US2263841A - Method of making steel - Google Patents

Description

Patented Nov. 25, 1941 UNITED STATES PATENT OFFICE METHOD OF MAKING STEEL Albert E. Greene, Seattle, Wash.

No Drawing. Application December 11, 1937,

' Serial No. 179,333

2 Claims.

This invention relates to improvements in the method of making steel of improved physical properties, and more particularly to an improved method of securing improved physical properties such as yield strength and ductility, and testing the molten steel prior to pouring or tapping it from the furnace.

I found, in the course of certain electric ,steel melting operations, that by taking spoon samples from the bath from time to time after the bath was melted and pouring these spoon samples. into test bars, theimprovement in physical properties could be readily checked. I had never before taken spoon samples of the bath prior to the alloy deoxidizing additions and pulled test bars made from these spoon samples from the bath while the bath was held in the furnace. I found that spoon samples from the bath could be poured into testbars which could be pulled to ascertain tensile properties, both strength and yield point of sample test bars increased during the treatment given the steel in the furnace, and these test bars were pulled in the as-cast and un-heattreated condition. These test bars were cast in green sand molds close to a diameter-of .505". The test bars had enlarged ends for holding by the grips of the'testing machine. An example of the results is as follows. A steel heat containing about .30% carbon and .30% manganese and not over 40% silicon, all residual except possibly a small amount of carbon, that is, without any alloy additions, showed increasing tensile results in the as-cast, un-heat-treated test bars, from about 50,000 psi at the start of taking samples to a tensile strength of 80,000 at the finish of the heat. Other heats ofthis same approximate composition showed tensile strength as high as 100,000 psi. Furthermore, the yield strength at the end of the heat was between 50,000 and 65,000 psi for these heats, and the ductility was excellent as measured by the improvement of grain and fracture appearance as well as in elongation and reduction of area. In the steel with the best physical tensile and yield strength for a carbon content under about .40% the fracture of the pulled and broken specimens was silky, that is for the fully reduced steels. This silky fracture in such as-cast test bars is new, as far as I am aware.

I have never seen itin an un-heat-treated test bar of any such composition, or even with much higher alloy contents. a I have found that the test bars made from the upper level or strata of the steel bath under the reducing slag will show the silky fracture and other correspondingly improved physical properties, whereas a test bar made from the steel farther down in a deep bath, which steel is not sufficiently reduced, will not show the silky fracture or corresponding high tensile properties.

My improved method of this application is intended to ascertain and check the quality of the steel during and after the deoxidizing or reducing treatment to which it is subjected. The tests which showed the improved physical properties were taken from the bath of steel after it had been sufliciently treated or deoxidized. These improved physical test results were obtained in steel made in electric arc furnaces where the temperature of the bath was maintained only slightly above themelting temperature, that is enough so;

that spoon samples of the molten steel could be readily taken and poured from the spoon, and where the slag composition was controlled and where the bath was subjected to reducing action of added reducing agents.

An example of the method of this invention will now be given. In the case of a heat of high strength steel I may use either an acid hearth electric furnace or a basic hearth electric furnace. Using an acid hearth, a scrap charge is selected which is sufliciently low in phosphorus and sulphur to not require removal of either, and the content of carbon is preferably below that which is desired in the finished steel, for example under .30 percent carbon. This scrap charge is put in the furnace on the hearth. Sand and limestone to make slag are also charged, in suificient quantities to give a covering slag preferably at least a half inch thick. The proportions of sand and limestone may be about equal and the slag, after physical strength. If this is the case the reduc-v The first test bar thus made ing action on the steel is continued. This reducing action can be accomplished by throwing on the slag covering a fine carbon reducing agent or some other reducing agent, in particulansilicon. However, without any silicon addition, and without any other alloy additions, continuance of the reducing treatment on the slag bath will result in the improved physical properties, if carried out as above described, that is, at the relatively low molten bath temperatures. Then, when the steel is sufl'iciently reduced, the tensile test bars will show the improved properties already described, and furthermore, these improved results are found to occur in the test bars as-cast and pulled without heat treatment. Thus, this invention provides a means for making the steel and having assurance that it is in the high strength condition before it ever leaves the furnace. When the steel is in the improved condition, the as-cast and un-heat-treated test bar will show the silky fracture in the pulled apart specimen containing carbon not over about .40 per cent.

The operation can be carried out in a basic furnace as well as one with an acid (silica) hearth. In the basic furnace the slag will preferably be on the basic side, that is, it may be made of sand and lime or limestone, but the silica in the basic slag is preferably kept down to be- .tween 25 and per cent of the total silica andlime content of the slag, that is a slag containing about 18102 to 2Ca0.

What I claim is:

1. In the production of steel and iron, the

method of determining the quality of the metal tensile machine while holding the molten steel in the furnace, and continuing the treatment in the furnace until the desired tensile or yield strength is attained in a sample tensile specimen.

ALBERT E. GREENE.