JPS59129730A - Production of high strength crank shaft - Google Patents

Abstract

PURPOSE:To improve strength and toughness by incorporating specific alloy elements in a crank shaft made of a spheroidal graphite cast iron, subjecting the shaft to an austemper treatment and further subjecting the fillet part of the pin and journal thereof to surface rolling. CONSTITUTION:A crank shaft is cast of a spheroidal graphite cast iron contg. 3.0-4.5% C, 1.5-3.0% Si, 0.02-0.10% Mg, and further contg. 0.05-1.0% Mo, 0.1-0.7% Ni, 0.1-0.5% Cu and 0.2-1.2% Mn alone or in combination. The crank shaft is heated and held to and at 850-950 deg.C for 0.5-3hr and right thereafter the crank shaft is subjected to an austemper treatment wherein the crank shaft is quickly cooled by dipping the same in a salt bath kept at 300-430 deg.C and is held at said temp. for >=1hr. The crank shaft is then machined according to need and thereafter the fillet part of the pin and journal of the crank shaft is subjected to surface rolling, whereby the strength and toughness of the crank shaft made of the cast iron are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a manufacturing technique for a crankshaft for an engine, and a manufacturing technique for improving the strength of a special cast iron crankshaft.

Conventionally, for crankshafts for automobile engines.

Cast iron and steel are used.

And with cast iron crankshafts, in general.

High strength materials such as JIS FCI J7U or FCMP70 are used.

On the other hand, in engines with high loads, steel crankshafts are mainly used because they have high strength and stability despite the high manufacturing costs due to the materials and manufacturing process.

Moreover, in response to the recent demands for lighter engines and higher output, attempts have been made to reduce the shaft diameters of crankshaft pins and journals, and cast iron crankshafts have less margin in terms of strength. 9. Due to the lack of strength and stability, there is an increasing tendency to use steel crankshafts.

However, as mentioned above, a steel crankshaft has the drawback of significantly increasing manufacturing costs compared to a cast iron crankshaft.

The present invention improves the strength and toughness of the crankshaft body by austempering the crankshaft made of spheroidal graphite cast iron, and by applying surface roll processing to the fillet portions of the crankshaft pins and journals. An object of the present invention is to provide a method for manufacturing a high-strength crankshaft that significantly improves the fatigue strength of the crankshaft.

Such purpose is to reduce C:a, O to 45% by weight (hereinafter the same).
1/), 'Si 1.5-3.0%,
Mg: 0.02 to 0.10%.

1 vlo to the main component with the remainder essentially consisting of F'e.
: 0. '05-1.0%, Ni:Q. 1-0.7%,
Cu: 0.1-0.5%.

Mn: 850-9
After heating and incubating at 50℃ for 0.5 to 3 hours,
After being rapidly cooled to 30°C and held for one hour, the finished crankshaft is austempered to a depth of at least 3III11 from the surface to a bainitic structure. This is achieved by a method for manufacturing a high-strength crankshaft, which is characterized by performing one-surface roll processing on the fillet portions of pins and journals.

The method for manufacturing a crankshaft according to the present invention will be described in detail below.

First, the chemical composition of spheroidal graphite cast iron for producing crankshafts was changed to C:3. 0 to 4.5% by weight (the same applies hereinafter).

Si: 1.5-3.0%, Mg: 0.02-0
．． 10%, the balance substantially consisting of Fe, M
o: 0.05-10%, Ni: 0.1-0-
7%, Cu: 0.1~0.5%, Mn: 0.2~
The reason why 1.2% is added alone or in combination will be explained.

Note that C, Si, and Mg are in the same range as generally known spheroidal graphite cast iron, and the reason for limiting the range is also based on well-known reasons, so the explanation will be omitted.

1vio C41 'Ik also accompanies the austempering process.

It has the effect of delaying pearlite transformation in isothermal transformation treatment and is useful, but if it exceeds 0.05%, the effect is insufficient, and if it exceeds 1.0%.

Since a large amount of free cementite tends to crystallize in the cast iron matrix and increases material cost, the content is set at 0.05 to 1.0%.

Cu and INi, like Mo, are effective in delaying pearlite transformation in isothermal transformation treatment.

Its effect is weaker than that of MO, so it should be added as an auxiliary.Ni: 0.2-0.7%, Cu:Q,
The content was set at 1% to 0.5%.

Both Cu and Mn have the effect of easily turning the base into pearlite in the as-cast state and facilitating austempering treatment, but too much Mn tends to crystallize free cementite in the cast iron base.

The content was set at 0.2 to 1.2%.

In addition to the effects of single additions such as Mo,
By adding a combination of Ni, Cu, and Mne.

The base is made into pearlite in the as-cast state to facilitate austempering treatment, and even if the crankshaft is finished by machining as necessary, it can be used for parts that require high strength, such as pin parts, journal parts, and their fillets. This makes it possible to secure a bainite structure layer on two surfaces and three sides in the area.

In addition, the amount added in the case of compound addition naturally varies depending on the thickness of the crankshaft, but it is sufficient to prevent pearlite transformation in the isothermal transformation treatment accompanying the austempering treatment, in other words.

It is sufficient to form a bainite structure layer at least on the surface of the crankshaft after machining, but it is also possible to add a large amount of alloying elements.

As long as the bainite structure is uniform all the way to the core, there is no problem with performance.

However, as mentioned in the effect of adding it alone.

Machinability and durability: The amount of IVio, Mn is sufficient to prevent harmful free cementite from crystallizing into the cast iron base, and the amount of Mo, Ni, Cu is sufficient to not impair castability (segregation, pinholes, shrinkage cavities, etc.). , Mll i.

In these isothermal transformation treatments. The types and amounts of elements that contribute to inhibiting pearlitization are desirably as small as possible to reduce production costs.

After a crankshaft made of spheroidal graphite cast iron having the chemical composition described above is cast into a rough shape or rough-processed in advance,
0.5 at 850-950℃ as austenitizing conditions
After heating and holding for ~3 hours, immediately reduce the temperature to 300~430
The sample is immersed and rapidly cooled in a salt bath at ℃, kept for 1 hour or more to undergo bainite transformation, and then cooled to room temperature.

After that, the crankshaft is finished by machining as necessary.

In this way, the material that is machined and shaved after austempering has a fatigue strength lW of 20% compared to the same hardness of JISPCI) 70 or quenched and tempered spheroidal graphite cast iron.
However, for high-load engines, it is necessary to further improve the fatigue strength.

The crankshaft according to the method of the present invention has a bainite structure in three or more of the surface areas where strength is required.

Furthermore, by applying one-surface roll processing to the fillet portions of pins and journals,
Alternatively, by using a crankshaft made of spheroidal graphite cast or quenched and tempered iron, the fatigue strength is significantly improved, increasing to about 300% of that without gable roll processing.

Additionally, it is generally used as a means of improving fatigue strength.

In addition to surface roll processing, we also offer shot peening, etc.

Although it is sometimes applied as an effective means for growth, it is not as good as surface rolls in terms of treated surface roughness 1 surface hardening depth for parts such as crankshafts.

The structural state of the crankshaft after austempering treatment is that it is entirely bainite with no pearlite mixed in.
The depth of the layer must be 3 mm or more from the diamond surface in the required part of the crankshaft after machining, and if it is less than 3 mm, the durability will not be sufficient.

Next, the reasons for limiting the austempering conditions will be explained below.

Austenitization heating at 850~950°cxO, 5~
The reason for the 3 hours is that at temperatures below 850°C, the time required for austenite formation in thick-walled parts such as crankshafts becomes longer, and at temperatures above 950°C, austenite crystal grains become coarser, resulting in lower strength and toughness. This is because

The holding time varies depending on the wall thickness, but the minimum time necessary for austenitizing a crankshaft is 0.5 hours, and even for thick-walled products, holding for 3 hours is sufficient.

Holding conditions in a salt bath as isothermal transformation treatment.

Below 300~b, the hardness becomes Hv350 or higher, making it difficult to perform VJ drilling/drilling. Therefore, the hardness limit is set at 300°C, and when processing at a temperature above 430°C, the fatigue strength decreases. This is because it does not provide much heat and is disadvantageous in terms of thermal energy.

Therefore, from the balance of machinability and strength, Hv
A range of 350-390°C is optimal to obtain a hardness of 260-320°C.

How long does it take to complete bainite metamorphosis?

Even in the case of regular spheroidal graphite cast iron, it takes about an hour.
If the time is shorter than this, residual austenite may be present, or untransformed austenite may transform to martensite during cooling, resulting in a decrease in strength and toughness, which is not preferable.

Finally, the conditions for 9-surface roll processing will be described.

Fatigue strength increases particularly when the Hertzian contact stress is in the range of ao o "y, y,
``y, the residual stress influence depth is 0.3 mm or more.

Even with JIS FCD70, the fatigue strength can be significantly increased by surface rolling, but increasing the contact stress causes bending in the crankshaft, which limits its practical range.

BJ ability is to obtain high fatigue strength with low contact stress.

Note that the present invention provides a method for manufacturing a high-strength crankshaft, and the strength and toughness of the nine parts are high, and
Since the combination of face rolling provides a significant improvement in fatigue strength, it is obvious that it can be applied to other parts used under similar conditions.

The present invention will be described in detail below based on the accompanying drawings.

Embodiment 1 In FIG. 1, a semicircular annular cutout of R1 was provided. Ono rotary bending fatigue test specimens were made from austen and N6-treated bainitic spheroidal graphite cast iron, and the fatigue strength was compared after the surface was rolled. The shape of the test piece is shown in Figure 2, and the rolling conditions are shown in Figure 2.

Table 2 shows the material and heat treatment conditions of the Y block, which is the test piece material.

After heat treatment, it is finished into the shape shown in Figure 2 by machining.
The surface was rolled under the conditions shown in the table.

The fatigue test was conducted at 4400 rpm, and the fatigue limit of 107 cycles is shown in FIG.

As is clear from Fig. 1, the fatigue strength of bainite* and W subjected to austempering according to the method of the present invention is 2.
One surface roll processing is higher than 0% [Thus, the difference becomes even more remarkable.

The fatigue strength of the ausstepper-treated bainitic cast iron according to the method of the present invention is a contact stress of 618 k5/'. JIS surface roll processing under the same conditions
The fatigue strength is 1.5 times that of FCI) 70, and about 4 times that of JIS FCD without rolling on one surface.

It is possible to further increase the contact stress during surface roll processing, but considering the roller strength, practically 600
To! It is sufficient to consider degrees below 4°.

In Figure 1, the austenite-treated bainitic cast iron specimen according to the present invention showed a hardness of Hv 275, but the relationship between the hardness and fatigue strength of spheroidal graphite cast iron is proportional up to about Hv400. Therefore, it can be easily determined that the same rise occurs even in the case of surface roll processing.

Figure 3 shows the results of X-ray measurement of compressive residual stress.

The main reason why the fatigue strength of the bainitic cast iron according to the present invention is significantly different from that of JIS FCI J70 is thought to be due to the difference in residual stress level, and as is clear from FIG. The results show that this is obtained by the bainite cast iron ten-tomo roll processing.

Example 2 Two crankshafts of a diesel four-cylinder engine were made from austempered bainitic cast iron according to the present invention, and the surfaces were rolled.

A severe durability test was conducted on an actual machine.

The test crankshaft has a bainite structure up to the core, so it is made of ordinary spheroidal graphite cast iron, 0.2% Mo + 0.5
%Ni-added cast iron was used.

In addition, the test crankshafts were subjected to the heat treatment shown in Table 2 in the form of rough shapes, and after being processed for one or more precepts.

The fillet portions of the pin and journal were machined with 9-step rolls.

The surface roll processing conditions are: roller diameter R7.5mm;
Roller tip radius R1.5mm, roller pressure load 500
kg.

The number of roller passes was 30 times, and the contact stress was 490 ~.

Durability test conditions are 4BOOrpm x 300 hours engine continuous high speed endurance test and 700 rpm x 4 se
c and 4800 rpm x 4 sec for 8 seconds is 1 cycle.

The uptown test was conducted under two conditions, with 200,000 cycles being repeated.

The test results are shown in Table 3.

Table 3 Durability test results As is clear from the test results, the surface rolled product of austempered bainitic cast iron according to the present invention has the following properties:
It was confirmed that the durability of the actual product was significantly superior to that of the conventional JIS FCL 70 product.

Example 3 Surface Bainite 1 Crankshafts for gasoline engines were manufactured by varying the depth of the flange, and a single plane bending fatigue test was conducted.

The test conditions were a partial oscillation test with a minimum load of 1 [On] of 10
Compare the maximum front claw after repeated tests.

The surface rolling processing conditions for the sample were such that the contact stress was constant at 430-. The test results are shown in Table 4. Table 4: Bending fatigue test results for single products.

Endurance limit load hardly increases, JIS FCI J70
However, if the entire bainitic structure layer on one surface is 3 mm or more thick, the durability limit load will increase significantly.

As is clear from the following, the crankshaft manufacturing method according to the present invention not only improves the strength and toughness of the crankshaft body compared to conventional cast iron crankshafts, but also improves the fatigue strength of the crankshaft. It becomes the weak link. There is an advantage in that it is possible to manufacture a crankshaft with significantly improved fatigue strength in the fillet portions of the pins and journals.

[Brief explanation of drawings]

Figure 1 shows bainite cast iron and JISFC according to the method of the present invention.
Figure 2 shows a comparative example of fatigue strength of D70, Figure 2 shows the shape of the test piece used in the fatigue test, Figure 3 shows the compressive residual stress after gable roll processing of bainitic cast iron and JIS FCD70 according to the method of the present invention. FIG. 3 is a diagram showing a comparative example of distribution. Applicant Toyota Motor Corporation

Claims (1)

[Claims] (1) C: 3.0 to 4.5% by weight (same hereafter), Si:
15 to 3.0%, Mg: o, o2 to 0.10%, the remainder substantially consisting of Fe, Mo: 0.05
-1.0%. Ni: 0.1-0.7%, Cu: 0.1-0.5%
, a crankshaft made of spheroidal graphite cast iron with Mn: 0.2-1.2% added singly or in combination.
After heating and holding at 0℃ for 0.5 to 3 hours, 300 to 43
A high-strength crankshaft characterized by an austempering process in which the material is rapidly cooled to 0°C and held for 1 hour, and then the fillet portions of the crankshaft pins and journals are rolled on one surface. manufacturing method.