Method to process long steel part

FIELD: metallurgy.

SUBSTANCE: long steel part is processed. During processing the preliminary and final ion-vacuum nitriding in a glow discharge, restriking and honing are carried out. Restriking and honing are carried out after the preliminary and before the final nitriding, at that the preliminary nitriding is performed at a temperature of 510-530°C and a pressure of 350-600 Pa during 8-14 hours. The final nitriding is performed at a temperature of 500-540°C for 2.0-4.0 hours and a pressure of 390-650 Pa.

EFFECT: provision of required geometric characteristics of the processed parts and preservation of integrity, uniformity and continuity of the nitrided layer.

 

The invention relates to the field of surface treatment of metallic material by surface interaction with ionized gas and can be used, for example, for processing of long precision cylinder borehole pumps operating in the conditions of abrasive wear.

A known method of manufacturing parts made of structural steel (U.S. Pat. EN 2250273, IPC7SS 8/26, publ. 2002.12.20), including rough machining stabilizing vacation, final machining and two-stage gas nitriding aged in an atmosphere of ammonia at a temperature 510-515°C, then at 540-545°C and subsequent cooling. Final machining is carried out by double fine machining of the intermediate and final release in saltpeter bath at temperature ranges from 520 to 540°C for 0.25 to 0.5 h, and two-stage gas nitriding parts is carried out in a constant magnetic field of 100-150 e within 1-2 h and then cooled at a speed of 20-30°C/min

This method is complicated because of the need for before nitriding final machining by double fine machining of the intermediate and final release in saltpeter bath at temperature ranges from 520 to 540°C for 0.25 to 5 H. In addition, when processing in this way, in the nitriding process happen deformation of long parts requiring subsequent mechanical processing - editing and honing that significantly affects the quality of the nitrided layer.

There is a method of ion-vacuum nitriding long steel parts in a glow discharge (EN 2044801 C1 IPC SS 8/36, 27.09.1995, including the nitriding with a combined heating at a pressure of 2-3 mm Hg, the temperature at the working edge 430-480°C, the ion current density of 0.3 mA/cm2duration 24 h, after which additional heating in vacuum or nitrogen-containing atmosphere at a temperature higher than the temperature of nitriding, but not exceeding the softening temperature of the material.

When processing this way happen deformation of long parts requiring subsequent mechanical processing - editing and honing that degrades the quality of the nitrided layer.

Closest to the claimed and accepted as a prototype is the way gas nitriding of steel products (inventor's certificate SU 1502656, IPC4SS 8/26, publ. 1989.08.23), including heating parts, pre-nitriding at a temperature of 510±10°C, the final nitriding at a temperature of 530±5°C, then cool. To ensure the accuracy of the geometry is practical settings lengthy details require subsequent machining - edit and honing.

The disadvantages of this method are the reduced hardness and wear resistance of the treated surfaces, the lack of uniformity and homogeneity of the nitrided layer. Subsequent mechanical processing - editing and honing violates the integrity, uniformity of the nitrided layer, breaks the continuity nitride zone and, consequently, significantly degrades the performance properties of the part.

The task of the invention is to provide a method of ion-vacuum nitriding long steel parts, ensuring geometric accuracy of details and the integrity, uniformity and continuity of the nitrided layer.

The problem is solved by the improvement of the method of processing of long steel parts, including ion-vacuum pre-and post-nitriding in a glow discharge, editing and honing.

This improvement is that editing and honing is carried out after the preliminary to the final nitriding, while pre-nitriding is carried out at a temperature of 510-530°C for 8-14 h and a pressure of 350 to 600 PA, and the final nitriding is carried out at a temperature of 500-540°C for 2,0-4,0 h and the pressure 390-650 PA.

The implementation of the pre-nitriding at those the temperature 510-530°C for 8-14 h and a pressure of 350 to 600 PA allows to obtain a nitrided layer thickness of 0.2-0.3 mm from the surface nitride zone 6-10 μm and a hardness of HV 800-1100.

However, for example, in the manufacture of cylinders downhole pump having a varying wall thickness ≥0.4 mm, residual stresses ≥5 kgf/mm2and de-carbonized layer ≥0.2 mm, obtained in the blanking area, do not allow to obtain the required straightness of the channel of the cylinder and the required diametral sizes.

Therefore, to ensure the required straightness of the channel and the required diametrical sizes required after pre-nitriding conducting editing and honing. However, the nitrided layer is disturbed, its size is locally reduced to 0.15-0.2 mm, and the hardness up to 750-800 HV.

Run after editing and honing the final nitriding at a temperature of 500-540°C for 2,0-4,0 h and the pressure 390-650 PA allows to obtain a uniform nitrided layer thickness of 0.25-0.35 mm with advanced nitride zone thickness of 8-12 μm and a hardness of HV 900-1200, saving obtained by editing and honing straightness axis lengthy details and the required diametrical sizes.

Thus, in the process of pre-nitriding, editing, honing and final nitriding enables the formation of uniform nitrided layer of the desired hardness with advanced nitride area and obtain lengthy details of the required geometric precision is.

The method is as follows.

Steel long items placed in the vacuum chamber of the ion-vacuum chemical-thermal treatment and carry out the heating in a glow discharge, pre-nitriding at a temperature of 510-530°C for 8-14 h and a pressure of 350 to 600 PA, providing nitrided layer with the required thickness of 0.2-0.3 mm from the surface nitride zone 6-10 microns and the desired hardness HV 800-1100 desired hardness. Then perform the edit on a hydraulic press, ensuring the straightness of 0.08 mm and length of 1000 mm, and honing on the horizontal honing machine for maintaining the required nominal diameter of the cylinder, the tolerance on the diameter of up to 0.005 mm and raznozazornost to 0.02 mm. Then perform the final nitriding at a temperature of 500-540°C for 2,0-4,0 h and the pressure 390-650 PA to obtain the required thickness and hardness of the nitrided layer, while preserving the geometric parameters of the channel of the cylinder obtained after editing and honing.

The proposed method has handled the cylinders downhole sucker rod pumps of steel MOI length 4262+10mm, an inner diameter 44,45+0,05mm, outer diameter 57,85-0,3. Items were placed in the chamber with the use of special tooling for 18 pieces. Azotosoderjashchig gas (a mixture of 1 part of nitrogen and 3 parts in Dorada) was applied during the entire cycle of pre-nitriding. Pre-nitriding was performed at a temperature of 530°C for 10 h and a pressure of 420 PA.

Then perform the edit on a hydraulic press with the control of the internal channel of the cylinder, ensuring straightness to 0.08 mm to 1000 mm and honing to size 44,45+0,mwith the provision of raznozazornost 0.02 mm for the entire length of the cylinder. The final nitriding produced within 3 hours at a temperature of 510°C and a pressure of 450 PA.

He got the details with evenly developed nitrided layer thickness of 250-300 microns and a hardness on the surface 1100-1200 HV, at a depth of 10 μm - 1000-1100 HV, at a depth of 20 μm - 950-1000 HV, at a depth of 50 μm - 850-920 HV, at a depth of 150 μm - 600-650HV, at a depth of 250 μm - 350-400HV. Nitrided layer had a uniform and moderately developed nitride zone thickness of 5-8 μm. While the straightness of the cylinder was in the range of 0.08 mm to 1000 mm, and the increase in internal diameter did not exceed 0.01 mm and has not gone beyond the field of tolerance and the required parameters for raznozazornost.

Thus, the use of the proposed method to provide the required geometric characteristics of the machined workpiece and to obtain a uniform nitrided layer of the desired hardness.

The method of processing of long steel parts, including ion-vacuum pre-and post-nitriding in a glow p is the would be loaded on, editing and honing, characterized in that the editing and honing is carried out after the preliminary to the final nitriding, while pre-nitriding is carried out at a temperature of 510-530°C for 8-14 h and a pressure of 350 to 600 PA, and the final nitriding is carried out at a temperature of 500-540°C for 2,0-4,0 h and the pressure 390-650 PA.



 

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