EP0508574A1 - Gegenstand aus martensitisches rostfreies Stahl und Verfahren zu ihrer Herstellung - Google Patents

Gegenstand aus martensitisches rostfreies Stahl und Verfahren zu ihrer Herstellung Download PDF

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Publication number
EP0508574A1
EP0508574A1 EP92301473A EP92301473A EP0508574A1 EP 0508574 A1 EP0508574 A1 EP 0508574A1 EP 92301473 A EP92301473 A EP 92301473A EP 92301473 A EP92301473 A EP 92301473A EP 0508574 A1 EP0508574 A1 EP 0508574A1
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EP
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Prior art keywords
amount
weight percent
stainless steel
hardness
hrc
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Application number
EP92301473A
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English (en)
French (fr)
Inventor
Kenneth E. Pinnow
Carl J. Dorsch
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Crucible Materials Corp
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Crucible Materials Corp
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Publication of EP0508574A1 publication Critical patent/EP0508574A1/de
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten

Definitions

  • the invention relates to a martensitic stainless steel article used for anchoring molds and dies and to a method for producing the same.
  • Molds and dies used to produce parts made from materials such as plastic are anchored in place during operation by frames, holder blocks, backers, and similar articles.
  • These articles are usually made from steel of a composition exhibiting high strength and toughness to withstand the stresses incident to these applications and to provide sufficient service life.
  • the steel must also have good machinability to facilitate manufacture of these articles and must be easily heat-treatable in relatively large section sizes to the necessary hardness limits.
  • Typical steels used in the manufacture of frames and holder blocks are prehardened within the hardness range of about 30 to 40 Rockwell C (HRC). This eliminates the need for heat-treatment by the user, and avoids the distortion normally encountered in heat-treating of machined articles.
  • the hardness range of 30 to 40 HRC is significant, because the machinability of most steels at hardnesses above 40 HRC is reduced to a level that makes the required machining too expensive for most applications. Although lowering the hardness of the steel improves machinability, at hardnesses below about 30 HRC the steel lacks sufficient mechanical strength for these intended applications.
  • the low-alloy carbon steels conventionally used for the production of holder blocks such as the sulfur-bearing modifications of AISI 4140 and AISI 5150, provide an excellent combination of mechanical properties, in combination with good machinability. They, however, lack sufficient corrosion resistance to resist rusting and other forms of corrosion during both service and storage. This corrosive attack reduces the operating safety, efficiency and service life and moreover requires that the holder blocks and frames be covered with a protective coating when they are not in use.
  • a number of corrosion resistant steels have been evaluated as replacements for the conventional low-alloy carbon steels used in holder block applications.
  • High quality stainless mold steels such as AISI Type 414, AISI Type 420, and those disclosed in U.S. Patent No. 3,720,545 have been considered; however, they are not widely used for holder block applications because of their cost, properties, and comparatively poor machinability.
  • AISI Type 420 and AISI Type 430 have been developed.
  • Another related object of the invention is to provide a method for producing a martensitic stainless steel article having these characteristics by the use of a simple hardening and tempering heat-treatment.
  • a martensitic stainless steel article having an improved combination of strength, toughness, corrosion resistance, and machinability may be produced by controlling carbon and nitrogen to achieve the desired hardness.
  • Sulfur is controlled in accordance with carbon plus nitrogen to maintain a drill machinability rating equal to or greater than 100 (when compared to a commercial stainless holder block steel).
  • sulfur must be increased with increases in the carbon and nitrogen content.
  • Chromium, and also nickel, are present for maintaining corrosion resistance.
  • Molybdenum is also added for corrosion resistance and specifically to counteract the adverse effects of increased sulfur in this regard. Consequently, molybdenum is increased with increased sulfur contents.
  • a martensitic stainless steel article which may be used for holder blocks, frames, backers, and similar articles for anchoring molds and dies, is of a composition within the limits set forth in Table 1.
  • the article is characterized by a hardness within the range of 30 to 40 HRC, preferably 35 to 40 HRC for higher strength applications.
  • steel in accordance with the composition limits set forth in Table I is austenitized at a temperature within the range of 1500 to 1750°F for about 1 hour per inch of thickness and either oil quenched or air cooled to achieve a martensitic structure. Thereafter, the article can be tempered or stress-relieved at a temperature between about 500 and 850°F for about 1 hour per inch of thickness and for a minimum of 2 hours. After these heat treatments, the articles will exhibit a hardness within the range of 30 to 40 HRC, preferably 35 to 40 HRC for high strength applications, and a drill machinability rating equal to or greater than 100.
  • the article after tempering in addition exhibits a corrosion rate in inches per year of less than 9 when tested in accordance with the procedure disclosed hereinafter.
  • Stainless steel holder blocks are generally made by hot rolling or forging an ingot to slab or billet that is subsequently heat-treated to the desired final hardness and then sawed and machined into blocks of the required shapes and dimensions. Less commonly, the holder blocks are cut and rough machined from fully annealed slabs or billets, heat-treated separately to the desired hardness, and then machined to final shape.
  • the hardness typical of standard holder block applications ranges from about 30 to 35 HRC, whereas that for high strength holder block applications ranges from about 35 to 40 HRC. In order to attain these hardnesses without undue cost or difficulty, it is essential that the steel used in the holder block be readily heat-treatable to the required hardness levels.
  • FIG. 2 shows that steel holder blocks produced in accordance with the invention and within the composition limits given in Table I provide the desired hardnesses in both the as-hardened condition and when tempered or stress-relieved over a broad range of temperatures.
  • a steel holder block made from Heat V1056 containing 0.043% carbon plus nitrogen achieves a hardness well within the range needed for standard holder blocks (30 to 35 HRC) in the as-hardened condition and also when tempered or stress relieved at temperatures up to about 850°F.
  • a holder block made from Heat V1020 with 0.079% carbon plus nitrogen achieves a hardness well within the range 35 to 40 HRC needed for high strength holder blocks in the as-hardened condition and also when tempered or stress relieved over a wide range of temperatures.
  • steel holder blocks produced within the scope of the invention can be austenitized from temperatures as low as about 1550°F, which achieves considerable energy savings in heat-treatment.
  • the chemical composition of the steels used in the holder blocks of this invention it is necessary within the composition ranges given in Table I to control their overall composition so that the holder blocks will be substantially fully martensitic in the as-hardened condition.
  • the composition of the steels be balanced with respect to the austenite forming elements, such as carbon, nitrogen, nickel, and manganese, and the ferrite forming elements, such as chromium, molybdenum, and silicon, to minimize the formation of delta ferrite. Large amounts of delta ferrite are detrimental in the steel from the standpoint of reducing the hardness and toughness of holder blocks made therefrom.
  • the hardness of the steels used in the holder blocks of the invention in the as-hardened condition is primarily a function of the carbon plus nitrogen content. To obtain the desired hardnesses within the range of 30 to 40 HRC, it is therefore necessary to control the carbon and nitrogen contents within the ranges indicated in Table I. With a carbon plus nitrogen content that is too low, the holder blocks will not achieve the minimum desired strength and hardness; with a carbon plus nitrogen content that is too high, the holder blocks will exceed the desired maximum hardness and exhibit unacceptable machinability.
  • Manganese is a desirable element in the steels used in the holder blocks. Manganese imparts hardenability and, in combination with sulfur, is also present for purposes of improving machinability through the formation of manganese sulfide. Also, manganese is an austenite forming element and can be used to partially replace nickel in the steel for composition balance and to thereby reduce steel costs.
  • Silicon is used in steelmaking for deoxidation and increasing chromium recovery. It also slightly improves corrosion resistance, but is a ferrite forming element and thus increases the amount of costly nickel or manganese needed to obtain a fully martensitic structure.
  • Nickel is required within the indicated ranges to obtain the desired austenite-ferrite balance and to thereby obtain a substantially fully martensitic structure in the holder blocks. It also improves corrosion resistance; but is a costly element, and for this reason is not desirable above the indicated ranges.
  • Chromium is essential for corrosion resistance, but above the indicated amounts increases the amount of nickel, manganese, and other austenite forming elements that are required to be present to avoid the formation of delta ferrite and to obtain a substantially fully martensitic structure in the holder blocks.
  • Molybdenum is an expensive alloying element, but in small amounts and together with chromium has a very beneficial affect on the corrosion resistance of the holder blocks, and a minimum of about 0.25% is necessary for reducing the adverse effects of sulfur on this property. Consequently, molybdenum generally should be increased in the presence of increased sulfur for this purpose.
  • Sulfur is used for improving machinability, but decreases notch toughness and corrosion resistance.
  • sulfur should be limited to about 0.10%; but when greater machinability is desired, it can be increased to about 0.25% without lowering toughness and corrosion resistance to unacceptable levels.
  • Molybdenum should be increased with increased sulfur to maintain corrosion resistance at the desired level.
  • Copper is a common residual element in stainless steel melting, and is useful for controlling the austenite-ferrite balance. However, in amounts greater than about 1.0% it can have an undesirable hardening effect during tempering of the holder blocks.
  • Ingots of the experimental holder block steels were hot worked from a reheating temperature of about 2150°F to bar stock from which samples were taken for metallographic evaluation and testing. Except for those samples used to determine attainable hardness, all the test samples were austenitized at 1550°F, air cooled to room temperature, and then tempered for two hours at 550°F. None of the experimental holder block steels were found to contain any delta ferrite after this heat-treatment.
  • the samples of the commercial stainless holder block steel were received in the prehardened condition at a hardness of 33 HRC. In order to test this material at a higher hardness of 38 HRC, samples of the commercial holder block steel were austenitized at 1850°F, oil quenched to room temperature and then tempered for 2 hours at 975°F.
  • Figure 3 The attainable hardnesses of the experimental holder block steels in the as-hardened condition are plotted in Figure 3 as a function of their carbon plus nitrogen contents.
  • the specimens for these tests were austenitized for 15 minutes at 1600°F and then air cooled to room temperature. Allowing for some normal scatter in the results of the hardness tests, Figure 3 shows that the attainable hardness of the steels used in the holder blocks of the invention has a strong relationship with their carbon plus nitrogen contents.
  • Figure 3 shows that the carbon plus nitrogen contents of the holder blocks of the invention must be controlled in a range between about 0.02 to 0.09%.
  • the carbon plus nitrogen content of the steels used in the holder blocks of the invention must be controlled from about 0.02 to 0.06% and from about 0.06 to 0.09%, respectively.
  • the impact properties of the steels used in the holder blocks of the invention are still significantly better than that of the commercial stainless holder block steel.
  • the notch toughness of Alloy V1055 with 0.20% sulfur is 15.0 ft-lb in the longitudinal direction; whereas, that of the commercial stainless holder block steel (Alloy 90-45) with 0.09% sulfur is only 5.0 ft-lb.
  • the tensile properties of the steels used in the holder blocks of this invention are largely a function of their hardness and are at least comparable to those of the commercial stainless holder block steel at the same hardness.
  • About the same mechanical properties and notch toughness are obtained for the higher manganese and lower nickel containing experimental holder block steels (Alloys V1022 and V1055) as for the comparable steels with higher nickel and lower manganese (Alloys V1020 and V1056).
  • manganese can be used to replace part of the nickel in the steels used in the holder blocks of this invention.
  • the steels used in the holder blocks of this invention must contain at least 0.05% sulfur.
  • the holder block steels of the invention at a hardness of 38 HRC must contain at least 0.10% sulfur.
  • corrosion rate in inches per year refers to the corrosion rate exhibited by an alloy article subjected to this test procedure.
  • These tests were conducted on specimens that were passivated and not passivated prior to testing in a solution of 20% nitric acid containing 3% by weight of potassium chromate at 120°F for 1/2 hour.
  • the other test was a salt spray test in which specimens were exposed for three hours at 90°F to vapors generated from an aqueous solution containing 2.5% by weight of sodium chloride. In this latter test, material performance was ranked visually by estimating the percentage of the surface area that was affected by corrosion.
  • Table V Photographs of five of the specimens subjected to the salt spray test are shown in Figure 5.
  • Alloys V1009, V1020, and V1020 The relative corrosion resistance of three of the experimental holder block steels (Alloys V1009, V1020, and V1020) and of two steels (Alloys V1087 and 90-45) outside the scope of the invention is further illustrated in Figure 5.
  • Alloys V1009, V1020, and V1021 having compositions within the scope of the invention, show considerably better corrosion resistance in the salt spray test than do Alloys V1087 and 90-45.
  • the composition of Alloy V1087 is similar to that of Alloys V1009 and V1020, except that it contains less than 0.01% molybdenum.

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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 Articles (AREA)
EP92301473A 1991-04-11 1992-02-21 Gegenstand aus martensitisches rostfreies Stahl und Verfahren zu ihrer Herstellung Withdrawn EP0508574A1 (de)

Applications Claiming Priority (2)

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US683825 1984-12-19
US68382591A 1991-04-11 1991-04-11

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JP (1) JPH05171366A (de)
CA (1) CA2061765A1 (de)
MX (1) MX9201431A (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1233080A1 (de) * 2001-02-14 2002-08-21 BÖHLER Edelstahl GmbH Stahl für Kunststofformen und Verfahren zur Wärmebehandlung desselben
FR2872825A1 (fr) * 2004-07-12 2006-01-13 Industeel Creusot Acier inoxydable martensitique pour moules et carcasses de moules d'injection
WO2009024069A1 (fr) * 2007-08-15 2009-02-26 Baofeng Jin Alliage de fe
CN102719627A (zh) * 2012-07-04 2012-10-10 中原特钢股份有限公司 一种高铬马氏体不锈钢的热处理方法

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5362337A (en) * 1993-09-28 1994-11-08 Crs Holdings, Inc. Free-machining martensitic stainless steel

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1478469A (fr) * 1966-02-28 1967-04-28 Crucible Steel Co America Aciers inoxydables se prêtant facilement à un usinage
US3720545A (en) * 1971-08-20 1973-03-13 Crucible Inc Steel mold and method for producing the same
EP0039052A1 (de) * 1980-04-28 1981-11-04 Kabushiki Kaisha Toshiba Martensitischer rostfreier Gussstahl mit guter Beständigkeit gegen Kavitationserosion
EP0170598A1 (de) * 1984-07-04 1986-02-05 Ugine Savoie Verfahren zur Herstellung von Stäben oder Walzdraht aus martensitischem rostfreiem Stahl und so hergestellte Gegenstände

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1478469A (fr) * 1966-02-28 1967-04-28 Crucible Steel Co America Aciers inoxydables se prêtant facilement à un usinage
US3720545A (en) * 1971-08-20 1973-03-13 Crucible Inc Steel mold and method for producing the same
EP0039052A1 (de) * 1980-04-28 1981-11-04 Kabushiki Kaisha Toshiba Martensitischer rostfreier Gussstahl mit guter Beständigkeit gegen Kavitationserosion
EP0170598A1 (de) * 1984-07-04 1986-02-05 Ugine Savoie Verfahren zur Herstellung von Stäben oder Walzdraht aus martensitischem rostfreiem Stahl und so hergestellte Gegenstände

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1233080A1 (de) * 2001-02-14 2002-08-21 BÖHLER Edelstahl GmbH Stahl für Kunststofformen und Verfahren zur Wärmebehandlung desselben
US6893608B2 (en) 2001-02-14 2005-05-17 Boehler Edelstahl Gmbh Steel for plastic molds and process for their heat treatment
KR100500263B1 (ko) * 2001-02-14 2005-07-11 뵈러 에델스탈 게엠베하 마레이징 강 및 그 마레이징 강의 열처리 방법
CN100558926C (zh) * 2001-02-14 2009-11-11 博哈里尔特种钢有限公司 一种塑料成型模具用钢和其热处理方法
FR2872825A1 (fr) * 2004-07-12 2006-01-13 Industeel Creusot Acier inoxydable martensitique pour moules et carcasses de moules d'injection
WO2006016043A3 (fr) * 2004-07-12 2007-01-25 Industeel Creusot Acier inoxydable martensitique pour moules et carcasses de moules d'injection
US9267197B2 (en) 2004-07-12 2016-02-23 Industeel France Martensitic stainless steel for injection moulds and injection mould frames
WO2009024069A1 (fr) * 2007-08-15 2009-02-26 Baofeng Jin Alliage de fe
CN102719627A (zh) * 2012-07-04 2012-10-10 中原特钢股份有限公司 一种高铬马氏体不锈钢的热处理方法
CN102719627B (zh) * 2012-07-04 2013-11-06 中原特钢股份有限公司 一种高铬马氏体不锈钢的热处理方法

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CA2061765A1 (en) 1992-10-12
MX9201431A (es) 1992-10-01
JPH05171366A (ja) 1993-07-09

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