CN105671434A - Magnesium, calcium and sulfur containing 20MnCr free-cutting gear steel and preparation method thereof - Google Patents

Magnesium, calcium and sulfur containing 20MnCr free-cutting gear steel and preparation method thereof Download PDF

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CN105671434A
CN105671434A CN201610163260.XA CN201610163260A CN105671434A CN 105671434 A CN105671434 A CN 105671434A CN 201610163260 A CN201610163260 A CN 201610163260A CN 105671434 A CN105671434 A CN 105671434A
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steel
magnesium
refining
calcium
temperature
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付建勋
徐杰
朱玉员
胡德林
张明
龚涛
李健
曹中佳
李徐
吴彦欣
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University of Shanghai for Science and Technology
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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
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0056Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using cored wires
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04Removing impurities by adding a treating agent
    • C21C7/06Deoxidising, e.g. killing
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10Handling in a vacuum
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C33/00Making ferrous alloys
    • C22C33/04Making ferrous alloys by melting
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/04Ferrous alloys, e.g. steel alloys containing manganese
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/06Ferrous alloys, e.g. steel alloys containing aluminium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/60Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00Technologies related to metal processing
    • Y02P10/20Recycling

Abstract

The invention discloses magnesium, calcium and sulfur containing 20MnCr free-cutting gear steel and a preparation method thereof. The steel is prepared from, by weight percent, 0.15%-0.25% of C, not larger than 0.12% of Si, 0.80%-1.50% of Mn, not larger than 0.035% of P, 0.02%-0.055% of S, 0.80%-1.30% of Cr, 0.015%-0.055% of Al, 0.004%-0.015% of N, 0.0006%-0.004% of Mg, 0.0006%-0.005% of Ca, not larger than 0.0025% of [O] and the balance iron and inevitable impurities. Composite modification is carried out on inclusion by adding a small quantity of calcium and magnesium elements in the refining process, and the composite inclusion with oxide (including multiple oxide) as a core is formed, wherein the core of the composite inclusion is wrapped by sulfide; splitting of the oxide to a steel substrate can be relieved, the anti-fatigue performance can be improved, and the transverse mechanical property of the steel can be improved; and the magnesium, calcium and sulfur containing 20MnCr free-cutting gear steel both good in mechanical performance and cutting performance is produced, and has large economic benefits.

Description

A kind of 20MnCr free-cutting pinion steel containing magnesium calcium sulphur and its preparation method
Technical field
The present invention relates to technical field of ferrous metallurgy, specifically a kind of 20MnCr free-cutting pinion steel containing magnesium calcium sulphur and its preparation method.
Background technology
Gear is the important transmission parts of automobile and machinery manufacturing industry, and gear is transmitting power and changing in the operational process of speed, and existing rolling between mesh tooth face, has again slip, and wheel root portion also can be subject to the effect of pulsation and alternate flexural stress. And Pinion Steel is the critical material manufacturing automobile, mechanical transmission system gear, bar class and shaft element, its specification of quality is extremely strict. In recent years, good processing characteristics (comprising hot and cold processibility and free-cutting machinability) is the important indicator that gear industry is concerned about.
Currently, the Main way that high-performance, economical Pinion Steel have become Pinion Steel technical development is developed. Current Mn-Cr system Pinion Steel is mainly used on the gear of Santana, Audi and Jetta car, and wherein the part trade mark also can be used for Fukang Car, IVECO Light-duty Vehicle and high-power marine gearbox etc. The main trade mark has 16MnCr5,20MnCr5,25MnCr5 and 28MnCr5 etc. of producing by germany volkswagen company standard. Pinion Steel should ensure that mechanical property has good machinability again, and with regard to making, the content of sulphur and oxygen in steel becomes the key parameter of pinion Steel Properties for this.
In current Pinion Steel smelting process, logical product to be passed through Calcium treatment technology, and sulfide inclusion (GB/T10561-2005 regulation is called that A class is mingled with) and oxide inclusion (GB/T10561-2005 regulation is called that B class is mingled with) to existing in molten steel carry out denaturing treatment. By Calcium treatment technology, make that molten steel exists certain calcium contents, it is possible to the dystectic fragility Al of the macrobead that deoxidation of molten steel is produced by employing aluminium2O3The low melting point calcium-aluminate that being mingled with sex change becomes calcium content higher is mingled with (12CaO 7Al2O3Deng), the inclusion of low melting point can be made to float in molten steel removal, it is possible to improve and be mingled with the nozzle clogging causing molten steel casting process because of refractory oxide, also reduce high-melting-point brittle inclusion to the impact of steel product quality simultaneously.
The present invention adds formation in steel by calcium and magnesium: oxide compound (containing composite oxides) is core, and the complex inclusion of outside parcel sulfide, can alleviate oxide compound isolating steel matrix, it is to increase anti-fatigue energy, can improve again the horizontal mechanical performance of steel. Steel inclusion, by adding the calcium magnesium element of trace to compound in sulfur-containing free-cutting pinion steel, is carried out upgrading by the present invention, under the prerequisite ensureing mechanical property, and then improves the machinability of steel.
The Chinese patent that publication number is CN102703817A discloses a kind of free-cutting pinion steel and production technique thereof, the composition (weight percent) that it is characterized in that it is: C0.14% ~ 0.22%, SiO.20% ~ 0.35%, Mn0.95% ~ 1.15%, Cr0.95% ~ 1.15%, Al0.020% ~ 0.060%, P≤0.035%, S0.012% ~ 0.030%, surplus is Fe and inevitable impurity. The place that the present patent application is different with it is: contained by this patent Pinion Steel, silicon, magnesium, calcium component (wt%) are respectively: Si≤0.12%, Mg0.0006% ~ 0.004%, Ca0.0006% ~ 0.005%.
The Chinese patent that publication number is CN102011062A discloses a kind of free-cutting pinion steel and smelting process thereof, it is characterised in that its composition (weight percent) is: carbon 0.10% ~ 0.35%, silicon 0.15% ~ 0.45%, manganese 0.60% ~ 1.50%, phosphorus 0.001% ~ 0.03%, sulphur 0.015% ~ 0.030%, chromium 0.80% ~ 1.50%, titanium 0.03% ~ 0.12%, aluminium 0.01% ~ 0.10%, nickel 0.005% ~ 0.30%, aluminium 0.005% ~ 0.20%, copper 0.005% ~ 0.20%, nitrogen 0.004% ~ 0.015%, surplus is iron. The place that the present patent application is different with it is: contained by this patent Pinion Steel, silicon, magnesium component (wt%) are respectively: Si≤0.12%, Mg0.0006% ~ 0.004%, and this patent is not containing Ti.
The Chinese patent that publication number is CN1410583A discloses a kind of calcium sulfur magnesium series free-cutting steel, the composition (weight percent) that it is characterized in that it is: C0.42% ~ 0.50%, Si0.20% ~ 0.50%, Mn1.00% ~ 1.20%, P0.01% ~ 0.04%, S0.01% ~ 0.07%, Ca0.002% ~ 0.016%, Mg0.0001% ~ 0.002%, surplus is Fe and inevitable impurity. The place that the present patent application is different with it is: contained by this patent Pinion Steel, carbon, silicon, magnesium, calcium component (wt%) are respectively: C0.15% ~ 0.25%, Si≤0.12%, Ca0.0006% ~ 0.005%, Mg0.0006% ~ 0.004%.
Summary of the invention
The present invention is directed to existing enterprise and produce in 20MnCr type Pinion Steel difference and the not problem such as Cutting free fatigue lifetime, it provides a kind of 20MnCr free-cutting pinion steel containing magnesium calcium sulphur and its preparation method. The technical problem to be solved in the present invention is: by adding Ca, Mg element of trace to the molten steel compound of refining, the sulfide inclusion in upgrading 20MnCr free-cutting pinion steel, thus improve its inclusion morphology, and then the antifatigue of steel and cutting ability.
It is an object of the invention to be achieved through the following technical solutions:
Containing 20MnCr free-cutting pinion steel and the smelting process thereof of magnesium calcium sulphur, group part (weight percentage) of steel is: C0.15% ~ 0.25%, Si≤0.12%, Mn0.80% ~ 1.50%, P≤0.035%, S0.020% ~ 0.055%, Cr0.80% ~ 1.30%, Al0.015% ~ 0.055%, N0.004% ~ 0.015%, Mg0.0006% ~ 0.004%, Ca0.0006% ~ 0.005%, [O] :≤0.0025%, surplus is iron and inevitable impurity. The interpolation of its calcium, magnesium elements realizes by feeding the iron base cored-wire containing calcium, magnesium elements after vacuum refinement operation.
The present invention provides a kind of preferred composition range especially: the 20MnCr free-cutting pinion steel containing magnesium calcium sulphur of the present invention, and group part (weight percentage) of its steel is: C0.18% ~ 0.22%, Si≤0.10%, Mn1.15% ~ 1.40%, P≤0.030%, S0.025% ~ 0.030%, Cr1.00% ~ 1.15%, Al0.018% ~ 0.025%, N0.004% ~ 0.012%, Mg0.0010% ~ 0.0028%, Ca0.0010% ~ 0.0025%, [O]≤0.0020%, surplus is iron and inevitable impurity.
The effect of each element of the present invention:
C: the strong hardness of steel and plasticity and toughness are had very important impact by the height of carbon content. In all elements, the ability that carbon improves intensity is maximum, and the strengthening effect of quenched and tempered steel is approximately 5 times of silicon by carbon, 9 times of chromium and 18 times of manganese, so for ensureing that Pinion Steel has enough intensity, hardness, must containing suitable carbon content in steel. In this 20CrMn steel, carbon content is: 0.15% ~ 0.25%.
Si: if silicon as reductor can the deoxidation degree of pinion steel, be affect the key element that steel medium sulphide content is mingled with distortion and cutting ability, be also one of element worsening cutting rolled steel performance simultaneously. Silicon can improve the hardening capacity of infiltration layer strongly, but easily grain boundary oxidation occurs in cementation process and form the netted defect of black; With the increase of alloying element addition, the martensite point decline of steel, contains abundant residues austenite in infiltration layer after making quenching, affects fatigue property and the wear resistance of part. In the application 20CrMn steel, silicone content is: Si≤0.12%.
Cr: be carbide forming element, can improve the intensity of material, hardness elastic limit, yield strength and wear resistance, can also improve hardening capacity and the corrosion resistance nature of steel simultaneously. In the application 20CrMn steel, Cr content is: 1.00% ~ 1.15%.
Mn: manganese can improve pearlitic nucleating work and change intensity of activation, reduce pearlitic nucleation rate and coarsening rate, manganese element and carbide thereof are dissolved in austenite, austenite isothermal transformation diagram is moved to right, increase supercooled austenite stability, suppress perlitic transformation, it is to increase hardening capacity, the MnS that sulphur in manganese and steel generates is a kind of important free-cutting phase, it is possible to help improve cutting ability. In order to ensure good cutting ability and mechanical property, the present invention controls the content of manganese 0.8 ~ 1.5%.
S: sulphur is one of main Cutting free element, and along with the increase of sulphur content in steel, the machinability rating of steel significantly improves. But MnS easily extends along rolling direction when hot rolling simultaneously, reduce the horizontal mechanical performance of steel. Therefore the present invention controls sulphur content is 0.020% ~ 0.055%.
Al: the austenite crystal of crystal grain fine uniform, to the H of stable Pinion Steel, reduces the distortion after gear heat treatment, it is to increase the anti-power of brittle failure and the anti-power of crack propagation are significant. Consider that Ti is to tooth steel rolling disadvantageous effect, mainly by adding Al crystal grain thinning, usually realize thin brilliant control with Al unit. In order to crystal grain thinning better, adopt refining to feed Al line mode, conservative control wire-feeding velocity and line feeding opportunity so that acid-soluble aluminum content can stability contorting within internal control scope, reach grain fineness number 8 grades. The present invention controls the content of manganese at Mn0.80% ~ 1.50%.
In Ca:Al deoxidized steel, main inclusions is Al2O3, and Al2O3It is mingled with hardness height and with sharp-pointed corner angle, very easily draws in steel following process process and hinder matrix, and due to its fusing point height, it is easy to adhere at mouth of a river inwall, carrying out smoothly of impact casting, even can cause the serious accidents such as nozzle clogging. In order to avoid pure Al2O3The generation being mingled with, adopts Ca treatment process to make Al2O3It is mingled with the calcium aluminate occurring reaction to generate low melting point with CaO to be mingled with, meanwhile, it is transformed to CaS or CaO Al owing to the MnS in steel is mingled with2O3CaS complex inclusion, it is to increase the isotropy of steel plate, it is to increase the performance of firm matrix.
In molten steel, [Ca], [S], [O] move to Al with diffusion way2O3It is mingled with surface, along with the continuation of reaction is goed deep into, the Al in steel2O3It is mingled with and experienced by CaO 6Al2O3→CaO·2Al2O3→CaO·Al2O3→12CaO·7Al2O3→3CaO·Al2O3Process, but in this process, when [O] content around inclusion surface is reduced to lower, the CaS of generating structure densification will be mingled with, be wrapped in the periphery that calcium-aluminate is mingled with, prevent CaO and Al2O3Carrying out further of reaction, so before inclusion is changed into liquid state, it is necessary to ensure that inclusion has enough CaO content.
Make that molten steel exists certain calcium contents by Calcium treatment, it is possible to the dystectic fragility Al of the macrobead that deoxidation of molten steel is produced by employing aluminium2O3The low melting point calcium-aluminate that being mingled with sex change becomes calcium content higher is mingled with (12CaO 7Al2O3Deng), the inclusion of low melting point can be made to float in molten steel removal, also the nozzle clogging being mingled with because of refractory oxide and causing molten steel casting process can be improved, also reduce high-melting-point brittle inclusion to the impact of steel product quality in solidification of molten steel process simultaneously, the oxidation products of calcium is as sulfide shape core core, it is possible to promote the precipitation of sulfide and being uniformly distributed of sulfide. Calcium can also play the effect changing oxide morphology. Calcium adds (Mn, the Ca) S forming compound in steel, thus the distortion ability reducing sulfide improves the horizontal mechanical performance of steel. Following the composition of 20CrMn steel, the suitable calcium addition that the present invention proposes is: 0.0006% ~ 0.005%.
Mg: the fusing point of magnesium is 649 DEG C, boiling point is 1090 DEG C, is 2.038MPa the vapour pressures of 1600 DEG C, and its solubleness in the molten steel of 1600 DEG C is 0.1%(mass percent). Magnesium is the metallic element more more active than calcium, is commonly used for steel making deoxidant and sweetening agent. After MAGNESIUM METAL joins molten steel, violent vaporization occurring, therefore, there are following two processes with steel water oxygen, sulphur generation reaction in magnesium: it one contacts with molten steel for Mg steam, and reacts with [O], [S] that be present in interface; It two is dissolved in molten steel for Mg and Mg steam by molten steel face, reacts with O, the S in molten steel. Reaction generates the oxide compound of magnesium or sulfide, and [O] in molten steel and [S] are reduced to lower level, the inclusion floating of generation or adsorbed removal from molten steel by crucible wall, plays the effect of deoxidization desulfuration. Magnesium participates in shown in the thermodynamic data following (chemical formula one, two) of deoxidization desulfuration reaction in molten steel:
(chemical formula one) [Mg]+[O]=MgO (s) △ G1 θ=-731400+239.68T
(chemical formula two) [Mg]+[S]=MgS (s) △ G2 θ=-537258.5+205.77T
The activity quotient of each element, because the concentration of each element in molten steel is very little, it is possible to thinks that these elements observe Henry's law. The activity quotient of each element can calculate by formula one:
lgfi=∑ei j[%j]
F in formulaiThe activity of element i;
ei jElement j is to the function coefficient of i;
The massfraction of [%j] element j.
Each element interaction coefficient in molten steel when 1873K listed by table 1:
Can calculating, when 1873K, the Henry activity quotient of each element is in table 2:
MgO and MgS owing to generating is solid-state when 1873K, and getting its activity is 1. According to activity theory and standard Gibbs free energy parameter, the thermodynamic(al)equilibrium relation of Mg and O, S in 1600 DEG C of molten steel can be obtained:
(balanced type one) [Mg]+[O]=MgO (s) △ G1 θ=-731400+239.68T
a[Mg]·a[O]=1.31×10-8
(balanced type two) [Mg]+[S]=MgS (s) △ G2 θ=-537258.5+205.77T
a[Mg]·a[S]=5.79×10-5
By the thermodynamic(al)equilibrium relation of Mg and O, S, when can obtain 1873K balance, in steel, the concentration relation of [Mg] and [O] and [S] is as depicted in figs. 1 and 2.
As seen from Figure 1, magnesium is a kind of very strong reductor, along with the increase of [Mg] content in steel, when reaching balance, it is possible to the dissolved oxygen content in steel is reduced to extremely low level.
As seen from Figure 2, when sulphur content initial in steel is higher, magnesium is a kind of very strong sweetening agent, it is possible to very soon dissolving sulphur content is dropped to lower level, but Mg sweetening power is obviously weaker than its deoxidizing capacity.
Generally when refining adopts the deoxidation simultaneously of magnesium aluminium, except generation metal is independent and dissolved oxygen reaction, also there is reaction below:
(chemical formula three) 2 [Al]+3 [O]=Al2O3(s)△G3 θ=-1202070+386.28T
(chemical formula four) MgO (s)+Al2O3(s)=MgO·Al2O3(s)△G4 θ=-35600-2.09T
Calculate by formula chemical formula one, chemical formula three and chemical formula four:
(chemical formula five) [Mg]+4 [O]+2 [Al]=MgO Al2O3(s)△G5 θ=-1969070+623.87T
When 1873K reaction reaches balance, that is:
△G5=△G5 θ+RTln=0
Get=1, in substitution, formula draws:
(balanced type three)=4.6×10-23
The vertical chemical formula three of connection and chemical formula five, and the activity quotient substituting into each element draws:
[%Mg]3/[%Al]2=1.5×10-14
The pass drawn between [Mg] and [Al] is that in molten steel, composition of inclusions is Al2O3With MgO Al2O3Critical condition, in following Fig. 3 shown in curve 2.As [%Mg] in molten steel3/[%Al]2> 1.5 × 10-14 time, composition of inclusions is MgO Al2O3; As [%Mg] in molten steel3/[%Al]2< during 1.5 × 10-14, composition of inclusions is Al2O3
The vertical chemical formula one of connection and chemical formula five, and the activity quotient substituting into each element draws:
[%Al]2/[%Mg]3=2.64×109
The pass drawn between [Mg] and [Al] is that in molten steel, composition of inclusions is MgO and MgO Al2O3Critical condition, in following Fig. 3 shown in curve 1. As [%Al] in molten steel2/[%Mg]3>2.64×109Time, in molten steel, composition of inclusions is MgO Al2O3; As [%Al] in molten steel2/[%Mg]3<2.64×109Time, in molten steel, composition of inclusions is MgO.
As seen from Figure 3, during 1873K, in steel, dissolved aluminum is in 0.01% ~ 0.1% scope, as long as there being oligodynamical magnesium to exist, so that it may can generate MgO Al2O3, when dissolved magnesium content reaches certain value, steel just there will be magnesium oxide and it be mingled with; This it appears that, in molten steel, [O] content is more high, and [Mg] and [Al] that balance with it is more low; It can also be seen that by figure, [Mg] content in change molten steel is utilized can sooner, more effectively to change steel inclusion composition, because in [Mg] content very minizone, composition of inclusions just changes, and to change composition of inclusions by changing [Al] content in molten steel, it is necessary to make [Al] content in molten steel that very big change occur, it is not easy to reach, to scheme middle polyline 3, to make composition of inclusions in molten steel be changed into Al from MgO2O3, in steel, [Al] need to be increased to about 970ppm from about 300ppm, and in steel, [Mg] only need to drop to about 0.05ppm from about 0.67ppm. Therefrom can show that the deoxidizing capacity of magnesium is stronger than aluminium.
Its spinel oxidation products (MgO Al2O3) as the shape core core of sulfide, it is possible to promote the precipitation of sulfide and it is uniformly distributed.
Non metallic oxide inclusion remaining in the steel of aluminium deep deoxidation is with Al2O3Being main, in molten steel, dissolved oxygen content has dropped to lower level, when the ratio of [Mg] Yu [Al] reaches certain value, in steel [Mg] can with the Al of [O] and remnants in steel2O3It is mingled with reaction, and two reactions carry out simultaneously. First, [Mg] generates MgO with [O] reaction and is mingled with, subsequently, due to MgO and Al2O3React steel-making temperature under △ G < 0, therefore in molten steel generate MgO be mingled with can with Al2O3It is mingled with and continues reaction and precipitate out thereon, then easily generate MgO Al2O3It is mingled with, [Mg] can be stoped to go and Al2O3It is mingled with and reacts, but making steel MgO and Al at temperature2O3Reaction belongs to solid-solid reaction, and the difficulty that reaction occurs is very big, thus [Mg] can also with the Al in molten steel2O3Constituent phases mutual effect generates MgO and is mingled with, if the MgO generated is mingled with splits away off from original inclusion, then the MgO becoming independent is mingled with. Under normal circumstances, the reaction existed in steel is [Mg] and Al2O3It is mingled with the MgO that reaction generates to be attached to original inclusion generates the MgO Al that composition and structure is more complicated2O3Compound is mingled with, along with the carrying out of reaction likely becomes surface for MgO Al2O3, heart portion be Al2O3The inclusion of layering, reacts further and becomes MgO Al2O3Spinel inclusion, the decline of [Mg] and Al in this and steel2O3Size is directly related. The reaction process of three kinds of reactions is as shown in Figure 4 and Figure 5.
Following the composition of 20CrMn steel, the suitable magnesium calcium addition that the present invention proposes is: Mg0.0006% ~ 0.004%, Ca0.0006% ~ 0.005%.
The production technique of a kind of free-cutting pinion steel, it is characterised in that: this technique comprises smelting, even casting and rolling process, and its technical process is:
A. smelt: electric furnace or converter smelting; Adopt the quick decarburization of high temperature; Control terminal composition, end point carbon 0.08%-0.12%, terminal silicon≤0.05%; Without slag or few slag tapping; Tapping process adopts strengthening pre-deoxidation technology, it is ensured that be not more than 60ppm to refining station molten steel dissolved oxygen content;
B.LF refining: process adopts refining rapid slagging slag making technology, Refining Clean Steel in ASEA-SKF technology; By adopting gas content in external refining, Fruit storage to chemical composition and steel to meet the requirements, in steel hydrogen richness be not more than 2.5ppm, oxygen level be not more than 20ppm; Adopt Feed aluminum wire to insert to molten steel inside containing magnesium heart yearn and the control deoxidation of pure calcium core-spun yarn, feed silk amount fixed according to steel grade and recovery rate, blow hydrogen, white slag refining, final deoxygenation hello aluminum steel by ladle.
C. vacuum refinement: processing station by RH or VD vacuum argon blowing degassing method, vacuum tightness≤0.10KPa that VD is degassed, hold-time 10-15min, namely vacuum breaker keeps whipped state; Finely tune by optimization target values, then feed S line, finely tune other composition to optimal value, when omnidistance argon bottom-blowing stirs, reach degassed, go to be mingled with, the object of evenly composition and temperature.
D. casting is connected: adopting superheating temperature 30 DEG C ± 5 DEG C, 60mm × 300mm base type to be 0.55 ~ 0.90mm/min, 180mm × 220mm base type is 0.90 ~ 1.5mm/min, molding casting and crystallizer and end electromagnetic agitating technology, specific water 0.7-0.8Kg/L;
E. rolling: continuously cast bloom is 1130-1280 DEG C in the Heating temperature of process furnace, start rolling temperature 1100 DEG C, heating and High temperature diffusion time are 1.5 ~ 3.5h, finishing temperature 850-980 DEG C; Empty cold or slow cooling after rolling.
A kind of technological process of production containing the 20MnCr5 free-cutting pinion steel of magnesium calcium sulphur is:
Supplementary material examination → batching → electrosmelting or converter → LF refining → VD is degassed or RH vacuum → company's casting → strand cold → inspection → blank examination → heating → de-scaling → rolling → shearing in hole or sawing → cheat cold → aligning → reconditioning → inspection after construction → packing indicate → weigh.
It is an advantage of the invention that:
The impact of safe range of stress is less than the impact of rigid inclusion by soft inclusion, so, attempt the method making non-metallic inclusion innoxious, namely control the non-metallic inclusion of hard. Making it to become inclusion (MnS) core that periphery is soft is rigid inclusion (Mg-Ca-Al-O inclusion), inclusion morphology is improved by molten steel being controlled deoxidation containing magnesium heart yearn and pure calcium core-spun yarn, control the form of nonmetallic inclusionsin steel, make steel obtain excellent mechanical property and good cutting ability. Smelting utilizes containing magnesium heart yearn have pure metal magnesium, Ni-Mg alloy, Mg-Al alloy and containing magnesium alkaline earth alloy etc. as magnesium source, insert in molten steel with pure calcium core-spun yarn simultaneously, calcium magnesium can dissolve in molten steel comparatively steadily, big splash can not be caused, also can guaranteeing the recovery rate of magnesium calcium, application calcium magnesium Combined Processing is effective way.
Accompanying drawing explanation
Fig. 1 is magnesium of the present invention-oxygen thermodynamic(al)equilibrium figure.
Fig. 2 is magnesium of the present invention-sulphur thermodynamic(al)equilibrium figure.
Fig. 3 is 1873K of the present invention [Mg]-[Al]-[O] balance.
Fig. 4 is [Mg] and remaining Al in molten steel2O3Interaction process schematic diagram.
Fig. 5 is [Mg] and [O] interaction process schematic diagram in molten steel.
Embodiment
Below in conjunction with embodiment, the present invention is described in detail:
Embodiment 1
The production of the novel 20MnCr free-cutting pinion steel containing magnesium calcium sulphur:
Concrete parameter is in table 3
A. just refining: first furnace carries out the fusing of just steel-making liquid, and first furnace adopts electric furnace or converter; Control terminal composition, end point carbon 0.12wt.%, terminal silicon≤0.07wt.%, terminal [S]≤0.020wt.%, and desulfurization degree should >=55%; Without slag or few slag tapping; First furnace obtains temperature and controls at 1660 DEG C; Tapping within the scope of 1630 DEG C, tapping process forbids slag; Tapping process adds synthetic slag by 13Kg/t steel. Tap 1/3 time add 2Kg/t steel core aluminium pre-deoxidation with steel stream, it is ensured that be not more than 70ppm to refining station molten steel dissolved oxygen content. Alloying in bag, Mn, Cr composition presses lower specification limit control.
B.LF refining: the refining carrying out molten steel at ladle refining furnace, ensures arc stability, and top of the slag fine motion, molten steel face is not exposed. Adopt carbon dust residue adjustment, suitably feeding Al line.Refining process keeps white slag, 20 minutes white slag refining hold-times. Select suitable refining slag system, refining slag basicity >=3.0, good fluidity, it is convenient to absorption be mingled with, adopts Feed aluminum wire to control deoxidation to the insertion of molten steel inside containing magnesium heart yearn and pure calcium core-spun yarn, reduce [O], [S], inclusion content in molten steel, control [O]≤20PPm, [S]≤0.015%, having a power failure when slag turns white, feeding aluminum steel, in tapping front control steel, aluminium content is 0.035%. Control temperature 1580 DEG C, tap to tap time taps at 40min. Slag system ingredient controls: SiO20%~10%、Al2O320%~30%、CaO50%~60%、MgO5%~10%、FeO+MnO≤1%。
C. vacuum refinement: process station by RH or VD vacuum argon blowing degassing method, vacuum tightness≤0.10KPa, hold-time 15min. Namely vacuum breaker keeps whipped state, finely tunes by optimization target values, then feeds S line, finely tunes other composition to optimal value, when omnidistance argon bottom-blowing stirs, reaches degassed, goes to be mingled with, the object of evenly composition and temperature. Hydrogen flowing quantity controls in 40L/min soft blow, after line feeding soft blow time >=10min. Out-station temperature is casting the first stove even: 1580 DEG C, even waters stove: 1560 DEG C.
D. full guard even casting: middle bag storing temperature >=1100 DEG C, arc, mouth of a river centering are met the requirements by crystallizer, and nozzle atomization effect is good, and casting process wants whole process protection to pour into a mould, and unwraps greatly and must add lid after watering. Wrap in during cast first add alkaline covering agent, after add carbonization rice husk. Pouring basket liquid level 700 ± 50mm, liquid level fluctuation of crystallizer≤± 2mm. Middle bag superheating temperature presses 30 DEG C ± 5 DEG C target controls, casting speed control: 260mm × 300mm base type is 0.75mm/min, 180mm × 220mm base type is 1.2mm/min, and strand enters straightening machine temperature >=920 DEG C. Crystallizer and end induction stirring are guaranteed normally to use its crystallizer stirring parameter for electric current 198A, frequency 3.0Hz; End current 110A, frequency 12Hz, specific water 0.7Kg/L.
E. rolling is become a useful person: steel ingot or steel billet are 1200 DEG C in the soaking temperature of process furnace, and heating and High temperature diffusion time are 2.5h, start rolling temperature 1100 DEG C, finishing temperature 930 DEG C.
Embodiment 2
The production of the novel 20MnCr free-cutting pinion steel containing magnesium calcium sulphur:
Concrete parameter is in table 4
A. just refining: first furnace carries out the fusing of just steel-making liquid, and first furnace adopts electric furnace or converter; Control terminal composition, end point carbon 0.12%, terminal silicon≤0.05%, terminal [S]≤0.015%, and desulfurization degree answer >=65%, terminal P≤0.015%; Without slag or few slag tapping; First furnace obtains temperature and controls at 1660 DEG C; Tapping within the scope of 1620 DEG C, tapping process forbids slag, and slag stove must take off slag. Tapping process adds synthetic slag by 13Kg/t steel. In ladle, pre-deoxidation is forbidden to add the Si matter reductor tappings such as Si iron, SiC and is added special pre-melted slag, forbids to add fluorite etc. containing Si material. Tap 1/3 time add 2.0Kg/t steel core aluminium pre-deoxidation with steel stream, it is ensured that be not more than 60ppm to refining station molten steel dissolved oxygen content. Alloying in bag, Mn, Cr composition presses lower specification limit control.
B.LF refining: the refining carrying out molten steel at ladle refining furnace, ensures arc stability, and top of the slag fine motion, molten steel face is not exposed. Adopt carbon dust residue adjustment, suitably feeding Al line. Refining process keeps white slag, 30 minutes white slag refining hold-times. Select suitable refining slag system, refining slag basicity >=3.0, good fluidity, it is convenient to absorption be mingled with, adopts Feed aluminum wire to control deoxidation to the insertion of molten steel inside containing magnesium heart yearn and pure calcium core-spun yarn, reduce [O], [S], inclusion content in molten steel, control [O]≤10PPm, [S]≤0.010%, having a power failure when slag turns white, feeding aluminum steel, in tapping front control steel, aluminium content is 0.045%.Control temperature 1590 DEG C, tap to tap time taps at 40min. Slag system ingredient controls: SiO20%~10%、Al2O320%~30%、CaO50%~60%、MgO5%~10%、FeO+MnO≤1%。
C. vacuum refinement: process station by RH or VD vacuum argon blowing degassing method, vacuum tightness≤70Pa, hold-time 15min. Namely vacuum breaker keeps whipped state, finely tunes by optimization target values, then feeds S line, finely tunes other composition to optimal value, and S content, 0.026%, when omnidistance argon bottom-blowing stirs, reaches degassed, goes to be mingled with, the object of evenly composition and temperature. Hydrogen flowing quantity controls in 40L/min soft blow, after line feeding soft blow time >=10min. Out-station temperature is casting the first stove even: stove waters in 1580 DEG C of companies: 1570 DEG C. Full guard is casting even: middle bag storing temperature >=1150 DEG C, and arc, mouth of a river centering are met the requirements by crystallizer, and nozzle atomization effect is good, and casting process wants whole process protection to pour into a mould, and unwraps greatly and must add lid after watering. Wrap in during cast first add alkaline covering agent, after add carbonization rice husk. Pouring basket liquid level 700 ± 30mm, liquid level fluctuation of crystallizer≤± 2mm. Middle bag superheating temperature presses 30 DEG C ± 5 DEG C target controls, casting speed control: 260mm × 300mm base type is 0.7mm/min, 180mm × 220mm base type is 1.3mm/min, and strand enters straightening machine temperature >=920 DEG C. Crystallizer and end induction stirring are guaranteed normally to use its crystallizer stirring parameter for electric current 198A, frequency 3.0Hz; End current 110A, frequency 12Hz, specific water 0.8Kg/L.
D. rolling is become a useful person: steel ingot or steel billet are 1130 ~ 1280 DEG C in the soaking temperature of process furnace, and heating and High temperature diffusion time are 2h, start rolling temperature 1125 DEG C, finishing temperature 925 DEG C.

Claims (3)

1. the 20MnCr free-cutting pinion steel containing magnesium calcium sulphur, it is characterised in that for: by weight percentage, the chemical composition of this Pinion Steel is C:0.15% ~ 0.25%, Si≤0.12%, Mn:0.80% ~ 1.50%, P :≤0.035%, S:0.02% ~ 0.055%, Cr:0.80% ~ 1.30%, Al:0.015% ~ 0.055%, N:0.004% ~ 0.015%, Mg:0.0006% ~ 0.004%, Ca:0.0006% ~ 0.005%, [O] :≤0.0025%, surplus is iron and inevitable impurity.
2. the 20MnCr free-cutting pinion steel containing magnesium calcium sulphur as claimed in claim 1, it is characterised in that group part of this steel is by weight percentage: C:0.18% ~ 0.22%, Si :≤0.10%, Mn:1.15% ~ 1.40%, P :≤0.030%, S:0.025% ~ 0.030%, Cr:1.00% ~ 1.15%, Al:0.018% ~ 0.035%, N:0.004% ~ 0.012%, Mg:0.0010% ~ 0.0028%, Ca:0.0010% ~ 0.0025%, [O] :≤0.0020%, surplus is iron and inevitable impurity.
3. containing a preparation method for the 20MnCr free-cutting pinion steel of magnesium calcium sulphur, the method comprises smelting, even casting and rolling process, it is characterised in that following step:
A. smelt: electric furnace or converter smelting; Adopt the quick decarburization of high temperature; Control terminal composition, end point carbon 0.08%-0.12wt.%, terminal silicon≤0.05wt.%; Without slag or few slag tapping; Tapping process adopts strengthening pre-deoxidation technology, it is ensured that be not more than 60ppm to refining station molten steel dissolved oxygen content;
B.LF refining: process adopts refining rapid slagging slag making technology, Refining Clean Steel in ASEA-SKF technology; By adopting gas content in external refining, Fruit storage to chemical composition and steel to meet the requirements, in steel hydrogen richness be not more than 2.5ppm, oxygen level be not more than 20ppm; Adopt Feed aluminum wire to insert to molten steel inside containing magnesium heart yearn and the control deoxidation of pure calcium core-spun yarn, feed silk amount fixed according to steel grade and recovery rate, blow hydrogen, white slag refining, final deoxygenation hello aluminum steel by ladle;
C. vacuum refinement: processing station by RH or VD vacuum argon blowing degassing method, vacuum tightness≤0.10KPa that VD is degassed, hold-time 10-15min, namely vacuum breaker keeps whipped state; Finely tune by optimization target values, then feed S line, finely tune other composition to optimal value, when omnidistance argon bottom-blowing stirs, reach degassed, go to be mingled with, the object of evenly composition and temperature;
D. casting is connected: adopting superheating temperature 30 DEG C ± 5 DEG C, 60mm × 300mm base type to be 0.55 ~ 0.90mm/min, 180mm × 220mm base type is 0.90 ~ 1.5mm/min, molding casting and crystallizer and end electromagnetic agitating technology, specific water 0.7-0.8Kg/L;
E. rolling: continuously cast bloom is 1130-1280 DEG C in the Heating temperature of process furnace, start rolling temperature 1100 DEG C, heating and High temperature diffusion time are 1.5 ~ 3.5h, finishing temperature 850-980 DEG C; Empty cold or slow cooling after rolling.
CN201610163260.XA 2016-03-19 2016-03-19 Magnesium, calcium and sulfur containing 20MnCr free-cutting gear steel and preparation method thereof Pending CN105671434A (en)

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