US3674468A - High-strength silicon steel - Google Patents

Abstract

A HIGH-STRENGTH SILICON STEEL CONSISTING OF LESS THAN 0.03% C, 4-6% SI, 5-10% NI, 6-18% CR, LESS THAN 4% EACH OF MN, MO AND CU, LESS THAN 2% V AND RESIDUE ESSENTIALLY FE, IN WHICH THE TOTAL AMOUNT OF NI AND MN IS VARIED SO AS TO APPROACH 2 TIMES THE SI CONTENT AND THE CR VARIED ABOUT 2.5 TIMES TO THE SI CONTENT, SO THAT THE AC3 TRANSFORMATION POINT IS LOWERED TO LESS THAN 1400*F.

Description

United States Patent 3,674,468 HIGH-STRENGTH SILICON STEEL Keiichi Ota, 54 Nakagawara-cho, Sakyo-ku,

Kyoto, Japan I No Drawing. Continuation-impart of application Ser. No. 708,530, Feb. 27, 1968. This application Nov. 23, 1970, Ser. No. 92,144

Int. Cl. C22c 39/20, 39/44 U.s. cl. 7s-'-12s A 4 Claims ABSTRACT OF THE DISCLOSURE CROSS REFERENCES This application is a continuation-in-part of copending application, Ser. No. 708,530 filed Feb. 27, 1968 and now abandoned.

BACKGROUND OF THE INVENTION.

The present invention relates to a new high-strength silicon steel possessing improved and unusual combinations of metallurgical and mechanical properties.

It is well known by anyone skilled in the metallurgy of steel that silicon is an effective alloying element for increasing strength and toughness of ferrite and also that the upper limit of silicon for structural steel is about 2%, since larger amounts cause an unacceptable lowering of toughness.

SUMMARY OF THE INVENTION It is thus a principal object of the present invention to obviate the above drawback and to provide a new structural steel possessing a high strength and toughness which is characterized in that Fe-Si alloy containing 46% Si is alloyed witha suitable amount of Mn, Ni and Cr to lower the Ac transformation point to less than 1400" F., thereby preventing the alloy from suifering grain-gross while successfully imparting toughness thereto.

It is another objectof this invention to provide a new structural steel having a high degree of castability and which is well suited for the precision casting of thin and complex machine parts.

Another object of this invention is to provide a novel structural steel which has a high toughness in the as-cast condition.

Still another object of this invention is to provide a new structural steel having excellent forging properties and which may be subjected to electric welding in open air vw'thout preliminary heating.

A further object of this invention is to provide a new structural steel which has very high corrosion resistance to various acids.

The product of this invention is characterized by consisting of, by weight: less than 0.03% C, 4-6% -Si, 5l0% Ni, 6-18% Cr, less than 4% each of Mn, Mo and Cu, less than 2% V, the residue being essentially Fe.

It is important that the amount of C, Si, Mn, Ni and Cr be provided Within the above ranges. For example, the amount of C should not exceed about 0.03% because more carbon impairs the toughness of the product to some degree. The amount of Si employed has been found to be most important. When the Si content is less than about 3%, the strength is adversely affected; whereas with Si content above 7%, the toughness is impaired. For the best combination of strength and toughness, it has been found that the Si content should be within the range of 4% to 6%.

- The total amount of Ni and Mn (Mn is usually held to about 2%) is varied soas to approach 2 times the Si content, and the Cr varied about 2.5 times the Si content, so that the Ac transformation point is lowered to less than 1400 F., thereby preventing the alloy from suffering grain-gross, which imparts toughness thereto.

'By using Cu, the corrosion resistance of this alloy to various acids has been elevated remarkably, especially with respect to sulfuric and hydrochloric acid, while at the same time the forging property is lowered. Therefore, it is recommended to add 1-2% Cu for rust-resisting forging and 34% for stainless casting.

For the purposes of deoxidation and refining of austenite grain-size, it is preferable to add less than 1% each of Al, Ti, Cb and B.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order that those skilled in the metallurgy of steel have a better understanding of the properties which can be obtained by the present invention, the standard composition ranges suitable for certain uses are set forth in the following Table 1.

The characteristics of the high-strength silicon steel according to the invention are illustrated by the data in Tables 2 and 3, setting forth the mechanical properties of round bars with diameter of 1 inch. These round bars have been prepared in such a way that the raw materials are melted in a high frequency electric furnace in open air to produce ingots of 0.5 ton weight which are taken place witha hot-roll to obtain those round bars.

TABLE 2 Chemical composition of steel A tested, percent :0 0.018, Si 4.6, Mn 2.8, Ni 6.6, Cr 10.4, Mo plus V 2.2

Ni CrMo steel Steel A Steel A (4337) Heat treatment Mechanical properties:

Hardness, Hv 325 350 350 S., lb./s in 150,000 165, 000 160, 000

Elongation in 2 inch, perc 52. 48. 2 25. 3

R A., percent 68. 3 74. 4 46. 3

Charpy I.V., kg. m./sq. cm..." 28.1 32. 4 16.2

In the above Table 2, the high-strength silicon steel A according to the invention is compared with the 'NiCrMo structure steel (4337) and comparing these values of elongation, R.A., Charpy impact value and quality factors. It

will be appreciated that steel A has a very high toughness approximately 2 times higher than that of the quench-andtempered NiCrMo steel. On the other hand this data shows that steel A does not have practically any mass-effect on heat-treatment and this enables massive steel forgings, such as rotor-shafts, to have uniform and high strength and toughness even over the core thereof.

Table 3 illustrates the mechanical and corrosion-resisting properties of the high-strength silicon steel B according to the invention in comparison with those of 18-8 stainless steel (30.4). It will be appreciated that the steel B has overcome the poor resistance of 18-8 stainless steel against chlorine and hydrochloric acid and many new uses in the field of chemical industry therefore become possible.

TABLE 3 Chemical composition of steel B tested, percent: 0.022, Si 1.8, Mn 1.8, Ni 7.3, Cr 16.8, Cu 3.4, Mo plus V 1.6

18-8 Stainless Steel In addition to the foregoing mechanical and corrosionresisting properties, it has been confirmed that the highstrength silicon steel according to this invention has the following excellent characteristics and properties:

(a) It is rich in castability and well adapted for precision casting of thin and complex machine parts such as turbine blades.

(b) It has excellent forging properties and permits the manufacture of a music string having a tensile strength of 350,000 lb./s'q. inch and 38 turns in twisting.

(c) It has a very high toughness of more than 8 kg. m./sq. cm. of Charpy impact value in the as-cast condition.

(d) Reduction of toughness is negligible even at temperatures below 32 F., and an impact value of "kg. m./sq. cm. may be obtained in liquid nitrogen.

The present invention may be applied to the manufacture of a wide variety of ferrous products and articles T which will be apparent to those skilled in the metallurgy of steel from the properties of the ferrous alloy provided by the invention. These products and articles include machine parts such as reaction vessels for chemical engineering, turbine-discs of jet engines, exhaust valves of internal combustion engines, chassis of cars, bulletproof plates of tanks, protecting covers for missiles, wire ropes for suspension bridges and marine use, many kinds of springs and various rust-resisting instruments for medical and home uses.

I claim: 1. A high-strength silicon steel consisting essentially of:

Ingredient: Wt. percent C Less than 0.03. 5 Si 4-6.

Ni 5-10. Cr 6-18 and about 2.5 times Si content. Mn Less than 4.

Mo Do. 10 Cu Do.

V Less than 2. 7 Fe Essentially the remainder. Ni-l-Mn About 2 times Si content.

wherein the Ac transformation point of said steel is less than l400 F.

2. A high-strength silicon steel according to claim 1 which also includes less than about 1% of any one of Al, Ti, Cb and B.

3. A high-strength machine structural silicon steel according to claim 1 consisting essentially of:

Ingredient: Wt. percent C Up to 0.03. Si 4-5. Mn 1-3.

Mo-i-V' l-3. Cu Up to 1. Fe Essentially the remainder.

4. A high-strength corrosion resisting silicon steel according to claim 1 consisting essentially of:

Ingredient: p Wt. percent C Up to 0.03. Si 4.5-5.5.

Mn l-3.

Cr 12-18. Mo-]V 1 3. Cu 1-4. Fe Essentially the remainder.

References Cited UNITED STATES PATENTS 2,747,989 5/ 1956 Kirkby 75-128 C 2,839,392 6/1958 Streicher 75-128 3,337,331 8/1967 Ljungberg 75l28 C 1,555,395 9/1925 Armstrong -428 3,294,527 12/ 1966 Floreen 75-l23 2,7 50,283 6/1956 Loveless 75l24 L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGR-U, Assistant Examiner US. Cl. XJR.

75l25, 128 C, 128 F, 128G, 128 T, 128 W