JPH0726149B2 - Method for manufacturing high-strength stainless steel section - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a shaped steel made of austenitic stainless steel used for a structural member for construction, for example, H-shaped steel, chevron shaped steel, groove made of austenitic stainless steel. The present invention relates to a method for manufacturing shaped steel and further steel sheet piles.

(Prior Art) Steel used for structural members for construction is stipulated by the Building Standards Law, but the regulations do not include stainless steel shaped steel. It is considered that the reason is not because the mechanical properties of stainless steel as a structural member are not appropriate, but because the price of stainless steel is too high because it is too expensive to use as a structural member.

However, the rapid rise in land prices in recent years has relatively reduced the cost required for buildings built on it, and relatively expensive materials have also been used as building structural materials. For example, buildings in the center of the city tend to be designed based on the idea of respecting landscape or function, unlike conventional designs based on cost.

Activities that follow this trend include activities such as the "Landscape Materials Study Group" as an advisory body of the Ministry of International Trade and Industry Bureau of the Ministry of International Trade and Industry, and "Comprehensive Technology Development Project" of the Ministry of Construction. Especially in the latter, the “Structural Material Design and Construction Standards Preparation Subcommittee” established in April 1986 by the Stainless Steel Association conducted a survey and experimental research for two years and six months, and austenitic stainless steel with excellent appearance quality. An attempt was made to apply steel as a structural member for construction, and the mechanical properties necessary for using austenitic stainless steel (JIS SUS304) as a structural member for construction were clarified. Table 1 shows the contents of austenitic stainless steel (referred to as “S1” in Table 1) as the structural member for construction, which is a general austenitic stainless steel, SUS 304 (in Table 1, S2 ”).

The composition of both S1 and S2 alloys was C: 0.08% by weight.
Below, Si: 1.00 wt% or less, Mn: 2.00 wt% or less, P: 0.04
5% by weight or less, S: 0.030% by weight or less, Ni: 8.00 to 10.50% by weight, Cr: 18.00 to 20.00% by weight, which are the same.

(Problems to be Solved by the Invention) However, the austenitic stainless steel materials currently manufactured cannot always satisfy the mechanical properties.

Of these, rolled steels represented by H-shaped steels are particularly problematic.

In general, austenitic stainless steel is subjected to solution treatment for the purpose of improving corrosion resistance, but rolled shaped steel is different from other plate materials, bar materials, and wire materials because it does not undergo a cold straightening process. The yield point is low. Therefore, 0.
In order to guarantee 1% proof stress, it is necessary to newly install cold working equipment in the existing equipment and perform cold working after solution treatment to improve the strength.

However, since the sectional shape of the shaped steel is complicated, it is difficult to perform cold working, and the working equipment for the cold working is also required.

Therefore, the facility introduction cost for cold working the shaped steel becomes enormous and the feasibility is poor.

That is, in order to apply the rolled shape steel of austenitic stainless steel to the structural member for construction, it is not necessary to newly install cold working equipment, and the proof stress and the like can be obtained by the low cost manufacturing method using the existing equipment. It is necessary to improve and secure the mechanical strength.

As described above, in the conventional technology, since there was no demand for high yield strength and yield ratio upper limit type stainless steel, its manufacturing technology was not established, and it is generally considered that ordinary stainless steel In the manufacturing method of No. 1, it is impossible to manufacture stainless steel with high yield strength (0.1% yield strength: 24 kgf / mm ² or more) and upper limit of yield ratio (yield ratio: 60% or less). Therefore, it was not possible to produce high yield strength and yield ratio upper limit type stainless steel.

Here, an object of the present invention is to use for a structural member for construction, which has excellent corrosion resistance originally possessed by austenitic stainless steel, and further satisfies the strength standard as the structural member for construction (see Table 1 above). The present invention provides a method for manufacturing a shaped steel made of austenitic stainless steel.

(Means for Solving the Problems) The present inventors have made various studies in order to solve the above problems.

First, as a method of improving the yield strength of austenitic stainless steel, a technique of introducing working strain by rolling (hot rolling) was considered.

However, normally, in the austenitic stainless steel, it is not possible to suppress the formation of carbides at the grain boundaries in the as-rolled state, and it becomes impossible to avoid the reduction in corrosion resistance due to the formation of the Cr-deficient layer at the grain boundaries. I will end up.

On the other hand, in order to secure and guarantee the excellent corrosion resistance originally possessed by austenitic stainless steel, solution treatment must be performed by all means, and when this solution treatment is performed,
The yield strength will be greatly reduced.

Further, although the yield strength is recovered by performing cold working after the solution treatment, there is a big problem in performing cold working on the shaped steel and it cannot be actually performed as described above. .

Therefore, as a result of further various investigations by the present inventors,
The results shown below were obtained. That is, in order to prevent the deterioration of corrosion resistance due to the Cr-deficient layer at the grain boundaries, it is necessary to perform solution treatment at a temperature of 800 ° C or higher, and L / C anisotropy due to rolling, that is, the rolling direction and rolling direction. In order to eliminate the variation in the characteristic values of the test pieces taken from the direction perpendicular to, and to reduce the yield ratio to 60% or less, heat at 900 ° C or more to complete the recrystallization of γ crystal grains. What is necessary is that if solution treatment is performed at a temperature higher than 1100 ° C, 0.1% proof stress: 24 kgf / mm ² or more cannot be satisfied.

That is, the present inventors, based on these findings, in order to satisfy both corrosion resistance and mechanical properties, 900-110
It was found that it is important to perform solution treatment in the temperature range of 0 ° C.

The present inventors have completed the present invention as a result of further studies based on such knowledge.

Here, the gist of the present invention is, in% by weight, C: 0.06% or less, Si: 1% or less, Mn: 0.3 to 2.0%, P: 0.04% or less, S: 0.03% or less, Cr: 17.0% ~ 20.0%, Ni: 7.0 ~ 10.5%, N: 0.06 ~ 0.14%, and, if necessary, Mo: 0.05 ~ 0.70%, Nb: 0.005 ~ 0.08%, V: 0.005 ~ 0.15%, Cu: 0.10 ~ 0.50%, Ti: 0.005 to 0.60%, 1 or 2 selected from the group consisting of
A steel slab having a steel composition consisting of at least a seed and the balance Fe and unavoidable impurities is heated in a temperature range of 1000 ° C or higher, and hot working is performed under the condition that the finishing temperature is 600 to 900 ° C to obtain a predetermined shape. 900 ~ 1100 ℃ after forming into shaped steel
Is a method for producing a high yield strength stainless steel section, which is characterized in that the solution treatment is performed in the temperature range.

(Operation) Hereinafter, the present invention will be described in detail together with operation effects. In the present specification, “%” means “%” unless otherwise specified.
It means "% by weight".

First, the reason for limiting the composition of the billet used in the method for producing a high yield strength stainless shaped steel according to the present invention will be described.

C: 0.06% or less C is an element that stabilizes the austenite phase,
If it is contained in the steel in an amount of more than 0.06%, it is not possible to suppress the preferential precipitation of carbides at the grain boundaries, and depending on the thermal history, a large amount of Cr carbides may be precipitated and In the vicinity
A Cr-deficient layer is formed, resulting in deterioration of corrosion resistance. So C
The content is limited to 0.06% or less, preferably 0.03% or less.

Si: 1% or less Si is required as a deoxidizing agent at the time of steel making, but if the content exceeds 1%, the deterioration of ductility becomes remarkable. Therefore,
The Si content is limited to 1% or less.

Mn: 0.3-2.0% Mn is an austenite-forming element and contains S in steel.
Fixing as MnS improves hot workability.
In order to obtain such an effect, the content of 0.3% or more is required, but if the content exceeds 2.0%, the effect is not increased, and the material price is only increased. Therefore,
The Mn content is limited to 0.3% or more and 2.0% or less.

P: 0.04% or less P is an element contained in steel as an unavoidable impurity, and the smaller the content, the better. However, since the significant reduction is accompanied by a corresponding increase in cost, the upper limit of the allowable amount of P is 0.04%.
Limited to

S: 0.03% or less S, like P, is an element contained in steel as an unavoidable impurity, and in steel, it precipitates as a low-melting point compound at the grain boundary and remarkably improves hot workability. Lower. Therefore, the lower the S content is, the more preferable it is. However, if it is 0.03% or less, practically no problem occurs in terms of hot workability, so the allowable upper limit value is limited to 0.03%. More preferably, it is 0.01% or less.

Cr: 17.0 to 20.0% Cr is an essential element for guaranteeing corrosion resistance. If the Cr content is less than 17.0%, sufficient corrosion resistance cannot be obtained, while if the Cr content is more than 20.0%, it is necessary to increase the addition amount of Ni in order to suppress the production amount of ferrite. This will significantly increase the cost. Therefore, the content of Cr is limited to 17.0% or more and 20.0% or less.

Ni: 7.0 to 10.5% Ni is a basic element that constitutes austenitic stainless steel and is an element that improves corrosion resistance. Therefore, it is necessary to contain 7.0% or more, but even if the content exceeds 10.5%, only by increasing the material price, the effect of improving the corrosion resistance tends to be saturated. Therefore, the Ni content is 7.
It is limited to 0% or more and 10.5% or less.

N: 0.06 to 0.14% N is a stabilizing element of austenite, and acts to maintain the austenite balance of steel in place of expensive Ni. That is, when the content exceeds 0.14%, surface cracking of the continuously cast slab increases, which leads to an increase in manufacturing cost due to a decrease in yield, while when the content is less than 0.06%,
The amount of Ni required to maintain a proper austenite balance increases, which also raises the manufacturing cost. So N
The content is limited to 0.06% or more and 0.14% or less.

Further, in order to achieve high toughness or high strength, one or more selected from the group consisting of Mo, Nb, V, Cu and Ti can be contained within the range of the content described below. .

Mo: 0.05 to 0.70% Mo is an element effective in increasing the strength, and if this effect is expected, it is necessary to contain 0.05% or more. However, if the content exceeds 0.70%, austenite becomes unstable, so the upper limit is made 0.70%. Therefore, the Mo content is limited to 0.05% or more and 0.70% or less.

Nb: 0.005-0.08% Nb is an element that refines the crystal grains to increase the strength. For that purpose, it is necessary to contain 0.005% or more, but even if added over 0.08%, the effect is saturated.
Therefore, the Nb content is limited to 0.005% or more and 0.08% or less.

V: 0.005-0.15% V is an element that increases strength, like Nb. For that purpose, 0.005% or more must be contained, but 0.15%
If the content exceeds 5, the effect will not increase and only the material price will increase. Therefore, the V content is 0.
Limited to 005% to 0.15%.

Cu: 0.10 to 0.50% Cu is an element effective for improving high temperature strength and corrosion resistance, but for that purpose, it is necessary to contain 0.10% or more. However, if it exceeds 0.50%, surface cracking during rolling tends to increase and weld cracking tends to be promoted.
Therefore, the Cu content is limited to 0.10% or more and 0.50% or less.

Ti: 0.005 to 0.60% Ti is an element that increases the strength, like V and Nb described above. For that purpose, the content of 0.005% or more is necessary, but if it exceeds 0.60%, the toughness of the base material is impaired.
Therefore, the Ti content is limited to 0.005% or more and 0.60% or less.

Steel pieces having the above composition are heated to a temperature range of 1000 ° C or higher in the present invention, and the finishing temperature is 600 ° C or higher and 900 ° C.
Perform hot working at ℃ or below.

The reason for limiting the heating temperature of the billet to 1000 ° C. or higher is that austenitic stainless steel generally has a large resistance to hot deformation, so if it is not heated to a temperature of 1000 ° C. or higher,
This is because molding in the subsequent hot working process may become difficult. Further, it is because unless it is 1000 ° C. or higher, solid solution of carbonitrides such as Nb and V cannot be achieved, and precipitation strengthening of these carbonitrides cannot be utilized.

From such a viewpoint, the upper limit of the heating temperature is not particularly required to be set, but from the viewpoint of suppressing γ (austenite) crystal grain coarsening, it is preferably 1290 ° C. or lower.

An example of hot working in the present invention is hot rolling, but is not limited to this.

Utilizing the processing strain introduced by this hot working, in order to accelerate recrystallization by a solution treatment performed after hot working in a short time, hot working in the unrecrystallized region of austenite below 900 ° C Need to do. The lower the finishing temperature, the larger the accumulated energy, so the driving force for recrystallization increases, which is more effective, but considering the case of performing hot rolling as hot working, the load on the rolling mill also increases. Therefore, it is necessary to determine the finishing temperature in consideration of these. In actual operation, the appropriate finishing temperature is 600-900.
℃, the most effective is to finish around 800 ℃.

In this way, with respect to the shaped steel formed into a predetermined shape by the hot working, in the present invention, 900 ° C. or higher 110
Solution treatment is performed in a temperature range of 0 ° C. or lower.

In the present invention, the solution treatment temperature is 900 ° C. or higher and 1100.
The reason for limiting the temperature to not more than ° C will be described.

First, from the viewpoint of ensuring the corrosion resistance of the obtained shaped steel, it is effective to perform the solution treatment in a temperature range of 800 ° C. or higher in order to remove the adverse effect of the Cr-deficient layer in the vicinity of the grain boundaries. In addition, to reduce the yield ratio to less than 60%, 900
It is effective to carry out in the temperature range of ℃ or more. Furthermore, 0.1
In order to satisfy the% proof stress: 24 kgf / mm ² or more, it is effective to perform it in the temperature range of 1100 ° C or less. Considering these factors, the solution treatment temperature is limited to 900 ° C or higher and 1100 ° C or lower.

In this way, according to the present invention, the austenitic stainless steel having excellent corrosion resistance originally possessed, yet satisfying the strength standard as a structural member for building, is made of austenitic stainless steel used for the structural member for building. It has become possible to provide a steel manufacturing method.

Further, the present invention will be described in detail with reference to Examples,
This is merely an example of the present invention, and the present invention is not limited thereby.

Example 1 A steel slab having the composition shown in Table 2 was heated to 1250 ° C.
After finishing hot rolling at the finishing temperature of ℃, H-shaped steel (flange width: 300 mm, flange thickness: 9.0 mm, web height: 150 mm,
Web thickness: 6.5 mm) was produced.

From the flange and web of this sample, sample (flange width: 200 mm, flange thickness: 12 mm, web height: 200 mm,
Web thickness: 8mm, length: 400mm) 5 sets (10 pieces in total) were cut out and 800 ℃, 900 ℃, 950 ℃, 1000 for these samples
Solution treatment was performed by changing the temperature to 5 ° C. and 1100 ° C.

The solution treatment was carried out by holding the treatment temperature for 0.4 hours and then quenching.

And 0.1% yield strength was measured about these samples.

The results are shown graphically in FIG.

As is clear from Fig. 1, in order to obtain 0.1% proof stress: 24 kgf / mm ² or more, which is required as a structural member for construction,
It can be seen that the solution treatment temperature needs to be 1100 ° C. or lower.

Example 2 An H-section steel was manufactured using an austenitic stainless steel having the composition shown in Table 3. Steel types A to H in Table 3 are billets satisfying the range defined in the present invention, and steel types I to N are comparative steels whose Ni content and N content are out of the range of the present invention.

The H-section steel was rolled using an existing universal rolling mill.

Further, a part of Table 4 shows manufacturing conditions in this example. Test Nos. 1 to 8 are examples showing the method according to the present invention, and Test Nos. 9 to 18 are comparative examples in which the composition of raw materials or the production conditions are out of the scope of the present invention.

A test piece is cut out from the H-shaped steel thus manufactured,
0.1% proof stress (kgf / mm ² ), TS (kgf / mm ² ), YR (%), EL
(%) Was measured, and an intergranular corrosion test (sulfuric acid-copper sulfate corrosion test, JIS G 0575, 72 hours) was performed to evaluate the corrosion resistance.

The results are also shown in Table 4.

As is clear from Table 4, the sample according to the present invention has sufficient mechanical properties and corrosion resistance, and a high yield strength austenitic stainless steel having desired performance could be obtained.

On the other hand, although the compositional standard of SUS 304 is sufficiently satisfied, it falls outside the scope of the present invention.
Results in that the desired performance cannot be satisfied.

That is, Test Nos. 9 to 14 are not preferable because the N content of the used steel slab is below the lower limit of the range of the present invention, and the Ni content increases.

Further, in Test Nos. 15 to 18, since the solution treatment temperature exceeds the upper limit of the range of the present invention, the 0.1% proof stress is 24 kgf.
It is less than / mm ² .

The effect of the present invention is clear from the above results.

(Effect of the invention) As described in detail above, according to the present invention, the austenitic stainless steel has excellent corrosion resistance originally possessed, and the strength standard as a structural member for construction, that is, "0.1%".
Proof strength: 24kgf / mm ² or more, tensile strength: 53kgf / mm ² or more, yield ratio: 60% or less, elongation: 35% or more ", and made of austenitic stainless steel that can be used for building structural members. It has become possible to provide shaped steels, such as H-shaped steels, angled steels, channel steels, as well as steel sheet piles.

The significance of the present invention having such effects is extremely remarkable.

[Brief description of drawings]

FIG. 1 shows the solution temperature and 0.1% in the embodiment of the present invention.
It is a graph which shows the relationship with yield strength.

Claims (2)

[Claims] 1. By weight%, C: 0.06% or less, Si: 1% or less, Mn: 0.3 to 2.0%, P: 0.04% or less, S: 0.03% or less, Cr: 17.0 to 20.0%, Ni: 7.0 ~ 10.5%, N: 0.06 ~ 0.14%, a steel slab with a steel composition consisting of the balance Fe and unavoidable impurities is heated in the temperature range of 1000 ℃ or more, and the finishing temperature is 600 ~ 900 ℃ 900-1100 ° C after processing and shaping into a shaped steel
A method for producing a high-strength stainless steel section, characterized by performing solution treatment in the temperature range of. 2. The steel slab, in% by weight, Mo: 0.05-0.70%, Nb: 0.005-0.08%, V: 0.005-0.15%, Cu: 0.10-0.50% and Ti: 0.005-0.60%. The method for producing a high yield strength stainless steel section according to claim 1, which comprises one or more elements selected from the group consisting of: