JPH10251808A - Ferritic stainless steel for precombustion chamber type diesel engine insert excellent in cold and warm forgeability and cracking resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a precombustion chamber type diesel engine insert material formed by cold and warm forging which is an inexpensive ferritic stainless steel excellent in cracking-resistance and oxidation resistance. SOLUTION: This stainless steel has a compsn. contg., by weight, 0.002 to 0.03% C, <=0.25% Si, <=0.25% Mn, 17.0 to 20.0% Cr, 1.0 to 3.0% Mo, one or two or more kinds among Nb, Ti, V and Zr by 0.2 to 0.6% and <=0.03% N, in which the total content of C+N is regulated to <=0.04%, and the balance Fe with impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an insert material for a diesel engine pre-combustion chamber formed by cold and warm forging.

[0002]

2. Description of the Related Art Conventionally, in the production of a pre-combustion type diesel engine pre-combustion chamber material, there are mainly those produced by cold / warm forging and those produced by precision casting. Materials formed by cold and warm forging include ferrites described in JP-A-56-55553 and JP-A-3-115544, and JP-B-63-37182. A ferrite-martensite type material and a ferrite-austenite type material described in JP-A-3-257142 are disclosed.
0S is used. On the other hand, those molded by precision casting are disclosed in Japanese Patent Publication No. 54-18647,
Examples thereof include ferrite-based materials described in JP-A-6-41354 and materials described in Japanese Patent Publication No. 62-17021 as gasoline engine pre-combustion chamber materials.

[0003]

In recent years, as the output of an internal combustion engine has been increased, the heat load applied to each component in the engine has gradually increased, and some components have exceeded the limits of conventional materials. Among them, the pre-combustion chamber is operated by high-temperature, high-pressure gas, and is subjected to severe heating and cooling repeatedly.
In such materials, problems such as cracks and missing materials have arisen. Therefore, the emergence of new materials that can cope with such problems has been desired in many cases. The emergence of materials that can be manufactured by cold forging is particularly strongly desired. Therefore, an attempt was made to develop a material that can satisfy all of those requirements.

[0004] First, as a result of investigating the materials disclosed to date, the following findings have been obtained. Among the materials to be cold and warm forged, martensitic materials are inferior in cold forgeability and cost increases due to complicated heat treatment processes in the manufacturing process, and the environment in which they are used becomes 900 ° C or more. At a high temperature, there is a disadvantage that the material is easily oxidized and melted due to transformation.

[0005] As for austenitic materials,
Since the material itself is very expensive and is a difficult-to-cut material, there is a disadvantage in that the manufacturing cost is high.
Furthermore, even when the pre-combustion chamber is put to practical use, the thermal expansion coefficient is much larger than that of ferrite-based materials, so that a fatal crack is easily generated in the pre-combustion chamber body and the engine head.

The conventional ferritic stainless steel has a low coefficient of thermal expansion but does not sufficiently satisfy the crack resistance as an insert material for a pre-combustion chamber due to insufficient high-temperature strength. On the other hand, for precision castings,
There are drawbacks that the cost is increased due to the large number of man-hours in manufacturing, and that the characteristics as a pre-combustion chamber are deteriorated due to casting defects.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive ferritic stainless steel which solves the above-mentioned problems and has excellent crack resistance and oxidation resistance. Another object of the present invention is to provide a material at a lower cost by improving the properties. Therefore, in order to achieve this object, the present invention provides a method for producing a steel sheet containing: C: 0.002 to 0.03%, and Si:
0.25% or less, Mn: 0.25% or less, Cr: 17.
0 to 20.0%, Mo: 1.0 to 3.0%, Nb, T
i, V, Zr are one or more of 0.2 to 0.6
%, N: 0.03% or less, and the total amount of C + N is 0.1%.
It was specified that the content was not more than 04% and the balance was Fe and impurities. The feature of the present invention is to improve the crack resistance and oxidation resistance, which are the main required properties of the pre-combustion chamber insert, and further reduce the manufacturing cost, by using a pre-combustion chamber insert having a complicated structure. The components are blended so that they can be easily forged in cold and warm shapes.

Next, the reasons for limiting the components of the steel of the present invention will be described below. C: 0.002 to 0.03% C combines with Nb, Ti, V, and Zr to form a carbide,
It is an element that refines crystal grains by the peening effect to improve crack resistance. For this purpose, the content is preferably at least 0.002% or more, and the cost is preferably 0.002% or more. However, 0.0
Addition of more than 3% not only lowers the oxidation resistance but also lowers the cold forgeability, so the upper limit is 0.03%.
And

[0009] Si, Mn: 0.25% or less Reduction of both Si and Mn elements can be achieved without deteriorating oxidation resistance.
It has been found that one of the main characteristics of cold forgeability evaluation is to improve the deformation resistance characteristics. However, since both elements are indispensable elements for deoxidation at the time of refining, the upper limit of each element is set to 0.25% in order not to lower the cold workability.
It was specified.

[0010] Cr: 17.0 to 20.0% Cr stabilizes a ferrite structure having a low coefficient of thermal expansion and further improves oxidation resistance at high temperatures, that is, is a necessary main characteristic as a pre-combustion chamber. It is an indispensable element for crack resistance. To ensure these properties, it is necessary to contain at least 17.0% of Cr.
If it exceeds 0%, the effect of improving the oxidation resistance is saturated and the cost increases, so the upper limit was made 20.0%. Mo: 1.0 to 3.0% Mo is an element that improves the crack resistance by increasing the high-temperature strength. Therefore, it is necessary to add at least 1.0%. , The formation of the σ phase is promoted to lower the high-temperature strength, so the upper limit is made 3.0%.

Nb, Ti, V, Zr: at least one or more of 0.2 to 0.6% of Nb, Ti, V, Zr is added to form carbides. In addition to improving the crack resistance by miniaturization of the element, it also has the effect of preventing the decrease of Cr in the metal matrix effective for oxidation resistance and suppressing the reduction of oxidation resistance in practical use. , It is necessary to add 0.2% or more of one or more. However, these elements may be used alone or in combination of two or more.
If the addition exceeds 6%, the cold forgeability decreases due to an increase in the deformation resistance value in the cold working or the cost increases, so the upper limit is made 0.6%.

N: not more than 0.03% N reduces the critical cold-compression working properties and deformation resistance properties,
Aggressive addition is undesirable because it significantly reduces cold forgeability. However, when the atmospheric melting method is used, which is advantageous in terms of production cost, N is contained as an impurity. Therefore, the upper limit of N is set to a value that does not significantly add cold forgeability, that is, 0.03%. C + N ≦ 0.04% It is understood that a critical cold working ratio of 70% or more is necessary to cold-forge the pre-combustion chamber insert into the actual machine shape in a favorable manner, and to secure 70% or more, steel is required. Since it has been found that the total C and N contents need to be limited to 0.04% or less in total, the total of C and N contents is defined as 0.04% or less.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the invention and various test results will be described. The components A to M according to the present invention shown in Table 1 were melted in a vacuum high frequency induction electric furnace to obtain 10
After making a 0-kg steel ingot, performing hot forging and annealing at predetermined temperatures, and cutting (partially polishing) the test pieces, they were subjected to various tests. Comparative steels a to h in Table 1 and Conventional steel 1
Test pieces were prepared in the same manner for Nos. 1 to 2. However, regarding the crack resistance evaluation test, the material subjected to hot forging and annealing was subjected to rough forging → intermediate annealing → final forging → finish cutting to produce a pre-combustion chamber 1 shown in FIG. In addition, as for the comparative steels b and c having poor cold forgeability, the annealing and the forging process had to be increased once each in the previous forging process. For the conventional steel 2, all materials quenched and tempered at a predetermined temperature are
The pre-combustion chamber 1 was produced.

[0014]

[Table 1]

(1) Crack resistance evaluation test First, the pre-combustion chamber shown in FIG. 1 (FIG. 2 shows I-II of the pre-combustion chamber shown in FIG. 1)
The cross-section) is shown in FIG.
After heating to 950 ° C. from the upper surface with a gas burner 5 using propane gas containing oxygen, the apparatus 3 is rotated, and water is sprayed on the test piece.
Water-cool to 0-100 ° C. FIG. 4 is a schematic view of fixing a pre-combustion chamber in a crack resistance evaluation test. The heating / cooling pattern as shown in FIG. 5 was repeated 400 times using such a crack resistance evaluation apparatus, and the lengths of all the cracks 7 generated near the injection port shown in FIG. 6 were measured. And finally,
The lengths of all the cracks that occurred were added together, and the total crack length was used as an index for evaluating crack resistance. Table 2 shows the test results.
The total crack length of the invented steel and the comparative steel is the same as that of the conventional steel 1
About 1/4 to 1/5 for conventional steel 2 and about 1 for conventional steel 2.
The value was about ４ to ３, and the crack resistance of the invention steel and the comparative steel was very good.

(2) Oxidation resistance test A width 2 cut and finished from inventive steels A to M, comparative steels a to h, and conventional steels 1 to 2 which were hot forged and annealed at a predetermined temperature.
Test pieces of 0 mm, length of 30 mm, and thickness of 3.5 mm were prepared, and these test pieces were kept at 950 ° C. for 100 hours in an experimental furnace. After the experiment was completed, the test piece cooled to room temperature by air cooling was measured for the increase in oxidation, and the oxidation resistance was evaluated based on the increase in oxidation. Table 2 shows the experimental results. The oxidation resistance of the invention steel as a whole was equivalent to SUS310S of the conventional steel 1, which is generally said to have good oxidation resistance, and was very excellent. In addition, the invention steel D in which Si and Mn were reduced showed no decrease in oxidation resistance. However, the oxidation resistance of the comparative steel, which was good in the crack resistance evaluation test, was generally inferior to that of the invention steel. In particular, the comparative steel e, in which the Cr content was low, was about twice as large as the invention steel. Was shown.

[0017]

[Table 2]

(3) Critical cold-compression rate A diameter of 14 mm and a length cut from inventive steels A to M, comparative steels a to h, and conventional steels 1 to 2 which were hot forged and annealed at a predetermined temperature. A 21 mm test piece was prepared, and the critical cold working ratio (hereinafter, the critical cold working ratio) of each steel type was measured using a compression tester. The limit cold working ratio is a working ratio at the time when cracks are first recognized when compressed in a cold state, and when it is 70% or less, the cold forging step and the annealing step in the production of the pre-combustion chamber. Has been obtained, and the boundary of the evaluation is set to 70%. Table 2 shows the test results. Due to the performance of the test machine, it is impossible to measure a processing rate of 78% or more, so the processing rate is 78%.
78% of materials that do not show cracks
It is written above. The critical cold work rate of invention steel is usually 7
Most of them were 8% or more, and all satisfied a critical cold working rate of 70% or more. On the other hand, the comparative steel is inferior in the critical cold working ratio to the invention steel, and the comparative steel c having a high C and N content is 6%.
Only a processing rate of about 0% was shown.

(4) Deformation resistance value Using the same test piece and testing machine as in the above-mentioned critical cold working rate, the deformation resistance value at a working rate of 60% at which no crack occurred in any of the materials was measured. Table 2 shows the results. It was found that the invention steel improved the deformation resistance by about 10% compared to the comparative steel, and reduced the load on the cold forging machine. Also especially Si
It has been found that Invention Steel D having a low content of Mn and Mn is about 10% lower than the deformation resistance value of the other invention steels. Note that, among the materials in Table 1, the comparative steel c having the highest C and N contents and the conventional steel 1 of the austenitic stainless steel had the largest deformation resistance value.

(5) Comprehensive evaluation as a pre-combustion chamber material capable of cold / warm forgeability Table 3 shows a comprehensive evaluation of the properties obtained above for the inventive steel, comparative steel and conventional steel. Since the properties of the invention steels are better than the comparative steels and the conventional steels, the steels of the invention are suitable for use as pre-combustion chamber materials that require good crack resistance and also cold and warm forgeability. It was shown that there is.

[0021]

[Table 3]

[0022]

As described above, according to the present invention, cracking resistance is remarkably improved with respect to SUS310S or the like conventionally used as an insert material for a diesel engine pre-combustion chamber, and more favorable cooling is achieved. -Warm forgeability has made it possible to provide inexpensive insert materials for pre-combustion chambers.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an insert for a diesel engine pre-combustion chamber,

FIG. 2 is a schematic cross-sectional view of an insert for a diesel engine pre-combustion chamber,

FIG. 3 is a schematic diagram of a crack resistance evaluation test apparatus,

FIG. 4 is a schematic view of fixing an insert for a pre-combustion chamber in a crack resistance evaluation test;

FIG. 5 shows a heat pattern in a crack resistance evaluation test,

FIG. 6 is a schematic view of a crack generated in a pre-combustion chamber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pre-combustion chamber insert 2 Injection part 3 Crack resistance evaluation device 4 Pre-combustion chamber holder 5 Heating burner 6 Spray 7 Crack 8 Holder fixing jig

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuji Kawakami 4-14-1, Suehiro, Kumagaya-shi, Saitama Pref. Inside Riken

Claims (1)

[Claims] C .: 0.002 to 0.03%, Si: 0.25% or less, Mn: 0.25% or less, Cr: 17.0 to 20.0%, Mo: 1% by weight 0.0 to 3.0%, Nb, Ti, V, and Zr may be used alone or in combination of two or more.
0.6%, N: 0.03% or less, C + N content is 0.04% or less in total, and pre-combustion chamber type with excellent cold / warm forgeability and crack resistance consisting of balance Fe and impurities Ferritic stainless steel material for diesel engine inserts.