A composite heat treatment process for improving surface compactness of nitrocarburizing strengthening layer

A composite heat treatment and nitrocarburizing technology, applied in the field of surface heat treatment, can solve the problems of prolonging the austenitizing treatment time, reducing the density, increasing the degree of nitrogen loss, etc., to improve the surface density and comprehensive performance, Eliminates the effects of weak areas of surface hardness, brittle toughness and wear resistance enhancement

Active Publication Date: 2017-01-11
HUNAN UNIV
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Problems solved by technology

Through austenitization and isothermal aging treatment, the compound layer of the infiltrated layer is dissolved, and the following phase transformation occurs in the compound layer: austenitization process, ε-Fe 2-3 Phase transformation of N→γ-Fe(N), followed by isothermal aging, γ-Fe(N)→(α-Fe+γ′-Fe 4 The phase transformation of N) transforms the compound layer of the infiltrated layer into an ultra-fine bainite layer. This strengthening layer has excellent toughness due to fine grain strengthening, but it is found that its compactness is lower than that of the original compound layer. large drop
[0006] In addition, in the invention patent with the application number 201110026979, the sample after nitrocarburizing cooling is then subjected to subsequent heat treatment such as austenitization, which is not only cumbersome and time-consuming, but is not conducive to mass production in industrial applications, and more The biggest problem is that the "cooling treatment" after nitrocarburizing has a great negative effect on the subsequent austenitizing treatment and isothermal aging treatment, which is specifically reflected in the following two aspects: a) If it is used after nitrocarburizing Water quenching treatment (rapid cooling) will cause [N] to segregate to the surface (ε phase), which will greatly prolong the austenitizing treatment time (the time for complete decomposition of ε phase), and at the same time increase the nitrogen The degree of loss; b) If furnace cooling (slow cooling) is used after nitrocarburizing, the Fe in the subsurface layer (diffusion layer) α matrix 4 The precipitated phases such as N have all precipitated and grown up, and the subsequent artificial aging treatment for controlling the precipitated phases is meaningless
[0007] In short, the process is not only complicated and time-consuming, but also due to the denitrification behavior of the nitriding strengthening layer in the austenitizing treatment stage, a large number of holes and cracks appear on the surface of the final sample, resulting in a series of surface properties due to the hole layer. Existence but can not get a true reflection, and it is contrary to the nitriding treatment of precision workpieces with high requirements on size and surface finish, so the practical application value of this process is greatly reduced

Method used

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  • A composite heat treatment process for improving surface compactness of nitrocarburizing strengthening layer
  • A composite heat treatment process for improving surface compactness of nitrocarburizing strengthening layer
  • A composite heat treatment process for improving surface compactness of nitrocarburizing strengthening layer

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Experimental program
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Effect test

Embodiment 1

[0077] The sample is made of No. 10 carbon steel, and there are 9 groups of samples in total. After 2 hours of bulk treatment, water quenching, and then isothermal aging at 180°C±10°C for 14 hours, see Table 1 for the specific process parameters and the strengthening layer of the sample (thickness of the hole layer is adopted FEI Quanta200 type Observation by scanning electron microscope, and measure with electronic ruler, take the average value of 20 measurement data for each value; surface hardness adopts HV-1000Z type Microhardness tester test, the experimental load is 0.49N, the duration is 15s, and the average value of 20 test points is taken for each value);

[0078] Table 1

[0079]

[0080] use FEI Quanta200 type Environmental scanning electron microscope was used to characterize the cross-section strengthening layer of 9 groups of samples, and the results are shown in the attached figure 2 ;from figure 2 see:

[0081] Samples (a) to (c) with nitrocarburiz...

Embodiment 2

[0095] The sample is made of 0Mn12Ni2 alloy steel, and the test method and operation steps are the same as those of Scheme 1. One group of test pieces, after ferrite nitrocarburizing at 580°C±10°C, is heated to 680°C±10°C with the furnace, nitrogen protection Austrian After tempering treatment for 2 hours, water quenching, and then isothermal aging at 180℃±10℃ for 14 hours.

[0096] Nitrocarburizing treatment time is 1h, and the experimental nitriding potential value is 0.42atm -1 / 2 . The microhardness test was carried out on the surface and section of the sample by a microhardness tester, and the results are shown in the appendix Image 6 , from attached Image 6 It can be seen that the nitriding potential value K in nitrocarburizing treatment N 0.42atm -1 / 2 , when the nitriding time is 1h, the surface hardness of the specimen reaches 987HV, and the thickness of the strengthening layer is about 100μm.

[0097] From the experimental data and test results of Examples 1 and...

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Abstract

The invention discloses a composite heat treatment process for improving the surface compactness of a nitro-carburizing strengthened layer, which is a heat treatment process for improving the surface compactness of the strengthened layer after the properties of the nitro-carburizing steel workpiece strengthened layer are improved and achieves the integration of nitro-carburizing treatment and austenitizing treatment. The process comprises the following steps: performing the composite process of short-time low nitrogen potential nitro-carburizing at 580 DEG C+ / -10 DEG C with the experimental nitriding potential value of 0.40-0.80 atm<-1 / 2> for 0.5-1.5 hours and austenitizing treatment at 680 DEG C+ / -10 DEG C, and performing isothermal aging treatment at 180 DEG C+ / -10 DEG C. The heat treatment disclosed by the invention is simple and convenient to operate and easy to implement, effectively restrains denitrification during austenitizing treatment, solves the problem that nitro-carburizing strengthened layer gets loose due to pores, and obtains the fully compact surface strengthened layer; and the surface hardness, toughness, smoothness and abrasion resistance of steel workpieces treated by the heat treatment process disclosed by the invention are further improved.

Description

technical field [0001] The invention relates to the technical field of surface heat treatment, in particular to a composite heat treatment process for improving the surface compactness of a nitrogen-carburized strengthening layer; specifically, it refers to a short-term low-nitrogen potential nitrogen-carburizing direct austenitization treatment to improve Composite heat treatment process for the compactness of the seepage layer. Background technique [0002] Nitriding / nitrocarburizing treatment on the steel surface can improve the comprehensive properties of the steel surface such as hardness, wear resistance, corrosion resistance and fatigue resistance. Therefore, it is widely used in many industrial fields. Nitrocarburizing (soft nitriding) is divided into gas nitrocarburizing, liquid nitrocarburizing, and ion nitrocarburizing according to different media. [0003] According to the teaching of the national standard CBT18177-2008, the traditional steel gas nitriding proc...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C23F17/00C21D1/20C23C8/32
Inventor 伍翠兰王津洪悦陈兴岩陈江华
Owner HUNAN UNIV
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