DE668579C - Manufacture of chromium-containing malleable cast iron pieces with increased strength and forgeability - Google Patents

Description

Manufacture of chromium-containing malleable castings with increased strength and forgeability White cast iron, which is suitable for the tempering process (so-called malleable cast iron), is usually composed as follows: 0.5 to 2 % Si, 0.18 to 0.7% Mn, 1 .5 to 3 % C (in the originally annealed state and somewhat less after the annealing has taken place), 0.05 to 0.3 % P, up to about 0.2% S, the remainder being iron. A preferred composition of malleable cast iron is 0.9 ° Jo Si, 0.3 ° / a 1% 1n, 2, q. ° / o total content of C, 0.16 % P, remainder iron and S.

The composition, in particular the content of carbon and silicon, depends, however, to a large extent on the cross-sectional dimensions of the casting and on the cooling rate during casting and does not let itself into any general rules devour, rather. is made by the specialist on the basis of practical experience always selected.

Castings from such hard and brittle iron are then made is known to be made malleable by a longer annealing treatment (tempering). These Treatment usually consists of annealing the casting, sometimes in a packing made of iron oxide or an inert substance, at about 700 to 100 ° C for 6 to 60 hours (depending on the temperature used), whereupon the casting is slowly cooled so that a substantially complete Conversion of the bound carbon into free carbon in the form of graphite nodules (or temper carbon) takes place. A preferred heat treatment is that the temperature rise of the casting up to about 9oo ° C within 36 hours carried out and the casting then for q.2 hours at the temperature reached of goo ° C, whereupon it is cooled down from goo ° to 6oo ° C in such a way that the Temperature drops by 10 ° in each case within an hour, whereupon the Cooling from 600 ° C to room temperature is carried out slowly. Sometimes it will either the particularly slow cooling from goo ° down to 600 ° or the slow one Cooling from 600 ° C to room temperature omitted.

This heat treatment softens the brittle white cast iron and ductile, it has a black fracture, the carbon is in the form of Graphite nodules or tempered carbon present.

The malleable cast iron produced in this way is used for a great many purposes usable, its low resistance to wear and tear and also its limited But form elasticity certain and essential limits for his Lifespan in the company and thus for its suitability for corresponding purposes. -The Invention has the task; Such iron castings forged iron with he 'higher Strength and forgeability heart p = '.

It is known that low chromium contents can increase the strength and hardness of malleable cast iron. But it is also known that even small amounts of chromium favor the formation of large nests of permanent carbides and have a greater inhibitory effect on tempering, because these carbides resist any transformation into graphite during annealing. It was therefore practically impossible to make cast iron, which contained chromium in amounts of about 0.15 % and more, completely malleable.

Chromium is therefore rightly regarded as one for malleable cast iron in general undesired alloy component called.

It has now been found that by the simultaneous presence of silicon and chromium within certain proportions in white cast iron (malleable cast iron) Production of castings is possible, which after tempering due to their special Structure has a significantly higher tensile strength, hardness and resistance to Show wear than the previously known malleable castings.

According to the invention, a malleable cast iron of the following composition is assumed: 1.5 to 3% carbon, 0.15 to 2% chromium, 0.53 to 1⁄4 ° / ° silicon, 0.18 to 0.7 ° / ° Manganese, 0.05 to 0.3 °% phosphorus, up to 0.2 d / ° sulfur, remainder iron, and the silicon and chromium content within the limits mentioned so that the @, casting solidifies and is white The structure after the graphitizing annealing consists essentially only of pearlite, chromium ferrite and free carbon (graphite nodules or tempered carbon).

If the ratio of silicon to chromium is too small, then it will difficult or impossible, sufficient tempering carbon formation during annealing to ensure; but if the ratio is too high, then will. Hardness, strength and ductility of the tempered casting is adversely affected.

The advantages of the malleable castings obtained according to the invention have been confirmed by extensive tests. The following compilation contains some values that were occasionally obtained from these investigations. The castings on which these investigations were based had approximately the following initial composition: total carbon 2.35 ° / °, manganese 0.37'1 ", phosphorus 0.160 /" sulfur 0.25 ° / °, silicon 1.02 ° / °, remainder iron. Chromium and silicon were added to this starting composition so that the tempered castings contained Cr and Si contents as indicated in the list. The addition took place in the ladle in the form of ferrochrome and ferrosilicon. Usual test bars of 15.6 mm diameter or edge height were cast and the usual Ratio of o elasticity Test rod #o Si in addition to- Highest Brinell- No. o Cr in addition to Si (stretch) elongation # ° joint tensile strength hardness 1.02 o / ° to the limit put Cr 1; g / mm2 1g m m3 1 oo - 39.24 27.0o 18.5 131 2 o, 22 o, o8 *) o, 36 50.40 3053 1 1.0 175 3 0.23 o, 22 o, 96 52.49 31.39 9.0 1 79 4 0.24 0.25 1.04 55s23 3384 9.0 168 5 o, 37 o, 26 0.70 55.77 3546 9.5 179 6 0.40 o, 42 1, o5 4932 34.56 6, o 183 7 0.56 0.37 o. 61 57.96 37.8o 6, o 2o1 8 o, 73 o, 64 o, 88 48, 7 4 3942 4.5 212 9 0.84 o, 55 o, 66 57.6o 42.48 4.0 213 1o o, 87 o, 6o o, 69 45.72 37.8o 3.0 2o1 = I =, o8 0.70 o.65 55.15 4464 310 223 12 1.14 1.00 o. 88 48.24 45.00 2.5 2o2 *) The additional silicon was added here in the form of an alloy consisting of 61.9% silicon, ro, 5% manganese, 21.8 % zircon, the remainder aluminum. Chromium and silicon can be added together in the melting furnace or in the pouring ladle or one in the furnace and the other in the pouring ladle, or the addition itself can either be in the form of the elements or their alloys or compounds, depending on the composition of the white malleable cast iron the dimensions of the casting and the cooling rate has, as usual, been determined empirically beforehand.

Claims (1)

PATENT CLAIM: Production of chromium-containing malleable castings with increased strength and forgeability, characterized in that a malleable cast iron of the following composition is assumed: 1.5 to .3% carbon, 0.15 to z % chromium, jb931 to q. ° / o silicon, 0.18 to 0.7% angan, 0.05 to 0.33% phosphorus, to Ö, 2 P /, sulfur, remainder iron, and that the silicon and chromium content are adjusted to one another within the limits mentioned so that the casting solidifies white and its structure after the graphitizing annealing essentially consists only of pearlite, chromium ferrite and free carbon (Graphite nodules or tempered carbon).