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Composite heat treatment process for improving surface compactness of nitro-carburizing strengthened layer

A composite heat treatment and nitrocarburizing technology, which is applied in metal material coating process, coating, solid-state diffusion coating, etc., can solve the problem of prolonging the austenitizing treatment time, decreasing the compactness, and increasing the nitrogen loss and other problems, to achieve the effect of improving surface compactness and comprehensive performance, improving brittle toughness and wear resistance, and improving brittle toughness and wear resistance

Active Publication Date: 2015-05-27
HUNAN UNIV
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  • Abstract
  • Description
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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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  • Composite heat treatment process for improving surface compactness of nitro-carburizing strengthened layer
  • Composite heat treatment process for improving surface compactness of nitro-carburizing strengthened layer
  • Composite heat treatment process for improving surface compactness of nitro-carburizing strengthened layer

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Experimental program
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Effect test

Embodiment 1

[0077] The samples are No. 10 carbon steel, there are 9 groups of samples, the sample numbers are in sequence: ai, after 580℃±10℃ ferrite nitrocarburizing, the furnace is heated to 680℃±10℃, and the austenite is protected by nitrogen After body treatment for 2h, water quenching, then 180℃±10℃ isothermal aging for 14h, the specific process parameters and sample strengthening layer situation are shown in Table 1 (the thickness of the hole layer is adopted FEI Quanta200 type Observed by scanning electron microscope and measured with an electronic ruler, each value is taken from 20 measurement data and the average value; the surface hardness is adopted HV-1000Z type Microhardness tester test, the experimental load is 0.49N, the duration is 15s, each value is the average of 20 test points);

[0078] Table 1

[0079]

[0080] use FEI Quanta200 type Environmental scanning electron microscopy performed secondary topography characterization of the cross-section strengthening layer of 9 gr...

Embodiment 2

[0095] The sample is made of 0Mn12Ni2 alloy steel. The test method and operation steps are the same as those of the plan one. One set of test pieces is heated to 680℃±10℃ in the furnace after 580℃±10℃ ferrite nitrocarburizing. After 2h of aging treatment, water quenching, then 180℃±10℃ isothermal aging for 14h.

[0096] The nitrocarburizing treatment time is 1h, and the experimental nitriding potential value is 0.42atm -1 / 2 . The microhardness test on the surface and cross-section of the sample by a microhardness tester, the results are shown in the attachment Image 6 , From the attached Image 6 It can be seen that the nitriding potential value K in the 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 2, it can be seen that the method of the present invention for carbon steel...

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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 nitrocarburizing strengthened layer; specifically, it refers to a short-term low nitrogen potential nitrocarburizing and direct austenitizing treatment to improve Compound heat treatment process for infiltration layer compactness. Background technique [0002] Nitriding / nitrocarburizing treatment on the surface of steel can improve the comprehensive properties of steel surface hardness, wear resistance, corrosion resistance and fatigue strength. Therefore, it is widely used in many industrial fields. Nitrocarburizing (nitrocarburizing) is divided into gas nitrocarburizing, liquid nitrocarburizing, ion nitrocarburizing, etc. according to the different media. [0003] According to the teaching of the national standard CBT18177-2008, traditional steel gas nitriding processes usually include conve...

Claims

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Application Information

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Patent Type & Authority Applications(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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