JPS6169949A - Corrosion resistant stainless steel - Google Patents

Abstract

PURPOSE:To obtain a stainless steel superior in corrosion resistance without adding plenty of precious alloying element, by regulating contents of S, Mn, Mo, Cu in a 18-8 stainless steel contg. specified compsn. quantities of C, Si, P, Ni and Cr. CONSTITUTION:In the 18-8 stainless steel contg. <=0.08wt% C, <=1.00% Si, <=0.04% P, 8.0-10.5% Ni, 18.0-20.0% Cr, corrosion resistant stainless steel having durability against corrosion as member in contact with drinking water is obtd. by adjusting to <0.005% S, <=150 in Mn/S, <=0.2% (Mo+Cu). Said steel is heated to about 1,300+ or -50 deg.C, solution treated at the temp. for >=about 2min, then cooled to room temp. at a rate of air cooling or above. Thereby, the corrosion resistance can be further improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to austenitic so-called 18-8 stainless steel.

(B) Prior Art Conventionally, 5US304, typified by 18-8 stainless steel, has been mainly used for beverage liquid contact parts in beverage dispensing machines for cola and other beverages. The elemental content of this 18-8 stainless steel is less than 0.08% carbon and 1% silicon.
．． 00% or less, phosphorus is 0.04% or less, chromium is 18.0% or less
Within the range of 0% to 20.00%, nickel is 8.00%
It is well known that the content ranges from 10.5% to 10.50%. Further, the manganese content in this general 18-8 stainless steel is 1.0% to 1.5%, and the sulfur content is 0.01% to 0.02%.

(c) Problems to be Solved by the Invention The conventional 18-8 stainless steel pot has low corrosion resistance, and as a member that comes into contact with drinking liquid, has a drawback in its durability against corrosion.

Furthermore, in order to improve the corrosion resistance, it is possible to reduce the sulfur content by 4 Jtj, but even in that case, if the mixing ratio of manganese and sulfur (MrL/S) is large, the corrosion resistance cannot be improved. That is, in FIG. 1, the sulfur content is 0.0051% to 0.01%.

1 with a mixture ratio of manganese and sulfur (M, /S) of 79
8-8 stainless steel with 10% ascorbic acid and 1%
This is a micrograph showing the corrosion state when immersed in sodium chloride, and it can be seen that the surface dissolves within a short time.

In view of the above, the present invention provides a stainless steel with excellent corrosion resistance.

2) Means to solve the problem Carbon: 0.08% or less, Silicon: 1.00% or less, Phosphorus: 0.04% or less, Nickel: 8.0% to 10.5%
In so-called 18-8 stainless steel containing 18.0% to 20.0% of chromium by weight, 18% of sulfur
Stainless steel with a content of less than 0.005%, a weight mixing ratio of manganese and sulfur (MrL/S) of 150 or less, and a combined weight content of molybdenum and copper of 0.2% or less.

(e) Effect The present invention provides a method for controlling the weight mixing ratio of manganese and sulfur (M3/S') to 150% when the weight content of sulfur is less than 0.005%.
The weight content of molybdenum and copper combined is 0.
Adjust to 2% or less to improve corrosion resistance.

(F) Examples Carbon: 0.08% or less, Silicon: 1.00% or less, Phosphorus: 0.04% or less, Nickel: 8.0% to 10.5%
The amounts of sulfur and manganese in the normal element content of so-called 18-8 stainless steel containing 18.0% to 20.0% chromium by weight are adjusted as follows.

Example 1゜When sulfur (S) is less than 0.005%, the weight mixing ratio (MW/S) of manganese (M) and sulfur (S) is set to 150 or less, and molybdenum (MO) and copper ( The combined weight content of Crt) is adjusted to 0.2% or less.

Example 2゜When sulfur (S) is 0.0051 to 0.01%, the weight mixing ratio CM, /S of manganese (MfL) and sulfur (S)
) is 50 or less, and molybdenum (MO) and copper (C,1
, ) to a total weight content of 0.2% or less.

Example 3゜When sulfur (S) is 0.011 to 0.015%, the weight mixing ratio of manganese (M) and sulfur (S) (M, /S)
20 or less, molybdenum (MO) and copper (C, L)
The combined weight content is adjusted to 0.2% or less.

Stainless steel contained in the above mixing ratio has extremely high dissolution resistance in various solutions and is stable even when exposed to a corrosive environment for a long time.

The photograph shown in Figure 2 shows sulfur (S) ranging from 0.0051 to 0.
．． Steel containing in the range of 0.01%, ie, the above Example 2.
This is a micrograph showing the corrosion state when immersed in 10% ascorbic acid and 1% sodium chloride under zero conditions, and it is clear that the corrosion resistance is superior compared to the micrograph shown in Figure 1. It is. That is, under conditions other than those of the above embodiments, stainless steel melts in a short time. The corrosion resistance of stainless steel, which is used in corrosive environments such as various beverages, is limited by manganese (
The rate is determined by the electrochemical properties of sulfide-based inclusions consisting of MrL) and sulfur (S). In other words, if the dissolution resistance of sulfide-based inclusions is increased by any means, the anodic reaction of corrosion will be significantly suppressed, and the corrosion resistance will increase.

Figures 3 to 5 show representative examples of experimental comparisons of the corrosion resistance of steel types in which manganese (MrL) and sulfur (Sl) were adjusted and those in which they were not adjusted.
The figure shows a 5% sulfuric acid solution (Hz 30
It shows the amount of corrosion reduction in a solution in which 0.01% sodium chloride (N, CI) was added to 4). When sulfur (Slt) is less than 0.005%, the amount of corrosion is determined by the amount of corrosion when the mixing ratio of manganese (Mi) and sulfur (S) (Mn/8) is 60.95.13.
It was found that the mixing ratio of manganese (Myu) and sulfur (S) (Mn
/S) and the amount of corrosion. Figure 4 shows that the amount of sulfur is 0.
For steel types with 0.051 to 0.01%, the mixing ratio (Mn, /S) of manganese (M) and sulfur (31) is 28 and 7.
The results of measuring the anode polarization behavior of No. 9 steel in a 5% sulfuric acid solution (H, 5o4) are shown. Manganese (MrL
) and sulfur (S) with a mixing ratio (MrL/S) of 28, the active current is small and the corrosion resistance is large, but the mixing ratio (MrL/S) is 28.
When L/S) is 79, the current value is large and the corrosion resistance is extremely small. As shown in FIG. 5, it can be seen that these trends are similar in corrosion in organic acids.

In addition, at the same time as the adjustment according to the above embodiment, IC 1300±5
Corrosion resistance can be further improved by heating to 0 degrees Celsius, performing solution treatment at that temperature for 2 minutes or more, and then cooling to room temperature at a rate faster than air cooling.

(G) Effects of the Invention The present invention provides a method in which the weight mixing ratio of manganese and sulfur (MrLZS) is 150 when the weight content of sulfur is less than 0.005%.
The weight content of molybdenum and copper combined is 0.
Since the corrosion resistance is improved by adjusting the content to 2% or less, it is possible to provide stainless steel with excellent corrosion resistance without adding large amounts of expensive alloying elements such as nickel, chromium, and molybdenum.

[Brief explanation of the drawing]

Fig. 1 is a micrograph showing the corrosion state of stainless steel other than the range of component treatment of the present invention, Fig. 2 is a micrograph of stainless steel according to an example of the present invention, and Fig. 3 is an effect on the amount of corrosion reduction of stainless steel. Mixing ratio of manganese and sulfur (Myu/S
), FIG. 4 is a graph showing the effect of the MrLZS ratio on the anode polarization behavior, and FIG. 5 is a graph showing the effect of the MrLZS ratio on the elution amount of iron ions. Applicant Sanyo Electric Co., Ltd. and 1 other representative Patent attorney Shizuo Sano Figure 3 S<0.005% S=α0051~0.
010%-Mn/S- Fig. 4 Current flow rate (mA/cm") Fig. 5-Mn/+-

Claims (1)

[Claims] 1. Carbon is 0.08% or less, silicon is 1.00% or less, phosphorus is 0.04% or less, nickel is 8.0% to 10.
In so-called 18-8 stainless steel containing 5% chromium and 18.0% to 20.0% chromium, the weight content of sulfur is less than 0.005% and the weight mixing of manganese and sulfur ( A corrosion-resistant stainless steel characterized in that it has been adjusted to have a Mn/S) of 150 or less and a combined weight content of molybdenum and copper of 0.2% or less.