 Proceedings of Engineering and Technology Innovation , vol. 2, 2016, pp. 08 - 10 8 Study on the Wear Resistance of Sinter Alloying Steel by Deep Cryogenic Treatment Chao-Hsu Cheng * Department of Mechanical and Automatic Engineering, Chung Chou University of Science and Technology, Changhua, Taiwan. Received 19 February 2016; received in revised form 16 March 2016; accept ed 20 April 2016 Abstract Sintered alloy steel powder with four d if- ferent hardenability of FN0200, FN0208, FD0408, and FLNC4808 are applied to form the sintered alloy steel. The sintered alloy steel, being cooled down to room te mperature, is fur- ther soaked in -196℃ liquid nitrogen for 4hrs deep cryogenic treatment. With deep cryogenic treatment, the retained austenite in the sintered a lloy steel would change the phase and become martensite, and the ap- parent hardness of sintered alloy steel would be enhanced. Further analy zing the effect of deep cryogenic treatment on the wear resistance of sintered alloy steel, the wear resistance would be improved when the apparent hardness of sin- tered alloy steel is enhanced. However, the deep cryogenic treatment would change the sintered alloy steel microstructures because of distinct hardenability. Such research findings show the significant effect of deep cryogenic treatment on the sintered alloy steel with high hardenability, where the best hardness and wear resistance could be acquired from FLNC4808 sintered alloy steel through the deep cryogenic treatment. Keywor ds : sintered alloy steel, deep cryogenic treatment, hardenability, wear re- sistance 1. Introduction Research on sub-zero treat ment actually has been done in the early 20 th century to change the structure and function of steel by lower than free zing point. In 1937, A. P. Gu lyaev [1] first researched sub-zero treat ment fo r h igh-speed steel and proposed the theory of sub-zero down to -80℃. So far, it is known that deep cryogenic treatment (-196℃) could enhance the ratio of ma rtensite and reduce austenite residue to im- prove the wear resistance of steel. Deep cry o- genic treat ment is a lso broadly used for ma - chinery industry internationally to enhance the wear resistance of ferrous products, such as die steel [2], powder h igh-speed steel [3], and cast iron [4], and the performance o f non -ferrous products, like magnalium [5]. Nevertheless, deep cryogenic treatment has not been applied to the research on sintered alloy steel. This study therefore intends to discuss the effects of deep cryogenic treat ment on the me - chanical properties and wear performance of sintered alloy steel. 2. Method Sintered alloy steel with four d ifferent mu l- tiplying factors of FN0200 (Fe- 1.2Cu- 2.5Ni- 0.3C), FN0208 (Fe - 1.2Cu- 2.5Ni- 0.9C), FD0408 (Fe - 1.5Cu- 4.0Ni- 0.5Mo- 0.9C), and FLNC4808 (Fe - 2.0Cu- 2.7Ni- 1.25Mo- 0.2Mn- 0.9C) is utilized in this study. The alloy contents are shown in Table 1. The as -sintered steel are further proceeded deep cryogenic treatment fro m roo m te mpera - ture down to cryogenic temperature -196℃ with 0.3℃/ min for 4hr and then slowly increased to room te mperature with 0.3℃/ min. Finally, sin- tering sintered alloy steel and cryogenically treated sintered steel are tempered with 180℃ for 1hr to re move residual stress caused by phase change. Furthermore, the mechanical p roperty is e xperimented. The above test pieces are meas- ured the s urface Vic kers mic ro hardness (Hv 1) with 1Kg load. The prepared φ5 cylinder wears test pieces and placed on the Pin-on-disc wea r test platform, *Corresponding aut hor. Email: chaohsu@dragon.ccut.edu.t w Proceedings of Engineering and Technology Innovation , vol. 2, 2016, pp. 08 - 10 9 Copyright © TAETI Fig. 1. The wear test platform rotates an SKD11 disc with the speed 60 rp m, and the wear test piece is placed 47.5 mm a way fro m the disc center shaft, while a 2 Kg load is loaded on top of the wear test piece. Each test piece is pro- ceeded the wear test of the wear distance 15,000m, and the measured wear we ight loss is calculated the wear coeffic ient of the test piece with the following equation. K＝       m mm NF m 3  (1) where K: wear coefficient; m: wear amount, g; ρ: density, g/mm 3 ; F: positive load on wear test piece, N; t: wear distance, m. Table 1 Sintered alloy steel contents Fig. 1 Pin-on-disc wear test schematic 3. Results and Discussion 3.1. The Hardness of Sintered Alloy Steel The effects of deep cryogenic treatment on the hardness of sintered alloy steel with different har- denability are further analyzed. The as -sintered steel after deep c ryogenic treat ment, where the apparent hardness could be improved by deep cryogenic treatment, regard less of the harden- ability. Sintered a lloy steel with d istinct har- denability would enhance the apparent hardness with increasing hardenability, revealing that sintered alloy steel would be hardened with deep cryogenic treatment. Especially, most of the austenite structure in high ca rbon high harden- ability alloy steel (FD0408) is changed into ma rtens ite and the austenite residue is dropped down to the lowest that the apparent hardness is increased from Hv1 516 to Hv1 733. The im- provement of wear resistance could enhance sintered alloy steel parts to a higher level. 3.2. The Wear Resistance of Sintered Alloy Steel The sintered alloy steel wear test pieces with diffe rent hardenability are placed on the Pin-on-disc wear test platform for the 15,000m wear test to measure the wear we ight. The sin- tering FN0200 a lloy steel with the lowest har- denability is worn the weight 0.0547g with 15,000m, wh ile the sintering FLNC4808 a lloy steel with the highest hardenability is mere ly worn 0.0014g with 15,000m; a fter deep cryo- genic treat ment, FLNC4808 further drops down to 0.0009g, Fig. 2. The result e xpla ins that sin- tered alloy steel could be imp roved the wear resistance with deep cryogenic treatment. Fig. 2 Wear we ight of sintered alloy steel wea r test Substituting the density (ρ), wea r distance (t), test piece wear we ight (m), and wear load (F) of the sintered alloy steel test pieces for Eq. (1) to analyze the wea r coefficient, the results are shown in Fig. 3. Fig. 3 Co mparisons of wear coefficient of sintering sintered alloy steel after cryogenic treatment Proceedings of Engineering and Technology Innovation , vol. 2, 2016, pp. 08 - 10 10 Copyright © TAETI Fro m the curve in Fig. 3, the sintered a lloy steel with deep cryogenic treatment could ef- fectively reduce the surface wear of sintered alloy steel parts. High carbon high hardenability sintered alloy steel (FLNC4808) with deep cryogenic treatment could further enhance the wear coefficient fro m K=0.72(× 10 -6 mm 3 /Nm) to K=0.46(× 10 -6 mm 3 /Nm), and the metallurgi- cal structure is mostly changed into martensite. Among sintered alloy steel with distinct hardenability, the wear coefficient (K=0.46× 10 -6 mm 3 /Nm) of FLNC4808 sintered alloy steel with deep cryogenic treatment outperforms the wear coeffic ient (K=2.25× 10 -6 mm 3 /Nm) of FN0208 sintered alloy steel with deep cryogenic treatment, and even better than FD0408 sintered alloy steel (K=0.93× 10 -6 mm 3 /Nm). The result presents that a mong sintered alloy steel with diffe rent hardenability, FLNC4808 sintered alloy steel with deep cryogenic treatment could acquire the best wear resistance and effectively reduce the surface wear of sintered alloy steel parts. 4. Conclusions (1) As-sintered alloy steel with higher hardenabil- ity would enhance the apparent hardness as austenite changes the phase into martensit. (2) Austenite of sintered alloy steel with deep cryogenic treatment would change into mar- tensite. Such a change enhances the structure apparent hardness. (3) Regarding the hardness performance and wear resistance of sintered alloy steel with distinct hardenability, high hardenability alloy steel (FLNC4808) with the hardenability above 40 presents the best hardness performance and wear resistance combination. (4) FLNC4808 sintered alloy steel with deep cryogenic treatment presents the best wear resistance, which is suitable for machine parts requiring high wear resistance. Acknowledgement This research (project No.: NSC 101-262 2-E-235-001-C C3) was cosponsored by the National Science Council of R.O.C. and Ja- bon International Technology Co. Ltd., which is gratefully acknowledged . References [1] A. P. Gu lyaev, “Imp roved methods of heat treating high speed steels to improve the cutting properties ,” Metallurgy, vol. 12, pp. 65-70, 1937. [2] B. Podgornik, et. al., “Imp roving tribolog- ical p roperties of tool steels thro ugh com- bination of deep-cryogenic t reat ment and plasma nitriding,” Wear, vol. 288, pp. 88-93, 2012. [3] V. Leskovšek and B. Podgornik, “ Vacuu m heat treatment, deep cryogenic treat ment and simultaneous pulse plasma nitrid ing and tempering of P/M S390MC steel,” Materials Sc ience and Engineering: A, vol. 531, pp. 119-129, 2012. [4] T. Slatter, R. Lewis , and A. H. 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