US2082783A - Method of making alloy steels - Google Patents

Description

Patented June 8, 1937 METHOD OF MAKING ALLOY STEELS Thomas N. Armstrong, Jr., and Fred B. Anderson, Portsmouth, Va.

No Drawing. Application September 30, 1935, Serial No. 42,861

4 Claims. (Cl. 75-127) (Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) This invention relates to the. manufacture of corrosion resisting ferro-alloys, particularly of the austenitic stainless steel type, and has for its object to prevent the formation of undesirable carbides and in general toimprove the quality lime and fluorspar. When the melt is practically free of carbon the oxidizing slag is removed and the bath is covered with a mixture of burnt lime and either titanium oxide or rutile. As soon as this mixture becomes fluid there is charged into of the product. the furnace, preferably in small portions, a mix- 5 It is important that alloys of the type menture of lime, aluminum in the form of shot or tioned, usually containing approximately 18 per turnin and rutile- T e quantity of titanium cent chromium and 8 per cent nickel, be free from desire which p ds upon t e car t.

10 oxides and from dissolved gases. The oxides are will determinethe qua i Of titanium de a d ordinarily removed by drawing ofi the oxidizing lime added to the slag. Lime is added in small 10 slag under which the charge has been melted quantiti s as n d d o prevent the Slag from down and refined and replacing it with a basic thinning down too greatly. slag which is, in the final operation, brought to Theoretically, one pound of aluminum will rea reducing condition with carbon, silicon, ferroduce 2.22 pounds of titanium oxide to yield 1.34

silicon, or aluminum. When lime slags are empounds .of titanium. In practice, because of the 15 ployed these agents form calcium carbide, caloxidized condition of the bath after being subcium silicate, and calcium aluminate respectively. je te t0 the oxidizing sla d because Qf the Austenitic steels of the 18-8 type usually concomplexity of the slag formed, it requires more tain more than 0.02 per cent carbon. It is genthan the theoretical quantity of aluminum, and 0 erally accepted that this quantity is the maxialso more than the theoretical quantity of tita- 20 mum that is retained in solution, and all carbon nium oxide to obtain the desired recovery of titain excess thereof unites with chromium to form illm and to keep the slag in a redu d t o chromium carbide. The formation of the chro- Part of the titaniumremains in the slag. It remium carbide impoverishes the iron of chromium quires approximately four times the titanium 5 and makes the metal susceptible to intergranuoxide theoretically necessary. The following ralar corrosion. It has been shown that the formatio, by weight, should be maintained: tion of chromium carbides can be prevented by 7 Part adding to the alloy a suflicient quantity of some Titanium oxide 2% metal having greater affinity for carbon than has Aluminum 1 chromium. Titanium, vanadium, molybdenum Lime 1 ai g gi gfi fi gg fi fig i f g 325 8 223 The slag is calculated on the quantity of titanium th oxide required by the carbon in the melt. A

e most powerful carbide former. For this reaigher percentage of recovery of titanium can son titanium is usually the metal added to the alloys of the type to prevent formation of be had by increasing the aluminum content but 35 as the latter is more costly than titanium oxide chroimum carbide, and for this purpose the titath e aluminum ratio is kept low. mum is added in suificient quantity to insure the A110 1 t l h h d k l f 6 times as much titanium as the cary ng a sue 1 romlmp an me e g g z of 0 02 er cent in the ano The are added in small quantities at a time after the 40 is iisually aided in the form o ferm- Slag is a reducing I} smal-l additim of a mixture of lime and aluminum is usually tttamum or low carbon lmn'chronuum'tlta' madeafter each addition of the alloying metals. mum a These costly as a After the alloying metals have been added small contain some carbon which necessitates adding quantities of the mixture of aluminum and additional titanium to compensate therefor. titanium Oxidev are charged at intervals until 45 Under the present method a reducmg Slag 15 the melt has the desired composition. Approxiformed without carbon or silicon and this slag mately five minutes after t t; addition of reduces titanium from the inexpensive titanium aluminum and t t oxide some lime is oxide, or rutile, which is a titanium oxide ore. charged 't metal is tapped 5 Any desired q y of titanium, p to pe The invention described herein may be manuc t (P a y higher) can be added by this factured for use by or for the Government of the method- United States, without the payment of any royal- We subject the melt to any of the usual oxidizti th reon, ing slags, or if the charge is low in, or practically What i claim d is; I

free from carbon, the charge is melted down with 1, A ro of making ferrous alloys contain- 55 ing substantially 18 per cent chromium and 8 per cent nickel, the remainder being predominantly iron, which comprises refining molten steel under an oxidizing slag, removing the slag and covering the bath with a mixture consisting substantially of lime and titanium oxide which is substantially devoid of carbon-silicon-containing material, then after said covering has become fluid adding titanic oxide, burnt lime, and aluminum in proportions having the ratio 2 :1:1, respectively, then adding chromium and nickel at intervals to supply the desired percentages of these two metals, with further additions of small quantities of-lime and aluminum after each addition of chromium and nickel, and titanic oxide if necessary to maintain the said ratio, the quantity of titanic oxide supplied being such that the percentage of titanium ranges from the quantity thereof necessary to form carbide with the carbon in the metal in excess of the carbon held in solution up to 4 per cent of the total metal.

2. A process of making ferrous alloys containing substantially 18 per cent chromium, 8 per cent nickel and up to 4 per cent titanium, the remainder being predominantly iron, which comprises covering a bath of molten steel, that has been treated under an oxidizing slag, with a mixture consisting substantially of lime and titanium oxide which is substantially devoid of carbon-silicon-containing material, then after said covering has become fluid adding titanic oxide, lime and aluminum in proportions having the ratio 2 :1:1, respectively, then adding chromium and nickel in the form of ferro alloys at intervals to supply the desired percentages of these two metals, with further additions of small quantities of lime and aluminum, and also titanic oxide if necessary to maintain the said ratio after each addition of chromium and nickel, the quantity of titanic oxide supplied being more than that necessary to form a carbide with the carbon present in excess of 0.02 per cent and less than will leave in the alloy titanium substantially in excess of 4 per cent.

3. A process of making ferrous alloys containing nickel and chromium, which comprises covering a bath of molten steel, that has been treated under an oxidizing slag, with a mixture consisting substantially of lime and titanium oxide which is substantially devoid of carbon-siliconcontaining material, then after said covering has become fluid adding titanium oxide, lime and aluminum in proportions having the ratio 2 :1: 1, respectively, then adding chromium and nickel in the form of ferro alloys at intervals to supply the desired percentages of these two metals, with further small quantitiesof lime and aluminum, and also titanium oxide if necessary to maintain the said ratio, after each addition of chromium and nickel.

4. A process of making ferrous alloys containing nickel and chromium, which comprises covering a bath of molten steel, that has been treated under an oxidizing slag, with a mixture consisting substantially of lime and titanium oxide which is substantially devoid of carbon-siliconcontaining material, then after said covering has become fluid adding titanium oxide, lime and aluminum in proportions having the ratio 2 :1: 1, respectively, then adding chromium and nickel in the form of ferro alloys at intervals to supply the desired percentages- 0f these two metals, with further small quantities of lime and aluminum, also titanium oxide if necessary to maintain thesaid ratio, after each addition of chromium and nickel, adding small quantities of aluminum and titanium oxide until the melt is in satisfactory condition, adding more lime approximately five minutes after the last addition of aluminum and titanium oxide, and then tapping the melt.

THOMAS N. ARMSTRONG, JR. FRED B. ANDERSON.