SE543422C2 - Steel strip for flapper valves - Google Patents

Steel strip for flapper valves

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Publication number
SE543422C2
SE543422C2 SE1950679A SE1950679A SE543422C2 SE 543422 C2 SE543422 C2 SE 543422C2 SE 1950679 A SE1950679 A SE 1950679A SE 1950679 A SE1950679 A SE 1950679A SE 543422 C2 SE543422 C2 SE 543422C2
Authority
SE
Sweden
Prior art keywords
equal
steel strip
carbides
steel
vol
Prior art date
Application number
SE1950679A
Other languages
Swedish (sv)
Other versions
SE1950679A1 (en
Inventor
Boris Iwanschitz
Chris Millward
Original Assignee
Voestalpine Prec Strip Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Voestalpine Prec Strip Ab filed Critical Voestalpine Prec Strip Ab
Priority to SE1950679A priority Critical patent/SE543422C2/en
Priority to BR112021024371A priority patent/BR112021024371A2/en
Priority to EP20817981.2A priority patent/EP3980571A4/en
Priority to CN202080041948.5A priority patent/CN113939608A/en
Priority to PCT/SE2020/050569 priority patent/WO2020246937A1/en
Publication of SE1950679A1 publication Critical patent/SE1950679A1/en
Publication of SE543422C2 publication Critical patent/SE543422C2/en

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/22—Martempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/58—Oils
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/60—Aqueous agents
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/02—Hardening by precipitation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0268—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment between cold rolling steps
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/02—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for springs
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B39/00—Component parts, details, or accessories, of pumps or pumping systems specially adapted for elastic fluids, not otherwise provided for in, or of interest apart from, groups F04B25/00 - F04B37/00
    • F04B39/10—Adaptations or arrangements of distribution members
    • F04B39/1073—Adaptations or arrangements of distribution members the members being reed valves
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • General Engineering & Computer Science (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Turbine Rotor Nozzle Sealing (AREA)
  • Structures Of Non-Positive Displacement Pumps (AREA)

Abstract

The invention relates to a cold rolled and pre -hardened martensitic steel strip for flapper valve reeds in the compressors, wherein the steel strip is made from steel comprising in weight % (wt. %):C 0.9 - 1.1Si 0.1 - 0.5Mn 0.2 - 0.8Cr 0.05 - 0.3V 0.05 - 0.20Nb 0.02 - 0.09optional elements, Fe and impurities balance, wherein the steel strip has a matrix consisting of tempered martensite and up to 8 volume % carbides and wherein the steel strip has a thickness of 0.07- 3.5 mm and a width of 7 - 350 mm.

Description

Flapper or reed valves are used in various types of applications where a specific type ofcompression cycle is regulated for a specific purpose. It can be a refrigeration cycle in ahermetic reciprocating compressor working uninterrupted in a refrigerator or in the airconditioner of a car. A flapper valve is basically a spring made from a pre-hardenedsteel strip. In its simplest form, the flapper valve has a tongue shaped reed, where oneend is fixed and the opposite end hangs free and regulates the liquid or gas flow in thecompressor. The flapper valve reed (called “valve reed” in the following) suffers fromboth cyclic bending stresses and cyclic impact stresses during its service. Usually, thesecyclic stresses eventually cause fatigue failure. Accordingly, the fatigue properties are of the utmost importance for the flapper valve reed material.
A valve reed made of a steel strip of this invention has its fatigue properties optimizedby the combined effect of modifications to the chemical composition and the heat treatment of the steel, plus superior control of non-metallic inclusions.
Compressor OEMs require new materials that have a higher fatigue life than prior art materials in order to improve the compressor”s performance and life.
Furthermore, there is a growing interest in the industry to develop more energy efficientand quieter compressors. The coefficient of performance (COP) can be increased byincreasing the valve lift and by reducing the thickness of the valve reeds. Compressor designers therefore require valve materials that have enhanced fatigue strength.
The 1 % carbon unalloyed steel of the type ASTM 1095 or EN Nr.: l. 1274 has in the past been the standard choice for non-stainless applications and various attempts have been made in order to improve the fatigue properties of said steel. J PS60l2824ldescribes such an attempt by specifying the average size of the spheroidal carbides inthe hot rolled strip. US20l5/0030870 Al discloses a steel strip having a limited arearatio of carbides not less than 0.5 um in the metallographic structure. WO2007/ 129979Al is directed to the improvement of the fatigue life by providing a coating on at least one side of the steel strip.
However, increasing industry demands and resulting performance requirements meanthat future valve reeds Will increasingly need to be made out of very thin strip steel With an increased fatigue life expectancy.
DISCLOSURE OF THE INVENTION The general object of the present invention is to provide a pre-hardened steel strip forflapper valve reed having an optimized combination of properties such that it can bemanufactured by conventional methods of valve production and subsequently be used to produce more efficient and reliable compressors.
The foregoing objects, as Well as additional advantages are achieved to a significantmeasure by providing a cold rolled, hardened and tempered martensitic steel strip having a composition, microstructure and physical properties as set out in the claims.
The invention is defined in the claims.
DETAILED DESCRIPTION The importance of the separate elements and their interaction With each other as Well asthe limitations of the chemical ingredients of the claimed alloy are briefly explained inthe following. All percentages for the chemical composition of the steel are given inWeight % (Wt. %) throughout the description. The amounts of microstructural phases aregiven in volume % (vol. %). Upper and lower limits of the individual elements can be freely combined Within the limits set out in the claims.
The arithmetic precision of the numerical values can be increased by one or two digits.
Hence, a value of given as e. g. 0.1 % can also be expressed as 0.10 % or 0.l00%.
Carbon (0.90 - 1.10 %)Carbon is to be present in a minimum content equal to or greater than 0.9 %, preferablyat least 0.95 % for obtaining the desired mechanical properties after hardening. The upper limit for carbon is equal to or less than l.l % and may be set to 1.05 %.
Silicon (0.1 - 0.5%) Silicon is used for deoxidation. Si is a strong ferrite former and increases the carbonactivity. Si is also a powerful solid-solution strengthening element and strengthens thesteel matrix. This effect appears at a content of about 0.1 % Si and preferably the amount of Si is equal to or greater than 0.10 % Si and equal to or less than 0.50%.
Manganese (020 - 0.80 %) Manganese is an austenite stabilizer and contributes to improve the hardenability of thesteel. Manganese shall therefore be present in a minimum content equal to or greaterthan 0.2 %, preferably at least equal to or greater than 0.30 or equal to or greater than0.35 or equal to or greater than 0.40 %. When the content of Mn is too large the amountof retained austenite after finish tempering may be too high. The steel shall thereforepreferably the amount of Mn is equal to or less than 0.80 % Mn, more preferably equal to or less than 0.60 %.
Chromium (0.05 - 0.30 %) Cr contributes to improve the hardenability of the steel. Therefore, Cr is present at acontent equal to or greater than 0.05 %, preferable equal to or greater than 0.10 %.HoWever, if more than 0.30 % is added then there is a risk for the undesired formation of pearlite, so preferably the amount of Cr is equal to or less than 0.30 %..
Molybdenum (0.15 - 0.40 %)Mo may optionally be added to the steel. Mo is a ferrite stabilizer and is known to have a very favourable effect on the hardenability. Molybdenum can be used for improving the secondary hardening response during tempering. The minimum content is preferablyequal to or greater than 0.15 % and more preferably equal to or greater than 0.25 %.Molybdenum is strong carbide forming element and also a strong ferrite former. The maximum content of molybdenum is therefore preferably equal to or less than 0.40 %.
Vanadium (005 - 0.20 %) Vanadium forms evenly distributed fine precipitated carbides, nitrides and carbonitridesof the type V(N,C) in the matrix of the steel. Vanadium shall therefore preferably bepresent in an amount equal to or greater than 0.05 % and less than or equal to- 0.20 %.More preferably the upper limit may be equal to or greater than 0.15 %. The lower limit may be equal to or greater than 0.07 %.
Niobium (002 - 0.09 %) Niobium is similar to Vanadium in that it fonns carbonitrides of the type M(N,C) andmay in principle be used to replace part of the Vanadium but that requires the doubleamount of niobium as compared to Vanadium. In addition, Nb(C,N) are much morestable than V(C,N) and may therefore not be dissolved during austenitising. Theminimum amount of Nb preferably is equal to or greater than 0.02 % and maximumamount is equal to or less than 0.09 %. More preferably the maximum amount is equal to or less than 0.07 %.
V+0.5Nb (0.l0 - 0.16 %)The combined amount of V and Nb preferably may be restricted to fall Within the rangeaccording to the equation V+0.5Nb is equal to or greater than 0.10 % and equal to or less than 0.16 %. in order to optimize the amount of primary precipitated hard phases.
Nitrogen (001 - 0.15 %) Nitrogen is an optional element. N is strong austenite former and also a strong nitrideformer. N is restricted to be equal to or less than 0,15% in order to obtain the desiredtype and amount of hard phases, in particular MX, Wherein M is mainly V and Nb butother metals like Cr and Mo may be present to some extent. X is one or both of C and N.
However, a high nitrogen content may lead to Work hardening, edge cracking and/or ahigh amount of retained austenite. When the nitrogen content is properly balancedagainst the contents of V and Nb, carbonitrides of the above type Will form. These maybe partly dissolved during the austenitizing step and then precipitated during thetempering step as particles of nanometre size. The thermal stability of vanadium-carbonitrides and, in particular, niobium-carbonitrides is considered to be better thanthat of the corresponding carbides. Therefore, the resistance against grain growth athigh austenitizing temperatures may enhanced by a deliberate addition of nitrogen.However, if nitrogen is not deliberately added than it may only be present at the impurity content level of N.
Aluminium (S 0.05 %) Aluminium may optionally be used for deoxidation in combination With Si and Mn. Theupper limit is restricted to being less than or equal to 0.05% to avoid precipitation ofundesired phases such as AlN and hard, brittle Alumina inclusions. Preferably, Al is not deliberately added to the steel but is only present at the impurity level Ti, Zr and Ta (S 0.02 % each)These elements are carbide formers and may be present in the alloy in the claimedranges for altering the composition of the hard phases. However, normally none of these elements are deliberately added.
Boron (S 0.01 %)B may be used in order to further increase the hardness of the steel. The amount is limited to being equal to or less than 0.01%, preferably S 0.005 or even S 0.001 %.Ca and REM (Rare Earth Metals)These elements may be added to the steel in the claimed amounts in order to further improve the hot Workability and to modify the shape of non-metallic inclusions.
Impurity elements P and S are the main impurities, Which can have a negative effect on the mechanicalproperties of the steel strip. P may therefore be limited to 0.04 %, preferably equal to orless than 0.02 %. S may be limited to being equal to or less than 0.03 % or 50.01, or 50.008 or í 0.001 or 5 0.0005 %.
The present inventors have systematically investigated the effect of a modified chemicalcomposition and a modified heat treatment on the mechanical properties of the flappervalve reed material. The modifications made to the chemical composition relative to theconventional material Were mainly focused on increases in the contents of vanadium, niobium and molybdenum.
EXAMPLEIn this example two steel strips according to the invention is compared to theconventional steel strip UHB 20C. The composition (in Wt %) of the investigated steels Was as follows: ASTM 1095 UHB 20C N0. 1 No. 2C 0.90 - 1.03 0.97 1.01 1.03Si Not specified 0.25 0.29 0.29Mn 0.30 - 0.50 0.46 0.43 0.42Cr Not specified 0.15 0.17 0.17V Not specified < 0.01 0.10 0.10Nb Not specified < 0.001 0.07 0.06Mo Not specified < 0.01 0.03 0.31N Not specified 0.011 0.008 0.008Al Not specified 0.011 0.006 0.006P 50.040 0.0055 0.012 0.011S 50.050 0.001 0.001 0.001 Fe and impurities balance.
The cold rolled strips used in these trials Were produced from a route that included: 0 Melting, including but not limited to: Si and or Al deoxidation, use of calcium-aluminate slag with a low oxygen potential, ladle degassing and stiriing withinert gas 0 Casting, including pouring within an inert gas shroud and the use of anexothermic hot-top 0 Hot rolling to strip from temperature range of 1100 to l250°C, finishing withcoiling in the range of 400 to 700°C. 0 Annealing of the hot rolled strip in the temperature range 720 to 770°C 0 Descaling 0 Depending on final thickness, a number of cold rolling and sub-criticalannealing cycles (temperature range 690 to 720°C) 0 Final cold rolling with a minimum of 20% reduction.
Wherever prior processing is thought to have any potentially significant influence onthe inventive materials, the key parameters have been listed.
The cold rolled strips used for the trials all had a thickness of 0.381 mm and a width of330 mm. The strips were subjected to martempering in a continuous hardening line byaustenitizing at 850 - 870 °C for approximately 3.5 minutes followed by quenching in alead bath to about 350 °C and thereafter in an oil bath followed by cooling betweenwater cooled copper plates. The strips were thereafter subjected to an inline singletempering at temperatures ranging between 400 - 500°C for 2 minutes with the aim of achieving a target Rm of 1860 MPa i l00MPa (Tested in accordance with ISO 6892).
It was found that both the inventive steels achieved the target mechanical properties for a number of the iterations within the reported trial temperature ranges.
The hardened and tempered microstructures of the trial materials all consisted ofapproximately 4 - 7.5% retained secondary carbides with a mean diameter of 0.60 -0.85um (measured by image analysis based optical microscopy @xl000 magnification)with no measurable retained austenite (measured by XRD according to ASTM E975- l 3).
Subsequent reverse bending fatigue testing (R-1, staircase method designed accordingto ISO 12107 using a 2000000 cycle run-out, ) revealed that, at the same tensile strengthas the conventional steel, the reverse bending strength Was increased by approximately20% relative to a standard level of ~900MPa that is typically achieved using this testmethod ( 10 % Probability of failure, With 95 %Confidence level).
INDUSTRIAL APPLICABILITYThe inventive steel strip can be used for producing flapper valve reeds for compressors having improved properties.

Claims (4)

1. A cold r011ed and pre-hardened niartensitic steel strip for flapper Valve reeds in conipressors, Wherein the steel strip has: a) a coniposition consisting of, in Weight %: C 0.9 - 1.1Si 0.1 - 0.5Mn 0.2 - 0.8Cr 0.05 - 0.3V 0.05 - 0.20Nb 0.02 - 0.09optionally Mo 0.15 - 0.40N 0.01 - 0.15A1 S 0.05 Ti S 0.02 Zr S 0.02 Ta S 0.02 B S 0.01 Ca S 0.009REM S 0.
2. Fe and inipurities balance, b) a matrix consisting of tempered martensite, retained austenite and up to 8vol. % carbides, wherein the content of carbides is measured by image analysis based optical microscopy at x1000 magnif1cation.c) a tensile strength of 1860 MPa i 100MPa d) a thickness of 0.07- 3.5 mm and a width of7 - 450 mm. . A strip according to claim 1 fulf1lling at least one of the following requirements: a) a composition consisting of in weight %: C 0.9 - 1.1Si 0.2 - 0.4Mn 0.3 - 0.6Cr 0.1 - 0.2V 0.07 - 0.15Nb 0.03 - 0.07optionally Mo 0.25 - 0.35A1 S 0.01 wherein the impurity contents of P and S fulf1ls the following requirementsP S 0.02S S 0.006 b) a matrix comprising tempered martensite, up to 4 Vol. % retained austenite and up to 7.5 Vol. % carbides 11 c) a thickness of 0.1 - 1.5 mm. . A strip according to any of the preceding claims, fulfilling the following requirements: a) a composition consisting of in Weight %: C 0.95 - 1.05Si 0.25 - 0.35Mn 0.3 - 0.6Cr 0.1 - 0.2V 0.07 - 0.15Nb 0.03 - 0.07Mo 0.25 - 0.35Al S 0.01 b) a matrix consisting of tempered martensite, up to 2 Vol. % retainedaustenite and up to 4.5 - 7.5 vol. % carbides With a range of mean carbide diameters of 0.55 to 1.0 um. c) a thickness of 0.1 - 1.0 mm. . A strip according to any of the preceding claims Wherein the amount of (V+0.5Nb) is equal to or greater than 0.10 % and equal to or less than 0.16%.
SE1950679A 2019-06-07 2019-06-07 Steel strip for flapper valves SE543422C2 (en)

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SE1950679A SE543422C2 (en) 2019-06-07 2019-06-07 Steel strip for flapper valves
BR112021024371A BR112021024371A2 (en) 2019-06-07 2020-06-05 Steel strip for flapper valves
EP20817981.2A EP3980571A4 (en) 2019-06-07 2020-06-05 Steel strip for flapper valves
CN202080041948.5A CN113939608A (en) 2019-06-07 2020-06-05 Steel belt for flap valve
PCT/SE2020/050569 WO2020246937A1 (en) 2019-06-07 2020-06-05 Steel strip for flapper valves

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JPS61165079A (en) * 1985-01-14 1986-07-25 Hitachi Metals Ltd Valve with excellent impact fatigue strength
EP0462779A2 (en) * 1990-06-19 1991-12-27 Nisshin Steel Co., Ltd. Method of making steel useful in springs
US5118469A (en) * 1990-10-22 1992-06-02 Mitsubishi Steel Mfg. Co., Ltd. High strength spring steel
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CN113939608A (en) 2022-01-14
SE1950679A1 (en) 2020-12-08

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