| Phosphoric acid plays a very important part in industrial and agricultural production, impeller of slurry pump has to bear severe erosion corrosion during wet process phosphate production as slurry contains many solid impurities. Therefore, scientific institution attempt to develop a new stainless steel used for impeller of phosphoric acid slurry pump all the time. Cr30, a ferrite stainless steel, is an import choice due to its low cost and high hardness. The bad thing is that Cr30 has a low yield and could not be heat treated as its high brittleness. Thus it is import to develop a new kind of steel based on Cr30 which has low cost, high toughness and excellent wear-corrosion resistance.As the research result shows, Cr30 added Cu and Mo have higher hardness and better corrosion resistance. Cu plays more importance role on hardness while Mo does a better job in promoting corrosion resistance. Hardness could be 42HRC with a suitable heat treatment. Ferrite stainless steel has a higher hardness as N added. Appropriate N could also be used to promote toughness and corrosion resistance.A duplex stainless steel is obtained which have high toughness and corrosion resistance since Ni is added in the ferrite stainless steel, but the hardness is lower. N could promote hardness, toughness and corrosion resistance of duplex stainless steel if it is added with Ni. N content will be higher with Mn and Ti added while phase ratio is maintained unchanged, hardness of steel is higher as a result. However, Mn content should be limited because of its adverse effect on corrosion resistance. Lower Cr content is accepted as performance will not seriously go down. On the contrary, a higher cost performance is obtained.Hardness does play a more important part in wear-corrosion resistance under this wear circumstance as the test result shows. Duplex stainless steels with only Ni added have a poor wear-corrosion resistance because of lower hardness. Compared with the ferrite stainless steel, duplex stainless steels do better due to their work hardening properties. The best performance is obtained with Ti is added in steel contain of N. Wear resistance is advanced as Mn adding work hardening properties of duplex stainless steel. Material has the best cost performance with adding Mn together with Ti. When chemical composition is confirmed heat treatment has great influence on performance. Material in as-cast state with lowest hardness does the worst performance while steel under appropriate aging treatment has the beat wear corrosion resistance performance. |
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