Squeeze Pulp Terminal Helix Corrosion Wear Of Materials Research And Development

Cr60 deposited material for helix in decker falls short of operating requirement, though its degree of hardness is HRC60. For this reason, we want to exploit a new material to replace it according to the requirement of equipment maker.The first place is to confirm the inactivation reason of Cr60 deposited material. Chemical experiments indicate that the consistency of chloride ion is 221.1mg/l in pulp, pH value is 8. According to this, we confirm that the inactivation of Cr60 deposited material is wear in corrosive media, scilicet corrosive wear. It is known that the controlling factor of corrosive wear is corrosion in which the pulp contains strong corrosive media, e.g. Cl~- .The base of Cr60 deposited material is martensite. In base, large quantity thick carbide distribute. On surface, there are lots of microcracks. Chromium element accumulates on intergranular, making chromium element poor round intrgranular zone. These factors result in corrosion resisting property of Cr60 deposited material of a sort.When the substitute is selected, both the corrosion resisting property and wear-resisting property are considered. Duplex stainless steel to use substitute because of its better corrosive wear resisting property. For reinforcing wear-resisting property more, the carbon content is increased in duplex stainless steel. The selected alloy is 3Cr20Ni5Mo. Because it contains chromium and nickel more than general steels, the new alloy is named high-chromium-nickel steel.Because of scavenging interface, thinning carbide, and increasing corrosion of Cl~- resisting property, when high-chromium-nickel steel is smelted, it is modified by a compound containing kalium, natrium and molybdenum. The purpose of solution treatment is to make the netlike carbide breaking up and granulating and to avoid the effect that the increment of molybdenum element makes the carbide strong. After modification, part of carbide intermingle in base,its effect is second-phase aggrandizement. Because high-chromium-nickel steel has a structure of duplex, it contains part of soft ferrite. There is not microcrack in its surface when machining. Austenite transits martensite after heat treatment. The degree of hardness of high-chromium-nickel steel reaches HSD45, so the alloy has better wear resisting property. EPMA test indicates that the phenomenon of chromium poor in intergranular zone of high-chromium-nickel steel is weaker than that of Cr60 deposited material. Simulative corrosion test indicates that high-chromium-nickel steel occur pit corrosion on surface only. By way of comparison, Cr60 deposited material occurs strong corrosion in large acreage on surface. On the face of corrosion pattern, the corrosion resisting property of high-chromium-nickel steel is better than that of Cr60 deposited material clearly.On the result of installed test, the employing time of the helix used high-chromium-nickel steel reaches nine months. Service performance of high-chromium-nickel steel is better that of Cr60 deposited material, because the latter's employing time is three months. This indicates that our new material can be used to work condition of pulp completely.