Технические науки/1. Металлургия

Zhiguts Yu.Yu., Antalovskyy V.V.

Uzhhorod National University, Ukraine

ON THE POSSIBILITY OF SYNTHESIS OF HARD ALLOYS

The urgent industrial problem of nowadays is not only creation of new materials but also improvement of traditional material properties and advance development of technologies of their production. Detailed studies of the problem allow us to state that this task could be successfully solved by using specially synthesized alloys produced by combined processes based on the combustion of exothermic powder mixtures.

The above technologies are based on the combined processes and allow the predetermined structure to be synthesized with specified alloy properties at cast formation with the use of synthesized materials for the emergency repairs of products, part surface layer recovery and for the use of the synthesized alloy for the cast saving in the exothermic cast additive technologies.

The synthesis technologies developed in this work differ from traditional ones by a series of obvious advantages: the lack of need in the powerful electric energy power supplies, the possibility to use simple and cheap casting equipment, the high process productivity (alloy synthesis time may vary from 30 seconds to a couple of minutes), the possibility of using secondary production waste – graphite electrode grinding, aluminium or magnesium chips, iron cinder, blue powder, i.e. the dust from the filters of the casting shops producing manganese alloys. All the aforementioned have caused an urgent need in carrying out research described in this paper. The above technologies could be successfully applied to save metal at the high-volume and mass production factories producing casts and instruments. Creating materials on the basis of the self-propagating high-temperature synthesis (SHS) and combined (metallothermy+SHS) processes as well as studying the influence of new technological methods of metal production on the cast microstructure, chemical composition and mechanical properties have gained large practical importance. Their use in the existing casting technologies, e.g. in producing steel casts with thermite cast additives increases considerable process efficiency.

We succeeded to combine the metallothermic and the SHS processes to obtain the tungsten-cobalt hard alloys according to the following reaction scheme:

and ,

where А, В, С are the synthesis elements; О is the oxidizer (say, oxygen etc.); АС are the reaction products (i.e. carbides, silicide’s and so on); ВО is a slag.

Technologies developed on the basis of the above schemes allowed us to produce by using the "non-traditional" method the rapid steels (Р9, Р6М5 – analogue S6-5-2, Р12 with the microstructure shown in fig. 3), the cast hard alloys (ВК3 – analogue HG012, ВК4, ВК6, ВК8, ВК15-like [1]), and others. The microstructure of the carbide steel produced in accordance with the classical SHS-reaction with the tungsten carbide (15 mass % of the thermite mixture) is shown in fig. 3.

Figure 3. The dendrite microstructure of the tool steel Р12 [2]

The so-called "carbide steels" have been synthesized for the first time being the analogue of the hard tungsten-cobalt alloy having a structure with soft and pliable cobalt being replaced by the rapid steel. The microstructure of one of the carbide steel types is shown in fig. 4 [1, 3].

The studies of the microstructure and the properties of the alloys produced allow the following results to be presented, e.g., for the high-speed steel “Р18” (analogue 3355): grain size – 10, hardness НRC – 65–67, σ_b=2600 МPа, heat resistant
913–928 К.

а) b)

c) d)

Figure 4. Microstructure of: а) hard alloy ВК4l, b) carbide steel В(Р18)15l with a matrix in a form of a rapid steel Р18 – 15% and tungsten carbides W₂C (small globular light inclusions) and WC (large grains) – 85%, c) – the massive carbides WC in the rapid steel matrix; d) – the rapid steel matrix with a sphere-like complex carbides of the W₂C type (left – х1500, right – х250)

Literature:

1. Zhiguts, Yu.Yu. (2009). Synthesis and properties of cast carbide alloys. Physical metallurgy and heat treatment of metals, 3, 26-29.

2. Zhiguts, Yu.Yu., & Lazar, V.F. (2014). The technologies and features of alloys synthesized by combined processes. Uzhgorod, Invazor.

3. Zhukov, А.А., Zhiguts, Yu.Yu., & Shylina, E.P., & Mazhumdar J. Datta. (1998). Combined surface treatment by laser surface hardening and the self-propagating high-temperature synthesis. Ferrous metallurgy, 5, 60-63.