SU1486887A1 - Method of determining succeptibility of steel to thermal cracking - Google Patents

Description

The invention relates to a testing technique, in particular to the tests for strength. The purpose of the invention. 2

- the sensitivity is increased while reducing the time of testing by forming a high degree of heterogeneity of the deformation field in the surface layer. Steel samples are subjected to a double-cycle heating-cooling. In the first cycle, heating is carried out to a martensitic transformation, and cooling is carried out at a rate that ensures the formation of a hardened layer. In the second cycle, heating is carried out to temperatures below the temperature of phase transformations, which creates prerequisites for cracking due to the creation of a non-uniform deformation field. 2 tab. about

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The invention relates to a testing technique, in particular to the tests for strength.

The purpose of the invention is to increase the sensitivity while reducing the time of testing by forming a high degree of heterogeneity of the deformation field in the surface layer.

The method is as follows.

Steel samples are subjected to cyclic heating and cooling. Heating is carried out using an inductor, and cooling - using a sprayer. Moreover, during testing, the inductor is moved along the sample and the sprayer directly behind it, which allows creating the condition of localization of both heating and cooling and using the entire sample length for testing, which is equivalent to N number of samples. Spray cooling with direct following the inductor reduces to a minimum the time between heating and cooling, which contributes to an increase in volumetric changes on the sample surface from thermal effects. The tendency to temperature cracking is determined in two heating-cooling cycles.

In this case, in the first cycle, heating is carried out to the austenitic state, and cooling to the creation of a hardened layer with a martensitic structure, i.e. the first cycle provides a martensitic transformation that determines the degree of embrittlement; in the second cycle, heating is carried out to temperatures below the phase pre-temperature

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rotations. The second cycle creates the prerequisites for cracking by the formation of a high degree of inhomogeneity of the deformation field due to the superposition of volumetric changes in the surface layer due to structural transformations of tempering and cooling conditions. High heterogeneity | deformation field determines the high sensitivity of the method. A double heating-cooling cycle shortens the test time compared to the prototype where multiple heating-cooling cycles were performed.

Example. The tendency to cracking is determined on cylindrical specimens with a diameter of 70-117 mm and a length of 180 mm with a surface treated with 1, 25 steels: HVG, 9x2MF, 50x2F. Steel samples are made from rolled products without any prior heat treatment. Samples of 9x2MF and 50x2F steels were forged from. ingots (15 kg) melted in an induction furnace with a capacity of .60 kg. The chemical composition of the steel is given in table. G.

Samples of 9x2MF and 50x2F steels with an allowance for heat treatment (~ 1 mm per radius) are subjected to preliminary ^ heat treatment according to the mode: heating temperature 920930 ^o C, time, holding for 3 hours, cooling in calm air, again heated to 770-780 ° C , holding 3 h, cooling to 600 ° C at a speed of 25 / h, further cooling at a quiet

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The test is carried out on the installation with the generator of high-frequency currents LZ 207, the sample is rotated at a speed of 109 rpm, the speed of movement of the inductor varies from

0.5 to 4 mm / s depending on the set heating temperature. The data of the tests to determine the tendency of steel to cracking both the proposed and known methods are given in table. 2

From tab. 2, it follows that a two-time heating-cooling cycle according to the proposed method causes cracking of the steel during the cooling cycle of the second cycle, which makes it possible to estimate the tendency of the steel to crack. At the same time, even a tenfold heating - cooling cycle, by a known method, does not lead to cracking of the tested steels. To obtain the effect of cracking it is necessary to spend a significant number of cycles.

Claims (1)

Claim The method for determining the tendency of steel to temperature cracking is that the steel sample surface is subjected to heating and cooling and its cracking tendency is determined, characterized in that, in order to increase sensitivity while reducing the test time by forming a high degree of non-uniformity of the deformation field in the surface layer , heating and cooling are carried out twice; in the first cycle, heating is carried out to the austenitic state, cooling to the creation of hardened sl oya with martensitic structure, and in the second cycle e heating is carried out to temperatures below the temperature of phase transformations. steel grade 9x2MF 50x2F Table 1 Content elements weight.% WITH Mp 8ί Goog _g --- Moe eight Νί 0 _? 94 0.43 0.61 1, 95 0.14 0.28 0.021 0.035 0.26 0.51 0.55 0.50 2.14 0.14 0.05 0,019 0.034 0.27 1486887 ^θ table 2 Mark Diameter Length Cycle Tempera- Original Availability become form- sample, tour on state cracks ca, mm mm warming ° s ______ ___________ , - | | g - hvg 117 180 . one 2 1150 690 Rental Yes 9x2MF 90.70 180 one 950,970 FKS, 220NV, 2 650,690 grain number 10-11 Yes 50x2F 90.70 180 one 970 FKS.210NV, 2 690 grain number 10-11 Not hvg 117 180 ten 690 53-55 NKS Also 117 180 ten 750 53-55 NKS 9x2MF 90 180 ten 690 53-55 NKS 90 180 ten 750 53-55 NKS 50x2F 90 180 ten 690 53-55 NKS 90 180 ten 750 53-55 NKS Note “The cooled medium is water.