| The type of Crl3 martensitic stainless steel is choosed by domestic steel users as corrosion resistant plastic die steel materials, such as (2～4)Crl3, etc. But this kind of steel usually cannot meet the use requirement because of low resistance, strength and hardness. Compared with the traditional martensitic stainless steel, the high nitrogen martensite stainless steel can combination with wear resistance and good corrosion resistance in different environmental. At present, the use of high nitrogen martensite corrosion resistant plastic die steel in business is less,and less research in domestic. This paper has designed and smelted with different nitrogen content of high nitrogen martensite corrosion resistant plastic die steel, and compared with the non-nitrogen steel. The organization, mechanical properties, corrosion resistance were studied with the test equipments of OM, SEM, TEM, brinell, rockwell hardness tester (tensile, impact), mechanical equipment and salt spray corrosion on the tested steels.The vacuum induction were used respectively to positive pressure melting furnace (high nitrogen steel), vacuum induction melting furnace smelting (non nitrogen steel).The calculation with thermodynamic software showed that the austenite stabilization interval was increased by add of nitrogen.The precipitation of M23C6 carbide was reduction and the precipitation of nitrides at low temperature area was romoted with the increase of nitrogen content.The edge of as-cast organization of 0-N tested steel did not appear obvious dendrite, and the heart cubic was non-uniform, the larger eliquation carbides were found around the grain boundary. Nitrogen steel side appeared fault of dendrite and the core network of isometric is relatively uniform.0-N steel microhardness is relatively uniform, but the value is lower than nitrogen steel, The hardness of as-cast organization of 0.08N and 0.2N tested steel is higher than that of 0-N tested steel.The organizations of annealing, quenching and tempering of nitrogen steel were more uniform and the size of quenching grain were fine.The quenching hardness of 0.08N tested steel was higher than 0-N tested steel, the maximum difference is 8 HRC. The hardness of 0.08 N tested steel remained at about 55HRC between the temperature of 1000℃～1130℃. The hardness of 0.2N tested steel drop a lot after 1050℃. The tempering hardness of nitrogen steel is higher than the non-nitrogen steel, the maximum difference is 6HRC, and the peak of secondary hardening is more steep. The temperature of peak point is increased with the increase of nitrogen content.The ballistic work of nitrogen steel is lower than that of the non-nitrogen steel, the brittle turning point delay and the ballistic work was decreased with the increase of nitrogen content. The fracture of nitrogen steel was relatively flat, the tearing arris can be found of the fracture microstructure before the tempering temperature of 520℃.The strength of tensile and yield of nitrogen steel were higher than that of non-nitrogen steel. The contribution on tensile strength is higher than the yield strength of nitrogen. The showed of nitrogen steel was lower than that of non-nitrogen steel, and the showed was decreased with the increase of nitrogen content. The tempering temperature of curve inflection point of nitrogen steel were delayed around 100℃ than that of non-nitrogen steel. The area of reduction of nitrogen steel was lower than the non-nitrogen steel, and the trend of curve was more steep. The elongation value was close to test steels and the curve is relatively flat between (200～400)℃.The tensile fracture of nitrogen steel was neat, and the phenomenon of necking was not obvious.Nitrogen steel maintained high strength and hardness with good corrosion resistance between the temperature of (150～200)℃. But a lot of corrosion pits were found at the temperature of 500℃, the degree of corrosion was more serious with the increase of nitrogen content.The best quenching temperature of 0.08N and 0.2N tested steel are between (1000 ～1030)℃ and(980～1020)℃, they have excellent toughness, strength, and corrosion resistance with the tempering temperature at about 200℃. After the secondary hardening peak temperature for 20℃ at about (0.08N is 520℃) and (0.2N is 540℃) are considered while the higher requirements of strength and toughness, the low corrosion resistance requirements. |
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