HEAT TREATMENT OF LOW-CARBON AND LOW-ALLOYED STEELS
(UIX: 669.15-194 : 621.~85.~4)
A. E. Xakharov , N F. Lege ida , V . S . No$ov , and E. V.. Vo l
' te r
Tramlared from Metallovedenie i Termicheskaya Obrabotk a
Metallov. No. 11, pp. 20-21. November, 1965
The Ukrainian Scientific Re~earch Institute of Metals and the
Central Scientific Institute of Ferrous Metals together with the
Kommunar Metal Plant have developed a heat treatment (quenching and
tempering) for thick sheets of steel St. 3, This treatment consists
of quenching from 890-910"(= in waier after the sheets are kept at
this temperature for 1,5-2 rain per mm of thickness. The sheets
with the maximum concentration of carbon (0.20-0.22~) have a low
relative elongation (6 < 10~) after quenching; the relative
elongation can be increased by tempering at 500"(=. This tempering
ensures the best combination of mechanical properties.
At the Kommtmar Metal Plant the sheets wer~ heat treated in a
roller furnace; The quenching process makes it possible to cool
sheets 4-50 mm thick and up to 12 m long. Tim pressure of the
sprayer system is 2-3 arm. The sheet is clamped in sprayers placed
perpendicular to the press, which exerts 130 t on the sheeL
% *0
30
. 2o 70
(SKhL-4); - - - ) accelerated cooling;
' ( I ~ ,o
o r . kg/mm ~ ab, kg /mm t &9 ,aH'kgm/cm= 2I 3~ CZ ,r 5Z ,'0
Z8 2 t It OT, kg/mmZ Ob,kg/mm~t 6 ,9 a H.
tcgm/em t
. . . . . . . . . . . . .
r eJ .'r 62 70f4. ZE Z $fO o T. kg/mm t ob.kg/mm ~ 6.9 OH.
kgm/cm t
Frequency distribution of mechanical properties after
accelerated cooling in water and cooling in air for the following
steels: a) 14KhGS; b) 09G2; c) steel of the st. 3 type; d)
10KhSND
) cooling in air.
721
The mictostructure of the sheets in the initial state (after
rolling) consists of ferrlte with a small amount of pearhte. After
heat treatment the structure is pearlitic-fertitic (the amount of
pearlite increases).
The study' of the mechanical properties of St. 3ps steel before
and after heat treatment using samples cut in the directions
parallel and perpendicular to the rolling directions shows that the
impact strength of the heat-treated steel is higher than that of
untreated steel up to -40"C (3.9-7.4 and 1-1.5 kgm/cm 2.
respectively). The cold brit o tleness threshold determined by the
relative reduction in section of fiat samples with holes in the
center was the same for the treated and untreated steel between-2,5
and-30"C. Heat treatment increases the fatigue limit from 6 to 3~0;
the sensitivity to stress concentrations (ratio between the
ultimate strength of samples with and without holes) in heat
treated steel is lower than that immediately after roUing (0.92 and
0.89, respectively}.
We investigated not only the effect of heat treatment on thick
sheets quenched aRer heating in the furnace but also the
possibility of heating during rolling for the purpose of improving
the mechanical characteristics of steels 14KhGS, SKhL-4
(10KhS,'qD), 09G2, 45, SK, M16C, 3M, 20K (sheets 10-24 mm thick).
For this purpose an apparatus for accelerated cooling of thick
sheets was constructed behind the 2800 mill in the Kommunar Metal
Plant. This apparatus made it possible to utilize the rolling heat
to improve the mechanical properties. TO dete~ mine the influence
of accelerated cooling on the mechanical properties and structure
of these steels some of the sheets were cooled wi',h water in the
apparatus and some in air.
The sheets weie tested according to the GOST specifications
(rupture. bending, and fracture). The impact strength was measured
a t -40"c . Figure 1 shows the frequency distribution of the
mechanical properties of the steels investigated.
It can be .~.en that on the average o b and oTincrease by 2-4
kg/mm z as the result of beat treatment, the relative elongation
docreases by about '2%, and the impact strength increases by 0.5-L5
kgm/cm z, i.e., the improve- merit of the mechanical properties is
not very great. With increasing thickne~ of the sheet the effect of
water coolo ing decreases and is nonexistent when the thickness is
20 mm or mote.
