STUDY OF M23C6 PRECIPITATION IN A 45Ni-35Cr-Nb ALLOY

<p class="AMSmaintext">The 45Ni-35Cr-Nb alloy, commonly known as ET45 micro, produced in the form of centrifugally cast tubes, was studied by means of optical microscopy after aging treatments at 1073 and 1173 K for different times. A description of M₂₃C₆ secondary carbides precipitation phenomenon was made as a function of time. The purpose of carrying out a kinetic study of the precipitation of this phase is to be able to calculate the activation energy required for secondary precipitation. This allows to infer what is the mechanism associated with it. Analysis after using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model showed that secondary carbide precipitation occurs in a single stage. It was found that this phenomenon, which is assisted by diffusion, has an activation energy of 196 kJ/mol. This value would indicate that the diffusion of Cr atoms in the austenitic matrix is the phenomenon that dominates the precipitation of the M₂₃C₆ secondary carbide.</p>

Kajian Perbandingan Komposisi Kimia, Sifat Mekanik dan Ketahanan Aus terhadap Baja Perkakas AISI D2 pada Aplikasi DIES

Material dies yang digunakan dalam proses stamping harus memiliki kekerasan, ketangguhan, ketahanan aus dan umur pakai yang optimal, untuk menghasilkan perpaduan sifat tersebut diperlukan pemilihan material dies dan proses perlakuan panas yang tepat. Pemilihan material merupakan faktor terpenting untuk mendapatkan umur pakai yang tinggi sehingga dapat mengoptimalkan proses produksi. Salah satu material yang dapat digunakan sebagai dies adalah material baja perkakas AISI D2. Pada penelitian ini di gunakan tiga jenis material baja perkakas AISI D2 dari tiga distributor berbeda, metoda penentuan material baja perkakas AISI D2 yang tepat dilakukan berdasarkan analisis dan sifat mekanik yang dihasilkan setelah proses perlakuan panas. Material yang memiliki ketahanan aus yang tinggi merupakan material yang memiliki struktur mikro martensit temper dengan primary carbide dan small secondary carbide yang dihasilkan setelah proses tempering yang dipengaruhi oleh komposisi kimianya.

Influence of Cryogenic Treatment on Wear Resistance and Microstructure of AISI A8 Tool Steel

The effects of deep cryogenic treatment (DCT) on the wear behavior of different tool steels have been widely reported in the scientific literature with uneven results. Some tool steels show a significant improvement in their wear resistance when they have been cryogenically treated while others exhibit no relevant amelioration or even a reduction in their wear resistance. In this study, the influence of DCT was investigated for a grade that has been barely studied in the scientific literature, the AISI A8 air-hardening medium-alloy cold work tool steel. Several aspects were analyzed in the present work: the wear resistance of the alloy, the internal residual stress, and finally the secondary carbide precipitation in terms of lengths and occupied area and its distribution into the microstructure. The results revealed a reduction in the wear rate of about 14% when the AISI A8 was cryogenically treated before tempering. The number of carbides that precipitated into the microstructure was 6% higher for the cryogenically treated samples, increasing from 0.68% to 0.73% of the total area they covered. Furthermore, the distribution of the carbides into the microstructure was more homogenous for the cryogenically treated samples.

Microstructure and Tempering Behaviour of 28Cr-2.5C-1W Cast Irons

In this work, the effects of 1 wt.% tungsten addition and variation in tempering times on the microstructure and hardness of nominal 28 wt.%Cr high chromium irons were investigated. As-cast samples were destabilised at 1050 °C for 4 hours and then hardened by air cooling. Tempering after destabilisation was carried out at 450 °C for 2, 4 and 6 hours followed by air cooling. X-ray diffractometry, light microscopy and scanning electron microscopy were used to characterize the microstructures of the irons. The results show that the as-cast microstructure of the iron without W addition consisted of primary austenite dendrites with eutectic M7C3 and eutectic austenite partially transformed to martensite. The iron with 1 wt.%W addition contained primary M7C3 and eutectic M7C3 in an austenite matrix. Destabilisation treatment of the austenite matrix in both irons allowed precipitation of secondary carbides and transformation to martensite during air cooling. Phase transformation of eutectic M7C3 was also found in the iron with W addition. The formation of primary M7C3 in the 1 wt.%W iron increased the as-cast macro-hardness from 500 (no W) to 576 HV30. Destabilisation increased the macro-hardness up to 736 (no W) and 780 HV30 (1 wt.%W) since secondary carbide precipitation allowed austenite to transform to essentially martensitic matrices. At longer tempering times, the macro-hardness further increased up to about 820 HV30.

Effect of Two Different Solutionizing Heat Treatments on the Microstructure of the CMSX-4 Ni-Based Superalloy

The heat-treatment processes for the precipitation-strengthened nickel-based superalloys are extremely complicated. The solution heat treatments are designed to dissolve the gamma-prime and the secondary carbide phases and allow the optimum re-precipitation of these phases upon cooling or after aging, for various precipitation-strengthened superalloys. The study was conducted to examine the effects of two solutionizing heat treatments on the microstructure of the CMSX4 superalloy. A comparison between the two obtained microstructures was performed.

Research of Microstructure and Hardness of Co55 and W Coating Made by Laser Cladding

The experiment of laser cladding on the surface of 20 steel was made. The mixed powder of cobalt-based alloy powder (Co55) and tungsten powder was used as cladding material. There were three kinds of weight percent of tungsten powder, 5%, 10% and 15%. The microstructure and hardness of three kinds of laser cladding layer were studied. The microstructure of cladding zone was greatly refined after adding tungsten powder to Co55 powder. When the proportion of tungsten powder was 5%, the cladding zone was made up of dendritic crystal. The average hardness of cladding zone was 590 HV0.2. When the proportion of tungsten powder rose to 10%, there was reticular secondary carbide precipitating along the grain boundary. The average hardness of cladding zone was 648 HV0.2. When the proportion of tungsten powder rose to 15%, much granular carbide would diffusely distribute in Ni-based solid solution. The average hardness of cladding zone was 831 HV0.2.