Improvement sorbitizing wire in granular media with a view to abolishing patenting in molten salts
Heavy wire is widely used in various industries, including the manufacture of ropes, springs, steel cord reinforcement for prestressed concrete. Most of which are made from high-strength wire products are critical components of complex machines and structures, so they are subject to high standards of quality, which are constantly increasing in the modern technogenic world.
The main problem in the production of high-carbon wire steels is to obtain the limit of technological, physical, mechanical and performance properties, the solution of which many papers, but to date this issue remains relevant.
Well established that the optimal properties of the wire provides a structure of sorbitol interlamellar distance in the blank of 0.2 - 0.4 microns and microhardness Íμ = 2500-3500 N/mm2.
To obtain the optimal structure of rods subjected to patenting salts on steel wire factories, that is dangerous, harmful and costly. So it is still quite a lot of attention is paid to the search for more environmentally-friendly, safe and resource-saving way to produce sorbitol structures in high-carbon wire rod intended for redistribution to high-strength wire.
The purpose of this research is to study the conditions of formation of the structure of sorbitol in high carbon wire rod, designed for redistribution to high-strength wire using granular media, in particular the study of the kinetics of the processes occurring during cooling medium silver wire in graphite as a clean environment and less costly than melts of salts used in the heat treatment of wire.
Material, methods and equipment for research.
During the study used a wire diameter of 2 mm eutectoid steels (carbon content 0.8%) which had been previously subjected to cold plastic deformation with different degrees of deformation of 0%, 27%, 47%, 61%, 69%, 75%.
In the first experiment studied the effect of the conditions of formation of the structure of sorbitol in high carbon wire rod by austenitizing and then cooling in bulk graphite powder.
This sample 6 was selected (l = 30 mm, d = 2 mm) of the eutectoid steel after HFA with different degrees of deformation of 0%, 27%, 47%, 61%, 69%, 75%. Samples were charged into the electric heating furnace preheated to a temperature T = 800 ± 10°C. The total time of heating and holding at that temperature was = 6 min. The samples were then cooled in a medium of particulate graphite dispersion - 0.0063 mm at room temperature.
Experiments by the construction of the kinetic curve was carried out on wire samples of eutectoid steel (0.83% C) dimensions (l = 30 mm, d = 2 mm) with an initial pearlite.
Samples were charged into the electric heating furnace ÌÏ-2ÓÌ preheated to a temperature of 900 ± 10°C. Total heating and soaking at this temperature was 10 minutes.
After exposure the sample was first quenched in water and the subsequent one quickly transferred to a graphite crucible containing silver dispersity grade = 6,5 mkm (Trp = 25°C) to prevent heat loss, and held for 1 - 120 seconds, and then quenched in water.
The samples were mounted into thin sections with subsequent etching. Then studied the microstructure of the longitudinal and cross-sectional samples on microscope MIM - 7, followed by photographing them. Determination pearlite lamellar dispersion was performed using a microscope NEORNOT-21 in three different fields of view at a magnification of 2,000 times using immersion media.
Also studied the microhardness on a PMT-3 microhardness under a load of 0.5 H.
On the microstructures of the samples was evaluated by the percentage of transformation of austenite grain boundary-crossing method (GOST 5639-82) and built the kinetic curve.
Experimental results
1.The microstructure of the sample with a degree of deformation of 47% after sorbitizing shown in figure 1.
Figure 1 - The microstructure of a sample with a degree of deformation 47% after sorbitizing (longitudinal section, *2000).
2.Hardness of the specimens after cold plastic deformation (HFA) and a heat treatment is shown in figure 2.
Figure 2 - The microhardness of samples after cold plastic deformation (HFA) and heat treatment.
It can be seen that the microhardness and microstructure patterns consistent with structure type sorbitol features due to preliminary cold deformation thereof.
3.Microstructure of the longitudinal section of the samples after heat treatment with shutter speed of 1, 5, and 10 are shown in figure 3.
Figure 3 - The microstructures of the samples after aging heat treatment: a) 1c b) 5c c) 10 c (longitudinal section, *476).
From the pictures it is clear that at 1 with the structure consists of martensite when exposed 5 with a partly consists of martensite and pearlite transformation products, and 10 - completely out of the perlite.
4.Microhardness of the structural components of the samples from the isothermal holding time in the graphite is shown in figure 4.
Figure 4 - The dependence of the microhardness of the structural components of the sample on the time of isothermal holding.
From the graph it is seen that in the range 1 - 8 with sufficiently high micro-hardness and microhardness correspondence martensite in the range of 5 - 8 is part of the structural components microhardness proper martensite, and a part varies in the range 2000 - 3200 N/mm2, which corresponds microhardness Product pearlite transformation, including sorbitol and after 8 microhardness correspondence microhardness perlite.
5.The experimental kinetic curve of austenite to pearlite is shown in figure 5. The percentage of conversion of austenite delayed on the ordinate plotted on the horizontal axis corresponding to the holding time of the sample at the appropriate temperature T. Thus, a kinetic curve, which shows the start time (5% P) and end (95% P) transformation.
Figure 5 - kinetic decay curve of austenite during cooling in graphite.
From the resulting curve shows that the transformation of austenite > pearlite begins at 4 and ends at 8.
Conclusions.
1. The heating wire 2 mm in diameter and 800°C and subsequent cooling the graphite powder, located at room temperature, lead to the formation of the structure of sorbitol, which allows to replace the saline bath during patenting, thereby leading to improved working conditions.
2. Experimentally derived kinetic curve austenite to pearlite structure that determines the possibility of further construction of isothermal curves with a view to establishing conditions for the formation of sorbitol structure during wire sorbitizing graphite medium.
List of references
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