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Improved Martensitic Steel for High Temperature Applications

A stainless steel composition and heat treatment process for a high-temperature, titanium alloyed 9 Cr-1 molybdenum alloy

National Energy Technology Laboratory

Ames Laboratory

Contact NETL About This Technology

Technology Marketing Summary

NETL has developed a stainless steel composition and heat treatment process for a high-temperature, titanium alloyed 9 Cr-1 molybdenum alloy exhibiting improved creep strength and oxidation resistance at 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 Cr 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 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.

Description

The operating efficiency of coal-fired power plants is directly related to combustion system temperature and pressure. Incorporation of ultra supercritical (USC) steam conditions into new or existing power plants can achieve increased efficiency and reduce coal consumption, while reducing carbon dioxide emissions as well as other pollutants. Traditionally used materials do not possess the optimal characteristics for operation under USC conditions. Advanced stainless steel alloys and fabrication processes are needed for operation under such extreme conditions. Development of USC boilers and turbines will require materials with high temperature creep strength, oxidation resistance, corrosion resistance, thermal fatigue resistance, and deformation resistance. Martensitic grades of stainless steel which contain chromium (Cr) and carbon offer an alternative for high temperature applications due to their corrosive resistance and ability to be hardened by heat treatment. Further, these alloys offer a potentially more cost-effective solution when compared to nickel-based superalloys.

NETL has developed a stainless steel composition and heat treatment process for a high-temperature, titanium alloyed 9 Cr-1 molybdenum alloy exhibiting improved creep strength and oxidation resistance at 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 Cr 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 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.

Benefits

Improved high temperature operating characteristics including increased creep strength and oxidation resistance under USC steam conditions

Comparable cost to commonly used high temperature stainless steels

Heat treatment process does not require hot-working in the austenite temperature range

Applications and Industries

Other applications where heat and oxidative-resistant stainless steel components are required

Advanced high-temperature power plant componentry including coal-fired boilers, steam and gas turbines, tubing, and piping

Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Date
Patent 8,317,944
Patent
8,317,944
9 Cr-- 1 Mo steel material for high temperature application
One or more embodiments relates to a high-temperature, titanium alloyed, 9 Cr-1 Mo steel exhibiting improved creep strength and oxidation resistance at service temperatures up to 650.degree. C. The 9 Cr-1 Mo steel has a tempered martensite microstructure and is comprised of both large (0.5-3 .mu.m) primary titanium carbides and small (5-50 nm) secondary titanium carbides in a ratio of. from about 1:1.5 to about 1.5:1. The 9 Cr-1 Mo steel may be fabricated using exemplary austenizing, rapid cooling, and tempering steps without subsequent hot working requirements. The 9 Cr-1 Mo steel exhibits improvements in total mass gain, yield strength, and time-to-rupture over ASTM P91 and ASTM P92 at the temperature and time conditions examined.
U.S. Department of Energy 11/27/2012
Issued
Patent 8,246,767
Patent
8,246,767
Heat treated 9 Cr-1 Mo steel material for high temperature application
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.degree. 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.
U.S. Department of Energy 08/21/2012
Issued
Technology Status
Development StageAvailabilityPublishedLast Updated
Development - Available for licensingAvailable01/18/201302/23/2016

Contact NETL About This Technology

To: Jessica Sosenko <Jessica.Sosenko@netl.doe.gov> <techtransfer@netl.doe.gov>