Nickel-base alloy with improved resistance to wear and corrosion

Nickel-Base Alloy with Improved Resistance to Wear and Corrosion It is not every day of the week that a quantum improvement to PM materials is reported. but it would seem that Kobe Steel have achieved that feat. A paper presented at PM90 by Dr N Morishita reports results obtained on a nickel based alloy developed for handling plastics such as PPS (poly phenylene sulphide) ABS (acrylonitric butadiene-styrene co-polymer) which materials are assuming increasing industrial importance. They are shaped by injection moulding or extrusion and the materials used for the cylinders .must be resistant to the corrosive gases· HF. S02. Nf), for examples that these plastics generate. Furthermore. engineering plastics are often re-inforced by hard materials such as glass or carbon fibres and therefore wear resistance is also a major requirement. A standard material for the cylinders is steel onto which a layerofHastelloy (Ni with 13.5 Cr. 4.8 Fe. 0.8 C. 4.3 Si and 3 B) has been deposited by centrifugal casting. This alloy which contains a dispersion of CrB. and NiJB shows good wear resistance but its corrosion resistance is not good. the borides

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FIG. 1 Effect of Cu content on mass Joss of Ni-15.0Cr-15.0Mo-3.0 Si-3.0B alloys in lO%HF {from paper by N Morishita et a]. presented at PM90. London] being cathodic to. the matrix. HastelloyC (Niwith 15Cr.15Mo.4\V. 5Fe and 2Co) being a homogeneous solid solution. is highly corrosion resistant but does not have good wear resistance. A research programme was undertaken at KobeSteel to try to find a composition that combined the corrosion resistance of Hastelloy C with good wear resistance. The initial tests were done on argon-are-melted specimens containing Si and B to

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FIG, 4 Bimetallic twin cylinder produced by HIP process {from paper by N Morishita et of. presented at PM90, London]

FJG. 2 Effect of MolCr ratio on mass Joss of Ni-Cr-Mo-3.0$i-3.0Bl.0Cu alloys in lO%HF and 6%HNOJ {from paper by N Morishita et a]. presented at PM90, London] provide wear resistance to oxidising temperature of 1223K was used. agents such as nitric acid. and of Mo Corrosion tests were done at 323K for which improves the resistance to 100 hr and the wear resistance halogen compounds HF. HCl.etc. evaluated by the Ohgoshi test. Fig. 3 Additionally copper wasadded and it shows the microstructure of the alloy was found that this inhibits the produced in this way. electrochemical corrosion of the Corrosion tests showed that C-703 matrix. Fig. 1 shows the effect of gave weight loss figures similar to copper additions on the resistance to those forHastelloyC in HFand H2SO.. corrosion by HF at 323K while Fig. 2 and only marginally worse in HNO J. shows how varying the ratio of Cr to The centrifugally cast Hastelloy lost 100 times as much weight as C-703. Mo affects corrosion resistance. The eventual outcome of these tests The wear test results show that the was an alloy designatedC-703having new alloy is up to 150 times as good the composition Ni with 17.5Cr. as Hastelloy Cand significantlybetter than the centrifugally cast Hastelloy, 24Mo. 3.613. 2.9Si and l%Cu. Having decided on the optimum Fig. 4 shows a cylinder lined with composition. alternative methods of C-703 by reaction sinter HIPing. and manufacturewere explored and it was this part is now in service. The table found that better results were shows the mechanical properties of obtained by HIPing a mixture of a the new alloy. AGD prealloyed argon atomized powder containing 31Mo. 3.8Si and .-::---::-----:---:;----;;::=-;------::-:;::-. Tensile strength (MPal 1.1Cu·balance Ni and a CrB powder at a temperature at which Compression strength (MPal reactive sintering takes place. A Elastic modulus (MPal pressure of 98 MPa at a Poisson's ratio

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FIG. 3 SEM photograph of HIP-processed alloy {from paper by N Morishita et a]. presented at PM90. London]

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Bahr Geratebau GmbH Systems for Thermal-Analysis 0-4971 HOlihorst so. Box 1105·Tonstr.5 Tel. 05744/1002·Telex 972174 Fax 05744/1006 Production Range: • Oilatometer·Thermal Balance • STA·OTA·OSC·Oata Systems • High-Temperature Viscometer

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