JP2988336B2 - Corrosion resistant high strength martensitic stainless steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a corrosion-resistant high-strength martensitic stainless steel, and in particular, does not contain Cu.
The present invention also relates to a highly recyclable corrosion-resistant high-strength martensitic stainless steel.

[0002]

In recent years, building materials, such as plant structural member and mechanical structural member, strength and toughness that is of course is good, (maintenance-free due to be unnecessary painted) good corrosion resistance and Material recyclability is required.

As a conventional high-strength corrosion-resistant material, precipitation hardening stainless steel 17-4PH (Precipitation) is used.
SUS630 (JIS:
Fe-0.07C-17Cr-4Ni-4Cu-0.2Nb), which is used alone or welded to forgings and castings.

[0004]

However, 17-
Since 4PH stainless steel is a stainless steel utilizing precipitation hardening of Cu, it contains 4 wt% of Cu, which is considered to be very difficult to remove by scouring. Therefore, 1
Recycling 7-4PH stainless steel as scrap material is costly and may be avoided. Further, since Cu is contained, weldability and toughness are deteriorated, and there is a problem that pitting corrosion is easily caused in a corrosive environment.

[0005] Therefore, an object of the present invention is to solve the above-mentioned problems and to provide a high-strength, highly recyclable, corrosion-resistant material containing no Cu.

[0006]

In order to solve the above-mentioned problems, the present invention provides a composition comprising C: 0.055 to 0.20 wt% Ni: 4.5 to 7.5 wt% Cr: 14.5 to 17. 5 wt% Mo: 0.5 to 2.0 wt% Si: 1.0 wt% or less Mn: 1.0 wt% or less V: 0.05 to 0 . 08 wt% Al: 0.05 wt% or less P: 0.025 wt% or less S: 0.025 wt% or less Rare earth metal (REM): 0.001 to 0.01 wt% The balance consists of Fe.

With the above composition, it is possible to obtain a corrosion-resistant high-strength martensitic stainless steel excellent in pitting corrosion resistance in a weldability, toughness and corrosive environment.

C is an element related to the formation of martensite, and the lower limit is set to 0. 0 from the problem of balance between strength and toughness.
0 55 wt% and the upper limit is 0.20 wt%.

[0009] Ni and Cr are effective in terms of corrosion resistance, wear resistance and quenching effect.
When Ni is less than 4.5 wt% and Cr is less than 13 wt%, only a martensite phase is formed, which is effective for obtaining only strength, but is inferior in toughness and weldability. Ni is 3 ~
At 4.5 wt% and 13 to 14.5 wt% Cr, the delta ferrite in the martensite matrix increases and the proof stress decreases. Ni is 7wt% and Cr is 17.5wt
%, More stable austenite is formed, and it is difficult to easily transform into martensite even after quenching, that is, the amount of so-called retained austenite increases, and the hardness and proof stress decrease significantly. Therefore, as an economical addition range of Ni and Cr, Ni is 4.5 to 7.5 wt%,
When Cr is set to 14.5 to 17.5 wt%, retained austenite after quenching can be controlled to the minimum necessary.

Mo is effective for corrosion resistance (especially pitting corrosion resistance) and has a high tendency to form carbides, and is effective for improving strength because it exhibits tempering softening resistance by tempering after quenching. Addition of less than 0.5 wt% has no effect on improving pitting corrosion resistance and strength, and adding more than 2.0 wt% causes embrittlement.

[0011] Si has an effect of deoxidation and strengthening of the base material and is a ferrite-forming element. However, if the addition amount is large, it becomes a factor of embrittlement.

Mn is an element for generating austenite as well as having the effect of deoxidation and desulfurization. However, if the amount of Mn increases, the dissolution of the anode is accelerated and the corrosion resistance is impaired.

V has a higher tendency to form carbides than Mo, and shows resistance to temper softening by tempering after quenching. For the addition of trace amounts, since it is effective in ductility and corrosion resistance, to significantly reduce the quenching effect the amount is increased, 0. 0 5
~ 0 . 08 wt % .

Al is added because it is effective for improving toughness by deoxidation and fine-grain action. However, if the addition amount is large, there is a problem of contamination by nonmetallic inclusions in steel.
The content is set to 0.05 wt% or less.

P and S are unavoidable impurities, exhibit remarkable solidification segregation and cause cracks due to the formation of a melt. Therefore, the content of each is set to 0.025 wt% or less. Since it is said to have an action of uniformly depositing carbides, it is considered to have intergranular corrosion resistance in a corrosive environment. If the REM content is less than 0.001 wt%, a small amount of La, Ce, Pr, Nd, etc. may be positively added, respectively. I do.

[0016]

Embodiments of the present invention will be described below.

The corrosion-resistant high-strength martensitic stainless steel of the present invention is HT780, a typical tempered high-strength steel.
It is considered to have mechanical properties equivalent to or higher than 0.25% proof stress of 685 MPa (70 kgf / mm
² ) Above, the tensile strength is 780MPa (80kgf / mm
² ) Not less, elongation is not less than 16%, and ² mm V notch Charpy absorbed energy at 0 ° C. is 47 J (4.
8 kgf-m) or more, 27 J (2.8 kgf
-M)

After producing stainless steel in which the amounts of the added elements are adjusted to have the above-described composition, heat treatment is performed. In this heat treatment, it is preferable to perform quenching with oil cooling after heating at 1,040 ° C. for 2 hours, and then perform tempering with air cooling after heating at 550 ° C. for 3 hours. The martensitic stainless steel has a problem in corrosion resistance, especially stress corrosion cracking susceptibility, in addition to the range where strength is increased in the range of 350 to 550 ° C. For this reason, tempering in this temperature range is generally avoided, and 700 ° C.
The tempering is preferably performed at about 600 ° C. if the main focus is on corrosion resistance and corrosion resistance. However, the tempering is performed at 550 ° C., which is the upper limit at which brittleness occurs at 475 ° C., focusing on hardness. By heat treatment, stainless steel base is martensite,
A martensitic stainless steel having a structure containing austenite as the second phase and delta ferrite as a part as the third phase is obtained.

[0019]

Next, embodiments of the present invention will be described.

First, the composition of the martensitic stainless steel of the present invention is shown in Table 1.

[0021]

[Table 1]

As shown in Table 1, the martensitic stainless steel of the present invention contains: C: 0.14 wt% Ni: 6.17 wt% Cr: 14.69 wt% Mo: 0.99 wt% Si: 0.24 wt% Mn : 0.26 wt% V: 0.05 wt% Al: 0.05 wt% P: 0.007 wt% S: 0.006 wt% REM: 0.003 wt% The balance has a composition consisting of Fe.

That is, since the martensitic stainless steel of the present invention does not contain Cu unlike the 17-4PH stainless steel, scouring at the time of recycling as a scrap material is facilitated and the weldability and toughness are improved. Become. Further, the martensitic stainless steel of the present invention has C
By not containing u, corrosion resistance (especially pitting corrosion resistance) in a corrosive environment is improved, and there is no fear of rusting in a normal environment, so that painting is unnecessary and maintenance-free can be achieved. Furthermore, since the martensitic stainless steel of the present invention contains Cr, Ni, and Mo sufficiently, it becomes a stainless steel excellent in high-temperature strength, high-temperature oxidation, and high-temperature corrosion. Therefore, it can be expected as a structural member resistant to fire.

Next, Table 2 shows the mechanical properties of the martensitic stainless steel of the present invention.

[0025]

[Table 2]

As shown in Table 2, the martensitic stainless steel of the present invention was heated at 1,040 ° C. for 2 hours, quenched by oil cooling, then heated at 550 ° C. for 3 hours, and then tempered by air cooling. Mechanical properties after the
2% proof stress is 875 MPa (89.2 kgf / mm ² ),
Tensile strength of 980 MPa (99.9 kgf / mm ² ),
20.0% elongation, 66.7% drawing, 2mmV at 0 ° C
Notch Charpy absorbed energy is 74.6J on the other hand
(7.6 kgf-m), while 85.3 J (8.7 kgf-m)
fm), the lateral swelling amount is 0.74 mm on one hand and 1.40 on the other hand.
It had excellent characteristics that greatly exceeded the target value of 04 mm.

That is, the martensitic stainless steel of the present invention is not only excellent in corrosion resistance as described above, but is also a stainless steel having high strength, high ductility and high toughness.

Further, HT78 which is a martensitic stainless steel of the present invention, which is an as-quenched and tempered high-strength steel.
Table 3 shows the Vickers hardness (Hv) of 0.

[0029]

[Table 3]

As shown in Table 3, the as-quenched Vickers hardness of the martensitic stainless steel of the present invention is 371.
Hv, which is a heat-affected zone (HAZ) of a tempered high-strength steel (HT780) which is a low-alloy steel having the same strength level as the martensitic stainless steel of the present invention.
d Zone) is significantly lower than the normal maximum hardness of 400 to 440 Hv.

That is, since the martensitic stainless steel of the present invention is not expected to have a very hard HAZ, it is advantageous in terms of weldability and susceptibility to hydrogen brittle cracking in the environment, and is also advantageous in toughness and fatigue strength. Stainless steel.

[0032]

In summary, according to the present invention, the construction
Used for materials, plant structural members and mechanical structural members
, Not containing Cu , high strength almost equivalent to 17-4PH
And exhibits an excellent effect that a corrosion-resistant material having high recyclability can be obtained.

Claims (1)

(57) [Claims] The composition is as follows: C: 0.055 to 0.20 wt% Ni: 4.5 to 7.5 wt% Cr: 14.5 to 17.5 wt% Mo: 0.5 to 2.0 wt% Si: 1 .0wt% or less Mn: 1.0wt% or less V: 0.0 5~0. 08 wt% Al: 0.05 wt% or less P: 0.025 wt% or less S: 0.025 wt% or less Rare earth metal (REM): 0.001 to 0.01 wt% The balance is made of Fe, with high corrosion resistance. Strength martensitic stainless steel.