Delaminations by Cleavage Cracking in Duplex Stainless Steels at Sub-zero Temperatures
- PDF / 1,756,351 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 68 Downloads / 206 Views
INTRODUCTION
DUPLEX stainless steels (DSS) consist of ferrite and austenite. For hot-rolled plates, the phase composition is usually 50 pct of each phase. The advantage of mixing the two phases is that the resulting material has good retained properties from both phases. Some examples are the high mechanical strength and resistance to stress corrosion cracking in the ferrite and the high toughness in the austenite. These alloys are often used in applications that require high corrosion resistance and mechanical strength. Some examples are pipelines for the offshore industry, production equipment for the pulp and paper industry and pressure vessels.[1] Due to the ductile to brittle transition temperature (DBTT) region for the ferritic phase at sub-zero temperatures (°C), the use of DSS at these service temperatures has traditionally been limited. However, fracture mechanical testing shows that both the base metal and weldments have high fracture toughness at low temperatures.[2–4] For hot-rolled plates of DSS, a delamination phenomenon, also known as splits, occurs during fracture and impact toughness testing.[2,3,5] It has been shown that the delaminations increases the toughness of the DSS by the creation of free surfaces inside the specimen which decreases the triaxial stress state in the specimen.[6] For impact toughness testing, the measured energy absorption is the sum of the energy for crack initiation, Ei, and the energy for crack propagation, Ep.[7] An JOHAN PILHAGEN, Ph.D. Student, and ROLF SANDSTRO¨M, Professor, are with the Materials Science and Engineering, Royal Institute of Technology, KTH, Brinellva¨gen 23, 10044 Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted September 15, 2012. Article published online October 17, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
initiated cleavage fracture can either arrest in neighboring grains or propagate unstably through the specimen and cause failure. In the latter case, Ei is the controlling factor and Ep is in many cases negligible, as for example in neutron-irradiated steels.[8] Delamination increases the proportion of Ep of the total absorbed energy and can be the controlling factor.[9,10] This article aims to analyze the origin of the delaminations and how the microstructure influences the toughness of hot-rolled DSS at the DBTT region. The methodology used was fractographic investigation of impact toughness specimens tested in different orientations for 2205 base metal and LDX 2101Ò base metal. Interrupted fracture toughness tests of specimens from 10 and 50 mm plates of 2205 base metal were also performed.
II.
MATERIAL, FRACTOGRAPHY, AND TESTING PROCEDURE
A. Material The materials used in this work were commercially produced DSSs designated 2205 (EN 1.4462, UNS S32205) and LDX 2101Ò (EN 1.4162, UNS S32101), produced by Outokumpu Stainless AB. The material was hot-rolled to the desired plate thickness (10, 30 and 50 mm for the 2205 and 30 mm for the LDX 2101Ò) followed by solution treating at 1373 K (1100 °C) and water quenching.
Data Loading...
