JPS6028901B2 - High corrosion resistance and high strength martensitic stainless steel cast steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly corrosion resistant and high strength martensitic stainless steel.

As a general martensitic stainless steel, S
There is 13 chromium stainless steel represented by CS-1.
These materials have been widely used in industrial components that require strength and insect resistance, but although this type of stainless steel has excellent mechanical properties such as yield strength and tensile strength, it has a low chromium content. Because of its low resistance to insects, its resistance to strong acids was unfortunately incomplete.

For example, the above-mentioned SCS-1 material has been mainly used for paper-making rolls, but it cannot sufficiently withstand severe corrosive conditions, resulting in a short roll life, and a material with excellent corrosion resistance is required. ing. In view of these circumstances, the present invention not only has the excellent mechanical properties of martensitic stainless mirror steel, but also has high insect resistance, with significantly improved corrosion resistance, especially against strong acids. This was made to provide a high-strength martensitic stainless steel, and its characteristics are, in weight percent, C: 0.15% or less, Sj: 10% or less, Mn: 1.0 % or less, P; 0.
04% or less, S: 0.04% or less, Cr: 14-16%
, Ni; 1-3.5%, Mo: 0.5-4%, W; 0.
1 to 4%, the balance essentially consisting of Fe, and the Mo
The addition of and W is 0.6% Mo+WS4.5%,
And the amount of 6-ferrite is 20% or less. Next, the reason for limiting the chemical components of the steel of the present invention as described above will be described.

C, Si, and Mn belong to the composition range of ordinary martensitic stainless steel and have no particular characteristics, but within this range they can be easily produced industrially by atmospheric melting.

P and S are elements that inhibit weldability and pitting resistance, so it is better to have as little as possible, but from the viewpoint of atmospheric dissolution, the limit for each is 0.04% or less.

Cr is an important element in stainless steel, and is an element that improves corrosion resistance.
%, and if it exceeds 16%, the ferrite phase increases and it becomes difficult to obtain a stable martensitic structure, so the range was limited to 14 to 16%. Ni is Cr
It is an element that is effective in improving corrosion resistance as well as strength and toughness due to the combined effect with .

In terms of corrosion resistance and ballability, the steel of the present invention has at least 1
It is necessary to exceed 3.5% from the economic point of view.
The above is disadvantageous, so the range is limited to 1 to 3.5%. Mo is an element that significantly improves local corrosion resistance, but if it is less than 0.5%, no effect can be expected, and if it is more than 4%, the effect is saturated, and on the contrary, it causes a decrease in toughness. It was limited to 4%.

W is an element that significantly improves local corrosion resistance and corrosion fatigue strength due to its combined effect with Mo. It is necessary to have at least 0.1% or more, but if it exceeds 4%, the effect will be saturated and the toughness will deteriorate. The content was set at 0.1 to 4%. Each of the above elements can be combined to provide an effect greater than that of each element alone.

Next, the features of the present invention will be described in detail below using an inventive steel as an example of the present invention and a comparative steel as a comparative example.

Table 1 below shows the chemical composition of the comparative steel, and Table 2 shows the chemical composition of the steel of the present invention.

Table-1 Chemical composition of comparative steel (martensitic stainless steel) ☆ 6-Perite force is measured by area method ☆☆ Comparative steel F is CA6NM material of ATSM standard-
2 Chemical component powder of the steel of the present invention (martensitic stainless steel) ☆ The amount of a-ferrite was measured using the area method, and then the mechanical properties and corrosion resistance of each steel in Tables 1 and 2 were measured. The test results are shown in Table 3, Table 4, and Figure 1.

However, each steel test piece was quenched from 980 to 100,000 and agglomerated at 650 to 750°C. Tensile tests and impact tests were measured using JIS No. 4 test pieces, and corrosion resistance tests were performed using JIS No. 4 test pieces. ○Tested against 5% boiling sulfuric acid according to 0591. Table-3 Mechanical properties of comparative steel Table-4
Mechanical properties of the steels of the present invention By comparing Tables 3 and 4, it can be seen that the strength of the steels of the present invention in terms of yield strength and tensile strength is significantly increased compared to comparative steels A to E. Even when compared with Comparative Steel F (CA Iso M material), which has a high Ni content, it is equal to or even better than Comparative Steel F (CA Iso M material), and it is clear that the strength is superior.

In addition, although improvement effects are not necessarily observed in ballability as seen in elongation, reduction, and impact values, the present invention provides sufficient measured values for practical use, and does not cause a decrease in grain quality even with increased strength. This is a characteristic of steel. In the steel of the present invention, a decrease in toughness is prevented by limiting the amount of 6-ferrite, which causes a decrease in ballability, to 20% or less. That is, the above-mentioned Mo and W are ferrite-forming elements, and as shown in FIG. 2, the amount of 6-ferrite increases compared to the sum of the weight percentages of Mo and W, and this 6-ferrite In site-based stainless steel, the impact value is reduced as shown in the shaded area in FIG. In order to obtain the desired toughness, especially 6-
The amount of ferrite was limited to 20% or less, and in order to stably keep the 6-ferrite amount below 20%, the amount of Mo and W added was limited to 0.6% SMo + 4.5% WS. Next, as shown in Fig. 1, all of the steels of the present invention have several times the corrosion resistance compared to comparative steels A, B, and C. It is clear that the steel of the present invention has superior corrosion resistance even when compared with Comparative Steel F (CA Kishu material) having a high Ni content.

Next, comparative steels 1, 1, J, and K shown in Table 1 do not have Mo and W added in combination like the steel of the present invention, but have only one of them added, and the pond composition is the same as the steel of the present invention. It is approximately the same as steels L to Q. These comparative steels have an 8-ferrite content of 20% or less, similar to the steel of the present invention, and as is clear from Table 3, each mechanical property is at the same level. However, looking at FIG. 1, it is clear that its corrosion resistance is considerably inferior to that of the steel of the present invention. This means that the steel of the present invention is within the specified composition range mentioned above and has a specific amount of combined addition of Mo and W.
It was found that the combined addition of W and W produced a remarkable synergistic effect. The present invention is as described above, and has a composition that is within the specified composition range as described above, and also contains Mo and W. 20% or less, its corrosion resistance and mechanical properties both exceed those of conventional martensitic stainless rust steel, and its corrosion resistance is particularly excellent. Therefore, it is very suitable for various industrial parts that require both mechanical properties and corrosion resistance, such as paper rolls, stainless steel pipes, etc., and its practical effects are significant.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the corrosion test results of the invention steel and comparative steel, FIG. 2 is a graph showing the relationship between the weight percent of (Mo+W) and the amount of 6-ferrite, and FIG. is 6
- It is a figure showing the relationship between the amount of ferrite and the impact value.

Figure 2 Figure 3 Figure 1

Claims (1)

[Claims] In 1% by weight, C; 0.15% or less Si; 1.0% or less Mn; 1.0% or less P; 0.04% or less S; 0.04% or less Cr; 14 to 16% Ni; 1-3.5% Mo; 0.5-4% W; 0.1-4% The remainder essentially consists of Fe, and the sum of Mo and W is 0.6%≦Mo+W ≦4.5%, and δ-
A highly corrosion-resistant, high-strength martensitic stainless cast steel characterized by a ferrite content of 20% or less.