Properties of Stainless Steel Precision Casting

1. Chromium is the main alloying element in stainless steel. Chromium tends to produce an oxide film on the surface of molten steel, and the tendency to add steel to titanium is greater, which reduces the fluidity of molten steel. However, chromium can lower the melting point of steel. When chromium is more than 5%-8%, the solidification time is prolonged and the fluidity is improved. Nickel, manganese and copper all lower the melting point and improve fluidity. The addition of titanium forms a large number of refractory points, which affects the fluidity of the molten steel.

2. Due to the high chromium content, the chromium oxide film is easily formed on the surface of the molten steel during the casting process, which causes defects such as oxidized spot, cold partition, surface wrinkles and inclusions. The lower the temperature of the molten steel, the longer the casting time and the more severe the oxidation phenomenon. Therefore, the pouring temperature should be appropriately increased and the pouring time should be shortened. The pouring temperature of chrome-nickel stainless steel castings is generally not lower than (immersion thermocouple temperature). The section size of the casting casting system should be 30%-50% larger than the same carbon steel casting. Experience has shown that increasing the temperature of the molten steel, the oxide film on the surface of the liquid gradually disappears, and the casting defects are significantly reduced.

3. Stainless steel body shrinkage is large, easy to produce shrinkage and shrinkage. From the perspective of the shrinkage, the casting should have the conditions of sequential solidification, and the riser size should be 20%-30% larger than the carbon steel casting.

4. Casting shrinkage, steel with martensite structure and carbon steel (1.7% -2.0%) ferrite structure of steel is 1.4% -1.6%, while austenitic steel is larger, 2.1% -2.3%.

5. Stainless steel has a greater tendency to hot cracking, especially high chromium and chrome nickel stainless steel has a greater tendency to crack. In order to avoid hot cracking, it is necessary to strengthen the retractability of the shell and appropriately increase the casting fillet. High chromium and chromium manganese nitrogen stainless steels are also prone to cold cracking.

6. Stainless steel castings are prone to pinholes, the reason is that there is more gas in the molten steel. Therefore, it is required that the molten steel has good degassing and deoxidation during the smelting process, and the shell is sufficiently roasted, and the cauterization time after the shell roasting is not too long.

7. Due to the high temperature of molten steel, it is easy to produce hot sticky sand. In order to ensure the surface quality of the casting, the first and second coatings can be made of high refractoriness materials, such as corundum powder, zircon sand powder, aluminum vanadium powder, etc., while the surface layer also selects the sand of the corresponding material.

8. Chromium-manganese-nitrogen stainless steel has poor thermal conductivity and slow solidification of molten steel, so it is different from other stainless steels in terms of fluidity. This steel grade is particularly good in fluidity, which is its advantage. However, the shortcoming is that the solidification time is longer than other stainless steels, and the dissolved nitrogen in the steel is more likely to precipitate, resulting in pores. Therefore, the nitrogen-containing bunker of steel should be controlled to the lower limit.