US2025016A - Method of normalizing steel - Google Patents

Description

Patented Dec. 17, 1935 LIETHOD OF NORMALIZING STEEL William C. Chancellor, Elyria, Ohio, assignor to National Tube Company, a corporation of New Jersey No Drawing. Application April 18, 1933,

, Serial No. 666,732

4 Claims.

This invention relates to methods of treating steel and more particularly to methods of treating steel products comprised of steel of the'socalled non-austenitic type to produce a desired and beneficial crystal structure therein.

Heretofore in the art it has been customary when it is desired to obtain a so-called grain refinement in steel products comprised of steel of the so-called non-austenitic type to heat the steel to temperatures approximating but above the critical temperature for a time interval sufficient to obtain entire conversion of the steel to its gamma or austenitic form and then to cool the steel to a temperature below the lower critical temperature to transform the I austenite to its ferritic or alpha form.

It is known that the toughness of non-austenitic steels depends largely on the amount and arrangement of excess ferrite which. together with some form of pear1ite'or sorbite constitutes the structural composition of such steels. I have found that, in the art of normalizing as heretofore practiced, this excess ferrite is often incompletely developed during the changes which take place when the steel 'cools through the critical temperature range, and the deficiency in excess ferrite causes a lowering of resistance to impact and a decrease. in toughness.

One of the objects of the present invention is to provide a method of treating steel which will operate to produce a uniform grain structure independently of the prior history of the steel.

Another object of the present invention is to produce a structure containing a maximum proportion of excess ferrite consistent with the chemical composition of the steel.

A further object of the present invention is to provide. an improved method of normalizing steel.

Still another object of the present invention is to provide an improved method for normalizing" the grain structure of fabricated steel products such as sheet, rods, bars, rails and the like.

Other objects and advantages will become apparent as the invention is more fully disclosed.

In accordance with the objects and advantages I have discovered that the non-uniformity of the grain or crystal structure of steel normalized by the method heretofore proposed in the art can be substantially eliminated'by subjecting the steel while cooling through the critical range to what may be Broadly defined as an internal agitation or disturbance. Preferably this internal agitation or disturbance is not accompanied by any material or permanent alteration of the external size,

Shape or configuration of the steel article, but in some instances some permanent reduction in area may accompany the internal agitation or disturbance.

The'preferred type of internal agitation or dis- 5 turbance is obtained by flexing the steel through the application thereto of alternate tensile and compressive stresses. Preferably also the application of these alternate tensile and compressive strains should be made transverse to and pro- 0 gressively along the longitudinal axis of the steel product.

By. reason of this internal agitation or disturbance the non-uniform sized austenite crystals formed at the temperature of heat-treating are 15 broken up during transformation and caused to recrystallize into smaller grains than tend to develop when agitation is absent. By further reason of this internal agitation the separation of excess ferrite from the pearlitic constituents 20 is rendered more complete and tends to form a network of ferrite around the pearlitic grains; which type of structure is best suited to withstand impacts and sudden deformation without failure. As the customary rate of cooling through the 25 critical temperature range is relatively slow, the application of the internal agitation or disturbance should be terminated as soon as practical after the steel has passed through the transformation temperature and before cold working eflects 30 incident to such internal agitation and disturbance developto a deleterious or undesired extent.

As a specific embodiment of the practice of the present invention of work-normalizing steel the method as applied to steel sheets will be described. 35

The steel sheets are first heated to a temperature approximating but above the upper critical temperature which temperature will vary somewhat depending upon the specific steel composition and carbon content. Then the sheet is al- 40 lowed to cool slowly in still air down to a temperature withinthe critical range but above the transformation temperature and passed lengthwise through staggered rolls positioned to bend the present invention as it is independent of the specific apparatus employed. One skilled in the art of rolling sheet can readily adapt apparatus to practice the present invention.

In the application of the present invention to elongated articles such as rails, bars, rods and the like substantially the same'practice as described with respect to sheet may be employed.

In the adaptation of the present invention to tubular articles such as seamless tubing the tinished rolled tube is heated to its normalizing temperature, which is above the upper critical temperature, and then while the tube is cooling from that temperature through the critical range is run through the reeling, sizing and cross-rolling machines heretofore employed in the art. The action of these machines results at first in a distortion of the circular section of the tube to an oval shape, and then reshapes the same to a circular section of substantially the same size as the original tube, thereby introducing within the metal structure the desired internal agitation or disturbance. In some instances there is a slight reduction in area accompanying the internal agitation or disturbance which is not-deleterious due to the temperature at which it is applied.

The advantages obtained by the practice of the present invention are reflected in the physical properties of the steel product resulting therefrom. I have found that as a result of the better grain refinement obtained, the steel product is found to be tougher, and to show greater resistance to impact and exhibits greater freedom from f brittleness as compared to steel products heretofore produced by the prior art normalizing method. By the practice of the present invention it is not necessary to closely control the temperature to which the steel is heated, nor is it necestsary to vary the temperature of heating with 40.

slight variations in chemical composition of the .steel as is required in the prior art normalizing method. These advantages all serve. to simplify and to improve the art of normalizing steel.

It is apparent from the above description of the present invention that the broad inventive idea of the present'invention is capable of extensive modification and adaptation in the application oi the same and. all such modifications and adaptations are anticipated as may fall within the scope of the following claims.

What I claim is:

1. The method of treating steel which comprises heating the steel to a temperature slightly 1 above the critical temperature range, cooling the steel to a temperature below the critical range, and subjecting the steel during cooling through the critical range and while aboveits transforma-,.

tion temperature to alternate tensile and compressive stresses effecting a slight reduction in area. Y I

2. The method of treating steel which comprises heating the steel to a temperature slightly above the critical temperature range, cooling the steel to a temperature below the critical range,

and subjecting the steel during cooling through the critical range and while above its transformation temperature to alternate tensile and com--.

' prises heating the steel to a temperature slightly I above the critical temperature range, cooling the steel to a temperature below the critical range, and subjecting the steel during cooling through the critical range and while above its transformation temperature to mechanical deformation, said deformation including the application of alternate tensile and compressive stresses applied transversely and progressively along the length of the steel.

WILLIAM C. CHANCELLOR.