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EP1784519A2 - Acier de cementation et son procede de production - Google Patents

Acier de cementation et son procede de production

Info

Publication number
EP1784519A2
EP1784519A2 EP05773330A EP05773330A EP1784519A2 EP 1784519 A2 EP1784519 A2 EP 1784519A2 EP 05773330 A EP05773330 A EP 05773330A EP 05773330 A EP05773330 A EP 05773330A EP 1784519 A2 EP1784519 A2 EP 1784519A2
Authority
EP
European Patent Office
Prior art keywords
ppm
case
content
weight
steel according
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Withdrawn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
EP05773330A
Other languages
German (de)
English (en)
Inventor
Hans Roelofs
Ulrich Urlau
Martin Kuhnemund
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.)
Swiss Steel AG
Original Assignee
von Moos Stahl AG
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 von Moos Stahl AG filed Critical von Moos Stahl AG
Publication of EP1784519A2 publication Critical patent/EP1784519A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/076—Use of slags or fluxes as treating agents
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • the invention relates to a case steel according to the preamble of the claim
  • Case hardening steels are low-alloyed, relatively low-carbon stainless steels intended for carburizing or carbonitriding and subsequent hardening. Such steels have, after this treatment, a high hardness facing and a tough core.
  • case steel For carburizing the case steel must be kept at a temperature above 900 0 C for a long time. Under these conditions, unwanted austenite grain growth takes place. The tendency for such grain growth is reduced in the known case steels by alloying these steels with aluminum (typically> 0.02% aluminum). Aluminum forms precipitates (nitrides) in the steelmaking and processing process, which inhibit grain growth. For case-hardening steels, which are to be hardened at even higher temperatures, niobium and / or titanium are added in addition to the aluminum.
  • Titanium in contrast to aluminum, leads to larger precipitations or to a low particle density, which makes the replacement of aluminum by titanium appear unfavorable.
  • a generic aluminum-rich case hardening steel and a process for des ⁇ sen production are described in EP O 933 440 A1. This contains 0.015 to 0.04 wt .-% aluminum, 0.005 to 0.04 wt .-% niobium and a low Sau ⁇ erstoffgehalt of ⁇ 25 ppm.
  • case hardening steels can be further improved by the addition of toxic additives such as lead or bismuth.
  • toxic additives such as lead or bismuth.
  • the use of these elements is undesirable.
  • the object of the invention is to provide an improved case steel, with which in particular the above disadvantages are avoided.
  • Another object of the invention is to provide a method for producing a Ein ⁇ sentence steel.
  • the case hardening steel according to the invention has a weight fraction of 0.14 to 0.23% carbon, 0.2 to 0.4% silicon, 0.6 to 1.7% manganese, up to 0.035% phosphorus, up to 1.5% nickel, 0.7 to 1.7% chromium, up to 0.5% molybdenum, bis to 0.04% titanium, 0.01 to 0.02% nitrogen and 0.02 to 0.06% niobium and other customary admixtures on.
  • the fact that the ⁇ steel according to the invention has an oxygen content of 40 to 70 ppm and an aluminum content of less than 45 ppm, resulting in comparison to the known aluminum-alloyed case-hardened a significantly improved machinability, without the known mechanical and technological properties of this Steels are adversely affected.
  • the case hardening steel according to the invention contains glassy, non-crystalline silicate inclusions, which do not lead to problems when casting the melt. This allows a more controlled process control in continuous casting. In the machining, the silicate inclusions are harmless in contrast to the hard abrasive Al 2 O 3 -rich inclusions and under certain conditions (at high Zerspa ⁇ nungstemperaturen) even lubricating.
  • non-crystalline silicate precipitates are already being used selectively in other non-aluminum-alloyed steels such as spring steels or automatic steels.
  • spring steels the improvement of the fatigue properties is in the foreground, while in the case of free cutting steels the improved machinability is important.
  • the known inclusion-modified free-cutting steels have significantly higher oxygen contents (> 70 ppm) than the case-hardening steels described here.
  • the proportionate ratio zwi ⁇ low melting oxides of the secondary deoxidation (of the type MnO-SiO 2 -AI 2 O 3 ) and Ca-treated oxide precipitations of the primary De ⁇ soxidation (of the type CaO-SiO 2 -AI 2 O 3 ) is included the free-cutting steels differently.
  • case-hardening steels according to the invention despite the comparatively low oxygen contents of 40-70 ppm and the small number of inclusions of secondary deoxidation (about 20 ppm), are significantly easier to machine than existing case-hardened steels.
  • the mentioned spring and free-cutting steels are not subjected to a heat treatment of more than 900 ° C. for several hours, so that in these known applications no pronounced austenite grain growth is to be expected. This is different in the case of stäh ⁇ .
  • carbide or nitride precipitates must be present before case hardening, which suppresses the growth of austenite grains.
  • Aluminum can not be dispensed with without replacement. In the case of case-hardening steel according to the invention, aluminum is replaced by 0.02 to 0.06% by weight of niobium. The weight fraction of niobium is preferably 0.04 to 0.06% by weight.
  • Nb-containing precipitates For aluminum to be successfully replaced by niobium, fine Nb-containing precipitates must be produced in sufficient numbers. For this purpose, a suitable process control must be selected during the hot forming of the steel.
  • the case hardening steel produced according to the invention has a volume fraction of Nb-containing precipitates with a mean particle diameter ⁇ 100 nm of> 100 ppm.
  • EP 1 312 689 A1 describes an aluminum-poor steel for use with machine components. This contains ⁇ 90 ppm of aluminum and 10 to 100 ppm of oxygen and various oxide inclusions with the composition CaO - Al 2 O 3 - SiO 2 - TiO 2 . In contrast to the present invention, this steel is not austenite com- pact stabilized and therefore not suitable for heat treatment such as case hardening.
  • the process according to the invention relates to the production of a use steel which contains non-crystalline oxide inclusions with 20 to 50% CaO, 35 to 65% SiO 2 and less than 25% Al 2 O 3 , where:
  • b) performs a metallurgical melting treatment with a slag whose composition has the following relative proportions by weight: 25 to 50% CaO, 25 to 50% SiO 2 , ⁇ 15% Al 2 O 3 and a ratio CaO / SiO 2 ⁇ 1.1, in order to adjust a dissolved aluminum content of ⁇ 5 ppm in the melt, and to condition present oxide inclusions;
  • This method avoids the known manufacturing problems with aluminum-alloyed case-hardened steels.
  • silicon ensures the formation of non-crystalline oxide inclusions in steel production. Higher silicon contents delay the carbide formation, which has a negative effect on the required Nb-containing precipitates. Furthermore, it is desirable to achieve the highest possible oxygen activity in the liquid steel bath. This dissolved oxygen content is precipitated during the solidification of the steel in the form of very low-melting oxides ("secondary oxidation" oxides), which further improves the machinability of the steel For these reasons, the silicon content is limited to 0.4% by weight.
  • manganese serves, on the one hand, to deoxidize the molten steel (Si-Mn deoxidation) and, on the other hand, to set mechanical-technological properties, such as strength and hardenability.
  • a minimum content of 0.6% by weight is common for case-hardening steels.
  • Manganese delays the conversion behavior and tends to segregation. Since excessively high manganese content must be expected locally with undesirable martensite contents, the manganese content should be at most 1.7% by weight.
  • a manganese content of up to 1.5% by weight, in particular of up to 1.4% by weight is used.
  • Phosphorus is a steel pest. It collects at the austenite grain boundaries and thereby deteriorates toughness and fatigue properties. For this reason, the Phoshorgehalt is limited to 0.035 wt .-%. Nickel stabilizes the austenite, so that the Austenitzerfall is shifted to lower temperatures. This leads to a finer structure and improves the cold toughness of the steel. Furthermore, nickel improves the hardenability of the steel. For case-hardening steels, a nickel content of up to 1.5% by weight is usual.
  • chromium By adding chromium, the hardenability of the steel is adjusted in the desired range. Further, chromium improves the wear resistance of case hardened parts. Too high a chromium content degrades the cold formability.
  • the specified chromium content of 0.7 to 1.7% by weight is typical for case-hardening steels.
  • Molybdenum improves tempering resistance, wear after case hardening and hardenability. For reasons of economy, molybdenum is used sparingly and is limited to 0.5% by weight in case of case-hardening steels.
  • Titanium forms Ti (CN) precipitates. These arise at high temperatures and tend to coarseness. For this reason, titanium is limited to 0.04%. Titanium alone can not produce sufficient precipitate density to prevent coarse grain formation during case hardening.
  • niobium leads to the formation of Nb (CN) precipitates. If these are small enough and present in sufficient numbers, coarse grain formation during case hardening can be suppressed. In order for sufficient precipitates to be formed, at least 0.02% by weight of niobium must be alloyed. The addition of niobium alone does not guarantee an effective distribution of the excretions.
  • the carbon and nitrogen content, the temperature control and the hot forming are to be coordinated so that a Volumen ⁇ share of Nb-containing precipitates with an average particle diameter results in> 100 nm of> 100 ppm. By lowering the rolling end temperature during conventional hot rolling, a finer separation distribution is generally achieved.
  • Nb (CN) precipitates arise even at high temperatures (from about 1300 0 C), they have an adverse effect on the casting behavior of these steels.
  • the niobium content is therefore limited to 0.06%.
  • Nb (CN) nitrogen must be present.
  • the free nitrogen (not bound in Nb (CN)) is a steel pest and causes embrittlement.
  • the optimum nitrogen content depends on the niobium and titanium content. Below 0.01% by weight, too little precipitate forms, above 0.02% by weight there is in any case an excess of nitrogen.
  • the preferred case hardening steel defined in claim 2 contains oxidic inclusions with the following relative proportions by weight: 20 to 50% CaO, 35 to 65% SiO 2 and less than 25% Al 2 O 3 .
  • the manganese content is 0.6 to 1.5 wt .-%, in particular 0.6 to 1.4 wt .-% and according to claim 4, the niobium 0.04 to 0.06 wt .-% is.
  • the machinability of the case-hardening steel produced according to the invention improves even without additional addition of sulfur. This allows the setting of very low sulfur contents ( ⁇ 50 ppm), which is advantageous for very high demands on the fatigue behavior of the steel component.
  • the sulfur content is 0.02 to 0.2% by weight.
  • the chipping properties chip breakage, tool life
  • the optimum sulfur content depends on the required mechanical and technological properties such as notched impact strength and alternating strength. At a sulfur content of 0.12 to 0.17% by weight, optimum machinability is expected without significantly impairing the mechanical-technological properties in the heat-treated state.
  • the addition of calcium according to claim 8 makes it easier to achieve the desired composition of the oxide inclusions.
  • the case steel then typically contains 5 to 10 ppm calcium.
  • the addition of larger amounts of calcium the sulfides are modified (there are large sulfides with nied ⁇ rer plasticity), which has an advantageous effect on the Spanbrüchmaschine. Since calcium has a negative effect on the pourability of the melt due to the formation of CaS, the calcium content must be limited to 50 ppm.
  • the machinability can be improved similarly to the addition of lead or bismuth.
  • the case hardening steel can be alloyed with 5 to 400 ppm by weight of tellurium or selenium. These elements enter with manganese or, if present, with lead compounds which have melting points below 200 ° C. ("liquid Due to the similar crystal structure, manganese lanthanide or selenide act as seedlings for the formation of sulfides, which results in larger amounts of sulfides and promotes chip breakage.
  • suitable metallurgical measures shall be taken: Use low-aluminum alloying agents; the metallurgical vessels used (eg the pans) must not be contaminated with aluminum, and a ladle slag must be selected which can take up Al 2 O 3 from the melt.
  • the oxide precipitates produced in steel production are non-crystalline or glassy and have the lowest possible softening point or low viscosity. In the present case, this is achieved by producing inclusions of the pseudo-wollastonite type.
  • the production parameters must be set within narrow limits.
  • the five most important steps for the execution of the invention are: A. avoiding aluminum uptake in the steel bath as is possible, for example, by the use of aluminum-containing alloying agents;
  • the melt should be in thermodynamic equilibrium with the slag.
  • the predominant deoxidation is silicon deoxidation.
  • thermodynamic simulation programs To monitor the process, it is advisable to use thermodynamic simulation programs.
  • a calcium treatment can be carried out.
  • the amount of calcination addition depends on the oxygen content. If sulfur is added to the steel, it is advisable to add it after the calcium treatment, otherwise part of the calcium will form CaS.
  • Type 16MnCrS5 described in an electric steelworks: 1. Electric oven
  • slag formers and alloying elements are already added during the pouring of the melt into the ladle vessel. If a large amount of follow-up slag is to be expected, the slag should be removed after parting off and a clearly defined ladle slag should be applied.
  • the melt arrives at the pan treatment station with the following chemical composition:
  • the melt Before a meaningful melt treatment can be started, the melt must be homogenized by rinsing and the temperature losses must be compensated again.
  • the slag should be in thermodynamic equilibrium with the melt.
  • the FeO content of the slag should be ⁇ 2.5% and the oxygen activity of the melt should be constant.
  • the slag can be reduced by adding CaC 2 .
  • the cover slag is adjusted by addition of the synthetic slag and taking into account the deoxidation reactions during the tapping of the melt so that the following relative proportions by weight are present:
  • This chemical composition is located at the SiO 2 -side edge of the given target area in the ternary phase diagram. Since not all excretions reach the same level come many weight, many inclusions are closer to the Si ⁇ 2 corner (since Si deoxidation prevails).
  • Niobium is added during pan treatment (to 0.05% by weight).
  • the fine grain stability of the case hardening steel is only ensured by the addition of niobium, if a fine distribution of Nb (CN) precipitates is produced.
  • the nitrogen content should not be less than 100 ppm. If this value is exceeded by the process control, must be embroidered.
  • calcium may be added.
  • calcium is alloyed in the form of CaSi filler wire.
  • the Ca content of the melt is 7 ppm.
  • the melt is rinsed for several minutes (for Homo ⁇ genization). Subsequently, the desired amount of sulfur is added ben (in the example 0.06 wt .-%).
  • the melt is 1575 0 C for continuous casting.
  • a 35 mm steel rod is rolled mechanically with a final rolling temperature of 880-950 0 C thermo-.
  • the rod is cooled in the temperature range of 800-600 0 C with a cooling rate of 0.2-1 K / s in air.
  • the desired Nb (CN) particles are released.
  • Particularly important for austenite grain stabilization are the particles with a mean diameter ⁇ 100 nm.
  • the volume fraction of these particles must be greater than 100 ppm.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

L'invention concerne un acier de cémentation comprenant une fraction de pourcentage en poids, de 0,14 à 0,23 % de carbone, de 0,2 à 0,4 % de silicium, de 0,6 à 1,7 % de manganèse, jusqu'à 0,035 % de phosphore, jusqu'à 1,5 % de nickel, de 0,7 à 1,7 % de chrome, jusqu'à 0,5 % de molybdène, jusqu'à 0,04 % de titane et de 0,01 à 0,02 % d'azote et d'autres mélanges utilisés pour l'acier. Cet acier contient également une fraction, exprimée en pourcents en poids, de 0,02 à 0,06 % de niobium, de préférence de 0,04 à 0,06 % de niobium ainsi qu'une teneur en oxygène de 40 à 70 ppm et une teneur en aluminium < 45 ppm et une fraction volumique de dépôt contenant du Nb ayant des particules d'un diamètre moyen < 100 nm de > 100 ppm.
EP05773330A 2004-08-26 2005-08-26 Acier de cementation et son procede de production Withdrawn EP1784519A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH14002004 2004-08-26
PCT/CH2005/000499 WO2006021123A2 (fr) 2004-08-26 2005-08-26 Acier de cementation et son procede de production

Publications (1)

Publication Number Publication Date
EP1784519A2 true EP1784519A2 (fr) 2007-05-16

Family

ID=34973952

Family Applications (1)

Application Number Title Priority Date Filing Date
EP05773330A Withdrawn EP1784519A2 (fr) 2004-08-26 2005-08-26 Acier de cementation et son procede de production

Country Status (2)

Country Link
EP (1) EP1784519A2 (fr)
WO (1) WO2006021123A2 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112831723A (zh) * 2020-12-31 2021-05-25 钢铁研究总院 一种抗高温渗碳晶粒长大的齿轮钢及控制方法

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5845354A (ja) * 1981-09-10 1983-03-16 Daido Steel Co Ltd はだ焼鋼
FR2682686B1 (fr) * 1991-10-17 1994-07-01 Vallourec Ind Acier au carbonne-manganese destine notamment au decolletage.
WO1999005333A1 (fr) * 1997-07-22 1999-02-04 Nippon Steel Corporation Acier cemente particulierement capable d'empecher la recristallisation secondaire des particules pendant la cementation, procede de fabrication, et matiere brute formee pour pieces cementees
CN1169992C (zh) * 2001-11-15 2004-10-06 住友金属工业株式会社 机械结构用钢

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO2006021123A2 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112831723A (zh) * 2020-12-31 2021-05-25 钢铁研究总院 一种抗高温渗碳晶粒长大的齿轮钢及控制方法

Also Published As

Publication number Publication date
WO2006021123A2 (fr) 2006-03-02
WO2006021123A3 (fr) 2006-04-20

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