JPS59177317A - Manufacture of supertough steel - Google Patents

Abstract

PURPOSE:To manufacture a supertough steel having high strength, superior ductility and toughness as well as especially superior drawability and rupture toughness by quenching a high Si tough steel contg. aspecified amount of Si from a proper temp. and by properly tempering it. CONSTITUTION:A high Si tough steel consisting of, by weight, 1.8-3.0% Si, about 0.25-0.55% C, about 0.35-1.0% Mn, about 0.6-1.2% Cr, about 0.15-1.2% Mo, about 0.001-0.01% Ca and the balance Fe with impurities is quenched from 890-1,150 deg.C which is higher than a conventional temp., and it is properly tempered to obtain a super-tough steel. Said high Si tough steel may further contain about 0.3-4.0% Ni and/or about 0.0005-0.02% B, one or more among about 0.01-0.2% Ti, about 0.01-0.3% Nb+Ta and about 0.05-0.3% V, and one or more among Cu, Pb, Se and Te.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ultra-strong steel that has high strength, ductility and toughness, and particularly excellent drawing and U-fracture toughness values.

In recent years, transportation equipment such as aircraft and automobiles has become more and more important in terms of operational performance such as acceleration and economic efficiency such as fuel consumption. In order to improve
, g FlF is particularly required, and therefore the tensile strength is 160 kgf/rr.
The use of high-strength steel of +m2 class or higher is being promoted. In this case, the material for the above-mentioned parts is required to have both high strength and sufficient ductility and toughness, but with conventional steel types, the above-mentioned ductility and toughness are still sufficient. I couldn't say that.

Therefore, the present applicant has developed an ultra-strong steel that has even higher strength than the conventional 11 types and has sufficient ductility and toughness, and has already filed a patent application (Japanese Patent Application Laid-Open No. 5
Published in Publication No. 7-41354). This ultra-strong steel has higher strength and sufficient ductility and toughness than conventional steel types, and has been able to gain some acclaim, but the inventors have We have developed a variety of steels with the aim of developing high strength steels with sufficient ductility and toughness, and especially high lateral reduction of area and fracture toughness values when tempered to high strength. As a result of repeated experimental research, this invention was completed.

That is, in this invention, a high-Si type strong steel containing 1.8 to 3.0% Si by weight is quenched at a temperature of 890 to 1150°C, which is higher than that normally performed, and then appropriately tempered. By the way, super strong 'tA tl! It is characterized by producing l.

The steel to which this invention is applied is a high-Si type high-strength steel containing 1.8 to 3.0% Si. :0.25-0.5
5%, Si: 1.8-3.0%, Mn: 0, 3
5-1, 0%, Cr:0.6-1.2%, Mo+0.
15-1.2%, Ca0.001-0.01% as basic components, Ni: 0.3-4.0%, B:
One or two of 0.0005 to 0.02%, and Ti: O, Ol to 0.2%, Nb+Ta:
0, 01-0, 3%, V: 1 of 0.05-0.3%! I8 or 2 or more, other Cu, Pb
, Se, and Te, with the remainder being Fe and impurities. In order to provide such high strength and sufficient ductility and toughness at the same time, and further improve the lateral constriction and fracture toughness values when tempered to particularly high strength, S≦
0.005%, 0≦0.0015% to reduce undesirable inclusion accumulation, and the addition of Ca creates spherical composite inclusions of oxide and sulfide.Applicable to rust. can do. In this invention, G- whose composition has been adjusted in this way is quenched at a temperature of 890 to 1150°C, which is higher than the usual temperature, and then tempered as appropriate, which has four characteristics. There is.

Next, a more preferable chemical composition range (wt%) of ultra-strong steel to which this invention is applied will be explained.

If C is less than 0.25%, it is not sufficient to ensure sufficient hardenability or strength, and if it exceeds 0.55%, the deterioration of ductility or toughness will be significant. 5
A range of 5% is more desirable.

Si is an element added to increase strength without significantly impairing ductility and toughness, and to avoid low-temperature tempering brittleness, but if it is less than 1.8%, this effect is not sufficient; If it exceeds .0%, the deterioration of ductility and toughness becomes significant, so it is necessary to keep it in the range of 1.8 to 3.0%.

If Mn is less than 0.35%, the effect of improving hardenability is small, and if it exceeds 1.0%, there is no particular advantage, and if anything, the ductility of the steel is adversely affected. 0%
It is more desirable to set it within the range of .

Cr is an element effective in improving hardenability, but at 0.6%
If it is less than 0.6% to 1.2%, the improvement in second hardenability will not be sufficient, and if it exceeds 1.2%, the ductility and toughness of the steel will deteriorate when tempered to high strength. It is more desirable to have a range.

Mo is an element necessary for improving hardenability and discoloring ductility and toughness, but if it is less than 0.15%, the effect is not sufficient, and if it exceeds 1.2%, the effect becomes smaller. , and is expensive, so it is more desirable to keep the content in the range of 0.15 to 1.2%. Create spherical composite inclusions. That is, the added Ca forms oxysulfides, which float during Pf formation and re-melting (more preferably during vacuum re-melting), and remain after re-melting (more preferably after vacuum re-melting). It makes the inclusions spheroidal and improves the toughness compared to the ductility of steel. However, if it is less than 0.001%, the above effect will be small, and if it exceeds 0.001%, inclusions will increase and the ductility of the steel will deteriorate, so it should be in the range of 0.001 to 0.01%. is more desirable.

Furthermore, in addition to the above basic components, Ni, B or T
One or more of i, Nb, Ta, and V can be contained as appropriate.

Among these, Ni and B are effective in improving hardenability, but when these elements are included, Ni:
If it is 0.3 to 4.0%, B: the effect of improving hardenability and discoloration of ductility and toughness will be small, and if it exceeds 4.0%, the above effects will not be noticeable and it will become expensive. Therefore, it is desirable to keep the range as described below. Also, B is 0.00
If it is less than 0.05%, the effect of "hardening tendency" will be small;
If it exceeds 0.02%, the above-mentioned effect will be reduced and it will also cause hot cracking, so it is desirable to keep it in the range shown in 2.

Furthermore, Ti, Nb, Ta, and V are effective for refining crystal grains, but when these elements are included, Ti:o
, 01-0.2%, Nb+Ta: 0.01-0.3%,
V: It is more desirable to add 0.05 to 0.3% of JJ, l. In this case, if T1 is less than 0.01%, the effect of grain refinement will be small, and if it exceeds 0.02%, the cleanliness and toughness of the steel will decrease significantly, so it is preferable to keep it within the above range. If it is less than 0.01%, the effect of improving grain toughness due to grain refinement will be small, and if it exceeds 0.3%, carbonitrides will increase and toughness will deteriorate, so it is desirable to keep it within the above range. . Furthermore, if ■ is less than 0.05%, crystal grain refinement and hardening tendency will occur.
The effect of - is small, and if it exceeds 0.3%, the hardenability will deteriorate, so it is desirable to keep it in the above range.

Furthermore, if S exceeds 0.005% among the impurities, even if the ductility and toughness are improved by Ca, sufficient ductility and toughness cannot be obtained. Therefore, it is more desirable to keep S in a very small amount of 0.005% or less.

In addition, when the O content in impurities is high, the amount of inclusions increases,
Since it impairs the toughness of steel, it is more desirable to keep it at 0.0015% or less.

In addition, Cu is added to improve strength and corrosion resistance, and Pb and Se are added to improve machinability.

One or more of Te and Bi may be contained.

In addition, when AM is used as a deoxidizing agent, it may be contained in a range of 0.01 to 0.04% for deoxidizing and grain refinement. That is, if it is less than 0.01%, the above effect is small, and if it exceeds 0.04%, the ductility and toughness deteriorate when tempered to high strength.

When refining steel with such chemical composition, the conventional thinking is that it is usually quenched at a temperature of 820 to 880'C and tempered at an appropriate temperature before use. After this tempering, it is possible to obtain a tough steel with high strength and excellent ductility and toughness. As a result of various tests on conditions, especially Si
In high-Si type strong steel containing 1.8 to 3.0% of 890
It has been newly discovered that by quenching from a temperature of ~1150°C and then appropriately tempering, the drawing strength and fracture toughness can be significantly improved without reducing yield strength and tensile strength. Here, the quenching temperature is 890°
If it is lower than C, the ductility and toughness are only the same as before.
If the temperature exceeds 1150° C., the fracture toughness value will become flat, but the diameter and aperture value will increase, which is not preferable.

The cooling rate during quenching in the manufacturing method of the present invention is desirably selected appropriately depending on the hardenability of the steel. For example, water quenching, oil quenching, blast quenching, air cooling or will be done.

Hereinafter, this will be explained in more detail with reference to Examples.

Steel having the chemical composition shown in Table 1 was melted, then ingot-formed and forged to produce an Inno I sample material with a diameter of 170 mm.

Next, tensile test pieces and fracture toughness test pieces were prepared from a 172-radius section of each specimen, and each test piece was held at each quenching temperature shown in Table 2 for 1 hour, and then oil quenched from that temperature. Subsequently, after subzero treatment was performed under the conditions of -73°C x 1 hour, each sample listed in Table 2 was tempered by holding at the same temperature for 2 hours and air cooling twice.

Next, the tensile properties and fracture toughness values of each test piece after tempering were examined, and the results shown in Table 2 were obtained.

As shown in Tables 1 and 2, those quenched from the conventional quenching temperature range of 850 to 870 degrees Celsius have high strength and sufficient ductility and toughness, but -
890 to 1150 as specified in the present invention, which is higher than the temperature specified in
Quenching from a temperature of °C 1. In this case, it not only has high strength but also sufficient ductility and toughness, and even when tempered to a particularly high strength, the reduction of area, which is an index of ductility, and the fracture toughness, which is an index of toughness, are It is clear that each is significantly improved.However, when the temperature exceeds 1150°C, it is clear that the elongation and the area of area are extremely reduced.

As explained below-1-, according to the present invention, 1.
In producing ultra-strong steel containing 8 to 30% by weight of Si, the steel is heated to a temperature of 890 to 115% higher than normal temperature.
By quenching from a temperature of 0°C and then appropriately tempering, it has high strength and sufficient ductility and toughness, and even when tempered to a high strength, it has an even better drawing capacity than conventional ultra-strong steels. It is possible to manufacture ultra-strong steel with +fi and fracture toughness values, and if such ultra-strong steel is used to manufacture aircraft parts (particularly suitable for launch ink gear materials) and automobile parts, etc. It is possible to increase the strength and toughness of these parts, and it is also possible to reduce the weight and extend the lifespan of these parts.

Patent applicant: Daido Steel Co., Ltd. Representative Patent Attorney Yutaka Shio

Claims (1)

[Claims] (1) Ultra-strong steel characterized by i;-%, high Si-based strong steel containing 1.8 to 3.0% Si, quenched at a temperature of 890 to 1150°C, and then appropriately tempered. manufacturing method.