CN107761048A - The method that N C V Mo RE multicomponent thermochemical treatments strengthen steel material surface - Google Patents

The method that N C V Mo RE multicomponent thermochemical treatments strengthen steel material surface Download PDF

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CN107761048A
CN107761048A CN201711209201.2A CN201711209201A CN107761048A CN 107761048 A CN107761048 A CN 107761048A CN 201711209201 A CN201711209201 A CN 201711209201A CN 107761048 A CN107761048 A CN 107761048A
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sample
layer
permeation
temperature
advance
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庞祖高
黄双健
韦世宝
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Guangxi University
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Guangxi University
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C12/00—Solid state diffusion of at least one non-metal element other than silicon and at least one metal element or silicon into metallic material surfaces

Abstract

The method that N C V Mo RE multicomponent thermochemical treatments strengthen steel material surface, step are as follows：First the base salt of J 2 is heated to pre- oozing temperature and being incubated ageing；Steel material is put into and carries out being incubated pre- ooze；Nitrogen carbon, which is obtained, after taking-up air cooling oozes sample in advance；Quantitative borax anhydrous, potassium carbonate, sodium fluoride, vanadic anhydride, molybdenum trioxide, aluminium powder and rare earth first are weighed according to mass percentage, when graphite crucible is heated into 900 DEG C, first borax anhydrous is added in batches, adds potassium carbonate and sodium fluoride；Then vanadic anhydride and the molybdenum trioxide and aluminium powder that have been coated with aluminium foil are added, stirring makes it fully react；Then add rare earth and nitrogen carbon and ooze sample in advance, then adjust resistance furnace temperature and to permeation temperature and be incubated, finally carry out oil cooling, obtain polynary pre- oozing sample.Experience wear performance test and thermal fatigue resistance experiment find that the more other two methods of steel surface processed by the invention have more excellent abrasion resistance properties and thermal fatigue resistance.

Description

The method that N-C-V-Mo-RE multicomponent thermochemical treatments strengthen steel material surface
Technical field
The present invention relates to mould and machinery part surface to strengthen field, is used for 65Nb matrix steel surfaces more particularly, to one kind The N-C-V-Mo-RE multicomponent thermochemical treatment materials of reinforcing.
Background technology
65Nb steel (65Cr4W3Mo2VNb) is the matrix steel retrofited using W6Mo5Cr4V2 high-speed steel as parent, is commonly used for cold Make mould and hot forming dies materials；As typical matrix steel, 65Nb has tough the characteristics of having both, and has and is better than Cr12MoV Deng the matrix toughness of Cold Working Die Steels, but hardness and wearability are not so good as some conventional cold mold materials, have impact on mould The service life of tool and machine components.The failure of mould often starts from the surface of mold materials, due to surface microscopic group be present The reason such as defect or surface abrasion resistance deficiency is knitted, die life tends not to reach design requirement.Therefore, mould is carried out Surface Hardening Treatment is to improve the effective ways of die life.Conventional mould and machinery part surface reinforcement technique can substantially divide For three classes；The first kind is Surface heat-treatent technology, and such as surface hardening and Surface thermo-chemical treatment technology, surface hardening is according to surface The different of quick heating means can be divided into flame hardening, impewdance matching and pulsed quenching etc. again, thermo-chemical treatment such as nitriding, ooze Carbon, nitrocarburizing, metallic cementation and each element and RE co-permeating etc.；Second class is plating and chemical plating；3rd class is that gas phase is sunk Product technology, including PVC (physical vapour deposition (PVD)), CVD (chemical vapor deposition), PCVD (plasma activated chemical vapour deposition) etc.. By surface strengthening technology, the performances such as case hardness and the surface abrasion resistance of mould and machine components can be further improved, are improved The service life and performance of mould and machine components.
The content of the invention
The purpose of the present invention is for 65Nb matrix steel surfaces form a kind of dense structure, that hardness is high, wearability is good is polynary Co-penetration layer, the defects of not only successfully managing unit metallic cementation or nonmetallic rear material property deficiency of the invention, moreover it is possible to shorten cold Make and hot forming dies materials and machinery part surface process cycle.
To achieve these goals, present invention employs following technical scheme：
It is a kind of for steel material surface strengthen N-C-V-Mo-RE multicomponent thermochemical treatment materials, described permeation material include with Lower two sections of material：J-2 types nitrocarburizing base salt and V-Mo-RE multicomponent thermochemical treatment materials, according to mass percentage, the V- The raw material components of Mo-RE multicomponent thermochemical treatment materials are as follows：Potassium carbonate 6~8%, sodium fluoride 6~8%, vanadic anhydride 7~10%, Molybdenum trioxide 6~8%, rare earth 3~5%, aluminium powder 8~15%, surplus are borax anhydrous, above each component mass percent summation For 100 percent.
Further, it is as follows according to mass percentage, the raw material components of the V-Mo-RE multicomponent thermochemical treatments material：55% Borax anhydrous, 7% potassium carbonate, 7% sodium fluoride, 10% vanadic anhydride, 8% molybdenum trioxide, 9% aluminium powder, 4% rare earth.
A kind of processing method using the N-C-V-Mo-RE multicomponent thermochemical treatments material reinforcement steel material surface, including it is as follows Step：
(1) nitrogen carbon oozes processing in advance
First block J-2 bases salt is smashed to graininess, is put into ceramic crucible, then is placed in chamber type electric resistance furnace with stove heat Ooze temperature to pre- and be incubated ageing；
By surface be polished to the Steel material sample of minute surface and cleaning by ooze in advance it is face-up in a manner of be put into ceramic crucible In carry out being incubated pre- ooze；
Finally take out Steel material sample and carry out air cooling, that is, complete nitrogen carbon and ooze processing in advance, obtain nitrogen carbon and ooze sample in advance；
The pre- temperature of oozing is 565~575 DEG C, and the insulation digestion time is 1.5~2.5 hours, and the insulation is oozed in advance Time is 3.8~4.5 hours；
(2) salt bath multicomponent thermochemical treatment is handled
1. first weigh quantitative borax anhydrous, potassium carbonate, sodium fluoride, vanadic anhydride, three oxygen according to mass percentage Change molybdenum, aluminium powder and rare earth,
2. load weighted aluminium powder and molybdenum trioxide are coated with aluminium foil, to reduce oxidization burning loss and the weakening when aluminium powder adds Influence of the volatility of molybdenum trioxide at high temperature to experiment,
3. graphite crucible when furnace temperature rises to 900 DEG C, is first added into borax anhydrous as altogether in batches with resistance stove heat Substrate is oozed, treats that borax all after melting, adds the mixture of potassium carbonate and sodium fluoride；Then add vanadic anhydride and use aluminium The molybdenum trioxide and aluminium powder that paper tinsel has coated, quickly stirring makes it fully react；Then substep adds rare earth and nitrogen carbon oozes in advance Sample carries out multicomponent thermochemical treatment, and each time interval added between step is 8~10 minutes；
4. then adjustment resistance furnace temperature to permeation temperature and is incubated, permeation temperature is 950~1050 DEG C, and soaking time is 3.5~4.5 hours, finally take out sample and carry out oil cooling, that is, complete the processing of salt bath multicomponent thermochemical treatment, obtain polynary pre- oozing sample.
Further, also comprise the following steps：
(3) the polynary pre- sample that oozes is subjected to temper, during eliminating high-temperature salt bath permeation internal stress caused by sample and Fragility, temperature are 500~600 DEG C, are incubated 1~2h, are tempered 2 times, and sample is placed in boiling water to remove after the completion of tempering The residual salt of specimen surface.
Further, in step (1), after air cooling, nitrogen carbon is oozed to the loose oxygen of furvous of the layer surface of sample in advance Change layer gently mill and polishing.
Further, the Steel material sample is 65Nb matrix steels.
Compared with prior art, the beneficial effect that the present invention possesses：
Using micro-hardness measurement, SEM (SEM) observation, energy disperse spectroscopy (EDX) analysis and X-ray diffraction (XRD) analysis is to the case hardness of 65Nb matrix steel N-C-V-Mo-RE multicomponent thermochemical treatment layers, tissue topography, grain morphology, element point Cloth and thing phase composition carry out research and analysis, it is found that multicomponent thermochemical treatment layer tissue is continuous fine and close and thickness is uniform, and polynary common Alloying layer thickness is mainly made up of at 10 μm or so the tiny equiax crystal of crystal grain；The main thing phase composition of multicomponent thermochemical treatment layer be VN, Mo2N、V8C7、Mo2C, the co-penetration layer being made up of these hard phases can significantly improve the case hardness of 65Nb matrix steels extremely 2656.3HV0.1.Experience wear performance test and thermal fatigue resistance experiment are found, are handled through N-C-V-Mo-RE multicomponent thermochemical treatments The more other two kinds of samples of 65Nb steel surfaces have more excellent abrasion resistance properties and thermal fatigue resistance.Therefore, using through N-C-V- The 65Nb matrix steels of Mo-RE multicomponent thermochemical treatments processing make as mold materials steel to improving die life and reducing mould It is of great significance with cost tool.
Brief description of the drawings
Fig. 1 is wear test principle.Fig. 2 is V-notch Crack Extension schematic diagram.In Fig. 1 and 2,1, sand paper, 2, rotating disk, 3rd, sample, 4, loading force, 5, secondary cracks, 6, lead crack, 7, micro-crack.Fig. 3 is nitrocarburizing thickness degree and time relationship.Figure 4 be V2O5Influence of the content to infiltration layer.Fig. 5 is MoO3Influence of the content to infiltration layer.Shadow of the content to infiltration layer that Fig. 6 is RE Ring.Fig. 7 is K2CO3Influence of the content to infiltration layer.Fig. 8 is influence of the NaF content to infiltration layer.Fig. 9 is permeation temperature to infiltration layer The influence of thickness.Figure 10 is influence of the permeation temperature to infiltration layer microhardness.Figure 11 is influence of the permeation time to alloying layer thickness. Figure 12 is influence of the permeation time to infiltration layer microhardness.Figure 13 is the pre- infiltration layer section microstructure of nitrogen carbon.Figure 14 is N-C-V- Mo-RE infiltration layers section microstructure.Figure 15 is N-C-V-Mo-RE infiltration layer grain morphologies (a) Cross Section Morphology (b) surface topography.Figure The 16 V-Mo infiltration layers section grain morphology to be oozed in advance without N-C.Figure 17 is the pre- infiltration layer line scan element distribution of nitrogen carbon.Figure 18 is N- C-V-Mo-RE permeation layer lines scan element is distributed.Figure 19 is that pre- nitriding carbon-coating (b) N-C-V-Mo-RE of XRD diffracting spectrums (a) is more First co-penetration layer.Figure 20 is sample microhardness distribution.Figure 21 is sample unit area wear extent with load change situation.Figure 22 is The relative wear resistance increment of the relative tempering sample of quenching of permeation sample.Figure 23 is N-C-V-Mo-RE permeation sample wear morphologies (a) 5N (b)15N(c)30N.Figure 24 is N-C permeation sample wear morphologies (a) 5N (b) 15N (c) 30N.Figure 25 is tempering sample abrasion of quenching Pattern (a) 5N (b) 15N (c) 30N.Figure 26 is N-C-V-Mo-RE permeation specimen surface crack morphologies (a) 100 times (b) 300 times (c) 500 times (d) 600 times.Figure 27 is N-C permeation specimen surface crack morphologies (a) 100 times (b) 300 times (c) 500 times (d) 600 It is secondary.Figure 28 is tempered specimen surface crack morphology (a) 100 times (b) 300 times (c) 500 times (d) 600 times to quench.Figure 29 is that sample exists V-notch crack morphology (a) N-C-V-Mo-RE permeation samples (b) N-C permeation samples (c) after 300 fatigues, which are quenched, is tempered examination Sample.Figure 30 is V-notch crack morphology (a) N-C-V-Mo-RE permeation sample (b) N-C permeation examination of the sample after 600 fatigue Sample (c), which is quenched, is tempered sample.Figure 31 is sample lead crack length and cycle-index relation.
Embodiment
Technical scheme is further elaborated below by embodiment.
Embodiment 1
It is prepared by the 1st chapter experiment material and sample
1.1 experiment material
1. matrix material
Test the 65Nb matrix steels that matrix used material is the production of Shanghai Baoshan Steel stock Co., Ltd, its permeation experiment Preceding condition of heat treatment is Q-tempering state, and material chemical composition is as shown in table 2-1.65Nb steel used in contrast experiment chemistry into Divide the regulation with GB/T1299-2000, it is known that experiment material meets Standard.Material is through Wire-cut Electrical Discharge Machining into size For 8mm × 8mm × 12mm samples, specimen surface is polished to 5000# with sand paper, sample is polished afterwards and is washed away to minute surface, then with acetone Specimen surface spot and impurity.
65Nb steel chemical compositions and its mass fraction (wt%) are used in table 2-1 experiments
2. penetration enhancer material
(1) stage is oozed in advance：This stage is that nitrogen carbon oozes in advance, to improve specimen surface N, C content, is connect down so as to reach promotion The purpose of the multicomponent thermochemical treatment come.Penetration enhancer selects the carbon-based salt of nitrogen of star heat treatment material Co., Ltd of Anqiu City of Shandong Province nine production (trade name J-2), penetration enhancer are that outward appearance is canescence blocks of solid, chemical composition (mass fraction)：CNO-(38%~ 42%), M+(M+For Na+、K+、Li+And 44%~46%), CO3 -(14%~18%), be nontoxic base salt, can provide simultaneously N, C active atomics, optimal use temperature are 520 DEG C~580 DEG C.
(2) the multicomponent thermochemical treatment stage：This stage is salt bath vanadium molybdenum rare earth multicomponent permeation, excellent so as to obtain performance in specimen surface Good V and Mo nitrogen carbide coating.Choose borax anhydrous (Na2B4O7) multicomponent thermochemical treatment base salt is used as, for the oxidation of vanadium agent selection five Two vanadium (V2O5), select molybdenum trioxide (MoO for molybdenum agent3), both reducing agents are aluminium powder (Al)；Add potassium carbonate (K2CO3) make To improve the neutral salt of fused salt mobility, and addition sodium fluoride (NaF) to improve the activity of salt bath；The present embodiment selects market (La contents are that 37.1%, Ce contents are 62%) to be used as energizer to upper common mixed rare earth of lanthanum and cerium, can play catalytic action Other rare earths are also selectable as the catalyst in this stage.
1.2 preparation technologies and equipment
N-C-V-Mo-RE multicomponent thermochemical treatments are divided into following three steps：
(1) first step progress nitrogen carbon oozes processing in advance.First canescence bulk J-2 base salt is smashed to graininess, weighs 200g Base salt is put into ceramic crucible, then is placed in chamber type electric resistance furnace with stove heat, after base salt is aged 2 hours at a temperature of pre- ooze, By surface be polished to the sample of minute surface and cleaning by ooze in advance it is face-up in a manner of be put into the guarantor of a period of time carried out in crucible Temperature is oozed in advance, is finally taken out sample and is carried out air cooling, completes nitrocarburizing.Pay attention to after sample cools down, by the furvous of layer surface Gently mill and the polishing of loose oxide layer, otherwise will have a negative impact to the multicomponent thermochemical treatment quality layer of next step；
(2) second step carries out salt bath vanadium molybdenum rare earth multicomponent permeation.First weigh quantitative borax anhydrous, potassium carbonate, sodium fluoride, Vanadic anhydride, molybdenum trioxide, aluminium powder and rare earth, for oxidization burning loss when reducing aluminium powder addition and weaken molybdenum trioxide in height Influence of the volatility to experiment under temperature, load weighted aluminium powder and molybdenum trioxide are coated with aluminium foil, then add each examination successively Agent.
By graphite crucible with resistance stove heat, when furnace temperature rises to 900 DEG C, borax anhydrous is first added in batches as permeation Substrate, treat that borax all after melting, adds the mixture of potassium carbonate and sodium fluoride, then add vanadic anhydride and use aluminium foil The molybdenum trioxide and aluminium powder coated, quickly stirring makes it fully react, and then substep adds mixed rare earth of lanthanum and cerium and nitrogen Carbon oozes sample and carries out multicomponent thermochemical treatment in advance, and each time interval added between step is 8~10 minutes.Then adjustment resistance furnace temperature Degree is to permeation temperature and is incubated a period of time, finally takes out sample and carries out oil cooling；
(3) the 3rd steps are tempered.Internal stress and fragility caused by sample during in order to eliminate high-temperature salt bath permeation, and obtain Preferable combination property is obtained, temper need to be carried out to sample.Temperature is 550 DEG C, is incubated 1h, is tempered 2 times.Tempering is completed Sample is placed in boiling water afterwards to remove the residual salt of specimen surface.
Chapter 2, the analysis method and equipment for the treatment of effect
2.1 fabric analysis method and apparatus
Test Equipment for Heating Processing：It is box to carry out multicomponent thermochemical treatment processing firing equipment used in experiment to 65Nb matrix steels Resistance furnace, model SX2-10-10,1200 DEG C, rated power 10kw, rated voltage 390V of its temperature upper limit, size of burner hearth are 400mm×250mm×160mm.The supporting temp controlled meter model used of the resistance furnace is KSG-12-12.
(1) sample corrodes：Sand paper grinding and buffing is carried out to multicomponent thermochemical treatment specimen cross section.For for infiltration layer section structure The sample of morphology observation, corrode 10s with 4% nital at normal temperatures；For being seen for infiltration layer section crystal grain distribution The sample examined, the 1 of saturation liquor potassic permanganate and 10%KOH solution is placed at 50 DEG C:Corrode 90s in 1 mixed solution, then Clean simultaneously air-dried sample.
(2) infiltration layer morphology observation and element distribution analysis：After sample infiltration layer etches, with Hitachi (Hitachi) S- The displaing micro tissue topography of 3400N types SEM (SEM) observation infiltration layer and crystal grain distribution situation, and it is attached with SEM Each element distribution situation in energy disperse spectroscopy (EDX) analysis infiltration layer.
(3) infiltration layer material phase analysis：Layer surface is scanned and obtained with D/MAX 2500V types X-ray diffractometers (XRD) To scanning spectra, XRD running parameters are：Operating current 100mA, operating voltage 20KV, 20 °~90 ° of scanning angle scope, scanning 10 °/min of speed；Scanning result is finally imported into MDI Jade5.0 softwares and carries out material phase analysis.
According to Bu Lade laws, when meeting equation below 2-1 between X ray incidence angle θ and incidence wave wavelength X,
Diffraction maximum collection of illustrative plates can just be produced；The interplanar distance of formula middle finger different crystal, n are natural numbers.XRD is scanned into gained Diffraction maximum collection of illustrative plates carries the contrast of PDF cards with MDI Jade5.0 softwares, is made up of element known to determination, can draw the thing of infiltration layer Mutually form.
2.2 performance test methods and equipment
2.2.1 hardness measuring method
The hardness of infiltration layer is to study an important indicator of penetrated layer property, and it also reflects infiltration layer matter to a certain extent Amount.The case hardness of infiltration layer and the compound layer thickness of infiltration layer and the consistency of infiltration layer are closely related, it is generally the case that infiltration layer is got over Thick and finer and close, then its case hardness is higher.Infiltration layer section hardness gradient can help us to understand the hardness distribution shape of infiltration layer The combination situation of condition and infiltration layer and matrix.Using layer surface hardness obtained by the measurement experiment of HVT-1000 micro Vickerses and Section microhardness.The measurement range of Vickers is wider, whether the soft material of only several Vickers hardness numbers or The hard material of up to 3000 Vickers units, it can be measured with Vickers.Vickers hardness measures another One big advantage is that Vickers hardness number obtained by sample is unrelated with experiment loading force size, and this make it that Vickers hardness is very wide at one In the range of have a unified scale.The present embodiment vickers hardness test chooses loading force 0.1N, load time 10s.Sample exists Carry out layer surface and the light grinding and polishing light in section before hardness test, the case hardness of infiltration layer takes being averaged for five test point Vickers hardnesses Value；The measurement of infiltration layer section hardness distribution situation measures 10 points successively on the basis of layer surface, by surface along matrix direction, Test result chooses the average value of five groups of measurement data.
2.2.2 abrasion resistance test method
Abrasion test, experiment reference standard JB/T 7506- are carried out to the 65Nb matrixes steel curved beam Jing Guo different disposal 1994 (bonded-abrasive abrasive test (pins-sandpaper disk skimming wear method)), are entered using ML-100 type grain-abrasion testing machines Row wear test.Wear test principle is as shown in Figure 1：
Experiment uses testing machine as pin dish-type swinging grain-abrasion testing machine；As illustrated, after specimen clamping is got well, Sample is under certain load F and to grinding material perpendicular contact, firing test machine, and disk is rotated with certain rotating speed, sample Quantitative feeding radially then is done along disk, its friction route on to mill material is a spiral of Archimedes, this spiral The length of line is the friction stroke of sample.When the starting point of the spiral of Archimedes is in disc centre, its length S calculates public Formula is as follows：
In formula, N is the total revolution of disk, the radial feeds of sample when a circles for disk.
In actual tests, sample starting point is not worn in least radius 10mm and maximum radius 110mm in disc centre, sample Region in carry out, the length S of caused helix can calculate with following simple formula：
S=π aN2 (2-3)
The disc rotation speed of abrasion tester is 60r/min, and peak load is 100 newton.Specimen size used in experiment is Φ 4mm × 30mm, its feed speed are 4mm/r, and to ensure that it wears circuit exact contact but not overlapping, gained friction stroke is 2116πmm.The carborundum paper for being model 800# to mill material used by experiment, silicon-carbide particle hardness are about 2800HV；Experiment loading force chooses 5N, 10N, 15N, 20N and 30N respectively.
The sample that will be contacted with sand paper after processing is processed by shot blasting to flour milling, removes surface scratch.Sample Cleaned up before and after wear test with supersonic wave cleaning machine, weigh quality W before its abrasion respectively0With quality W after abrasion1, it is poor Value is sample wear extent, you can calculates various sample unit area wear extent by formula 2-4, and enters under SEM ESEMs Row wear morphology is observed.
W in formula0And W1Unit be mg, S (cm2) it is sample wear area, G (mg/cm2) it is unit area wear extent.
2.2.3 thermal fatigue resistance method of testing
Standard HB 6660-1992 are sheet metal the thermal fatigue test methods more than unique industry-level in China.Standard Test period is：55s cool times heat time+5s；Its defect is that heat time and cool time are too short, is insufficient to allow examination Sample temperature rises to and is down to required temperature upper limit and lowest temperature；In addition, the firing equipment that the present embodiment uses is SG2- 7.5-12 type crucible electrical resistance furnaces, the switch fire door of high frequency will cause in stove that actual temperature and design temperature difference are big, and furnace temperature is difficult to Keep stable, it is therefore desirable to which experimental program is adjusted.65Nb matrix steels are in the application based on cold work die steel, due to height The reasons such as speed impact, friction, surface highest transient temperature during its work is up to 300 DEG C -400 DEG C, and it is as hot-work die Operating temperature during steel is up to 500 DEG C -700 DEG C.
In summary, the sample that size is 8mm × 8mm × 12mm is chosen, opens V-notch in its one end to study crackle life Long situation, temperature upper limit are 700 DEG C, and lowest temperature is 20 DEG C, to carry outCold cycling；Heat time is 2min, cool time 10s, cooling medium are running water；Cycle-index is respectively 100 times, 200 times, 300 times, 400 times, 500 times With 600 times.
By specimen surface sanding and polishing to minute surface before experiment, to eliminate influence of the surface scratch to experiment, resistance furnace temperature is treated After degree reaches the temperature upper limit of setting, sample is quickly put into stove with homemade fixture, heats and protects under the design temperature upper limit Quickly sample is taken out and is dipped in running water after warm 2min and cools down 10s, that is, completes a cold cycling process, Ran Houji Continuous sample is put into stove is heated, and after so circulating 100 times, 200 times, 300 times, 400 times, 500 times and 600 times, takes out sample By the oxide jettisoning on its surface on polishing machine, then under the microscope to crackle at sample V-notch and face crack shape Looks are observed.
It there is no unified standard for material thermal fatigue property decision method both at home and abroad at present.Thermal fatigue property evaluation can root After regulation cold cycling number, length of surface fatigue crack or crack width that sample occurs are evaluated, can also according to table Facial cleft line when reaching certain length required cold cycling number evaluate.
It is expected that stress concentration can be produced at the V-notch of sample one end, so that preferentially cracked in this place germinate and split Line extends, and is embodied in lead crack and the secondary cracks being connected with lead crack and micro-crack.When test cycle number reaches After set cycle period, with reference to lead crack length L and the thermal fatigue property of surface fatigue crack morphology evaluation material.It is identical Under the thermal cycle cycle, connect that the lead crack of V-notch is more thin short and face crack is more tiny, then the thermal fatigue resistance of material is got over It is excellent.It is wherein most long and continuous one if there is a plurality of lead crack, measurement；If lead crack is meander-shaped, it is equal Measured respectively for multistage straight line, finally calculate its summation, as lead crack length.
3rd chapter multicomponent thermochemical treatment formula and technical study
The pre- cementation process researchs of 3.1N-C
, could be by TRD salt baths metallic cementation process in matrix material table only when the carbon content of matrix material is higher than 0.4% Face forms the effective codiffusional layer of adequate thickness, and for the of a relatively high middle and high steel alloy of some alloy contents, although its carbon Content is higher than 0.4%, but more alloy carbide is formd in these steel, secures the part carbon in matrix, therefore energy The carbon content being used effectively is relatively fewer, it is impossible to effectively forms effective alloy carbide infiltration layer in material surface.In addition by Less nitrogen is not contained or comprised only in general matrix material, can not obtain the conjunction of function admirable using TRD salt bath metallic cementation processes Golden nitride infiltration layer.
In order to improve the nitrogen carbon content of 65Nb steel material surfaces, in order to during the V-Mo-RE multicomponent thermochemical treatments in later stage More preferable alloy co-penetration layer is obtained, experiment carries out N-C to 65Nb material surfaces first and oozed in advance.The J-2 type nitrogen that the present embodiment uses Carbon permeation base salt can not only obtain effective nitrogen carbon penetration in material surface, and cost is cheap, and experimental implementation is easy.Using J- 2 type base salt nitrogen carbon ooze in advance belongs to salt bath nitrocarburizing method, and it is mainly by urea CO (NH)2Formed with carbonate, if J-2 base salt In carbonate by taking sodium carbonate as an example, following chemical reaction occurs when heating and melting in it：
CO(NH2)2+Na2CO3→2NaCNO+2H2O (3-1)
4NaCNO→2NaCN+Na2CO3+CO+2[N] (3-2)
2CO→CO2+[C] (3-3)
Chemically reacted more than, melt in base salt and generate required active nitrogen carbon atom, these active atomics pass through Diffusion penetrates into matrix surface, and the nitrogen carbon penetration with certain depth is formed in matrix surface.Nitrogen carbon is carried out using J-2 bases salt Permeation has been the chemical heat treatment process of comparative maturity, and experiment is no more than 580 DEG C with the optimal use temperature of J-2 base salt, The infiltration layer of certain depth can be obtained in 2h~5h time range, thus designs the technique for carrying out N-C using J-2 bases salt and oozing in advance Scheme is：560 DEG C × (2h, 3h, 4h, 5h), 570 DEG C × (2h, 3h, 4h, 5h), 580 DEG C × (2h, 3h, 4h, 5h),To ooze in advance Thickness degree is as foundationJudge the optimal pre- cementation process of nitrogen carbon, obtain nitrogen-carbon cocementing process scheme and experimental result such as table 3-1 institutes Show, obtaining the pre- alloying layer thickness of nitrogen carbon according to data in table, to change over time trend at different temperatures as shown in Figure 3.
Table 3-1 nitrogen-carbon cocementing process scheme and result
With the increase for oozing the time in advance and the pre- rise for oozing temperature it can be seen from above chart, pre- alloying layer thickness is whole What body rose.According to Fick's second law, obtain alloying layer thickness x and oozing diffusion time t has following relation in advance：
In formula, A is constant, because material, diffusion temperature, diffusion time and it is different, D is diffusion coefficient, and it is temperature T letter again Number, relational expression are：
In formula, Q be material diffusion activation energy, D0For diffusion constant, Q and D are generally thought0Size only and material Material is relevant with flooding mechanism, and temperature independent.It is i.e. available, when the timings of temperature T mono-, diffusion of N, C atom in 65Nb steel Coefficient is constant, and pre- alloying layer thickness increases with the increase of time；The timings of time t mono- are oozed when pre-, as the rise of temperature, N, C are former The diffusion coefficient increase of son, pre- alloying layer thickness increase therewith.
By Fig. 3 it has been also found that pre- alloying layer thickness it is pre- oozing increase early stage it is very fast, when it is pre- ooze temperature 5h risen to by 4h when, Pre- infiltration layer increasing degree is relatively reduced, because now diffusion length increases, infiltration layer increases and slowed down；Pre- alloying layer thickness is oozing temperature in advance Increase obvious when increasing to 570 DEG C by 560 DEG C, and when temperature continues to increase to 580 DEG C, pre- alloying layer thickness increases very little, may It is because with the progress oozed in advance, the less N atoms of diffusion activation energy diffuse rapidly into matrix (N, C are in α-Fe in α-Fe Middle diffusion activation energy is respectively 77KJ/mol and 88KJ/mol), pre- infiltration layer composition is changed, different from 65Nb material matrix Composition, its eutectoid temperature may drop to it is pre- ooze below temperature, occur in pre- infiltration layer γ-Fe, N, C atoms diffusion coefficient reduce. In summary analyze, the optimised process that N-C oozes in advance is 570 DEG C × 4h.
3.2V-Mo-RE salt bath permeation formulas and technical study
3.2.1V-Mo-RE salt bath permeation formulating
3.2.1.1V-Mo-RE the selection of co-diffused salt bath penetration enhancer
1. the selection of base salt
The species of metallic cementation salt bath mainly includes borax bath, neutral salt bath and mixed salt-bath.Borax bath metallic cementation process Using borax as base salt, penetration enhancer after chemical reaction is set to generate active metal atom in borax base salt, so as in workpiece surface The exsertile metallic compound coating of formative.This method major advantage is that borax density is bigger, makes penetration enhancer and its generation Active metal atom be easy to be uniformly suspended within salt bath, so the segregation of salt bath is smaller, oozed what workpiece surface was formed Thickness degree and quality are also more stable；And borax bath can remove the oxide-film of workpiece surface, can reach cleaning workpiece surface With the effect for promoting infiltration layer to be formed.But the highdensity feature of borax bath also makes its mobility poor, fused salt cleaning is relatively tired Difficulty, and borax bath to equipment corrosion than more serious.The problem of existing for borax bath have developed good fluidity and right Workpiece corrosion acts on small neutral salt bath, but the volatility of neutral salt bath is bigger, and fused salt therein is easy to be segregated in Salt bath bottom, cause the stability of alloying layer thickness and quality and uniformity all poor, therefore its practical value ratio is smaller.Therefore originally Embodiment selection combination property preferably mixed salt-bath, based on borax bath, adds appropriate neutral salt, is keeping borax bath Improve its mobility while being segregated small advantage, improve salt bath and ooze effect.The present embodiment chooses K simultaneously2CO3As neutral salt plus Enter in borax.
2. the selection of activator
With the progress of each constituent element chemical reaction in borax bath, the activity of salt bath will reduce, and particularly reducing agent is anti- The generation of product is answered, coating function may be played to reducing agent, inhibition will be played to reagent and reacting to each other for reducing agent, Moreover, reducing agent reaction product can also increase salt bath viscosity, its mobility is greatly declined, and cause the activity in salt bath former Son diffusion is difficult, it is therefore desirable to chooses activator and improves salt bath activity.And sodium fluoride (NaF) can effectively improve salt bath mobility and Activity, therefore test and choose NaF as activator.
3. the selection for vanadium agent and for molybdenum agent
This stage is to carry out V-Mo-RE multicomponent thermochemical treatments, for vanadium agent and for molybdenum agent be exactly for permeation provide active vanadium atom with Molybdenum atom.Common has V-Fe alloy powders and vanadic anhydride (V for vanadium agent2O5), can be in metal material with both penetration enhancers Surface obtains effective vanadium-containing compound coating, but V-Fe alloy powder proportions are larger, easy segregation in crucible bottom, it is necessary to Periodic agitation, and its obtained Vanadized layer quality is unstable.In addition, metal dust is not easy to be dissolved completely in borax bath, Possibly even sinter agglomerating under high temperature, be bonded in specimen surface, cause that the surface roughness of infiltration layer is bigger, and quality layer is poor. And V2O5Energy Effective Suspension chooses V in borax glass2O5As for vanadium agent.It is alternative to have molybdenum powder, molybdenum for molybdenum agent Iron powder, molybdenum trioxide (MoO3), molybdenum dioxide (MoO2).It is bigger that molybdenum powder and molybdenum-iron powder easily cause workpiece surface roughness, and And it is similar with vanadium iron powder, molybdenum-iron powder is segregated also than more serious in borax glass, therefore is not selected.In practical operation is tested, It was found that add MoO under high temperature2When powder is into the borax bath of melting, MoO2Powder can be come up with vaporific from crucible, be caused Serious MoO2Mass loss, experimental implementation are poor.Therefore molybdenum agent is supplied to choose MoO3Powder, it should be noted that MoO3In height The lower volatility of temperature is stronger, and directly addition easily makes it float over salt bath top layer and vapor away.In order to suppress MoO3Volatilization, adding Before, first with aluminium foil by MoO3Powder coats, and is then added to again in borax glass, rapid stirring, is uniformly distributed in it molten Melt in borax, its volatility is inhibited, and adding reducing agent immediately makes it restore active Mo atoms.
4. the selection of reducing agent
Whether the selection of reducing agent properly directly influences the concentration of permeation active atomic, so as to have influence on alloying layer thickness and Quality layer.Selective reducing agent has aluminium powder, SiC, BC etc., and V is reduced in the experiment of salt bath metallic cementation with aluminium powder2O5 It is relatively common, in addition, in the steel-making of molybdenum oxide direct Reducing and Alloying, aluminium the reproducibility of molybdenum trioxide is also significantly larger than silicon and Reproducibility of the carbon to molybdenum trioxide.In summary, the present embodiment chooses aluminium powder and makees reducing agent.Aluminium powder and five oxidations in the present embodiment The chemical equation of two vanadium and molybdenum trioxide is as follows, and the calculating temperature in reaction equation is 1200K (927 DEG C), its standard free enthalpy Less than zero, it is seen that reaction can be with spontaneous progress.After the dosage of vanadic anhydride and molybdenum trioxide is determined, according to chemical anti- The proportionate relationship between the reactant in formula 3-6 and 3-7 is answered to calculate the theoretical addition of aluminium powder, in order to tackle the part of aluminium powder Scaling loss situation, excessive 10% or so on the basis of theoretical addition.
5. the selection of energizer
Rare earth has to salt bath plasma surface alloying process significantly urges the effect of oozing, and can significantly improve metallic cementation speed.Therefore choose Energizer of the rare earth as the present embodiment, and further explore effect of the rare earth in salt bath metallic cementation.
3.2.1.2V-Mo-RE the research of co-diffused salt bath formula
V-Mo-RE permeations are the major parts of N-C-V-Mo-RE multicomponent thermochemical treatments, and the main purpose in this stage is to provide more Higher V, Mo atom of activity, combined its N, C active atomic formed in specimen surface oozes in advance with N-C with formed vanadium and The nitrogen carbide of molybdenum, so as to form certain thickness compound co-penetration layer, it is effectively improved the surface property of material.For More efficiently analyze influence of each penetration enhancer to the V-Mo-RE permeation stages, introduce orthogonal test analysis side in the present embodiment Method.
The addition of V-Mo-RE permeation stage of reduction agent aluminium powders is by V2O5And MoO3Addition determine that borax addition is Totally remove the surplus of other penetration enhancer proportions, therefore, choose V2O5、MoO3、RE、K2CO3, NaF be 5 of orthogonal test because Element, each factor chooses 4 levels, therefore uses L16(45) orthogonal arrage, 16 represent that the number of trials of orthogonal tests is 16 in formula. 4 levels of 5 factors of orthogonal test are chosen as shown in table 3-, choose 950 DEG C of permeation temperature, permeation time 4h.According to L16 (45) specific formula of each penetration enhancer of co-diffused salt bath that orthogonal arrage obtains and obtained alloying layer thickness and infiltration layer microhardness result such as table Shown in 3-3,Using alloying layer thickness and infiltration layer microhardness as criterionVariance analysis to each factor is as shown in table 3-4.
Table 3-2 orthogonal test factor levels
Table 3-3 orthogonal test permeation formulas and result
Table 3-4 orthogonal test the results of analysis of variance
Note：1. K in table1、K2、K3、K4The average value of respectively each factor orthogonal experiments under corresponding level, Range For the extreme difference of each way crossover study result average value, SS is the sum of squares of deviations of each way crossover study result average；
2. level of significance α=0.10 given in table, tables look-up：F (3,3)=5.39.
For the apparent influence for intuitively analyzing each factor and its varying level to co-penetration layer performance, according to orthogonal test The results of analysis of variance makees each factor level and performance indications relation and tendency chart as shown in Fig. 4~Fig. 8.In each figure, abscissa is 4 respective horizontals of corresponding penetration enhancer, ordinate is alloying layer thickness and infiltration layer microhardness.
(1)V2O5Mass fraction in salt bath permeation：From orthogonal test the results of analysis of variance, V2O5To polynary common The thickness and microhardness of infiltration layer, which all have, to have a significant impact, and as seen from Figure 4, works as V2O5When addition is less than 8%, With V2O5The increase of addition, the thickness and microhardness of co-penetration layer, which are presented, to be obviously improved, and thereby it is assumed that out, V-Mo- The RE multicomponent thermochemical treatment stages are based on vanadinizing；Work as V2O5Amount when increasing to 10% by 8%, co-penetration layer thickness is substantially unchanged, and The amplification of co-penetration layer hardness is also smaller, and from the angle to save material, it is V to choose 8%2O5Optimum addition.
The V-Mo-RE permeation stages be primarily due to based on vanadinizing active V atoms and N, C atom have it is stronger affine Power, the chemical affinity between element can be judged with the electronegativity of element, and the chemical affinity between element is represented by：
X (i, j)=(Xi-Xj)2 (3-8)
In formula, XiAnd XjRespectively it is element i and element j electronegativity, X (i, j) value is bigger, then the change between i, j element It is stronger to learn affinity.Table look-up, N and C electronegativity is respectively 3.04 and 2.55, and V and Mo electronegativity are respectively 1.63 Hes 2.16, it is seen that V and N, C chemical affinity are larger, and permeation is based on vanadinizing.Again because the nitrogen carbide of vanadium have it is very high hard Degree, so co-penetration layer microhardness larger change also occurs with the change of the infiltration capacity of vanadium, and general trend is, the infiltration of vanadium Amount is bigger, and co-penetration layer hardness is higher.V permeation initial stage can micro infiltration matrix surface, because V atomic radiuses are more than Fe atoms half Footpath, V infiltration cause larger distortion of lattice in 65Nb matrix surfaces, and this can make N, C to the diffusion flux in matrix surface direction Increase, so as to promote the progress of permeation.
(2)MoO3Mass fraction in salt bath permeation：MoO3Influence to co-penetration layer thickness and microhardness is more complicated, Co-penetration layer hardness is in MoO3Amount reach peak value when increasing to 6%, hereafter with MoO3Content increase, co-penetration layer hardness is under slowly The trend of drop；And co-penetration layer thickness is with MoO3Reach maximum when content increases to 8%, lifting amplitude it is more apparent, then with MoO3Content continues to increase, and co-penetration layer thickness is decreased obviously again.The hardness of Mo nitrogen carbide is high not as V nitrogen carbide, again Because the multicomponent thermochemical treatment stage is based on vanadinizing, therefore MoO3Content do not have a significant impact to co-penetration layer hardness, it is contemplated that MoO3 The conspicuousness of alloying layer thickness is influenceed, it is MoO to choose 8%3Optimum addition.Work as MoO3Amount when increasing to 10% by 8%, altogether Alloying layer thickness and microhardness are all on a declining curve, because working as MoO3Amount addition it is larger when, it is necessary to more aluminium powder pair It is reduced, and generates more Al2O3, and the relative reduction of amount of " solvent " borax, the mobility of salt bath is greatly lowered, is glued Denseness increases, and V, Mo atoms permeating are difficult, causes permeation efficiency to decline.
(3) mass fractions of the RE in salt bath permeation：From orthogonal test the results of analysis of variance and Fig. 6, in this implementation In example, RE contents have a significant impact to co-penetration layer microhardness, when RE contents are 4%, co-penetration layer thickness and microhardness All reach higher value, when RE contents increase to 6%, co-penetration layer microhardness is substantially unchanged, and co-penetration layer thickness declines on the contrary, therefore 4% is RE optimum additions.
Rare earth, which has, significantly urges the effect of oozing, and rare earth first has stronger reproducibility, can promote penetration enhancer V2O5And MoO3's Decompose, and rare earth has the characteristics of micro solid solution in matrix surface, can increase the diffusion flux of active N, C atom, in addition one The reason for individual important be because the electronegativity difference of rare earth atom and permeation atom larger (La electronegativity is that 1.1, Ce electronegativity is 1.05), there is stronger adsorptivity, activated centre can be formed in specimen surface.As shown in fig. 6, when rare earth addition is less, Rare earth is less in the activated centre atomic group that specimen surface is formed, and urges and oozes effect unobvious；When rare earth addition reaches 4%, The active rare-earth central atom group for being adsorbed in specimen surface is covered with specimen surface, can be to active V, Mo atom and matrix in salt bath Active N, C atom of near surface produces effective suction-operated, so as to form quality and the preferable co-penetration layer of performance；Work as rare earth When addition is excessive, there is certain thickness rare earth atom accumulation horizon because the strong adsorptivity of rare earth can be formed in specimen surface, So as to produce certain inhibition to permeation.
(4)K2CO3With mass fractions of the NaF in salt bath permeation：K2CO3Multicomponent thermochemical treatment salt bath mobility can be improved with NaF And activity, so as to play indirect complementary effect to permeation.As shown in Figure 7, K2CO3It is smaller to co-penetration layer thickness effect, and When its content is 7%, co-penetration layer hardness reaches maximum, therefore it is K to choose 7%2CO3Optimum addition.It can separately be obtained by Fig. 8, NaF then has a significant impact to co-penetration layer thickness, and when its content is 7%, co-penetration layer thickness is substantially compared with 3% and 5% two level Co-penetration layer thickness it is high, and co-penetration layer microhardness reaches peak value, and when its content increases to 9%, co-penetration layer thickness is substantially unchanged, Microhardness reduces on the contrary, therefore 7% is NaF optimum additions.Both influences to co-penetration layer performance are embodied in them to altogether In the influence of quality layer, when both additions are moderate, they can promote active permeation atom V, Mo formation and diffusion, So as to ensure that active V, Mo atom there are enough supplys near layer surface, make the co-penetration layer even compact to be formed, so as to Reduce permeation layer defects, co-penetration layer is showed preferable performance.
Determine that optimal V-Mo-RE multicomponent thermochemical treatments formula is according to above experimental result and analysis：8%V2O5, 8%MoO3, 4%RE, 7%K2CO3, 7%NaF.
3.3V-Mo-RE salt baths co-penetration technology is studied
The purpose of V-Mo-RE salt bath permeations is on the basis of N-C oozes in advance, and it is fine and close to form continuous tissue in 65Nb steel surfaces Co-penetration layer, so as to improve the synthesis surface property of 65Nb matrix steels, extend its service life.The tissue and property of multicomponent thermochemical treatment layer Can be not only relevant with permeation component prescription, permeation temperature and permeation time equally have a great impact to co-penetration layer, improperly altogether Preferable co-penetration layer may all be cannot get by oozing treatment temperature and processing time.Experiment is by exploring multicomponent thermochemical treatment temperature and time pair The influence of V-Mo-RE salt bath permeation layer tissues and performance, optimize the technological parameter of salt bath permeation, to obtain preferably co-penetration layer.
The process program of V-Mo-RE salt bath permeations is set to by experiment：950℃×(2h、4h、6h)、1000℃×(2h、4h、 6h), 1050 DEG C × (2h, 4h, 6h), andCriterion is used as using the thickness of co-penetration layer and hardnessDetermine that optimal V-Mo-RE salt baths are total to Cementation process, obtain V-Mo-RE co-penetration technologies scheme and result as shown in Table 3-5, alloying layer thickness and table are obtained according to data in table Surface hardness and the graph of a relation of permeation temperature and permeation time are as follows.
Table 3-5V-Mo-RE co-penetration technologies scheme and result
V-Mo-RE salt bath permeation alloying layer thicknesses and hardness are as shown below with the situation of change of permeation temperature, can by Fig. 9 See, with the rise of permeation temperature, multicomponent thermochemical treatment thickness degree generally increases under each time, because with the rise of temperature, N, C atom active of V, Mo atom and specimen surface in salt bath improves, but when permeation temperature increases to 1050 DEG C by 1000 DEG C, Co-penetration layer thickness increase is smaller, and particularly when the permeation time is 6h, sample alloying layer thickness is in permeation temperature by 1000 DEG C of increases Substantially unchanged during to 1050 DEG C, this explanation permeation atom has had enough activity at 1000 DEG C；As seen from Figure 10, When the permeation time is 2h and 4h, co-penetration layer case hardness is increased when permeation temperature increases to 1000 DEG C by 950 DEG C Larger, when the permeation time is 6h, with the further rise of permeation temperature, specimen surface hardness declines on the contrary, and this is probably Because now permeation temperature is higher, under prolonged heating, infiltration layer crystal grain is grown up rapidly, intensity decreases.In summary analyze Choose 1000 DEG C and be used as the optimal permeation temperature of V-Mo-RE salt bath permeations.
V-Mo-RE salt bath permeation alloying layer thicknesses and hardness with the permeation time situation of change as is illustrated by figs. 11 and 12, by Figure 11 is visible, and with the increase of permeation time, alloying layer thickness generally increases at a temperature of different permeations, because longer The permeation time under, permeation active atomic has time enough to diffuse near specimen surface, be combined with each other and forms co-penetration layer； But when the permeation time extends to 6h by 4h, sample alloying layer thickness amplification is less than amplification of permeation time when 4h is extended to by 2h, Because the permeation time is in short-term, the diffusion path of active atomic is shorter, and diffusion is easy, and as the permeation time increases, infiltration layer becomes Thickness, N, C active atomic will pass through thicker and fine and close co-penetration layer, and diffusion difficulty increases, and infiltration layer growth rate is slack-off.Can by Figure 12 See, when permeation temperature is 950 DEG C and 1000 DEG C, as the permeation time increases, co-penetration layer case hardness increase, when permeation temperature For 1050 DEG C, when the permeation time increases to 6h by 4h, layer surface hardness slightly declines, now sample hardness and permeation temperature For 950 DEG C when sample hardness it is suitable, this also by infiltration layer crystal grain grown up under long-time high temperature it is very fast caused by.It is comprehensive with Upper analysis chooses 4h as the V-Mo-RE salt bath permeations optimal permeation time.
4th chapter multicomponent thermochemical treatment diffusion layer organization and structural analysis
4.1 infiltration layer morphology analysis
Figure 13 is the infiltration layer section microstructure that nitrogen carbon oozes in advance, it can be seen that pre- infiltration layer is divided into obvious 3 layers.Outermost layer is Sponge Porosity thin layer is specimen surface at a temperature of pre- ooze because of high-temperature oxydation and caused by aoxidize weaker zone, it forms main It is due to the oxidation of C element, the hardness of weaker zone is relatively low, is needed this weaker zone jettisoning before ensuing multicomponent thermochemical treatment.It is middle Dull gray layer be compound layer, be the major part of pre- infiltration layer, because its after corrosion under an optical microscope in Bai Liangzhuan it is also normal It is referred to as nitride layer, white layer, its thickness accounts for the 2/3 of pre- alloying layer thickness.Light gray layer close to matrix is between compound layer and matrix Diffusion layer, account for the 1/3 of alloying layer thickness.As seen from the figure, the thickness of compound layer and diffusion layer is more uniform, and tissue is finer and close, There is no a common infiltration layer defect such as obvious hole, and both interfaces are serrated mutual insertion, realize compound layer With effective combination of transition zone, transition zone is in the form of a column the combination that embedded matrix is likewise advantageous to infiltration layer and matrix.
Figure 14 is that (specimen cross section is molten through 5% nitric acid alcohol for the Cross Section Morphologies of 65Nb sample N-C-V-Mo-RE multicomponent thermochemical treatment layers Corrosion), it is seen that whole co-penetration layer thickness is consistent with even tissue, and co-penetration layer continuity is very good with compactness, infiltration layer and base Without appearance " black-tape " isotonic layer defects between body, the interface between infiltration layer and matrix is clear and smooth.Between metallic cementation layer and matrix The fluctuating quantity at interface is relevant with temperature, and temperature is higher, and interface undulation is bigger, and smooth interface also illustrates permeation experiment temperature in figure Spend moderate, sample does not produce obvious deformation.It is worth noting that, do not occurred in N-C-V-Mo-RE multicomponent thermochemical treatment layers obvious Transition zone, it is and often common to occurring transition zone between compound layer and matrix in metallic cementation Cr.This is primarily due to Cr nitrogen Solubility of the carbide at high temperature in austenite is bigger, and the compound of chromium can dissolve in Austria in the Chromizing Layer close to matrix In family name's body matrix, supersaturated solid solution is formed；Ooze in rear cooling procedure, compound solubility reduction in austenite of chromium, from And separated out in matrix at compound layer and form transition zone.And V and Mo nitrogen carbide is in austenite in the present embodiment Solubility it is smaller and to dissolve in austenitic temperature higher, so not forming obvious transition zone.
Figure 15 be 65Nb samples N-C-V-Mo-RE multicomponent thermochemical treatments layer through saturation liquor potassic permanganate+10%KOH solution 50 Infiltration layer section and surface microstructure shape appearance figure after corroding at DEG C.It can be seen from Figure 15 (a) whole multicomponent thermochemical treatment layer be all by etc. Axialite grain is formed, and for equiax crystal opposed cylinder crystalline substance, the orientation of each crystal grain of equiax crystal is different, meets isotropism, in the absence of bright Aobvious plane of weakness, there is more excellent combination property.Examine it has been also found that along matrix to layer surface direction, crystal grain chi It is very little to become larger, but overall crystallite dimension or relatively fine；Because at permeation initial stage, nitrogen carbon atom diffusion length is short, So nitrogen carbon atom is in liberal supply, compound forming core is easy, and nucleus mushrooms out and contacts with each other and form tiny equiax crystal.And As infiltration layer is thickening, nitrogen carbon atom, which is diffused into infiltration layer and liquid level reaction front, becomes further difficult, causes the supply of nitrogen carbon atom to subtract Few, nucleation rate step-down, crystal grain becomes larger.Figure 15 (b) is the surface microstructure shape appearance figure after the corrosion of multicomponent thermochemical treatment layer, it is seen that surface Equi-axed crystal is uniform in size consistent, and the isometric crystalline region of whole surface is dense, and this provides group to improve the combination property of infiltration layer Knit guarantee.
Figure 16 is the 65Nb sample V-Mo infiltration layers section grain morphology figure without oozing in advance, it is seen that due to the nitrogen of its matrix supply Carbon activity atom is not so good as to ooze the more of sample in advance through nitrogen carbon, causes infiltration layer thin, and with the growth of infiltration layer, the supply of nitrogen carbon atom Deficiency, the grain size of outer layer crystal grain are noticeably greater than internal layer crystal grain, poor-performing, it is seen that N-C ooze in advance can play optimization it is polynary The effect of co-penetration layer institutional framework and performance.
4.2 infiltration layer energy spectrum analysis
Ooze the infiltration layer obtained afterwards in advance through N-C to 65Nb matrix steels and carry out N, the scanning of C element line, obtain in each position N, the intensity of C element is as shown in figure 17.As seen from Figure 17, it is more due to having accumulated in the oxide layer within 5 μm away from surface Carbon black, C element content is higher, and this is primarily due to metastable phase Fe3C decomposites the stone of simple substance carbon form in 65Nb specimen surfaces Ink.The distribution for observing C element understands that C element is higher in the top layer content of infiltration layer, and its content is concentrated mainly on nitrocarburizing layer Compound layer, and its content persistently reduces along infiltration layer to matrix direction, intensity gradient is larger, and during to diffusion layer, its content is It is fewer.The N element then distribution uniform in the infiltration layer including compound layer and diffusion layer, shows as a width in fig. 17 Larger peak, and its content is higher than C element content in most of region of infiltration layer, illustrates that N-C oozes based on nitriding in advance.Can To see during pre- ooze, N atoms are more stronger than what C atom was carried out in the infiltration of 65Nb specimen surfaces and interior diffusion, this Aspect is due in α-Fe, and the diffusion activation energy of N atoms is less than the diffusion activation energy of C atoms, and its diffusion is easier to make for； On the other hand, the ferrite in 65Nb matrixes and cementite may also serve facilitation to the infiltration of N atoms, be allowed to penetrate into Depth is bigger.
EDX line scannings are carried out to N-C-V-Mo-RE multicomponent thermochemical treatments layer, obtain Fe, V, Mo, N, C element along oozing Intensity distribution of the layer to matrix direction is as shown in figure 18, and scanning residence time of the EDX energy disperse spectroscopies in each position is 600 milliseconds. As seen from Figure 18, it is the separation of each element intensity at 10 μm away from surface or so, illustrates it is multicomponent thermochemical treatment infiltration layer and matrix at this Interface position.Fe element-intensities exist in interface to be mutated, and its content in co-penetration layer is almost nil, illustrates altogether Infiltration layer is due to not that metallic element penetrates into matrix material and formed, and is due to metallic element on 65Nb steel curved beams surface and expands Be dissipated to the N of matrix surface, C element with reference to and form the nitrogen carbide of permeation metallic element, so as to " raw in 65Nb specimen surfaces It is long " go out a co-penetration layer.Distribution uniform of the content of V element and Mo elements in co-penetration layer, and the intensity of V element is high, Much larger than the intensity of Mo elements, this demonstrates being based on vanadinizing in the V-Mo-RE multicomponent thermochemical treatment stages, this is primarily due to phase For Mo atoms, the electronegativity difference between active V atoms and N, C atom is larger, has stronger affinity each other, This point has been analyzed above, and here is omitted.N element is relatively evenly distributed on whole co-penetration layer, because N-C The nitrogen source provided in pre- infiltration layer is more sufficient, and N element is also having higher intensity from matrix surface remote position, and this is main Have benefited from the relatively small atomic radius of N atoms, make its diffusivity stronger, and crystal grain tiny in infiltration layer is also N atoms Diffusion provides more diffusion admittances for being advantageous to improve N atomic diffusivities, and this facilitate expansion of the N atoms in co-penetration layer Dissipate the formation with co-penetration layer.C element is then more in the distribution of the near interface of multicomponent thermochemical treatment layer and matrix, because C element exists Main in the pre- infiltration layers of N-C to concentrate the surface for being present in pre- infiltration layer, it is easier the interface and the activity that diffuse to salt bath and sample V, Mo atoms with reference to and form corresponding carbide；And at a temperature of 1000 DEG C of permeation, matrix of samples is γ-Fe states, C is former Son diffusion activation energy wherein it is small compared with N atoms (diffusion activation energy of N, C atom in γ-Fe be respectively 145KJ/mol and 138KJ/mol), can diffuse out quickly.
4.3 infiltration layer material phase analysis
X-ray diffraction is carried out to pre- nitriding carbon sample infiltration layer and N-C-V-Mo-RE multicomponent thermochemical treatment samples infiltration layer, obtained such as figure Diffracting spectrum shown in 19.It can be seen that nitrogen carbon primarily forms ε phases (Fe in infiltration layer in advance from Figure 19 (a)3N), the phase hardness Height, corrosion resistance, wearability are preferable, are the main components of infiltration layer SEM picture nitride layer, white layers.In nitriding process, it will usually ooze The lamination of nitrogen layer, for most of steel, infiltration layer is along, with the rise of nitrogen concentration, phase composition is successively from matrix to surface direction For：α (martensite containing N) → γ ' (Fe4N)→ε→ξ(Fe2N), the XRD results using ε phases as main component of pre- infiltration layer also indicate that Nitrogen gesture in salt bath is higher, and the infiltration capacity of nitrogen is bigger, and this also oozes the stage with nitriding in advance with the nitrogen carbon of line scanning Based on it is consistent.Figure 19 (b) shows that the main thing of N-C-V-Mo-RE multicomponent thermochemical treatment layers is mutually VN, Mo2N、V8C7、Mo2C, explanation V, Mo elements are realized in infiltration layer forming process and effectively be combined with each other with N, C element, form respectively the nitrogen carbon of vanadium and molybdenum Compound, these compounds virtually all have high-melting-point, high rigidity and good high-temperature stability, to improving multicomponent thermochemical treatment The combination property of layer is extremely important.
In the nitrogen carbide of preferable vanadium, N, C are respectively 1 with V atomic ratio:1, it is the gap of face-centred cubic structure Compound, V atomic building face-centered cubic lattices, N, C atom are located in its octahedral interstice respectively.Because face-centered cubic knot The crystal cell atomicity of structure is 4, and (interstitial radii is about 0.146a, and a is crystalline substance containing the larger octahedral interstice of 4 interstitial radiis Born of the same parents' lattice constant or lattice constant), so as to provide space for nitrogen carbon atom.But N, C atomic radius are slightly larger than face-centered cubic The octahedral interstice radius of the nitrogen carbide of the vanadium of structure, so squeezing into for nitrogen carbon atom causes certain distortion of lattice, only When N, C atomic concentration are larger, it is respectively 1 with V atomic ratio that could form N, C:1 face-centred cubic structure.So actual feelings In condition, N, C atom may not fully take up its octahedral interstice, so as to form the deduction solid solution using compound as base, and In the present embodiment multicomponent thermochemical treatment stage, N relative infiltration capacity is bigger, forms the compound VN of nitrification, and content is relative slightly Low C and V then forms deduction solid solution V8C7。Mo2C be C atoms be filled in octahedral interstice in Mo close-packed hexagonal structure and The compound of formation, Mo2N is then face-centred cubic structure, both stable Mo compound.
4.4 infiltration layer microhardnesses are analyzed
Figure 20 is N-C-V-Mo-RE multicomponent thermochemical treatments sample, N-C permeations sample and tempering sample (1120 DEG C of quenchings+550 of quenching DEG C × 1h is tempered 2 times) hardness distribution situation, as seen from the figure, N-C-V-Mo-RE multicomponent thermochemical treatments sample and N-C permeations sample by In foring the certain thickness infiltration layer different from matrix in specimen surface, there is hardness gradient distribution, and sample Maximum hardness appears at layer surface, and quench tempering sample hardness be then distributed it is homogeneous.
Maximum hardness of the N-C-V-Mo-RE multicomponent thermochemical treatments sample on top layer has reached 2656.3HV0.1, because permeation Layer is made up of a large amount of fine and close and tiny crystal grain V and Mo nitrogen carbide, and these hard phases are that infiltration layer shows higher hardness Provide guarantee.Along infiltration layer to matrix direction, due to not forming effective transition zone between the infiltration layer and matrix of high rigidity, firmly Degree decline it is very fast, but it is noted that still have that certain hardness is excessive between co-penetration layer and matrix, because V and Mo Atomic radius is although larger, so that its diffusion activation energy in 65Nb matrixes is larger, it is difficult to remotely spread, but in permeation Starting stage, the coating of formation is also relatively thin, still there is that micro V, Mo atomic energy is diffused into matrix skin and N, C are combined to form Hard disperse phase, or the Fe atoms of displacement matrix surface form substitution solid solution, and it is abnormal that certain lattice is produced at matrix skin Become, so as to play certain invigoration effect；Further, since the pre- alloying layer thicknesses of N-C, up to 30 μm, N, C atom spread in 65Nb matrixes Depth is larger, in the V-Mo-RE permeation stages, nitrogen carbon that N, C atom left behind after terminating to matrix skin diffusion aggregation, permeation Same can produce of compound that atom is formed necessarily is strengthened, and this all promotes the combination between infiltration layer and matrix.
The layer surface hardness of N-C permeation samples is 981.2HV0.1, have certain lifting compared with matrix hardness, this is main It is because the formation of ε phases promotes the raising of nitrided layer hardness.Because hardness difference is not very big between N-C co-penetration layers and matrix, and Infiltration layer containing compound layer and diffusion layer is thicker, and along infiltration layer to matrix direction, infiltration layer downward gradient is gentle, and infiltration layer and matrix combine Preferably.Because N-C permeation samples soaking time at a temperature of permeation is longer, more cementite and agglomeration are separated out in matrix, Make matrix hardness relatively low.65Nb steel is organized as tempered sorbite after the quenching of routine and tempering heat treatment are strengthened, and hardness is about For 725.6HV0.1。
5th chapter multicomponent thermochemical treatment penetrated layer property is studied
5.1 Wear Resistance
5.1.1 the wear out failure of material
Abrasion is due to object under the effect such as machinery, chemistry, electricity, and its work surface material is due to relative motion and continuous The phenomenon of loss.According to statistics, about 60%~80% machine components failure is due to caused by various forms of abrasions, it is seen that Wear out failure is that machine components are main and a kind of most common failure mode, therefore the research to material wear-resistant performance is extremely It is important.Abrasion is a sufficiently complex process, and the abrasion of material is not only by extraneous factors such as load working condition, media environments Influence, it is also relevant with material tissue in itself and performance.Due to the complexity of abrasion, the classification for abrasion not yet reaches so far Come to a conclusion into unified, according to the mechanism and feature of abrasion, abrasion mainly includes adhesive wear, abrasive wear, fatigue wear and corrosion The forms such as abrasion, in various wear forms, abrasive wear accounts for 50%, is most important wear form.
Abrasive wear refers in the abrasive particle or ridge and the mutual friction process of part of hard, makes piece surface generating material The phenomenon of loss.Abrasive Wear Mechanism mainly includes：(1) micro cutting mechanism：In wear process, particularly ground in bonded-abrasive Under the conditions of damage, abrasive particle cuts material surface because plus load acts on, and due to the relative motion of abrasive particle and material surface, It is cut piece surface and forms the less ditch dug with a plow of more narrow and deep degree and micro- chip.(2) multiple plastic deformation wear mechanism：Work as material Expect plasticity preferably or abrasive particle corner angle it is relatively round blunt when, most of abrasive particle in Relative friction, surfacing push to ditch dug with a plow both sides or Leading edge and form plough wrinkle, portion of material is not fallen off there occurs larger plastic deformation, and it is then due to flattening-pushing away repeatedly Squeeze effect and eventually flake off.(3) fatigue wear mechanism：Under periodic loading, material surface is processed within incubation period Hardening, sliding plastic deformation layer and crackle are formed on its surface afterwards, and abrasion is produced with Crack Extension, belong to low week Fatigue wear.(4) micro-fracture wear mechanism：For the material that fracture toughness is poor, abrasive particle effect produces band on the material There is the impression of face crack, as these crackles internally extend from material surface, crackle then intersects or extended to surface, material Material will occur fracture and peel off and produce abrasion.
5.1.2 polishing machine is analyzed
Respectively N-C-V-Mo-RE multicomponent thermochemical treatments sample, N-C permeations sample and tempering of quenching are prepared according to optimum process and formula Sample (+550 DEG C × 1h of 1120 DEG C of quenchings is tempered 2 times) is each 15, and per sample (p.s.) is respectively divided into 3 groups, every group 5, entered respectively The certain abrasive grain wear test of row loading force.Loading force scope is 5~30N, the load increment using 5N as every group of experiment loading force. After wear test terminates, the average abrasion weightlessness of 3 samples under sample same load of the same race is calculated, and calculates its unit area Wear extent, as unit area wear extent of the sample under the load, to reduce experimental error.To per sample (p.s.), load is chosen Respectively 5N, 15N, 30N carry out the worn surface observation of sample.
The unit area abrasion of N-C-V-Mo-RE multicomponent thermochemical treatments sample, N-C permeations sample and tempering 3 kinds of samples of sample of quenching Amount as shown in Table 5-1, the unit area wear extent of each sample is obtained with load change situation such as Figure 21 according to wear test result It is shown.
Unit area wear extent (the mg/cm of table 5-1 samples2)
With the increase of load, the unit area wear extent of 3 kinds of samples generally increases, and has tempering sample list of quenching all the time Plane product wear extent is more than N-C permeation samples, and the wear extent of N-C permeation samples is more than N-C-V-Mo-RE multicomponent thermochemical treatment samples, In this 3 kinds of sample of explanation, the wearability of multicomponent thermochemical treatment sample is optimal, and the wearability for tempering sample of quenching is worst.Although each sample mill Damage amount generally increases and risen with load, but their situation of growth is different.Tempering sample quench under initial load 5N Unit area wear extent it is just relatively large, reached 50.16mg/cm2, but sample is in 5N~10N load section Unit area wear extent increases also than shallower, but when load is more than 10N, sample unit area wear extent increases sharply, Increase in near-linear, this is mainly relevant (see abrasion shape with multiple plastic deformation wear mechanism with tempering sample abrasion of being quenched under low load Looks analysis part), it is also possible in part because 65Nb specimen surfaces are most initially forming layer oxide film, serve certain Lubrication, abrasion is slow down, and as oxide-film is worn away, sample wear extent increases sharply.N-C permeations sample then due to Surface forms nitrocarburizing layer, forms the preferable ε phases of a large amount of wearabilities, so wearability is better than tempering sample of quenching.When adding When load power is less than 25N, with the increase of loading force, co-penetration layer is constantly ground off, and infiltration layer internal layer wearability is less than outer layer, so The growth trend of N-C permeation sample unit area wear extenies constantly increases, but its growth trend is consistently less than tempering sample of quenching；And When loading force increases to 30N by 25N, N-C permeation sample unit area wear extenies growth trend is tempered sample beyond quenching suddenly, Because as infiltration layer is worn away, matrix continues to participate in abrasion, and N-C permeation matrix of samples hardness is tempered sample less than quenching, Wearability is poor compared with tempering sample of quenching.Unit area wear extent of the N-C-V-Mo-RE multicomponent thermochemical treatments sample under 5N loading forces only has 13.27mg/cm2, with the increase of loading force, the growth of its unit area wear extent is also shallower, presents preferably wear-resisting Performance.The classical model proposed with reference to Rabinowicz
In formula, W is that material unit rubs the wear extent of stroke, and P, H are respectively the hard of external load and material wear surface Degree, K is associated wear coefficient.From the model, under certain operating mode, the wear extent of material is directly proportional to load p, with material Wear surface hardness H is inversely proportional.Multicomponent thermochemical treatment layer contains a variety of V and Mo carbonitride, has the characteristics of high rigidity, makes material Wearability be substantially improved.
On the basis of the wearability for tempering sample of quenching, the relative wear resistance through different disposal sample is as shown in table 5-2；N-C- V-Mo-RE multicomponent thermochemical treatments sample and N-C permeations sample are as shown in figure 22 relative to the relative wear resistance increment for tempering sample of quenching.By Table and figure understand that the wearability of N-C-V-Mo-RE multicomponent thermochemical treatment samples is much better than N-C permeations sample and tempering sample of quenching.Due to The excellent wearability of multicomponent thermochemical treatment layer, the abrasion incipient stage for being 5N in abrasion loading force, it is relative to the resistance to of tempering sample of quenching Mill property is 3.78, has reached maximum；And N-C permeations sample is then 15N in loading force relative to the wearability for tempering sample of quenching When reach maximum, its increment has reached 29%.
Relative wear resistance of the table 5-2 samples under different loads
5.1.3 worn surface is analyzed
For comprehensive analysis and judge the surface abrasion resistance through different disposal sample, selection loading force be respectively 5N, The wear morphology of 15N, 30N various samples carries out SEM observation analysis.Figure 23 is that N-C-V-Mo-RE multicomponent thermochemical treatments sample is carrying Lotus is the wear morphology under 5N, 15N and 30N.The wear trace of specimen surface is not particularly evident it can be seen from Figure 23 (a), Only there is slight scratch.Because multicomponent thermochemical treatment layer is finer and close, case hardness is up to 2656.3HV0.1, and wear test Middle use is SiC sand paper to mill material, and the SiC particulate hardness on its surface is in 2800HV or so, and its hardness is for multicomponent thermochemical treatment Layer is without obvious advantage, so in the case of load ratio is less, SiC particulate is difficult to be pressed into multicomponent thermochemical treatment layer surface and formed Abrasion.As loading force increases to 15N, there is obvious groove in sample wear surface, and there occurs larger pushing to be plastically deformed, But the characteristics of these grooves is shallow and wide, as shown in Figure 23 (b), because under larger load, the sharp rib of SiC abrasive particles Angle is easily by blunt when with harder specimen surface to mill, thus the groove pattern formed is compared with shallow and wide.Find out from Figure 23 (c), When loading force is 30N, the sample degree of wear significantly becomes big, and obvious ditch dug with a plow occurs in wear surface and plough wrinkles, and this is due to altogether Infiltration layer is relatively thin, matrix has been milled under 30N load, matrix hardness is much smaller than co-penetration layer hardness, therefore wear extent is rapid Increase, the degree of wear become big.
Figure 24 is the N-C permeations sample wear morphology under 5N, 15N and 30N loading force respectively.From Figure 24 (a), when When loading force is 5N, there is shallower and queueing discipline ditch dug with a plow in specimen surface, and the degree of wear is relatively light, abrasion hair now Life is about 981.2HV in N-C permeation layer surfaces, layer surface hardness0.1, not as good as SiC hardness of the abrasive grain, but also compare matrix hardness There is certain lifting, ε phases existing for a large amount of disperses also effectively increase the anti-wear performance of infiltration layer, therefore mill now in infiltration layer Damage degree is also smaller.As loading force reaches 15N, in the worn surface shown in Figure 24 (b), ditch dug with a plow density substantially increases Add, remained much because of micro- cutting of the abrasive particle to material surface and caused by chip, illustrate now abrasive particle pressing in sample surface Depth increase, abrasion increases, but because N-C permeations thickness is up to 30 μm, the mill to matrix has effectively been completely cut off under 15N loading forces Damage, the ditch dug with a plow for wearing formation is not still very wide.Under 30N loading forces, abrasive particle has been ground to matrix completely, and N-C permeations Matrix of samples hardness (671.5HV0.1) than 65Nb steel routine quenching and tempering treatment sample hardness (725.6HV0.1) will be low, it is wear-resisting Poor-performing, therefore violent abrasion is generated in specimen surface, in being total to for micro- cutting scheme and multiple plastic deformation wear mechanism Under same-action, specimen surface experienced micro- cutting repeatedly and push flow, form a large amount of irregular, incomplete ploughs Wrinkle, ditch dug with a plow and remaining micro- chip.
Figure 25 is the tempering sample wear morphology under 5N, 15N and 30N loading force respectively of quenching, it is known that compared to N-C-V-Mo- RE multicomponent thermochemical treatments sample and N-C permeation samples, the degree of wear of the tempering sample under each load of quenching is overall all larger, but each load Under wear morphology still have nothing in common with each other.Because 65Nb matrix steels have the excellent toughness and plasticity better than corresponding high-speed steel, in 5N Low load under, abrasive particle directly can not be cut material completely, worn based on multiple plastic deformation wear mechanism, abrasive particle exists When being moved relative to material surface, the plough that material pushes wear track both sides or leading edge to and forms protuberance is wrinkled, then connect again The abrasive particle that gets off flattens, pushed with this-pressing mechanism is repeated, so material plasticity deforms in Figure 25 (a) wear morphology Big but remaining chip is few.Because load is smaller, after abrasion, only portion of material is peeled off and departs from specimen surface, and this is also explained When load is relatively small, 65Nb quenches the unit area wear extent increment less phenomenon of tempering sample.As loading force increases 15N and 30N are added to, cutting aggravation of the abrasive particle to material surface, produces a large amount of mixed and disorderly ditch dug with a plows, plough wrinkle and remaining chip.
Sample is tempered in different abrasion loads by contrasting N-C-V-Mo-RE multicomponent thermochemical treatments sample, N-C permeations sample and quenching Under unit area wear extent and wear morphology, it is known that because N-C-V-Mo-RE multi element copermeation technologies effectively increase 65Nb bases The surface strength of body steel, its unit area wear extent is smaller, and its unit area wear extent also increases with abrasion load increase Gently, understand that its degree of wear is also relatively small from wear morphology, have better than N-C permeations sample and the wear-resisting of tempering sample of quenching Performance.
5.2 thermal fatigue resistance Journal of Sex Research
5.2.1 the heat fatigue cracking germinating and extension of mould steel
The thermal fatigue failure of material is a kind of common failure mode in mechanical engineering field, and the heat fatigue of metal material is lost Effect may be summarized to be four-stage：A. the change of metal microstructure and substructure causes the generation of the microdefects such as micro-crack； B. the microdefect such as micro-crack, which is grown up, converges to form lead crack；C. lead crack is stable extends；D. instable growth of crack, fracture is produced Destroyed etc. structure.Wherein, the germinating of micro-crack and Crack Extension are the major parts of thermal fatigue failure process.With cool-hot fatigue Process repeats, and the intensity of material constantly reduces, with the continuous accumulation of internal stress, in the interior tissue weakness of material The microdefects such as micro-crack can be produced because bearing incessantly internal stress.Micro-crack generation mechanism is a lot, comes from fatigue stress state See, in a heated state, the rise of material surface temperature, internal temperature is relatively lower than surface, cause both in speed of expansion Difference, generate compression thermal stress；On the contrary, under the state of cooling, thermal stress is stretched inside sample.When compression thermal stress Or stretching thermal stress be more than material yield strength when, materials microstructure weakness zone will preferentially produce plastic deformation.With cold The progress of thermal cycle, constantly accumulation is plastically deformed, and then forms fold, thus crack initiation.Analyzed from micro-scale, room, The presence of the weakness zones such as aggregation and crystal boundary, impurity of the defects of dislocation under thermal cycle effect can induce sprouting for crackle It is raw.
After micro-crack is formed, thermal stress redistribution, stress concentration is formed in crack tip, the stress intensity at this is big When threshold value, crackle extends, and is finally grown to long crack.Micro-crack and long crack extension characteristic are as follows：(1) micro-crack It can be extended under the nominal driving force less than long crack, under same nominal external drive power, the expansion rate of micro-crack is remote Far above long crack；(2) micro-crack can be with Dispersed precipitate in material, and microcrack density increases and increased with fatigue life cycle Greatly, it can be converged between crackle and continue to extend；(3) extension of the microstructure of material to fatigue statistic has important influence, Extension is easily carried out along material internal defect orientation.
5.2.2 face crack morphology analysis
Choose N-C-V-Mo-RE multicomponent thermochemical treatments sample, N-C permeations sample and three kinds of tempering sample of quenching is by different process Sample, every kind of technique choose 6 samples, and 3 kinds of samples are carried out respectivelyThermal fatigue test, be recycled to regulation A sample is respectively taken out after number to be further analyzed, cycle-index is respectively 100 times, 200 times, 300 times, 400 times, 500 It is secondary and 600 times.
The growing state of each specimen surface face crack after the different cold cycling cycles is observed respectively.Figure 26 is N-C- The face crack situation of V-Mo-RE multicomponent thermochemical treatment samples, from figure it will be seen that after 100 cool-hot fatigues circulate, There is the few short crack of quantity in specimen surface.The short crack increasing number of specimen surface after 300 circulations, but overall flaw shape Looks are not still apparent.After 500 circulations, thin short crackle just gradually clearly gets up before；Final sample is cold by 600 times After heat fatigue circulation, its surface forms several wider crackles.
Figure 27 is face crack pattern of the N-C permeations sample after the different cold cycling cycles.Through 100 cold cyclings Afterwards, specimen surface produces extremely unconspicuous elongated crack；After 300 circulations, elongated crack originally broadens by extension. When cycle-index reaches 500 times, crack length sharply increases, and long crack runs through whole observing interface；After 600 circulations, carefully Long crack contacts with each other connection, and the wider place of crackle material occurs and peels off sign.
Figure 28 is the face crack situation quenched and be tempered sample.After 100 cool-hot fatigues circulate, specimen surface occurs Sparse strip short crack.By 300 circulations, these short crack quantity showed increaseds, crack density increase, and sample table There are many tiny formation of crack in face；Circulated afterwards by further cool-hot fatigue, crackle extends up in different positions, occurs Branch.After 600 circulations, increasing and its further expand with crack number, they, which interweave, is joined together to form net Shape crackle.It can be found that in the thermal fatigue test later stage, the face crack length for tempering sample of quenching does not have significant change, and It is that most short cracks connect into grid by contacting with each other, is destroyed surface.
Sample is tempered in different cool-hot fatigues by contrasting N-C-V-Mo-RE multicomponent thermochemical treatments sample, N-C permeations sample and quenching Face crack pattern after cycle-index is it was found that three kinds respectively have feature by the face crack pattern of different disposal sample. In three kinds of samples, the distinguishing feature of N-C permeation samples is that its crack propagation velocity is very fast, easily forms elongated crack；Tempering of quenching tries The distinguishing feature of sample is its crack initiation speed, easily forms highdensity crackle grid；And N-C-V-Mo-RE permeation samples Face crack quantity it is relatively fewer, crack initiation speed, expansion rate are all relatively small, have preferably thermal fatigue resistance Energy.
5.2.3V shape otch analysis on cracks
The V-notch bottom of specimen surface is that sample produces stress raiser due to the drastically change of shape, cold in alternation Under heat fatigue circulation germinating and Crack Extension are cracked by preferential.N-C-V-Mo-RE permeations sample, N-C permeations sample and quench It is tempered V-notch crack morphology of the sample after 300 times and 600 cool-hot fatigue circulations as shown in Figure 29 and Figure 30.
It can be seen that under same test conditions, N-C-V-Mo-RE multicomponent thermochemical treatment samples are at V-notch Lead crack length is significantly less than other two kinds of samples.N-C-V-Mo-RE permeations sample and tempering sample of quenching only have a lead crack, Illustrate that the formation of both specimen surface lead cracks effectively alleviates the stress concentration phenomenon at tip, make the extension of other micro-cracks It is eased.And a plurality of lead crack along otch radially is generated at the V-notch of N-C permeation samples, and through 600 After secondary cold cycling, incision cracks have also appeared obvious material peeling phenomenon.In addition from Figure 29 and Figure 30, sample Lead crack length with cold cycling number increase and increase；Master of three kinds of samples after different cold cycling numbers is measured to split Line length, the relation curve (also referred to as a-N curves) for obtaining lead crack length and cycle-index are as shown in figure 31.
As seen from Figure 31, after 100 cold cyclings, N-C-V-Mo-RE multicomponent thermochemical treatments sample, N-C permeations examination The lead crack of sample and tempering sample of quenching has been completed to germinate, in macroscopic cracking extension phase.The crackle length of multicomponent thermochemical treatment sample Degree and crack propagation velocity are significantly less than other two kinds of samples, and with the increase of fatigue life cycle, its crack length increases Gently, terminate to thermal fatigue test, its crack length is 551.26 μm.Quench tempering sample crack propagation velocity be faster than it is polynary common Sample is oozed, but expansion rate is also relatively stable, and after 600 cold cyclings, crack length is 1334.2 μm.N-C permeation samples Initial crack length after 100 thermal cycles is less than tempering sample of quenching, but its expansion rate is larger, to 300 thermal cycles When, its crack length alreadys exceed tempering sample of quenching, and during final off-test, its crack length reaches 1772.3 μm.Thus may be used , according to V-notch lead crack length and expansion rate, multicomponent thermochemical treatment sample has the thermal fatigue resistance better than other two kinds of samples Performance.
Intensity and plasticity are the factors being had a great influence to the thermal fatigue resistance of material.N-C-V-Mo-RE multicomponent thermochemical treatments try The surface infiltration layer of sample is mainly VN, Mo2N、V8C7、Mo2The V such as C and Mo nitrogen carbide, and surface diffusion layer organization is fine and close, crystal grain is thin Small, this makes specimen surface show higher intensity and plasticity.The combination of this intensity and plasticity makes the yield strength of material incline To in larger, this can effectively suppress plastic deformation tendency of material, and preferably plasticity is easy to the local thermal stress for making material It is released, so as to alleviate stress concentration, reduces the driving force of Crack Extension, suppress the extension of crackle.In addition, plasticity is preferable Multicomponent thermochemical treatment layer can store a part of residual tension under the state of cooling of thermal cycle, and this part internal stress adds thermal cycle A part of compression can be offset in thermal process, so as to play a part of relief of thermal stress.And there is research to point out, crystal grain is tiny VC organizes that the heat endurance and heat resistance of steel can be improved, and improves the thermal fatigue resistance of material.
N-C permeation layer tissues are mainly ε phases (Fe2-3N), it is mainly characterized by hard and crisp, and this obtains the surface strength of material To certain lifting, so its crack length after 100 thermal cycles is less than tempering sample of quenching；Yet with its plasticity compared with Difference, crackle will be poor with faster speed expanded, thermal fatigue resistance after once germinating.65Nb, which quenches, is tempered the surface of sample Plasticity is better than N-C permeation samples, and overall thermal fatigue resistance is placed in the middle.
Embodiment 2
A kind of N-C-V-Mo-RE multicomponent thermochemical treatment materials strengthened for steel material surface, it is characterised in that described permeation Material includes following two sections of material：J-2 types nitrocarburizing base salt and V-Mo-RE multicomponent thermochemical treatment materials, according to mass percent Meter, the raw material components of the V-Mo-RE multicomponent thermochemical treatments material are as follows：Potassium carbonate 8%, sodium fluoride 8%, vanadic anhydride 10%, Molybdenum trioxide 8%, rare earth 5%, aluminium powder 15%, surplus are borax anhydrous, and above each component mass percent summation is percent 100.
Embodiment 3
A kind of N-C-V-Mo-RE multicomponent thermochemical treatment materials strengthened for steel material surface, it is characterised in that described permeation Material includes following two sections of material：J-2 types nitrocarburizing base salt and V-Mo-RE multicomponent thermochemical treatment materials, according to mass percent Meter, the raw material components of the V-Mo-RE multicomponent thermochemical treatments material are as follows：Potassium carbonate 6%, sodium fluoride 6%, vanadic anhydride 7%, three Molybdenum oxide 6%, rare earth 3%, aluminium powder 8%, surplus are borax anhydrous, and above each component mass percent summation is 1 percent Hundred.
Embodiment 4
A kind of processing method using N-C-V-Mo-RE multicomponent thermochemical treatments material reinforcement steel material surface described in claim 1, Comprise the following steps：
(1) nitrogen carbon oozes processing in advance
The pre- temperature of oozing is 565 DEG C, and the insulation digestion time is 1.5 hours, and it is small for 3.8 that the time is oozed in the insulation in advance When；
(2) salt bath multicomponent thermochemical treatment is handled
Permeation temperature is 950 DEG C, and soaking time is 3.5 hours,
(3) the polynary pre- sample that oozes is subjected to temper, temperature is 500 DEG C, is incubated 1h, is tempered 2 times.
Other steps are identical with the operating method of embodiment 1, do not repeating.
Embodiment 5
A kind of processing method using N-C-V-Mo-RE multicomponent thermochemical treatments material reinforcement steel material surface described in claim 1, Comprise the following steps：
(1) nitrogen carbon oozes processing in advance
The pre- temperature of oozing is 575 DEG C, and the insulation digestion time is 2.5 hours, and it is small for 4.5 that the time is oozed in the insulation in advance When；
(2) salt bath multicomponent thermochemical treatment is handled
Permeation temperature is 1050 DEG C, and soaking time is 4.5 hours,
(3) the polynary pre- sample that oozes is subjected to temper, temperature is 600 DEG C, is incubated 2h, is tempered 2 times.
Other steps are identical with the operating method of embodiment 1, repeat no more.

Claims (5)

1. a kind of N-C-V-Mo-RE multicomponent thermochemical treatments strengthen the processing method of steel material surface, it is characterised in that including following step Suddenly：
(1) nitrogen carbon oozes processing in advance
First block J-2 bases salt is smashed to graininess, is put into ceramic crucible, then is placed in chamber type electric resistance furnace with stove heat to pre- Ooze temperature and be incubated ageing；
By surface be polished to the Steel material sample of minute surface and cleaning by ooze in advance it is face-up in a manner of be put into ceramic crucible Row insulation is oozed in advance；
Finally take out Steel material sample and carry out air cooling, that is, complete nitrogen carbon and ooze processing in advance, obtain nitrogen carbon and ooze sample in advance；
The pre- temperature of oozing is 565~575 DEG C, and the insulation digestion time is 1.5~2.5 hours, and the insulation oozes the time in advance For 3.8~4.5 hours；
(2) salt bath multicomponent thermochemical treatment is handled
1. V-Mo-RE multicomponent thermochemical treatment materials are weighed, according to mass percentage, the raw material of the V-Mo-RE multicomponent thermochemical treatments material Component is as follows：Potassium carbonate 6~8%, sodium fluoride 6~8%, vanadic anhydride 7~10%, molybdenum trioxide 6~8%, rare earth 3~ 5%, aluminium powder 8~15%, surplus is borax anhydrous, and above each component mass percent summation is 100 percent；
2. load weighted aluminium powder and molybdenum trioxide are coated with aluminium foil, to reduce oxidization burning loss when aluminium powder adds and weaken three oxygen Change influence of the volatility to experiment of molybdenum at high temperature,
3. graphite crucible when furnace temperature rises to 900 DEG C, is first added into borax anhydrous as permeation base in batches with resistance stove heat Bottom, treat that borax all after melting, adds the mixture of potassium carbonate and sodium fluoride；Then add vanadic anhydride and use Aluminium Foil Package The molybdenum trioxide and aluminium powder covered, quickly stirring makes it fully react；Then substep adds rare earth and nitrogen carbon oozes sample in advance Multicomponent thermochemical treatment is carried out, each time interval added between step is 8~10 minutes；
4. then adjustment resistance furnace temperature to permeation temperature and is incubated, permeation temperature is 950~1050 DEG C, soaking time 3.5 ~4.5 hours, finally take out sample and carry out oil cooling, that is, complete the processing of salt bath multicomponent thermochemical treatment, obtain polynary pre- oozing sample.
2. processing method as claimed in claim 1, it is characterised in that also comprise the following steps：
(3) the polynary pre- sample that oozes is subjected to temper, internal stress and fragility caused by sample during eliminating high-temperature salt bath permeation, Temperature is 500~600 DEG C, is incubated 1~2h, is tempered 2 times, sample is placed in boiling water to remove sample table after the completion of tempering The residual salt in face.
3. processing method as claimed in claim 1, it is characterised in that in step (1), after air cooling, nitrogen carbon is oozed into examination in advance Gently mill and the polishing of the loose oxide layer of furvous of the layer surface of sample.
4. processing method as claimed in claim 1, it is characterised in that the Steel material sample is 65Nb matrix steels.
5. processing method as claimed in claim 1, it is characterised in that step (2), 1. in, it is described according to mass percentage The raw material components of V-Mo-RE multicomponent thermochemical treatment materials are as follows：55% borax anhydrous, 7% potassium carbonate, 7% sodium fluoride, 10% 5 oxidation Two vanadium, 8% molybdenum trioxide, 9% aluminium powder, 4% rare earth.
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CN109255190A (en) * 2018-09-09 2019-01-22 五邑大学 Plane multiple cracks Fatigue analysis method based on distributed dislocations method
CN109280879A (en) * 2018-12-06 2019-01-29 宇龙精机科技（浙江）有限公司 A kind of H13 hot-work die multicomponent thermochemical treatment surface modifying method
CN112090973A (en) * 2020-09-08 2020-12-18 锦州捷通铁路机械股份有限公司 Process for manufacturing high-performance seamless steel tube cold-drawing die by using low-carbon low-alloy steel

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CN109033576A (en) * 2018-06-28 2018-12-18 五邑大学 A kind of particulate composite Fatigue Propagation of Cracks analysis method
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CN109280879A (en) * 2018-12-06 2019-01-29 宇龙精机科技（浙江）有限公司 A kind of H13 hot-work die multicomponent thermochemical treatment surface modifying method
CN112090973A (en) * 2020-09-08 2020-12-18 锦州捷通铁路机械股份有限公司 Process for manufacturing high-performance seamless steel tube cold-drawing die by using low-carbon low-alloy steel
CN112090973B (en) * 2020-09-08 2022-03-15 锦州捷通铁路机械股份有限公司 Process for manufacturing high-performance seamless steel tube cold-drawing die by using low-carbon low-alloy steel

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