Expansion curve analysis method for steel critical point test and use thereof

Abstract

The invention provides an expansion curve analysis method for a steel critical point test and a use thereof. The expansion curve analysis method comprises drawing an expansion curve by temperatures T as horizontal coordinates and expansion amounts L as vertical coordinates in data recorded by a dilatometer, respectively carrying out linear fitting on linear expansion parts at the left and right sides of the expansion curve to obtain straight line equations L alpha and L gamma of the corresponding expansion amounts and temperatures, calculating a high temperature phase (gamma phase) volume fraction X gamma, drawing a curve by T as a horizontal coordinate and X gamma as a vertical coordinate, selecting an appropriate critical volume fraction C according to concrete experimental requirements, finding temperatures T respectively corresponding to two points with X gamma equal to C and X gamma equal to 100%-C from the X gamma-T curve, wherein the temperatures T are used as critical points, and expressing test results comprising the transformation critical points and critical volume fractions C. The expansion curve analysis method solves the problem that the tangent method, the extremum method, the angular cut method and the average method have undefined physical significance or easily is influenced by a subjective factor, and improves an objective quantification degree of expansion curve analysis.

Description

technical field [0001] The invention relates to an expansion curve analysis method suitable for steel critical point testing, which belongs to the field of material testing. Background technique [0002] The basis for formulating the heat treatment system of steel is its solid-state phase transformation critical point. One of the main methods of critical point testing is the inflation method. The low-temperature phase (α-phase) and high-temperature phase (γ-phase) of steel have different specific volumes. When polymorphic phase transition occurs, the volume effect caused by the phase transition is superimposed on the effect of thermal expansion and contraction, destroying the relationship between expansion and contraction. Therefore, the critical point of phase transition can be determined according to the change of thermal expansion behavior reflected by the expansion curve (expansion amount-temperature curve). [0003] The expansion curve analysis methods for testing the...

AI Technical Summary

Problems solved by technology

[0004] However, there are deficiencies in the above-mentioned various expansion curve analysis methods.

The tangent method conforms to the principle of metallurgy and is theoretically correct, but the judgment of the separation point between the extension line of the straight line and the curve is easily affected by the subjective factors of the observer, and the analysis results of the same expansion curve by different observers have large deviations

The judgment of key points by extreme value method, angle cut method and average method is not easily affected by subjective factors of observers, but the physical meaning of key points is not clear, and there is actually a systematic error between the corresponding temperature and the real phase transition critical point

Therefore, the existing expansion curve analysis methods are difficult to meet the requirements of clear physical meaning and objective quantification at the same time.

Images