JPS6246623B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an acid- and corrosion-resistant alloy having high strength and toughness with high impact resistance. Generally, in order to improve the corrosion resistance of steel, steel is alloyed with Cr and the composition is selected so that it becomes a martensitic structure through quenching, and is called martensitic stainless steel. This kind of steel has a Cr content of about 9~
It contains 15% by weight and is commonly used as a high-strength, heat-resistant, and corrosion-resistant steel, but it has some drawbacks in terms of impact resistance, and there is a need for an alloy with even better heat and corrosion resistance. . This invention attempts to provide an alloy that satisfies the above requirements by further adding Co to the conventional martensitic stainless steel and appropriately adjusting the quantitative relationships of other elements. Mo0.3~1.5wt%, Ni1.5~4.5wt%, Co0.5
-2.5% by weight, 9 to 13% by weight of Cr, 0.08% by weight of C or less, and the balance is essentially Fe.It is a strong acid- and corrosion-resistant alloy. In addition to the above-mentioned Fe, Cr, Mo, Ni, Co, and C, the present alloy also contains 0.1 to 1.0% by weight of Si and 0.1 to 2.0% by weight of Mn.
are contained because they are necessary as deoxidizing agents, and P and S are also contained in very small amounts as impurities. The tests that led to the development of the present alloy and their results are shown below. (1) Test piece A specimen obtained by overlay welding the alloy obtained by melting onto a mild steel base metal using the TIG welding method (hereinafter referred to as
) and those obtained by subsequent annealing at 650°C for 2 hours (hereinafter referred to as Y) were used as test materials. Its chemical composition is shown in Table 1 below.

[Table] (2) Test conditions (a) Hardness test (Bitzkers hardness, load 500g) The hardness value is the average value of data measured at 1 mm intervals, and its standard deviation is the uniformity of hardness. Representing sexuality. (b) Tensile test The tensile strength and elongation values are average values measured at room temperature on two JISA No. 2 test pieces. (c) Impact test The impact value is the average value measured at 0°C on three test pieces of JIS No. 4 (width 5 mm). (d) Corrosion resistance test 1 part water: 20 parts by volume in a solution of hydrochloric acid (20°C)
Corrosion loss was measured after a test piece of 10 x 5 mm was immersed for 48 hours. (e) High temperature hardness test (Bitzkers hardness, load 500
g) For the hardness value, the average value of data at 5 points at each temperature was determined for a Y test piece measuring 5 x 10 x 5 mm. (3) Test results The test results of (a) to (d) above are shown in Table 2 below, and (e)
The test results are shown in Table 3, and the microstructure photographs of test pieces No. 1 to No. 29 are shown in FIGS. 1 to 29, respectively. Note that this microscopic structure photograph is for Y, and in each photograph, one scale in the photograph is 10μ.

【table】

【table】

【table】

[Table] Based on the test results described above, the appropriate amount of each alloying element will be considered. Of the test results shown in Table 2, hardness, tensile strength, elongation, and impact value are illustrated in easy-to-understand diagrams in FIGS. 30 and 31. In other words, Figure 30 is for X, and the numbers shown below each plot are impact value, tensile strength (elongation), and hardness (standard deviation of hardness) from the top, and Figure 31 is for Y. The numerical values shown below each plot are the same as in FIG. Further, FIG. 32 is a graph plotting the change in the impact value of Y with respect to the change in Co weight % from the results in Table 2. Co
When adding 1, 2, and 3% by weight of When this amount is exceeded, the effect of Co reaches a plateau, and properties are even seen to deteriorate rather than when the optimum amount of Co (1 to 2% by weight) is used. Also, looking at the results of high-temperature hardness shown in Table 3, it increases as the amount of Co increases from 1, 2, and 3% by weight. Furthermore, looking at the microstructure photographs, it is clear from Figures 1 to 4 that as Co is added, free ferrite (δ ferrite) gradually decreases, and at Co3% by weight, it becomes almost entirely martensite. . From the above, it can be seen that Co improves the mechanical properties of martensitic stainless steel, and that an addition amount of up to 3% by weight is effective. Next, as is clear from Fig. 32, which is a graph when adding 5% by weight or less of Ni and varying the amount of Co added, when the amount of Ni added is 5% by weight, the above-mentioned mechanical properties due to the addition of Co No improvement in
As the amount of Co added increases, the properties deteriorate even more. Also, regarding samples that do not have any Ni added,
Although the impact value improves as the amount of Co added increases, the tensile strength and hardness are insufficient, and Ni1% by weight
For these reasons, the amount of Ni added was 1.5 to 4.5% by weight, as there was almost no effect of Co addition.
Moreover, it can be said that the preferable amount of Co added is 0.5 to 2.5% by weight. Next, considering the amount of Cr, Cr is an element that generally improves the corrosion resistance of steel, and at least 9% by weight is required to maintain that corrosion resistance, but from the results of this test, Ni, From the data of No. 14, No. 27, and No. 28 with the same amounts of Mo and Co but different amounts of Cr, the amount of Cr is 9.01% by weight, 10.83% by weight,
Even if it changes to 12.74% by weight, there is almost no difference in performance such as corrosion resistance, toughness, strength, etc., all of which are good, but when it increases to 13% by weight, toughness tends to decrease, so the upper limit of Cr The amount was 13% by weight. Regarding the carbon content, if it is too large, notch toughness and elongation will decrease as well as weldability, so it should be kept at 0.08% by weight at most. Next, to consider the amount of Mo added, we changed the amount of Mo added for various samples whose Ni and Co amounts were selected to have high impact resistance while maintaining high strength as described above. According to the results of investigating the corrosion loss (Table 2), as Mo is added, the amount of corrosion decreases, peaking at about 1% by weight, and when it exceeds that amount, the amount of corrosion increases again and reaches almost 1.82% by weight.
It can be seen that no effect of Mo contributing to corrosion resistance is observed. Also, looking at the effect of Mo addition on impact resistance, it is found that Mo
Sample No. 29 with Mo added at 0.55% by weight has a larger impact value than sample No. 25 without Mo added, and similarly the impact values of various samples containing about 1% by weight are also large. However, test No. 26 with 1.83% by weight of Mo added
It can be seen that the impact value drops rapidly. The same thing can be said from other test results such as tensile strength and high temperature hardness, so the amount of Mo added is approximately 0.3
~1.5% by weight is considered desirable. As is clear from the above description, the cobalt-containing martensitic alloy of the present application has the following superior properties compared to conventional martensitic alloys, and is an alloy with excellent toughness and corrosion resistance. (i) Notch toughness is 10 to 15 times better. (ii) High strength, hardness, and excellent wear resistance. (iii) Excellent corrosion resistance, especially against hydrochloric acid. (iv) There is little decrease in high temperature hardness.

[Brief explanation of the drawing]

Figures 1 to 29 are microscopic photographs of Y for samples No. 1 to No. 29, respectively, and Figures 30 to 32.
The figures are graphs summarizing the test results.

Claims (1)

[Claims] 1 Mo0.3-1.5% by weight, Ni1.5-4.5% by weight,
A tough acid- and corrosion-resistant alloy consisting of 0.5 to 2.5% by weight of Co, 9 to 13% by weight of Cr, and 0.08% by weight or less of C, with the balance being substantially Fe.