Effect of quenching and partitioning process on MA constituent in Nb-bearing HSLA steel

Abstract

The effect of quenching-partitioning (Q-P) process on martensite-austenite (MA) constituent is investigated by the thermo-analysis simulator for a niobium-bearing HSLA steel. The process includes quenching from 950 °C to the intermediate temperature of 350–550 °C at the rate of 30 °C/s and subsequent reheating at the rate of 20–50 °C/s and partitioning at 660–800 °C. The microstructure is characterized by nano probe, EBSD, colored metallograph, optical microscope and graphic analytic method. The results show that the improvement of distribution homogeneity of MA in microstructure, the diminishment of the MA average grain size and increment of the MA volume fraction is caused by the intermediate temperature decrease, the reheating rate increase and a proper partitioning temperature. The volume fraction of MA is up to 7.9% while the sample is quenched to 450 °C, reheated at 50 °C/s and partitioned at 750 °C. The grain is granular or equiaxed in shape and the average grain size of MA is about 0.77–1.48 μm after treated by Q&P process. The grains tend to be coarse and with sharpy-angle as the intermediate temperature is up and the reheating rate and the partitioning temperature rises. The MA volume fraction depends on the untransformed austenite volume fraction after quenching and carbon diffusion time and temperature during partitioning process.

Keywords

quenching / partitioning / transformation / martensite-austenite / HSLA

References

[1] N Suzuki, A Kato, M Yoshikawa, et al. Development of the Linepipe Superior to Buckling Resistance Property[R]. NKK Technical Report, 1999:44–49

[2] Ishikawa N., Parks D. M., Socrate S., . Micromechanical Modeling of Ferrite-Pearlite Steels Using Finite Element Unit Cell Models [J]. ISIJ, International, 2000, 40(11): 1 170-1 179.

[3] Thomas H., Shigru E., Noboyuki I., . Effect of Volume Fraction of Constituent Phases on the Stress-Strain Relationship of Dual Phase Steels [J]. ISIJ International, 1999, 39(3): 288-294.

[4] Endo S., Nagae M. Ferrite-Martensite Dual Phase Anti-erosion Steel[J]. ISIJ international, 1996, 36: 95-100.

[5] Ishikawa N., Okatsu M., Endo S. High Deformability UOE Linepipes Produced by Advanced TMCP Technology[C]. Proceedings of International Symposium on Microalloyed Steels for Oil and Gas Industry, 2006 Brazil Araxa-MG

[6] Li H. L., Li X., Ji L. K. Strain-based Design for Pipeline and Development of Pipe Steels with High Deformation Resistance [J]. Welded Pipe and Tube, 2007, 9(5): 5-11.

[7] Shikanai N., Mitao S., Endo S. Recent Development in Microstructural Control Technologies through the Thermomechanical Control Process (TMCP) with JFE Steel’s High-Performance Plates[R]. JFE Technical Report, 2007, 18: 1-6.

[8] M C Zhao, K Yang, Y Y Shan. The Effects of Thermo-mechanical Control Process on Microstructures and Mechanical Properties of a Commercial Pipeline Steel [J]. Materials Science and Engineering, 2002: 14–20

[9] Speer J., Matlock D. K., De Cooman B. C., . Carbon Partitioning into Austenite after Martensite Transformation[J]. Acta Materialia, 2003, 51(9): 2 611-2 622.

[10] Mitsuhiro O., Nobuo S., Joe K. Development of a High-Deformability Linepipe with Resistance to Strain-Aged Hardening by HOP[R]. JFE Technical Report, 2007, 17: 20-25.

[11] Li J. X., Ohmura T., Tsuzaki K. Effect of Microstructure on Nanohardness Distribution of Middle Carbon Martensite Steel [J]. Science in China (Series E), 2005, 35(11): 1 127-1 136.

[12] Ohmura T., Tsuzaki K., Matsuoka S. Nanohardness Measurement of High-purity Fe-C Martensite[J]. Scripta Mater., 2001, 45: 889-894.

[13] Kang M. K., Guan D. H., Guo C. D. The MA Constituent of Low Alloy High Strength Steel[J]. Journal of Northwestern Polytechnical University, 1979, 2: 10-14.

[14] He X. L., Shang C. J., Yang S. W., . High Performance Low Carbon Bainite Steel[M], 2008 Beijing Metallurgical Industry Press

[15] Xu Z. Y., Li X. M. Diffusion of Carbon during the Formation of Lowcarbon Martensite[J]. Acta Metallurgica Sinica, 1983, 19(2): 83-84.