Measuring and testing – Hardness
Patent
1996-06-19
1997-10-21
Dougherty, Elizabeth L.
Measuring and testing
Hardness
324228, G01R 3312, B23Q 1720, G01N 300
Patent
active
056798873
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to testing of hardness steels. In particular, the invention relates to a method of estimating mechanical hardness of a steel from its magnetic properties.
2. Description of the Related Art
In the production of steel, and especially low-carbon non-oriented electrical steels, the hardness of the steel is one parameter which is frequently tested. In the continuous decarburisation annealing of electrical steels, hardness is sometimes used as a parameter to determine the correct working of a continuous processing line, but up till now it has only been measurable accurately by off-line mechanical means. This has meant that the line is often stopped and destructive testing of a sample undertaken.
It is known that the mechanical hardness of steels, particularly magnetically soft electrical steels but including hard steels, is related to the magnetic properties of the steel but in a way that is difficult to use for mechanical hardness determination.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of estimating mechanical hardness of steel from its magnetic properties.
According to the present invention in one aspect there is provided a method of estimating mechanical hardness of a steel, the method comprising the steps of determining a plurality of magnetic parameters of the steel, estimating for each such measured parameter one or more probable hardness ranges by reference to a stored set of hardness ranges and associated parameters and combining these estimates to provide an estimate of mechanical hardness of the steel.
Preferably three parameters are measured and these may be coercivity, power loss and permeability. The parameters may be measured simultaneously. For a magnetically soft steel, the steel may be enwrapped by a pair of coils the first carrying an alternating electrical current to apply to the steel an alternating magnetic field and the other measuring the magnetic flux density thereby induced, said measurements being used to determine the measured parameters.
In another aspect, the invention provides a method of estimating mechanical hardness of a steel, the method comprising the steps of measuring the mechanical hardness and magnetic parameters of a multiplicity of steel samples of like chemistry and storing these measured values in a data bank in a plurality of quantised groupings of hardness against each measured magnetic property, measuring a plurality of magnetic parameters of the steel whose hardness is to be estimated, comparing each such measured parameter with the quantised groupings of stored value of that parameter in the data bank to determined in which quantised grouping the parameter falls, comparing the determined quantised grouping for each measured parameter, and estimating thereon the mechanical hardness of the steel.
The invention will now be described by way of example and with reference to the accompanying drawings,
DESCRIPTION OF THE FIGURES OF DRAWINGS
FIG. 1 is a typical hysteresis loop for a magnetic steel;
FIG. 2 is a schematic diagram of an arrangement of continuous tester for on-line magnetic measurements;
FIGS. 3, 4 and 5 show respectively the coercive field strength, specific total power loss and relative permeability against Vickers hardness for a silicon steel; and
FIGS. 6 and 7 show the results of approximated hardnesses for two steels.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As has been explained, the magnetic parameters of steels show a correspondence to the mechanical hardness of the steel. Three parameters that have been shown to have a relationship with mechanical hardness are coercivity, power loss, and permeability. These standard parameters are illustrated in FIG. 1 which is a typical hysteresis loop showing the relationship of magnetic field strength H against magnetic flux density B for a typical material. It should be noted that, on the scales normally used, the H axis has been exaggerated in scale for clarity in respect of
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IEEE Transducer Conference, Washington, D.C., USA, 10-11 Feb. 1969, vol. ieci-16, ISSN 0018-9421, IEEE Transactions On Industrial Electronics and Control Instrumentation, Jul. 1969, USA, Gibson C. A. et al., "A Magnetic Means of Monitoring Hardness Due to Heat Treatment in Steel Production".
Beckley Philip
Meydan Turgut
Moses Anthony J.
Page James H. R.
Salmasi Zareh S.
Dougherty Elizabeth L.
Noori Max H.
Orb Electrical Steels Limited
University College Cardiff Consultants Limited
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