CN1069527A - Carbon arc carburizing - Google Patents

Abstract

The present invention relates to a kind of novel process of relevant diffusion hardening.

Original diffusion hardening complex process equipment, the cycle is long, cost is high.The present invention adopts common welding source, utilizes carbon (or graphite) to produce electric arc carbon atom is transitted directly to the metallic surface, forms cementation zone, thereby reaches the purpose of metal-surface strengthening.

Carburizing of the present invention rapidly, processing ease, equipment be convenient, is particularly suited for the surface of heavy parts and the local carburization of piece surface.

Description

Carbon arc carburizing

The present invention relates to a kind of novel process of relevant diffusion hardening.

For metal-surface strengthening, increase its surface hardness, wear resistance and fatigue strength, it is a kind of existing traditional processing method that reaches this purpose that carburizing is carried out in the metallic surface.

Existing carburization process promptly is that the soft steel workpiece is placed in the carburizing medium, is heated to single-phase austenitic area (generally adopting 920～930 ℃), is incubated the sufficiently long time, makes a kind of heat treating method of the carbon concentration raising of upper layer.It belongs to a kind of of thermo-chemical treatment.

Carburizing is generally formed by decomposing, absorb, spread three primary processes:

Decomposition course is exactly by the process that decomposites active atomic in the compound as active media.For example during carburizing, by CO or CH ₄Decomposite active atoms of carbon (C), react as follows:

Absorption process is exactly active atomic is entered the lattice of iron by the surface of steel a process.Owing on the surface of steel, exist a large amount of end of dislocations and crystal boundary to appear, for the infiltration of active atomic provides passage easily.Because the carbon atom radius is less, so be the lattice that enters iron in the gap mode.

Diffusion process is exactly to infiltrate carbon atom in the steel by the process of surface to inner diffusive migration.Temperature is high more, spreads soon more, thereby infiltration layer increases fast more.Surface concn is high more, spreads also soon more, and it is also fast more that infiltration layer increases.

In general, in above-mentioned three primary processes, diffusion is a slowest process, and the speed of whole carburizing process is controlled by velocity of diffusion exactly, and it is a most time-consuming process.

In the middle of the thermo-chemical treatment of steel, carburizing is most widely used a kind of technology, mainly is to be applied to part in addition such as gear, wrist pin, axle class.Case hardening steel all is soft steel and the steel alloy that contains 0.10～0.25%C, as 15,20,20C _r, 20C _rMnTi etc.

Carburizing in addition part is mostly worked under repeated load, shock load, very big contact stress and heavy wear condition, therefore requires upper layer hard and wear-resisting, and heart portion is strong and tough, has high fatigue strength, sunken, not spot corrosion are not burst apart, do not pressed in the top layer.

Recognize through a large amount of scientific researches and production practice, the surface carbon concentration of cementation zone between 0.8～1.1% for well, especially best between 0.85～1.05%.Surface carbon concentration is crossed low then not wear-resisting, and fatigue strength is also low.Otherwise surface carbon concentration is too high, and then cementation zone becomes fragile, in case occur netted or massive carbide, easier peeling off.

State difference according to carburizing medium can be divided into solid carburizing, paste carburizing, liquid carburizing and gas cementation.

Wherein solid carburizing, paste carburizing and liquid carburizing, are all replaced by gas cementation except that using under individual cases because the shortcoming of himself is limit.

Gas cementation is to carry out in the pit carburizing furnace of special use or through cementing furnace, and workpiece carries out carburizing in the pyritous carburizing atmosphere.

Carburizing atmosphere in the stove has two kinds of supply modes: a kind of is heat absorption type gas and enriched gas (CH ₄, C ₃H ₈Deng) feed in the stove by pipeline; Another kind is that organic liquids such as kerosene, benzene, methyl alcohol are directly splashed in the stove, and Pintsch process forms carburizing atmosphere.

Carburizing atmosphere is mainly by CO, CO ₂, H ₂, H ₂O and CH ₄Deng composition, general requirement CO ₂＜0.5%, H ₂O＜0.5%, CH ₄＜1.5%.

The gas cementation reaction is as follows:

By last this " water-gas reaction ", several gas contents in the atmosphere remain balance, as long as therefore measure H ₂O or CO ₂The just carbon potential of atmosphere height as can be known of content.Because CH ₄The carburizing activity greater than CO, CH ₄The subtle change of content just makes the atmosphere carbon potential that very great fluctuation process takes place, and is difficult to control, so CH ₄Content do not wish too much, generally all is controlled at below 1.5% to get final product.Therefore gas cementation mainly is to rely on CO to decompose to form active atoms of carbon.

What extensively adopt in the factory at present is to drip the kerosene carburizing in pit carburizing furnace.

Each factory of the processing parameter of pit furnace gas cementation is different, and relatively more successful at present typical process is shown in accompanying drawing 1 and accompanying drawing 2.

As can be seen from the figure, gas cementation generally is divided into three phases:

1) exhaust phase: go into stove intensification beginning by workpiece, till furnace atmosphere meets the requirements of carbon potential, be called exhaust phase.Exhaust phase not only comprises the whole heating-up time, also will comprise the 30-60 minute soaking time of instrument after the temperature.This stage also claims " aeration phase ".

2) ooze the stage by force: when entering this stage, furnace atmosphere has been set up high carbon potential, and workpiece also heats, so the surface carbon concentration of steel reaches the carbon potential value very soon, and inwardly diffusion soon.Three primary processes of carburizing this moment are all being carried out consumingly.The time of oozing the stage by force requires to decide according to depth of penetration, generally about 1～2 hour.

3) diffusion phase: the purpose in this stage is to regulate surface carbon concentration to reach optimum range, and makes infiltration layer reach the requirement degree of depth.The soaking time in this stage can be 2 times of the stage of oozing by force.

As can be seen from the above analysis, although gas cementation is extensively adopted at present, still there are a lot of shortcomings in it:

1) need specific equipment, facility investment is big.As 60 kilowatts of pit gas carburizing furnaces (charging basket is of a size of φ 450 * 600), its price is 40,000～50,000 yuan.If adopt the controlled atmosphere gas carbruizing furance, its cost will be more expensive, can reach hundreds of thousands of even unit up to a million.

2) be not suitable for jobbing work, limited by size of burner hearth, more be not suitable for the production of big part.

3) the carburizing cycle long, the cost height, productivity is low.The general gas cementation time is all more than tens hours, thus cause waste of electric energy, and reduced productivity, increased the cost of product.

At the shortcoming and the limitation of above-mentioned gas carburizing, in order to solve the especially large-scale carburizing of part in addition of the small quantities of part in addition of single-piece and the needs of other part local carburization, the present invention will provide a kind of fast and convenient carburizing novel process-carbon arc carburizing.

Principle of the present invention is to utilize carbon (or graphite) to do electrode, produces electric arc by welding source, and carbon atom is transitted directly to the metallic surface, forms cementation zone in the metallic surface, thereby reaches the purpose of metal-surface strengthening.

During with the carburizing of carbon (or graphite) electrode, electric arc is oozed burning (seeing accompanying drawing 3) between the workpiece at the electrode and the quilt of carbon (or graphite).Because the fusing point (3800 ℃) of carbon dioxide process carbon electrode is close with its boiling point (4200 ℃), so when carburizing, be not the fusing of carbon dioxide process carbon electrode, and mainly be its evaporation.

When adopting straight polarity (carbon electrode is for negative, workpiece for just), arc stability, but this moment owing to electrode temperature lower (being lower than boiling point), consumption of electrode is slower, only (arc length＜5mm) Shi Caineng causes the carburizing of workpiece, but not strong at short arc.This kind electric arc only is suitable for carbon arc welding.

(workpiece connects negative when adopting the direct current reversed polarity, electrode just connects), because anode (carbon electrode) temperature height (suitable) with the boiling point of carbon, this moment, carbon dioxide process carbon electrode evaporated in a large number, produce a large amount of carbon steam, and, make the strong carburizing of workpiece surface of fusing to the workpiece transition, maximum carbon content can reach about 1%, just in time in the carburizing scope of routine.When making arc energy works better, reversed polarity, arc length can not be greater than 10mm.

When adopting the reversed polarity carburizing, can in welding circuit, connect one and enclose the telefault of forming, can increase the stability of electric arc greatly by 6～12.Also can be coated with paste that water glass, solution of potassium carbonate and other easily ionizable material released with the Xi make on workpiece surface increases the stability of electric arc.

During carburizing, the consumption of carbon dioxide process carbon electrode is several millimeters of per minutes, and it depends on the size of arc current density.For the consumption that reduces electrode with prevent its oxidization burning loss, when the big area carburizing (as the roller surface carburizing) need to adopt nitrogen or argon shield, and adopt corresponding device thereof to come automatic delivery electrodes, regulate arc length automatically, to guarantee the stability of cementation process.

Its degree of depth of carbon arc carburizing is the 3-5 millimeter.When required infiltration layer thin (＜3mm) time, reduce process redundancy in order to ooze the back, can be after having oozed, (TiG) carries out the electric arc lift face to the surface with argon tungsten-arc welding, makes workpiece surface smooth, carries out machining surface then and processes (as turning and grinding).

During carbon arc carburizing, for preventing that oozing the rear surface forms crackle, should give heat with workpiece.Give hot temperature by the decision of workpiece infiltration layer composition, generally below 500 ℃, actual temp prevents cold crack in the time of can welding with reference to the workpiece of corresponding composition and gives hot temperature.

After oozing, for reaching desired properties, the reply workpiece carries out corresponding thermal treatment (taking into account workpiece heart portion and top layer).Concrete technology can be carried out with reference to the thermal treatment process after the general gas cementation.

The degree of depth of infiltration layer and the control of carbon concentration depend primarily on arc current density, arc length and translational speed.The selection principle of electric current is the certain stability that had both guaranteed electric arc, does not make electrode rubescent along whole length again, in case the too fast scaling loss of electrode.In order to obtain required depth of penetration and top layer carbon concentration, should adopt sample to test in advance, when meeting the requirements, available this parameter is carried out during welding.When carrying out smallclothes or local carburization by hand, welder's experience is depended in the degree of depth of infiltration layer and the control of top layer carbon concentration, and manual carburizing generally is used for less demanding place.

Used power unit can adopt common automatic welding power supply or manual welding power supply during carburizing.

Because Graphite Electrodes has high electroconductibility and antioxidative stabilizer is preferably arranged during high temperature,, should preferentially select (comparing) for use with carbon dioxide process carbon electrode so allow the bigger current density of employing and correspondingly reduce their diameter in air.

In sum, carbon arc carburizing technology is a kind of with traditional different new processing method of carburization process principle.It has simple equipments (utilizing common welding set), processing ease (identical) with general welding, the low advantage of cost fast,, be particularly suited for the large-scale carburizing of part in addition, for example local carburization of the carburizing of cold roll surface overlaying layer and surface cementation of large module gear monodentate and workpiece etc., have its distinctive feature this moment, is that existing other method for carburizing is incomparable.

Claims (1)

1, between carbon (or graphite) electrode and metallic surface, forms electric arc, carbon atom is transitted directly to the metallic surface form cementation zone.

Images