Stainless steel strip for flapper valves
A cold rolled and hardened martensitic austenitic stainless steel strip for flapper valves in compressors is made from steel combining, in weight %(wt. %), the following elements: C: 0.3-0.5, Si: 0.2-0.8, Mn: 0.2-1.0, Cr: 12.0-15.0, Mo: 0.50-2.00, N: 0.02-0.15, and V: 0.01-0.20. The steel strip has a matrix consisting of tempered martensite and between 5 and 15 volume % austenite and a tensile strength (R m ) of 1970-2300 MPa. The steel strip has a thickness of 0.07-3 mm and a width of ≦500 mm.
1. A cold rolled and hardened martensitic and austenitic stainless steel strip for flapper valves in the compressors, wherein the steel strip
a) has a composition consisting of, in weight %:
C 0.3-0.5
Si 0.2-0.8
Mn 0.2-1.0
Cr 12.0-15.0
Mo 0.5-2.0
N 0.02-0.15
V 0.01-0.20
Ni≦2.0
Co≦2.0
Cu≦2.0
W≦2.0
Al≦0.06
Ti≦0.05
Zr≦0.05
Nb≦0.05
Ta≦0.05
B≦0.01
Ca≦0.009
REM≦0.2
Fe and impurities balance,
b) has a matrix consisting of tempered martensite and between 5 and 15 volume % austenite,
c) has a tensile strength (R m ) of 1970-2300 MPa, and
d) has a thickness of 0.07-3 mm and a width of ≦500 mm.
2. A strip according to claim 1 , wherein the composition fulfills at least one of the following requirements:
C 0.35-0.41
Si 0.30-0.60
Mn 0.40-0.65
Cr 13-14
Mo 0.8-1.2
N 0.03-0.13
V 0.02-0.10
Ni≦0.5
Co≦0.5
Cu≦0.5
W≦0.5
Al≦0.01
Ti≦0.01
Zr≦0.01
Nb≦0.01
Ta≦0.01
B≦0.001 and
Ca 0.0005-0.002.
3. A strip according to claim 1 , wherein the composition fulfills the following requirements:
C 0.35-0.41
Si 0.30-0.60
Mn 0.40-0.65
Cr 13-14
Mo 0.8-1.2
N 0.03-0.10 and
V 0.03-0.09.
4. A strip according to claim 1 , fulfilling at least one of the following requirements:
a tensile strength (R m ) of 2000-2200 MPa,
a yield strength (R P0.2 ) of 1500-1750 MPa,
a Vickers Hardness (HV1) of 570-650, and
a ductility A50 of 4-9%.
5. A strip according to claim 1 , fulfilling the following requirement:
a reverse bending fatigue greater than 850 MPa.
6. A strip according to claim 1 , wherein the strip has a thickness of 0.1-1.5 mm and/or a width of 5-150 mm.
7. A strip according to claim 1 , wherein the strip has a maximum globular inclusion size is 6 μm.
8. A strip according to claim 1 , wherein the has a primary inclusion species of Silicate type with a maximum width of 4 μm.
9. A method of producing a strip according to claim 1 , comprising:
a) hot rolling the composition of claim 1 to produce a hot rolled strip,
b) cold rolling the hot rolled strip to produce a cold rolled strip having a thickness of 0.07-3 mm,
c) continuously hardening and tempering the cold rolled strip, and
d) optionally, slitting the cold rolled strip.
10. A method according claim 9 , wherein:
in step c) an austenitizing temperature is 1000-1150° C., and
a tempering temperature is 200-600° C.
11. A method according claim 9 , wherein:
the hardening involves quenching the strip in a bath of molten lead and/or lead alloy, and
the bath is held at a temperature of 250-350° C.
12. A method according to claim 9 , further comprising:
producing the steel strip by powder metallurgy,
wherein a maximum globular inclusion size in the cold rolled strip is 6 μm.