Production method of pearlite matrix ultrahigh-strength ductile cast iron crankshaft

Abstract

The invention provides a production method of a pearlite matrix ultrahigh-strength ductile cast iron crankshaft. The production method comprises the following steps of: selecting low-sulfur low-titanium pig iron, common carbon steel and self-produced recirculated iron as main furnace charges, and adding 75 ferrosilicon, 65 high-carbon ferromanganese, electrolytic copper and a graphite type carburant in a specific proportion; smelting in an intermediate frequency furnace at a specific frequency, adding a nodulizer, an inoculant and a silicon-calcium-manganese deoxidizer, and then tapping and nodulizing, wherein the nodulizing process requires a specific tapping position, speed and tapping steps, and the pouring process selects a specific inoculant flow rate and total amount; and performinga specific normalizing process on a crankshaft casting to prepare an ultrahigh-strength ductile cast iron material of which the strength exceeds 1000MPa, the elongation is greater than or equal to 5%and the matrix material is pearlite. The comprehensive performance of the ultrahigh-strength ductile cast iron material is far better than that of common ductile iron and ADI (all-purpose ductile iron) materials with the same tensile strength. The preparation method is applied to parts such as J4200 crankshafts and JX400 crankshafts to realize the preparation of the pearlite matrix ultrahigh-strength ductile material, and the cost is reduced and remarkable benefits are obtained.

Description

technical field [0001] The invention belongs to the field of ductile iron casting technology, and in particular relates to a production method of a pearlite matrix ultra-high-strength ductile ductile iron crankshaft with a tensile strength exceeding 1000 MPa and an elongation exceeding 5%. Background technique [0002] When designing engine crankshaft parts, designers usually select materials that can meet the yield strength from the national standard materials according to indicators such as strength and elongation. Currently, among ductile metal materials with a strength exceeding 1000MPa and an elongation of not less than 5%, usually only 40Cr, 42CrMo, engineering high-strength cast steel or ADI materials can meet the design requirements of the crankshaft structure. [0003] 1. According to the standard of GB / T1348-2009: the maximum strength of ordinary ductile iron can reach 900MPa, and the elongation rate is 2%. There are a few domestic manufacturers who can make QT800-...

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Problems solved by technology

[0004] 2. Ordinary cast steel cannot reach the strength above 1000MPa, and only low-alloy cast steel materials can meet the design requirements

Low-alloy cast steel is not suitable for forming crankshafts with uneven wall thickness;

[0006] 4. The material price of 4.40Cr and 42CrMo is generally 15-17 yuan / ㎏, which is much higher than the material cost of 8-10 yuan for ordinary ductile iron, and the forging process of this material cannot meet the design requirements of the hollow weight reduction in the crankshaft journal of the National VI, and waste material and limited contribution to lightweight

[0008] 5.1 The cost of heat treatment is very high, and the process range is very narrow (ADI materials have high requirements for austempering, cooling too fast transforms into martensitic structure, cooling too slow transforms into pearlite structure), usually only the heat treatment equipment is more than 10 million

And for castings with a wall thickness difference of more than 20mm, it cannot be hardened through, and the parts cannot be uniform in structure and performance;

[0009] 5.2 The cost of ADI material preparation reaches 17-20 yuan / kg, even reaching twice the value of ordinary ductile iron; the material cost is not affordable by ordinary enterprises

[0010] 5.3 The processing of ADI materials is very difficult, and the austenite structure at room temperature will produce work hardening phenomenon, and the tool cost is very high

[0011] 5.4 Based on the above, the main reason why ADI materials are still unable to be widely promoted due to the limitation of preparation technology, preparation cost, processing cost and structure

In this production method, stable residual Mg and residual RE can be obtained through reasonable composition, spheroidizing agent ratio and stable spheroidizing process, and a reasonable inoculation process can be used to achieve graphite spheroidizing grade above 2 , round graphite balls with graphite diameter grade 5-8, but the spheroidization rate is only 90-92%, and the graphite diameter is 0.015-0.06mm. For crankshaft parts that require high-strength materials, the graphite spheroidization rate and graphite diameter did not achieve optimal results

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