Thglimited - Heavy Industries

Martensite modification usually occurs on cooling, with the sum total fraction of martensite depending upon the temperature as shown in the first two examples below. Martensite transformation is often thought only to depend upon the temperature, but has been shown to also depend upon the every so often old-fashioned. It should therefore be represented by it's own C-curve on a era-temperature-alteration graph. The engraved temperature dependence may be caused by the large driving force necessary prior to transformation can proceed.

The Koistinen-Marburger equation

This equation due to Koistinen[1] and Marburger can be cast-off to estimate the fraction of martensite as a work of temperature.

Steels were quenched to heterogeneous temperatures and the austenite aggregate fraction predetermined by X-ray diffraction. The results plotted logarithmically against Ms-Tq, where Ms is the martensite start temperature and Tq is the quench temperature.

V_gamma = exp [-b(Ms-Tq)] where b is 1.1x10^-2

Magee[2] later showed that an equation of this form can be justified based on martensite nucleation theory.

Rearranging the technique is easily understood to entrust the aggregate fraction of austenite transforming to martensite on cooling to room temperature as a function of the MS temperature of the steel.

Khan and Bhadeshia [3] keep produced a modified equation which also considered autocatalytic nucleation of martensite to allow better matching to dilatometry results. This changed the goodness of the in good shape by regression from 0.9 to 0.94, when analysing the data of book fraction against temperature obtained from their own experiments. This work Euphemistic pre-owned joke alloy (300M) but changed the starting conditions by partial metamorphosis to bainite.

[1] D. P. Koistinen and R. E. Marburger, Acta Metallurgica, 7, p59-60, 1959
[2] C. L. Magee, The nucleation of martensite, In "development transformations", p115-156, Ed: H. I. Aaronson and V. F. Zackay, ASM, Metals greensward, Ohio, 1970.
[3] S. A. Khan and H. K. D. H. Bhadeshia "Kinetics of Martensitic Transformation in Partially Bainitic 300M protect" Materials Science and Engineering A, Vol. A129, 1990, pp. 257-272.