US1954344A - Chromium-containing steels - Google Patents

Description

Patented Apr. 10, 1934' p ,v 1,954,344

CHROMIUM-CONTAININ G STEELS Frederick M. Becket, New York, and Russell Franks, Jackson Heights, N. Y., assiznors to Electro Metallurgical Company, a corporation of West Virginia No Drawing. Application November 2, 1932, Serial No. 640,900

'1 Claims. 75-1) This invention relates to chromium-containing TABLE I steels, and more especially to chromium steels that are substantially non-hardenable. A. Metal in as-rolled condition One well known method of hardening iron depends, among other things, on a solution of car- 55 bon in the form of carbides in the iron, and the 7 Brinresulting product is known as steel. When chro- Cr o Cb Rerf. oi i3, mium is added to iron containing carbon as car- Yleld ness t t bide, the effect of carbon in producing hardness pom S ms is even more pronounced. If chromium is pres- ,10 60 ent to the extent of about 12% in iron, the amount 3 0e 04 33% ,2 it i 253 of carbon required to attain the euteotoid com- 12.02 0.12 149 000 204,000 3 s 5 position 1s only about 0.30%, thus showing that 12,42 ,1 1,18 301200 63,300 54 7 the presence of a given amount of carbon is more 8-82 g 3 g H8 influential in producing hardness in these steels 22150 11 (51:000 04,500 7 11 5:50 170 than in. the plain carbon steels. This fact has 22-35 L47 75,000 19 39 6 been used to advantage in the production of stainless steels employed-for cutlery purposes. 0 0

It is also well known that chromium imparts Heated at 7 7 4 and cooled excellent corrosion resistance to steel, and the use of a steel containing chromium is advanta- 1262 Q12 [m 80,000 30 73 M0 149 geous in applications other than cutlery. In such 42 29 67 00 128 other applications great hardness is detrimental in a large number of cases, and in order to obtain softer steels, the practice is to lower the It IS shown m sectlon A (If Table I that low carbon content. ,At the present time large tonbon Steels ntaining approximately 5, 12, 18 and nages of high chromium steels containing not 23% chromium inthe as-rolled state possess v y more than 0.15% carbon, and in some cases 0.10% little dufitility and t se C ntaining 5 and 12% or less, are manufactured for use in resisting ch are also quite a e data g ven corrosion. Steels having even these low carbon for a similar series of steels treated. with oolum contents still possess hardening ability, as shown bium, show that in the same state these steels are by the fact that they must be annealed for at ductile and soft. Section B of Table I shows the least several hours at the proper temperatures to relative effefits of annealing on a nable 2% impart softness or ductility, or both. However, ehfOmiuIn Steel a d On a 1 chromium steel the hardening ability of such steels depends treated with columbium; i i s that the props5 greatly on t i chromium t t, because if erties of the steel without columbium aregreatly this element is present to an extent greater than altered by annealing, While the P Pert eS of the about 16% the metal cannot be appreciably hardcolumbium treated Steel are I101; pp y ened, although it is still necessary to anneal the d- It can also be noticed that the steel wrought alloy to improve its ductility and to imcontaining columbi m' is Softer n the p n part maximum softness. chromium steel, evenin the annealed state.

We have found that if steels containing sub- The plain chromium steels containing in the stantial amounts of chromium are treated with neig of about hromium with 10W certain elements their hardening ability is greatly carbon are hardened appreciably by coolingthem reduced, and may in many cases be substantially rapidly from temperatures in the neighborhood of eliminated. An element that produces this result 950 C. Our tests have shown that when such a is columbium. The effect of this element'when steel is treated with a sufiicient amount of columit is added to high chromium steels is indicated bium the metal is not appreciably hardened by by the data given in Table I. cooling rapidly from these temperatures. The

data given in TableII show this advantage resulting from the addition of columbium to chromium steels.

' TABLE II Heated at 950-1000" 6'. 5 minutes and air cooled While the data given above show that in the rolled state the columbium-bearing steels are soft and ductile, we believe it is advantageous to anneal the metal at least to relieve the strains produced by hot working. These results show that this can be done in a few minutes at these higher temperatures, whereas when the untreated steels are softened it is necessary to anneal them for several hours at lower temperatures.

It is realized that as the chromium content is gradually increased beyond 12% in low carbon steels the tendency to harden is lessened. When the chromium content reaches about 16% the steels cannot be greatly hardened, although they must be annealed to render them ductile. As the chromium rises further to 20% and upwards, this tendency to harden is further lessened, but it is again necessary to anneal to impart ductility.

. These steels are all rendered soft and ductile in the rolled state by the'presence of columbium, and

ably should not exceed about 1.5%, of the total alloy. In order to secure the very soft steels of the invention, the carbon content should not exceed about 0.5%, and preferably, in the case of steels containing up to about 16% chromium, the carbon content should not exceed about 0.2%;- while in the steels containing approximately 16% to 30% chromium, the carbon should not exceed about 0.35%.

The data given in Table III illustrate the effects of various ratios of columbium to carbon on a representative chromium steel.

Our researches have included the addition of other elements to high chromium steels; for example, such elements as uranium, molybdenum, and tungsten. The results have shown that when appreciable amounts of these elements are present the steels are still comparatively hard in the rolled state, showing that they do not produce. the same-result as columbium. This is shown in the data given below, in Table IV.

TABLE IV 7mm 711d 1 E'h l3 e o or O U w Mo o 2 0 area V3210 hai d n e s s Yield point Max. stress 13. 48 0. l8 0. 72 Tensile sample could not be obtained because metal was not 4. 00 430 machinable as rolled 13. 62 0.07 0.89 118,000 144,000 4 I 6 6.00 269 13. 57 0.05 2.67 73,000 101. 500 3 7 6. 00 196 12. 78 0. 14 1. 64 is one shown 148, 000 None shown 4. 418 13. 02 0. 10 149, 000 184, 500 3 8 5. 00 375 13. 79 0. 04 127, 600 152, 500 8 l3 5. 00 170 additions of this element can be beneficially made to metal containing as much as about 25 %-30% chromium.

We do not depend on the eifect of alloying columbium with the solid solution of chromium and iron to modify the physical characteristics of the alloy. Indeed it is found that if a considerable excess of columbium over that required to combine with the carbon is added, or if a relatively large amount of columbium carbide is present, the resulting steels are rendered somewhat less soft and ductile than those in which these excesses are avoided. Nevertheless, a substantial excess of columbium may in some cases be present without destroying the excellent ductility and softness of the metal and without otherwise modifying greatly the properties of the alloy. More specifically, the ratio of columbium to carbon We have further found that if the carbon present in these chromium steels is combined with columbium, their resistance to oxidizing media is enhanced. This is shown by the fact that low carbon steels containing less than about 12% chromium exhibit greater resistance to nitric acid when they are treated with this element. Thus, it will be noted that treating these steels with columbium apparently leaves practically all of the chromium present in solid solution to impart inherently more corrosion resistance.

columbium produced from the common ores of this element is usually associated to some extent with tantalum. Traces of tantalum will therefore usually be present as an impurity in the steels of the invention, but it is found that traces of this impurity do not modify markedly the properties of the alloys.

There will be instances in which it is desirable to leave a part of the carbon in combination with the iron and chromium. For example, optimum softness may not be desired under all conditions, and a high chromium steel containing 0.20% to 0.50% carbon may serve admirably if say approximately one-half of the carbon is combined with columbium, that is, if the ratio or columbium to carbon is say about 4 to 1. In such a case the steel would have equivalent softness to an untreated steel containing about 0.10% to 0.25% carbon. Such a procedure may also prove to be economical in remelting high chromium steel scrap, during which operation there is a marked tendency to pick up carbon.

It will usually be desirable not to exceed about 1% manganese, 1% silicon, or a total of about 1% of other metals and metalloids in the alloys of the invention, where highly soft and ductile alloys are to be obtained.

We claim:

1. Alloys comprising iron, chromium, columbium and carbon, the chromium content being between about 2% and about the carbon content being not more than about 0.50%, and the columbium content being at least about four times the carbon content and not more than about eight times the carbon content plus 2% of the total alloy; the balance being substantially iron.

2. Alloys containing iron, chromium, columbium and carbon, the chromium content being between about 2% and about 30%, the carbon con tent being not more than about 0.5%, and the columbium content being at least about eight times the carbon content and not more than about eight times the carbon content plus 2% of the total alloy; the balance being substantially Iron.

3. Alloys containing iron, chromium, columbium and carbon, the chromium content being between about 2% and about 30%, the carbon content being not more than about 0.5%, and the columbium content being at least about eight times the carbon content and not more than.

about eight times the carbon content plus 1.5% of the total alloy; the balance being substantially iron.

4. Alloys containing iron, chromium, columbium and carbon, the chromium content being between about 2% and about 16%, the carbon content being not more than about 0.2%, and the columbium content being at least about eight times the carbon content and. not more than about eight times the carbon content plus 1.5% of the total alloy; the balance being substantially iron.

5. Alloys containing iron, chromium, columbium and carbon, the chromium content being between about 16% and about 30%, the carbon content being not more than about 0.35%, and the columbium content being at least about eight times the carbon content and not more than about eight times the carbon content plus 1.5%

of the total alloy; the balance being substantially 6. Alloys containing iron, chromium, columbium and carbon, the chromium content being-between about 4% and about 8%, the carbon content being not more than about 0.5% and the columbium content being at least about eight times the carbon content and not more than about eight times the carbon content plus 1.5% of the total alloy; the balance being substantially iron.

'7. Alloys containing iron, chromium, columbium and carbon, the chromium content being between about 2% and about 30%, the carbon content being not more than about 0.5%, and the columbium content being at least about eight times the carbon content and not more than about eight times the carbon content plus 2% of the total alloy; not more than about 1% manganese, not more than 1% silicon, and not more than about 1% of incidental impurities; the balance of the alloy being iron.