US3887362A - Nitridable steels for cold flow processes - Google Patents

Nitridable steels for cold flow processes Download PDF

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US3887362A
US3887362A US316212A US31621272A US3887362A US 3887362 A US3887362 A US 3887362A US 316212 A US316212 A US 316212A US 31621272 A US31621272 A US 31621272A US 3887362 A US3887362 A US 3887362A
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weight percent
steels
nitriding
hardness
percent
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Maria Ronay
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International Business Machines Corp
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International Business Machines Corp
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Priority to JP48134911A priority patent/JPS4990208A/ja
Priority to DE2361801A priority patent/DE2361801A1/de
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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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium

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  • the steels are alloys which contain 0.005 0.03 weight percent of carbon and at least one element selected from the group consisting of titanium in a weight percent of 0.2 to 3.0, zirconium in a weight percent of 0.1 to 1.0, hafnium in a weight percent of 0.1 to 1.0, vanadium in a weight percent of 0.2 to 3.0, niobium in a weight percent of 0.2 to 3.0 and tantalum in a weight percent of 0.1 to 1.0, or aluminum in a weight percent of to 2.0 alone or in combination with elements of the aforementioned group.
  • these steels may also contain nickel in a weight percent of 0 to 15.0, silicon in a weight percent of 0 to 4.0 and manganese in a weight percent of 0 to 1.5.
  • the balance of the alloys is iron.
  • FIG. 1 l l l l l I00 "/0 PERCENTAGE REDUCTION IN HEIGHT PATENTEUJUH3 1975 FIG. 1
  • VICKERS HARDNESS ALLOY Fe0.03C-1.0Ti5Ni-0.5 Si-04Mn lllllllllllll 02468i01214161820222426 DISTANCE FROM SURFACE (mils) NlTRlDABLE STEELS FOR COLD FLOW PROCESSES BACKGROUND OF THE INVENTION
  • This invention relates to steels suitable for use for cold flow processes. More particularly, it relates to improved nitridable steels adantageously suitable for such processes.
  • the forming step is only one phase which has to be considered.
  • the high plasticity and low strength required by the forming process prohibits the use ofa finished steel part made thereby in applications where higher strength and wear resistance are required. Accordingly, it is also necessary to increase the strength and surface hardness of the part after the forming process is completed.
  • one method which has been employed to increase the hardness of a steel part produced by a cold flow process has been to apply a carburizing heat treatment to the part.
  • This treatment consists of diffusing carbon at a relatively high temperature (860-920C) into the surface of a low carbon steel part, quenching it in water or oil from the carburizing temperature, and thereafter tempering the quenched part at a relatively low (l50l90C) temperature.
  • This method has produced deleterious effects in that the high temperature of the carburizing and the subsequent rapid cooling causes considerable distortions in the hardened parts, the severity of these distortions essentially being dependent upon the shape of the part. Such distortions have to be corrected such as by straightening and grinding operations which are quite expensive.
  • the carburizing heat treatment is not suitable for the surface hardening of parts of complicated shapes or parts produced from sheet metal since distortions would be particularly prevalent in the latter types of parts. However, it is just these parts of complex shapes, or parts produced from sheet metal which are most economically manufactured by severe cold flow processes.
  • the hardness of a carburized and quenched case of a cold formed steel part depends primarily on the carbon content which results from the carbon diffusion thereinto and only secondarily on the presence of eventual carbide forming alloying element.
  • the reason for this primary dependence is that the size of metal carbide particles is relatively large. Accordingly, in small quantities, they do not impart great hardening. Consequently, the hardness of the carburized layer can only be varied within a limited range.
  • neither the hardness nor the depth of the carburized layer can be closely controlled.
  • nitriding there is meant the case hardening process wherein atomic nitrogen made available from ammonia or ammonia-nitrogen gas mixtures is diffused into the surface of a nitridable steel.
  • Nitridable steels contain alloying elements that form finely dispersed stable nitrides at the nitriding temperature and these nitrides provide the high hardness of the nitrided case of a steel part.
  • the nitriding temperature is relatively low," (500600C), and, in the nitriding process, this low temperature treatment is followed by slow cooling.
  • nitriding results in a minimum of distortions and in most situations, finished parts of complex shapes can be nitrided without the need for subsequent straightening and grinding.
  • the conventional nitridable steels are medium carbon alloyed steels that are hardened throughout their cross section by quench and tempering prior to their nitriding to increase the overall strength of the steel.
  • the alloying elements present in the nitridable steel in part contribute to this hardenability and in part form nitrides in the case of the part during the nitriding process.
  • a conventional nitridable steel typically contains alloying elements in the following weight percents.
  • the carbon very greatly hinders the diffusion of nitrogen since it occupies the same interstitial position as nitrogen in the crystal lattice. Concomitantly, it hinders the nitriding process. Because of this hindering effect of carbon, the rate of nitrogen diffusion in known conventional nitridable steels is quite slow and it may take as many as fifty hours to produce an 0.020 inch thick case at a temperature of 560C. In addition to this undesirably slow nitridability, parts cannot be formed from these conventional nitridable steels by severe cold flow processes because their medium carbon content results in low plasticity. Accordingly, up to now, no steel parts which are formed by severe cold flow processes have been nitrided even though such nitriding would be advantageous in reducing of distortions and the concomi tant need for subsequent straightening and grinding.
  • the conventional nitridable steels are medium car bon alloyed steels that are hardened through the cross section by quench and tempering before nitriding to in crease the overall strength of the alloy. Alloying elements partly serve this hardenability and partly form nitrides in the case during the nitriding process.
  • These conventional steels typically comprise 0.35 to 0.40 weight percent of carbon, 0.5 to 0.8 weight percent of manganese, 0.2 to 0.4 weight percent of molybdenum, 1.2 to 1.6 weight percent of chromium, 0.85 to 1.50 weight percent of aluminum and 0.3 to 0.5 weight percent of silicon.
  • the carbon, manganese and molybdenum promote the overall hardenability while chromium and aluminum are the active nitride forming elements which cause the hardness of the nitrided layer.
  • Aluminum and chromium form nitrides which are sufficiently small and impart great hardness to the nitrided case only in a quenched and tempered structure that has a high dislocation density.
  • aluminum and chromium are less effective in an annealed structure.
  • the carbon very greatly hinders the diffusion of nitrogen since it occupies the same interstitial position in the crystal lattice as nitrogen. Consequently, it hinders the nitriding process.
  • nitridable steels comprising 0.005 0.03 weight percent of carbon. at least one element selected from the group consisting of titanium in a concentration of 0.2 to 3.0 weight percent, zirconium in a concentration of 0.] to 1.0 weight percent, hafnium in a concentration of 0.1 to 1.0 weight percent, vanadium in a concentration of 0.2 to 3.0 weight percent, niobium in a concen tration of 0.2 to 3.0 weight percent, tantalum in a concentration of 0.1 to 1.0 weight percent, or up to 2.0 weight percent of aluminum alone or in combination with elements of the aforementioned group.
  • these steels may also contain up to 15 weight percent of nickel, up to 4.0 weight percent of silicon and up to 1.5 weight percent of manganese.
  • FIG. 1 shows a grop of semilogarithmic plots which illustrates the effect of nitriding time on the depth of the nitrided layer at various temperatures of the novel nitridable steels, according to the invention
  • FIG. 2 is a graph which illustrates the hardness of the nitrided layer of the nitridable steels according to the invention as a function of the free titanium content thereof;
  • FIG. 3 is a group of curves which illustrate hardness as a function of reduction in height brought about by cold rolling of nitridable steels according to the invention
  • FIG. 4 is a group of graphs which illustrates nickel and silicon plus manganese alloying and also their combined effect on the strength properties of nitridable steels according to the invention
  • FIG. 5 is a group of graphs which illustrates profiles of a web made by a nitridable steel according to the invention before and after nitriding;
  • FIG. 6 is a graph illustrating the hardness of the nitrided layer as a function of the distance from the surface of nitridable steel according to the invention.
  • the complex process of forming parts by severe cold flow and hardening them to a high surface hardness by nitriding is enabled to be performed by the cold formable-nitridable steels provided according to the invention.
  • These steels are characterized by a very low carbon content and an alloying element that forms a sub stitutional solid solution with iron.
  • this alloying element forms a stable carbide and thereby depletes the iron of carbon in interstitial solid solution and forms a very stable nitride with the nitrogen diffusion into the iron, the size of the nitride particle being formed in annealed or cold worked iron being very small (max 40 A) thereby imparting great hardness to the iron.
  • the alloying element forms intermetallic compounds with nickel or silicon thereby providing a capability for overall precipitation hardening.
  • the novel steels, provided according to the invention may have additional alloying elements to increase strength. They comprise the following compositions, with the balance iron.
  • the reason for this range of carbon is that, since carbon hinders both the diffusion of nitrogen and plastic deformation and because the intent is to bind even the smallest quantities of the carbon in a stable carbide form, the carbon content of the steel has to be as small as possi' ble to prevent isolation of too much of the carbide forming alloying element, and the formation of large quantities of carbides.
  • the stability of the nitrides in these groups of elements is quite great and increases progressively from titanium to hafnium and also from vanadium to tantalum.
  • the solubility of these Group IV.B and Group V.B elements in iron at the nitriding temperatures however decreases progressively from titanium to hafnium and from vanadium to tantalum.
  • titanium, niobium and vanadium are the most significant alloying elements of those set forth.
  • all of the elements of Group [VB and Group V.B set forth hereinabove form intermetallic compounds with iron and with nickel to provide a capability for overall precipitation hardening.
  • titanium group (lV.B) and the vanadium group (VB) on nitridability Considering the effect, for example, of titanium on nitridability, first, during the alloying process titanium forms titanium carbide, TiC, with the small amount of carbon present in the iron and thereby depletes it from carbon in solid solution. Consequently, in the nitriding step, the nitrogen diffuses into the alloy almost as rapidly as it would in pure iron and the times required for nitriding are quite short as compared to the times required for nitriding for conventional nitridable steels having a medium carbon content.
  • FIG. I there are shown semilogarithmic plots at 500, 550 and 600C of the effect of nitriding time on the depth of the nitrided layer at various temperatures.
  • the abscissa is hours and the ordinates are depths in mils.
  • the alloy which is considered is one that contains 0.03 weight percent of carbon, 0.53 weight percent of titanium, 3.5 weight percent of nickel, 0.3 weight percent of silicon and 0.4 weight percent of manganese. It is to be noted that because the atomic weight of titanium is 48 and that of carbon is 12, 5
  • the weight percent of titanium should be at least four the hardness to the nitrided layer.
  • the maximum surface hardness of nitrided iron binary alloys containing different nitride forming alloying elements is approximately inversely related to the nitride particle size which is formed.
  • irontitanium alloys include irontitanium alloys,
  • the hardness of the nitrided layer depends upon the quantity of the small TiN particles. It has been found that the hardness of the nitrided layer depends linearly upon the titanium content of the alloy and is 5001 HV (Vickers Hardness) for the titanium percentage range set forth hereinabove, i.e., 0.2 3.0 weight percent (at 0.03 percent C).
  • FIG. 2 there is shown a graph which sets forth the hardness of the nitrided layer as a function of the free titanium content of the alloy. Because of this effect. i.e., dependency upon the titanium content, the control of the hardness of the nitrided layer within a wide range is readily attained by concomitantly varying the titanium content of the alloy.
  • titanium first removes the yield point and produces a non-strain-aging steel; and secondly assures easy glide on slip planes whereby relatively large plastic deformation can take place with little work hardening.
  • FIG. 3 comprises a series of curves which show the results of cold rolling tests on some examples of the novel steels.
  • the abscissa is percent reduction in height brought about by cold rolling and the ordinates are Vickers Hardness.
  • Precipitation hardening of iron-titanium alloys containing less than 4 percent Ti is also possible provided that nickel or silicon is present in sufficient concentrations.
  • the constituent which causes precipitation hardening is Ni Ti or titanium silicide.
  • the tensile strength of iron 0.03 percent C 0.75 percent Ti is increased from 42,000 psi to 95,000 psi while the yield strength is increased from l6,000 psi to 82,000 psi by the addition of 5 percent nickel, 0.3 percent silicon and 0.4 percent manganese.
  • the structure of the alloys is ferrite and a small amount of TiC prior to nitriding. After nitriding, the structure of the nitrided layer is ferrite, TiN and a small amount of TiC. These alloys have a very fine grain size ASTM 8-10 which is substantially insensitive to overheating.
  • Nickel 3-l5 wt pct Alloys with 3-15 weight percent nickel content coupled with 1.5 3.0 weight percent titanium content readily lend themselves to precipitation hardening.
  • the constituent which can be employed to cause such precipitation hardening is Ni Ti (or one of the following, viz., Ni,N b, Ni lr, Ni,llf, Ni v, Ni Ta).
  • the alloy is solution annealed at l000C, water quenched, subsequently cold formed, and then manufactured into the final desired shape.
  • the precipitation hardening of the core and the nitriding of the case take place simultaneously (and in the case in competition for titanium) in the machined part in one heat treatment, typically at 500C for 5 hours.
  • an iron alloy containing 2 percent Ti and 5 percent Ni after such a heat treatment has a 155,000 psi core strength while the maximum hardness of the nitrided layer is 1200 HV.
  • These precipitation hardened nitridable steels which can be formed by cold flow processes, are advantageously utilizable for tools, dies, etc.
  • the structure of the steels is ferrite Ni Ti some TiC in the core, and ferrite Ni Ti TiN some TiC in the nitrided case.
  • the sulphur and phosphor content of the alloys is as for any alloyed steel
  • the Nitriding Process The nitriding of the alloys may take place at any temperature between 480C and 700C. The time necessary for achieving a given layer of thickness concomitantly decreases with increasing temperature (FIG. 1 The hardness of the nitrided layer increases with increasing nitriding temperature between 500-600C. Nitriding at 650C produces a nitrided layer of somewhat less hardness than at 600C.
  • the new alloys may be nitrided in pure ammonia (NH;,) gas or any mixture of ammonia and nitrogen gases, or ammonia and hydrogen gases, provided that the gas mixture contains at least 10 percent ammonia. It is advantageous to use a relatively low percentage of ammonia concentration in order to minimize the formation of brittle iron nitrides and to increase the layer thickness.
  • FIG. 5 shows the profile of a web taken with a suitable recorder before and after nitriding. It is to be noted that both profiles are parallel. The growth is 0.0002 inch, such growth resulting from the sum of two 0.010 inch thick nitrided layers on the opposite sides of the web.
  • EXAMPLE 1 Type made for a high speed line printer is manufactured from an alloy comprising from 0.005 to 0.03 percent C, 0.5 0.75 percent Ti, 3.5 percent Ni, 0.3 percent Si, 0.4 percent Mn, and the balance iron.
  • This steel has the following strength properties: tensile strength 78,600 psi; yield strength 62,000 psi; and elongation, 3l percent.
  • the manufacture of a type slug begins with fine flow blanking, continues with kneading of the characters and is completed by a plurality of grinding There is no measurable distortion of the type slug. The uniform growth of about 1 percent of the thickness of the nitrided layer is accounted for in the grinding operation. A tolerance of 0.0003 mil can be kept on the web.
  • the advantage ensuing from the making of this type slug in accordance with this example as compared to making it from carburizing steels is that the high cost of straightening operations to correct distortions is eliminated.
  • a gear is made of an alloy comprising 0.005 0.03 percent C, 0.75 1.0 percent Ti, 5.0 percent Ni, 0.3 percent Si, 0.4 percent Mn, and the remainder Fe.
  • the alloy has the following strength properties: tensile strength 95,000 psi; yield strength 82,000 psi; and elongation 25 percent.
  • the fatigue limit in rotating bending is as follows.
  • the gear is cut for rough dimensions and then formed by the form flow process for the final dimension and surface finish. It. is thereafter nitrided at 600C for hours to obtain a 17 mils thick layer.
  • the hardness of the nitrided layer is 900 HV or 64 R if the titanium content is 1.0 percent.
  • FIG. 6 is a curve which illustrates the hardness of the nitrided layer as a function of the distance from the surface.
  • the advantage of the novel alloys in this application is that the economical form flow" process can be employed and nitriding preserves the final dimensions on the gear. In addition, fatigue and impact strength of the gear is high.
  • a matrix for type forming is made from the alloy which comprises 0.005 0.03 percent C, 1.5 2.0 percent Ti, 6.5 percent Ni, and the remainder Fe.
  • the negative of the character is formed into the matrix by a master tool in the solution annealed (soft) alloy.
  • the overall dimensions of the matrix are obtained by forming.
  • there is applied to the tool a joint precipitation hardening and nitriding heat treatment at 500C for 5 hours.
  • the core of the tool has imparted thereto a tensile strength of l70,000 psi and the maximum hardness of the nitrided case is 1200 HV, if the titanium content is close to 2.0 percent.
  • EXAMPLE 4 An automobile body or parts of it are made of a steel comprising 0.005 0.03 percent C, 0.3 0.5 percent Ti, 0.3 percent Si, 0.4 percent Mn, and the remainder substantially Fe.
  • the automobile body is manufactured by conventional press forming technologies and, before its painting (enameling), is nitrided at 500C for 5 hours.
  • the nitriding produces an 8 mils thick corrosion resistant layer having a hardness of about 600 HV.
  • the advantages which flow from the use of the novel steels are better control of case hardness and thickness, no distortions whereby no operations are needed after the nitriding step. small and constant growth (l percent of layer thickness), and higher case hardness, i.e., a maximum of 1600 HV as against a maximum of 900 HV.
  • the nitrided layer is heat resistant and retains its hardness even up to the nitriding temperature as compared to a carburized layer which is not heat resistant.
  • the parts also are characterized by greater wear resistance both at room temperature and at elevated temperature.
  • parts made with the novel steels offer better machinability prior to nitriding and improved weldability prior to nitriding.
  • novel steels provided according to the invention are also eminently well suited for carburizing with any conventional carburizing process because of their low carbon content and titanium and nickel alloying. 1n the course of such carburizing, TiC forms and this formation provides for increased hardness and wear resistance of the surface. The Ti and Ni greatly improve the impact strength of the core and the Ni improves its machinability. Thus, some of the advantages of these new steels employed for carburizing as compared to known conventional carburizing steels are greater ease hardness and wear resistance, greater impact strength, and better machinability.
  • a steel alloy consisting essentially of 0.005 0.03 weight percent of carbon, 0.5 0.75 weight percent of titanium. 3.5 weight percent nickel, 0.3 weight percent of silicon, 0.4 weight percent manganese and the balance iron.

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US316212A 1972-12-18 1972-12-18 Nitridable steels for cold flow processes Expired - Lifetime US3887362A (en)

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US316212A US3887362A (en) 1972-12-18 1972-12-18 Nitridable steels for cold flow processes
FR7342431A FR2210671B1 (US08197722-20120612-C00042.png) 1972-12-18 1973-11-20
JP48134911A JPS4990208A (US08197722-20120612-C00042.png) 1972-12-18 1973-12-04
DE2361801A DE2361801A1 (de) 1972-12-18 1973-12-12 Nitrierbare staehle

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1172454A1 (en) * 2000-07-04 2002-01-16 Mazda Motor Corporation Formed member made of steel sheet and method for producing same
US20100055496A1 (en) * 2006-02-23 2010-03-04 Iljin Light Metal Co., Ltd. Steel having high strength

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2446825C2 (de) * 1974-10-01 1982-03-11 Armco Steel Corp., Middletown, Ohio Verfahren zur Herstellung eines kaltverformten Stahlbleches und von daraus hergestellten tiefgezogenen Gegenständen
GB8608717D0 (en) * 1986-04-10 1986-05-14 Lucas Ind Plc Metal components
DE102008026154A1 (de) * 2008-05-30 2009-12-03 Bayerische Motoren Werke Aktiengesellschaft Stahllegierung hoher Festigkeit

Citations (4)

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US2736648A (en) * 1952-03-06 1956-02-28 United States Steel Corp Low metalloid enameling steel and method of producing same
US3110635A (en) * 1961-07-24 1963-11-12 Lukens Steel Co Normalized alloy steels
US3162751A (en) * 1962-09-24 1964-12-22 Robbins Lawrence Welding electrode
US3239332A (en) * 1962-03-09 1966-03-08 Fuji Iron & Steel Co Ltd Electric alloy steel containing vanadium and copper

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Publication number Priority date Publication date Assignee Title
DE547965C (de) * 1926-06-03 1932-04-05 Fried Krupp Akt Ges Herstellung von Gegenstaenden, die in den Randschichten durch Versticken gehaertet sind
US3472707A (en) * 1964-04-09 1969-10-14 British Iron Steel Research Alloy steels

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2736648A (en) * 1952-03-06 1956-02-28 United States Steel Corp Low metalloid enameling steel and method of producing same
US3110635A (en) * 1961-07-24 1963-11-12 Lukens Steel Co Normalized alloy steels
US3239332A (en) * 1962-03-09 1966-03-08 Fuji Iron & Steel Co Ltd Electric alloy steel containing vanadium and copper
US3162751A (en) * 1962-09-24 1964-12-22 Robbins Lawrence Welding electrode

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1172454A1 (en) * 2000-07-04 2002-01-16 Mazda Motor Corporation Formed member made of steel sheet and method for producing same
US6723175B2 (en) 2000-07-04 2004-04-20 Mazda Motor Corporation Formed member made of steel sheet and method for producing same
US20100055496A1 (en) * 2006-02-23 2010-03-04 Iljin Light Metal Co., Ltd. Steel having high strength

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JPS4990208A (US08197722-20120612-C00042.png) 1974-08-28
DE2361801A1 (de) 1974-06-20
FR2210671A1 (US08197722-20120612-C00042.png) 1974-07-12
FR2210671B1 (US08197722-20120612-C00042.png) 1976-11-19

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