EP0187935A1 - Aciers instables - Google Patents

Aciers instables Download PDF

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Publication number
EP0187935A1
EP0187935A1 EP85115253A EP85115253A EP0187935A1 EP 0187935 A1 EP0187935 A1 EP 0187935A1 EP 85115253 A EP85115253 A EP 85115253A EP 85115253 A EP85115253 A EP 85115253A EP 0187935 A1 EP0187935 A1 EP 0187935A1
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EP
European Patent Office
Prior art keywords
steel
steels
austenitic
nitrogen
manganese
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP85115253A
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German (de)
English (en)
Inventor
Ursula Ruth Lenel
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Chamber of Mines Services Pty Ltd
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Chamber of Mines Services Pty Ltd
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Publication date
Application filed by Chamber of Mines Services Pty Ltd filed Critical Chamber of Mines Services Pty Ltd
Publication of EP0187935A1 publication Critical patent/EP0187935A1/fr
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    • 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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese

Definitions

  • THIS invention relates to corrosion resistant steels, known generally as "stainless" steels.
  • Corrosion resistance in steels is achieved by providing chromium as a major constituent of the steel. Whilst many corrosion resistant steels are available, the commonly used steels are classified by their crystal structure as austenitic, which has a face centered cubic structure, martensitic which has a body centered cubic structure or a body centered tetragonal structure (both known as martensite), and ferritic, which again has a body centered cubic structure.
  • nickel is a relatively expensive material and, thus, the use of nickel inevitably increases the cost of the resultant steel.
  • the present invention is concerned particularly with austenitic and martensitic steels. It is well known that the same steel can present either an austenitic or a martensitic microstructure, depending upon the ambient temperature. For example, a typical austenitic steel can be transformed to a martensitic steel by decreasing the ambient temperature by an appropriate amount.
  • the transformation from austenite to martensite occurs over a temperature range the upper temperature of which is referred to as the M s and the lower temperature of which is referred to as the M f .
  • the martensite transformation may be induced by deformation of the material at temperatures above the M.
  • the upper s temperature at which transformation to martensite may be induced by deformation is known as the M d .
  • the M d temperature is also dependent upon the amount of deformation applied, the M d temperature being higher for heavier deformations and lower for lesser deformations. All of these temperatures also depend upon the composition of the steel.
  • an austentic steel can be considered to be a steel in - which the temperature at which the transformation from austenite to I martensite starts (the M temperature) is below room temperature. Where the M temperature is above room temperature the steel will be martensitic, at least in part.
  • Austenitic steels (such as AISI 304 and 316) have the advantage of high ductility and toughness but are not generally very hard and not very wear-resistant whilst being relatively expensive. Austenitic steels do, however, have the advantage of being non-magnetic. The properties of martensitic steels contrast markedly to those of austenitic steels. In the quenched state, martensitic steels are strong and hard, the strength and hardness increasing with increasing content of the interstitial alloying elements, such as carbon or nitrogen. In this state, martensitic steels lack ductility and toughness. Whilst ductility and toughness can be improved by tempering this leads to a reduction of the strength and hardness of the steel. A significant advantage of martensitic steels is that the high hardness generally results in a high wear resistance. Martensitic steels are magnetic.
  • a steel comprises by mass 9 to 15% chromium, 7 to 13% manganese and 0,05 to 0,35% nitrogen, while the sum of nitrogen and carbon does not exceed 0,35%, the balance being iron and unavoidable and incidental impurities, and the proportions of chromium, manganese, nitrogen and carbon being so chosen that the resultant steel is austenitic at room temperature but transforms significantly to martensite upon deformation.
  • the amount of chromium is preferably selected to be in the range from 9 to 13%, and more preferably in the range from 11 to 13%.
  • the amount of manganese is preferably selected to be in the range from 8 to 11% and more preferably in the range from 9 to 11%.
  • the amount of nitrogen is selected to be in the range from 0,15 to 0,35% and more preferably in the range from 0,15 to 0,25% and in the latter case the sum of nitrogen and carbon should not exceed 0,25%.
  • a still further advantage of the use of manganese is that it increases the solubility of the steel for nitrogen which could provide substantial benefits during manufacture of the steel.
  • a typical steel of the invention has been found to provide very good wear resistance.
  • a steel of the invention provides these advantageous features but; in addition, provides further work hardening due to the deformation ) induced transformation to martensite thus leading to even higher wear resistance:
  • a 10kg steel ingot was made having the composition 12.8% Cr, 9.1% Mn i and 0.215% N. Levels of other elements were: 0.049%C; 0.01%S; 0.018%P; 0.05% Mo; 0.052%V; 0.58Ni; 0.67%Si;0.08% Cu; 0.06%Co.
  • the ingot was hot hammered and hot rolled to 12 mm thick plate and samples were heat treated at 1050°C for one hour and air cooled.
  • the steel was austensitic at room temperature, and cooling to liquid nitrogen temperatures revealed that the Ms temperature in this steel is below -196°C. Nevertheless, the austensitic steel is unstable and transforms to a martensitic steel under deformation (e.g. by cold rolling, abrading, impact or tensile testing) at room temperature, indicating that Md is above room temperature.
  • the mechanical tests were carried out in the standard manner.
  • the wear tests were carried out on a pin-on-disc abrasion testing machine on dry abrasive papers at a load of lMNm and a velocity of 0.2 ms
  • a standard AISI 304 austensitic stainless steel yielded RWR (relative wear resistance) values of 1.55 on sand and 1.48 on quartz in the same conditions.
  • Corrosion tests were also carried out, comprising potentiodynamic polarisation tests in a typical mine water at pH 5.9 and in 10 wt.% sulphuric acid. There was no significant difference between the corrosion resistance of an AISI 410 martensitic stainless steel and the exemplary steel of the invention.
  • a steel was made having the composition 10.6%Cr, 9.5%Mn and 0.192%N.
  • the steel was fully austensitic at room temperature with an Ms temperature below -196°C.
  • the steel transformed to martensite on deformation.
  • a steel was made having the composition 11.8%Cr, 8.1%Mn and 0.203%N. Levels of other elements were similar to those given in Example 1. The steel was treated and tested as in Example 1, giving the following properties:
  • the M s temperature of this steel was measured by a resistivity technique to be 30°C. At room temperature therefore the steel comprises austenite and some martensite, and further martensite formed readily on deformation.
  • the drawing is a schematic stress/strain graph having curves marked 1 to 5.
  • the curve marked 5 represents a steel of example 2.
  • the transformation of austenitic steels it is well known that appropriate selection of the composition of a steeel can provide marked changes in the M temperature.
  • the composition of the steel is so chosen that the M temperaure lies below room temperature and thus, in normal (unstressed) circumstances the steel is austenitic and provides many of the advantages of known nitrogen enhanced austentic steels.
  • transformation from an ustenite to a martensite can also be achieved by deformation of the steel.
  • the amount of deformation required to bring about the onset of transforation to martensite depends upon the precise composition-of the particular steel, the composition affecting the M d .
  • the composition is selected such that, at room temperature, the steel is austenitic but, again at room temperature, the application of deformation causes the onset of transformation.
  • unstable steels Such steels are termed “unstable” steels. This selection of composition to provide an unstable steel is in marked distinction to presently available nitrogen containing austenitic steels which, even upon deformation, remain austenitic and may therefore ' .be termed “stable”. As used herein, the term “unstable austenitic steel” is intended to refer to an austenitic steel which can be transformed from an austenitic microstructure to a martensitic microstructure upon deformation at room temperature.
  • One of the most significant advantages of the present invention is the provision of a steel with a very high capacity for work hardening.
  • Work hardening can be considered as the hardening of a steel that is achieved during working thereof.
  • martensitic steels are generally hard but are generally not ductile and have only a limited capacity for work hardening.
  • austenitic steels have a very reasonable capacity for work hardening but cannot achieve a degree of hardness approaching that of a martensitic steel. It has been found that the wear resistance of a steel is greatly enhanced if that steel has a large capacity for work hardening, and achieves a high surface hardness during wear.
  • line 1 is a plot for a typical austenitic steel (A.I.S.I.304)
  • line 2 is a plot for a typical nitrogen enhanced austenitic steel (304N)
  • line 3 is a plot for Hadfield's manganese steel
  • line 4 is a plot for a typical martensitic steel (A.I.S.I. 410)
  • line 5 is a plot for a chromium-manganese-nitrogen steel of Example 2 above.
  • a typical martensitic steel (lightly tempered) has little ductility or work hardening but is very hard and strong, the hardness and strength largely being due to the presence of carbon.
  • the typical austenitic steel (A.I.S.I. 304) has considerable ductility and work hardening but the hardness achieved, even after full work hardening, does not approach that of a martensitic steel.
  • the work hardening of the illustrated austenitic steel may be partly due to transformation to martensite (as A.I.S.I. 304 is unstable) but the martensite produced is not very hard as it contains little or no carbon or nitrogen.
  • the illustrated nitrogen enhanced austenitic steel (304N) presents very similar properties to the unenhanced A.I.S.I. 304 but is somewhat stronger.
  • the strengthening is due to the presence of nitrogen but, in this steel the nitrogen has the effect of making the alloy stable and thus there is no additional strengthening due to transformation.
  • Hadfield's manganese steel does provide a fairly high capacity for work hardening and has somewhat higher strength than the others, the increased strength being due to a high level of carbon (usually greater than 1%). Again the Hadfield's manganese steel is stable and thus no strengthening or increase in work hardening occurs due to transformation to ⁇ martensite.
  • a steel of the invention provides very high work hardening, due to a combination of strengthening by transformation to martensite and strengthening by nitrogen, the nitrogen acting to strengthen both the austenitic and martensitic forms of the steel.
  • Steels of the invention have similar ductility to other austenitic steels but are much more ductile than available martensitic steels.
  • Steels of the invention have a toughness similar or superior to other austenitic steels but are very much tougher than available martensitic steels.
  • Steels of the invention provide considerably superior work hardening to all of the other steels shown in the Table and, in fact, to all known austenitic and martensitic steels.
  • Steels of the invention provide a considerably superior wear resistance to the other stainless steels shown in the Table and a wear resistance that is similar to Hadfield's manganese steel (a proprietary wear resistant steel that contains no chromium and is thus not corrosion resistant).
  • Steels of the invention may have slightly inferior corrosion resistance to presently available austenitic stainless steels but have corrosion resistance that is similar to available martensitic stainless steels and very much superior to Hadfield's manganese steel.
  • a preferred steel of the invention has been found to have a very high resistance to wear, much higher than previously available in useful corrosion resistant alloys, whilst retaining the desired corrosion resistance and being relatively cheap, by virtue of the use of manganese rather than nickel.
  • a steel of the invention has been found to be tough and weldable. This provides another significant contrast to known martensitic steels which may be expected to have a wear resistance similar to steels of the invention.
  • Such known martensitic steels contain appreciable amounts of carbon and thus have a major drawback in that they are not ductile or tough. Moreover, wear resistant martensitic steels cannot easily be welded.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)
  • Arc Welding In General (AREA)
EP85115253A 1984-12-07 1985-12-02 Aciers instables Withdrawn EP0187935A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8430962 1984-12-07
GB08430962A GB2168077A (en) 1984-12-07 1984-12-07 Improvements in or relating to stainless steels

Publications (1)

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EP0187935A1 true EP0187935A1 (fr) 1986-07-23

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EP85115253A Withdrawn EP0187935A1 (fr) 1984-12-07 1985-12-02 Aciers instables

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EP (1) EP0187935A1 (fr)
JP (1) JPS61179854A (fr)
AU (1) AU5057385A (fr)
GB (1) GB2168077A (fr)
ZA (1) ZA859030B (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0904154A1 (fr) * 1997-02-21 1999-03-31 GS Technologies Operating Company Milieu de broyage fin comprenant un acier martinsitique/austenitique renfermant une austenite transformable par l'effet des contraintes

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB506905A (en) * 1938-01-22 1939-06-06 Krupp Ag Improvements in the manufacture of parts of chemical apparatus and other articles from chromium-manganese steel alloys
US2862812A (en) * 1958-05-16 1958-12-02 Crucible Steel Co America Substantially nickel-free austenitic and corrosion resisting cr-mn-n steels
US3075839A (en) * 1960-01-05 1963-01-29 Crucible Steel Co America Nickel-free austenitic corrosion resistant steels
FR2071667A5 (en) * 1969-12-27 1971-09-17 Nisshin Steel Co Ltd Austenitic stainless steel with high resist- - ance to corrosion and to fissures forming during welding
US3893850A (en) * 1970-04-30 1975-07-08 Nisshin Steel Co Ltd Nickel free austenitic stainless steels

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1097862A (en) * 1963-10-03 1968-01-03 Wilkinson Sword Ltd Improvements in or relating to razor blades
GB1281017A (en) * 1969-07-28 1972-07-12 United States Steel Corp Meta-stable austenitic stainless steels of improved hot workability
BE754371A (fr) * 1970-01-13 1971-01-18 Nisshin Steel Co Ltd Aciers inoxydables austenitiques
GB1350434A (en) * 1971-04-13 1974-04-18 Uss Eng & Consult Metastable austenitic stainless steel
SE373387B (sv) * 1973-06-08 1975-02-03 Sandvik Ab Forfarande for framstellning av band eller trad, exv. rundtrad for fjederendamal
GB2075550B (en) * 1980-05-05 1984-04-04 Armco Inc Abrasion resistant austenitic stainless steel
JPS6059981B2 (ja) * 1981-07-08 1985-12-27 日新製鋼株式会社 粒界腐食割れ特性および加工性にすぐれた高強度ステンレス鋼

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB506905A (en) * 1938-01-22 1939-06-06 Krupp Ag Improvements in the manufacture of parts of chemical apparatus and other articles from chromium-manganese steel alloys
US2862812A (en) * 1958-05-16 1958-12-02 Crucible Steel Co America Substantially nickel-free austenitic and corrosion resisting cr-mn-n steels
US3075839A (en) * 1960-01-05 1963-01-29 Crucible Steel Co America Nickel-free austenitic corrosion resistant steels
FR2071667A5 (en) * 1969-12-27 1971-09-17 Nisshin Steel Co Ltd Austenitic stainless steel with high resist- - ance to corrosion and to fissures forming during welding
US3893850A (en) * 1970-04-30 1975-07-08 Nisshin Steel Co Ltd Nickel free austenitic stainless steels

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
C.W. WEGST: "Stahlschl}ssel", 13th edition, 1983, page 344, Verlag Stahlschl}ssel Wegst GmbH, Marbach, DE. *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0904154A1 (fr) * 1997-02-21 1999-03-31 GS Technologies Operating Company Milieu de broyage fin comprenant un acier martinsitique/austenitique renfermant une austenite transformable par l'effet des contraintes
EP0904154A4 (fr) * 1997-02-21 2003-04-09 Mc Bvi Ltd Milieu de broyage fin comprenant un acier martinsitique/austenitique renfermant une austenite transformable par l'effet des contraintes

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Publication number Publication date
GB2168077A (en) 1986-06-11
JPS61179854A (ja) 1986-08-12
AU5057385A (en) 1986-06-12
ZA859030B (en) 1986-08-27

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Inventor name: LENEL, URSULA RUTH