DE2350370A1 - Forging carbon-manganese steel - micro-alloyed with vanadium or niobium and cooling in air at room temp. - Google Patents

Abstract

Steel forgings, esp. used as crankshafts for vehicle engines, are produced by forging a C-Mn steel contg. >=0.2% C, micro-alloyed with 0.05-0.15% V or Nb, and contg. no further alloying components, at 900-1280 degrees C with V addn. or at 1250-1280 degrees C with Nb addn., followed by cooling the forgings, esp. individually, in air at >= room temp. Micro-alloying additives improve yield strength but do not alter tensile strength. Re-heating after cooling is obviated; a pearlite structure is formed and forgings can be machined with tools used for forgings of heat-treatable steels.

Description

VOL-KSW AGEKWESK
Corporation
5180 Wolfsburg

Our symbols: K 1583
1702-pt-hu-sa

H. 10.73

Method of making a forging from steel

The invention relates to a method for producing a Forged part made of steel, for example on a crankshaft is intended for a motor vehicle engine.

It is known to forge such parts from carbon steel and normalizing after forging, which results in only relatively low yield strengths in the material of the part can be achieved. On the other hand, it is also known to use the part after cooling to achieve a higher yield point quenched and tempered, i.e. to an austenitizing temperature of To be heated to 860 to 880 ° 0, quenched in oil or water and tempered to the desired strength.

While the first-mentioned procedure of the Hörmalglowens.also often does not bring the desired strength values, the tempering process mentioned in the second place has the Disadvantage of increased manufacturing and energy expenditure, in particular with regard to the necessary * re-heating after the first cooling.

The invention is based on the object. © in the method of to create the type mentioned at the beginning, on the one hand a higher-

guarantees a lying yield point than normal annealing, but on the other hand avoids the considerable additional work involved in quenching and tempering. The method of achieving this object the invention is characterized in that a with 0.05 to 0.15 # vanadium or niobium microalloyed, unalloyed in the rest of carbon-manganese steel having a carbon content of at least 0.2 i »in the temperature range 900-1280 ° C with the addition of vanadium or 1250 - 1280 ° C with the addition of niobium and the part - preferably individually - is cooled in air at at least approximately room temperature.

The invention thus avoids renewed heating of the forged part After cooling, controlled cooling in the air takes place directly from the forging heat. ! This cooling, for which the part is hung up individually or stored individually in another way, results in a pearlitic structure formation. The heating (austenitizing), quenching and tempering required for quenching and tempering are omitted, which results in a considerable saving in manufacturing effort and energy consumption.

The micro-alloy deposits cause precipitation hardening a higher yield point than occurs in normalizing other materials without affecting the tensile strength. the material of the part is significantly changed. This is important for the possibility of machining the forged part. As has been shown, according to the invention Process produced forged parts are machined with the same tools as forges parts that are manufactured using heat-treatable steels.

It is advisable to carry out the cooling in an air flow, which can be achieved in a simple manner by

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that the workpiece is transported by the forging press, for example, floating freely to a storage location, with of course the distance must be sufficiently great. Even with such a process-wise conceivably simple cooling occurs to increase the yield strength without any significant influence Precipitation hardening required for tensile strength on. -.

FIG. 1 shows the course of the yield point s in a diagram above the austenitizing temperature t for a normalized steel C 53 (curve a) and according to the method according to the invention treated materials, namely curve b with addition of niobium and curve c with addition of vanadium,

While curve a runs below 50 units for the yield point s in the entire temperature range, curve b shows between about 1150 and 1280 ° C and curve c between about 1250 and 1280 ° C a sharp rise; beyond about At 1280 ° C, on the other hand, there is again a sharp drop in the yield point be. While the material used here with the addition of Hiöb (Curve b) an exact adherence to the boiling temperature to increase the yield strength s required, the vanadium offers additional (Curve c) the possibility of increasing the yield strength even with fluctuating forging temperatures.

That the increase in the yield strength in the inventive Process not associated with a disruptive increase in tensile strength FIG. 2 shows the dependence of the yield strength ratio S, that is to say the quotient of the yield strength and tensile strength, plotted from the austenitizing temperature e is. The curves a, b and c correspond to the curve in FIG. 1, which is identified by the same name.

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Claims (1)

235037Q CLAIM Process for producing a forged part made of steel, characterized in that a carbon-manganese steel microalloyed with 0.05-0.15 ° vanadium or niobium, otherwise unalloyed, with a carbon content of at least 0.2 $ in the temperature range 900-1280 ° C with the addition of vanadium or 1250 - 1280 ° C with the addition of niobium and the part is cooled in air with at least approximately room temperature. 509816/0530