Kanayev A.T., Bakizhanova D.S.

Eurasian National University named after L.N. Gumilev

Deformative and thermic strengthening of mooving corner profiles in the stream of rolling machine

Shaped profiles of rolling (corners, channels, double-T and others) are characterized by irregular distribution of metals in section, which demands regulated selection of heat from different parts of their section in combined deformational and thermic working with rolling heat. During thermic correcting and deformational and thermic working of corner profiles it is necessary to consider that metal volume per unit top, therefore it is necessary to supply increased heat selection from the cornet top for equal cooling. In this connection the water quantity given to the top must be more over 15-20% than on the leg.[1]

For the providing with equal structural and phase transformation in section of the profile the water outlay correlation per unit cornet surface from above and below for the legs must be 1:1, for the top 1: (1,2 – 1,4). The researchings show that in the process of interupted heat strengthening hogging happens to the side of more intensive cooling. In the result of this the maintenance in the process DTU of given water outlay correlation from above and below for the top and it will provide equal cooling and prevent hogging.[2]

According to these conditions the universal installation of intensive and regulated cooling was used for the thermic correcting and DTU of equal corner profiles, which allowed, from the first side, to prevent large thermic and phasal voltage calling hogging and from the second side, to intensity cooling process, which is important for DTU low-carbon steel (Art. 3, art. 5) with high sense of critical heat strengthening speed.[1,2]

The installation of rapid and regulated cooling includes two important blocks: the block of selected cooling of different elements of corner profile water stream and the block of deep cooling in vortical water stream.

Owing to good steam conditions and uninterrupted blows of steams on the metal surface film boiling stage by stream cooling is practicaly absent, that is conform to the cooling increasing.

Moreover at the result of rich inflow to the cooling surface and short – term contact with it water has no time to overheat and its cooling ability does not change. Stream cooling dignity, which is realized in the installation of rapid cooling, is an opportunity of intensive cooling changing in wide limits due to the changing of quantity and speed of water stream from the nozzle, and also cooling zone width by means of nozzle turning in collectors during tuning on definite profile size.

High cooling effectiveness in the second knot – in the rapid water stream on big stages of vortical water stream – may be explained by intensive diversions and team condensation, and also uninterrupted renewal incoming to the reaction water volume on the whole surface of cooling corner part, which is not possible to reach on the other ways of cooling.

For the installation of the technological factors on the machanical means of corner profiles from the art. 3 kp and art. 3 sp. the deformational and thermic working was realized by different conditions. Temperature of rolling rinks was changed, and also duration of a pause between the end rolling rinks and the beginning of intensive cooling. Duration of intensive cooling and pressure of water in the chamber of intensive cooling constantly supported. Keeping Si in the steel was estimated on its mechanical properties. Technological conditions of processing and measured on standard methods mechanical properties of the strengthened structures from steel art. 3 kp and art. 3sp. are presented in the table 1 – 2.

Table 1. Mechanical properties of steel art. 3kp after rolling and intensive cooling during 2 seconds under pressure 0,6 MPa

°				,%
		/	/
900	≤ 1	390	280	24
1000	≤ 1	370	250	25
1070	≤ 1	365	235	25
940	5	370	260	25
1000	5	355	245	26
1070	5	350	230	25
940	10	365	240	25
1000	10	350	235	26
1070	10	345	225	26

Commentary – st. 3kp (%: - 0,19; Mn – 0,56; Cr – 0,23; Si – 0,04; P < 0,04; S< 0,04).

Table 2. Mechanical properties of steel art. 3sp after rolling and intensive cooling during 2 seconds under pressure 0,6 MPa

°				,%
		/	/
900	≤ 1	580	400	14
975	≤ 1	525	380	19
1070	≤ 1	485	370	21
900	5	560	385	15
975	5	515	375	20
1070	5	485	345	21
900	10	515	375	16
975	10	480	340	19
1070	10	460	325	20

Commentary – st. 3kp (%: - 0,19; Mn – 0,56; Cr – 0,23; Si – 0,04; P < 0,04; S< 0,04).

The given tables show, that important technology factors DTU of lowcarbonic steels in which strengthening processes during and upon termination of hot deformation proceed with the big speed, is t, r, and r, directly influencing temperature and final mechanical properties of a strengthened product.

The temperature of the rolling end has special value, which for the investigated angular structures makes 880-900°C. Coolings from such temperatures can pass processes static cell formation and recrystallization, that changes structure in comparison with that, which was at the moment of the end of rolling.

Therefore among parameters on which the structure formed during hot rolling is estimated, for results of deformational and thermal hardening its thermal stability is important. As it was already marked, it is connected with the structure and properties of martensite, formed at deformational and thermic hardening, in many respects inherit subgrain structure and dislocational textures of initial heat formed austenite. In this connection the preservation of optimum structure, formed during and upon termination of hot deformation, has important and in some cases defining value.[3]

The results of industrial experiments on influence establishment of the temperature of the end of rolling t, pauses between the end of rolling and the beginning of intensive cooling r, at constant duration of intensive cooling r on mechanical properties of equal corner 50x50x50 from the steel %: C – 0,21, Mn – 0,62, Si – 0,27, S< 0,03, P< 0,04, Cr – 0,26 are given in the table 3.

Table 3. Influence of technological parameters on mechanical properties of the equal corner from the steel.

°	900	975	1070	Parametres of cooling
, MPa , MPa , %	580 397 14,0	523,0 380,0 19,0	485 371 21,0	Δτ = 0,2 с τ = 2 с Р = 0,6 MPa
, MPa , MPa , %	559 383 14,0	515,0 376,0 20,5	483 347 21,0	Δτ = 0,2 с τ = 2 с Р = 0,55 - 0,6 MPa
, MPa , MPa , %	513 375 16	482,0 339,0 19,0	461 288 19,0	Δτ = 6 с τ = 2 с Р = 0,5 - 0,6 MPa

From experimental data follows, that decrease in the end of rolling with 1070 C up to 900 C leads to growth of strong properties though at pauses 3 c and 6 c growth of strengthening properties weakens in a greater degree, than more pause (6 c). Mechanical properties of carbonaceous steel St.3 sp by deformational and thermic hardening can be raised up to a level of mechanical properties of low-alloyed steels 12G2S, 09G2S by the standard 27772-88 rolling for thew building steel constructions. It gives the opportunity to replace low-alloyed steel 12G2S, 09G2S by deformational and thermic hardening of carbonaceous steel with the economy of alloying elements. Besides such replacement allows to improve technology of hot rolling as a rolling of firmer and less plastic alloyed steel, it is replaced soft rolling with more plastic low-carbon steel. The experiments show, that, despite of a heat of the end of rolling, the effect of high-temperature machining expressed in additional increase of durability at satisfactory of plasticity in comparison with properties, received at usual training from oven heating, comes to light absolutely definitely.

References:

1. Uzlov I.G., Savenkov V.Y., Polyakov S.N., Thermic working of the rolling. Kiev, Tehnika, 1991, 159 p.

2. Byhin B.B., Kanayev A.T., Kapuchak A.F. The researchings of thermic stropping process and deformational and thermic hardening of the corner profiles. News of universities, Black metallurgy, 1999, N 12, p. 24-27.

3. Kanayev A.T., Nechaev U.S., Prohorchenko N.V. To the question of mechanism of the thermic and mechanical hardening of low-carbonic and low-alloyed steel. Metals, News RAN, 1995, N2, p. 57-60.