Generation of high-strength nickel-cobalt-iron alloy R & D

[Abstract] tungsten carbide cobalt alloy is commonly used materials. It's excellent performance is widely used in industrial production, but the cobalt is limited by scarce and expensive, people have wanted to use other materials instead, and thus Co elements of the same family of iron-nickel were studied. on the WC-F-NI Department of powder metallurgy technology and performance study shows that the role of additives to optimize the organizational structure, and in a vacuum and the appropriate preparation, pressing and sintering, it can be be compact and have high flexural strength of the material, such as analog YG20C material, the A rod bending strength ��bb> = 2400Mpa, hardness HRA> = 82 for excellent performance.

[Keywords:] iron-nickel alloy of cobalt additive on behalf of

Summary
Die of cold heading the Research, there are two main failure modes, one is wear and tear damage, mainly in the constantly repeated upsetting punch, the workpiece and the mold caused by abrasive wear of the friction, caused by the size tolerance damage, the other is cracking damage, mainly due to repeated impact, fatigue cracking in the die .. in many cases, cracking is the main failure modes of mold. Strengthening fatigue resistance of the mold and become the life of impact resistance The main way. of carbide, the extension is on the left in the alloy increase the free path length to increase strength, while alloy hardness decreased. the hardness of the mold to ensure a good wear resistance. high leaving the mold to increase the hardness of brittle, impact resistance to decrease, resulting in the mold easy to crack, with low hardness can not meet requirements. we need to maintain high hardness values ​​but also to meet the bending strength alloy mold is high enough, in the selection is very important. in the selection of alloys, the high cobalt alloy YG20 or YG20C Die cold pier to be the preferred material, widely used in Industry, but proved YG20 and YG20C material damage is rarely worn size problem, and often is the second form of destruction - crack damage, so in order to improve die life, comes down to improving the bending strength and impact resistance.

Bending strength of high-cobalt carbide and cobalt alloy than the low impact resistance is much better, but also increased the cost of the alloy. Although selection of high-cobalt alloy is cold heading YG20 and YG20C Die material of choice, its comprehensive performance is better than the other alloys, practice has proved this point. YG20C widely used YG20 and cold heading Die damage in the form of its common damage is still cracking the same time, the high cost of cobalt, its application has also been limit. How can developed an economical, performance, and good material to replace the cobalt alloy Industry is pursuing a goal.

At present, Fe, Ni Zuo Wei cementation often appear in the hard alloy materials, but still can not completely replace the Cobalt. Fe, Co, Ni for the same family of elements, and the composition of the phase diagram of WC very similar, on the wettability of WC , in a vacuum of cobalt, nickel, like wetting angle is equal to zero, while the iron is poor, not the same solubility, Ni dissolved WC is 12 ~ 20%, Co 10 to 15% Fe minimum, its bound to affect the sintering recrystallization rate of the cementation bond strength and phase WC grain size, thus affecting the strength properties of alloys. thus improving wettability improve the alloy strength will also be an effective means.

Fe added in a number of Ni, can improve the wettability of WC cemented relatively the same time, Fe and Ni to form unlimited solid solution, Fe can be strengthened. Practice shows, Fe: Ni = 3:1 in the iron-nickel cementation system Alloy best. This cemented carbide their tissues prone to �� phase, �� phase in order to prevent the emergence of a small amount in the mixture of carbon black, but also to strengthen the iron-based organizations. cementation to alloying and improve the connection strength with the WC adding a certain amount of Co powder, Co-WC and Ni-WC solid solution hardness results show that the nickel-cobalt phase strengthening effect compared to the larger, and the Co and Fe, Ni can form an infinite solid solution, the cementation to further improve and enhance wetting, this organizational structure through optimization of alloy, the alloy significantly improved service life.

Based on the above discussion and the Research results, for the destruction of the common cold pier Die form to Fe-Ni-Co alloy as the main binding phase to improve the organizational structure, strengthen the alloy, developed on behalf of high-strength nickel-cobalt-iron the strength of materials.


1 experiment
(1) the ingredients milling: WC70%-FeNiCo30%, particle size -200 mesh, C content of recruitment. Ball ratio of 3:1, wet 20h, vacuum drying, mixed plastic pellet.

(2) pressing and sintering: A standard sample suppression (5 �� 5 �� 30mm) and nail clip mode. Experiment to determine the appropriate suppression of compaction pressure (150-350Mpa) and contraction coefficients (1.18-1.25), vacuum sintering (1360-1400 ��).


2 results
(1) Sintering Results
Ts (��) 1360 1370 1380 1400
�� 12.3712.4112.4212.35
��bb 26302882 2560 2316
HRA82.382.882.8 82.7
(2) The application results
Nail in the system over a hundred sets of 7 varieties of enterprise continuous evaluation results show that the life of the service life 5.5 times higher than the YG20C, no crack damage.

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(1) of the alloy sintering densification
Densification process of a necessary factor is the liquid - solid phase of the wetting angle, the capillary pressure of liquid on the WC particles with the decrease of wetting angle increased, and thus the ability of liquid filled pores of the solid phase as the Run reduction and improvement of the wet corner. followed by the number of liquid phase, when the liquid does not exceed 50%, the number of capillary pressure as the liquid increases. Meanwhile, WC particles with the increase of flow resistance is reduced. this material, its cement phase composition of about 30%, and Ni, Co melting capacity of the larger WC, therefore, WC faster dissolution, liquid phase sintering increased, usually to keep the number of liquid 36% in 15 should, thus, sufficient to ensure adequate densification phase. guarantee coated WC particles in the liquid flow under the complete dissolution, precipitation, solid-phase sintering process of the three to make it fully dense, and finally achieve the sintering purpose. In the experiment, a fine alloy completely bridge the defect in the low magnification observation and flaw detection without any defects, indicating that this material to improve wetting, so that filling capacity enhancement.

(2) sintering temperature on the Alloy
With the amount of liquid phase sintered bodies increased with the increase of sintering temperature, this material is concerned, due to the formation of Fe-Co-Ni solid solution unlimited, effective crystallization temperature range is narrow, a slight change when the sintering temperature, the concentration of the liquid will tonsure changed greatly, experimental results show that the range of 1360-1380 ��, the performance is relatively stable, when it reaches 1400 ��, the bending strength decreased 500Mpa much, and the sample around the edges blunt, stating the diaspora tend to exist temperature a little higher, you may have under the seat. which illustrate the narrow range of sintering temperature, large temperature sensitivity in the production should be strictly controlled.

(3) the role of elements in the alloy
Carbon bond in the Fe-Ni alloy is mainly produced by inhibition of highly rigid phase occurs, and to strengthen the cement phase, their number also affects the level of high and low sintering temperature. Co, Ni Fe improved the wettability of WC, Co within the solution in the cementation played a "pinning" effect, preventing dislocation motion, and strengthen the matrix, optimize organizational structure, strengthening the bond phase to ensure complete densification.

(4) strength characteristics
Bending strength of cemented carbide is an important index to measure it a sign of toughness of alloy. Flexural strength, indicating that toughness, impact resistance and good performance. This material is sintered strength A single value scale 3370Mpa, the average of 2880Mpa.


4 Conclusion
(1) of this material in an ordinary vacuum sintering conditions, the available high strength, good resistance to impact organizational structure, is an ideal material for replacement YG20C.

(2) of this material during the sintering process of WC cemented metal, good wetting, liquid filling ability
(3) The sintering temperature-sensitive materials, the best sintering temperature range of 1360-1380 �� good.

(4) this material product manufacturing process with the same carbide.


References
[1], Metallurgical Industry Press. <<Carbide production>>.

[2], Metallurgical Industry Press. <"Metallic Science>>.

[3] <<PM Principles>>. Links http://www.hi138.com Research Papers Download