Process for producing steel article
The invention concerns an article of a steel which is characterized in that it consists of an alloy which contains in weight-%: 1.2-2.0 C, 0.1-1.5 Si, 0.1-2.0 Mn, max. 0.2 N, max. 0.25 S, 4-8 Cr, 0.5-3.5 (Mo+W/2), 5-8 V, max. 1.0 Nb, balance essentially only iron and unavoidable impurities, and that the steel has a micro-structure obtainable by a manufacturing of the steel which comprises spray forming of an ingot, the micro-structure of which contains 8-15 vol-% carbides of essentially only MC-type where M substantially consists of vanadium, of which carbides at least 80 vol-% have a substantially rounded shape and a size in the longest extension of the carbides amounting to 1-20 μm.
1. Process for producing a steel article comprising an alloy which contains in weight-%:
1.2-2.0
C
0.1-1.5
Si
0.1-2.0
Mn
max 0.2
N
max 0.25
S
4-8
Cr
0.5-3.5
(Mo + W/2)
5-8
V
balance essentially only iron and unavoidable impurities,
said process comprising spray forming an ingot to produce an ingot comprised of a steel having a micro-structure containing 8-15 vol-% MC-carbides where M substantially consists of vanadium, of which carbides at least 80 vol-% have substantially rounded shape and a size in the longest extension of the carbides amounting to 1-20 μm.
2. Process according to claim 1 wherein droplets of molten alloy are sprayed against a rotating substrate to form said ingot.
3. Process according to claim 2 wherein said droplets undergo solidification at a rate which permits formation of carbides in which said at least 80 vol-% have said substantially rounded shape and said size in the longest extension of the carbides amounting to 1-20 μm.
4. Process according to claim 3 , wherein said carbides formed upon solidification of said droplets are evenly distributed in said ingot.
5. Process according to claim 1 , wherein said alloy contains in weight-%:
1.2-2.0
C
0.1-1.5
Si
0.1-2.0
Mn
max 0.2
N
max 0.25
S
4-8
Cr
0.5-3.5
(Mo + W/2)
5-8
V
max. 1.0
Nb
balance essentially only iron and unavoidable impurities.
6. Process according to claim 5 , wherein said alloy contains max 0.5% Nb.
7. Process according to claim 6 , wherein sad alloy contains max. 0.3% Nb.
8. Process according to claim 7 , wherein said alloy contains max. 0.1% Nb.
9. Process according to claim 8 , wherein said alloy does not contain an intentionally added niobium.
10. Process according to claim 1 , wherein the micro-structure contains 10-14.5 vol-% MC-carbides, of which the main part with reference to volume has a size in the longest extensions of the carbides larger than 3.0 μm and max. 10 μm.
11. Process according to claim 1 , wherein, after spray forming, the alloy is subjected to hardening and tempering to thereby possess a hardness of 45-60 HRC.
12. Process according to claim 11 , wherein, after the alloy is hardened and tempered, the martensitic matrix of the alloy contains 0.1-0.5 weight-% C in solid solution.
13. Process according to claim 1 , wherein the total content of C in the alloy is at least 1.3%.
14. Process according to claim 1 , wherein the total content of C in the alloy is at least 1.4%.
15. Process according to claim 1 , wherein the total content of C in the alloy is max. 1.9%.
16. Process according to claim 1 , wherein the total content of C in the alloy is max. 1.8%.
17. Process according to claim 1 , wherein the alloy contains 0.1-1.0% Si.
18. Process according to claim 1 , wherein the alloy contains max. 0.65% Si.
19. Process according to claim 1 , wherein the alloy contains 0.2-1.5% Mn.
20. Process according to claim 1 , wherein the alloy contains at least 4.2% Cr.
21. Process according to claim 1 , wherein the alloy contains max. 6.5% Cr.
22. Process according to claim 21 , wherein the alloy contains 4.5-5.5% Cr.
23. Process according to claim 1 , wherein the alloy contains at least 6.0% V.
24. Process according to claim 1 , wherein the alloy contains max. 7.8% V.
25. Process according to claim 24 , wherein the alloy contains 6.8-7.6% V.
26. Process according to claim 1 , wherein the alloy does not contain more than max. 0.04% Nb.
27. Process according to claim 1 , wherein the alloy contains at least 1.5% Mo.
28. Process according to claim 1 , wherein the alloy contains 1.8-2.8% Mo.
29. Process according to claim 1 , wherein the alloy does not contain more than max. 1.0% W.
30. Process according to claim 1 , wherein the alloy does not contain more than max. 0.5% W.
31. Process according to claim 1 , wherein the steel does not contain more than max. 0.15% S.
32. Process according to claim 1 , wherein the steel does not contain more than max. 0.08% S.
33. Process according to claim 11 , wherein, after spray forming, said alloy is subjected to hardening from an austenitizing temperature in the temperature range 1000-1150° C., followed by tempering at a temperature in the temperature range between 590-640° C., twice for two hours each, to thereby possess a hardness of 48-53 HRC.
34. Process according to claim 11 , wherein, after spray forming, said alloy is subjected to hardening from an austenitizing temperature in the temperature range 1000-1150° C., followed by tempering at a temperature in the temperature range between 540-610° C., twice for two hours each, to thereby possess a hardness of 54-58 HRC.
35. Process according to claim 11 , wherein, after spray forming, said alloy is subjected to hardening from an austenitizing temperature in the temperature range 1050-1150° C., followed by tempering at a temperature in the temperature range 540-580° C., twice for two hours each, to thereby possess a hardness of 58-60 HRC.