CN103103435A - Preparation technology for nodular cast iron with TRIP (transformation-induced plasticity) effect - Google Patents
Preparation technology for nodular cast iron with TRIP (transformation-induced plasticity) effect Download PDFInfo
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Abstract
The invention relates to a preparation technology for nodular cast iron with a TRIP (transformation-induced plasticity) effect. The preparation technology can be used for producing a nodular cast iron part, of which the strength of extension is greater than 700MPa, the elongation is 8%, and the product of strength and elongation is greater than 6000MPa%. The cast tissue is a complex phase tissue of ferrite base, bainite, retained austenite, a bit of martensite and graphite, soft ferrite base endows the whole cast with good ductility, hard bainite, distributed in the ferrite base in a complex intertwining manner, serves as a skeleton so as to improve the strength of the cast, a bit of martensite is the hardest phase in the tissue and plays a role in improving the strength of the cast, furthermore, a bit of retained austenite not only improves the ductility of the cast, but also can produce a TRIP effect at room temperature. Therefore, the nodular cast iron with the TRIP effect has better comprehensive property than common isothermal quenching nodular cast iron, improves both the ductility and strength of the cast, and has higher product of strength and elongation.
Description
Technical field
Present technique relates to the preparation technology of the spheroidal graphite cast iron with TRIP effect, it is mainly concerned with preparation a kind of high strength, high rigidity and high strength and ductility nodular iron casting, the spheroidal graphite cast iron progressive austempering after austenite ferrite critical zone insulation that obtains complete ferrite+graphite after high temperature annealing to obtain the heterogeneous structure of ferrite matrix+bainite+residual austenite+a small amount of martensite+graphite, possessed good intensity, hardness and high-elongation.
Background technology
20th century the fifties spheroidal graphite cast iron (Ductile Iron, abbreviation DI) appearance makes the over-all properties of cast iron materials close to steel, just be based on its excellent performance, be successfully used to cast stressed complexity, the automobile component that intensity, toughness, wear resistance are had relatively high expectations, because the graphite of nearly 10% left and right is arranged in its tissue, therefore the part of same volume is about lighter by 10% than forged steel pieces.Late 1970s interim state, Finland Kymi Kymmene company and General Motors Corporation's research of the U.S. in succession succeed in developing bainite ductile iron.Bainite ductile iron is through austempering thermal treatment with ductile cast iron casting, acquisition is take bainite as main matrix, obtain very high intensity, so this austempering bainite ductile iron ADI (Austempered Ductile Iron) is a kind of high-intensity spheroidal graphite cast iron.Due in matrix except bainite, also have the austenite of some amount, therefore be called again Austenite-Bainite Ductile Iron, be called for short austempered ductile iron.
The tensile strength of ADI in equal elongation situation is the twice of common magnesium iron, and in the equal tensile strength situation, the elongation of ADI is more than common magnesium iron twice, and the tensile strength of ADI also is better than the carbon steel of modifier treatment, and is suitable with low alloy steel.ADI tensile strength can reach 800～1600 MPa, and elongation reaches as high as more than 10%.According to the American-European trade mark, the intensity of austempering ductile iron and high strength or ultrahigh-strength steel are suitable.General Motors Overseas Corporation is in adopting isothermal quench bainitic ductile cast iron to replace forged steel to make the back axle paired bevel gears of Pontiac car, and year output reaches 1,000,000 pairs, this shows the performance of ADI excellence.
The general spheroidal graphite cast iron of the fatigue ratio of ADI is high by 50%, and the rotoflector fatigue strength of ADI can reach 400 ~ 500Mpa, and is suitable with modifier treatment low alloy steel; The contact fatigue strength of ADI can reach 1600～2100Mpa, and is higher than the contact fatigue strength of low alloy steel nitriding treatment.Because there is the graphite pebbles of some amount in enterprise's tissue, reduced the notch sensitivity of material.The ADI notch factor is 1.2～1.6, and the sensitivity coefficient of general forged steel is 2.2～2.4), so the ADI notch sensitivity is lower than forged steel.
ADI adds to have graphite pebbles in matrix because Young's modulus is low, and absorbing vibration has also increased noise damping rapidly, makes the operation of parts quieter and steady.Therefore when working Deng the cast pieces of spheroidal of quenching, noise is little, this specific character is very favourable to the machine of automobile and other various runnings.Compare with forged steel, make same intensity rank part, adopt the cost of ADI low.The magnesium iron of quenching such as per kilogram is lower than its rival (forged steel, aluminium casting).If with the pricing of yield strength unit tenacity, waiting the magnesium iron of quenching is the most cheap material.
The technological process of production of austempering ductile iron is as follows: comprise the operations such as melting, spheroidizing, cast, cleaning and thermal treatment.Wherein crucial Technology is as follows:
(1) reasonable component design
General austempering ductile iron adopts three high two low chemical compositions, i.e. high-carbon, high silicon, carbon equivalent high, low-sulfur, low manganese.High-carbon quantity can improve austenitic stability, and high silicon can improve the ability that suppresses carbide formation, thereby forms carbide-free Bainite when isothermal.
In order to guarantee to obtain enough hardening capacity, prevent from producing in matrix perlite, also must add appropriate total element, as Mo, Ni and copper etc., the add-on of these alloying elements is relevant with the size of part, and the alloying element that the part that size is larger needs is more, certainly will increase production cost.
In order to guarantee to obtain good spheroidizing effect, require to contain in austempering ductile iron anti-graphited impurity element and advance and to lack.
(2) good spheriodization process thereof
During spheroidizing cast iron solidified be to add nodulizing agent, graphite is separated out with form.Solidify the graphite of separating out more rounding, distribute more evenly, i.e. nodularization effect is better, the performance of the magnesium iron that obtains is better.Therefore will obtain high performance austempering ductile iron, must guarantee good spheriodization process thereof, particularly for the part of thick and large section, spheroidizing is more crucial.
(3) the accurate control of isothermal quenching technique
Isothermal quenching is that part is heated to austenitizing temperature, general cast iron is 840～950 ℃, insulation is quenched after for some time isothermal for some time in 300～400 ℃ of fused salts, make part cooling as far as possible fast in the temperature range of 600～700 ℃ of perlitic transformations, escape the C curve tip of the nose, avoid perlitic transformation, obtain take bainite as main matrix.Accurately controlling isothermal quenching technique is one of gordian technique of ADI production.
The phase transformation of isothermal quenching process is divided into two stages: one, high temperature austenite is decomposed into ferrite and high-carbon stable austenite, if the next stage will occur the isothermal quenching time sufficiently long.Two, after the fs phase transformation finishes, be decomposed into ferrite and carbon (normally cementite) if continue to be incubated the high-carbon stable austenite, yet the carbide here is the unnecessary phase that causes the material cracking, technique need be avoided the appearance of carbide so formulation etc. are quenched.If the fs does not carry out may obtaining martensitic stucture fully after cool to room temperature yet.
For energy-conservation, people wish to select the lower material of ratio of density and tensile strength.Material is light and firm, can satisfy the light-weighted requirement of product.By the contrast ADI ratio less than or equal to 20CrMnTi quenched and tempered steel and aldural.
Summary of the invention
The object of the invention is to the method for utilizing the critical zone austenitizing to combine with progressive austempering, produce ferrite matrix+bainite+residual austenite+a small amount of martensite+graphite structure ADI.
For achieving the above object, technical scheme of the present invention is: a kind of preparation technology of spheroidal graphite cast iron of the TRIP of having effect, and the nodular cast iron alloy chemical quality per-cent that this technique is applicable to is as follows:
C 1.5～3.6% ;
Si 2.0～2.8% ;
Mn 0.1～2.5% ;
P ≤0.05% ;
S ≤0.02%;
Mg ≤0.05%;
All the other are Fe and inevitable impurity;
Its concrete steps are as follows:
1) spheroidal graphite cast iron casting takes raw material by above-mentioned chemical composition mass percent, smelting, spheroidizing, casting;
2) cast iron that above-mentioned steps is prepared is through 930 ℃～1100 ℃ heating, is incubated furnace cooling after soaking in 2～4 hours, obtains ferrite ductile cast iron;
3) ferrite ductile cast iron critical zone austenitizing is with 2) in ferrite ductile cast iron at A
c1~ A
c3Between select austenitizing temperature, soaking time 30min ~ 120min according to destination organization;
4) casting of the spheroidal graphite after austenitizing slowly cools to A with stove
c1+ 5 ℃ are continued insulation 5min, speed of cooling with 40 ℃/S cools to rapidly 200 ~ 230 ℃ of Bainite Region lesser tempss, insulation 10 ~ 30min, be raised to 250 ~ 450 ℃ of insulation 60～120min of Bainite Region comparatively high temps with the rate of heating of 5 ℃/S more subsequently, last air cooling, the spheroidal graphite cast iron that namely obtains having the TRIP effect.
That the present invention is guaranteeing to improve the principal character of its plasticity under the prerequisite of ADI excellent properties with ferrite ductile cast iron at progressive austempering after the austenitizing of critical zone.
The intercritical annealing temperature is to guarantee that ADI finally has heterogeneous structure and obtains the most critical processing parameter of excellent toughness, can obtain the ferritic phase of different volumes mark by adjusting critical temperature, and in final ADI tissue, ferrite content is higher, and toughness is better.Conventional ADI material hardness is generally between HRC40 ~ 50, and the technique by this patent can obtain hardness from the ADI tissue with TRIP effect of HRC19 ~ 49 scopes.Isothermal quenching technique in the past can only obtain high-carbon stable austenite and bainitic ferrite tissue, and this being organized in when obtaining high tensile strength sacrificed toughness, so Application Areas is restricted.High-strength ADI generally is used for wear-resisting field, must guarantee the high-intensity high toughness that has simultaneously if ADI will be applied in auto parts.Therefore in the present invention, adopt two critical processes, intercritical annealing and low temperature progressive austempering technique, not only keep the higher proeutectoid ferrite of carbon content and can also obtain a certain amount of newborn ferrite, obtain to organize thinner bainite ferrite after classified isothermal quenching, make material finally obtain higher-strength and higher toughness by soft phase with hard combination mutually.
Because new ferritic phase generates, when having improved because of follow-up isothermal quenching, Bainite Phases of Some concentrates on this drawback of proeutectoid ferrite crystal boundary, has improved the final strength of material in the process of furnace cooling.As without annealing process, in the tissue that obtains, hard phase bainite concentrates on the ferrite crystal boundary substantially, and this performance to material is and is disadvantageous.
During progressive austempering, first be quenched to the bainitic transformation lowest temperature, because phase deformed nucleus at this moment is to carry out under excessively cold high, it is maximum that kinetics-driven power reaches, and is conducive to the forming core of cenotype.Begin to be incubated during this period of time in isothermal quenching, a large amount of Bainite Phases of Some cores generates, when slightly high-temperature district insulation subsequently because the required condensate depression of nucleus growth is less, therefore nearly all nucleus is Fast Growth simultaneously, can make like this bainite structure in final tissue more tiny, intensity is higher.
Beneficial effect of the present invention:
1) possesses excellent comprehensive mechanical property.The tensile strength of the spheroidal graphite cast iron that the present invention relates to is 700～850Mpa, unit elongation 〉=8%.
2) operation feasible, equipment is simple.The present invention adopts conventional smelting and spheronization techniques, and thermal treatment process control simple and feasible, and present isothermal quenching device is many and specification is numerous, can carry out industrialized production.
3) application prospect is extensive.The ADI that the present invention prepares, high because of its intensity, unit elongation is large, it is applied on motor car engine or web member, strut member, prospect is considerable.
4) can realize auto parts lightweight, favourable automotive energy-saving emission-reducing.Compare with conventional ADI, go up not down carrying high-intensity while unit elongation, higher as web member and strut member security.When making auto parts, compare with plain cast iron and can reduce the part wall thickness, can realize significantly loss of weight of auto parts by optimizing design of part.
Description of drawings:
Fig. 1 is thermal treatment process schematic diagram of the present invention.
Embodiment
Below in conjunction with specific embodiment, technical side of the present invention is described further.
The chemical composition given according to table 1 is cast as base after nodularization, inoculation, machining is heat-treated after removing the surface.
Table 1 is the mass percent of each composition
Table 1
| Numbering | C | Si | Mn | S | P | Mg | Surplus |
| 1 | 3.42 | 2.5 | 0.18 | 0.016 | 0.041 | 0.047 | Fe and inevitable impurity |
The casting nodular cast iron obtains ferrite+graphite structure magnesium iron through 980 ℃ of insulations furnace cooling after four hours.Enter subsequently 835 ℃ of insulation 30min of process furnace, slowly cool to 805 ℃ of insulation 5min with the furnace, speed of cooling with 40 ℃/S is cooled to respectively rapidly 200 ℃, 210 ℃., 220 ℃ and 230 ℃ insulation 5min, heat up respectively to 280 ℃, 300 ℃, 350 ℃ and 450 ℃ with the rate of heating of 5 ℃/S again, insulation 2h, air cooling.
The present invention has adopted four kinds of different two-phase region austenitizing temperatures, and 835 ℃, 830 ℃, 825 ℃ and 820 ℃, the corresponding tissue of different technical parameters and hardness are as shown in table 2:
Table 2 is corresponding Main Tissues content and hardness of main technologic parameters
Table 2
Claims (1)
1. preparation technology with spheroidal graphite cast iron of TRIP effect, the nodular cast iron alloy chemical quality per-cent that this technique is applicable to is as follows:
C 1.5～3.6%；
Si 2.0～2.8% ；
Mn 0.1～2.5%；
P ≤0.05%；
S ≤0.02%；
Mg ≤0.05%；
All the other are Fe and inevitable impurity, it is characterized in that, it comprises the steps:
Spheroidal graphite cast iron casting takes raw material according to the chemical composition mass percent, smelts, spheroidizing, casting;
The cast iron that above-mentioned steps is prepared is through 930 ℃～1100 ℃ heating, is incubated furnace cooling after soaking in 2～4 hours, obtains ferrite ductile cast iron;
Ferrite ductile cast iron critical zone austenitizing is with 2) in ferrite ductile cast iron at A
c1~ A
c3Between select austenitizing temperature, soaking time 30min ~ 120min according to destination organization;
Spheroidal graphite casting after austenitizing slowly cools to A with stove
c1+ 5 ℃ are continued insulation 5min, then cool to rapidly 200 ~ 230 ℃ of insulation 10 ~ 30min of Bainite Region lesser temps, are as cold as soon subsequently 250 ~ 450 ℃ of insulation 60～120min of Bainite Region comparatively high temps, last air cooling.
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104388810A (en) * | 2014-11-13 | 2015-03-04 | 四川南车共享铸造有限公司 | Preparation method of as-cast nodular cast iron and nodular cast iron |
| CN106471138A (en) * | 2014-07-03 | 2017-03-01 | 安赛乐米塔尔公司 | For producing the method for superhigh intensity coated steel plates or uncoated steel plate and the plate obtaining |
| CN107099649A (en) * | 2017-04-24 | 2017-08-29 | 湖北东舟重工科技股份有限公司 | A kind of heat treatment method of the sub- warm normalizing thinning microstructure of Medium Carbon Steel Containing Manganese two-phase section |
| TWI657145B (en) * | 2017-11-30 | 2019-04-21 | 財團法人金屬工業研究發展中心 | Method for manufacturing easy-cutting two-phase Worth tempered ductile iron |
| US11035020B2 (en) | 2015-12-29 | 2021-06-15 | Arcelormittal | Galvannealed steel sheet |
| CN113699433A (en) * | 2021-09-07 | 2021-11-26 | 鹰普机械（宜兴）有限公司 | High-performance high-nickel austenitic ductile iron |
-
2013
- 2013-01-23 CN CN201310024360.0A patent/CN103103435B/en not_active Expired - Fee Related
Non-Patent Citations (1)
| Title |
|---|
| 周世权: "分级等温淬火球墨铸铁的组织与性能", 《热加工工艺》 * |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106471138A (en) * | 2014-07-03 | 2017-03-01 | 安赛乐米塔尔公司 | For producing the method for superhigh intensity coated steel plates or uncoated steel plate and the plate obtaining |
| US10378077B2 (en) | 2014-07-03 | 2019-08-13 | Arcelormittal | Method for producing an ultra high strength coated or not coated steel sheet and obtained sheet |
| US11001904B2 (en) | 2014-07-03 | 2021-05-11 | Arcelormittal | Method for producing an ultra high strength coated or not coated steel sheet and obtained sheet |
| US11124853B2 (en) | 2014-07-03 | 2021-09-21 | Arcelormittal | Method for producing a ultra high strength coated or not coated steel sheet and obtained sheet |
| US11131003B2 (en) | 2014-07-03 | 2021-09-28 | Arcelormittal | Method for producing an ultra high strength coated or not coated steel sheet and obtained sheet |
| CN104388810A (en) * | 2014-11-13 | 2015-03-04 | 四川南车共享铸造有限公司 | Preparation method of as-cast nodular cast iron and nodular cast iron |
| CN104388810B (en) * | 2014-11-13 | 2017-01-11 | 四川南车共享铸造有限公司 | Preparation method of as-cast nodular cast iron and nodular cast iron |
| US11035020B2 (en) | 2015-12-29 | 2021-06-15 | Arcelormittal | Galvannealed steel sheet |
| US11512362B2 (en) | 2015-12-29 | 2022-11-29 | Arcelormittal | Method for producing an ultra high strength galvannealed steel sheet and obtained galvannealed steel sheet |
| CN107099649A (en) * | 2017-04-24 | 2017-08-29 | 湖北东舟重工科技股份有限公司 | A kind of heat treatment method of the sub- warm normalizing thinning microstructure of Medium Carbon Steel Containing Manganese two-phase section |
| TWI657145B (en) * | 2017-11-30 | 2019-04-21 | 財團法人金屬工業研究發展中心 | Method for manufacturing easy-cutting two-phase Worth tempered ductile iron |
| CN113699433A (en) * | 2021-09-07 | 2021-11-26 | 鹰普机械（宜兴）有限公司 | High-performance high-nickel austenitic ductile iron |
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