SU1499204A1 - Method of magnetic check of heat treatment of steel articles - Google Patents

Abstract

The invention can be used for non-destructive quality control of steel products. The purpose of the invention is to increase the reliability of the control. To do this, in the method of magnetic control of the heat treatment of steel products, magnetization is performed at a temperature above the Curie point of cementite and the measurement of the residual magnetization at the magnetization temperature, then the magnetized product is cooled, the residual magnetization is measured at least at one temperature below the magnetization temperature and the obtained value We judge the heat treatment mode. Remeasurement of the residual magnetization is performed, for example, after cooling the magnetized product to a normal temperature. 1 hp f-ly, 1 ill., 2 tab.

Description

The invention relates to non-destructive quality control of heat-treated steel products and is intended for use in the ferrous metallurgy and mechanical engineering to determine the compliance of the thermal treatment regime, for example quenching and tempering to isothermal quenching, given a technological process.

The purpose of the invention is to increase the reliability of the control by providing an unambiguous dependence of the control parameter on the heat treatment mode over the entire temperature range.

The drawing shows curves (1-4) of the dependence of the residual magnetization on temperature (for different heat treatment modes) obtained in one embodiment of the method.

The method of magically controlling the heat treatment of steel products is that the product is magnetized. at a temperature above the Curie point of cementite (), but below the Yori point of iron (768 C).

Then the magnetized product. cool- give, measure the residual magnetized. at least at one temperature below the magnetization temperature in the range of 20–600 ° C and judging by the totality of the obtained values, the mode of heat treatment is judged. These two values are compared with the table values of the corresponding values.

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residual magnetization for standard heat treatment conditions.

The entire temperature range of tempering or isothermal quenching can be divided into two intervals, in each of which one of the indicated values of the residual magnetization uniquely characterizes the mode. In the entire temperature range for a unique 10 mode characteristics, it is necessary to use a combination of two values of the residual magnetization.

For the implementation of the method, the product

magnetized at a temperature above the Curie point of cementite (220 ° C), but better than the Curie point of iron (). Magnetization at a higher temperature than the Curie point of iron does not make sense, since in this case the ferrite, which is the main structure of the component steel, practically loses its magnetic properties.

Example. Testing of the method is carried out on samples with a diameter of 3 mm and a length of 25 mm from steel 75G (C 0.74%; Ml 0.87%; Si 0.26%), which, after heating, underwent isothermal saKaJncy at temperatures of 300, 400 ,. 500 and 600 ° C. For the magnetic control, the sample is placed in a corundum tube with an outer diameter of 10 mm and a length of 250 mm and heated in a furnace to a temperature. Then, the sample tube is quickly removed from the furnace, magnetized by an electromagnet, and the residual magnetization of the sample is measured using an F 5050 microwebermeter. After cooling the sample to 20 ° C, its residual magnetization is measured again. The values of the residual magnetization of the samples at 300 ° C and after cooling to are given in

 Table

As can be seen from table 1 obtained for. For each sample, two different values of residual magnetization (at 300 ° C and after cooling to 20 ° C) unambiguously characterize the heat treatment mode.

Thus, the residual magnetization, measured only at one magnetization temperature of 300 ° C, has almost the same values for modes 1 and 2, which does not allow distinguishing these modes.

The method was also tested on samples of the same steel and of the same dimensions, but which, after heating to 900 C and quenched in water, were otiusk at temperatures of 300, 400, 500 and OOO C.

For the magnetic control of the mode from -1 start-up, the samples are magnetized at 300 ° C according to the described procedure, and the residual magnetization is measured at the magnetization temperature. Then the magnetized samples are cooled to SO with and the residual magnetization is measured at this temperature.

The obtained residual magnetization values are given in Table 2.

Table 2

As can be seen from abl.2, among the pairs of residual magnetization values obtained for each mode, there are no coinciding pairs. Therefore, the proposed method uniquely characterizes the mode, as a result of which the reliability of the control is increased.

Claims (2)

1. Method of magnetic control of heat treatment of steel products 51 that is, the product is magnetized at a temperature above the Curie point of cementite- and below the Curie point of iron and its magnetostatic parameter is measured at the magnetization temperature, which is so as to increase the reliability of the control, as a magnetostatic parameter the residual magnetization of the product is used, the product is cooled down after its measurement, and the residual magnetization is re-measured 700 Temlerotura azmeren1 /, C 99204 The strength at least at one temperature value less than the magnetization temperature, and the heat treatment mode of the product are determined from the totality of the measured residual magnetization values. 2. The method of Claim 1, about tlichi ay-10 u and in order to re-measure the residual magnetization after cooling the product to a normal temperature. 300 TSM / 7e / Sfffff / X7 a / vffgm / vf / sff- Ht / a, oc