US3000731A

US3000731A - Fine-grained steels

Info

Publication number: US3000731A
Application number: US740995A
Authority: US
Inventors: Ototani Tohei
Original assignee: Res Inst Iron Steel
Current assignee: Research Institute for Iron Steel and Other Metals of Tohoku University
Priority date: 1958-02-03
Filing date: 1958-06-10
Publication date: 1961-09-19
Anticipated expiration: 1978-09-19

Description

3,000,731 FINE-GED STEELS Tohei Ototani, Tokyo, Japan, assignor to The Research Institute for Iron, Steel and Other Metals of The Tohoku University, Sendai City, Japan No Drawing. Filed June 10, 1958, Ser. No. 740,995 Claims priority, application Japan Feb. 3, 1958 2 Claims. (Cl. 75-129) This invention relates to fine-grained steels and methods of manufacturing the same.

The object of this invention is to provide a fine-grained steel having improved toughness and machinability.

The control of the grain size of a steel has heretofore been effected by adding to the steel a suitable amount of an element such as Al, Ti, V, Zr and N.

According to this invention, in order to improve grain size control, a Fe-Ca base alloy, or other calcium alloys and, if desired, one or more elements such as cerium, lithium, barium, strontium and magnesium are used.

According to the invention, the iron-calcium base alloy contains 10 to 80% iron, 5 to 40% calcium and 5 to 55% of one or more elements selected from the group consisting of nickel, silicon, aluminum and manganese.

The method of this invention is characterized in that a molten bath of carbon and alloy steels containing less than about 1.7% of carbon is treated so as to retain 0.001 to 0.05% of calcium by adding the iron-calcium alloy.

An advantage of this invention is that it is not necessary to eifect deoxidation and de-sulfurization so perfectly that the product contains oxygen from 0.001 to 0.005% and sulfur from 0.003 to 0.015% in order to constitute finegrained steel. Even when the resulting steel contains more than 0.015 of sulfur and more than 0.005% of oxygen, it has a fine-grained structure provided that the amount of residual calcium in the product is more than 0.001%.

In carrying out the method of this invention it is necessary for the molten bath to be previously de-oxidized and de-sulfurized suitably. This is desirable for the effective use of the above mentioned additives.

This invention can be applied to carbon steels and all kinds of alloy steels containing less than 1.7% of carbon, that is, not only to an ordinary carbon steel but also to alloy steels containing less than 1.7% carbon together with one or more elements selected from the group consisting of silicon, manganese, nickel, cobalt, chromium, copper, aluminum, tungsten, molybdenum, vanadium, titanium and zirconium. The steel subjected to the above treatment has fine-grained structure and improved characteristics without substantial change in tensile strength and its machinability is improved. The improvement in the mechanical properties of such treated steels is remarkable, especially in quenched and annealed state.

Example I A molten bath of hypo-eutectoid steel containing 0.69%

Patented Sept. 19, 1961 carbon, 0.25% silicon, 1.03% manganese, 0.021% phosphor, 0.022% sulfur was prepared and to this bath was added 0.5% of Fe-Ca base alloy (Fe 15.6%, Mn 12;7%, Ca 20.5%, Si 45.7% and Mg 4.5%.)

A steel ingot manufactured by the above method of this invention after annealed at 900 C. for 6 hours had a tensile strength of 71.0 kg./mm. an elongation of 25.5% (gauge length, mm.) with a reduction of area of 31.6%, and a Brinell hardness number of 177; thus it is characterized in that the elongation and the reduction of area are high. The ingot contained a very small amount of non-metallic substances and the grain size was 7.5 according to the index of Timken A.S.T.M. grain size so that the steel was finer and cleaner than the grain size 5 of steel which is not treated with calcium.

Example 11 A molten bath of chrome molybdenum steel containing 0.35% C, 0.19% Si, 0.77% Mn, 1.00% Cr and 0.22% Mo was treated with 1% of iron-calcium base alloy (Fe 33.5%, Ca 29.5% and Si 36%).

A steel ingot manufactured by the above method of this invention was quenched and tempered after forging and rolling, and in comparing the results of the steel which was treated with calcium and that not treated, the former showed a grain size of 7.9, while the latter showed 6.5 A.S.T.M. grain size.

What I claim is:

1. A method of manufacturing a line-grained steel, which comprises adding to a molten bath of steel containing less than about 1.7 of carbon, an iron-calciumsilicon-manganese alloy consisting essentially of at least 10% of iron, 5 to 40% of calcium and 5 to of manganese and silicon respectively so as to retain 0.001 to 0.05% of calcium in the casting, and then casting the molten steel into a mold.

2. A method of manufacturing a fine-grained steel, which comprises adding to a molten bath of steel containing less than about 1.7 of carbon, an iron-calciumsilicon-manganese-aluminum alloy consisting essentially of at least 10% of iron, 5 to 40% of calcium, and 5 to 55% each of manganese, silicon and aluminum, so as to retain 0.001 to 0.05 of calcium in the casting, and then casting the molten steel into a mold.

References Cited in the file of this patent UNITED STATES PATENTS 2,280,283 Crafts Apr. 21, 1942 2,343,956 Crafts Mar. 14, 1944 I FOREIGN PATENTS 885,247 France May 24, 1943 OTHER REFERENCES Carlsson: Jernkontorets Annaler, vol. 137, No. 7, 1948, pages 221-236. Published in Stockholm, Sweden.

Claims

1. A METHOD OF MANUFACTURING A FINE-GRAINED STEEL, WHICH COMPRISES ADDING TO A MOLTEN BATH OF STEEL CONTAINING LESS THAN ABOUT 1.7% OF CARBON, AN IRON-CALCIUMSILICON-MANGANESE ALLOY CONSISTING ESSENTIALLY OF AT LEAST 10% OF IRON, 5 TO 40% OF CALCIUM AND 5 TO 55% OF MANGANESE AND SILICON RESPECTIVELY SO AS TO RETAIN 0.001 TO 0.05% OF CALCIUM IN THE CASTING, AND THEN CASTING THE MOLTEN STEEL INTO A MOLD.