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On diffractograms, produced from specimens, made of cast steel R6M5 (EBCHR) (Figure 3, a), in addition to interferences of a-solid solution (martensite) peaks of comparative intensity from carbide [M.sub.6]C, which enters into composition of skeleton eutectic, from metastable [M.sub.2]C (laminar eutectic), and from refractory carbide MC (VC) are present.
That's why amount of residual austenite in structure of cast high speed steel R6M5 (EBCHR) was determined by the method of magnetic analysis on magnetic austenometer MAK-2M, using calibration standard from hardened and annealed steel R6M5.
Results of X-ray microspectral analysis and data of scanning microscopy, obtained in the <<phase contrast>> mode in backscattered electrons (BEI), confirmed presence in the structure of cast steel R6M5 (EBCHR) of carbides [M.sub.6]C, [M.sub.2]C, MC, and disperse secondary carbides, uniformly distributed within grain volume (Figure 4).
Analysis of distribution of basic alloying elements over structural and phase components of cast steel R6M5 (EBCHR) proves high level of solid solution (martensite) alloying.
Produced ingots of steel R6M5 (EBCHR) were subjected to homogenization isothermal annealing according to the scheme: austenization--heating up to 880-900 [degrees]C, seasoning for 3 h (eutectoid transformation), cooling down to 760-780 [degrees]C, isothermal seasoning for 6 h (diffusion transformation) with subsequent slow cooling with furnace down to 400 [degrees]C.
For determining optimum conditions for final heat treatment of high speed steel R6M5 (EBCHR) influence of hardening and tempering parameters on its structure, phase composition, hardness and heat resistance was investigated (Table 2).
Hardness HRC values of steel R6M5 (EBCHR) were, depending upon cooling environment for hardening after additional tempering at temperature 580 [degrees]C for 180 min, as follows: [KNO.sub.3] + 30 % NaOH (400-420 [degrees]C)-61.0-62.0; oil--61.0-61.5; water--60.0-61.5; air--58.5-59.0.
Structure of high speed steel R6M5 (EBCHR) after hardening consists of acicular martensite, residual austenite, residues of carbide network over grain boundaries and structurally isolated carbides of compact form, uniformly distributed over the metallographic specimen section (Figure 1, c).
Structure of high speed steel R6M5 (EBCHR) after temper hardening consists of high-alloy tempered martensite, residual austenite (3-5 vol.%), residues of the torn carbide network over boundaries, and carbides, the main of which is [M.sub.6]C.
It is shown that structural changes, which occur at the stage of solidification of the R6M5 high speed steel melt in EBCHR, exerts favorable influence on phase transformations and formation of homogeneous disperse structure of cast metal.
It is detected that refractory carbides of MC type precipitate in steel R6M5 (EBCHR) during solidification at the stage of peritectic transformation and don't form eutectic.
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