JPS61117251A - Heat resisting steel - Google Patents

Abstract

PURPOSE:To obtain the ferritic heat resisting steel having superior thermal fatigue characteristic, by providing specific amounts of (C+N), Si, Mn, Cr, Al, and 1 or >=2 kinds among Nb, Ti, and Zr. CONSTITUTION:The heat resisting steel consists of, by weight, 0.05-0.4% (C+N), 0.5-3.5% Si, <2% Mn, 18-25% Cr, 0.2-2% Al, 0.1-1.5%, in total, of 1 or >=2 kinds among Nb, Ti, and Zr, and the balance Fe, or further contains 1 or >=2 kinds selected from 0.3-3% Ni, 0.3-3% Mo, 0.5-3% W, 0.2-2% V, and 0.001-0.01% B.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is used as a combustion chamber member for an internal combustion engine, such as a pre-chamber of a diesel engine, and has a thermal fatigue resistance required for such a combustion chamber member. , relates to heat-resistant steel with excellent heat crack resistance and corrosion resistance.

(Prior Art) In recent years, with the miniaturization and increase in output of diesel engines, the heat load on engine parts has become increasingly large, and various material problems have accordingly occurred. And especially the nozzle part of the vortex combustion chamber used in small diesel engines.

Since high-temperature combustion gas is ejected at high speed, it is exposed to high temperatures, and at the same time, it is cooled during air compression, so it is subjected to repeated heating and cooling, resulting in significant damage due to thermal fatigue.

Therefore, under these circumstances, there is a demand for the development of a heat-resistant steel for the vortex combustion chamber and the nozzle part, which has good thermal fatigue resistance and heat crack resistance.

Conventionally, pre-chamber materials for diesel engines include 5UH3, 5UH31, 5UH661 and Nimo
Heat-resistant steels and super heat-resistant alloys such as cast80 are used, but both have problems with thermal fatigue and heat resistance, which determine the life of the prechamber.

(Purpose of the Invention) Therefore, the present inventors conducted detailed studies on various alloys with the aim of meeting the above-mentioned needs, and found that:
It has been found that a ferritic heat-resistant steel having the chemical composition shown below has extremely superior thermal fatigue resistance and heat resistance compared to, for example, conventional prechamber materials.

(Structure of the Invention) That is, the steel according to the first invention of the present invention has, in weight%,
C+N: 0.05-0.40%, Si: 0.5-3.5
%, Mn: 2.0% or less, Cr: 18.0 to 25.0%
, Al: 0.2 to 2.0%, and one or more selected from Nb, Ti, and Zr in a total amount of 0.
．． It is a ferritic heat-resistant steel with excellent thermal fatigue properties, containing 1% to 1.5% and the remainder substantially consisting of Fe, and the steel according to the second invention has a content of 1% by weight and C+N: 0.05 to 0. .4
0%, Si: 0.5 to 3.5%, Mn: 2.0% or less,
Cr: 18.0-25.0%, AfL: 0, 2-2
, 0%, and one or more selected from N b , Ti and Zr in a total amount of 0.1 to 1
．． 5%, and further contains Ni: 0.3 to 3.0. Mo:
0.3-3.0%, W: 0.5-3.0%, V: 0.2
~2.0% Oyobi B: A ferritic heat-resistant steel with excellent thermal fatigue properties, containing one or more selected from O, 0O1-O, and oi%, with the remainder essentially consisting of Fe. be.

Next, the reason for limiting the alloy composition (wt%) of the heat-resistant steel according to the present invention will be described.

C+N: 0.05-0.40% These elements react with Cr, Nb, Ti, Zr, etc. to form carbonitrides, increasing high-temperature strength, preventing coarsening of crystal grains, and improving toughness. It has the effect of improving ductility. In addition, prechambers are often manufactured by precision casting, and in this case, these elements have the effect of improving the flowability of the metal, and in order to obtain the above effect, a minimum of 0.05
%, but if too much is added, the ferrite phase becomes unstable, an austenite phase is formed, and thermal fatigue properties are reduced, so the content is set to 0.40% or less. Note that the present invention also includes cases where the content of either C or N is less than the effective amount.

St: 0.5-3.5% Si is an element that not only acts as a deoxidizing refining agent, but also improves oxidation resistance, corrosion resistance, and carburization resistance, and also improves the flowability of the metal. 0.5% to get
The above additions are necessary.

However, if added in excess, the toughness and ductility would decrease due to the precipitation of the σ phase, leading to deterioration of thermal fatigue properties and heat crack resistance, so the content was limited to 365% or less.

Mn: 2.0% or less Mn acts as a deoxidizing refining agent like St, but
If added too much, oxidation resistance deteriorates, so the content was set at 2.0% or less.

Cr: 18.0-25.0% Cr is an essential element in order to obtain excellent oxidation resistance and corrosion resistance. However, if it is added too much, the toughness and ductility will decrease due to the precipitation of σ phase, etc., so it is limited to a range of ia, o to 25.0%.

An: 0, 2-2.0% AfL, like Cr, is an effective element for increasing oxidation resistance and corrosion resistance. In addition, in ferritic heat-resistant steel, it has the effect of suppressing the precipitation of σ phase, which causes a decrease in toughness and ductility. In order to obtain such an effect, a minimum of 0.2%
However, since it is an active element, excessive addition deteriorates manufacturability, so the amount was set at 2.0% or less.

Nb, Ti, and Zr: Total amount 0.1-1.5% These elements react with C and N to form carbonitrides, increasing high-temperature strength and, as mentioned above, reducing the coarsening of crystal grains. It works to suppress and improve toughness and ductility. In order to obtain such an effect, it is necessary to add at least 0.1%, but even if a large amount is added, the effect will not only be saturated;
6Ni:0 limited to a maximum of 1.5% due to high cost
．． 3 ~ 3.0%, MO: 0.3 ~ 3.0%,
W: 0.5-3.0%, V: 0.2-2.0% and B
:0', 001 to 0°01% or more Ni, Mo, W, V, and B are all effective elements for improving strength, so one or more of these may be used as necessary. Or add two or more kinds. Of these,
In particular, Ni is an element that is effective in strengthening the ferrite base and improving toughness and ductility, but if it is added too much, the ferrite phase becomes unstable and an austenite phase is generated, which reduces thermal fatigue properties, so the range should be limited to 0.3~ It was limited to 3.0%.

Also, M o, W.

(2) is an element that reacts with C and N to form carbonitrides and increases high-temperature strength, but excessive addition of the first element not only deteriorates oxidation resistance but also causes a decrease in toughness and ductility. For MO, it is 0.3-3.0%.

0.5-3.0% for W, 0.2-3.0% for ■
It was limited to 2.0%. Furthermore, B is an element that segregates at grain boundaries, strengthens the grain boundaries, and improves thermal fatigue resistance and heat crack resistance. In order to obtain such an effect, it is necessary to add at least 0.001%, but even if a large amount is added, the effect will not only be saturated, but also cause a decrease in oxidation resistance and the formation of fiFiA compounds. Since this leads to deterioration of high-temperature strength due to precipitation, the upper limit was set at 0.01%.

(Example) Next, the characteristics of the heat-resistant steel according to the present invention will be explained in detail using examples.

Inventive steel A-I and comparative steel J-M having the chemical compositions shown in Table 1 were melted in a high-frequency induction furnace, and JISA
A boat-shaped test piece was produced by casting in a boat-shaped shape.

Dice (Example 1 (thermal fatigue)) First, from a boat-shaped test piece to a heat fatigue test piece (parallel part metal diameter 10a
u+, parallel length 40 ms) was collected. In the thermal fatigue test, the amount of restraint strain was ±0.6% (low temperature side: tensile strain (300℃)
+0.6%), high temperature side: compressive strain (10 at 750℃, S
%)) and subjected to the thermal cycle shown in FIG. 1, and the number of cycles until breakage was determined. The results are shown in Table 2.

7'/'/', / /' As shown in Table 2, the invention steels A-I and comparative steel J
It is clear that the number of cycles until fracture is greater than that of conventional steel and -M, and that it has excellent thermal fatigue properties.

<Example 2 (Heat Crack Resistance)> Next, a prechamber having the shape shown in FIG. 2 was prepared by cutting from the 3-fly test piece, and a heat crack test was conducted.

Fig. 3 shows the test method, and Fig. 3(a) shows the heating status of the test piece. In the figure, 1 is an Al holder, 2 is a prechamber, and 13 is a burner. 3, a combustion flame 4 of oxygen + propane is generated to heat the prechamber 2. Moreover, FIG. 3(b) is a diagram showing a thermal cycle waveform, in which burner heating from room temperature→
Air cooling → spray water cooling → room temperature → burner heating is repeated every 112 seconds. Therefore, as mentioned above, the prechamber 2 is given a thermal cycle in which it is heated to 900°C by the burner 3 and then cooled, and the prechamber is heated every 50 cycles.
The presence or absence of heat cracks in No. 2 was checked. Table 3 shows the number of thermal cycles until the occurrence of beat cracks for the steels A to JNM of the present invention and comparative steel JNM.

As shown in Table 3, the timing of heat crack occurrence in Inventive Steel A-I is much later than that in Comparative Steel J-M, and it has excellent heat crack resistance, which is a very important property for a pre-chamber. It is clear that

<Example 3 (Oxidation resistance and corrosion resistance)> In addition to the above-mentioned thermal fatigue and heat crack resistance, the prechamber of a diesel engine is required to have oxidation resistance and high temperature corrosion resistance. These properties of the invented steel were also investigated.

Therefore, a cylindrical test piece with an outer diameter of 7 layers and a length of 15 intestine was prepared from a boat-shaped test piece of the sample material having the composition shown in Table 1, and an oxidation test and a corrosion test were conducted.

The oxidation test was conducted using an electric furnace by heating at 900° C. in a static atmosphere for 200 hours.

In addition, the oxidation resistance was evaluated using an oxidation loss method in which the weight of the test piece was measured after removing scale generated on the surface of the test piece after heating and compared with that before the test.

Diesel engines contain trace amounts of sulfur in their fuel, so
This sulfur is concentrated in the combustion products and the prechamber is attacked and corroded by sulfur. Therefore, the S attack test was also conducted on the steel of the present invention. Here, a synthesis method (IC+10Cu
8 in SOn +6BaSOa +2Na2304)
After heating for 0 hours, the corrosion loss after descaling was determined in the same manner as in the oxidation test.

Table 4 summarizes these results.

7'/' Table 4 (Ig/c112) As shown in Table 4, S, an element that improves oxidation resistance,
t, Cr and A! 2. It is clear that the steel of the present invention containing a considerable amount of oxidation and corrosion resistance is very good. In particular, it has better oxidation resistance and sulfur attack resistance than comparison steel K, which has a low Cr content, and it has better sulfur attack resistance than comparison steel and M, which have a high Ni content. That is clear.

(Effects of the Invention) As explained above, the heat-resistant steel according to the present invention contains 1% by weight, C+N: 0.05-0.40%, and Si: 0.5%.
~3.5%, Mn: 2.0% or less, Cr: 18.0-2
5.0%, All: 0.2~. 2.0%, as well as Nb
, Ti and Zr in a total amount of 0.1 to 1.5%, and if necessary, Ni: 0.3 to 3.0%, Mo: 0. 3-3.0%
, W: 0.5-3.0%, V: 0.2-2.0% and B: 0.001-0-01%, and the remainder is substantially Since it is essentially made of Fe, it has extremely excellent thermal fatigue resistance and heat resistance, and also has extremely excellent oxidation resistance and corrosion resistance. This provides a very good effect of being suitable for parts.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the heating and cooling conditions in the ripening cycle test, Fig. 2 is an explanatory diagram of the slope showing the shape of the pre-chamber, and Fig. 3 (a) is an explanatory diagram showing the heating situation for the pre-chamber. FIG. 3(b) is an explanatory diagram showing a thermal cycle waveform for the prechamber. Patent applicant Daido Steel Co., Ltd. Representative Patent Attorney Yutaka Oshio Figure 3 (a) 1 (b)

Claims (2)

[Claims] (1) In weight%, C+N: 0.05-0.40%, Si
: 0.5 to 3.5%, Mn: 2.0% or less, Cr: 18
．． 0 to 25.0%, Al: 0.2 to 2.0%, and one or more selected from Nb, Ti, and Zr in a total amount of 0.1 to 1.5%, with the remainder A ferritic heat-resistant steel with excellent thermal fatigue properties, consisting essentially of Fe. (2) In weight%, C+N: 0.05-0.40%, Si
: 0.5 to 3.5%, Mn: 2.0% or less, Cr: 18
．． 0 to 25.0%, Al: 0.2 to 2.0%, and one or more selected from Nb, Ti, and Zr in a total amount of 0.1 to 1.5%, and further Ni:
0.3-3.0, Mo: 0.3-3.0%, W: 0.5
~3.0%, V:0.2-2.0% and B:0.00
A ferritic heat-resistant steel containing one or more selected from 1 to 0.01%, with the remainder substantially consisting of Fe and having excellent thermal fatigue properties.