Development of a Press-Hardened Steel Suitable for Thin Slab Direct Rolling Processing
- PDF / 3,112,346 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 74 Downloads / 153 Views
TION
THE thin slab casting and direct rolling (TSDR) process is essentially a low cost alternative for the production of thin gauge conventionally hot-rolled steel strip. TSDR-specific advantages include reduction of capital investments, low energy consumption, and substantially reduced CO2 greenhouse gas emissions.[1–6] The original TSDR technology was the Compact Strip Processing (CSP) technology. After the development of the CSP technology, several alternative TSDR designs have been developed to maximize the advantages of TSDR as compared with conventional hot strip mill processing. The TSDR technology has up to now been used mostly to produce commercial steel grades. The present contribution shows that advanced ultra-high strength automotive steel grade can also be developed for TSDR processing. Hot press forming (HPF), also known as hot stamping, press hardening, or die-quenching, is a technology to produce advanced ultra-high strength steels (AHSS) for automotive applications. The HPF JEWOONG LEE, Graduate Student, is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang, South Korea. BRUNO C. DE COOMAN, Professor, is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, and also Director, with the Materials Design Laboratory, Pohang University of Science and Technology, Pohang, South Korea. Contact e-mail: [email protected] Manuscript submitted April 10, 2014. Article published online October 18, 2014 456—VOLUME 46A, JANUARY 2015
process was originally developed by Norrbottens Ja¨rnverks in 1973 to produce press-hardened steel (PHS). It is now widely used to produce passenger safety antiintrusion parts and structural reinforcements such as door beams, impact beams, bumpers, pillars, and tunnels.[7–9] The most widely used PHS grade is 22MnB5. This steel grade has an ultra-high ultimate tensile strength (UTS) (~1500 MPa). The total elongation is rather limited, approximately 6 pct, because of its fully martensitic microstructure.[10] In this work, the development of a TSDR-specific PHS is presented. Figure 1 shows a schematic flow chart for the production of conventional cold-rolled 22MnB5 and compares it to the production route for the new TSDR-specific PHS. In general, cold-rolled 22MnB5 steel is produced by a series of process step shown in Figure 1(a). 22MnB5 is first continuously cast. The slab is cooled down to room temperature and reheated to about 1523 K (1250 C) prior to hot-rolling. The hot-rolled microstructure contains ferrite and pearlite. The hot-rolled strip is pickled and cold-rolled to a thickness of about 1.5 mm. Annealing for recrystallization and coating of the full hard strip is carried out in a continuous galvanizing line (CGL) or a continuous aluminizing line. An ultra-high strength fully martensitic microstructure is obtained by the HPF process using water-cooled dies.[11–15] The production of the TSDR-compatible PHS steel is shown in Figure 1(b). The hot-rolled strip is produced in a more cost-e
Data Loading...
