CN101717884A - Austempering ductile iron (ADI) supercharged diesel engine six-cylinder crankshaft and production method - Google Patents

Abstract

The invention belongs to the class of metal materials. After a supercharged technology is used for a diesel engine, the load born by a crankshaft is improved by 45-67 percent. The fatigue property of ordinary ball iron cannot meet the requirement of service and is replaced by alloy steel. The invention provides an austempering ductile iron (ADI) supercharged diesel engine six-cylinder crankshaft and a production method which both determine chemical constituents, particularly determine the addition of alloying elements, propose definite requirements on the percent of spheroidization and the number of graphite pebbles and also determine the parameter of an isothermal quenching process. After quenching, the deformation of the six-cylinder crankshaft is controlled within a certain range, which is a key measure of the method. A special heat treatment tire for quenching the six-cylinder crankshaft is designed so as to obtain a satisfactory result. The application of a crankshaft fillet rolling technology greatly improves the fatigue property of the six-cylinder crankshaft. The invention makes a pioneering contribution to manufacturing the supercharged diesel engine six-cylinder crankshaft by the ADI and greatly reduces the production cost of the six-cylinder crankshaft.

Description

Austempering ductile iron (ADI) supercharged diesel engine six-cylinder crankshaft and production method

Technical field

The present invention relates to class of metal materials, particularly a kind of Austempering ductile iron (ADI) supercharged diesel engine six-cylinder crankshaft and production method.

Background technology

Behind the diesel engine using supercharging technology, the load that bent axle bears has improved 45%-67%, and the fatigue property of common magnesium iron can not satisfy the requirement of military service, faces by the displaced trend of steel alloy.Fatigue property significantly improves after the magnesium iron means of isothermal quenching, makes spherulitic iron crankshaft continue to obtain to use.

1, supercharged diesel engine is to the requirement of crankshaft material fatigue strength

The application of supercharging technology obviously improves the performance of diesel engine, and supercharged diesel engine has become the important directions of diesel engine development.Bent axle is the strength member of an energy transformation and output rating in diesel engine, and bent axle bears the effect of high frequency, alternation moving load in the time of under arms, and the main failure mode of bent axle is repeated stress failure, so the fatigue strength most important performance index that are crankshaft materials.Explosion pressure P with diesel engine _ZImprove, require the increase that is directly proportional of the fatigue strength of crankshaft material.Through the six-cylinder diesel engine crankshaft stress is analyzed and Calculation of Fatigue Strength, when explosion pressure is P _ZDuring=13～15MPa, the fatigue property of some steel alloy as 40cr and 42CrMo have.The normalizing attitude pearlite ductile iron of widespread use is inapplicable as QT800-2 in natural aspiration type unblown edition diesel engine.Because of its fatigue strength only is 280-300MPa.Have only the fatigue property energy of ADI material suitable with steel alloy.ADI becomes six cylinder supercharged diesel machine crankshaft desirable material.

Used ADI makes the feasibility of supercharged diesel machine crankshaft:

Technical feasibility:

The performance that so-called technical feasibility is exactly crankshaft material and crankshaft part all satisfies the requirement of being on active service.Be 40cr and 42CrMo at present in the extensive usefulness of China's supercharged diesel engine crankshaft material.Its performance is as shown in table 1.

According to the ASTM897M standard of the U.S., the typical performance that 5 kinds of other ADI of level reach in actual production is as shown in table 2.

Table 1 part carbon steel and steel alloy performance table

Material mark	Tensile strength sigma b/MPa	Yield strength σ 0.2/MPa	Fatigue strength σ-1/MPa	Elongation δ %	Hardness HB
						45 steel	??710	??355	??388	??16	??229
??40Cr	??940	??785	??422	??9	??207
						??42CrMo	??1134	??930	??502	??12	??217
??35CrMo	??924	??835	??431	??12	??229

Material mark	Tensile strength sigma b/MPa	Yield strength σ 0.2/MPa	Fatigue strength σ-1/MPa	Elongation δ %	Hardness HB
						??50Crv	??1275	??1130	??747	??10	??255

Table 2ADI performance table

Rank	Material mark	Tensile strength sigma b/MPa	Yield strength σ 0.2/MPa	Fatigue strength σ-1/MPa	Elongation δ %	Hardness HB
							??GRADE1	??850-850-10	??966	??759	??450	??11	?269-321
??GRADE2	??1050-720-07	??1139	??897	??485	??10	?302-363
							??GRADE3	??1200-850-04	??1311	??1104	??415	??7	?341-444
??GRADE4	??1400-1100-01	??1518	??1242		??5	?388-477
							??GRADE5	??1600-1300-00	??1656	??1449		??3	?444-＝555

By table 2 as seen, 1～3 grade of its fatigue strength of ADI is close with 40Cr, 42CrMo.Test shows that the fatigue strength that ADI is the highest can reach 507Mpa.Therefore from fatigue strength, ADI can satisfy the requirement of supercharged diesel machine crankshaft.

Select the following condition of crankshaft material reference:

$\frac{{\mathrm{\σ}}_J}{{\mathrm{\σ}}_{-1}}=0.9~1.2$

σ _J---the fatigue of materials intensity (Mpa) that draws according to the crankshaft stress distributed computation; σ _-1---press the fatigue of materials intensity (Mpa) that standard test specimen is measured.

Many Diesel Engine Plants are for fear of rupturing, and are very tight to the security requirement of bent axle, stipulate safety coefficient n=1.8～2.0 usually.ADI is the same with the Castingother material, compares with forged steel to have bigger sensitivity profile.Spherulitic iron crankshaft adopts the finish rolling hardening method usually in production process for this reason.The effect of finish rolling hardening is relevant with the plasticity of material, and the ADI elongation was far above the normalizing pearlitic ductile iron when tensile strength was identical, and this lays a good foundation for adopting the finish rolling hardening mode to reach n=1.8～2.0.A research report according to U.S. combine harvester company, model is that bending fatigue strength is respectively 414Mpa, 986Mpa before and after the 202 heavy-load automobile V-8 diesel engine ADI crankshaft rollings, improved 138%, and the employing trade mark is 5203 common magnesium iron, bending fatigue strength after the roll extrusion only is 669Mpa, and the ADI bent axle has better finish rolling hardening effect.

Production possibility:

Make the ADI bent axle, at first will produce stable high quality spherulitic iron crankshaft foundry goods, it is the basis that produces the ADI bent axle.This foundry goods should be that no casting flaw, chemical ingredients and metallographic structure are qualified and stable.The molding floor of the most Production of Crankshaft of China factory has realized electrosmelting substantially at present, has adopted Iron Mould Coated Sand, self-hardening sand, high pressure moulding and shell moulded casting, and starting material and technology have obtained strict control, and have more advanced reliable detection instrument.It is possible that high-quality ADI automatic modeling crankshaft casting is stablized in production.

Determining and carrying out suitable isothermal quenching technique is the key of producing the ADI bent axle.Since 20th century the seventies, a large amount of information disclosure exchanges, the ADI product constantly exploitation with use, it is ripe that the magnesium iron isothermal quenching technique has been tending towards, and determines that the magnesium iron isothermal quenching technique that is fit to has not been a difficult problem.And difficult point need to be a kind of special-purpose Equipment for Heating Processing of carrying out isothermal quenching technique that can guarantee to stablize.Bent axle, gear are the products that a class is more produced in enormous quantities, not only require to have enough securities, also require to have very high stability, adopt special-purpose isothermal quenching equipment can guarantee quality stability.This equipment occurs at home, has created favourable condition for producing stay-in-grade ADI bent axle in enormous quantities.

By bench testing and actual road test:

Though ADI bent axle performance reaches the requirement of supercharged diesel engine, can China possesses the condition of batch process again, but be applied, and finally depends on the result of bench testing and entrucking actual road test, test will be carried out according to the pertinent regulations of state, and the result of test needs to be approved.

Summary of the invention

The object of the present invention is to provide a kind of Austempering ductile iron (ADI) supercharged diesel engine six-cylinder crankshaft and production method, to solve the problem that at present general magnesium iron six-cylinder crankshaft can't satisfy the supercharged diesel engine service condition.Six-cylinder crankshaft with the expensive steel alloy die forging of ADI six-cylinder crankshaft replacement prevents that wherein six-cylinder crankshaft thermal treatment after strain from being one of gordian technique of the present invention.

Technical scheme of the present invention is: determine six-cylinder crankshaft chemical ingredients and foundry goods alloy structure span of control.Its nodularization rate must be kept under strict control more than 2 grades, 100/mm of number of graphite ball ²More than, to ferrite in the green casting matrix and pearlitic ratio control in a constant scope, guarantee that thermal effectiveness is stable in addition; Means of isothermal quenching will be carried out having on the salt stove production line of protective atmosphere, and guaranteeing does not have Decarburized layer after the heat treating castings.Because the long 990mm of six-cylinder crankshaft, very easily distortion after the heat, cause great difficulty to processing, this is a technology contents of patent of the present invention particularly important to be solved: adopt high Cr, the austenitic steel of Ni is made custom-designed thermal treatment mold, can guarantee that six-cylinder crankshaft thermal treatment after strain is in the fixed scope; Adopt rational crankshaft fillet rolling technology simultaneously.

Production method of the present invention:

1, operational path is:

1), produces high-quality bent axle strand;

2), to bent axle roughing, reserve suitable process redundancy (± 0.75mm);

3), means of isothermal quenching;

4), precision work and fillet rolling.

2, select for use the synthetic cast iron of steel scrap carburetting or high-purity magnesium iron pig iron as the major metal material of producing the Austempering ductile iron six-cylinder crankshaft and the add-on of alloy element; Melting molten iron in induction furnace, the winding-up argon gas is with purifying molten iron in electric furnace; Come out of the stove, carry out spheroidizing and inoculation for 1460 °-1500 °.

The add-on of alloy element (accounting for total mass %)

??C	??SI	??Mn	??P	??S	??Mg	??Re	??Cu	??Mo
									??3.50-??3.70	??2.00-??3.00	??＜0.30	??＜0.30	??＜0.02	??0.04-??0.06	??＜0.02	??0.50-??1.00	??0.15-??0.35

3, the metallographic structure of crank shaft blank requires:

The nodularization rate is more than 2 grades;

Number of graphite ball 100/mm ²

Perlite and ratio of ferrite are stable.

4, bent axle is carried out roughing.

5, means of isothermal quenching is carried out at the salt stove production line that has controlled atmosphere; And bent axle is placed in the distortion-free special-purpose thermal treatment mold carries out.

Austenitizing heating and be incubated 880 ° of-950 ℃/1-3h;

330 ° of-380 ℃/1-3h of means of isothermal quenching;

Sampling after the thermal treatment, metallographicinspection are also beaten hardness.

6, precision work and fillet rolling.

The invention has the advantages that: the economic benefit of ADI bent axle is obvious, compares with the steel alloy bent axle, and the ADI bent axle is in light weight, easily manufactured, less investment, cost are low.Compare with certain six cylinder engine with supercharger bent axle, ADI crank shaft blank weight reduces by 10.2%, can save the very expensive steel alloy of price, and the consumption ADI bent axle finished product price that reduces metallic substance is about 1300 yuan/, and its ADI bent axle price is about half of 42CrMo bent axle; More in light weight 10% than the 42CrMo steel alloy die forging bent axle of having used at present supercharged diesel engine, 1500 yuan of every bent axle low prices are for a Diesel Engine Plant that turnout is very big, because the economic benefit that adopts the ADI bent axle to be produced is very significant.Be to belong to high-performance metal materials and the very important project of energy-saving and emission-reduction.

Embodiment

Dalian Diesel Engine Plant supercharged diesel engine Austempering ductile iron 6110 six-cylinder crankshafts are an Application Example of the present invention:

1, bent axle principal dimension (mm) and service condition:

The bent axle total length	The main journal diameter	Rod journal	Fillet radius	Heavy degree of base
					??990	??85	??70	??5	??15

Service condition: explosion pressure Pz=15Mpa

Safety coefficient: n=1.8～2.0

2, chemical ingredients (accounting for total mass %) after the adding of alloy element

??C	??Si	??Mn	??p	??S	??Mg	??Re	??Cu	??Mo
									??3.66	??2.40	??0.16	??0.022	??0.011	??0.042	??0.013	??0.74	??0.23

3, metallographic structure

2 grades of nodularization rates

150/mm of number of graphite ball ²

4, bent axle detected result:

Tensile strength sigma _b1070Mpa

Elongation δ 9%

Rockwell hardness HRc 32

The crankshaft fatigue moment M _-1=3300N-M

Safety coefficient n ≈ 1.9.

Claims (5)

1. Austempering ductile iron (ADI) supercharged diesel engine six-cylinder crankshaft and production method, it is characterized in that: select for use the synthetic cast iron of steel scrap carburetting or high-purity magnesium iron pig iron to reach definite its chemical ingredients scope as the major metal material of producing the Austempering ductile iron six-cylinder crankshaft, the add-on of alloy element particularly, determine foundry goods alloy structure span of control after six-cylinder crankshaft spheroidizing and the inoculation, melting molten iron in induction furnace, winding-up purification for argon molten iron in electric furnace, come out of the stove, carry out spheroidizing and inoculation for 1460 °-1500 °; Means of isothermal quenching is carried out having on the salt stove production line of protective atmosphere: adopt custom-designed thermal treatment mold, guarantee six-cylinder crankshaft thermal treatment after strain require ± the 0.5mm scope in.

2. according to the described Austempering ductile iron of claim 1 (ADI) supercharged diesel engine six-cylinder crankshaft and production method, it is characterized in that: the basic chemical ingredients of six-cylinder crankshaft and alloy element component (accounting for the % of total mass) are:

??C ??Si ??Mn ??p ??S ??Mg ??Re ??Cu ??Mo ??3.5-??3.70 ??2.00-??3.00 ??＜0.30 ??＜0.03 ??＜0.02 ??0.04-??0.06 ??＜0.02 ??0.50-??1.00 ??0.15-??0.35

The nodularization rate is more than 2 grades, number of graphite ball 100/mm ²More than.

3. according to the described Austempering ductile iron of claim 1 (ADI) supercharged diesel engine six-cylinder crankshaft and production method, it is characterized in that: means of isothermal quenching is carried out having on the salt stove production line of controlled atmosphere, its:

880 °-950 ℃ of austenitizing heating, 1-3 hour;

330 °-380 ℃ of means of isothermal quenching, 1-3 hour.

4. according to the described Austempering ductile iron of claim 1 (ADI) supercharged diesel engine six-cylinder crankshaft and production method, it is characterized in that: the six-cylinder crankshaft quench treatment is carried out in special-purpose mold, hot after strain amount require ± the 0.5mm scope in.

5. according to the described Austempering ductile iron of claim 1 (ADI) supercharged diesel engine six-cylinder crankshaft and production method, it is characterized in that: adopt rational round corner rolling process.