CS199121B1 - Steel for most stressed products - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to steel for highly stressed products, in particular machine parts with high abrasion resistance, intended to operate under conditions of combined stress at temperatures up to 300 ° C, such as chutes, grinding balls, fever knives

Up to now, steels with hardnesses above 300 HB or tensile strengths above 1000 MPa have been used for the production of said machine parts. The service life of machine parts, such as bucket knives for excavators, is directly dependent on the plastic properties of the material, in particular the notch toughness value, which must exceed 25 J / m 2. Some low-alloy steels, such as cast steel with a chemical composition in an amount by weight of 0.35 to 0.45% carbon, are used to produce castings subjected to wear-free wear and / or wear with simultaneous higher stress or compression loads. 0.40 to 0.90% manganese, 0.20 to 0.42% silicon, 0.040% phosphorus, 0.040% sulfur, 0.50 to 0.80% chromium, 1.00 to 1.50% nickel , the remainder iron or cast steel having a chemical composition in an amount by weight of 0.70 to 0.82% carbon, 0.60 to 0.90% manganese, 0.20 to 0.50% silicon, to 0.040% phosphorus, up to 0.040% sulfur, 1.30 to 1.70% by weight, 0.50 to 0.80% nickel, 0.10 to 0.25% vanadium and 0.40 to 0.60% molybdenum, the rest iron, possibly other cast steel with chemical composition in amounts by weight 0,50 to 0,65% carbon, 0,60 to 0,80% manganese, 0,20 to 0,50% silicon, up to 0,040% lao

188121 phosphorus, up to 0,040% sulfur and 2,60 to 3,40% overwhelm, the rest of the iron, all of which do not reach the tensile strength above 1000 MPa and have minimum values of plastic properties, such as notch toughness, corresponding to the characteristic brittle materials.

Said drawbacks of the prior art are eliminated by the steels for the highly stressed products of the invention, which contain in a quantity by weight carbon 0.35 to 0.45%, manganese 1.30 to 1.80%, silicon 0.15 to 0.40% , phosphorus trace to 0.030%, sulfur trace to 0.020%, chromium 0.60 to 1.00% and zirconium 0.05 to 0.15%. It is an object of the invention that the steel further comprises molybdenum in an amount of 0.20-0.40% as well as 0.01-0.06% lanthanum, cerium or neodymium, individually or in combination, the remainder iron and the permissible admixtures.

The steel according to the invention intended for the production of machine parts subjected to combined wear, struts and pressure at temperatures of -20 to +300 [deg.] C. retains at the same time fully satisfactory notch toughness values at high tensile strength values. Heat treatment of designed steel products by normalization annealing with air-tempering or oil-annealing can result in castings and forgings of a tensile strength of at least 900 MPa, a tensile strength of at least 1100 MPa, and a short bar elongation of 10 % and notched toughness of 25 J / m ^{2 or more} . The steel according to the invention intended for machine parts subjected to wear only can be used in a state hardened from 850 to 870 ° C to oil, the tensile strength being above 1600 MPa.

To further elucidate the essence of the invention, examples of its heat treatment are given below:

Example 1

For the bucket wheel excavator teeth with a weight of 15 kg each, the steel according to the invention has a chemical composition in an amount by weight of carbon of 0.38%, manganese of 1.44%, silicon of 0.33%, phosphorus of 0.021%, sulfur of 0.016%, 82%, molybdenum 0.29%, zirconium 0.08%, and cerium 0.03%, the remainder iron and permissible impurities. The castings were annealed at 860 ° C with air normalization and locally turbid on the oil edge from 850 ° C, whereby the following mechanical properties were found on the specimens cut from the finished blank: tensile yield strength tensile 1004 MPa, tensile strength 1128 MPa, short bar elongation 13.2%, concentration 31% at average notch toughness 30.6 J / m ² . These mechanical values were determined by processing further specimens also cut from the same casting.

Example 2

Of steel with chemical composition in amounts by weight carbon 0.42%, manganese 3-, 60%, silicon 0.38%, phosphorus 0.024%, sulfur 0.012%, over 0.72 molybdenum 0.28%, zircon 0.07 %, cerium 0.02% and lanthanum 0.01%, the remainder iron and allowable impurities, casting screens of 36 kg coke screening unit were cast and heat treated by annealing at 870 ° C with normalization in air and cooled on air. Compared to the steels used previously for these sorting grates with a strength of about 850 MPa, a four times the service life has been achieved.

Example 3

Of steel with a chemical composition by weight of carbon 0,40%, manganese 1,35%, silicon 0,40%, phosphorus 0,025%, sulfur 0,018%, chromium 0,88%, molybdenum 0,31%, zirconium 0, 06%, cer 0.008% and neodymium 0.007%, the remainder iron and permissible impurities, were made of 18 kg piece knives, intended as ripper working elements for reclamation work. Knife castings were quenched from 860 ° C to oil. The blades showed a hardness of 460 HB as measured on the casting.

Similar mechanical values that meet dynamic environmental stresses at moderately elevated temperatures of up to 300 ° C are achieved with special forgings, such as grinding balls, hardened from a post-roll temperature.

OBJECT OF THE INVENTION

Claims (1)

OBJECT OF THE INVENTION Steel for highly stressed products, containing by weight of carbon 0.35 to 0.45%, manganese 1.30 to 1.80%, silicon 0.15 to 0.40%, phosphorus trace to 0.030%, sulfur trace to 0.020%, chromium 0.60 to 1.00 # and zirconium 0.05 to 0.15%, characterized in that it further comprises molybdenum in an amount of 0.20 to 0.40%, and 0.01 to 0.06% lantban, cerium or neodymium, individually or in combination, the rest of the iron and the permissible impurities.