Ultra-high strength maraging stainless steel with salt-water corrosion resistance
An ultra-high strength maraging stainless steel with nominal composition (in mass) of C≤0.03%, Cr: 13.0-14.0%, Ni: 5.5-7.0%, Co: 5.5-7.5%, Mo: 3.0-5.0%, Ti: 1.9-2.5%, Si: ≤0.1%, Mn: ≤0.1%, P: ≤0.01%, S: ≤0.01%, and Fe: balance. The developed ultra-high strength maraging stainless steel combines ultra-high strength (with σb≥2000 MPa, σ0.2≥1700 MPa, δ≥8% and ψ≥40%), high toughness (KIC≥83 MPa·m½) and superior salt-water corrosion resistance (with pitting potential Epit≥0.15 (vs SCE)). Therefore, this steel is suitable to make structural parts that are used in harsh corrosive environments like marine environment containing chloride ions, etc.
1. A maraging stainless steel comprising:
13 to 14 wt % chromium (Cr);
5.5 to 7.0 wt % nickel (Ni);
5.5 to 7.5 wt % cobalt (Co);
3 to 5 wt % molybdenum (Mo);
2.2 to 2.5 wt % titanium (Ti);
at most 0.03 wt % carbon (C); and
iron (Fe),
wherein the maraging stainless steel is prepared by melting and casting.
2. The maraging stainless steel of claim 1 having a silicon (Si) content of at most 0.1 wt %.
3. The maraging stainless steel of claim 1 having a manganese (Mn) content of at most 0.1 wt %.
4. The maraging stainless steel of claim 1 having a phosphorus (P) content of at most 0.01 wt %.
5. The maraging stainless steel of claim 1 having a sulfur (S) content of at most 0.01 wt %.
6. The maraging stainless steel of claim 1 having:
a silicon (Si) content of at most 0.1 wt %;
a manganese (Mn) content of at most 0.1 wt %;
a phosphorus (P) content of at most 0.01 wt %; and
a sulfur (S) content of at most 0.01 wt %.
7. The maraging stainless steel of claim 1 wherein said chromium is present at 13.0 to 13.1 wt %.
8. The maraging stainless steel of claim 1 wherein said nickel is present at 6.9 to 7.0 wt %.
9. The maraging stainless steel of claim 1 wherein said cobalt is present at 5.5 to 5.6 wt %.
10. The maraging stainless steel of claim 1 wherein said molybdenum is present at 3.4 to 3.5 wt %.
11. The maraging stainless steel of claim 1 wherein said titanium is present at 2.3 to 2.5 wt %.
12. The maraging stainless steel of claim 1 wherein said titanium is present at 2.4 to 2.5 wt %.
13. The maraging stainless steel of claim 1 wherein:
said chromium is present at 13.0 to 13.1 wt %;
said nickel is present at 6.9 to 7.0 wt %;
said cobalt is present at 5.5 to 5.6 wt %; and
said molybdenum is present at 3.4 to 3.5 wt %.
14. The maraging stainless steel of claim 1 further comprising:
at most 0.1 wt % silicon;
at most 0.1 wt % manganese;
at most 0.01 wt % phosphorus; and
at most 0.01 wt % sulfur.
15. A maraging stainless steel comprising:
13 to 14 wt % chromium (Cr);
5.5 to 7.0 wt % nickel (Ni);
5.5 to 7.5 wt % cobalt (Co);
3 to 5 wt % molybdenum (Mo);
2.2 to 2.5 wt % titanium (Ti);
at most 0.03 wt % carbon (C); and
iron (Fe),
wherein the maraging stainless steel is prepared by melting and casting, and
wherein the maraging stainless steel has ultra-high strength represented by ab 2000 MPa, has high ductility represented by δ≥8%, and has salt-water corrosion resistance represented by pitting potential Epit≥0.15 (vs SCE).
16. A method for heat processing the maraging stainless steel of claim 1 , the method comprising:
forging the maraging stainless steel in austenite phase region, with a forging ratio of 6-9, and air cooling to room temperature after forging; and hot-rolling the maraging stainless steel after forging, with a starting temperature of 1150-1250 ° C., and a finishing temperature of at least 900 ° C., and air cooling after hot-rolling.
17. The method of claim 16 wherein the forging ratio is greater than 8.
18. The method of claim 16 wherein an accumulated rolling reduction during the hot-rolling is at least 80 percent.
19. A method for heat treating the maraging stainless steel of claim 1 , the method comprising:
solution treatment of the maraging stainless steel at 1050-1150 ° C. for 1-2 h, and then air cooling to room temperature;
after the solution treatment, cryogenic treatment of the maraging stainless steel in liquid nitrogen (−196 ° C.) for at least 5 h; and after the cryogenic treatment, aging treatment of the maraging stainless steel at 450-520 ° C. for 30 min to 16 h, followed by air cooling.
20. The method of claim 19 wherein:
the solution treatment is performed at 1100 ° C. for 1.5 h;
the cryogenic treatment is performed for at least 10 h; and
the aging treatment is performed at 480 ° C. for 10 h.