Procedure for ion-vacuum chemical-thermal treatment of steel part with threaded surface

FIELD: metallurgy.

SUBSTANCE: procedure consists in part heating, in nitriding during heating in nitrogen containing gas from 390 - 410°C to 500 - 570°C during 1 - 4 hours and in cooling from 500 - 570°C to 350 - 400°C during 40 - 60 minutes in plasma of glowing discharge directly upon heating.

EFFECT: upgraded quality and consumer qualities of threaded parts, increased efficiency and reduced expenditure of resources by nitriding during heating and cooling.

 

The invention relates to the field of chemical-heat treatment of steels ion-vacuum nitriding and can be used for hardfacing parts with the screw surface.

The known method of chemical-heat treatment of steel parts with a threaded surface that is described in the method of manufacturing a spindle made of steel for pipeline valves (U.S. Pat. EN 2308543, IPC (2006.01) SS 28/00, publ. 2007.10.20), comprising heating the parts up to 320°C-450°C, isothermal nitration within 20-60 minutes and the subsequent application of multi-layer titanium-containing coating.

The disadvantage of this method is its high complexity, the complexity and cost of applying multilayer composite coatings.

There is a method of nitriding screw parts (inventor's certificate SU 981449, publ. 1982.12.15), comprising heating the parts up to 520°C, isothermal nitration within 10-14 hours and cooled.

This method is very long isothermal nitration and does not guarantee high-quality work-hardening due to embrittlement and uneven development of the nitrided layer on the screw surface.

Closest to the claimed and accepted as the prototype is a method of ion-vacuum nitriding of steel parts with a threaded surface (Mosk. The technology of hardening. Technologists the definition methods of hardening. Vol.2. - M.: Mashinostroenie, 1995, s-419), which includes heated in nitrogen gas at temperatures ranging from 350-400°C, isothermal aging and cooling.

This method allows to improve the quality and consumer properties of threaded parts.

However, the need isothermal aging increases the duration of the process and does not allow to obtain a uniform and homogeneous-developed layer and to maintain dimensional accuracy and surface roughness of the thread.

The task of the invention is to improve the quality and consumer properties of threaded parts, performance and cost reduction of resources by nitriding in the process of heating and cooling.

The problem is solved by the improvement of the method of ion-vacuum chemical-heat treatment of steel parts with a threaded surface, including heat, nitriding and cooling.

To solve this task, the nitriding is carried out in the heating process from 390-410°C to 500-570°C for 1-4 hours, and cooling with 500-570°C up to 350-400°C. is carried out for 40-60 minutes in a glow discharge plasma immediately after heating.

Such operations method allows to obtain a nitrided layer is not more than 200 μm and avoid embrittlement.

At temperatures below 390°C, the nitriding process is not performed, and the ri temperatures above 570°C To form the nitrided layer with low hardness due to possible overheating of the threaded surface in the ion plasma, with increased energy in the electric abnormal glow discharge.

After reaching the specified temperature heating carry out the cooling of the parts in the ion plasma to 350-400°C for 40-60 minutes, allowing you to increase the concentration of nitride phases for the formation of a more uniform and odnorodnosti layer, and also allows you to maintain dimensional accuracy and surface roughness of the thread.

This slow (soft) cooling helps reduce and favorable distribution of internal residual stresses in the dispersion hardening in thin, high-strength nitrided layer with high hardness >600 HV.

The method is as follows.

Steel parts with a threaded surface is placed in a vacuum chamber and the exercise of their ion-vacuum heat from 390-410°C to 500-570°C in nitrogen gas and at a pressure of p=4 to 10 hPa (mbar) within 1-4 hours. Directly after heating cooling 500-570°C up to 350-400°C. is carried out for 40-60 minutes in the ion glow discharge plasma at a pressure of p=4 to 10 hPa (mbar).

The proposed method was nitrate screw locks tubing (tubing 89 No. 45) of steel GM with the screw segment with a length of 53 mm, which was placed in a heating chamber at a special snap-in quantity 60 PCs in cages, heating of components was carried out in and is authorized plasma from 400°C to 540°C for 2.5 hours in a mixture of nitrogen and hydrogen (1/3) at a pressure of 6 hPa (mbar). Immediately after heating the spent cooling from 540°C to 400°C for 40 minutes under a pressure of 6 hPa (mbar).

Microstructural analysis of specimens and three items from each row of cages showed that the proposed method is ion-vacuum nitriding provides generation of qualitative and evenly developed nitrided layer on all the threads within 100-120 microns with a surface hardness >650 HV, which corresponds to the design and technological requirements.

Thus, using the proposed method provides the desired quality and properties of nitrided parts with a threaded surface and reduces labor and material costs.

The method of ion-vacuum nitriding of steel parts with a threaded surface, including its heating in nitrogen gas and cooling, characterized in that the nitriding is carried out in the heating process from 390-410°C to 500-570°C for 1-4 h, and cooling with 500-570°C up to 350-400°C. is carried out for 40-60 minutes in a glow discharge plasma immediately after heating.



 

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