Free-machining powder metallurgy steel articles and method of making same
A small diameter, elongated steel article, comprising fully consolidated, prealloyed metal powder is disclosed. The consolidated metal powder has a microstructure that has a substantially uniform distribution of fine grains having a grain size of not larger than about 9 when determined in accordance with ASTM Standard Specification E 112. The microstructure of the consolidated metal powder is further characterized by having a plurality of substantially spheroidal carbides uniformly distributed throughout the consolidated metal powder that are not greater than about 6 microns in major dimension and a plurality of sulfides uniformly distributed throughout the consolidated metal powder wherein the sulfides are not greater than about 2 microns in major dimension. A process for making the elongated steel article is also disclosed.
1. A small diameter, elongated steel article, comprising fully consolidated, prealloyed metal powder wherein the consolidated metal powder has a microstructure comprising:
a substantially uniform distribution of fine grains having a grain size of not larger than about 9 when determined in accordance with ASTM Standard Specification E 112;
a plurality of carbides uniformly distributed throughout the consolidated metal powder, said carbides being substantially spheroidal in shape and not greater than about 6 microns in major dimension; and
a plurality of sulfides uniformly distributed throughout the consolidated metal powder, said sulfides being not greater than about 2 microns in major dimension.
2. An elongated article as set forth in claim 1 wherein the consolidated metal powder comprises a spheroidal cementite structure.
3. An elongated article as set forth in claim 1 wherein the prealloyed metal powder has a weight percent composition consisting essentially of, about
C
0.88-0.98
Mn
0.40-0.55
Si
0.12-0.22
P
0.030 max.
S
0.010-0.075
N
0.060 max.
Cr
0.25 max.
Ni
0.25 max.
Mo
0.25 max.
and the balance being iron and usual impurities.
4. An elongated article as set forth in claim 1 wherein the prealloyed metal powder has a weight percent composition consisting essentially of, about
C
0.43-0.50
Mn
1.50 max.
Si
0.60 max.
P
0.030 max.
S
0.010-0.090
Cr
12.50-14.00
Ni
0.75-1.25
Mo
1.00-1.20
and the balance being iron and usual impurities.
5. An elongated article as set forth in claim 1 wherein the prealloyed metal powder has a weight percent composition consisting essentially of, about
C
0.43-0.50
Mn
1.00 max.
Si
1.00 max.
P
0.040 max.
S
0.010-0.090
Cr
12.50-14.50
Ni
0.75-1.25
Mo
1.20 max.
and the balance being iron and usual impurities.
6. An elongated article as set forth in claim 1 wherein the elongated article is wire having a diameter of 1.75 mm to about 6.5 mm.
7. A machinable, elongated, small cross-section coil or bar product comprising fully consolidated, prealloyed metal powder that is substantially free of lead, wherein the consolidated metal powder has a microstructure comprising:
a substantially uniform distribution of fine grains having a grain size of not larger than about 9 when determined in accordance with ASTM Standard Specification E 112;
a plurality of carbides uniformly distributed throughout the consolidated metal powder, said carbides being substantially spheroidal in shape and not greater than about 6 microns in major dimension; and
a plurality of sulfides uniformly distributed throughout the consolidated metal powder, said sulfides being not greater than about 2 microns in major dimension; and
said coil or bar product has a precision characterized by a Tolerance grade not greater than IT 6.
8. An elongated coil or bar product as set forth in claim 7 wherein the prealloyed metal powder has a weight percent composition consisting essentially of, about
C
0.88-0.98
Mn
0.40-0.55
Si
0.12-0.22
P
0.030 max.
S
0.010-0.075
N
0.060 max.
Cr
0.25 max.
Ni
0.25 max.
Mo
0.25 max.
and the balance being iron and usual impurities.
9. An elongated coil or bar product as set forth in claim 7 wherein said coil or bar product has a precision characterized by a Tolerance grade of IT 4 to IT 6.
10. An elongated steel article as set forth in claim 1 wherein the grain size is not larger than about 10 when determined in accordance with the ASTM Standard Specification E 112.
11. An elongated article as set forth in claim 1 wherein the prealloyed metal powder has a weight percent composition consisting essentially of, about
C
0.14-0.23
Mn
1.00 max.
Si
1.00 max.
P
0.045 max.
S
0.010-0.030
Cr
15.5-17.5
Ni
1.5-2.5
and the balance of the alloy is iron and usual impurities.
12. An elongated article as set forth in claim 1 wherein the prealloyed metal powder has a weight percent composition consisting essentially of, about
C
0.12-0.17
Mn
0.3-0.8
Si
0.2-0.6
P
0.04 max.
S
0.010-0.030
Cr
15.5-17.0
Ni
1.5-2.5
and the balance of the alloy is iron and usual impurities.
13. An elongated article as set forth in claim 1 wherein the prealloyed metal powder has a weight percent composition consisting essentially of, about
C
0.030 max.
Mn
1.50 max.
Si
0.80 max.
P
0.030 max.
S
0.010-0.030
Cr
17.0-20.0
Ni
11.5-14.0
Mo
2.0-3.0
Cu
0.50 max.
and the balance of the alloy is iron and usual impurities.
14. An elongated coil or bar product as set forth in claim 7 wherein the grain size is not larger than about 10 when determined in accordance with the ASTM Standard Specification E 112.
15. An elongated coil or bar product as set forth in claim 7 wherein the prealloyed metal powder has a weight percent composition consisting essentially of, about
C
0.14-0.23
Mn
1.00 max.
Si
1.00 max.
P
0.045 max.
S
0.010-0.030
Cr
15.5-17.5
Ni
1.5-2.5
and the balance of the alloy is iron and usual impurities.
16. An elongated coil or bar product as set forth in claim 7 wherein the prealloyed metal powder has a weight percent composition consisting essentially of, about
C
0.12-0.17
Mn
0.3-0.8
Si
0.2-0.6
P
0.04 max.
S
0.010-0.030
Cr
15.5-17.0
Ni
1.5-2.5
and the balance of the alloy is iron and usual impurities.
17. An elongated coil or bar product as set forth in claim 7 wherein the prealloyed metal powder has a weight percent composition consisting essentially of, about
C
0.030 max.
Mn
1.50 max.
Si
0.80 max.
P
0.030 max.
S
0.010-0.030
Cr
17.0-20.0
Ni
11.5-14.0
Mo
2.0-3.0
Cu
0.50 max.
and the balance of the alloy is iron and usual impurities.