d.t.s. Isagulov A.Z., Sultangaziev R.B., Tatibekov S.M., SultangazievаА.B.

Chemical and metallurgical Institute, Kazakhstan

PRODUCTION OF HIGH-FASTENERS WITH BORON STEEL

Fasteners are one of the most popular parts of machines and different designs. The need for them is 1.1-1.2% of steel production. Among the fasteners are threaded the highest percentage (up to 60% range of machine parts): nuts, bolts, screws, studs. The urgency of the planned research is due to the demand for high-strength fasteners for the mining and metallurgical industry of the country. Herethey are used inheavilyloadedgeartunneland miningharvesters, mine cars,rolling mills.High percentage of failure of fastener products in working in hostile environments with alternating loads of great magnitude.

The desire forhighqualityhardcoreparts of the carwithout the cost oftheirproductionputsthe numberinthe primarytask of expandingproduction andusesparinglyalloying,including micro-alloyed boron steels. Features of boron-containing steels is their high technological plasticity, a favorable ratio of the strength and plastic properties in the annealed and heat-treated conditions.

Work to improve the operational characteristics of fasteners under way in countries far and near abroad. This is due to their low stability in the aggregates, and subjected to high oscillating loads. These includescreens,gearmotorand mill, mount the working bodies ofexcavators andmany others.For the production ofhigh-strengthfastenersrecommendedgrades: 35ХA, 38ХA, 38ХГНМ, 40Х,40ХН2MA [1].

Fabrication of the steel fastener cold heading machines for multi-position requires complex and expensive technology training rolled by cold forming processes, including long spheroidizing annealing in order to obtain the corresponding microstructure containing a granular perlite> 80%. In addition, applying intermediate annealing, when the metal over hardened as a result of deformation and loses elasticity. Experience has shown that the use of these steels with a lamellar structure leads to a drastic decrease in resistance of the instrument. This raises the need for steel, which has a better stamped than traditionally used in the simplified scheme (provisional) was drawn to the cold landing. From the standpoint of such an approach most suitable for cold forming (you-cages) are steel with low carbon content (the element that most strongly affects the parameters of strain hardening), doped with manganese and boron.

Microalloying with boron to improve the machinability as low-alloy or steel and medium-automatic rifle with high sulfur content.

Feature of the boron-containing steels is their high technological plasticity, a favorable ratio of the strength and plastic properties in the annealed condition and improvedthermal, high level of performance at a much lower hardenability than alloy steels, the content of alloying elements and with less than mediumcarbonof medium-alloy steels at steel hardenability. It was established experimentally that the maximum increase hardenability characteristics were achieved in case the content of "effective" boron at 0.0010%, which is about two orders of magnitude less than the amount of alloying elements traditionally used.

Analysis techniques of mass production of boron-containing steels in Russia and CIS indicates a relatively high content of nitrogen (0.010 ... 0.012%), resulting in low (reaching as high as 20 ... 40%) share of the "effective" boron steel. This fact explains the observed instability in some cases the properties of boron-containing steels, boron steel so the quality is laid on the stage of melting, which requires strict observance of rational modes of deoxidation and microalloying.

As well asdata analysisTable 1shows that, as a rule, low-and srednouglerodistyesteelalloyed withmanganese,chromium,boron contentin the steelsare in the range0.0005...0.005%.

Thermodynamic analysis shows that for effective protection of boron (ensuring its content in the solid solution at 0.0010%) and increase the absorption coefficient of boron up to 50% in the traditionally used in the automotive industry to increase the boron-containing steels (at the current level of) the content of titanium and aluminum to level not lower than 0.025, respectively, 0.030 and 0.050-060% lower nitrogen content to 0.005-0.008% [2].

Table1. The chemical compositionof boron-containingsteels

Steel grade	Content,%
	С	Si	Mn	Cr	B
06ХГР 12Г1Р 20Г2Р 30Г1Р 35Г1Р 23MnB4 35B2	0,50-0,10 0,10-0,16 0,17-0,24 0,27-0,33 0,32-0,38 0,20-0,25 0,28-0,32	0,17-0,35 0,17-0,35 0,17-0,35 0,17-0,35 0,17-0,35 >0,30 <0,30	0,90-1,30 0,90-1,30 0,90-1,30 0,90-1,30 0,90-1,30 0,9-1,2 0,5-0,8	0,20-0,50 <0,25 <0,25 <0,25 <0,25 <0,30 0,9-1,2	>0,001 >0,001 >0,001 >0,001 >0,001 0,0008-0,005 0,0008-0,005

An important reserve for improving hardenability boron microalloyed steels is austenite grain size refinement, which in practice is achieved by microalloying strong carbonitrideformingelements (Al, Ti, Zr, Nb, V, etc.). Their introduction into the steel together with micro boron provides nitrogen fixation and carbon stable finely dispersed carbonitrides of type Me(CХN1-Х), which on the one hand, contribute to the inhibition of migration, borders, and therefore the preservation of fine grain structure to a sufficiently high temperature, on the other hand, having a high chemical affinity for nitrogen and oxygen, bind them in nitrides and oxides, thereby ensuring the protection of forest, thus increasing the concentration of "effective" boron and, consequently, increase the hardenability of steel.

In most cases, alloying steels produced using expensive aluminothermic method ferroboron containing from 6 to 20% of boron (the rest is iron). Known boron master alloys with chromium, manganese, nickel and other elements obtained by metallothermic way. With reserves of borate, chrome, manganese and other ores, alloys of Kazakhstan does not produce, but they make the country where these ores are shipped. As part of the fundamental subjects of budgetary institution developed the theoretical basis of the production boron-doped silico-manganese grades are not expensive metallothermic and cheap carbo-thermal method, which can be implemented at Aksu ferroalloy plant at the existing furnaces by additives in them Kazakh borate ores. The resultingfusionhas several advantages overferroboron, which includea more uniform distributionof boron insteelvolumeandhigher (at 1, 6times) the assimilation ofitsmetal,due toshielding effect ofsilicon and manganese [3].

Cooperation Works "Krivorozhstal" - Works "Avtonormal" have developed and mastered the pass-through pilot production technology of high-strength fasteners (bolts, studs, nuts) of boron-containing carbon (20R, 30R, 35R) and sparinglyalloying, (20Г2Р, 30Г1Р, 35Г1Р, 30ХР) steels.

Steel 12ГР fabricated by cold headingstamping piston pins instead of traditionally used 12ХН. The hardness of the core after carbonitriding and hardening of the steel 12ХН 32 ... 34 HRC, and steel 12ГР 37 ... 39 HRC due to the influence of boron on the hardenability and the formation of titanium nitride 4 ... 7 pm, aluminum, 3... 4mkm, a boron , 5 ... 2mkm and joint nitrides. In the static tests are average load fracture was 12ХНpcp = 95 kN and 12ГР P = 102 kN. In the dynamic tests are parts made of steel 12ГР withstood 1400 ... 1700 thousand cycles without failure, which is 1.5 times higher than the established requirements for these components [4].

Low alloyed boron steel are a special class of promising steels, which upon further study will be widely used in industry.Usforthe production of suchsteelwillusesilicomanganesewith boron.

Literature

1. State of standard 1759.4, state of standard 4543.

2. Tikhonov, A.K. Steel for the automotive industry. Metal Technology, 2008. - № 12. - Р.47-51.

3. Akberdin A.A. Selected trudy.-Karaganda: PC "Ekozhan", 2008. -754 р.

4. Tikhonov, A., Shenderev P.E., Sardana N.I. Application of boron steel 12ГР for manufacturing piston pins engines of VAP // MandTTM. 2001. - № 1. - p. 25-27.