CS202783B1 - Heat treatment of shafts exposed to contact stress - Google Patents

Description

The invention relates to the heat treatment of contact-stressed shafts, in particular textile spindles, made of 1% C bearing steel, 1.5% Cr.

Textile spindles are a special case of double row ball bearings, the inner ring being replaced in this case by a solid shaft, after which the spindles roll the balls at high speed when working. This is a classic example of fatigue crack contact stress.

Until now, such shafts are heat treated either by salt or atmospheric furnaces with a protective atmosphere, according to CS, AO No. 167796, by induction heating with hardening in an oil bath. A common feature of all these processes is that a heat treatment yields a homogeneous structure consisting of martensite, cementitious type / Fe, Mn / gC superaduttoid carbides and residual austenite over the entire volume of the component, the hardness after hardening reaching 62-64 HRc. This is followed by a low temperature tempering to a hardness of 60 to 62 HRc. Such a method of heat treatment corresponds to the classical conception of fatigue process in cyclic contact stress and its main disadvantages are unfavorable extension of residual stresses, existence in the structure of less advantageous plate-shaped martensite with inner twins, larger grain austenite and necessity to use demanding furnace aggregates.

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These deficiencies are eliminated by heat treatment e.g. by induction heating above the conversion temperature of the AC? finding, which is based on heating the shafts at a heating rate of 600 ° C, e ¹ to 100 000 ° C. with a * * followed by quenching with a corrosion inhibitor water spray.

The proposed method of heat treatment and based on modern knowledge of contact cyclic stress, according to which the limiting factors for the resistance of steels to cyclic contact fatigue are the properties of the surface layers at a depth greater than the maximum shear stress. The properties of the surface layer obtained according to the invention are more advantageous than those of classically worked structures, since it contains a favorable pressure residual stress, is predominantly acicular martensite and a dislocation substructure that has a more favorable strength characteristics and because it exhibits less eustenitic grain due to increased heating rate.

The quenching does not follow the low-temperature tempering, which in the present case can be converted either by classical heating in an atmospheric furnace to a temperature of 170 to 180 ° C, inductively or more efficiently by means of so-called. by self-discharge using the heat of the meal to supply the necessary thermal energy to conduct the tempering processes in the surface layer.

In the attached drawing, FIG. 1 shows the macro structure on the transverse section of the shaft β in FIG. 2 austenitic grain sizes are increased to the heating rate.

The structure of FIG. 1 is formed in the surface layer by fine martensite and in the core part by transition structures. In FIG. 2 is a method of plotting the horizontal oai graph under heading 1 ^ the mid-frequency conventional average method, under heading 2 the fer efferiea method and under heading 3 the ministerial method, wherein letter a denotes auatenitization in the furnace and protective atmosphere, letter b_ auatenitization in salt bath; letter £ auatenitization by induction heating. On the vertical oai graph, the mean grain area in 1.10 " ⁶ mm ² is plotted.

The heat treatment of the shaft of 8 to 16 mm according to the invention has achieved a hardness of the surface layers of 62 to 63 HRc. the structure consisted of mixed martensite and predominant dislocation martensite. The heating to the calibrated temperature above Ac ₃ proceeded inductively at a rate of approximately 650 ° C s ^-1 .

In addition to the advantages resulting from the improved properties of the surface layers as mentioned above, the invention also provides technological and acceleration of the heat treatment process, increased operational readiness of the plant, the possibility of building automatic production lines, reduced power consumption. energy, processing without hardening agents, smaller areas, etc.

Claims (1)

Method of quenching shafts subjected to contact cyclic grinding, in particular shafts 202 78 textile spindles made of bearing steel 0.9 to 1.1 wt. % carbon, 0.3 to 0.5 wt. 0.15 to 0.35 wt. % silicon, 1.3 to 1.65 wt. % Chromium induction ohre vom the transformation temperature Ac ₃ by cooling naeledjúcim 8 characterized in that the heating takes place at 600 ° C. s ”· ¹ to 10 ⁵⁰ C. with water spray with corrosion inhibitor.