PL204037B1 - Wear resistant cast steel, particularly for operation in low temperatures - Google Patents

Description

The subject of the invention is abrasion-resistant cast steel, especially for operation at low temperatures, especially useful for the production of heat-treated parts of mining, construction, transport and energy machinery and equipment.

It is commonly known that the failure rate of machines and devices operating in winter, at low temperatures, is much higher than that of the same machines operated in summer. Low-temperature breakdowns are particularly common in Siberia and the far North, but also in the climate of Central Europe, this phenomenon is one of the serious operational problems.

The causes of these failures are primarily:

- friction wear,

- cracking due to the brittleness of the material at low temperatures, which appears and clearly increases - practically speaking - from a temperature of -20 ° C.

Production of cast steel resistant to abrasion and, at the same time, to brittle low-temperature cracking, requires meeting contradictory, or even contradictory, structural requirements.

The tribological resistance is related to the specific heterogeneity of the dendritic structure, specific to most cast steel grades. This, in turn, is not conducive to fracture toughness, because the interdendritic zone rich in carbides is a zone of numerous stress concentrators initiating cracks.

Representative examples of parts working in conditions of wear by friction and significant mechanical loads at low temperatures are cast steel castings of excavator teeth, track links, crusher jaws, beaters in mills, rollers and gear wheels, etc. The most popular cast steel used for these castings is still Hadfield cast steel. and its various modern modifications. A serious disadvantage of this cast steel is the intense wear in loose abrasive material, e.g. in sand. There is also L26HG2NM cast steel used in Poland and Russia for operation at low temperatures, resistant to abrasion, containing the following alloying elements by weight: from 0.20 to 0.40%; preferably 0.25 to 0.30% C; from 0.17 to 0.37% Si; 0.80 to 2.20%; preferably from 1.50 to 2.00% Mn; 0.80 to 2.00%; preferably from 1.30 to 1.70% Cr; 0.80 to 2.00%; preferably from 0.80 to 1.10% Ni; from 0.20 to 1.00%; preferably from 0.30 to 0.50% Mo; from 0.08 to 0.12% of V; from 0.020 to 0.040% Al; 0.005 to 0.020% Ce; 0.005 to 0.020% Ca. Polish patent specification No. 15663 discloses an abrasion-resistant cast steel containing from 0.10 to 0.40% by weight of C; from 12 to 14% Cr; 1.7 to 2.0% Cu; 0.8 to 1.2% Mo; 0.4 to 0.6% Ni; 0.3 to 0.4% Si; from 0.3 to 0.4% of Mn; from 0.3 to 0.4% V, the rest is iron and unavoidable impurities. However, this cast steel is abrasion resistant, especially at elevated temperatures. For low-temperature operation conditions, the proportion of carbide-forming elements, especially Cr and Mo, should be reduced.

Companies: Sumitomo (Japan), Marion (USA), Demag - Kamatsu (Germany), for the teeth of excavators, they recommend low-alloy cast steel of the Cr-Mo-Ni-Ti type, including CFE - SS (Japan) and ESCO (USA) cast steel containing carbon, manganese, silicon, chromium, molybdenum, nickel in the following weight proportions: from 0.25 to 0.30% C; from 0.60 to 0.80% Mn; from 0.30 to 0.60% Si; from 0.50 to 0.70% Cr; from 0.20 to 0.60% Mo; 0.60 to 1.0% Ni. In Russia, a low-alloy 20GNMFL cast steel containing carbon, manganese, nickel, vanadium, molybdenum is known.

However, these cast steels are difficult to weld. Therefore, they do not meet one of the basic criteria for qualifying materials for low-temperature operation. Moreover, their tribological resistance is much lower than the abrasion-resistant Cr-Mo-V-Cu-Ni type known in the country. With high abrasion resistance, this type of cast steel is characterized by too low fracture toughness, especially at low temperatures.

The aim of the invention is to select the proportions and mutual quantitative relations of: carbon, chromium, molybdenum, vanadium, copper and nickel in the Cr-Mo-V-Cu-Ni type abrasion-resistant cast steel in order to obtain a dendritic structure which, after thermal improvement, will ensure high ductility and low temperature impact strength, at the cost of slightly reducing friction wear resistance.

The essence of the invention consists in developing cast steel resistant to abrasion, especially at low temperatures, with the following chemical composition and weight proportions: C - from 0.10 to 0.40%; preferably: from 0.20 to 0.30%; Cr - from 1 to 8%; preferably: from 2 to 4%; Mo - from 0.40 to 0.60%; V - from 0.10 to 0.40%; preferably: from 0.20 to 0.30%, Mn from 0.30 to 0.50%; Si - from 0.30 to 0.50%; Cu - from

PL 204 037 B1

1.5 to 1.8%; Ni - from 0.50 to 0.80%; P - max 0.025%, S - max 0.030%, the rest is iron and unavoidable impurities and admixtures.

It turned out that such a combination of the chemical composition and thermal improvement of the cast steel according to the invention provides high abrasion resistance at low temperatures, especially in dry friction conditions, and the impact strength at a temperature of 233 K (-40 ° C) not lower than 50 J / cm ² . The cast steel according to the invention at a temperature of 233 K has a consumption lower by at least 25% than that of cast steel L26HG2NM and by over 50% lower than that of cast steel according to the Polish patent No. 156663. The advantage of the cast steel according to the invention is its good weldability and the possibility of joining both castings with each other by welding techniques. with structural steels.

The cast steel according to the invention can be smelted in melting furnaces used in the foundry of this type of cast steel, and the metallurgical process is carried out in accordance with commonly known methods of smelting and secondary metallurgy of alloy cast steel.

The invention is characterized by the following embodiment.

Cast steel was smelted in an induction furnace with the following chemical composition and weight proportions: C - 0.21%; Cr - 2.8%; Mo - 0.48%; V - 0.26%; Mn - 0.46%; Si - 0.32%; Cu - 1.5%; Ni 0.65%; P - 0.020%; S - 0.028%. After quenching and tempering, this cast steel had the following properties:

• Tensile strength at 77 K (liquid nitrogen), Rm = 1130 MPa, • Impact strength at 233 K, KCU = 78 J / cm ² , • Wear in roller test 3 at 233 K, Iz (233) = 4.4 · 10 ^-2 mm / m.

The consumption of Iz (233) of the L26HG2Nm cast steel was 6.2 · 10 ^-2 mm / m, and the cast steel according to the Polish patent No. 156663 - 7.6 · 10 ^-2 mm / m.

Claims (1)

Wear-resistant cast steel, especially for operation at low temperatures, characterized in that it contains by weight: C - from 0.10 to 0.40%; preferably: from 0.20 to 0.30%; Cr - from 1 to 8%; preferably: from 2 to 4%; Mo - from 0.40 to 0.60%; V - from 0.10 to 0.40%; preferably: from 0.20 to 0.30%; Mn - from 0.30 to 0.50%; Si - from 0.30 to 0.50%; Cu - from 1.5 to 1.8%; Ni - from 0.50 to 0.80%; P - max 0.025%; S - max 0.030%, the rest is iron and unavoidable impurities and admixtures.