US2343956A - Deep hardening silicon titanium steel - Google Patents

Description

I 2,343,95 E-SQPATENT OFFICE Patented Mar. 14, 1944 Boegehold, Trans. Am. Soc.

than in. the a egate of steel hanced in some degree by adding in suitable NITE STAT DEEP HARDENING SILICON TITANIUM STEEL of West Virginia No Drawing.

Y., assignor to a corporation Application June 30, 1942, Serial No. 449,163

4 Claims. (CL 75-123) This invention relates to steels, and more specifically, to steels the hardness of which may be increased by rapid cooling from temperatures within or above the critical range. This application is a continuation-in-part of my copending 5 application, Serial N0. 321,915, filed March 2, 1940. The invention will be described herein as it may be applied to carbon steels containing between 0.2% and 1% carbon, up to about 2% manganese, between'0.50% and 2% silicon and 0 between 0.05%and 0.15% titanium.

When hardening steels by rapid cooling from hightemperatures, it is often desired to produce a deep or thick zone of hardened material rather than a thin or shallow hardened case. The depth to which a piece of steel will harden, at a given I rate of heat extraction, is difierent in difierent steels. The property of the steel which involves this relativesusceptibility to mass effect in hard ening seems to be inherent, and for convenience it will be termed herein deep-hardenability.

An accepted, convenient measure of deephardenability is afiorded by the Jominy test,

described in detail in A Hardenability Test for Carburizing Stee by W. E. Jominy and A. L.

for Metals, vol. 26, p. 574 (1938). To summarize briefly, the test is made on a small bar of steel of standardized shape and dimensions, and comprises heating the entire bar to the desired hardening temperature, quickly extracting heat through one end face or the bar, grinding ofi superficial scale and decarburized skin and producing a fiat surface suitable for a hardness test, and measuring the Rockwell C hardness along the length of the bar. The distance from the hardened end at which the hard ness becomes less than Rockwell C 50 is referred to herein as the Jominy depth." If the same hardening temperature and cooling conditions be used for a series of steels, thegrelative depths 40 of the hardened zones indicate the relative deephardenability of the steels or that series, each to the others.

An object. of this invention is to improve the deep hardenability of hardenable steels generally, and of plain carbon. and low-alloy steels (less -str k ening tungsten, mo-

elements, for example, chromnnn, lybdenum and nickel) especially.

A further object of this invention is to provide deep-hardenable steels of novel compositions, and deep-hardened articles made therefrom.

The deep-hardenability of steel maybe enper. 4 V centages any one of the elements which can taken into solid solution in steel at high temperatures, for instance, boron, silicon, molybdenum, tungsten, chromium, or nickel. These hardening elements differ widely in the minimum percentage required to imp art a useful degree or deep-hardenabillty, and in the maximum degree of deep-hardenab' 'ty obtainable while maintaining-other necessary properties of the steel.

I have observed that combinations of certain elements may be used to impart a greatly enhanced deep-hardenability without substantial sacrifice of other desirable properties of the steel.

. The present invention is based on these observations.

More specifically, the invention comprises the addition to a hardenable silicon steel of the special element titanium in 'a suitable percentage greater than that required for grain refinement. The silicon content of the steel of the invention is between 0.50% and 2%. The titanium content of the steel is between 0.05% and 0.15%.

when the above-described percentages of silicon and titanium are employed, a medium manganese oil hardening type of steel such as the S. A. E. 1345 type may be hardened to 50Rockwell C or higher throughout a circular section one inch, or even more, in diameter.

There appear to be optimum percentages of silicon and titanium which impart a maximum depth of hardenabillty and a frequent result of an increase in percentage beyond the optimum is a decrease of deep-hardenability below that imparted by the optimum. For-reasons of economy, or to obtain a steel having a certain desired combination of physical properties, it will often be desired to add either less or more of the elements than will impart a maximum depth of hardening. Hence. the invention is not limited to the use of the optimum percentages. I

It has also been found advantageous to add at least one of the elements calcium, barium and strontium in a total percentage between 0.03% and 0.50%.

- Typical effects of representative combinations used according to this invention are indicated mi 1 Table A, which contains figures derived from actual test data. The relative Jominy hardenability depths are given, in hundredths of an inch, of steels containing besides iron the percentage of silicon and special elements indicated; The same hardening temperature and. cooling conditions were used in all tests.

Table A Composition ol'steels:

about 1.6% Mn, Iomlny hardness test, 045% to 0.55% C, .depthin hundredths of Si and'llaslnd- -anineht0RockwellC catcd,rest Fe 50, corrected to 0.457 O by (actor: =l=0.0l% :l:0.012 inch Si T1 riomlnal.

The high quality ing to this invention is indicated in Table B by test data of the p fsicai properties 01' two representative steels aiter for ing, quenching .from 850 C., and drawing at 400 C. for one hour. In Table 1B, the yield point (Y. P.) and tensile strength (T. S.) of the steels are given in thousands of pounds per square inch; El. designates percentage elongation in a two inch initial gauge length, and %R. A. designates percentage reduction of area upon fracture of the 0.505 inch di-' ameter standard (A. S. T. M.) tensile test specimens. Under Izod test results, in loot pounds, using a standard specimen one-centimeter square with standard v notch two mm. deep. The Jominy hardness test depth isthat actually measured, in hundredths of an inch, to Rockwell C 50, the same hardening temperature and cooling conditions having been used in all hardness tests. The steels contain about 1.7% manganese, about 0.50% carbon, silicon and titanium as indicated, rest iron.

' Table B Composition Physical Properties of steels .Tominy %Si -%Tl Y.P. 'r.s. %El. %R.A. Izod is s depth The advantages of the invention may be exploited in any of several ways. For instance cheaper steels may be used instead pensive, more highly alloyed steels heretofore used to obtain the desired strength. Or, present high strength steels may be ev'n further strengthened by applying the principles of the invention, either by deeper hardening to a'lower average hardness or by deeper hardening to the of more ex-' 2,343,006 attainable in steels accord- J specific examples have been given herein to 11- I are given the Izod impact ions steels described, there is 7 Thus, the invention is same or even higher hardness. Amongthe varchoice in respect to such factors as cost, grain size control, ductility, strength, and toughness. capable of a wide held of application, which will gists and steel makers. Therefore, although lustrate the principles of theinv'ention, it will be understood that such examples are merely illustrative and do not restrict the invention beyond the requirements of the claims and the state of the art. a I

I claim: 1. A hardenable steel which is hardenable to at least Rockwell C throughout a one inch diameter circular section, comprising substan-- tially more than 0.5'% up to 2% silicon; between 0.2% and 1% carbo manganese in a percentage up to about 2%: titanium between 0.05% and 0.15%; remainder substantially alliron.

2. A-hardenable steel as defined in claim 1, also containing at least one of the alkaline earth metals calcium, barium, and strontium, the total addition of such alkaline earth metals being between 0.03% and 0.50%. f

3. A quench-hardened article composed of a deep-hardenable' steel comprising substantially more than 0.5% up to 2% silicon; between 0.2% and 1%'carbon; manganese in a, percentage up to about 2%; titanium between 0.05% and 0.15%; remainder substantially all iron, such steel having the property of being quench-hardenable to upwards of 50 Rockwell C throughout a one inch diameter circular section.

4. A quench-hardened article composed of a deep-hardenable steel as claimed in claim 3, also containing at least one of the,alkaline earth metals calcium, barium, and strontium, the total addition of such alkaline earth metals being between 0.03% and 0.50%.

WALTER. came.

a wide range of Y be apparent to metallur-v