High Manganese Alloyed Steels With Improved Cracking Resistance

Abstract

The present invention relates to ferrous alloys with high strength, cost-effective corrosion resistance and cracking resistance for refinery service environments, such as amine service under sweet or sour environments. More specifically, the present invention pertains to a type of ferrous manganese alloyed steels for high strength and cracking resistance and methods of making and using the same.

1 . A ferrous austenitic steel comprising less than 15 wt % chromium (Cr) equivalent and more than 7 wt % nickel (Ni) equivalent, wherein
 Ni equivalent is: Ni eq =Ni+Co+0.5·Mn+0.3·Cu+25·N+30·C;   Cr equivalent is: Cr eq =Cr+2·Si+1.5·Mo+5·V+15.5·Al+1.75·Nb+1.5·Ti+0.75·W; and   wherein the Ni equivalent satisfies 6·Ni eq +Cr eq ≥15, and   the Cr equivalent satisfies Ni eq +15≥1.5·Cr eq ; and   the ferrous austenitic steel comprises a predominantly austenite phase and one or more minor phases of ferrite, martensite, carbide, nitride, and carbonitride.   
     
     
         2 . The ferrous austenitic steel of  claim 1 , further comprising 18 wt % to 30 wt % manganese (Mn). 
     
     
         3 . The ferrous austenitic steel of  claim 1 , wherein the ferrous austenitic steel has a strength ranging from 20 ksi to 120 ksi. 
     
     
         4 . The ferrous austenitic steel of  claim 1 , further comprising 0.01 wt % to 2 wt % copper (Cu). 
     
     
         5 . The ferrous austenitic steel of  claim 1 , further comprising 0.1 wt % to 1.5 wt % carbon and 0.001 wt % to 1.0 wt % nitrogen. 
     
     
         6 . The ferrous austenitic steel of  claim 1 , further comprising 0.05 wt % to 15 wt % Al. 
     
     
         7 . The ferrous austenitic steel of  claim 1 , further comprising 0.05 wt % to 10 wt % Si. 
     
     
         8 . The ferrous austenitic steel of  claim 1 , further comprising one or more of niobium (Nb), titanium (Ti), vanadium (V), tungsten (W), tantalum (Ta), and molybdenum (Mo), wherein the total content of these elements ranges from 0.01 wt % to 5 wt %. 
     
     
         9 . The ferrous austenitic steel of  claim 1 , further comprising 0.1 wt % to 1.5 wt % carbon, 0.001 wt % to 1.0 wt % nitrogen, 0.05 wt % to 10 wt % Al, 0.1 wt % to 3 wt % Si, and 0.01 wt % to 5 wt % of one or more of niobium (Nb), titanium (Ti), vanadium (V), tungsten (W), tantalum (Ta), and molybdenum (Mo). 
     
     
         10 . The ferrous austenitic steel of  claim 1 , further comprising 0 wt % to 5 wt % Cr equivalent. 
     
     
         11 . The ferrous austenitic steel of  claim 1 , wherein the austenite phase is at least 95 vol %. 
     
     
         12 . The ferrous austenitic steel of claim, wherein the minor phases are less than 5 vol %. 
     
     
         13 . A processes for manufacturing the ferrous austenitic steel according to  claim 1 , the process comprising:
 melting ferrous steel constituents while controlling evaporation losses of N and Mn to produce a liquid alloy steel having the composition of  claim 1 ;   ingot or continuous casting the liquid alloy steel into a mold to form cast ingots while suppressing Mn segregation;   reheating the cast ingots to dissolve secondary phases at a temperature ranging from 900° C. to 1250° C.;   hot deforming at or above 600° C. to control grain size and shape of the alloy steel; and   cooling rapidly at at least about 10° C./sec to below about 300° C.   
     
     
         14 . The process for manufacturing the ferrous austenitic steel according to  claim 13 , further comprising improving the mechanical properties of the ferrous austenitic steel using a thermo-mechanical controlled processing.