 0.1-0.4 wt. % vanadium, 0.02-0.2 wt. % niobium, 0.05-0.2 wt. % titanium, balance Fe and unavoidable impurities, wherein the 9 Cr-1 Mo alloy contains primary TiC 0.5-3.0 μm in diameter, at a temperature wherein the solubility of the primary TiC is sufficient to dissolve about 40-60% of the primary TiC, placing titanium and carbon in solution;cooling the 9 Cr-1 Mo alloy using an initial cooling step to generate a martensitic microstructure wherein titanium and carbon remain in solution;tempering the 9 Cr-1 Mo alloy such that titanium and carbon in solution diffuse to precipitate secondary TiC, such that a mass ratio of secondary to primary TiC is from about 1:1.5 to about 1.5:1 in the tempered 9 Cr-1 Mo alloy, where the mass ratio of secondary to primary TiC is the mass of the primary TiC divided by the mass of the secondary TiC; and,cooling the 9 Cr-1 Mo alloy in a final cooling treatment. 2. The method of claim 1, wherein austenizing is conducted at a temperature of 1250+/−20° C. for a period of about ten minutes. 3. The method of claim 1, wherein tempering is conducted at a temperature of 755+/−50° C. for a period of about thirty minutes. 4. The method of claim 1, wherein austenizing is followed by cooling the 9 Cr-1 Mo alloy using an initial cooling step prior to any hot working of the 9 Cr-1 Mo alloy, and tempering is followed by cooling the 9 Cr-1 Mo alloy in a final cooling treatment prior to any hot working of the 9 Cr-1 Mo alloy. 5. The method of claim 1, wherein the initial cooling step provides a cooling rate of at least 2° C./second. 6. The method of claim 1, wherein the mass ratio of secondary to primary TiC is about 1:1. 7. The method of claim 1, wherein the composition of the heat treated 9 Cr-1 Mo material is further limited to 0.08-0.12 wt. % carbon, 8.0-9.5 wt. % chromium, 0.85-1.05 wt. % molybdenum, 0.2-0.5 wt. % silicon, 0.2-1.0 wt. % manganese, 0.18-0.25 wt. % vanadium, 0.06-0.1 wt. % niobium, 0.05-0.15 wt. % titanium, balance Fe and unavoidable impurities. 8. The method of claim 7, wherein austenizing is conducted at a temperature of 1250+/−20° C. for a period of about ten minutes, the initial cooling step provides a cooling rate of at least 2° C./second, and tempering is conducted at a temperature of 755+/−50° C. for a period of about thirty minutes. 9. A method of producing a heat treated 9 Cr-1 Mo material, consisting of the following steps in the order named: austenizing a 9 Cr-1 Mo alloy comprising 0.05-0.15 wt. % carbon, 8.0-13.0 wt. % chromium, 0.5-1.5 wt. % molybdenum, 0.1-1.0 wt. % silicon, 0.2-1.0 wt. % manganese, 0.1-0.4 wt. % vanadium, 0.02-0.2 wt. % niobium, 0.05-0.2 wt. % titanium, balance Fe and unavoidable impurities, wherein the 9 Cr-1 Mo alloy contains primary TiC 0.5-3.0 μm in diameter, at a temperature wherein the solubility of the primary TiC is sufficient to dissolve about 40-60% of the primary TiC and place titanium and carbon in solution;cooling the 9 Cr-1 Mo alloy using an initial cooling step to generate a martensitic microstructure wherein the titanium and carbon remain in solution;tempering the 9 Cr-1 Mo alloy such that the titanium and carbon in solution diffuse to precipitate secondary TiC, such that a mass ratio of secondary to primary TiC is from about 1:1.5 to about 1.5:1 in the tempered 9 Cr-1 Mo alloy, where the mass ratio of secondary to primary TiC is the mass of the primary TiC divided by the mass of the secondary TiC; and,cooling the 9 Cr-1 Mo alloy in a final cooling treatment. 10. The method of claim 9, wherein austenizing is conducted at a temperature of 1250+/−20° C. for a period of about ten minutes, the initial cooling step is water or oil quench, tempering is conducted at a temperature of 755+/−50° C. for a period of about thirty minutes, and the final cooling treatment is air cooling.