JPH0617545B2 - Precipitation strengthened stainless steel with excellent cold workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to Fe—Cr—Ni—Cu based precipitation strengthened stainless steel.

Fe-Cr-Ni-Cu based precipitation-strengthened stainless steels are high in strength and excellent in corrosion resistance. Therefore, they are often used in structures that receive high stress and need to be lightweight.

[Conventional technology]

Among Fe-Cr-Ni-Cu precipitation strengthened stainless steels, those having a martensite transformation point (Ms point) of room temperature or lower are soft because the structure after solution heat treatment is usually austenite. Therefore, conventionally, a method of obtaining high strength by performing forming by cold working in the state of the solution heat treatment and then performing deep-cooling (subzero) heat treatment followed by aging treatment has been used.

Therefore, this conventional precipitation-strengthened stainless steel has a remarkable feature that it can be cold-worked and has high strength. However, in many cases, it does not soften even by solution treatment. There are drawbacks such that a large-capacity press is required for processing, the equipment cost becomes enormous, and cracks often occur during cold working.

For this reason, precipitation-strengthened stainless steels having excellent cold workability with controlled (C + N) content have been developed (Japanese Patent Application No. 60-2).
69505). However, in the present invention, although the solution treatment is softened as it is and the cold workability is improved, there is a problem that cracks occur when performing the cold work again.

[Problems to be solved by the invention]

In view of this point, the present invention does not require a large-capacity press for easily softening by solution heat treatment, and the occurrence of cracks is not recognized during repeated cold working. The purpose is to develop a material that can obtain high strength by heat treatment and aging heat treatment.

[Means for solving problems]

As a result of detailed investigations on the cold workability of Fe—Cr—Ni—Cu system precipitation strengthened stainless steel and the tensile properties after aging heat treatment, the inventors have specified the amounts of (C + N) and N, and further specified It has been found that by adding an amount of titanium a steel can be obtained which can achieve the above mentioned objects. That is, the present invention is (C + N) 0.06% by weight.
0.10% and N 0.005% or more, Si 1.0% or less, Mn 0.5 to 2.0%, Ni 4.5 to 6.5%, C
r 14.5 to 17.5%, Cu 1.0 to 2.5%,
Mo 1.0 to 2.5%, V 0.5% or less, Of the precipitation strengthening type stainless steel having excellent cold workability, which contains Ti and the balance is Fe and inevitable impurities.

[Action]

 Next, the reasons for limiting each component are shown below.

Carbon + Nitrogen (C + N): 0.06 to 0.10% and Nitrogen (N): 0.005% or more If C + N is lower than 0.06%, cracking occurs when subject to solution treatment and cold working. To occur.

Further, in the range where C + N exceeds 0.10%, the increase in yield strength and tensile strength is not so large even after aging treatment after deep-chill heat treatment. Further, if N is less than 0.005%, austenite cannot be sufficiently stabilized.
Therefore, the content of C + N is 0.06 for the above reason.
.About.0.10%, and the content of N is limited to 0.005% or more.

Silicon (Si): 1.0% or less Si has the effect of stabilizing the austenite phase, but if its content exceeds 1.0%, it precipitates as inclusions and the cleanliness and toughness deteriorate.

Manganese (Mn): 0.5 to 2.0% Mn also has an effect of stabilizing the austenite phase, but if the content is less than 0.5%, the effect is small, while the content is 2.0%. If it exceeds, the tensile strength will decrease.

Nickel (Ni): 4.5-6.5% Ni stabilizes the austenite phase and synergizes with Cu to bring about precipitation hardening, but if the content is less than 4.5%, the effect is small, while the content is On the other hand, if it exceeds 6.5%, the tensile strength is lowered.

Chromium (Cr): 14.5 to 17.5% Cr is also an essential element from the viewpoint of stabilizing the austenite phase and resistance, but if its content is less than 14.5%, these effects are small, while , Its content is 17.
If it exceeds 5%, the tensile strength after aging treatment decreases.

Copper (Cu): 1.0 to 2.5% Copper is important as a precipitation hardening element, but if the content is less than 1.0%, its effect is small, while its content is 2.
If it exceeds 5%, the hot workability deteriorates.

Molybdenum (Mo): 1.0 to 2.5% Mo has the effect of increasing the strength, but if it is less than 1.0%, it has little effect, while if it exceeds 2.5%, the hot workability deteriorates. Let

Vanadium (V): 0.5% or less V fixes C and causes precipitation hardening, but 0.5
If it is contained in excess of%, the toughness decreases.

Ti has the effect of fixing C and N, On the other hand, the occurrence of cracks was recognized by the repeated cold bending work, while on the other hand, when Ti> (C + N), the cracks started to occur again during the repeated cold bending work.

〔Example〕

The materials shown in Table 1 were manufactured to demonstrate the effect of the present invention. These materials were subjected to a tensile test and a bending test at room temperature in the as-solution-treated state at 1035 ° C.

Further, a tensile test was conducted after the deep-cooling heat treatment at 10 ° C. was followed by the aging heat treatment at 540 ° C. The test results are shown in Table 2.

The (C + N) amount (% by weight) of the material shown in Table 1 and Ti
The relationship with the amount (% by weight) is shown in the figure.

[Effects of the Invention] By using the material according to the present invention, compared with the material generated in Japanese Patent Application No. 60-269505 after solution heat treatment,
Since the 0.2% proof stress is low, cold working is easy, the press capacity is small, and the equipment cost can be reduced significantly.

No more cracking during cold working. Furthermore, sufficiently high 0.2% proof stress and tensile strength were obtained by deep cold heat treatment and aging heat treatment after cold working.

BRIEF DESCRIPTION OF THE DRAWINGS The figure shows (C +) of the invention material and the comparative material having the compositions shown in Table 1.
FIG. 3 is a diagram showing the relationship between N) amount (wt%) and Ti (wt%).

Claims (1)

[Claims] 1. A weight percent of (C + N) 0.06-.
0.10% and N 0.005% or more, Si 1.0% or less, Mn 0.5 to 2.0%, Ni 4.5 to 6.5%, Cr 14.5 to 17.5%, Cu 1.0 to 2 0.5%, M
o 1.0-2.5%, including V 0.5% or less, Precipitation-strengthened stainless steel with excellent cold workability, which contains Ti and the balance is Fe and inevitable impurities.