B과 Cu가 포함된 고강도 저합금강의 연속냉각 변태와 미세조직 및 기계적 특성 = Continuous Cooling Transformation, Microstructure and Mechanical Properties of High-Strength Low-Alloy Steels Containing B and Cu

다국어 초록 (Multilingual Abstract)

This study investigated the continuous cooling transformation, microstructure, and mechanical properties of highstrength low-alloy steels containing B and Cu. Continuous cooling transformation diagrams under non-deformed and deformed conditions were constructed by means of dilatometry, metallographic methods, and hardness data. Based on the continuous cooling transformation behaviors, six kinds of steel specimens with different B and Cu contents were fabricated by a thermomechanical control process comprising controlled rolling and accelerated cooling. Then, tensile and Charpy impact tests were conducted to examine the correlation of the microstructure with mechanical properties. Deformation in the austenite region promoted the formation of quasi-polygonal ferrite and granular bainite with a significant increase in transformation start temperatures. The mechanical test results indicate that the B-added steel specimens had higher strength and lower upper-shelf energy than the B-free steel specimens without deterioration in low-temperature toughness because their microstructures were mostly composed of lower bainite and lath martensite with a small amount of degenerate upper bainite. On the other hand, the increase of Cu content from 0.5 wt.% to 1.5 wt.% noticeably increased yield and tensile strengths by 100 MPa without loss of ductility, which may be attributed to the enhanced solid solution hardening and precipitation hardening resulting from veryfine Cu precipitates formed during accelerated cooling.

참고문헌 (Reference)

1 J. Koo, 14 : 2-, 2004

2 B. Hwang, The Korean Institute of Metals and Materials 22 : 28-, 2009

3 D. Raabe, 11 : 547-, 2009

4 S. K. Ghosh, 519 : 88-, 2009

5 L. Karlsson, 36 : 1-, 1988

6 X. L. He, 37 : 147-, 1989

7 A. Ghosh, 374 : 43-, 2004

8 B. L. Bramfitt, 21 : 817-, 1990

9 G. Krauss, 35 : 937-, 1995

10 I. Tamura, "Thermomechanical Processing of High-Strength Low-Alloy Steels" Butterworth & Co. Ltd. 1988

11 T. Gladman, "The Physical Metallurgy of Microalloyed Steels" The Institute of Materials 1997

12 D. H. Werner, "Boron and Boron Containing Steels" Verlag Stahleisen mbH 1995