Korean Journal of Materials Research (한국재료학회지)

Materials Research Society of Korea (한국재료학회)
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Continuous Cooling Transformation, Microstructure and Mechanical Properties of High-Strength Low-Alloy Steels Containing B and Cu

B과 Cu가 포함된 고강도 저합금강의 연속냉각 변태와 미세조직 및 기계적 특성

  • Hwang, Byoungchul (Department of Materials Science and Engineering, Seoul National University of Science and Technology)
  • 황병철 (서울과학기술대학교 신소재공학과)
  • Received : 2013.08.27
  • Accepted : 2013.09.09
  • Published : 2013.09.27
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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.

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References

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