Olejnikova Oksana

Faculty: Physic-metallurgycal
Speciality: Metal science

Theme of master's work:

The impact of cold deformation on phase-structural transformations in steel after heat treatment

Scientific adviser: Alimov Valerij

Summary of research and developments

With the increase of strain-hardening level the strength properties of metals are improved but the ductility property are weakened. The strain-hardening is accompanied by lattice distortion of metal - formation of new dislocations, shattering of grains, their flattening and elongation in the direction of the largest metal flow, the anisotropy of properties is appeared in the metals [1].
The decomposition of cement carbide in hard-wrought steel is possible only at the heating up to А_c1 [2]. Short soaking at the little strains foster the growth of austenite grain, but at the big strains – brake it [3]. The preliminary strain-hardening extends the transformation range of perlite to the austenite [4].
The purpose of the work is the investigation of the behavior of the eutectoid steel at the heating lower and above the point А_c1.
The analysis of balling-up of hard-wrought steel was made. The specimens of steel 85 were annealed at T=670±10^oC and τ=0,08-6 h, after that the microstructure was examined, the micro hardness was measured.
The dependence of micro hardness from annealing duration is shown on figure 1.

Figure 1 - The steel 85 strain efficiency on the its micro hardness

It appears that the coalescence of cementite comes out at the soaking 5 minutes but after 6 h the cementite has the form of globules.
At the small durations of soaking the curve of steel micro hardness reshapes the curves of strain-hardening samples, at the big duration of soaking the steel strength degradation is appeared increasing the degree of strain.
The kinetics characteristics of diffusion decay of under cooled austenite in hard-wrought steel are fixed in conditions of continuous cooling. The results are shown on the figure 2.

The kinetics characteristics of diffusion decay of under cooled austenite in hard-wrought steel are fixed in conditions of continuous cooling. The results are shown on the figure 2 [5].

Figure 2 - The dependence of the decay time of 2, 50 and 100% of under cooled austenite

One can see that the preliminary strain-hardening of steel speeds up the diffusion decay of austenite in condition of continuous air cooling after austenization at 800-1100^oC. The received objective data are recommended to use in aero sorbitizing technology of blank of high-tensile wire.

The literature

1. www.delta-grup.ru/bibliot/
2. Белоус М.В., Черепин В.Т. Изменения в карбидной фазе стали под влиянием холодной пластической деформации//ФММ. – 1962, Т.14, вып.2. – С. 312-315.
3. Алимов В.И., Андреева Л.Н. Влияние холодной деформации на размер аустенитного зерна в эвтектоидной стали// Изв. вузов. Черн. Металлургия. – 1983, №10. – С. 149.
4. Майструк А.Я., Ткаченко Ф.К., Мельниченко А.И., Веселов И.А. О влиянии скорости нагрева на превращения в холоднодеформированной стали// Изв. вузов. Черн. Металлургия. – 1976, №6. – С. 109-111.
5. Алимов В.И., Олейникова О.В. О влиянии предварительной холодной деформации на процессы структурообразования при термообработке сталей//Вісник науковця-2009: Збірник матеріалів всеукраїнської науково-практичної конференції. – Миколаїв: НУК, 2009. – С. 222-224.