TEM Studies of Boron-Modified 17Cr-7Ni Precipitation-Hardenable Stainless Steel via Rapid Solidification Route
- PDF / 745,352 Bytes
- 9 Pages / 593.972 x 792 pts Page_size
- 119 Downloads / 221 Views
TRODUCTION
THE rapid solidification (RS) technique is well known for causing refinement in microstructure,[1–3] reduction in microsegregation,[1,2] and increased solid solubility which in turn improves the mechanical properties of the alloy and leads to the development of novel compositions. 17Cr-7Ni precipitation-hardenable (17-7 PH, AISI 631) steel is a special grade of stainless steel with a semiaustenitic structure. At room temperature, it consists of two phases, namely austenite (c-phase) and delta ferrite (d-ferrite, 5 to 20 pct). The amount of ferrite phase depends on the concentration of ferrite-forming elements such as Cr, Al, and/or Ti. This steel has a good combination of formability, high strength, and excellent corrosion resistance which is not easily matched by other materials and finds applications in nuclear power plants, petrochemical industries, and as a spring material.[4–6] 177 PH steel suffers from certain disadvantages. For example, (i) the fine intermetallic phases tend to coarsen at high temperature and long aging, thus making dislocations pass easily through them, leading to decrease in ANKUR GUPTA, Graduate Research Assistant, formerly with the Department of Materials Science and Engineering, Indian Institute of Technology, Kanpur, Kanpur 208016, India, and also with the Department of Metallurgical & Materials Engineering, Malaviya National Institute of Technology, Jaipur 302017, India, is now with the Advanced Materials Processing and Analysis Center, Department of Materials Science & Engineering, University of Central Florida, Orlando, FL 32816. Contact e-mail: [email protected] A.K. BHARGAVA, Professor, is with the Department of Metallurgical & Materials Engineering, Malaviya National Institute of Technology. R. TEWARI, Scientist, is with the Materials Science Division, Bhabha Atomic Research Centre, Mumbai 400085, India. A.N. TIWARI, Professor, is with the Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology, Bombay, Mumbai 400076, India. Manuscript submitted June 23, 2012. Article published online May 23, 2013 4248—VOLUME 44A, SEPTEMBER 2013
strength and (ii) this steel has high strength, but reduced toughness. The addition of boron is known to improve the mechanical properties of steels and therefore investigations have been carried out on the modified compositions of various grades of steels by addition of boron.[7–11] The normal solubility limit of boron in austenite and ferrite is 0.02 wt pct [1423 K (1150 C)] and 0.01 wt pct (eutectic temperature), respectively,[12] and hence the RS technique is preferred to enhance the solubility of boron in austenite. In this context, it is worth mentioning here that Bhargava and Tiwari[13] used the same technique for alloy 800 (nonhardenable alloy by heat treatment) with boron (0.45 to 1.35 wt pct) and titanium (1 to 3 wt pct) additions and observed age-hardening effect in the modified compositions. Previous studies show an improvement in creep strength of austenitic steels by the addition of boron up to 10
Data Loading...
