Cementite quenchs shallow talk

Exterior microstructure basically includes temper martensite and free carbide. The under 20 ％ leftover austenite that allows existence to see. 2.

Not the surrounds grain completely meshy carbide with coadjacent be patient of. 3.

In 500X not due and visible complete decarbonization phenomenon. 4.

Exterior carbon content from try a club to go up affirmatory, the good value that the surface contains carbon to measure should is 0.

7 ～ 0.

9 ％ . 5.

Not the tiny flaw with visible below 500X be patient of. 6.

The oxidation between brilliant is unfavorable 0 what try good appearance to fall more than.

025mm 7.

Core microstructure is achieved make gear can be changed by proper austenite, undertake sclerosis to its thereby. In enlarge 500X not the lump ferrite with visible be patient of, microstructure basically should include temper martensite. In the executive process of craft, a lot of manufacturer can encounter such situation; 1.

After cementite ends, test block surface layer has meshy carbide, this is the main reason that causes later period to quench crackle reachs grinding crackle. 2.

After cementite ends, hardness is worth ideal of short of of workpiece surface hardness, this kind of case is more complex, on the basis that eliminates equipment and craft reason, because decarbonization of surface of workpiece tooth flank is caused,majority considers as, because heat,also have temperature is undeserved, heat preservation time undeserved or it is cooling rate wait for a reason to cause not quite (following graph) . 3.

Leftover austenite slants much. Its formation as a result of,the reason is the first, heat temperature is high, the 2nd heat time is long, the 3rd, the limitation of cooling equipment, cause the addition of degree of supercooling. The existence of leftover austenite is inevitable, cool through quenching after complete austenite turns work, one part austenite has not enough time to transform, especially to cementite steel character, move on austenite area of whole (graph 3) , and austenite of area of surface layer tall carbon the area drops, at the same time Mf line drops 0 ℃ are the following, so, below the premise that has done not have cold treatment, austenite change is won't complete. In March 2005 portion, the φ of my factory 1.

6 × 1.

8 once had appeared successive 4 furnace second workpiece appears the phenomenon of meshy carbide, we did strict analysis to this. The surface is meshy the reason that the formation of carbide should be many sided, the first, in later period of phase of high temperature cementite, diffuse namely level, if carbolic situation on the high side, nature of exterior carbon content is met on the high side, move on the whole as austenite area, dot of exterior tall carbon has straddled Acm line lower part, while cementite ends, had had one share 2 times cementite separate out, edge austenite grain submits packet of purse net form. The 2nd, cementite temperature is exorbitant, time is too long, cause grain to be brought up quickly, in cooling process, if speed is insufficient fast, carbide is in separate out along bulky crystal boundary with respect to inevitable meeting, final web shape (if pursue one, 2) . Our jumping-off place is to solve itself of body of heater, above all situation of the carbon inside furnace cannot exorbitant, tell from craft next make sure carbide does not want separate out as far as possible. Settlement method is furnace air the sky below furnace condition is heated, eliminate body of heater to be in what cause for long in cementite process to accumulate carbon; With appropriative 100 thousand minutes of balance do Tie Bo to experiment, grant power of carbon of condition of a few cementite surely; Try a club to put condole to hang aperture with the cementite of φ 40mm, with the graph 4: 500 × (the quantity that contain carbon 0.

40 ％ , nitric acid alcohol is corroded) in order to do the test of exterior carbide, do at the same time pare an experiment. This effective surface carbide that controlled place of reason of itself of body of heater to cause exceeds bid. If normal circumstance leaves force of the carbon inside furnace, whether to also put in web? Have this kind of case, the layer is deep on certain level the final position that decided it, as the addition with deep layer austenite can be brought up gradually, if the cooling rate after cementite end is not quite rapid, carbide can be in web along the crystal boundary of bulky grain. This kind of circumstance can accelerate cooling rate appropriately, as a result of fast cold action, make this process made the process that refines grain, on one hand the amount of carbide separate out is little, on the other hand carbide shows grain shape to exist, make its form won'ts do meshy, removed the hidden trouble that net carbon brings greatly. If the cooling power short of of furnace, can use 2 times quench craft. In producing a course actually, we fumble according to the experience of oneself and existing equipment condition piece the following cementite of 3 kinds of feasibility quenchs craft: 1.

Cementite quenchs craft: Quench institute of plan of craft as above is shown, the refrigeration after workpiece passes cementite comes constant temperature heat preservation period of time, if rate is rapid, have only in the cementite layer of tall carbon a few carbide separate out, reduce the amount containing carbon of austenite, increase Ms point, make quench the quantity reduces the leftover austenite that come down, rise quench hardness. Heat afresh next quench, heat the choice of temperature should surface layer of give attention to two or morethings and core, make surface layer does not come overheat, and core has get sufficient aggrandizement, the temperature that offers to be able to choose AC3 of summary prep above (about 830 ～ 860 ℃ ) , if want to emphasize the organization of surface layer and performance, should heat to AC1 ～ undertake quenching not completely between AC3. Microtherm temper still needs after quenching (200 ℃ of 160 ～ ) , quench in order to eliminate stress, reduce brittleness. 2.

Cementite quenchs directly craft: Quench craft is directly workpiece from cementite temperature desire is cold to quench temperature, undertake oily Leng Cuihuo, beforehand cold to quench temperature while, also can quench in order to reduce thermal stress, reduce be out of shape; Have in the cementite layer of tall carbon a few carbide separate out, reduce the amount containing carbon of austenite, increase Ms point, make quench the quantity reduces the leftover austenite that come down, rise quench hardness. Microtherm temper still needs after quenching (200 ℃ of 160 ～ ) , quench in order to eliminate stress, reduce brittleness. But make workpiece grain easily bulky, suggest shallow ooze layer is used. 3.

Cementite quenchs 2 times craft: Very tall to performance demand spare parts, or it is the part that becomes by steeliness of substaintial thick grain, should use 2 times after cementite quench law, institute of plan of as above of its craft curve is shown, quench temperature is in for the first time advocate the AC3 above of the ministry (890 ℃ of about 850 ～ ) , the purpose is the organization that refines core, improve the performance of core, can eliminate the meshy carbide of surface layer at the same time; When the performance demand to core is not quite high, can replace first time to quench with normalizing. Quench the 2nd times heat to AC1+30 ～ 50 ℃ , undertake quenching not completely, the purpose is to refine surface layer organization, make surface layer obtains petty concealed brilliant martensite to add even and petty grain shape carbide to organize, reduce leftover austenite to measure. Microtherm temper still needs after quenching (200 ℃ of 160 ～ ) , quench in order to eliminate stress, reduce brittleness. After if pass the cementite above 12 times,quenching, add temper of 180 ℃ low temperature, metallographic organization comes out to show each index all achieves a requirement as a result, its amount to mark completely as a result. Next watches are us the cementite that the work that once had done makes be JS0405011 quenchs a constituent position that quenchs through 2 place is achieved, quench relative to and quench directly and character, the result that it achieves is close to our ideal outcome more, as to machinery function won't have too big difference. These technology measures solved above to produce the real problem that encounters currently greatly, be opposite especially meshy carbide, of course the execution of craft is final it is to achieve the performance characteristics of workpiece, no matter use the sort of cementite technology, want a basis to use a case actually its, the problem that appears in production perhaps is workpiece the germ that invalidation appears in using, so the progress of craft builds the change in workpiece use condition to go up, choose correctly and the key that flexible craft is technology progress. CNC Milling CNC Machining